Details of a Researcher - Beaucamp, Anthony

Papers - Beaucamp, Anthony

Division display >> ／ All the affair displays 1 - 115 of about 115

Material removal characteristics in submerged pulsating air jet polishing process

Han Y., Liu C., Yu M., Jiang L., Zhu W., Qian L., Beaucamp A.

International Journal of Mechanical Sciences (International Journal of Mechanical Sciences) 257 2023.11

ISSN 00207403

In this paper, the material removal characteristics and mechanism of submerged pulsating air jet polishing (SPAJP) process are investigated by polishing experiment on K9 glass and computational fluid dynamics simulation. The experimental results show SPAJP can etch almost perfect Gaussian footprints with high stability. Under comparable condition, SPAJP achieves nearly 300 times higher material removal rate (3.0 × 10−3 mm3/min) than that of traditional fluid jet polishing (FJP) (9.9 × 10−6 mm3/min) at the cost of a moderate degradation in processed surface roughness from Sa 3.97 nm by FJP to Sa 20.49 nm by SPAJP. Jet evolution, abrasive behavior and material removal mechanism in SPAJP are clarified by numerical modeling and experimental jet observation. It is found that SPAJP relies on jet instability of the submerged airflow beam to entrain and accelerate abrasive particles in the slurry, achieving stable and efficient polishing removal on the workpiece surface. To explore the potential of the process for deterministic polishing, an array structure surface is then designed and polished by SPAJP. The processing results are consistent with numerical prediction results, indicating that the new process has good material removal controllability which makes it applicable to deterministic polishing. This study highlights the possibility of using SPAJP to produce ultra-precise surfaces in terms of form control or fabricate high precision optical components in a more efficient and convenient manner.

Access to Document (DOI)

Feed scheduling for time-dependent machining processes by optimization of bulk removal and NC blocks

Beaucamp A., Mizoue Y., Yamato S., Sencer B.

Journal of Materials Processing Technology (Journal of Materials Processing Technology) 312 2023.03

ISSN 09240136

Time-dependent processes such as CNC fluid jet polishing require feed-rate scheduling through deconvolution of a target removal profile and tool influence function. The dynamic constraints associated with the machine tool driving the process should be considered when solving this numerical problem. This research investigates how material bulk removal affects the scheduled feed-rate and acceleration both in the spatial and time domain, and proposes a method for matching exactly the maximum acceleration with the machine tool limit. Furthermore, the influence of CNC interpolator dynamics is investigated by means of the controller pulse response method. An optimization method for NC blocks is then proposed in order to achieve feed-rates that best match the intended profile. The benefit of bulk removal and NC blocks optimization is validated by fabrication, with and without optimization, of cylindrical Fresnel lenses. Both the shape accuracy and optical performance of the optimally fabricated lens are shown to substantially improve, suggesting that the proposed optimization method has strong potential for industrial application.

Access to Document (DOI)

Hybrid tool combining stiff and elastic grinding

Ashwani Pratap, Shuntaro Yamato, Anthony Beaucamp

CIRP Annals (Elsevier BV) 72 ( 1 ) 281 - 284 2023

ISSN 00078506

The fabrication process chain for optically smooth surfaces tends to include several time-consuming grinding and polishing steps. To reduce process time, a hybrid tool is proposed in which a stiff grinding tool and a shape adaptive grinding (SAG) tool are fused together, by taking advantage of the elastic nature of SAG tools. The material removal achieved by the hybrid tool is equivalent to discretely using the stiff grinding and SAG tools in sequence. Under similar processing conditions, a smooth surface of ∼0.02 μm Ra can be obtained on BK7 glass with the proposed tool, instead of ∼0.2 μm Ra with the stiff grinding tool.

Access to Document (DOI)

Compliant polishing of thin-walled freeform workpiece

Zhu W.L., Gao W., Han F., Ju B.F., Chen Y.L., Beaucamp A.

CIRP Annals (CIRP Annals) 72 ( 1 ) 285 - 288 2023

ISSN 00078506

Compliant polishing using elastic tools can achieve ultraprecision surface quality on freeform workpieces. However, when it comes to thin-walled parts, the challenge arises with the complex polishing mechanics between the tool and freeform surface, without the knowledge of which the surface form can be easily degraded. To address this, an analytical model is established that can predict the interaction mechanics during polishing. On this basis, two adaptive strategies are proposed. Experiments with controllable material removal verify the high accuracy of the model, and compliant polishing of a thin-walled freeform workpiece with highly precise removal consistency below 0.5 µm was achieved.

Access to Document (DOI)

Reverse Engineering Algorithm for Cutting of Ruled Geometries by Wire

Beaucamp A.T.H., Takeuchi Y.

International Journal of Automation Technology (International Journal of Automation Technology) 16 ( 3 ) 349 - 355 2022.05

ISSN 18817629

Abrasive wire cutting (AWC) and wire electric discharge machining (WEDM) are efficient and econom-ical processes for the fabrication of precision parts from bulk material. Operating costs and manufacturing lead times are low compared to more general methods such as 5-axis CNC milling, turning, or electro-discharge machining. In this paper, an algorithm based on differential geometry in Euclidean space is proposed for reverse engineering of ruled geometries. The algorithm can determine whether a given geometry is producible by wire cutting, and can also de-rive the associated wire trajectories. Implementation is demonstrated by producing complex turbine blade geometries on 4-axis wire cutting machines with an overall shape accuracy of 20–40 μm peak-to-valley.

Access to Document (DOI)

Monolithic topological honeycomb lens for achromatic focusing and imaging

Zhu W., Duan F., Tatsumi K., Beaucamp A.

Optica (Optica) 9 ( 1 ) 100 - 107 2022.01

ISSN 23342536

Wavelength dispersion is a universal phenomenon in refractive optics that degrades optical performances. Current mitigation methods are being greatly challenged by the demanding requirements of miniaturization, low aberrations, high throughput, and accurate manufacture. Here, we propose an unconventional monolithic honeycomb-like lens concept with topological degrees of design freedom, capable of near diffraction-limited achromatic performance. To automate the design process, a methodological framework is presented that directly evolves the honeycomb lens from a flat window, instead of a knowledge-based starting geometry. The honeycomb lens performance at the full field of view is remarkably better than either traditional aspheric lenses or commercial cascaded lenses. It also overcomes limitations of flat metalenses, which have extremely small aperture sizes and suffer from multi-order aberrations. This topological honeycomb lens concept may pave the way to inexpensive and compact achromatic optics for focusing and imaging applications in consumer cameras, wearable optics, virtual reality, etc.

Access to Document (DOI)

Mechanism of mid-spatial-frequency waviness removal by viscoelastic polishing tool

Zhu W.L., Pakenham-Walsh O., Copson K., Charlton P., Tatsumi K., Ju B.F., Beaucamp A.

CIRP Annals (CIRP Annals) 71 ( 1 ) 269 - 272 2022.01

ISSN 00078506

Nanoscale roughness with ultra-precise form control can be readily achieved using compliant finishing methods such as bonnet polishing. However, their weak point lies in the difficulty of removing mid-spatial-frequency (MSF) waviness in the typical range from 0.1 to 5.0 mm wavelength. To overcome this shortcoming, a bonnet tool filled with viscoelastic fluid is developed and a comprehensive model is established to disclose its distinct removal behavior in the MSF range. The model considers tool viscoelasticity, stress distribution and workpiece topography. Experiments show high consistency with theoretical predictions, and show that MSF waviness can be effectively reduced using the proposed method.

Access to Document (DOI)

Generic three-dimensional model of freeform surface polishing with non-Newtonian fluids

Zhu W.L., Beaucamp A.

International Journal of Machine Tools and Manufacture (International Journal of Machine Tools and Manufacture) 172 2022.01

ISSN 08906955

Non-Newtonian fluids are being increasingly considered for application in manufacturing. Their combination with compliant polishing techniques offers a promising approach for ultraprecision finishing of freeform surfaces. However, in-depth understanding of the underlying material removal mechanism and its link with slurry rheology has not been disclosed yet. In this study, a comprehensive three-dimensional dynamic modeling framework is presented, which enables accurate prediction of stress distribution, rheological flow, compliant deformation in 3D, as well as material removal behavior on curved workpieces. Supported by experimental tests and theoretical analysis, it is demonstrated that the viscosity peak gets shifted to a higher frequency by mixing starch and polymer, which makes high speed polishing with improved material removal rate possible. Meanwhile, it is found that the polymer additive prevents large size starch agglomeration and has high affinity with fine abrasives, both of which greatly contribute to the obtained scratch-free and nanoscale surface finish. Finally, the controllability and predictability of the process are demonstrated by polishing a bi-sinusoidal freeform surface onto a planar workpiece coated with nickel.

Access to Document (DOI)

Elucidation of material removal mechanism in float polishing

Beaucamp A.T.H., Nagai K., Hirayama T., Okada M., Suzuki H., Namba Y.

Precision Engineering (Precision Engineering) 73 423 - 434 2022.01

ISSN 01416359

Float polishing (FP) is a non-contact polishing method in which a thin layer of fluid is maintained between the workpiece and precision lap by hydrodynamic pressure effect. While it is known to consistently produce atomically flat surfaces with little or no sub-surface damage, the characteristics of polishing fluid flow and material removal have not been studied in-depth. In this research, the underlying mechanism in FP is investigated by means of computational fluid dynamics (CFD) and molecular dynamics (MD) simulation. It is revealed that a fluid gap few microns in height is generated by the wedge effect of slurry. The near wall flow condition is further investigated by direct observation and tracing of cavitation bubbles. Abrasive particle trajectory tracing is carried out with a well calibrated CFD model, and suggests that single abrasive particles move almost parallel to the workpiece surface at a relative speed of around 0.5 mm/s. Next, single abrasive particle interactions with the surface of a Ni crystal are simulated by MD to predict the required conditions in terms of kinetic energy for effective smoothing of the surface. Finally, it is concluded that the material removal mechanism in FP is dependent on a minimum size of nano-abrasive agglomerates of several 100 nm, and the existence of two types of smoothing phenomena: atomic removal and atomic transfer.

Access to Document (DOI)

Advances in grinding tools and abrasives

Beaucamp A., Kirsch B., Zhu W.

CIRP Annals (CIRP Annals) 71 ( 2 ) 623 - 646 2022.01

ISSN 00078506

Because of their many applications, including automotive, aeronautics, optics, and so forth, demand for grinding tools sees unabated growth. But the energy and resource intensive nature of their manufacture leads to questions of sustainability. This paper details how recent developments in basic tool technology (structure, binder, abrasives) is increasing tool and abrasive resilience while reducing production inputs. The advent of smart grinding tools involving aspects of surface engineering, process hybridization, and process monitoring is also discussed. The paper concludes with an outlook of further energy savings, tool recycling and uses of additive manufacturing with the aim of achieving long-term sustainability.

Access to Document (DOI)

Reduction of mid-spatial frequency errors on aspheric and freeform optics by circular-random path polishing

Anthony Beaucamp, K. Takizawa, Y., Han, W Zhu

Optics Express (Optics Express) 29 ( 19 ) 29802 - 29812 2021.09

Accepted

Pseudo-random paths are a useful tool to reduce mid-spatial frequency errors created in the processing of optical surfaces by sub-aperture polishing tools. Several types of patterns have been proposed, including hexagonal, square and circular, but prior literature has largely focused on flat and gently curved surfaces. Here, an extension of the circular-random path to strongly curved aspheric and freeform surfaces is proposed. The main feature of the algorithm is to cover the entire surface to be polished with a uniformly distributed tool path. Aspheric condenser lenses are then polished with a regular raster and circular-random path. Analysis of the optical performance shows that the random path can reduce the amplitude of mid-spatial frequency errors and relative intensity of satellite images. These features are particularly desirable in short wavelength applications, such as mirrors for EUV and X-ray.

Access to Document (DOI)

Towards an understanding of surface finishing with compliant tools using a fast and accurate simulation method

Julien Chaves-Jacob, Anthony Beaucamp, Wule Zhu, Daisuke Kono, Jean-Marc Linares

INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE (International Journal of Machine Tools and Manufacture) 163 ARTN 103704 2021.04

Accepted, ISSN 08906955

Surface finishing with compliant tools is a widely used technology that still relies heavily on the trial-and-error approach. To predict surface evolution, one should ideally consider the tool as a set of grains and take into account the cutting action of each grain. In practice, the small size of abrasives renders this approach unpractical for industrial application. In this paper, the various aspects playing a role in surface generation, from micro-scale abrasives to macro-scale tool deformation as well as the time-dependent nature of compliant processes, are rationalized and modelled in a Folding Space (FS) rather than a classic geometrical space. This approach drastically reduces the computation time, and is found to be quite realistic as in each position the tool shape is distorted, taking into account the compliance level between the tool and local surface topography. Firstly, the concept of FS and methodology for physical representation of surfaces and processing by compliant tools in the FS are detailed. Next, predictions from the finishing model are analyzed for a variety of compliant grinding and polishing tools typically used in industry. Experimental testing confirms the accuracy and usefulness of the proposed method. To conclude, the model is exploited to offer a better understanding of finishing operations with compliant tools, while the limits and future possibilities of FS simulation method are discussed.

