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Mechanical property evaluation of the SLM support structure and lattice structure of SUS316L

Ikeda Y., Okochi W., Koike R., Maki T., Takaki K., Mori T., Hirono Y., Kakinuma Y.

Journal of Advanced Mechanical Design, Systems and Manufacturing （Journal of Advanced Mechanical Design, Systems and Manufacturing） 17 （ 1 ） 2023年

Selective laser melting (SLM) is one of the additive manufacturing (AM) methods which is applicable to metal. This technique makes it possible to form complex internal shapes such as lattice structures. The lattice structure is expected to have weight reduction and vibration suppression effects on the product. In addition, a support structure is essential for the SLM fabrication process, which has the role of supporting the product and dissipating heat from the product. However, steep temperature gradients due to local laser irradiation and non-uniform heat conduction during the process can cause bending and cracking of the product. In particular, the support structure and lattice structure consisting of thin metal struts are greatly affected by process conditions, so it is necessary to select conditions suitable for stable and high-precision modeling. In this study, the influence of laser power and scanning speed on the mechanical characteristics of the support structure and lattice structure formed by SLM is investigated. In the tensile test of the support structure, a positive correlation with the volumetric energy density was confirmed, and suitable laser conditions were examined. In the compression test of the lattice structure, it was clear that the amount of energy absorption changed depending on the laser power, and the condition of 240 W achieved the maximum energy absorption.

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Evaluation of fabrication parameters for foam stainless steel in directed energy deposition

Ikeda Y., Takeuchi T., Koike R., Kakinuma Y., Kondo M., Oda Y., Mori T.

Journal of Advanced Mechanical Design, Systems and Manufacturing （Journal of Advanced Mechanical Design, Systems and Manufacturing） 17 （ 1 ） 2023年

Directed energy deposition (DED), a metal additive manufacturing process, has attracted considerable attention in various industries. In the past few decades, several studies have been conducted to enhance the quality of DED-produced parts. Various studies on powder- and laser-based DED have focused on eliminating the residual pores in the fabricated parts, which decrease the mechanical strength. In contrast, this study aims at intentionally increasing the residual pores to produce a porous structure in metals called as foam metal, which realizes lightweight and excellent energy absorption properties. Despite being well-known for their attractive properties, Foam metals are rarely used due to the technical difficulties in their production, which requires special devices and entails considerable cost. The simplicity of the DED process makes it a promising approach to fabricate foam metals because it is easy to foam at the fabrication point by mixing a foaming agent, such as titanium hydride (TiH2), into the material powder. This study evaluates the DED foaming process in stainless steel alloys by changing the particle size of the TiH2 powder and the scanning path to obtain the optimal conditions for enhancing the pore dispersion. The experimental results show that, when the particle size of the foaming agent is small, the number of pores and their distribution increases. Additionally, the mechanical properties are also evaluated through compression experiments, and the energy absorption ratio is found to be higher when a smaller foaming agent is used.

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Basic study for lunar regolith powder bed fusion in high gravity

Koike R., AlKhaled A., Kashimoto T.

CIRP Annals （CIRP Annals） 2023年

ISSN 00078506

In-situ resource utilization has become a significant issue in recent space projects. For example, various studies have focused on lunar manufacturing using regoliths available on the moon's surface. Although regolith manufacturing will be conducted under lunar gravity, most studies have not considered the adverse effects of low gravity on additive manufacturing processes. This study evaluates the gravitational effect on lunar regolith powder bed fusion (PBF) by applying centrifugal acceleration to the PBF process. The experimental results show that gravitational acceleration influences the density, hardness, and transparency of the fabricated regolith blocks.

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Optimization of process parameters for hardness in high speed coating by Directed Energy Deposition

Satoh T., Koike R., Kakinuma Y., Hirono Y., Mori T., Oda Y.

Procedia CIRP （Procedia CIRP） 111 214 - 217 2022年

ISSN 22128271

In recent years, metal 3D printers have been attracting attention not only for building solid parts but also for repairing and coating processes. The goal of this study is to apply the directed energy deposition (DED), which is one of the additive manufacturing, to realize high-quality metal coating by depositing the coating material on a cylindrical object. To evaluate the effect of process parameters, experimental points were set up based on the central composite design and deposition was performed using Inconel 625 as the material powder. The hardness of the coating was measured and statistically analyzed by the response surface methodology. From the analysis results, it was found that laser power has the largest influence on the coating hardness, which was improved by 28% compared to the low rotation speed by depositing under the optimum processing parameters.

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Enhancement in fine powder availability for Powder Bed Fusion applying high gravity

Obe K., Koike R.

