Key Engineering Materials Vol. 625

Abstract: Uniformity is an important index of the template electrochemical etching. Due to the uneven current distribution between the two electrodes, the etching depth of the workpiece center and edge are significantly different,and the deviation of which is up to 15% or more. In this study, the causes of edge effect is analyzed. A compensation method is proposed and proved by experiments.The results show that: this method is simple, and the uniformity can be reduced to about 3%. It is suitable for the processing of high uniformity requirements in microstructure machining.

Abstract: In this paper, the influence of machining parameter in the driven rotary cutting was examined by using finite element simulation. Three dimensional modeling of rotary cutting of Inconel 718 was conducted and then cutting force, temperature distribution of chip and tool, chip thickness and its flow direction were analyzed. Then, the effect of the tool rotation speed was mainly focused on. When peripheral speed of the rotating tool increased, resultant cutting force decreased and the chip flow direction inclined to the tool rotating direction. Then high temperature region of chip became large. It was also shown that tool temperature on the driven rotary cutting was lower than that of the conventional turning. FEM simulation results were compared with the experimental results. As a result, the resultant cutting force, chip flow direction and the tool temperature of the experimental results and the analysis results showed the same trend.

Abstract: Reaction-sintered silicon carbide (RS-SiC) is a promising material for optical components used in space, or molds for precision glass lens because of its excellent properties. For processing of RS-SiC, diamond tools are utilized because RS-SiC is difficult-to-machine material due to its high hardness. In that case, subsurface damage (SSD) and scratches are inevitably introduced on the processed surface, and they deteriorate the qualities of products. To resolve these issues, we proposed a complex machining technique named anodic oxidation assisted process (AOAP), in which localized anodic oxidation and removal of the oxidation layer by grinding or polishing were combined, for figuring or polishing of RS-SiC without introducing any scratches and SSD. The grinding or polishing tool used in AOAP has a lower hardness than that of RS-SiC, but higher than that of the oxidation products. It is possible to figure the objective shape and polish the surface by changing the conditions including the oxidation time, the composition of electrolyte, the configuration of the cathode electrode, applied voltage, and so on. In our previous study, we found that RS-SiC was oxidized efficiently by anodic oxidation with various electrolytes such as phosphoric acid, ultrapure water, and a mixture of hydrochloric acid and hydrogen peroxide. In this research, we investigated the preliminary processing characteristics of AOAP for RS-SiC. We ascertained that irradiating UV light with photon energy higher than the band gap of processed materials is very effective for increasing the oxidation rate of anodic oxidation. And we proposed a novel polishing process of RS-SiC, which combining oxidation only SiC area in RS-SiC by anodic oxidation with the electrolyte of ceria slurry, with polishing by ceria slurry which removes both oxidized layer and unoxidized layer in RS-SiC. The results of investigation for the oxidation rate and the polishing rate of SiC, Si and SiO₂ with ceria slurry implies that we can remove SiC grain and Si grain in RS-SiC at the same MRR by combing the anodic oxidation and polishing with ceria slurry at the same time, and obtain the smooth surface.

Abstract: Tungsten carbide is widely used as molds and dies material due to its superior strength, hardness and wear resistance. However, these characteristics also make it very difficult to be machined. Because the material is removed by spark erosion, micro-EDM has been found to be an effective machining process to machine difficult-to-cut materials such as tungsten carbide. Notwithstanding that micro-EDM using deionized water yields many advantages compared to hydrocarbon oil such as higher removal rate, lower tool wear and thinner recast layer, it has not been widely used due to the poor dimensional accuracy of machined part. This is the result of stray material dissolution caused by the slight conductivity of deionized water. This unanticipated material removal is especially severe for tungsten carbide which is highly susceptible to corrosion. This paper presents an attempt to improve the accuracy of micro-EDM using deionized water by using short voltage pulses. A short pulses generator has been in-house developed for this purpose. The effects of pulse parameters on the stray material dissolution are investigated. It is observed that the stray material dissolution is localized when short voltage pulses are used. As a result, dimensional accuracy of machined parts is significantly enhanced.

