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Gyro finishing —a type of mass finishing—is one of the potential processes for finishing complicated shapes. This study proposes a cover plate located above a workpiece to improve finishing efficiency in gyro finishing. First, the effect of the cover plate on the force acting on the workpiece, which is related to the finishing efficiency, was investigated, and we confirmed that the force increased by using the cover plate. This was considered to be caused by the restriction of upward motion of the abrasive media. Subsequently, the effect of the cover plate on the finishing efficiency was evaluated by comparing the surface roughness variation with and without the cover plate. The finishing efficiency of the workpiece surface increased by approximately a factor of 2.0 with the cover plate due to the large force acting on the workpiece. Additionally, the bad effect caused by using the cover plate via larger force acting on the workpiece―worsening of the surface roughness―was not revealed. Therefore, the cover plate was confirmed a highly effective method to improve its performance. Furthermore, the effect of the cover plate was investigated under the workpiece-stopped condition for an improved understanding. We confirmed that the surface roughness obtained using the cover plate improved over the entire front surface of the workpiece due to the increase of the contact pressure.

A calculation method for workpiece profile variation during double-sided lapping was developed in this study. In this method, shell element in FEM deformation was used to formulate elastic deformation of workpiece, and spring element was used to formulate the contact between workpiece and platens to calculate distribution of their contact pressure considering workpiece elastic deformation. First, the developed method of the contact pressure distribution was evaluated by comparing with a method using a FEM software and the existing methods, and was confirmed to be quite valuable in terms of applicable process and calculation time. Subsequently, the workpiece profile variation was calculated using the developed method for several workpiece conditions, and it was clarified that the uneven workpiece thickness can be modified by the process, but it is difficult to modify the bow shape when the workpiece is not small. Furthermore, the decrease of the load applied to the workpiece was suggested to modify the bow shape of the workpiece.

Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components; however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. It is known that Ar gas is not suitable for welding steel because it cannot provide the desired arc stability and weld bead characteristics. The results reveal that the arc is stable in the multilayer deposition of the WAAM process, and the short-circuit of the metal transfer at the heat input of 1.17 kJ/cm enables smoothing of the fabricated surface with large irregularities. Better arc stability under Ar gas is achieved when the oxygen content of the fabricated surface is 22 wt%. Furthermore, the short-circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. The results indicate that proper use of Ar gas can improve the surface quality when depositing on rough surfaces.

In double-sided lapping and polishing processes, the friction coefficients between the workpiece and platens or pads are important parameters for understanding or improving the lapping and polishing processes. However, the friction coefficients have not been investigated in detail owing to insufficient measurement methods for the torques acting on the upper and lower platens, which are necessary to evaluate the friction coefficients. Thus, a novel measurement method for the torque acting on the upper platen in a three-way double-sided machine was proposed in this study. In the method, the torque is measured based on the forces acting on the holders supporting the upper platen rotation. The torques were measured with the method in double-sided lapping experiments, and they were confirmed to agree with the theoretical torque variation. Furthermore, the friction coefficient between the workpiece and upper pad identified with the proposed method was also verified by comparing with the friction coefficient measured in the single-sided lapping experiment. In addition, the estimation method of the lower platen torque based on the motor torque was investigated by utilizing the proposed method, and we found the lower platen torque was estimated accurately by taking a sufficient warm-up time or by modeling the torque loss in transmission path. Therefore, accurate measurement of the torques acting on the upper and lower platens, which is an effective tool for understanding or improving the process, was realized.

This paper focuses on an unconventional laser powder bed fusion (LPBF) technique in which the LPBF and machining processes were executed alternately to fabricate higher quality parts compared to those obtained using subtractive machining processes. The additional machining process modified the stress distribution inside the built part, resulting in the deformation of the surface morphology in the final part. The phenomenon resulting in the combined LPBF and machining-process-based fabrication was investigated, and the influence of the process parameters on the formation of surplus part and the deformation of machined surface was evaluated. In addition, a laser scanning and machining strategy were formulated to improve the surface quality of the built part. The surplus buildup at the edge of the fabricated part occurred owing to the difference in the thermal properties between the solidified part and the deposited metal powder. The principal factors affecting the formation of the surplus part were the laser-irradiated position at the first layer buildup and the energy density. Moreover, the formation of the surplus part was improved using the laser scan strategy, in which the laser-irradiated position was shifted inward. The peripheral face of the built part formed periodical steps, owing to the deformation induced by the change in the thermal distribution inside the built part. These steps could be reduced using a machining strategy combining the rough machining process with a finishing allowance and stepwise finishing process.