Procedia CIRP （Procedia CIRP） 111 121 - 124 2022年

ISSN 22128271

In recent years, additive manufacturing (AM) technology that can directly shape objects from three-dimensional data has attractedattention.AM technology is promising as a manufacturing method in space because of its resource and space-saving properties. Some studies have shown that gravity change is viewed as a problem to overcome. On the other hand, there has been no progress in the discussion of attempts to effectively utilize gravity changes for AM technology. In this study, we focus on powder bed fusion (PBF) among AM technologies, using gravity as a control factor. The high gravity PBF (HG-PBF) is expected to be able to solve the problems of the current AM technology such as improvement of shape accuracy and process stability. In this study, we used fine powders and experimentally discuss the effect of the high gravity field on improvement of PBF process.

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High-gravitational effect on process stabilization for metal powder bed fusion

Sugiura Y., Koike R.

Additive Manufacturing （Additive Manufacturing） 46 2021年10月

Additive manufacturing is a technology that enables mass customization of products owing to its flexibility and is one of the key technologies used in Internet-of-Things-based manufacturing systems. In recent years, industrial applications of additive manufacturing have been increasing, and expanding into space manufacturing. However, the controllability of gravitational acceleration has not been well explored. In this study, a high-gravitational powder bed fusion system is developed, which produces a high-gravitational field via the application of centrifugal acceleration. It is evident that the powder bed quality is improved, and the spatter generation is dramatically suppressed on applying a high gravitational acceleration of up to 10+ G. The experimental evaluations demonstrate that a high gravitational field improves the surface quality, density, and hardness of the fabricated parts.

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Metal powder bed fusion in high gravity

Koike R., Sugiura Y.

CIRP Annals （CIRP Annals） 70 （ 1 ） 191 - 194 2021年01月

ISSN 00078506

Many studies have focused on the stabilization of additive manufacturing (AM) in microgravity for its use in various space projects. Nevertheless, this paper presents a vital clue for innovating metal AM technologies from the perspective of high gravity. High-gravitational powder bed fusion has an excellent potential to address various challenges in AM, such as density enhancement, spatter suppression, and precise fabrication. This study summarizes an analogy among phenomena in different gravitational fields and establishes a combined machine for centrifuge and powder bed fusion. The results confirm the spatter suppression and fine-powder availability in high gravity, both theoretically and experimentally.

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Powder velocity-based nozzle design for directed energy deposition

Takemura K., Koike R., Kakinuma Y., Yamazaki K., Mori T., Hirono Y.

10th International Conference on Leading Edge Manufacturing Technologies in 21st Century, LEM 2021 （10th International Conference on Leading Edge Manufacturing Technologies in 21st Century, LEM 2021） 458 - 461 2021年

Directed energy deposition (DED), which is one of the metal-powder additive manufacturing processes, is a promising method suitable for repairing. Because the carrier gas that transports the metal powder and the shield gas that protects the optical system are supplied in DED, it is difficult to estimate the transport of metal powder due to the complex turbulence around the processing point, resulting the powder supply efficiency gets lowered. This study computationally analyzed the fluid dynamics of two types of DED nozzles for improving the powder supply efficiency by changing the number of powder channels, working distance and channel diameter.

Mechanical property evaluation of the SLM support structure and lattice structure of SUS316L

Okochi W., Ikeda Y., Koike R., Mori T., Hirono Y., Maki T., Takaki K., Kakinuma Y.

Selective laser melting (SLM) is one of the additive manufacturing (AM) methods which is applicable to metal. Although this technology enables to form complex inner shapes such as lattice structure, steep temperature gradients due to local laser irradiation and uneven heat conduction during the process may cause bending and cracking of the product. In this study, the influence of laser power and scanning speed on the mechanical characteristics of the support structure and lattice structure formed by SLM is investigated. In the tensile test of the support structure, a positive correlation with volumetric energy density was confirmed. In the compression test of the lattice structure, it was clear that larger amount of heat energy from the laser makes struts of lattice structure thicker and its Young's modulus higher.

Development of ice 3D printer applying supercooling phenomenon

Tanaka A., Koike R.

Undercooling state is metastable and immediately releasable by applying disturbance intentionally. Therefore, a 3D printer with considerably high modeling efficiency expectedly can be realized by using the supercooling phenomenon. This study discussed the applicability of the supercooling phenomenon in ice (H2O) to additive manufacturing. As a result, freezing of the supercooling phenomenon due to impact was observed. The freezing behavior depended on the flow rate, and freezing in the syringe was observed when the flow rate was high. In addition, when the conditions such as the amount of water droplet was adjusted, it was possible to fabricate shapes with simple structures by stacking.

Basic study of fabrication conditions for foam stainless in directed energy deposition

Takeuchi T., Koike R., Kakinuma Y., Kondo M., Oda Y., Mori T.

Directed energy deposition (DED) is one of additive manufacturing processes attracting attention from various industries. Foam metal is a material having beneficial characteristics, but is difficult to produce with conventional manufacturing system. This study proposes a simple foam metal fabrication method by applying DED. The proposed method produces foam stainless alloy in DED by adding a foaming agent, titanium hydride (TiH2), into the powder material. This study evaluates the foaming behavior of porous stainless in DED by changing the particle size of TiH2 and the number of layers per line, and obtains the optimal number of layers to improve the porosity dispersion.

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