Key Engineering Materials Vol. 516

Abstract: An FE model can be usedfor better understanding the micro cutting process. To identify an edge wear effect, the cutting forces and contact stress on the cutting tool were measured as edge wear progress. On the other hand, a series of orthogonal cutting tests was also carried out forcomparisonwith FEM simulation results in termsof chip formation and cutting forces. A scanning electron microscope (SEM) was used to observe the tools and chips for the purpose of taking measurements. A Kistler dynamometer was also utilized for cutting forces measurement. The FEM micro cutting simulation showed good agreement with experimentalresults in terms of the cutting forces and chip formation. And it was observed in both FEM simulations and experiments that larger edge wear caused higher cutting forces.

Abstract: This study deals with 5-axis control tool path generation to create microshapes dexterously and efficiently, while maintaining quality. Concerning 5-axis control machining, the use of ball end mills is generally employed. However, this method needs a lot of time to obtain high quality surface. To solve this problem, a side cutting edge of the ball end mill is positively utilized with its parallel to the ruled surface. Therefore, a new CAM system is developed to detect the surface to be machined with the side cutting edge, and to generate collision-free tool paths between the tool and the work piece. The effectiveness of the developed CAM system is experimentally confirmed by creating a tiny Möbius ring.

Abstract: The surface figure of the primary mirror in a large aperture telescope is one of the key factors influencing imaging quality. Space telescopes are used in weightless environments, which is different from the ground environment for optical machining and testing. Therefore the effect of the deformation induced by gravity on the imaging quality is not negligible and the mirror support is to be carefully designed to unload the gravity during the course of machining and testing. In this paper, finite element analysis software is adopted to simulate and compare the deformation induced by gravity of a metre-scale aspheric lightweight primary mirror with different support methods and different working conditions. The results are then imported into MetroPro software supplied by ZYGO Corporation, to remove the tilts and rigid body motion of the mirror and calculate the primary aberrations from the deformation. Finally, sensitivity analysis of support deformation is implemented and the principles of mirror support design are summarized. The research is instructive for design, machining and testing of large aperture mirrors.

Abstract: A novel polishing technique combined with the irradiation of atmospheric pressure plasma known as plasma assisted polishing (PAP) is proposed for the finishing of difficult-to-machine materials. In this paper, we mainly focus on the case of 4H-SiC substrate. We used helium-based water vapour plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy (XPS) measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was silicon oxide. A small amount of silicon oxycarbide was also observed which was identified as the interface oxide. The result of a nanoindentation test revealed that the hardness of oxidized SiC surface decreased by one order of magnitude compared with the unprocessed surface. The decrease of hardness of modified surface enables us to flatten the surface without forming any scratches and subsurface damage by using soft abrasive compared with the base material. We used CeO₂ as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The microscopic interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughnesses also decreased from 4.410 nm p-v, 0.621 nm rms to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy (AFM) images, a step and terrace structure was observed on the surface after PAP, which means that an atomically flat surface was obtained. We conducted reflection high-energy electron diffraction (RHEED) measurement to evaluate the residual strain of the PAP processed surface. The results indicate that the lattice constants approached the ideal value, which meansthat the PAP technique did not introduce crystallographical subsurface damage.

Abstract: In this research, machining characteristics of excimer laser ablation for three-dimensional machining of PMMA (Polymethyl methacrylate) is examined. In general, excimer laser ablation of polymeric material has features such as high precision and fine surface quality resulting from a less thermally-affected process, but in an earlier study, a thermal like effect on ablated surface was observed. Therefore, in this research the best machining condition of excimer laser ablation for PMMA by both numerical and experimental approaches was revealed.

Abstract: The linewidth of a direct laser writer is limited by the Rayleigh criteria. We propose a new direct laser writer that can overcome this limitation by employing the interference phenomenon. An interference generator is introduced into our system to separate an input beam into two orthogonally polarized beams. After going through an exposure lens, these two beams meet again on the focal point, and generate a small interferogram that sharpens the shape of the focused beam spot.

Abstract: This paper investigates thermal and strain behaviour in the selective laser sintering process with a mixture of SCM, Cu and Ni metal powder. In-process monitoring of strain change and temperature at the base plate is proposed in order to investigate thermal and strain behaviour induced by selective laser sintering. A strain gauge was attached to the bottom surface of the base plate while a thermocouple was inserted at a distance of 2 mm from the top surface of the base plate. Changes in the strain and the base plate temperature were observed using an oscilloscope during the laser sintering process. The results showed that the development of strain within the sintered structure was affected by the processing temperature. Besides that, after the laser sintering process was completed, the strain value increased gradually and became constant as it reached room temperature. This strain value was found to correspond with the test models deformation. In addition, the effects of laser scanning direction and laser energy density during the process were observed. Measurement of the test models deformation was also carried out to discover its relationships to strain change and processing temperature. The results showed that the sintered structure produced by laser scanning of a sector along the width induced less residual strain, which resulted in less deformation. In contrast, both residual strain and deformation were found to be higher when the laser scanning was carried out along the length. Furthermore, when a low laser energy density was used, less deformation of the sintered structure could also be obtained.

Abstract: When a cannonball collides with sea surface, an impulse force acts on the cannonball. Since the colliding occurs in a very short period of time, it is extremely unsteady. In order to find out if the cannonball fractures, analysis is performed to calculate the stress on the cannonball shell. In this study, an impulse force is applied to the elements of the cannonball colliding with sea surface and the analysis considers various collision conditions.

Abstract: Bamboo grows faster than other renewable natural materials. Bamboo fibre, in particular, has attracted attention as an environmentally superior material. Therefore, we proposed a sustainable manufacturing system using bamboo. An extraction method of bamboo fibres end-milled using a machining centre with in-situ measurement was also proposed. Bamboo fibres with high precision shapes are efficiently acquired. Previously, we proposed the fabrication of binder-free composite by a hot press forming method that only uses bamboo fibres extracted by a machining centre. We experimentally demonstrated various hot press forming conditions and achieved proper ones to optimize the forming process. However, when the environment changes, the characteristics of the binder-free composite are not known. If we want to use the binder-free composite, we have to know how much it is affected by the external environment for use as a mechanical object. Therefore, we investigated the changes of the characteristics at high temperature and high humidity.

Abstract: Smart materials have been developed in many leading technologies. Smart material is a material that gives a specific reaction to the change and stimulus of the external environment such as light, heat and electromagnetic fields. Electro-rheological Gel (ERG) is one smart material. ERG changes its surface adhesive properties rapidly according to the intensity of the applied electrical field. This unique property is named Electro-adhesive effect (EA effect). In this research, as a novel electro-adhesive film which is replaced with ERG, Electro-adhesive film with micro mesh sheets is developed and named EAMS. Furthermore, it is proved that the developed film using the mesh sheet produces the EA effect and that the performance of EAMS is enhanced according to the increase of the open space and the number of layers.