Access to Document (DOI)

Predictive topography model for shape adaptive grinding of metal matrix composites

W. Zhu, C. Jain, Y. Han, Anthony Beaucamp

CIRP Annals (CIRP Annals) 70 ( 1 ) 269 - 272 2021.01

Accepted, ISSN 00078506

Compliant finishing (e.g. shape adaptive grinding) can routinely achieve nanoscale roughness on diverse metal and ceramic materials. However, when processing multiphase materials consisting of distinct phases with different mechanical properties, non-uniform material removal often occurs and the inherent mechanism remains unclear. Here, a deterministic and stochastic model to predict processed surface topography is derived from the different material removal behaviours across phases. Experimental topographies, profiles and roughness on three selected Si-SiC samples show high consistency with theoretical predictions. Both model and experiments indicate that improved and stable surface finish can be achieved on metal matrix composites with small grain size.

Access to Document (DOI)

Identification and optimization of CNC dynamics in time-dependent machining processes and its validation to fluid jet polishing

Y. Mizoue, B. Sencer, Anthony Beaucamp

International Journal of Machine Tools and Manufacture 159 103648 2020.12

Accepted, ISSN 08906955

In time dependent CNC processes such as polishing, a target material removal profile is obtained by creating and inputting G-codes with varying feed into the controller of a machine tool. The input G-codes are firstly filtered by a CNC interpolator, and the real-time generated signal then goes to a feed drive system of the machine. Through these steps, the original signal is distorted and the ideal feed profile cannot be achieved in some areas. This distortion affects the material removal distribution, and thus the accuracy of the final polished surface profile. While a number of methods have been developed for predicting polished surfaces, most of them fail to consider the influence of controller dynamics. In this paper, a method for accurate prediction of polished surfaces is proposed that considers the error contribution from control signal distortion, and a strategy for compensation of this error. Firstly, the principles of identification of control system behavior in a machine tool are explained, and a process model for Fluid Jet Polishing (FJP) is introduced. Secondly, the transfer functions of the control system are identified, and the process model calibrated against experimental data. Thirdly, a simulator for predicting polished surface profiles is implemented that combines the control system and process model. A micro-groove polishing experiment is carried out that validates the reliability of the proposed method, and shows its limitations. Finally, an algorithm based on particle swarm optimization is proposed for reducing the impact of controller dynamics in micro-groove polishing.

Access to Document (DOI)

Compliant grinding and polishing: A review

Wu-Le Zhu, Anthony Beaucamp

International Journal of Machine Tools and Manufacture (Elsevier Ltd) 158 2020.11

ISSN 08906955

Compliant grinding and polishing refers to a class of fine material processing methods relying on one or more system element being compliant with the workpiece surface in a controllable and reversible manner, thus being distinct from conventional rigid wheel grinding and polishing. The resulting surface adaptability greatly facilitates the ultra-precision machining of freeform surfaces, with a level of accuracy and productivity difficult to achieve with conventional rigid processing systems. Aiming for a comprehensive review of signal advances on this topic in the last decades, this paper introduces a multi-level compliance categorization system to sort between distinctive processes. For each category, various perspectives are explored that pertain to principles, methodologies, and physical properties such as material removal and surface integrity. Finally, relative merits are analyzed, together with a discussion of the outlook and future trends.

Access to Document (DOI)

Region adaptive scheduling for time-dependent processes with optimal use of machine dynamics

Y. Han, W. Zhu, L. Zhang, Anthony Beaucamp

International Journal of Machine Tools and Manufacture 156 103589 2020.09

Accepted, ISSN 08906955

In time-dependent processes, such as bonnet and fluid jet polishing, surface quality and accurate processing critically depend on careful planning of the tool feed. CNC feedrate commands are usually generated from a dwell time map calculated by deconvolution or numerical iteration. These methods are time-consuming, numerically unstable, and fail to consider dynamic stressing of the machine tool. In this research, Gaussian mixture model (GMM) is proposed to model experimental tool influence functions (TIF). This leads to a general analytical convolution model integrating processing depth, volumetric removal rate of TIF, path spacing and feedrate. Based on this model, a novel direct feedrate scheduling method is proposed, which is suitable for any kind of smooth time-dependent processing beam. Optimal feedrate scheduling within dynamic constraints of the machine tool is achieved by establishing acceptable path spacing and feed ranges, whilst dynamic stressing of the machine tool is optimized concurrently through adaptive path spacing. Simulations and experiments demonstrate the enhanced stability and usefulness of the proposed feedrate model in deterministic material removal. It also verifies that path adaptability allows for improved machine tool dynamics, without incurring a process accuracy penalty.

Access to Document (DOI)

Study on removal mechanism at the tool rotational center in bonnet polishing of glass

Ihara Motohiro, Atsushi Matsubara, Anthony Beaucamp

Wear (Elsevier) 454-455 203321 2020.08

Accepted, ISSN 00431648

Preston's law is a widely used equation that expresses time-dependency of material removal in polishing process. In this research, it is experimentally found that Preston's law does not hold at the tool rotational center in glass polishing. Material removal observations point to a mechanical phenomenon accelerated by chemical reaction. To identify the underlying phenomenon, experiments are conducted that isolate the contribution from each constituent factor in Preston's law. By observing the motion of loose-abrasive particles during polishing, it is found that they travel as expected on concentric trajectories around the tool rotational center. By measuring the pressure distribution in static situation as well as the contact force during polishing, it can be concluded that no hydrodynamic increase in pressure occurs at the tool rotational center. Finally, experiments are performed to investigate the relationship between distance from tool rotational center and removal depth by a single abrasive particle. The depth of removal is observed to reach a maximum value at the tool rotational center in all polishing conditions tested, from which a modified expression of Preston's law is derived. Finally, hypotheses based on fracture and material mechanics are proposed to explain abrasion mode transitions in single particle abrasion.

Access to Document (DOI)

Chromatically multi-focal optics based on micro-lens array design

F. Duan, W. Zhu, Y. Han, B.-F. Ju, Anthony Beaucamp

Optics Express 28 ( 16 ) 24123 - 24135 2020.08

Accepted

CCD arrays encode color information via uniformly distributed red, green and blue pixels. Therefore, even a perfectly achromatic system projecting an image onto a CCD plane cannot possibly associate a single object point with the 3 or more discrete pixels encoding color content. Here, we propose and demonstrate a micro-lens array (MLA) design that simultaneously corrects chromatic aberrations and separates color channels to spatially distinct pixels. Starting from a commercially available aspheric condenser lens, methods to design and assess the performance of a few microns deep MLA etched on the convex optical surface are detailed. Actual fabrication is carried out by fluid jet polishing, with an optical form deviation of 0.24 μm rms. Finally, the MLA is assessed with a narrowly collimated beam containing two wavelengths, which produces distinct spots of diameter 10-15 μm as expected.

Access to Document (DOI)

Analytical and stochastic modeling of surface topography in time-dependent sub-aperture processing

Yanjun Han, Fang Duan, Wule Zhu, Lei Zhang, Anthony Beaucamp

International Journal of Mechanical Sciences 175 2020.06

Accepted, ISSN 00207403

© 2020 Elsevier Ltd Time-dependent sub-aperture surface processing is widely used in industry for finishing of optical surfaces. It can often be viewed as the convolution process between a tool influence function (TIF, also known as footprint) and the equivalent dwell time derived from the velocity at discrete locations across the tool path. While the direct convolution problem has been extensively studied through numerical computation, this approach leads to limited and inaccurate prediction of the processed surface. Therefore, this paper proposes a simple and universal analytical model that uncovers the intrinsic relationship between process parameters and processed surface, and which has potential for a wide range of manufacturing processes. Furthermore, sensitivity of the process to TIF fluctuations is considered, which leads to highly accurate stochastic predictions of the processed surface waviness variation by Monte Carlo simulation. Experimental results in fluid jet polishing confirm correctness of the proposed analytical solution and effectiveness of the waviness prediction model. The presented solution provides a better understanding and insight into time-dependent sub-aperture surface processing and opens the door to efficiently tackling the related direct and inverse problem.

Access to Document (DOI)

Controlling of compliant grinding for low-rigidity components

Yue Yang, Haonan Li, Zhirong Liao, Dragos Axinte, Wule Zhu, Anthony Beaucamp

INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE 152 ARTN 103543 2020.05

Accepted, ISSN 08906955

The machining of low-rigidity components (e.g. thin-walled) with compliant tools presents accuracy challenges as both sides in contact are being deformed. The controlling method presented in this paper enables, for the first time, to obtain the desired and uniform material removal rate by controlling the nominal tool offset when two bodies (workpiece and tool) are compliant in grinding. A contact deformation model is proposed to predict the relation between the nominal and actual tool offsets. The function of nominal tool offsets and material removal rates is obtained based on the calibration tests. Spot grinding tests have been performed for the validation of the calculated material removal rates, normal grinding forces and spot sizes, presenting position-dependent characteristics. The controlling method has been tested for the case of continuous grinding the whole area of a circular aluminium thin wall. The surfaces ground under the time-variant tool offsets (proposed approach) reach the desired removal depth with an average error of ≤10% and achieve 11.2 μm–24.2 μm (P–V) accuracy in the elastic domain, compared with the error of 76.8%~113.7% and accuracy of 42.6 μm–50.1 μm (P–V) in the circumstance of constant tool offsets (conventional approach).

Access to Document (DOI)

Development of a new computer aided manufacturing system for variable pitch screws fabrication

Nabeta Y., Jain S., Beaucamp A., Takeuchi Y.

Journal of the Korean Society for Precision Engineering 37 ( 3 ) 195 - 200 2020.03

ISSN 12259071

The study focused on the development of the CAM system restricted to the fabrication of variable pitch screws by using turning centers. To develop the dedicated CAM system at a low cost, open source programming language was used as much as possible. A commercially available 3D-CAD system was used to model variable pitch screws. The edge data of the variable pitch screw was extracted from 3D-CAD data of the variable pitch screw, and then a number of the edge data were copied by the amount of feed in the longitudinal direction of the screw to make a cutter path. The successive cutter path was repeatedly generated by reducing the size of the edge data. The advantage of this method of generating the cutter path is very simple and easy to use, compared with the conventional CAM systems. During the cutter path generation, the system can detect the collision between the cutting tool and the workpiece. As a result, the validity of the developed CAM system for variable pitch screws fabrication was confirmed from several examples of the cutter path generation.

Access to Document (DOI)

Effect of polymer relaxation in automated micro polishing

Soufian Ben Achour, Wule Zhu, Giuliano Bissacco, Anthony Beaucamp, Leonardo De Chiffre

AIP Conference Proceedings 2205 2020.01

Accepted, ISSN 0094243X

© 2020 Author(s). Micro polishing is a process used when a fine surface quality is desired. In optics, it represents the key process to achieve low surface roughness and form error required for optics application. Automated micro polishing with polymer-based tools requires a better understanding of the interaction between tool and workpiece than conventional polishing, and an important phenomenon that has to be taken into account is polymer relaxation. Stress relaxation is due to the non-linear viscoelastic behaviour of polymers. This relaxation is a time-dependent phenomenon that causes a decrease in stress, although the strain is kept constant. In this work, the effect of polymer stress relaxation on polishing is studied. While this effect can be neglected in conventional polishing, it becomes an essential and dominant factor in micro polishing. Characterization tests are conducted on a very common extruded polyurethane (LP-66) used in polishing. Subsequently, bonnet polishing using a spherical tool with a diameter of 1 mm is performed for 8 minutes on a nickel sample. Due to relaxation, the induced stress on the tool decreases during polishing, causing a reduction in the polishing pressure. This implies a reduction in the material removal rate in accordance with Preston's law. Experimental results are in accordance with the physical phenomenon. The polymer relaxation characteristics can be used to compensate the tool path to achieve uniform removal along the polished surface.

Access to Document (DOI)

Investigation of critical material removal transitions in compliant machining of brittle ceramics

Wu Le Zhu, Beaucamp Anthony

Materials and Design 185 108258-1 - 108258-13 2020.01

Accepted, ISSN 02641275

© 2019 The Authors Compliant machining processes, such as bonnet polishing, can be used on hard and brittle ceramic materials such as alumina and silicon carbide, to produce ultra-precise surfaces with sub-micron form accuracy and nanometric surface roughness. However, a comprehensive understanding of the removal mechanism in such process is lacking. In this paper, an analytical model is proposed that is based on the existence of “three zones” in compliant machining process, namely elastic recovery, plastic removal and brittle fracture. The inherent relationships of the three critical pressures with actual pressure, due to compression of the elastic bonnet tool and asperity effect, are established and analyzed in association with different material removal behaviors. Analysis indicates that pad asperity plays an important role in material removal and that lower material hardness combined with higher tensile strength contributes to enlarged plastic removal zone, and thus higher manufacturability. Removal footprints and polishing tests were then generated to verify accurate prediction of the material removal rate under different conditions and demonstrate effectiveness of the proposed model.