Abstract: In this study, drilling for nickel alloy was carried out with ultrasonic vibrating carbide drill. Micro drilling is not an easy machining process due to remarkable tool wear, lower stiffness of the tool, difficulty of chip and heat removal from cutting point. Ultrasonic vibration assisted machining has effects of decrease of cutting force, generation of fragmented small chip, extension of tool life and improvement of surface integrity. In this study, ultrasonic vibration drilling for nickel super alloy was investigated to improve the tool life and productivity. The drilling for heat-resisting nickel super alloy was performed with the drill of 0.3mm in diameter. As a result, ultrasonic vibration drilling performed 302 holes with thickness of 2.0mm by applying minimum quantity lubrication to blow off the chips on the flutes. Ultrasonic vibration improved deviation of position of drilled hole because the hammering motion of the chisel edge results in good bite of tool on work surface. The productivity is directly depends on feed rate. The increasing feed rate from 6mm/min to 60mm/min dramatically reduced the tool life one thirtieth under conventional drilling condition. On the other hand, the ultrasonic vibration drilling reduced the tool life only one half.

Abstract: For the production of mould inserts for precision glass moulding, the ultra precision grinding technique with a subsequent manual polishing operation is typically applied. These processes are time consuming and have a relatively low reproducibility. An alternative manufacturing technology, with a high predictability and efficiency, which additionally allows a higher geometrical flexibility, is the diamond turning technique. In addition the ultrasonic assisted ultra precision cutting process has already proven its potential for machining difficult-to-cut materials, such as steel and glass. By applying the ultrasonic assistance, the classic constraints of the process can be widened significantly. In this publication the process is applied on binderless, nanocrystalline tungsten carbide.

Abstract: Plasma chemical vaporization machining (PCVM) is an ultraprecise figuring technique for optical components without introducing the subsurface damage. In our previous study, the material removal volume was controlled by changing the scanning speed of the worktable. However, because of inertia of the worktable, a discrepancy between the theoretical scanning speed and the actual scanning speed will occur if the spatial change rate of speed is rapid. Therefore, we proposed the application of the pulse width modulation (PWM) control and the amplitude modulation (AM) control of the applied RF power to control the material removal rate (MRR). Experimental results showed that the relationship between the MRR and the average RF power had high linearity, the control range of the PWM control mode was from 0.19 x 10^-2 mm³/min to 3.90 x 10^-2 mm³/min (from 5% to 100%), which was much wider than that of the AM control mode.

Abstract: Anisotropic materials are used in various fields because of their superior mechanical properties such as high specific strength. However, the surface generation mechanism in loose abrasive machining such as multi-wire sawing of anisotropic materials has many unknown characteristics. This study mainly aims to clarify the sliced surface generation mechanism in multi-wire sawing of glass fiber reinforced plastics (GFRP). Therefore, the slicing experiments and the wet lapping experiments are carried out in this study. In this paper, we describe the fundamental slicing characteristics of GFRP and the influence that the orientation angle of reinforcement fibers has on the newly generated surface of GFRP. We find that high-precision machining of GFRP is possible using a multi-wire saw. The slicing rate and thickness variation are not dependent on the orientation angle. However, sliced surface roughness depends on the orientation angle, and it tends to decrease when the orientation angle increases. In addition, sliced surface generation and polished surface generation involve similar mechanisms and produce very similar surface characteristics.

Abstract: In ultrasonic vibration the cutting edge of a tool is vibrated in the principal or cutting direction, generally at a constant ultrasonic frequency. The main characteristic of this cutting method is its intermittent nature involving repeated cutting and pausing. In this paper, ultrasonic elliptical vibration cutting is used to assist micro-groove turning of cylindrical surfaces. The elliptical locus during the cutting process is generated by a newly designed 2D resonant ultrasonic vibrator. A series of experiments were performed to verify the effects of the ultrasonic elliptical vibrations. The generated cutting forces and burr formation were compared for the ordinary and the elliptical vibration-assisted cases. Comparison results show the effectiveness of the elliptical vibration cutting method in reducing cutting forces and alleviating burr formation.

Abstract: Recently, technologies for medical inspection have been increasing rapidly. In biomedical industry, a demand of Micro Total Analysis System (μ-TAS) has been growing which used in automatically inspection for chemical analysis. The μ-TAS have micro passageway which is constructed by many fine micro holes. Final polishing by skilled workers are carried out after drilling to obtain smooth surface of holes. Because new manufacturing technique is required instead of skilled workers, it increases productivity and cost performance of the μ-TAS. Drilling technique with low temperature environment around cutting edge is required to prevent heat crack or adhesion on holes surface, because acrylic resin heats sensitive material. In this study, ultrasonically assisted micro drilling technique is proposed to increase productivity of μ-TAS and quality of micro holes. Ultrasonically assisted machining has effective technique to improve machinability, e.g. reduce cutting force, increase chip removability and machined surface quality. This paper describes the cutting characteristics of ultrasonically assisted micro-drilling for acrylic resin to employ the μ-TAS manufacturing to solve above problems.