Details of a Researcher - Beaucamp, Anthony

Papers - Beaucamp, Anthony

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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).

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