Access to Document (DOI)

静電気力と超音波振動を用いたナノブラスト研磨用砥粒粒径均一化に関する研究

森有花, Beaucamp Anthony, 松原厚

精密工学会学術講演会講演論文集 (公益社団法人精密工学会) 2020 153 - 154 2020

ナノ粒子を用いた超微細ブラストの研究を行っている．自然状態ではナノ粒子は凝集粒子を形成し，その粒径のばらつきは精密仕上げに要求される砥粒の粒径分布より大きい．本研究では，粒子間の付着力を上回る外力を加えることで凝集粒子の平均径と分布幅を小さくする方法を提案する．有限要素解析と実験により，超音波振動と静電力を同時に印加すると粒径分布が改善するとわかったが，凝集粒子は完全には分離しなかった．

Access to Document (DOI)

Elucidation of levitation principle in float polishing method

Nagai Kotaro, Beaucamp Anthony, Matsubara Atsushi, Namba Yoshiharu, Suzuki Hirofumi

Proceedings of JSPE Semestrial Meeting (The Japan Society for Precision Engineering) 2020 157 - 158 2020

Machining conditions in float polishing method have been determined empirically and there is a need to elucidate the levitation principle of the workpiece and to propose a theoretical method to determine the machining conditions. In this research, the levitation quantity of the workpiece was measured by the displacement sensor and found to be about 4 µm. The order of this value agreed with the prediction in the literature. From the FEM simulation of the thin film fluid based on the Reynolds equation, it was predicted that the pressure distribution under the workpiece was non-uniform and cavitation was generated.

Access to Document (DOI)

Deterministic polishing of micro geometries

Soufian Ben Achour, Giuliano Bissacco, Anthony Beaucamp, Leonardo De Chiffre

CIRP Annals (Elsevier USA) 69 ( 1 ) 305 - 308 2020

ISSN 00078506

Ultraprecision polishing of miniature components and features with small curvature radii is limited by surface accessibility, availability of suitable tools and the capability to control material removal with sufficient spatial resolution. This paper presents the development of an approach for the application of nearly deterministic micro polishing using miniature tools with 400 μm radius. To enable implementation of the proposed approach, the effect of tool wear and polymer relaxation on the control of local contact pressure is characterized and compensation of tool wear along the tool path is introduced. The process is experimentally validated by application to features in nickel phosphor with lateral dimensions down to 2 mm, yielding roughness down to less than Sa 1 nm and profile accuracy better than 10 nm P-V.

Access to Document (DOI)

Non-Newtonian fluid based contactless sub-aperture polishing

Wu-Le Zhu, Anthony Beaucamp

CIRP Annals (Elsevier USA) 69 ( 1 ) 293 - 296 2020

ISSN 00078506

Compliant polishing (e.g. bonnet polishing) is widely used to finish freeform surfaces. However, direct pad/surface contact often causes scratches or embedding of abrasives, especially on metal moulds. Here, the use of non-Newtonian fluid (polymer and starch) to enable contactless polishing without need for a polishing pad is reported. Modelling and analysis are conducted to reveal the influence of fluid rheology on the material removal mechanism. Using #6000 grit alumina, Gaussian shaped removal footprints can be obtained, with a completely scratch-free roughness of 3.9 nm Ra on Nickel, in contrast with 70.3 nm Ra obtained by general water based bonnet polishing.

Access to Document (DOI)

Feed-rate scheduling by optimization of bulk removal

Mizoue Yuichi, Beaucamp Anthony, Matsubara Atsushi

Proceedings of JSPE Semestrial Meeting (The Japan Society for Precision Engineering) 2020 159 - 160 2020

The scheduling of feed-rate is an important procedure in CNC finishing of high-precision optical surfaces. Since the polishing process is described as the convolution operation between a tool influence function and a dwell-time map, deconvolution operation gives an optimal dwell-time map. However, physical achievability of the obtained dwell-time map is not considered. This research elucidates the effect of the bulk removal, a constant removal layer across the surface, on the convolution process in spatial domain and time domain. Based on this investigation, we propose a theory that has the potential to analytically adjust dwell-time, feed-rate, and acceleration without compromising the surface accuracy, and to predict the total machining time as a function of the bulk removal.

Access to Document (DOI)

Zernike mapping of optimum dwell time in deterministic fabrication of freeform optics

Wule Zhu, Anthony Beaucamp

Optics Express 27 ( 20 ) 28692 - 28706 2019.09

Accepted

© 2019 Optical Society of America. In optics fabrication technologies such as computer controlled optical surfacing (CCOS), accurate computation of the dwell time map plays an essential role in the deterministic performance of the fabrication process. However, it is still difficult for existing methods to derive smooth dwell time maps that reduce dynamic stressing on the machine especially at the aperture edge region, while retaining fine correction capability on freeform optics. To answer these challenges, we propose a new method based on Zernike decomposition and improved differential evolution optimization of the dwell time map, which can be applied to time-dependent optics fabrication processes such as fluid jet machining. Simulations and experiments based on a bi-sinusoidal freeform design were carried out to assess the feasibility of the proposed methodology. With appropriate fluid jet pressure, a bi-sinusoidal optical surface with demanding form error target of sub-100 nm in peak-to-valley was achieved, showing a remarkable improvement on the state-of-the-art, while keeping a good average surface roughness of 2.6 nm Ra on the optical glass.

Access to Document (DOI)

Theoretical and experimental investigation of material removal mechanism in compliant shape adaptive grinding process

Wu Le Zhu, Yue Yang, Hao Nan Li, Dragos Axinte, Anthony Beaucamp

International Journal of Machine Tools and Manufacture (ELSEVIER SCI LTD) 142 76 - 97 2019.07

Accepted, ISSN 08906955

© 2019 Elsevier Ltd Modeling of grinding process, especially the grinding forces, has been studied extensively. Most previous work concerns the conventional grinding process using a rigid wheel, where the forces are generally based on the preset depth of grinding. However, for compliant grinding such as Shape Adaptive Grinding (SAG) that adopts an elastic tool covered with abrasive pellets, the penetration depth of individual abrasive grains is not simply equal to the preset value. As elastic contact occurs between the tool and workpiece, previous models are not able to estimate the material removal mechanism. Besides, the progressive transitions in grain-workpiece interaction for compliant cutting tools have not been reported yet. To fill these gaps and to offer a fundamental understanding of the compliant grinding process, we propose in this study a new multi-scale model spanning from macroscopic tool-workpiece contact to microscopic grain-workpiece interaction in the unique conditions of using a compliant grinding tool, i.e. SAG tool. Based on the spring-grain model and considering the stochastic nature of grain size and wear flat area, the static penetration and dynamic removal of individual grain can be predicted. Particularly, the removal mechanism is clarified with a new consideration of the transition between rubbing, plowing and cutting stages for each individual grain of the compliant tool. Experiments including scratch tests and removal footprints were carried out, and the high consistency with theoretical predictions validates the proposed model. Finally, considering the progressive abrasive wear in grinding, in-process wear compensation was conducted to enable consistent material removal on aspheric steel molds. The proposed method is not only meaningful to reveal the mechanism of SAG process, but also offers a new foundation for studying other compliant grinding processes in future.

Access to Document (DOI)

Ultra-precision finishing of low expansion ceramics by compliant abrasive technologies: A comparative study

Wu Le Zhu, Anthony Beaucamp

Ceramics International (ELSEVIER SCI LTD) 45 ( 9 ) 11527 - 11538 2019.06

Accepted, ISSN 02728842

© 2019 Advanced ceramics have many attractive features such as high stability and wear resistance that find broad applications in various fields, e.g. optics, aerospace, etc. However, the accompanying difficult-to-machine property with complex geometry brings great challenges to the commonly used laser machining and rigid wheel based grinding in industry. To achieve optical surface quality with surface roughness below 10 nm Ra, three promising ultra-precision compliant machining technologies using adaptive elastic tools are presented in this paper, including bonnet polishing, compliant pitch polishing and shape adaptive grinding with fine grain size. A comparative study was conducted by machining three different low thermal expansion ceramics while continuously increasing attack angle, spindle speed and tool offset across rectangular regions. Material removal rate (MRR) and surface roughness (Ra) with respect to different process conditions are compared. With sufficient data, the processing ability using above three compliant machining technologies is summarized based on the MRR-Ra plots for different ceramics. In addition, microscopic observation and X-ray diffraction analysis are conducted to characterize differences in material behavior.

Access to Document (DOI)

Title advances in optical fabrication for astronomy

David D. Walker, Guoyu Yu, Hongyu Li, Brian W. Myer, Anthony T. Beaucamp, Yoshiharu Namba, Lunzhe Wu

Monthly Notices of the Royal Astronomical Society (OXFORD UNIV PRESS) 485 ( 2 ) 2071 - 2082 2019.02

Accepted, ISSN 00358711

© The Author(s) 2018. The fabrication of precision optical surfaces has undergone a revolution in recent years. The first purpose of this paper is to present case studies of novel optical designs not previously published, that utilize complex, or 'freeform', surfaces. These designs are described both for their own merits, and as pointers towards the types of adventurous designs for ground or space-based astronomy that might now be envisaged. The potential benefits are enhanced optical performance in more compact, lower mass, and rugged packages. Such designs would, until recently, have been impossible to fabricate, and so we also describe some of the recent technical advances that have materially changed this position.

Access to Document (DOI)

走査型原子間力顕微鏡を用いた単粒子研磨加工実験と準連続体解析の比較

永井孝太郎, Anthony Beaucamp, 松原厚

精密工学会学術講演会講演論文集 (公益社団法人精密工学会) 2019 54 - 55 2019

本研究では，走査型原子間力顕微鏡を用いて，ナノスケールでの単純押し込み実験と，単粒子による研磨加工の模擬実験を行った．また，準連続体解析と実験結果を比較することで，解析法の妥当性を検証した．その結果，単純押し込み実験においては，解析結果が実験結果と一致することがわかった．一方，単粒子研磨加工実験では，金属短針の摩耗という実験における問題点が明らかとなった．

Access to Document (DOI)

Abrasive processes for micro parts and structures

J. C. Aurich, Benjamin Kirsch, Dinesh Setti, Dragos Axinte, Anthony Beaucamp, Paul Butler-Smith, Hitomi Yamaguchi

CIRP Annals 68 ( 2 ) 653 - 676 2019

Accepted, ISSN 00078506

© 2019 The demand for miniaturized products and functionalized parts is increasing, and many such products are made of hard and brittle materials machined by abrasive processes. The first part of this keynote paper is dedicated to a discussion of micro parts and micro structures machined – at least in part – by abrasive processes, followed by a discussion of the associated abrasive processes. The strengths and limitations of these processes, among which include dicing, micro grinding, micro abrasive blasting, and vibration and magnet field assisted finishing are discussed. The paper concludes with a discussion of future trends in the field.

Access to Document (DOI)

Model of material removal in vibratory finishing, based on Preston's law and discrete element method

Yusuke Makiuchi, F. Hashimoto, Anthony Beaucamp

CIRP Annals (ELSEVIER SCIENCE BV) 68 ( 1 ) 365 - 368 2019

Accepted, ISSN 00078506

© 2019 Vibratory finishing is widely used in mass-finishing of components. However, it is difficult to guarantee shape accuracy and predict surface roughness evolution. Here, a material removal model is proposed that is based on Preston's law and statistical overlapping of particle trajectories computed by Discrete Element Method (DEM). After validating DEM motion by particle image velocimetry and rope experiment, the occupancy ratio is studied as function of media type and mixing. Predictions of removal volume and surface roughness agree with experimental results within 12% on average, making this simulation method a very practical tool that reduces the need for extensive trial runs and barrel reloading.

Access to Document (DOI)

Centrifugal and hydroplaning phenomena in high-speed polishing

Wu Le Zhu, Soufian Ben Achour, Anthony Beaucamp

CIRP Annals (ELSEVIER SCIENCE BV) 68 ( 1 ) 369 - 372 2019

Accepted, ISSN 00078506

© 2019 Super fine polishing with compliant tools can achieve nanoscale roughness, but has limited productivity due to low material removal rate (MRR). Increased spindle speed in high-speed polishing (HSP) might increase MRR, but significant challenges appear above 10,000 rpm because of centrifugal deformation of the tool and pad lifting due to hydroplaning phenomenon. Here, a tool offset compensation strategy is proposed for centrifugal deformation and novel pad patterning design that mitigates hydroplaning. Through this new approach, linear increase in MRR for spindle speed up to 24,000 rpm is demonstrated. This work lays the foundation for future developments of HSP in fabrication of ultraprecision optics.