In die-casting and injection molding, a conformal cooling channel is applied inside the dies and molds to reduce the cycle time. When the internal face of the channel is rough, both cooling performance and tool life are negatively affected. Many methods for finishing the internal face of such channels have been proposed. However, the effects of the channel diameter on the flow of a low-viscosity finishing media and its finishing characteristics for H13 steel have not yet been reported in the literature. This study addresses these deficiencies through the following: the fluid flow in a channel was computationally simulated; the flow behavior of abrasive grains was observed using a high-speed camera; and the internal face of the channel was finished using the flow of a fluid containing abrasive grains. The flow velocity of the fluid with the abrasive grains increases as the channel diameter decreases, and the velocity gradient is low throughout the channel. This enables reduction in the surface roughness for a short period and ensures uniform finishing in the central region of the channel; however, over polishing occurs owing to the centrifugal force generated in the entrance region, which causes the form accuracy of the channel to partially deteriorate. The outcomes of this study demonstrate that the observational finding for the finishing process is consistent with the flow simulation results. The flow simulation can be instrumental in designing channel diameters and internal pressures to ensure efficient and uniform finishing for such channels.

Gyro finishing, which is one of the mass finishing, is expected to be an excellent finishing process of a workpiece with a complex shape. However, its fundamental researches are few, and hence the development of techniques to address its issues/problems, such as the decline of shape accuracy and low process controllability, is hindered by a lack of understanding of the process. Thus, a fundamental investigation of gyro finishing is conducted in the present research. The contact force acting on a cylindrical workpiece, which was designated by simplifying a large gear, was measured under different conditions in workpiece position, amount of abrasive media, and rotational speed of the container. In addition, the abrasive media height above the workpiece was measured, and effects of various factors on the contact force were investigated. From the results, the height above the workpiece was confirmed to have a strong correlation with the contact force. This was considered to be caused by increasing of the resistance of the abrasive media motion, and it was considered a major factor of the contact force. On the other hand, the effect of the abrasive media momentum and the distance between the workpiece and the container wall on the contact force was confirmed weak. Moreover, the variation of the surface roughness was investigated under different contact force conditions, and the improving speed of the surface roughness was faster under the higher contact force condition. Thus, contact force was a significant factor affecting the finishing performance, and this investigation featuring the contact force acting on the workpiece was considered significant to understand the gyro finishing process and to increase the contact force and the finishing performance.

The cutting-edge temperature on the flank face in dry turn-milling of medium carbon steel (ISO C45) is measured using a two-color pyrometer with an optical fiber. In turn-milling, undeformed chip geometry is complex due to its dependence on several factors including diameter of the cutting tool, number of tooth, diameter of the workpiece, tool-work revolution speed ratio, depth of cut, feed per tooth, tool axis offset, and the cutting distance. In this study, the undeformed chip is analyzed and visualized by the 3D-CAD system, and the effects of the cutting parameters in turn-milling, especially relative cutting speed and tool axis offset on tool flank temperature, are investigated. It is interesting that the relative cutting speed does not significantly affect the tool flank temperature, where it increases by approximately 20 °C at most when relative cutting speed increases from 124 m/min to 217 m/min. In addition, tool flank temperature varies by approximately 40 °C when the tool axis offset is changed from 0 mm to 9.2 mm due to the change in the undeformed chip geometry.

The mechanical and tribological characteristics of the VN/AlCrN multilayered coating films are investigated for cutting tools by using the arc ion plating (AIP) method with a rectilinear magnetic filtering system. The VN coating film forms vanadium oxide VxO1–x that has low friction coefficient on a surface above 500°C, whereas AlCrN coatings exhibit higher hot hardness and oxidation resistance. Therefore, the VN/AlCrN multilayer coatings are expected to demonstrate both superior lubricity and heat resistance, whose characteristics depend mostly on the combination of VN and AlCrN films. Moreover, some lower cutting force, tool wear, and tool flank temperature are obtained at high speed end milling of a prehardened stainless steel, as expected.

Numerically controlled electrochemical machining is carried out using a parallel mechanism for the fast translation of the tool electrode. The fast translation of the tool electrode is known to improve surface finish. Therefore, in this study, a parallel mechanism is proposed to achieve high-speed translation of the tool electrode. A linear delta-type parallel mechanism which has 3 degrees of freedom is utilized, and experimental results of machining a groove show that the surface roughness decreases with increasing translation speed of the tool electrode. The results of large-area machining also show that a higher translation speed of the electrode is effective in improving the surface finish. In addition, there is an optimal pick feed to obtain both a flat surface and good surface quality when the electrode is translated at high speeds.

Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components, however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. However, when using Ar gas, the heat flux from an arc to the workpiece is relatively low, limiting the depth of the molten pool during welding. The effect of its characteristics on the stair steps that are inevitably produced on the side face of the multilayer structure in the WAAM process was verified, and for a heat input of 1.17 kJ/cm under Ar gas, a higher geometric accuracy of the multilayer structure was obtained without interlayer cooling. The short circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. Further, the metal transfer under Ar gas reduced the surface irregularities on the fabricated structure.

The influence of various process parameters on the building of maraging steel powder by the selective laser melting (SLM) processes is investigated. The microstructure in the built part was observed and the influence of the heat treatment was evaluated. As results, the depth of solidified layer was higher than that of deposited metal powder, and its value was influenced with the process parameters. The microstructure in the boundary between the built part and the substrate was quite different from the built part even if the suitable heat treatment was performed.

This study deals with high quality thermal stress cleavage of thick sapphire wafer with thickness of 5 mm. The influence of the distance from the edge to the initial crack, laser power, and plane orientation on the cleavage characteristics was experimentally investigated. The results indicate that the surface waviness Wa at the cleaved surface was influenced by the distance from the edge. A cleaved surface with good surface characteristics was obtained by cleaving with low laser power. The cleavage direction also affects the cleaved surface characteristics.

The powder bed fusion (PBF) technique is a metal-based additive manufacturing (AM) method in which metal powder is deposited on a substrate and melted by selective laser-beam irradiation. Given that the process and parameters of metal-based AM are complicated, there are various problems in high-precision fabrication. One of these is that although metal-based AM can be used for fabrication of high-density parts, pores can easily form inside the fabricated structure owing to process instabilities. Pore formation degrades the mechanical strength of the fabricated structure. Therefore, this study investigated the pore formation mechanism inside a structure fabricated by PBF. Pore suppression by controlling the substrate temperature was also evaluated. Small- and large-sized pores with diameters of 10 μm and more than 50 μm, respectively, were found. Furthermore, differences in pore formation in the cross-section of the fabricated structure were observed owing to a variation in the volume-specific energy density and substrate temperature. At a substrate temperature of 25°C, the number of pores decreased more at the upper position than at the lower position owing to repeated melting and solidification under the laser-beam irradiation. At a substrate temperature of 200°C, the number of pores decreased significantly more than at 25°C. Furthermore, as the substrate temperature increased, the wettability of the molten metal improved, resulting in smaller contact angles of the fabricated structure in the single-line track. In PBF, multiple lines are fabricated in each layer. At low substrate temperatures, interstices were formed between the lines owing to the low wettability of the molten metal. These interstices acted as the origins of pores when the next layer was fabricated. Heating the substrate made the surface of the structure smooth owing to the high wettability of the molten metal and a reduction in the number of pores. Therefore, the formation of large pores could be reduced by controlling the substrate temperature.

Behavior of a wafer is one of the most significant concerns in double-sided lapping since it depends on the distribution of material removal rate. Though the wafer behavior is affected by the friction coefficient between the wafer and a carrier, the coefficient has hardly been discussed. In this study, an identification method of the friction coefficient based on variation of wafer rotational speed with wafer position in the carrier during single-sided lapping operation on double-sided lapping machine is developed for accurate estimation of the wafer behavior. The friction coefficient is identified by comparing experimental and theoretical variation of the rotational speed of the wafer. The experiment is carried out under the condition where lubrication condition between the wafer and the carrier is similar to that in double-sided lapping, and the variation is measured by image processing of the wafer behavior. The theoretical variation is calculated based on the equilibrium of force and moment applied to the wafer. It is confirmed that the theoretical rotational speed of the wafer under a friction coefficient condition agrees well with the measured one in terms of not only the highest and the lowest speed but also the variation with the wafer position in the carrier. Thus, it is assumed that the practical coefficient is identified by utilizing this method. In addition, the behavior of the wafer in double-sided lapping is calculated using the identified friction coefficient, and it is suggested that precise consideration of the contact status between the wafer and the carrier, i.e., non-slip, slip, and non-contact is essential for practical estimation.

