Advanced Materials Research Vol. 797

Abstract: This study was performed to develop a non-destructive inspection system to detect grinding burn, which is capable of quantitative 100% inspection inside a production line. An eddy current sensor, which has advantages of short inspection time and low cost, was used. It was shown that the grinding burn detection technique had been developed and is possible to detect grinding burn by using this technique, in the 1st report¹⁾ and the 2nd report²⁾. In this report, we have attempted to apply the grinding burn detection technique to evaluate the residual stress of work piece surface. Residual stress of work piece surface is affected by both thermal and mechanical effects. It is shown that the residual stress is possibly evaluated in the case of the thermal effect is dominant.

Abstract: An investigation was made for application of ultrasonic vibration in electro discharge machining (EDM) and wire EDM, and only the vibration of wire was found to have been applied on WEDM. This paper studied on the effect of workpiece vibration to the WEDM process. The horizontal vibration of Ti-6Al-4V was applied on the rough cutting process of WEDM to study the variation of kerf width, machining rate and surface roughness. The results show that the workpiece vibration of WEDM has different effect with the wire vibration, which can improve the machining rate and kerf width, but increase the surface roughness.

Abstract: Ultrasonic vibration cutting can be widely used in lathe, planer, milling machine, grinding machine, thread processing and gear processing, etc. Ultrasonic vibration cutting system is composed mainly of ultrasonic generator, ultrasonic transducer, luffing rod, cutting tool, etc. Here, ultrasonic generator is the most important. The stand or fall of signal, which is produced by ultrasonic generator, has direct influence on anticipated effect and ability of ultrasonic machining. In order to generate a signal, which can be suitable for ultrasonic machining, ultrasonic vibration cutting system is studied, and ultrasonic signal generator based on direct digital frequency synthesis (DDS) is designed and conducted a cutting test with this ultrasonic machining system. The results show that the signal generator, which is made up by DDS technology, can generate the signal with stability, reliability and greater flexibility, and can be fully applicable to the ultrasonic machining.

Abstract: Zirconia (ZrO₂) is a promising material in the field of prosthetic and implant dentistry. Surface grinding has been used for surface roughening of zirconia ceramics to increase the mechanical retention of ceramic/resin cement bonding. In the present study, a three-dimensional (3D) ultrasonic vibration spindle, which can generate three ultrasonic vibration modes referred to as longitudinal vibration, circular vibration and 3D hybrid vibration, was employed to machine zirconia ceramics by slant feed grinding for producing tailored rough surfaces. Different micro/nanosurface textures were generated successfully, proving that the ultrasonic vibration assisted slant feed grinding is a viable method to fabricate tailored rough surfaces composed of micro/nanostructures. The surface texturing procedure was mathematically studied, and the influence of grinding and vibration conditions on the textural features was also analyzed.

Abstract: Ultrasonic assisted turning (UAT) is an efficient cutting technique for difficult-to-cut materials. In order to study the effect of vibration parameters on machining performance, tool-workpiece contact ratio (TWCR) was defined. A finite element model for ultrasonic assisted turning of Ti-6Al-4V was established. Effects of tool vibration frequency, tool vibration amplitude and workpiece cutting speed on cutting force and cutting temperature were analyzed. It is observed that both the increase in the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting forces and cutting temperature. By using the finite element model the appropriate tool vibration frequency, tool vibration amplitude and cutting speed can be obtained.

Abstract: Whirling Electrical Discharge Texturing (WEDT) was developed to create microstructures. It was thought that textured surface with low surface roughness could reduce friction coefficient on the sliding parts. In this research, surface quality was studied to evaluate the quality of WEDT textured surface. Surface quality was evaluated in terms of the surface roughness and surface integrity which were characterized by microstructure, composition and residual stress of the textured surface. The value of Rp and Rv of textured surface after finishing with improved finishing method were obtained as expected for low surface roughness to reduce friction coefficient. In addition, it was clarified that microstructure and composition of textured surface after texturing with WEDT and finishing with lapping-film depend on feed speed. Furthermore, the compressive residual stress was presented on WEDT textured surface and depended on feed speed. It was confirmed that good surface quality of textured surface could be obtained by WEDT.

Abstract: In this paper, a new machining method is proposed for the high efficiency turning of titanium alloy Ti-6Al-4V in which the cutting tool is ultrasonically vibrated. An experimental setup is constructed by installing an ultrasonic cutting unit onto a NC lathe followed by experimental investigations on the fundamental machining characteristics. The results obtained in the current work showed that (1) the cutting force decreases with the increase in the power supplying level (i.e., the ultrasonic vibration (UV) amplitude), e.g., the cutting force components in X-. Y-and Z-directions were decreased by 48%, 45% and 87%, respectively, once the UV has been applied to the tool at the power supplying level of 50%; (2) the cutting marks with knit pattern are formed on work-surface with UV while the parallel distributed cutting marks are generated without UV, and the surface roughness is decreased by up to 10% when the UV is applied at an appropriate power supplying level; (3) the work-surface straightness is improved by 46% once the UV is applied.

Abstract: In press forming, it is most important to prevent wrinkling and cracking. A small clearance between the upper and lower dies is effective for preventing wrinkle generation. However, the small clearance increases sliding resistance between sheet material and dies and causes cracking of sheet material. On the other hand, large deformation of sheet material requires multi-step press working which involves incremental small deformations in order to avoid wrinkling and cracking. But this method requires a number of dies so that it increases cost and development time. In press forming, lubricant to reduce sliding resistance of sheet material is used for preventing wrinkling and cracks. However, the use of lubricant such as chlorofluorocarbon and trichloroethane has been restricted due to environmental concerns. The development of new press working techniques that do not use lubricant is thus desired. Since wrinkling and cracking are mainly caused by friction between sheet material and dies, forming techniques which can decrease the friction without lubricant are needed.

Abstract: Ultrasonic assisted grinding experiments were carried out to evaluate the effects of the ultrasonic vibration (UV) on the face grinding characteristics of nickel based superalloy of Rene77. In experiments, an electroplated cBN grinding wheel was ultrasonically vibrated dominantly along its axis. The experimental results indicated that the X-axis and Y-axis components of grinding forces with UV were smaller by 44.5% and 31.6%, respectively, than those without UV. The usual fractures and debris on the surface of workpiece disappeared and the work-surface roughness Ra was decreased by 42.3% once the UV was applied. The abrasion of the grinding wheel without UV is more serious than that with UV.

Abstract: For a purpose to improve electric discharge machinability of PCD composed of coarse (25μm) diamond particles, which has been thought to be extremely difficult to EDM, in this study, a method (US-EDM) to give an ultrasonic vibration to an electrode in axial direction, flexural direction and complex direction that couples axial and flexural directions was attempted. As a result, it was found that EDM efficiency could be improved to 6 times higher (0.065mm³/min) than a standard efficiency (0.011mm³/min) obtained in machining conventional PCD (C-PCD) and the electrode wear could be reduced to 1/2 by giving vibrations to the electrode in axial direction (frequency f=28kHz, amplitude δ=18μm). Further, this method (US-EDM) was applied also to a new PCD (EC-PCD) composed of electrically conductive diamond particles. As a result, it was made clear that EDM efficiency could be improved to 0.22mm³/min. This value is equivalent to approximately 5 times higher efficiency obtained in the machining of ordinary die steel and cemented carbide materials.