Access to Document (DOI)

Theoretical study of path adaptability based on surface form error distribution in fluid jet polishing

Yanjun Han, Lei Zhang, Cheng Fan, Wule Zhu, Anthony Beaucamp

Applied Sciences (Switzerland) (MDPI) 8 ( 10 ) 1814 2018.10

Accepted, ISSN 2076-3417

© 2018 by the authors. In the technology of computer-controlled optical surfacing (CCOS), the convergence of surface form error has a close relationship with the distribution of surface form error, the calculation of dwell time, tool influence function (TIF) and path planning. The distribution of surface form error directly reflects the difference in bulk material removal depth across a to-be-polished surface in subsequent corrective polishing. In this paper, the effect of path spacing and bulk material removal depth on the residual error have been deeply investigated based on basic simulation experiments excluding the interference factors in the actual polishing process. With the relationship among the critical evaluation parameters of the residual error (root-mean-square (RMS) and peak-to-valley (PV)), the path spacing and bulk material removal depth are mathematically characterized by the proposed RMS and PV maps, respectively. Moreover, a variable pitch path self-planning strategy based on the distribution of surface form error is proposed to optimize the residual error distribution. In the proposed strategy, the influence of different bulk material removal depths caused by the distribution of surface form error on residual error is compensated by fine adjustment of the path spacing according to the obtained path spacing optimization models. The simulated experimental results demonstrate that the residual error optimization strategy proposed in this paper can significantly optimize the overall residual error distribution without compromising the convergence speed. The optimized residual error distribution obtained in sub-regions of the polished surface is more uniform than that without optimization and is almost unaffected by the distribution of parent surface form error.

Access to Document (DOI)

Process mechanism in ultrasonic cavitation assisted fluid jet polishing

Anthony Beaucamp, Tomoya Katsuura, Kie Takata

CIRP Annals (ELSEVIER SCIENCE BV) 67 ( 1 ) 361 - 364 2018.01

Accepted, ISSN 00078506

© 2018 Material removal rate in fluid jet polishing is significantly enhanced when ultrasonic cavitation bubbles are introduced at the nozzle outlet. In this paper, two theories are put forward to explain the process mechanism: a micro-scale hypothesis in which the surface is micro-jetted by collapsing bubbles, and a macro-scale hypothesis in which vibration of the fluid in the impingement region increases abrasive particle erosive action. Experimental investigation suggests the higher likelihood of the macro-scale phenomenon, and a material removal model is proposed accordingly. Process footprints simulated by this model were found to agree well with experimental measurements.

Access to Document (DOI)

Research on edge-control methods in CNC polishing

Guoyu Yu, David Walker, Hongyu Li, Xiao Zheng, Anthony Beaucamp

Journal of the European Optical Society (EUROPEAN OPTICAL SOC) 13 ( 1 ) 24 2017.12

Accepted, ISSN 1990-2573

© 2017, The Author(s). Background: We have developed edge-control for the Precessions TM process suitable for fast fabrication of large mirror segments, and other applications sensitive to edge mis-figure. This has been applied to processing of European extremely large telescope (E-ELT) prototype mirror-segments, meeting the specification on maximum edge mis-figure. However we have observed residuals that have proved impossible to correct with this approach, being in part the legacy of asymmetries in the input edge-profiles. Methods: We have therefore compared different proposed methods experimentally and theoretically and report here on a new edge-rectification step, which operates locally on edges, does not disturb the completed bulk area. Results: A new toolpath has been developed and experiments have been carried out to demonstrate that local edge rectification can be carried out. Conclusions: With this method, the residue error on edges can be removed separately and has potential to reduce total process time.

Access to Document (DOI)

Automated finishing of organ models created by 3D printing

Yoshihide Tamaki, Kohji Niwa, Anthony Beaucamp, Yoshimi Takeuchi

Proceedings of the 9th International Conference on Leading Edge Manufacturing in 21st Century, LEM 2017 2017.11

Accepted

In recent years, transparent resin organ models created by 3D printing have found application in the medical fields. The inside of the organ model contains diseased parts, blood vessels and so on, but they cannot be seen due to the layered appearance of printed surfaces. To address this issue, an automated system was developed using an industrial robot to replace the manual polishing currently needed. The automated system consists of three aspects: fixturing of the organ model, polishing tool path generation and polishing process conditions. From polishing experiments on a relatively simple shape, it was found that the system has the potential to deliver transparent surfaces on complex resin organ models.

Access to Document (DOI)

Virtual pivot alignment method and its influence to profile error in bonnet polishing

Junkang Guo, Anthony Beaucamp, Soichi Ibaraki

International Journal of Machine Tools and Manufacture (ELSEVIER SCI LTD) 122 18 - 31 2017.11

Accepted, ISSN 08906955

© 2017 Elsevier Ltd This paper proposes a measurement and adjustment procedure for virtual pivot errors using the R-test and investigates the influence of virtual pivot errors to the surface profile in bonnet polishing. Initially, kinematic modeling is carried out for describing the location errors of rotary axes and defining overall errors of the virtual pivot arm. Then, the R-test is introduced to measure the three-dimensional displacement of a sphere located at the virtual pivot point and identify location errors. The adjustment procedure for virtual pivot errors is developed by means of mathematical analysis. The measurement and adjustment approach is applied to an ultra-precision polishing machine, on which an adjustment experiment was conducted to validate the proposed method. Based on this, a contrastive polishing experiment on a concave lens is carried out under good and poor virtual pivot errors. The experiment result shows that the maximum form deviation of the polished surface profile is reduced from 241.0 nm to 89.6 nm when good alignment of virtual error is achieved. Analytical simulation based on a material removal model of the bonnet polishing tool and machine is implemented to reveal the influence of virtual pivot errors to polishing quality.

Access to Document (DOI)

Comparison of tool feed influence in CNC polishing between a novel Circular-random path and other pseudo-random paths

Ken Takizawa, Anthony Beaucamp

Optics Express (OPTICAL SOC AMER) 25 ( 19 ) 22411 - 22424 2017.09

Accepted, ISSN 1094-4087

© 2017 Optical Society of America. A new category of circular pseudo-random paths is proposed in order to suppress repetitive patterns and improve surface waviness on ultra-precision polished surfaces. Random paths in prior research had many corners, therefore deceleration of the polishing tool affected the surface waviness. The new random path can suppress velocity changes of the polishing tool and thus restrict degradation of the surface waviness, making it suitable for applications with stringent mid-spatial-frequency requirements such as photomask blanks for EUV lithography.

Access to Document (DOI)

Modelling the brittle/ductile transition in super-fine finishing of carbides

Anthony Beaucamp

APPLIED MECHANICS & MATERIALS 869 20 - 28 2017.08

Accepted

Access to Document (DOI)

Brittle-ductile transition in shape adaptive grinding (SAG) of SiC aspheric optics

Anthony Beaucamp, Peter Simon, Phillip Charlton, Christopher King, Atsushi Matsubara, Konrad Wegener

International Journal of Machine Tools and Manufacture (ELSEVIER SCI LTD) 115 29 - 37 2017.04

Accepted, ISSN 08906955

© 2016 Elsevier Ltd Silicon carbide is a ceramic material with a desirable combination of high thermal and mechanical stability, making it ideal for optical application in aerospace and next generation lithography. It is however notoriously difficult to machine down to super-fine finish when the shape is other than flat or spherical. In this paper, we describe the application of a “semi-elastic” machining method called shape adaptive grinding (SAG), in which an elastic tool is combined with rigid pellets made of nickel or resin, to which super abrasives are bonded. A comprehensive model of the physical interaction between SAG tool and workpiece is proposed, and used to understand the mechanics driving brittle-ductile transition on ceramic materials such as SiC. Machining parameters adequate for optical finishing are then derived from the model and demonstrated on an aspheric silicon carbide workpiece, which was manufactured by reaction bonding and coated with a layer of pure SiC by chemical vapour deposition (CVD). Through SAG processing and final polishing, this aspheric mirror was improved from an initial form error of 40 µm down to 112 nm Peak-to-Valley, with no residual damage visible on the surface.

Access to Document (DOI)

Development of drill property prediction system based on drill shape

KAWAI Kimio, BEAUCAMP Anthony, IMAIZUMI Noriyuki, SAKURAI Masatoshi, TAKEUCHI Yoshimi

Transactions of the JSME (in Japanese) (The Japan Society of Mechanical Engineers) 83 ( 855 ) 17 - 00162 2017.01

Accepted, ISSN 2187-9761

In recent years, the drill used to make holes is expected to exert both high machining accuracy and good processing capability. In order to meet those requirements, it is necessary to develop a new drill shape with good properties requested by designers. There is a strong need for a new system to shorten the drill fabrication time, to reduce material costs, and to create new drill configurations by predicting their characteristics. Current drill shape prediction systems cannot comprehensively and mathematically treat drill cross-section shape including the cutting edge, groove and so on. The prediction system would become more practical if the drill specification was mathematically formulated. This study reports the development of a system to predict not only the cross-sectional shape but also various parameters from the information of grinding wheels used in drill fabrication. Furthermore, this study proposes the new system to predict the most suitable grinding wheel setting from the grinding wheel shape and some drill specifications as the reverse process.

Access to Document (DOI)

5-Axis Control Finishing for Decreased Tool Wear

Soushi Uchikata, Anthony Beaucamp, Yoshimi Takeuchi

Procedia CIRP (ELSEVIER SCIENCE BV) 63 313 - 317 2017

Accepted, ISSN 22128271

© 2017 The Authors. Published by Elsevier. With increasing global competition, reduction in the machining cost is the most important issue after machining quality. The machining cost consists of various factors. Among them, the cost of cutting tool holds the first place. The reduction or suppression of tool cost results in an increase in competitive force. This study aims at lengthening the tool life, while decreasing the tool wear. Therefore, the cutting edge of a ball end mill is swung around its center by continuously changing the tool axis vector so that the cutting edge may be uniformly used. Taking account of the width of the flank wear of the ball end mill and the surface roughness of the workpiece in the finishing process, the study proposes an appropriate tool attitude and a suitable tool swing rate of the ball end mill. As a result, the machining method with the tool axis vector continuously swung allows for decreasing tool wear due to its dispersion across the entire tool surface. The proposed method can be applied to machining of workpieces with sculptured faces. From the experimental results, it is found that the proposed idea has the potential of saving tool cost.

Access to Document (DOI)

More steps towards process automation for optical fabrication

David Walker, Guoyu Yu, Anthony Beaucamp, Matt Bibby, Hongyu Li, Lee McCluskey, Sanja Petrovic, Christina Reynolds

Proceedings of SPIE - The International Society for Optical Engineering 10326 2017

Accepted, ISSN 0277786X

© 2017 SPIE. In the context of Industrie 4.0, we have previously described the roles of robots in optical processing, and their complementarity with classical CNC machines, providing both processing and automation functions. After having demonstrated robotic moving of parts between a CNC polisher and metrology station, and auto-fringe-Acquisition, we have moved on to automate the wash-down operation. This is part of a wider strategy we describe in this paper, leading towards automating the decision-making operations required before and throughout an optical manufacturing cycle.

Access to Document (DOI)

Dexterous Machining of Unstable Thin Plate

Yuya Kida, Kohei Toyoda, Anthony Beaucamp, Yoshimi Takeuchi

Procedia CIRP (ELSEVIER SCIENCE BV) 63 324 - 329 2017

Accepted, ISSN 22128271

© 2017 The Authors. Published by Elsevier. In recent years, miniaturization and light weightedness are required for industrial products as well as high functionality. Thin plates are appropriate in terms of weight, however they are usually difficult to produce only by cutting operation due to the deformation by cutting force or vibration of the thin plate. This study deals with the machining of a twisted thin plate, whose height, width and thickness are 50 mm, 30 mm and 0.1 mm respectively, without using any auxiliary tool. Such a thin plate with high aspect ratio is easily broken down by the cutting force. Thus, the machining of thin plate with high aspect ratio is approached by devising a tool path strategy in this study. As the cutting force easily allows for deformation of twisted thin plate with high aspect ratio, two methods are devised with regard to the generation of the tool path, the method with a supporting frame and the peeling method so that the stiffness of the plate can be kept high. Then, the actual machining of thin plate with high aspect ratio, made of aluminum alloy, was realized without any breakage. As a result, it is found that such cutting method allows the possibility of fabricating such a twisted thin plate.

Access to Document (DOI)

Development of drill property prediction system based on drill shape

BEAUCAMP, Anthony Tadeus Herve

Transactions of the JSME (The Japan Society of Mechanical Engineers) 83 ( 855 ) 17-00162 - 00162-17-00162 2017

Accepted

Access to Document (DOI)

A novel ultrasonic cavitation assisted fluid jet polishing system

Anthony Beaucamp, Tomoya Katsuura, Zensaku Kawara

CIRP Annals - Manufacturing Technology (ELSEVIER SCIENCE BV) 66 ( 1 ) 301 - 304 2017

Accepted, ISSN 00078506

© 2017 Fluid jet polishing is a versatile process used for super-fine finishing of small and complex optical and prosthetic surfaces. Advantages of this process include highly controllable sub-millimetre polishing footprints and absence of tool wear, though the main drawback is very low material removal rate. To address this issue, a novel system was developed in which ultrasonic cavitation causes micro-bubble generation directly upstream of the nozzle outlet. Experimental data shows that these micro-bubbles boost removal rate by up-to 380%, without causing any degradation of the surface finish. This paper reports on the modelling, implementation, and testing of this new polishing system.