In micro-electrical discharge machining (micro-EDM), the minimum machinable size is determined by the material removal per pulse discharge. In this study, two types of single-crystal silicon tool electrodes with high electrical resistivity were used to fabricate the micro-rod by minimizing the material removal per pulse discharge, and to reduce the machinable size for micro-EDM. The EDM characteristics of micro-rods using silicon tool electrodes with high electrical resistivity were investigated. Based on the experimental results, it is found that the peak discharge current decreases with an increase in the electrical resistivity of the tool electrode. Consequently, the average diameter of discharge craters generated on the micro-rods is reduced to approximately 0.4 μm. The silicon tool electrode has also disadvantage of their higher tool wear ratio compared with that of copper, which is probably due to the brittleness of the silicon. Moreover, the material removal rate is significantly lower for the silicon tool electrodes compared with that for the copper tool electrode. Because the average diameter of the discharge craters generated by the silicon tool electrodes is small, an attempt is made in this study to fabricate a cemented tungsten carbide micro-rod with a diameter less than 1 μm using the silicon tool electrode with an electrical resistivity of 1.2 × 10−3 Ω m. The result is indeed promising since the diameter of the micro-rod is 0.8 μm, indicating that it is possible to fabricate micro-rods with a diameter within the sub-micrometer range by only using silicon tool electrode with high electrical resistivity in micro-EDM.

This paper focuses on the unconventional laser powder bed fusion (LPBF) technique in which the LPBF and machining processes were executed alternately to fabricate higher quality parts compared to those obtained using subtractive machining processes. The additional machining process changed the stress distribution inside the built part, resulting in the deformation of the surface morphology in the final part. The phenomenon pertaining to the combined LPBF and machining process based fabrication was investigated, and the influence of the process parameters on the formation of the surplus part and deformation of the machined surface was evaluated. In addition, a laser scan and machining strategy was formulated to improve the surface quality of the built part. The surplus buildup at the edge of the fabricated part occurred owing to the difference in the thermal properties between the solidified part and deposited metal powder. The laser-irradiated position at the first layer buildup and energy density were the principal factors affecting the formation of the surplus part, and the surplus buildup could be reduced using the laser scan strategy, in which the laser-irradiated position was shifted inward. The peripheral face of the built part formed periodical steps, owing to the deformation induced by the change in the thermal distribution inside the built part. These steps could be reduced using the machining strategy combining the rough machining process with a finishing allowance and stepwise finishing process.

The quality of built parts by selective laser melting (SLM) relies on the comprehension of the phenomena that takes place during the melting and solidification of the metal powder. The scattering of spatter particle as liquid metal during SLM process affects the layer consolidation of powder bed in addition to the surface quality of built part. The present study is focused on the spatter particle behaviour of maraging steel during SLM to achieve a thorough understanding of the phenomena that occur during the melting and fusing of the metal powder. The spatter particles are tracked using high speed imaging, and the effects of the process parameters on the spatter particle behaviour are investigated. The spatter particles ejected from the melt pool are also physically and chemically evaluated. The results showed that the spatter particles were classified as being spherical or satellite types, according to their scattered volumes; some spatter particles were larger than the particles in the initial metal powder. Most spatter particles were ejected from the droplet formed around the melt pool and from the melted powder in front of the melt pool; the number of spatter particles ejected from the melt pool was relatively low. The surface roughness affected the generation locations and tracks of the spatter particles, and the substrate surface wettability was the principal factor affecting the spatter particle behaviour.

Tool flank temperature at various intervals after cutting in dry turn-milling of AISI 1045 steel is measured using a two-color pyrometer with an optical fiber. Complicated undeformed chip geometry, which depends on cutting tool diameter, nose radius, number of tooth, workpiece diameter, tool-work revolution speed ratio, depth of cut, feed per tooth, tool axis offset and cutting distance, is analyzed and visualized by the 3D-CAD system. The effect of cutting parameters associated with material removal rate MRR such as workpiece diameter, workpiece revolution speed and feed rate on tool flank temperature is investigated in this paper. Workpiece diameter affects tool flank temperature, and 10 mm larger diameter causes approximately 40 °C higher temperature in any workpiece revolution speed due to the variation of undeformed chip geometry analyzed by 3D-CAD. Tool flank temperature increases with feed rate and workpiece revolution speed because the cross-sectional cutting area of undeformed chip increases with workpiece revolution speed, and cutting time during the engagement of each flute also increases with feed rate. Almost same values are obtained between the tool flank temperature and the material removal rate MRR when both workpiece revolution speed and feed rate are changed.

