Key Engineering Materials Vols. 291-292

Abstract: Diamond tool based on Ni-Al self-propagating high temperature synthesis (SHS) was introduced in this paper. Different heating methods such as muffle furnace, vacuum furnace and induction were used to ignite the Ni-Al-diamond SHS system. The morphology and microstructure of the Ni-Al-diamond composite were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). It was found that SHS Ni-Al-diamond composite ignited by induction heating owned the best morphology and microstructure to work as diamond tool.

Abstract: Copper electroforming, together with rapid prototyping (RP) technology, provides a method for manufacturing EDM electrodes rapidly. However, the use of conventional electroformed copper electrodes is restricted because of the high electrode wear rate in EDM processes. This paper presents a study on the electroforming technique of copper/zirconium diboride (ZrB2) composite coating and its performance as an EDM electrode. Cu-ZrB2 composite coating is electroformed from a copper nitrate bath containing micro-sized ZrB2 particles in such a way that by varying the process parameters, ZrB2 particles approximate to 20 Vol.% are incorporated in the coatings. Analyses by optical microscopy and scanning electron microscopy reveal that ZrB2 particles are uniformly dispersed in the copper matrix and the grains of the coating are refined due to the incorporation of ZrB2 particles. The electroformed coatings deposited on copper substrates with approximately 1mm thickness are used as electrodes. EDM experiment shows that performance such as the spark-resistance of the new electrodes is improved compared with that of conventional electroformed copper electrodes because the incorporation of refractory particles in the copper matrix as well as the refinement of the grains of the coating, and the. Cu-ZrB2 composites show good performance in finish machining condition.

Abstract: The performance of electrically conductive CVD (called EC-CVD) diamond thick film possessing a high thermal diffusivity has been examined as an electrode for fine electrical discharge machining (EDM). The results indicate a possibility of zero wear in EDM as compared to copper and copper-tungsten (Cu-W) electrodes. It is particularly significant at short pulse EDM conditions, where the EC-CVD diamond electrodes showed increased machining efficiency and a remarkably low wear. In EDM of tungsten carbide, a very low electrode wear ratio of 0.3% was realized with the EC-CVD diamond electrode. Zero wear EDM could be achieved even for sharp V-shapes with included angles of 15 and 30° with V-shaped EC-CVD diamond electrodes. Thermal FEM analysis to examine the relation between the thermal diffusivity and temperature distribution at short pulse duration indicated lowest temperature on EC-CVD diamond electrode surface.

Abstract: Electrically conductive CVD diamond having a high thermal diffusivity, when used as an electrode for micro EDM, revealed very low wear compared to copper and Cu-W electrodes in the case of finish EDM condition, where the short pulse duration is adopted. In this research work polycrystalline diamond (PCD), which has a thermal conductivity similar to that of the electrically conductive CVD diamond, is introduced as a new composite electrode material for EDM. Various properties of PCD with respect to EDM of die-steel (SKD11) and tungsten carbide (G5) have been studied and compared with those of the electrically conductive CVD diamond, copper and copper-tungsten electrode materials. It is found that electrode wear and material removal rate decreased with an increase in thermal conductivity depending on the type of the PCD material when very short pulse duration of te=1µs is applied. Extremely low wear, 1/20~1/50 times of the Cu-W electrode in the case of EDM of tungsten carbide workpiece at short pulse duration and zero wear in the case of EDM at short and long pulse duration of SKD11 can be realized.

Abstract: In wire electro-discharge machining with high traveling speed(WEDM-HS), the emulsion is used as working liquid. Because there exists a functional electrolyte, this affects the surface quality of workpiece machined. An investigation has been made into the machining feasibility when the gas or air is employed as processing medium. The first cut on workpiece is done with emulsion, and then air or distilled water is used for the second cut and multi-cuts. After machining, the surface quality and mechanical performance of the specimen under different conditions are compared. The experimental results show that air and distilled water have little influence on the surface roughness, but they can improve the mechanical performance such as the increase of hardness and the decrease of surface cracks. An orthogonal design is adopted to optimize the electric parameters and cutting passes so as to obtain the best integrative result. The experiment with air as medium reveals that it is a feasible and effective way for eliminating the electrolytic layer and improving the surface integrity of workpiece.

Abstract: The dimensional accuracy of electro-discharge machining (EDM) is greatly influenced by the overcut resulting from discharge gap and electrode wear. In order to achieve fine accuracy, it is necessary to estimate the overcut according to an empirical formula. In this paper, experiments in electro-discharge machining were carried out. The effects of parameters on the overcut, such as peak current, pulse duration, were analyzed. Then an empirical formula for the overcut in EDM was established based on the experimental results using the least square method. Finally, reasonable agreement between calculated results and the further experimental results was obtained.

Abstract: Their efficiency and their power factor of conventional independent electrical discharge machining (EDM) pulse power supplies with the current-limiting-resistor circuit is so low that they do not meet the need of advanced EDM technologies. The design of highly efficient EDM pulse power supply based on switching circuit pulse width modulation current closed-loop principle has been initiated. It is composed of such three stages as a single-phase active power factor correction preregulator, a full-bridge phase shift resonant converter based on machining current closed-loop control and a pulse generator based on machining sequence control. Therefore, the efficiency of the new system is considerably increased to about 70%, its weight and size is decreased much. Its power factor is a great deal increased to about 0.95. Experiment results have demonstrated that the highly efficient EDM pulse power supply is capable of low electrode wear, high speed, stable machining.

Abstract: This paper deals with a new finishing technique called pulse electrochemical finishing technology (PECF) and its application to column surface of carbon steel. PECF makes use of pulse current and neutral electrolyte. There is nearly no wear of the cathode, and nearly no cutting force or cutting heat, which may result in the deformation of wokpiece. The principle of the technique is put forward, and the equipment as well as a typical finished sample is shown in this paper. The key technological parameters of PECF are studied and the favorable values are presented. With the moving cathode PECF technology, the roughness value of ground surface could be reduced from Ra 0.217～1.13μm to Ra 0.041μm. Combined with NC technology, PECF could be applied to the finishing field widely.

Abstract: In this paper, electrochemical finishing（ECF） is presented. Compared with conventional finishing technology, the characterization of surface topography machined by ECF and its effect on the performance, including friction coefficient, original wear and tear, precision durability, fatigue strength, contact stiffness, corrosion resistance and adhesiveness are analyzed and studied. Experimental results have testified that ECF can observably improve surface quality of parts and finally improve its physical mechanical performances and lifetime to a large extent.

Abstract: If a circular section tool is used for ultrasonic machining, cavitation occurs at its center. This cavitation suppresses the penetration of abrasive grains and leaves a projection at the center of a machined hole. On a square section tool, a cavitation vortex appears symmetrically on a diagonal line to promote the penetration of abrasive grains and makes the machining rate greater than that for a circular section tool. If the aspect ratio (ratio of vertical and horizontal dimensions) of the tool section is changed, the cavitation vortex changes the machining rate even when the sectional area is the same. For confirmation in detail, square section tools of different aspect ratios were created and used for SiC ultrasonic bottom die sinking to survey the machining characteristics. At the same time, tools having segmented square sections were checked for the occurrence of cavitation, and the influence on the height of the projection generated by machining was studied. Consequently, a 4-segmented tool of 3 × 4.2 mm minimized the cavitation in each element and produced the greatest machining rate of 2.26 µm/s. In every machined hole, the tool suppressed the projection height within 50 µm.