Access to Document (DOI)

超音波キャビテーションを利用した高速流体噴射研磨

勝浦知也, Anthony Beaucamp, 松原厚

精密工学会学術講演会講演論文集 (公益社団法人精密工学会) 2016 117 - 118 2016.01

Access to Document (DOI)

円弧ランダムパスを用いたCNC研磨による研削模様の除去

瀧沢賢, Anthony Beaucamp, 松原厚

精密工学会学術講演会講演論文集 (公益社団法人精密工学会) 2016 615 - 616 2016.01

Access to Document (DOI)

Brittle-ductile transition in shape adaptive grinding (SAG)

Peter Simon, Anthony Beaucamp, Phillip Charlton, Yoshiharu Namba

Optics InfoBase Conference Papers FW5G ( 2 ) 2016

Accepted

Access to Document (DOI)

Dexterous creation of soccer-ball pattern by using urethane rubber

Kosuke Funatani, Keiichi Nakamoto, Anthony Beaucamp, Yoshimi Takeuchi

International Journal of Automation Technology (Fuji Technology Press) 10 ( 2 ) 239 - 243 2016

Accepted, ISSN 18817629

© 2016, Fuji Technology Press. All rights reserved. It is important to establish new approaches to create value-added products, such as craftwork or artistic goods, that are different from traditional methods of realizing high-quality and low-cost products. Such a production technology is commonly called “dexterous machining.” This study addresses the creation of artistic products by using soft materials with complicated shapes by employing an aqueous solution of sodium acetate to fix a workpiece and to suppress the deformation. Experimental results show that the use of an aqueous solution of sodium acetate has the potential to realize the “dexterous machining” of soft objects.

Access to Document (DOI)

Modelling of drill shapes by a novel predictive system

Kimio Kawai, Anthony Beaucamp, Noriyuki Imaizumi, Masatoshi Sakurai, Yoshimi Takeuchi

Proceedings of the 8th International Conference on Leading Edge Manufacturing in 21st Century, LEM 2015 2015.10

Accepted

There is a strong need for a new system to shorten the drill fabrication time, to reduce material costs, and to create new drill configurations by predicting their characteristics. Current drill shape prediction systems cannot comprehensively treat drill cross-section shape including the cutting edge, groove and so on, mathematically. Modelling would become more practical if the drill specification was mathematically formulated. This study reports the development of a system to predict not only cross-section shape but also various parameters from grinding wheels used in drill fabrication.

Shape Adaptive Grinding (SAG): A new process for finishing of ceramics and high-performance alloys

Anthony Beaucamp, Atsushi Matsubara, Samyak Jain, Christophe Bouvier, Roger Morton

Proceedings of the 8th International Conference on Leading Edge Manufacturing in 21st Century, LEM 2015 2015.10

Accepted

Shape Adaptive Grinding (SAG) is a new process for freeform finishing of difficult materials such as ceramics and high-performance alloys. The basic principle of SAG can be described as "semi-elasticity": compliance is achieved with freeform workpieces by an elastic spherical tool, while hard contact is simultaneously achieved by small rigid pellets covering this elastic tool (diamond or cubic boron nitride super-abrasives are embedded in these pellets). In this paper, we present recent developments in the application of SAG to (1) corrective grinding of aspheric silicon carbide optics, and (2) smoothing of high-performance titanium alloy components produced by additive manufacturing.

Finishing of additively manufactured titanium alloy by shape adaptive grinding (SAG)

Anthony T. Beaucamp, Yoshiharu Namba, Phillip Charlton, Samyak Jain, Arthur A. Graziano

Surface Topography: Metrology and Properties (IOP PUBLISHING LTD) 3 ( 2 ) 024001 2015.04

Accepted, ISSN 2051-672X

© 2015 IOP Publishing Ltd. In recent years, rapid prototyping of titanium alloy components for medical and aeronautics application has become viable thanks to advances in technologies such as electron beam melting (EBM) and selective laser sintering (SLS). However, for many applications the high surface roughness generated by additive manufacturing techniques demands a post-finishing operation to improve the surface quality prior to usage. In this paper, the novel shape adaptive grinding process has been applied to finishing titanium alloy (Ti6Al4V) additively manufactured by EBM and SLS. It is shown that the micro-structured surface layer resulting from the melting process can be removed, and the surface can then be smoothed down to less than 10 nmRa (starting from 4-5 μmRa) using only three different diamond grit sizes. This paper also demonstrates application of the technology to freeform shapes, and documents the dimensional accuracy of finished artifacts.

Access to Document (DOI)

277 Development of system for new drill creation

KAWAI Kimio, BEAUCAMP Anthony, IMAIZUMI Noriyuki, SAKURAI Masatoshi, TAKEUCHI Yoshimi

東海支部総会講演会講演論文集 (The Japan Society of Mechanical Engineers) 2015 ( 64 ) 277 - 1 2015.01

Accepted

Process mechanism in shape adaptive grinding (SAG)

Anthony Beaucamp, Yoshiharu Namba, Phillip Charlton

CIRP Annals - Manufacturing Technology (ELSEVIER SCIENCE BV) 64 ( 1 ) 305 - 308 2015

Accepted, ISSN 00078506

© 2015 CIRP. Shape adaptive grinding (SAG) is a novel process for freeform machining of difficult materials such as ceramics and hard metals. Despite low stiffness requirement from the machining equipment, due to the "semi-elasticity" of the process (achieved by a combination of elastic tool with rigid pellets), ductile mode grinding can be achieved with high surface finish. In this paper, the SAG process mechanism is investigated by studying how the size and shape of the pellet bonded abrasives evolve over time, measuring grinding forces for various process parameters, and comparing the equivalent chip thickness and specific energy with the observed grinding modes.

Access to Document (DOI)

Dynamometric Analysis of Shape Adaptive Grinding (SAG)

Beaucamp Anthony, Namba Yoshiharu, Charlton Phillip

Proceedings of JSPE Semestrial Meeting (The Japan Society for Precision Engineering) 2015 983 - 984 2015

The novel Shape Adaptive Grinding (SAG) process, which uses diamond abrasives bonded in nickel or resin pellets attached to an elastic tool, has been previously demonstrated in finishing freeform ceramic molding dies with surface roughness below 1 nm Ra. In this paper, a dynamometer was used to characterize grinding forces and the results show that contrary to conventional grinding, in SAG the grinding force increases proportionally to the diamond grit size. The chip thickness was derived statistically, and the grinding mechanism was correlated with previous observations of the ductile to fracture grinding mode transition.

Access to Document (DOI)

Shape Adaptive Grinding of silicon carbide aspheric optic

Anthony Beaucamp, Yoshiharu Namba, Phillip Charlton, Samyak Jain

Proceedings of Frontiers in Optics 2015, FIO 2015 FM1G ( 2 ) 2015

Accepted

Access to Document (DOI)

Shape adaptive grinding (SAG) of complex additively manufactured parts

Anthony T. Beaucamp, Yoshiharu Namba, Phillip Charlton, Samyak Jain, Arthur A. Graziano

Proceedings - ASPE 2015 Spring Topical Meeting: Achieving Precision Tolerances in Additive Manufacturing 141 - 146 2015

Accepted

Shape adaptive grinding of optical surfaces for scientific applications and consumer products

Anthony Beaucamp, Yoshiharu Namba, Phillip Charlton, Arthur Graziano

Frontiers in Optics, FiO 2014 FTh4 ( G3 ) 2014.10

Accepted

Access to Document (DOI)

Shape Adaptive Grinding (SAG) - A novel fabrication method for freeform optical moulds

A. Beaucamp, Y. Namba

OPTICAL FABRICATION & TESTING - OSA TECHNICAL DIGEST OTu3 ( B5 ) 2014.08

Accepted

Access to Document (DOI)

Corrective finishing of extreme ultraviolet photomask blanks by precessed bonnet polisher

Anthony Beaucamp, Yoshiharu Namba, Phillip Charlton

Applied Optics 53 ( 14 ) 3075 - 3080 2014.05

Accepted, ISSN 1559128X

© 2014 Optical Society of America. The progressive transition from Excimer to extreme ultraviolet (EUV) lithography is driving a need for flatter and smoother photomask blanks. It is, however, proving difficult to meet the next-generation specification with the conventional chemical mechanical polishing technology commonly used for finishing photomask blanks. This paper reports on the application of subaperture computer numerical control precessed bonnet polishing technology to the corrective finishing of photomask substrates for EUV lithography. Full-factorial analysis was used to identify process parameters capable of delivering microroughness below 0.5 nm rms while retaining relatively high removal rates. Experimental results show that masks prepolished to 300-600 nm peak-to-valley (P-V) flatness by chemical/mechanical polishing can then be improved down to 50-100 nm P-V flatness using the automated technology described in this paper. A series of edge polishing experiments also hints at the possibility of increasing the quality area beyond the 142 mm square defined in the official EUV photomask specification.

Access to Document (DOI)

D04 Development of CAM system for new drill shape creation

KAWAI Kimio, BEAUCAMP Anthony, IMAIZUMI Noriyuki, SAKURAI Masatoshi, TAKEUCHI Yoshimi

The ... Manufacturing & Machine Tool Conference (The Japan Society of Mechanical Engineers) 2014 ( 10 ) 207 - 208 2014.01

Accepted

It is strongly requested to develop a new CAM system to shorten the drill fabrication time, to reduce material costs, and to create a new drill configuration by predicting its characteristics. Current drill shape prediction system cannot necessarily treat drill cross-section shape including the cutting edge, groove and so on, mathematically. The system becomes practical if these drill specification is mathematically formulated. The study reports the development of a system to predict not only cross-section shape but also various parameters from grinding wheel data of drill making.

Fabrication of parabolic wolter type-I molding die with 100 nm form accuracy

Anthony Beaucamp, Yoshiharu Namba, Richard Freeman

Proceedings - ASPE/ASPEN Summer Topical Meeting: Manufacture and Metrology of Freeform and Off-Axis Aspheric Surfaces 9 - 12 2014

Accepted

Technological advances in super fine finishing

Beaucamp A.T.H., Namba Y.

Conference Proceedings - 14th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2014 1 21 - 39 2014

Focusing short wavelength radiations such as Extreme Ultra-Violet (EUV) and X-rays can be accomplished by assemblies of reflective aspheric optics. Application of such systems ranges from research in X-ray astronomy and microscopy, to semiconductors production by EUV lithography. But such optical surfaces require finishing to very low levels of micro-roughness, in proportion to the wavelength of incoming radiation. In this paper, recent advances in super fine finishing technologies (capable of achieving micro-roughness below 0.5 nm rms) for aspheric and freeform optical surfaces are presented. The paper deals with both ultra-precision grinding and polishing technologies, with the performance and advantages/disadvantages of each method being discussed, and examples of applications provided.

Surface integrity of fluid jet polished tungsten carbide

Anthony Beaucamp, Yoshiharu Namba, Wilhelmus Messelink, David Walker, Phillip Charlton, Richard Freeman

Procedia CIRP 13 377 - 381 2014

Accepted

In recent years, Fluid Jet Polishing (FJP) has been studied for its potential as a finishing method on optical lenses, mirrors and molds for a number of materials, such a glass and nickel. In this paper, the surface integrity of binderless tungsten carbide after polishing by FJP was studied experimentally. Two aspects in particular were focused on: (1) identifying process conditions under which grain boundaries may dislocate (thus leading to unintentional loss of grains from the substrate) and (2) identify process conditions under which abrasive particles may become embedded into the substrate, in order to prevent surface contamination. © 2014 The Authors. Published by Elsevier B.V.

Access to Document (DOI)

Shape adaptive grinding of CVD silicon carbide

Anthony Beaucamp, Yoshiharu Namba, Herman Combrinck, Phillip Charlton, Richard Freeman

CIRP Annals - Manufacturing Technology 63 ( 1 ) 317 - 320 2014

Accepted, ISSN 00078506

Because of the direct relationship between removal rate and surface roughness in conventional grinding, ultra-precision finishing of hard coatings produced by chemical vapour deposition (CVD) usually involves several process steps with fixed and loose abrasives. In this paper, an innovative shape adaptive grinding (SAG) tool is introduced that allows finishing of CVD silicon carbide with roughness below 0.4 nm Ra and high removal rates up-to 100 mm 3/min. The SAG tool elastically complies with freeform surfaces, while rigidity at small scales allows grinding to occur. Since material removal is time dependent, this process can improve form error iteratively through feed moderation. © 2014 CIRP.