This study is the first attempt of applying thermal stress cleavage to a single-crystal round sapphire bar having a morphologically continuous circumference surface. Previously, thermal stress cleavage was only applied to brittle material substrates or wafers owing to the crack propagation behaviour induced by thermal stress distribution. To overcome this issue, a V-shaped groove was prepared on the circumference as an initial point for crack propagation, and a continuous-wave carbon dioxide (CO2) laser was used as the heat source. The thermal stress behaviour was simulated via finite element analysis, and the effect of the initial crack morphology on the thermal stress behaviour was evaluated. In addition, the crack propagation was monitored using an acoustic emission sensor, and the separation mechanism of the round sapphire bar was investigated. Results indicated that the thermal stress cleavage using the CO2 laser beam allowed the complete separation of the round sapphire bar with the V-shaped groove without any final edge remaining. The crack propagation behaviour was determined from the relationship between the thermal stress distribution and morphology change during crack propagation. The fabricated sharp V-shaped groove improved the quality of the cleaved surface, and the high aspect ratio of the groove enabled a high-quality cleavage. The initial crack propagation immediately after the start of laser beam irradiation was affected by the tip of the V-shaped groove, and the crack propagation direction could be controlled through the tip morphology of the V-shaped groove.

This paper pertains to the thermal and strain behaviour in laser consolidation of metal powders by additive manufacturing. The temperature and strain induced in the substrate during the laser consolidation process were theoretically estimated by the thermal-structure interactive analysis with two-dimensional finite element method, and experimentally evaluated in order to investigate the influence of thermophysical and mechanical properties on the resistance to thermal deformation in the consolidated structure. Additionally, the effects of different ferrous-based materials on the deformation were also investigated. The results reveal that the deformation of the consolidated structure was mainly caused by the thermal expansion and shrinkage induced by the laser beam which was repeatedly irradiated to the deposited powder. The deformation direction varied depending upon the temperature gradient which was induced inside the structure and stiffness of the consolidated structure which was added on the substrate. The analytical results obtained coincided well with the experimental results. The coefficient of thermal expansion was one of the most effective factors in restraining the thermal deformation, and the thermal deformation was reduced by combining the materials in which the coefficient of linear expansion was similar. In addition, the deformation was minimized by adjusting the temperature gradient induced by the laser beam irradiation.

A new tool electrode having a porous structure is developed for electrochemical machining (ECM), in which electrolyte fluid can be forced through its permeable structure. This electrode can be easily fabricated using a laser sintering technique of additive manufacturing. Small pores and large porosity can be obtained using a higher laser scanning speed, which increases the flow rate of the electrolyte. ECM results show that a nearly flat surface of the machined hole is obtained and small pores are less likely to cause protrusions on the machined surface. Moreover, the machining speed can be increased as the flow rate increases.

In micro electrical discharge machining (EDM), because the material removal per single pulse discharge mainly determines the minimum machinable size of a micro EDM, decreasing the material removal per single pulse discharge is important. In this study, in order to decrease the material removal per single pulse discharge, high electric resistance materials such as single-crystal silicon are used for electrodes. Analytical results show that when the electrode resistance increases, the peak value of the discharge current decreases, whereas the pulse duration increases. In addition, the discharge energy decreases when increasing the resistance. Silicon is used as a tool electrode, and the effect of resistivity of the silicon tool electrode on the diameter of discharge craters generated on the stainless steel workpiece is examined. Experimental results reveal that with increasing silicon electrode resistivity, the diameter of discharge craters decreases. Because the diameter of discharge craters can be decreased to 0.5 μm, improved finished surfaces of R z 0.03 μm are obtained.

It is necessary to strengthen glass surfaces to protect mobile electric devices from unexpected scratches and breakages, and various strengthening methods are available to this end. However, strengthened glass is difficult to cut and finish owing to the high compressive stress on the glass surface. In this work, chemically strengthened glass was separated using a fracture control technique. The initial crack for the crack propagation was generated through a thermal shock induced by laser beam irradiation, and the thermal stress distribution inside the strengthened glass was simulated via a finite element analysis. In addition, the influence of the laser conditions on the cleavage characteristics was evaluated experimentally, and a groove was fabricated via a short-pulsed laser to improve the quality of the cleaved surface. The thermal stress induced by the laser beam irradiation was affected by the stress distribution inside the strengthened glass, and the depth of the initial crack was required to exceed that of the compressive stress layer to realize the crack propagation through laser beam irradiation. The minimum energy density required for the thermal stress cleavage decreased with the increase in the initial crack depth, and the energy density required for the thermal stress cleavage was large when the compressive stress on the surface was high. The compressive stress layer on the surface helped reduce the lateral crack at the tip of the initial crack, and the tensile stress inside the specimen helped realize high-quality cleavage. In addition, the groove fabricated using the short-pulsed laser acted as the initial point for the crack propagation and helped prevent the thermal damage induced by the laser beam irradiation applied as the heat source.