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Permeability Control Method with Laser for Porous Bushings of Aerostatic Bearings
Keiji Yamada,Nobuyuki Onishi,Katsuhiko Sekiya,Yasuo Yamane 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
This paper presents the experimental results of investigating the feasibility of new method to control the permeability of porous bushings used for aerostatic bearings. Sintered bronze discs are used as porous bushings, and their surfaces are irradiated with pulsed Nd:YAG laser to generate re-solidified layer which plays role as an air restrictor in the air feeding line. After above surface modification process, the change in air permeability of bushings is examined and the influence of irradiating conditions is also investigated. Then, a stability test and a stiffness test are performed to exam the effect of the re-solidified layer generated by surface modification process. The surface modified bushings have achieved high fluid resistance for air, and high stability of bearing. Furthermore, it is confirmed that the surface modification with laser has improve the static stiffness of thrust bearing with porous bushing.
Improved Machinability of High Hardened Die Steel by Using Pulsed Laser Surface Treatment
Kamonpong Jamkamon,Keiji Yamada,Takuya Inoue,Katsuhiko Sekiya,Ryutaro Tanaka 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.10
In this study, pulsed laser surface treatment was carried out in order to improve machinability in the shape correction process by ball end milling for forging dies. The die steel with high hardened layer by ion nitrided process was used as a workpiece that was irradiated by pulsed laser, and then milling experiments were performed with inclined workpieces in order to simulate machining for walls of the dies with a draft. The machinability was evaluated from specific cutting force of the material, which was obtained from the cutting force components and the actual depth of cut calculated by tool deflection measured in the machining test. The results of improved machinability were shown as the hardness reduction of surface layer induced by the laser irradiation. Therefore, the laser irradiated surface responded to increase the actual depth of cut and uncut chip thickness, while the tool deflection and specific cutting force were small compared with those for non-irradiated surface.
Influence of Tool Posture and Position on Stability in Milling with Parallel Kinematic Machine Tool
Muizuddin Azka,Keiji Yamada,Mahfudz Al Huda,Ryutaro Tanaka,Katsuhiko Sekiya 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.12
This paper investigated the machining stability influenced by tool posture and position in ball-end milling with parallel kinematic machine tool (PKM). Initially, the geometric structure was identified, and the machinery stiff ness was measured by impulse respond method at several positions with four tool postures. Then, the milling tests were conducted on fl at work surface using a ball-end mills. Cutting force and acceleration signals of milling tests were measured by three-axis dynamometer and accelerometer. Furthermore, these signals were analyzed by using Fast-Fourier transform and Hilbert–Huang transform (HHT). The results showed that the length of arm change with tool posture, where the machinery stiff ness decreased with the total length of arms for any tool position. The experimental results also demonstrated the machining stability varied with tool posture; the trend of stability corresponds with the machinery stiff ness. The vibration analysis by HHT presented the increasing of power level in the time–frequency plot when the length of arm increase during milling process. Therefore, the geometric influence must be considered to support process planning on the PKM.