Access to Document (DOI)

Shape Adaptive Grinding (SAG): A Novel Fabrication Method for Freeform Optical Molds

Anthony Beaucamp and Yoshiharu Namba

Classical Optics 2014 ($\lbrace$OSA$\rbrace$) 2014

Access to Document (DOI)

Manufacture of aspherical molding dies for x-ray telescopes after ASTRO-H

Yoshiharu Namba, Anthony Beaucamp, Hironori Matsumoto, Keisuke Tamura, Yuzuru Tawara, Hideyo Kunieda, Tadayuki Takahashi

Proceedings of SPIE - The International Society for Optical Engineering 9144 2014

Accepted, ISSN 0277786X

© 2014 SPIE. Producing X-ray imaging space telescopes is a very expensive endeavor, due in great part to the difficulty of fabricating thin mirrors for Wolter type-I optical assemblies. To meet this challenge, replication from optical molding dies (also called mandrels) has become the preferred method, as it is reliable and economical. Several replication methods exist: in the case of the ASTRO-H mission, DC magnetron sputtering was used to deposit Pt/C multilayer coating on glass molding dies. The multilayer coating was then bonded with epoxy to aluminum shells and then separated from the die. Another mirror replication method consists of slumping thin glass sheets over a full (or a section of) revolution molding die under high temperature. This method was demonstrated in the case of the NuSTAR mission. But the challenge of fabricating truly aspheric Wolter type molding dies, which are capable of highly accurate angular resolution (below 5 arcs), remains very expensive and time consuming. In this paper, three methods for producing X-ray optic molding dies are presented. Each method uses a different substrate material and process chain, as follows: electroless nickel plated aluminum (first diamond turned then correctively polished), fused silica (first precision ground then correctively polished), and CVD silicon carbide (which can be finished entirely with a newly developed Shape Adaptive Grinding process). The process chains employed for each method are explained in details, and their relative merits discussed. A way forward for the next generation of X-ray telescopes after ASTRO-H is then drawn out.

Access to Document (DOI)

Interactions between manufacture and measurement of off-axis aspheres

David D. Walker, Anthony Beaucamp, Matt Bibby, Tony Fox-Leonard, Caroline Gray, Christopher King, Paul Rees, Guoyu Yu

Proceedings - ASPE/ASPEN Summer Topical Meeting: Manufacture and Metrology of Freeform and Off-Axis Aspheric Surfaces 72 - 77 2014

Accepted

High Energy Fluid Jet Machining (HEFJet-Mach): From scientific and technological advances to niche industrial applications

D. A. Axinte, B. Karpuschewski, M. C. Kong, A. T. Beaucamp, S. Anwar, D. Miller, M. Petzel

CIRP Annals - Manufacturing Technology 63 ( 2 ) 751 - 771 2014

Accepted, ISSN 00078506

With the increasing demands to generate complex parts on ever-more advanced, but difficult-to-cut materials, a group of technologies, generically called High Energy Fluid Jet Machining (HEFJet-Mach) has found niche applications that stimulated further development of science and technology in this field. Here HEFJet-Mach refers to unrestrained fluid jets used to remove and/or deform the workpiece material. The aim of this paper is to systematically present the recent developments of HEFJet-Mach from various perspectives: machine/system designs; modelling of both jet plumes and their interactions with the target surfaces; part quality including material integrity; supervision and control of the process; key aspects of machine maintenance and health and safety. © 2014 CIRP.

Access to Document (DOI)

Finishing of electron beam melted titanium (Ti6Al4V) using shape adaptive grinding tools

Anthony T. Beaucamp, Yoshiharu Namba, Phillip Charlton, Arthur A. Graziano

Proceedings - ASPE 2014 Spring Topical Meeting: Dimensional Accuracy and Surface Finish in Additive Manufacturing 62 - 65 2014

Accepted

Finishing of EUV photomask substrates by CNC precessed bonnet polisher

Anthony T.H. Beaucamp, Yoshiharu Namba, Phillip Charlton, Richard R. Freeman

Proceedings of SPIE - The International Society for Optical Engineering 8880 2013.12

Accepted, ISSN 0277786X

The progressive transition from Excimer to EUV lithography is driving a need for flatter and smoother photomasks. It is proving difficult to meet this next generation specification with the conventional chemical mechanical polishing technology commonly used for finishing photomasks. This paper reports on the application of sub-aperture CNC precessed bonnet polishing technology to the corrective finishing of photomask substrates for EUV lithography. Fullfactorial analysis was used to identify process parameters capable of delivering 0.5 nm rms surface roughness whilst achieving removal rates above 0.1 mm3/min. Experimental results show that masks pre-polished to 300~600 nm P-V flatness by CMP can then be improved down to 50~100 nm P-V flatness using the automated technology described in this paper. A series of edge polishing experiments also hints at the possibility of increasing the quality area beyond the 5 mm defined in the official EUV photomask specification. © 2013 SPIE.

Access to Document (DOI)

Development of hybrid "fluid jet / float" polishing process

Anthony T.H. Beaucamp, Yoshiharu Namba, Richard R. Freeman

Proceedings of SPIE - The International Society for Optical Engineering 8838 2013.11

Accepted, ISSN 0277786X

On one hand, the "float polishing" process consists of a tin lap having many concentric grooves, cut from a flat by single point diamond turning. This lap is rotated above a hydrostatic bearing spindle of high rigidity, damping and rotational accuracy. The optical surface thus floats above a thin layer of abrasive particles. But whilst surface texture can be smoothed to ~0.1nm rms (as measured by atomic force microscopy), this process can only be used on flat surfaces. On the other hand, the CNC "fluid jet polishing" process consists of pumping a mixture of water and abrasive particles to a converging nozzle, thus generating a polishing spot that can be moved along a tool path with tight track spacing. But whilst tool path feed can be moderated to ultra-precisely correct form error on freeform optical surfaces, surface finish improvement is generally limited to ~1.5nm rms (with fine abrasives). This paper reports on the development of a novel finishing method, that combines the advantages of "fluid jet polishing" (i.e. freeform corrective capability) with "float polishing" (i.e. super-smooth surface finish of 0.1nm rms or less). To come up with this new "hybrid" method, computational fluid dynamic modeling of both processes in COMSOL is being used to characterize abrasion conditions and adapt the process parameters of experimental fluid jet polishing equipment, including: (1) geometrical shape of nozzle, (2) position relative to the surface, (3) control of inlet pressure. This new process is aimed at finishing of next generation X-Ray / Gamma Ray focusing optics. © 2013 SPIE.

Access to Document (DOI)

Super-smooth finishing of diamond turned hard X-ray molding dies by combined fluid jet and bonnet polishing

Anthony Beaucamp, Yoshiharu Namba

CIRP Annals - Manufacturing Technology 62 ( 1 ) 315 - 318 2013.04

Accepted, ISSN 00078506

Fabricating super-smooth aspheric optics for future hard X-ray telescopes will require a new process chain. Whilst diamond turning of electroless nickel plating can generate ~100 nm P-V aspheric molding dies, associated turning marks must be removed before replication. An innovative two-step freeform finishing method is presented, that combines fluid jet and precessed bonnet polishing on a common 7-axis CNC platform. The removal rate and surface texture relationship of fluid jet with abrasive type and pressure is documented, and form correction demonstrated down to 27 nm P-V. A novel bonnet tool-pathing method called "continuous precessing" is then applied, which delivers super-smooth anisotropic surface texture of 0.28 nm rms. © 2013 CIRP.

Access to Document (DOI)

Edge control in CNC polishing, paper 2: Simulation and validation of tool influence functions on edges

Hongyu Li, David Walker, Guoyu Yu, Andrew Sayle, Wilhelmus Messelink, Rob Evans, Anthony Beaucamp

Optics Express 21 ( 1 ) 370 - 381 2013.01

Accepted

Edge mis-figure is regarded as one of the most difficult technical issues for manufacturing the segments of extremely large telescopes, which can dominate key aspects of performance. A novel edge-control technique has been developed, based on 'Precessions' polishing technique and for which accurate and stable edge tool influence functions (TIFs) are crucial. In the first paper in this series [D. Walker Opt. Express 20, 19787-19798 (2012)], multiple parameters were experimentally optimized using an extended set of experiments. The first purpose of this new work is to 'short circuit' this procedure through modeling. This also gives the prospect of optimizing local (as distinct from global) polishing for edge mis-figure, now under separate development. This paper presents a model that can predict edge TIFs based on surface-speed profiles and pressure distributions over the polishing spot at the edge of the part, the latter calculated by finite element analysis and verified by direct force measurement. This paper also presents a hybrid-measurement method for edge TIFs to verify the simulation results. Experimental and simulation results show good agreement.©2013 Optical Society of America.

Access to Document (DOI)

Ultra-Precision Machining of Aspheric Molds for Next Generation X-Ray Telescopes

Namba Yoshiharu, Beaucamp Anthony

Proceedings of JSPE Semestrial Meeting (The Japan Society for Precision Engineering) 2013 239 - 240 2013.01

Accepted

Access to Document (DOI)

Advances in corrective finishing of optical moulds for future aspheric hard X-ray telescopes

Beaucamp, A. and Namba, Y. and Charlton, P. and Freeman, R.

Optics InfoBase Conference Papers 2013

Advances in Corrective Finishing of Optical Moulds for Future Aspheric Hard X-ray Telescopes

Anthony T. Beaucamp and Yoshiharu Namba and Phillip Charlton and Richard R. Freeman

Frontiers in Optics 2013 ($\lbrace$OSA$\rbrace$) 2013

Access to Document (DOI)

Advances in corrective finishing of optical moulds for future aspheric hard X-ray telescopes

Beaucamp A., Namba Y., Charlton P., Freeman R.

Optics InfoBase Conference Papers 2013

Access to Document (DOI)

Advances in corrective finishing of optical moulds for future aspheric hard X-ray telescopes

Anthony Beaucamp, Yoshiharu Namba, Phillip Charlton, Richard Freeman

Optics InfoBase Conference Papers FTh4 ( E1 ) 2013

Accepted

Access to Document (DOI)

Automated finishing of diamond turned dies for hard X-ray and EUV optics replication

Beaucamp A., Namba Y., Freeman R.

Proceedings of SPIE - The International Society for Optical Engineering 8502 2012.12

ISSN 0277786X

Ultra-precision diamond turning can deliver very accurate form, often less than 100nm P-V. A possible manufacturing method for thin Wolter type-1 mirrors in hard X-ray space telescopes thus involves generating electroless nickel plated mandrels by diamond turning, before coating them with a reflective film and substrate. However, the surface texture after turning falls far short from the requirements of X-ray and EUV applications. The machining marks need to be removed, with hand polishing still widely employed. There is thus a compelling need for automated finishing of turned dies. A two step finishing method is presented that combines fluid jet and precessed bonnet polishing on a common 7- axis CNC platform. This method is capable of finishing diamond turned electroless nickel plated dies down to 0.28nm rms roughness, while deterministically improving form error down to 30nm P-V. The fluid jet polishing process, which consists of pressurizing water and abrasive particles for delivery through a nozzle, has been specially optimized with a newly designed slurry delivery unit and computer simulations, to remove diamond turning marks without introducing another waviness signature. The precessed bonnet polishing method, which consists of an inflated membrane rotated at an angle from the local normal to the surface and controlled by geometrical position relative to the work-piece, is subsequently employed with a novel control algorithm to deliver scratch-free surface roughness down to 0.28 nm rms. The combination of these two deterministic processes to finish aspheric and freeform dies promises to unlock new frontiers in X-ray and EUV optics fabrication. © 2012 SPIE.

Access to Document (DOI)

Finishing of electroless nickel plated dies for hard X-ray mirror replication

Anthony T. Beaucamp, Akihiro Matsumoto, Yoshiharu Namba

Proceedings - ASPE 2012 Annual Meeting ( 54 ) 414 - 417 2012.12

Accepted

Edge-control and surface-smoothness in sub-aperture polishing of mirror segments

D. Walker, A. Beaucamp, R. Evans, T. Fox-Leonard, N. Fairhurst, C. Gray, S. Hamidi, H. Li, W. Messalink, J. Mitchell, P. Rees, G. Yu

Proceedings of SPIE - The International Society for Optical Engineering 8450 2012.12

Accepted, ISSN 0277786X

This paper addresses two challenges in establishing a new process chain for polishing hexagonal segments for extremely large telescopes:- i) control of edge and corner profiles in small-tool polishing of hexagons, and ii) achieving the required smoothness of the bulk aspheric form. We briefly describe the performance of a CNC-grinding process used to create the off-axis asphere, which established the input-quality for subsequent processing. We then summarize processes for smoothing ground mid-spatials and pre- and corrective polishing using Zeeko CNC machines. The impact of two cases is considered; i) all processing stages are performed after the segment is cut hexagonal, and ii) final rectification of a hexagon after cutting from an aspherised roundel, as an alternative to ionfiguring. We then report on experimental results on witness samples demonstrating edges and corners close to the EELT segment specification, and results on a full-aperture spherical segment showing excellent surface smoothness. © 2012 SPIE.

Access to Document (DOI)

Edges in CNC polishing: From mirror-segments towards semiconductors, paper 1: Edges on processing the global surface

David Walker, Guoyu Yu, Hongyu Li, Wilhelmus Messelink, Rob Evans, Anthony Beaucamp

Optics Express 20 ( 18 ) 19787 - 19798 2012.08

Accepted

Segment-edges for extremely large telescopes are critical for observations requiring high contrast and SNR, e.g. detecting exo-planets. In parallel, industrial requirements for edge-control are emerging in several applications. This paper reports on a new approach, where edges are controlled throughout polishing of the entire surface of a part, which has been pre-machined to its final external dimensions. The method deploys compliant bonnets delivering influence functions of variable diameter, complemented by small pitch tools sized to accommodate aspheric mis-fit. We describe results on witness hexagons in preparation for full size prototype segments for the European Extremely Large Telescope, and comment on wider applications of the technology. © 2012 Optical Society of America.

Access to Document (DOI)

Dynamic multiphase modeling and optimization of fluid jet polishing process

Anthony Beaucamp, Yoshiharu Namba, Richard Freeman

CIRP Annals - Manufacturing Technology 61 ( 1 ) 315 - 318 2012.04

Accepted, ISSN 00078506

Fluid jet polishing is a machining process used increasingly in the ultra-precision manufacture of optical components and replication molds. While the process bears some similarities with abrasive water jet machining, it operates at much lower pressure and grit size. This paper presents a computational fluid dynamics model based on latest multiphase turbulent flow computational methods, simulating dynamically the interface between fluid and air. The model is then used to optimize surface texture performance down to 1 nm Ra on electroless nickel plated optical dies, while removing diamond turning marks. Some conclusions are drawn regarding the nature of the removal mechanism. © 2012 CIRP.

Access to Document (DOI)

Fluid jet and bonnet polishing of optical moulds for application from visible to X-ray

Beaucamp A., Freeman R., Matsumoto A., Namba Y.

Proceedings of SPIE - The International Society for Optical Engineering 8126 2011.11

ISSN 0277786X

Electroless Nickel (ENi) and binderless Tungsten Carbide (WC) are materials widely used in industry to make replication moulds for precision optics, with applications ranging from consumer camera lenses to high accuracy X-ray mirrors. The aspheric shape generation is generally performed by diamond turning in the case of Nickel, and microgrinding in the case of Tungsten Carbide. However, both machining methods fall short from meeting the ultra-precision criteria required by an increasing number of applications, because of insufficient form accuracy and the frequency content of the machining marks they leave on the surface. It is thus commonly observed in industry that moulds need to be subsequently polished by hand, a usually slow and human resource intensive operation. The Zeeko 7-axis CNC machine, equipped with sub-aperture fluid jet and precessed bonnet polishing technology, has been used to develop deterministic finishing processes on both Electroless Nickel and Tungsten Carbide. Corrective polishing to less than λ/20 (<31nm PV) form error can be achieved, as well as the ability to smooth surface texture down to 1nm Ra or less, in a time efficient manner. © 2011 SPIE.

Access to Document (DOI)

Finishing of optical moulds to λ/20 by automated corrective polishing

A. Beaucamp, Y. Namba, I. Inasaki, H. Combrinck, R. Freeman

CIRP Annals - Manufacturing Technology 60 ( 1 ) 375 - 378 2011.06

Accepted, ISSN 00078506

Tungsten carbide is widely used to make replication moulds for small aspheric and freeform optics, like camera lenses. Since aspheric generation by grinding generally fails to reach ultra-precision criteria, a time efficient method for finishing moulds is needed. Using a 7-axis CNC polishing machine, an on-machine tool forming technique and compensation software were developed to correctively polish a plano WC surface of diameter 25 mm from a form error above λ to below λ/20 (29 nm P-V) in under 1 h, while reducing roughness to 1.0 nm Ra. This automatic method and tooling are applicable to aspheric and freeform moulds. © 2011 CIRP.

Access to Document (DOI)

Fluid jet and bonnet polishing of optical moulds for application from visible to X-ray

Beaucamp, A.T.H. and Freeman, R.R. and Matsumoto, A. and Namba, Y.

Proceedings of SPIE - The International Society for Optical Engineering 8126 2011

Access to Document (DOI)

Fluid jet and bonnet polishing of optical moulds for applications from visible to X-Ray

A. Beaucamp, R. Freeman, A. Matsumoto, Y. Namba

Proceedings of the 11th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2011 1 29 - 32 2011

Accepted, ISSN 0277-786X

Electroless Nickel (ENi) and binderless Tungsten Carbide (WC) are widely used to make replication moulds for optics ranging from consumer camera lenses to high-accuracy X-ray mirrors. Aspheric shape generation is generally performed by diamond turning in the case of Nickel, and micro-grinding in the case of Tungsten Carbide. Both machining methods fail in general to meet the ultra-precision criteria required by an increasing number of applications. A 7-axis CNC machine equipped with sub-aperture fluid jet and precessed bonnet polishing technology was used to develop deterministic finishing processes on both Electroless Nickel and Tungsten Carbide. Corrective polishing to less than λ/20 (<31nm PV) form error can be achieved, as well as the ability to smooth surface texture down to 1nm Ra or less.

Access to Document (DOI)

Ultra-precision fluid jet and bonnet polishing for next generation hard X-ray telescope application

Anthony Th Beaucamp, Akihiro Matsumoto, Yoshiharu Namba

Proceedings - ASPE 2010 Annual Meeting 50 57 - 60 2010.12

Accepted

A study of automation of hard X-Ray molding dies polishing by FJP and BP was carried out. The following conclusions were drawn: 1. Surface roughness in the range 0.6-0.8nm rms can be obtained on electroless nickel samples by a combination of Fluid Jet polishing with micro-particles followed by Bonnet polishing with nano-particles. 2. Automated corrective polishing was demonstrated on a borosilicate cylindrical sample, with form error improvement from PV 3.2um down to 0.18um. 3. By using the automated process to get surface texture down to circa 0.6-0.8nm rms, it is possible to reduce the time of final hand polishing to 0.3nm by as much as 75% [3].

Edge-control on mirror segments

Walker D.D., Beaucamp A., Yu G., Li H.

Optics InfoBase Conference Papers 2010

Access to Document (DOI)

Active control of edges and global microstructure on segmented mirrors

D. D. Walker, A. Beaucamp, C. Dunn, R. Evans, R. Freeman, R. Morton, S. Wei, G. Yu

Proceedings of SPIE - The International Society for Optical Engineering 7018 2008.11

Accepted, ISSN 0277786X

In this paper we address two interrelated issues important to primary mirror segments for extremely large telescopes - edge-control, and the detailed topography over the segment surface. Both affect the intensity and distribution of stray light and infrared emissivity. CNC polishing processes typically deploy spiral or raster tool-paths, tending to leave repetitive features. We compare and contrast two novel families of pseudo-random tool-paths for Precessions CNC polishing. We then show how CNC control of the three-dimensional tool-path can optimize edge-profiles. Finally, we demonstrate fluid-jet polishing used to clean up residual edge defects.

Access to Document (DOI)

Removal of diamond-turning signatures on x-ray mandrels and metal optics by fluid-jet polishing

A. Beaucamp, R. Freeman, R. Morton, Karthik Ponudurai, D. D. Walker

Proceedings of SPIE - The International Society for Optical Engineering 7018 2008.11

Accepted, ISSN 0277786X

This paper describes a major advance in the post-treatment of diamond-turned surfaces to remove repetitive micro-structure; a result which could have a major beneficial impact on fabrication of Walter-type X-ray mandrels, and metal mirrors. Diamond-turning is highly deterministic and versatile in producing axially-symmetric forms, and through fast-tool servos, non-axially symmetric, free-form and micro-structured surfaces. However, the fine turning marks left in the metal surface limit performance. In this paper, we describe how fluid-jet polishing under CNC control can be used to eliminate these structures, without significantly degrading the surface roughness or form produced by the prior turning operation.

Access to Document (DOI)

Ultra-precision polishing of electroless nickel molding dies for shorter wavelength applications

Y. Namba, T. Shimomura, A. Fushiki, A. Beaucamp, I. Inasaki, H. Kunieda, Y. Ogasaka, K. Yamashita

CIRP Annals - Manufacturing Technology 57 ( 1 ) 337 - 340 2008.05

Accepted, ISSN 00078506

Electroless nickel is one of the best materials for making optical molding dies, because of its machinability with both single-point diamond turning and polishing, as well as its suitable hardness and durability. This paper deals with the ultra-precision polishing of aspheric molding dies for next-generation hard X-ray telescope mirrors, which require a super smooth surface with a roughness below 0.3 nm root-mean-square (rms). The material was machined using various methods, and a surface roughness of 0.23 nm rms was obtained on aspheric molding dies of 300 mm in diameter. A surface roughness of 0.16 nm rms was achieved on platinum/carbon multilayer mirrors, replicated from plano dies. © 2008.

Access to Document (DOI)

Improving Surface PSD Using a Random Tool Path

Christina R. Dunn and David D. Walker and Anthony Beaucamp and John Kelchner and Richard Freeman

Frontiers in Optics 2008/Laser Science XXIV/Plasmonics and Metamaterials/Optical Fabrication and Testing ($\lbrace$OSA$\rbrace$) 2008

Access to Document (DOI)

Commissioning of the first Precessions 1.2m CNC polishing machines for large optics

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Evans, R. Freeman, G. McCavana, R. Morton, D. Riley, J. Simms, G. Yu, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 6288 2006.11

Accepted, ISSN 0277786X

This paper reports on the commissioning of the first of Zeeko's 'IRP1200' 1.2m capacity 7-axis automated CNC polishing machines. These combo machines now support five different removal regimes, which are described. The machines differ substantially from Zeeko's more familiar 200mm machines on which we have focused before, in terms of overall architecture and detailed design. Large and small optics place different demands on part-fixturing, tooling, machine speeds and accelerations, metrology, slurry-handling, part-loading and access etc. These have had a profound effect on the development-path from 200 to 1.2m machines. Moreover, an advance in the kinematic design has extended the allowable range of surface slope-angles from typically 30° up to a hemisphere. The paper presents results from the pass-off trials, the first fluid-jet experiment, and the development of tooling to address a requirement to smooth a part with a local defect.

Access to Document (DOI)

Use of the 'Precessions'™ process for prepolishing and correcting 2D & 21/2D form

David D. Walker, Richard Freeman, Roger Morton, Gerry McCavana, Anthony Beaucamp

Optics Express 14 ( 24 ) 11787 - 11795 2006.11

Accepted, ISSN 10944087

The Precessions™ process polishes complex surfaces from the ground state preserving the ground-in form, and subsequently rectifies measured form errors. Our first paper introduced the technology and focused on the novel tooling. In this paper we describe the unique CNC machine tools and how they operate in polishing and correcting form. Experimental results demonstrate both the '2D' and '21/2D' form-correction modes, as applied to aspheres with rotationally-symmetric target-form. © 2006 Optical Society of America.

Access to Document (DOI)

Automated optical fabrication: First results from the new "Precessions" 1.2m CNC polishing machine

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Evans, R. Freeman, J. Kelchner, G. McCavana, R. Morton, D. Riley, J. Simms, G. Yu, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 6273 I 2006.10

Accepted, ISSN 0277786X

The requirements of space and defence optical systems and ground-based astronomy (especially extremely large telescopes) are providing optical fabricators with new challenges. These challenges particularly concern process speed, determinism and automation, and tighter tolerances on surface form and texture. Moreover, there is a growing demand for complex off-axis and 'freeform' surfaces and for larger components of the ~lm scale. With this in view, we first report on form-correction on a smaller analogue of the LRP1200 - an IRP400 in service in industry. We then report on the design, commissioning and preliminary process-development results from the first of the scaled-up 1.2m capacity CNC polishing machine from Zeeko, Ltd. This machine delivers the 'Classic' bonnet-based process, together with two new processes - fluid-jet polishing and the hybrid soft-grinding/polishing process called 'Zeeko-Grolish.' We indicate how this trio of processes running on the same machine platform with unified software can provide an unprecedented dynamic range in both volumetric removal rate and removal spot-size. This leads into a discussion of how these processes may be brought to bear on optimal control of texture and form. Preliminary performance of the 1.2m machine is illustrated with results on both axially-symmetric and more complex removal regimes. The paper concludes with an overview of the relevance of the technology to efficient production of instrumentation-optics, space optics and segmented telescope mirrors.

Access to Document (DOI)

Precessions 2.5D correction of an aspheric mirror

D. Walker, A. Beaucamp, R. Freeman, R. Morton, G. McCavana, J. Kelchner

FRONTIERS IN OPTICS - OSA TECHNICAL DIGEST PDPOF ( A1 ) 2006.08

Accepted

Access to Document (DOI)

New developments in the Precessions process for manufacturing free-form, large-optical, and precision-mechanical surfaces

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. Hobbs, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 6148 2006.03

Accepted, ISSN 0277786X

The recent upsurge in the demand for off-axis and complex "freeform" optical surfaces is driving the development of novel processes for their fabrication. This paper focuses on recent developments of the Precessions CNC polishing process for freeform surfaces, including off-axis as a special case. First, the surface-prescription and metrology-data, and their relation to the data-input for the polishing machines, are considered. The relevance of consistent coordinate frames is emphasised. An outline of how the process can 'polish' a ground freeform part (improve the texture), and then 'figure' the part (reduce the form errors) is given. Specific experimental case-studies are then presented, illustrating the versatility of the process on different materials and forms. Recent work is included in which the process-speed has been moderated in order to remove tens of nanometres of stock material, rather then the more usual hundreds of nanometres to tens of microns as in the standard Precessions process. The relevance of this to improving the ultimate surface-precision that should be achievable by this method is described. As a final illustration, the potential of the process to the rapid fabrication of the hundreds to thousands of 1-2 metre class mirror segments required for extremely large telescopes is considered.

Access to Document (DOI)

The application of optics polishing to free form knee implants

L. Blunt, P. Charlton, Anthony Beaucamp, X. Jiang

Proceedings of the 6th International Conference European Society for Precision Engineering and Nanotechnology, EUSPEN 2006 2 188 - 191 2006

Accepted

Free form surfaces have for some time played a part in the latest developments in the exploitation of new products in optics, from micro lenses up to ELT telescopes. The demands of the required tolerance on these "new" optics have led to significant improvements in manufacturing and metrology, as the capability to produce form in the tens of nanometre range coupled with nanometre surface roughness have become the critical enabler the their use. Free form surfaces are not limited to optics, and other product developments such as bio-implant surfaces in the prosthetics industry are utilising free form surfaces to make significant strides implant life. The prosthetic industry, have for some time, known from research into hip replacements, that significant reductions in the production of biologically damaging wear debris could be achieved by implementing hard on hard bearing couples rather than the traditional metal on polymer bearing couples. In these "new" knee joints the bearing couples comprise free form alumina on alumina or CoCr alloy on CoCr alloy surfaces. Unfortunately the application of these new materials for knee implants has been largely halted by the inability of manufacturers to polish their knee surfaces to the more demanding tolerances placed on free form hard on hard bearings of both form and roughness. These tolerances require micron level form deviation combined with nanometre surface finish in order to maintain full fluid film lubrication during in vivo functioning of the joint. This paper discusses the development of the capability to machine biomaterials for use as hard on hard knee joints. The surfaces are machined utilising a 7 axis CNC optics polishing machine, the Zeeko IRP200. The machine uses a novel precision technique to correctively polish components [1].

New results extending the Precessions process to smoothing ground asplieres and producing freeform parts

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 5869 1 - 9 2005.12

Accepted, ISSN 0277786X

Zeeko's Precession polishing process uses a bulged, rotating membrane tool, creating a contact-area of variable size. In separate modes of operation, the bonnet rotation-axis is orientated pole-down on the surface, or inclined at an angle and then precessed about the local normal. The bonnet, covered with standard polishing cloth and working with standard slurry, has been found to give superb surface textures in the regime of nanometre to sub-nanometre Ra values, starting with parts directly off precision CNC aspheric grinding machines. This paper reports an important extension of the process to the precision-controlled smoothing (or 'fining') operation required between more conventional diamond milling and subsequent Precession polishing. The method utilises an aggressive surface on the bonnet, again with slurry. This is compared with an alternative approach using diamond abrasives bound onto flexible carriers attached to the bonnets. The results demonstrate the viability of smoothing aspheric surfaces, which extends Precessions processing to parts with inferior input-quality. This may prove of particular importance to large optics where significant volumes of material may need to be removed, and to the creation of more substantial aspheric departures from a parent sphere. The paper continues with a recent update on results obtained, and lessons learnt, processing free-form surfaces, and concludes with an assessment of the relevance of the smoothing and free-form operations to the fabrication of off-axis parts including segments for extremely large telescopes.

Access to Document (DOI)

Recent advances in the control of form and texture on free-form surfaces

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. Hobbs, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 5965 2005.12

Accepted, ISSN 0277786X

Access to Document (DOI)

New results from the Precessions polishing process scaled to larger sizes

D. D. Walker, A. T.H. Beaucamp, D. Brooks, V. Doubrovski, M. Cassie, C. Dunn, R. Freeman, A. King, M. Libert, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5494 71 - 80 2004.12

Accepted, ISSN 0277786X

The Precessions process uses an inflated membrane-tool that delivers near-Gaussian polishing spots. The tool-motion over the part can be constructed to preserve an aspheric form whilst removing damage from preceding processes, or control the form through a tool-path prescribed by numerical optimization. The process has previously been validated on surfaces up to 200mm diameter and used extensively in industrial environments. In this paper we report the first trials on a substantially larger part - a 500mm diameter f/1 ellipsoidal mirror - as part of the UK's technology-development for Extremely Large Telescopes. We draw attention to subtle problems that have arisen along the way. We also report on developing the process for free-form surfaces, in contrast to the axially-symmetric parts worked hitherto. The paper concludes with an assessment of the lessons learnt from the experiments, as they may impact on realization in a practical ELT segment fabrication facility.

Access to Document (DOI)

Recent development of Precessions polishing for larger components and free-form surfaces

D. D. Walker, A. T.H. Beaucamp, D. Brooks, V. Doubrovski, M. Cassie, C. Dunn, R. Freeman, A. King, M. Libert, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5523 281 - 289 2004.12

Accepted, ISSN 0277786X

Since the 2003 Annual Meeting, the Precessions process has become accepted as an efficient method for polishing and figuring moderate-sized axially-symmetric aspheric parts in industry. In this paper, we report on some very significant new advances beyond this capability. The first is the demonstration of the process on substantially larger diameter parts than worked hitherto - in particular, a precision-ground 500mm diameter deeply-concave aspheric mirror. We describe the consequences of polishing large parts with the axis of the part vertical, in contrast to the horizontal axis of the smaller machines. Issues include slurry puddling and settlement in concave forms, process-uniformity, adequate support of the part and handling. We then report on recent work developing the Precessions process for non axially-symmetric surfaces including free-form. The correct relationship of the process with metrology has proved to be complex on several fronts, one example being differing descriptions of form either along a surface or its projection. We present our experience using profilometry and interferometry on precision-ground and polished surfaces, and in achieving absolute form with known base radius. Finally, we remark on the potential power of a priori predictions of achievable surface quality when optimizing optical system designs.

Access to Document (DOI)

Advances in small-tool polishing for free-form surfaces

R. R. Freeman, A. Beaucamp, D. Walker, R. Morton, G. McCavana

FRONTIERS IN OPTICS - OSA TECHNICAL DIGEST OM ( A4 ) 2004

Accepted

Access to Document (DOI)

Precessions aspheric polishing: - New results from the development programme

D. D. Walker, A. T.H. Beaucamp, R. G. Bingham, D. Brooks, R. Freeman, S. W. Kim, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5180 15 - 28 2003.12

Accepted, ISSN 0277786X

The Precessions process for producing aspheric and other optical surfaces is undergoing rapid development. In this paper, we summarise the considerable success achieved in controlling the repeatability of the process on both the 200mm and 600mm machines, and illustrate this with examples of aspherics that have been produced. We particularly describe our approach to fine form-control. This has required the development of various strategies to moderate the volumetric removal rates, in order to give the required sensitivity of removal. We conclude with a discussion of the scaling laws that apply when adapting the process to smaller and larger sized parts. This is illustrated by predicting the process-parameters for mass-producing segments for extremely large telescopes.

New polishing technology for large mirrors and lenses

D. D. Walker, A. T.H. Beaucamp, D. Brooks, A. King, R. Morton, G. McCavana

Proceedings of SPIE - The International Society for Optical Engineering 10314 31 2003.05

Accepted, ISSN 0277786X

Copyright © 2017 SPIE. The Precessions™ process, and the 200mm capacity 'All' machine which embodies it, are outlined in the accompanying paper 'New method to control form and texture on industrially-sized lenses'. In this paper, we summarise the development of the process to address larger optical components. The first machines constructed for this application are of 600mm capacity. A conceptual design of a 1-2m class machine of bridge-configuration has also been produced. Unlike the All machine, the work-piece on these larger machines lies in a horizontal plane i.e. with the rotation axis of the work-piece spindle vertical. This configuration is preferred because it allows the use of a hydrostatic support-system for the work-piece; important for large optics in general, and particularly so for light-weight optics. The machine can also provide a clear vertical path above the work-piece for optical testing, or for access by lifting gear. It is interesting to consider how the Precessions™ process can be scaled. As an example, consider first that the type of surface-form remains the same; it might, for example, be an f/2 parabola. Consider then that the work-piece diameter, the bonnet-diameter, the polishing spot-sizes used, and the tool-path on the surface, are all stretched by a factor of two. The area of the polishing spot and that of the work-piece have both increased by a factor of 4, but the number of convolutions of the spiral tool-path remains the same. Since the spot instantaneously addresses the same fraction of the overall work-piece surface-area, the terms all cancels in relation to cycle-time. However, for the same tool-rpm, the larger bonnet delivers a proportionally higher surface-speed, because the polishing action is further from the axis of rotation. Therefore, the volumetric removal rate (proportional to contact-area times surface-speed) tends to vary as the cube rather than the square of the scale-factor. As a result, the larger bonnet working over the larger work-piece with the same polishing pressure, will remove twice the depth of material in the same time. The above scaling could, in principle, reduce cycle times on larger parts. In practice, we have found that excessive removal-rates lead to impractically short dwell-times, especially near the centre of a spiral tool-path. Such scaling also demands increased traverse-speeds and accelerations from the machine, and this rapidly becomes a limitation. Moreover, as the process converges on final form, smaller depths of material need to be removed. In practice, we have found it necessary to moderate the process by diluting the slurry and by moving from a polyurethane tool-surface to a material that delivers a lower-removal rate, such as Multitex. We are also developing bonnets that are compatible with operation at a reduced polishing pressure, in order to give additional control for fine-removal. The current status of the process development is as follows. A form error of ∼80nm peak-to-valley has been achieved aspherising a 100mm diameter part. This work revealed some subtle but significant limitations in the optimisation code, mostly concerned with convergence and residual ripples. Recent work has focussed on this aspect, and the revised code is now ready for polishing trials. A 150mm diameter part is currently in-process, and work is about to commence on a 300mm fused silica mirror for a space application.

Access to Document (DOI)

<title>Precessions aspheric polishing: new results from the development program</title>

David D. Walker and Anthony T. H. Beaucamp and Richard G. Bingham and David Brooks and Richard Freeman and Sug-Whan Kim and Andrew King and Gerry McCavana and Roger Morton and David Riley and John Simms

Optical Manufacturing and Testing V ($\lbrace$SPIE$\rbrace$) 2003

Access to Document (DOI)

Novel CNC polishing process for control of form and texture on aspheric surfaces

D. D. Walker, A. T.H. Beaucamp, D. Brooks, R. Freeman, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 4767 99 - 105 2002.12

Accepted, ISSN 0277786X

We first consider the potential impact of a technology that could deliver polished, accurate aspheric surfaces in a routine and automated manner. We then summarise the technical challenge, and present an appraisal of the performance of the novel 'Precessions' process, which is a major advance in this direction. We outline the design concepts behind the productionized CNC polishing machines which executes the process, and then describe the progress developing strategies to preserve form when polishing ground surfaces, and to correct form on both pre-ground and polished surfaces. Particular consideration is given to resolving the inherent difficulties of control of centres on rotationally-symmetric parts. We then report on experimental results achieved with the machines. Finally, we present our programme to extend the control-algorithms to handle fully free-form surfaces, and draw conclusions about the effectiveness and generality of the 'Precessions' technique.

Access to Document (DOI)

The precessions process for efficient production of aspheric optics for large telescopes and their instrumentation

D. D. Walker, A. T.H. Beaucamp, R. G. Bingham, D. Brooks, R. Freeman, S. W. Kim, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 4842 73 - 84 2002.12

Accepted, ISSN 0277786X

We summarise the reasons why aspheric surfaces, including non-rotationally-symmetric surfaces, are increasingly important to ground and space-based astronomical instruments, yet challenging to produce. We mainly consider the generic problem of producing aspheres, and then lightweight segments for the primary mirror of an Extremely Large Telescope. We remark on the tension between manufacturability of spherical segments, and performance with aspheric segments. This provides the context for our presentation of the novel Precessions process for rapid polishing and form-correction of aspheric surfaces. We outline why this is a significant step beyond previous methods to automate aspheric production, and how it has resulted in a generalized, scaleable technology that does not require high capital-value tooling customized to particular types of optical form. We summarise implementation in the first two automated CNC machines of 200 mm capacity, followed by the first 600 mm machine, and the current status of the process-development programme. We review quantitative results of polishing trials, including materials relevant to large and instrumentation optics. Finally, we comment on the potential of the technology for space optics and for removing quilting in honeycomb substrates.

Access to Document (DOI)

　 Previous page - Next page 　