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Although helical electrodes have been proven to improve the EDM (electrical discharge machining) speed of small holes, there are few studies on the morphological characteristics of the machined small holes and the influence of electrode structures. In this paper, the influence of the helical electrode structure on the machining effect is studied by the method of orthogonal experiment, and the internal mechanism of the influence of the helical electrode on the machining is explained by the method of CFD (computational fluid dynamics) simulation. The results show that the larger depth and width of the helical groove and the helix angle of 60° are beneficial to increase the machining speed and reduce the relative loss rate, and at the same time, avoid serious defects in the small hole morphology. These conclusions provide a valuable reference for future researchers to choose the reasonable structure of the helical electrode, which is of great significance. [ABSTRACT FROM AUTHOR]

Laser-assisted machining (LAM) is a new manufacturing technology to improve the productivity of metal matrix composites (MMCs). However, there are many arguments about whether LAM is good for improving chip deformation, and there is also a lot of debate about surface integrity. The quality of surface integrity is closely correlated with the chip formation in LAM of MMCs depending on the processing conditions and constituents in composites. In this study, interaction process between 1064-nm diode laser and 45%SiCp/Al composites is theoretically described. The chip formation mechanism in LAM of 45%SiC/Al composites at different temperatures is revealed by analyzing the chip root morphology and chip chip-breaking process with an assistance of finite element model. The thermal mismatch stress of particles and matrix in the shear deformation zone are derived applying the Eshelby equivalent strain equations and thermal expansion coefficient and elastic modulus. Based on these, mechanisms of chip deformation and fracture in LAM are elucidated further. The various surface morphology (plastic side stream, surface scratches, particle pull-out, particles broken) dependent on the coupling of the force loads, thermal loads, and removal model of reinforcement particles are deeply investigated through LAM experiments. The surface morphology experiment results show that particle aggregation occurs between two or more adjacent SiC particles because the multiple SiC particles appear simultaneously at cutting path of tools. An analysis model was established to evaluate particle agglomeration in LAM according to the influence rules of tool geometry and particle size. Moreover, technological experiments focus on the effect of LAM variables, like laser power and scanning velocity on the microhardness and surface roughness of cross-section layer, mechanisms of which are analyzed from multiple perspectives. [ABSTRACT FROM AUTHOR]

The ZrB2-SiC-graphite composite is one of the most promising ceramics, which show significant potential in manufacturing parts served in ultra-high temperature. Micro-electrical discharge machining (micro-EDM) is an effective method in machining this conductive hard ceramic. However, the recast layer characterized by craters and micro-cracks is formed on the machined surface, resulting in poor surface quality. In this paper, micro-EDM and micro-ultrasonic machining (micro-USM) combined milling is proposed for manufacturing 3D micro-cavities in the ZrB2-SiC-graphite composite. The micro-cavity is firstly machined by micro-EDM milling, followed by micro-USM finish milling to remove the recast layer in the same system without changing the micro-tool. The machining performances are investigated with consideration of the surface topography and finishing depth. It is found that the more recast layer is removed when a higher ultrasonic amplitude, larger abrasive grain size, and lower tool feedrate are employed. Based on the preliminary experiments, the proper machining parameters are obtained and applied to the fabrication of micro-cavities. The machining results show that the surface quality is improved with the low surface roughness and absence of defect layer. Meanwhile, the high machining accuracy in the depth direction and processing efficiency are achieved. It is verified that the micro-EDM and micro-USM combined milling process is feasible for fabricating 3D micro-cavities in the ZrB2-SiC-graphite composite. [ABSTRACT FROM AUTHOR]

Ni-Al2O3 functionally graded materials (FGMs) have become important for high-temperature applications due to a continuous change in graded layers. However, the manufacturing process of Ni-Al2O3 FGMs with the traditional pulse power is a long process because the pulse power cannot real-timely adjust machining parameters to adapt the change of graded layers. This paper designed a real-time monitoring module and a parameter adjustment module, which can identify different graded layers and actively adjust machining parameters to adapt the change of graded layers. By means of the monitoring module, four major discharge states, normal, arc, insufficiency, and long pulse discharge state have been discriminated real-timely. The 70% Ni/30%Al2O3 layer and 30% Ni/70%Al2O3 layer have been distinguished based on the quantitative analysis of insufficiency and long pulse discharge waveforms. Multi-layers of Ni-Al2O3 FGMs are machined to validate the machining performance of the parameter adjustment module. Experiment results demonstrate that by adjusting the open voltage, the machining efficiency of 30% Ni/70%Al2O3 layer has been increased by six times, resulting in more time-efficient EDM process of Ni-Al2O3 FGMs. [ABSTRACT FROM AUTHOR]

With three-dimensional (3D) microelectrodes used to machine microcavities in microelectrical discharge machining (micro-EDM), the processing efficiency can be greatly improved. However, the surfaces of a laminated 3D microelectrode always have stair steps, which will be further copied to the machined surfaces of the microcavities, reducing the processed surface quality. To solve the problems, the paper proposed using layer-by-layer scanning microelectrochemical machining (micro-ECM) to eliminate the stair-stepping effect of the laminated 3D microelectrodes. First, wire electrical discharge machining (WEDM) was chosen to cut Cu foils for obtaining multilayer two-dimensional (2D) microstructures. Second, the multilayer 2D microstructures were applied to thermal diffusion bonding to form 3D microelectrode blanks. Then, the 3D microelectrode blanks were processed via layer-by-layer scanning micro-ECM to eliminate the stair steps on the surfaces. The influences of applied voltage, offset distance, and layer thickness on the elimination of the stair-stepping effect were investigated in details. Experimental results show that the stair steps on the laminated 3D microelectrode surfaces were eliminated obviously under 4.0 V applied voltage, 200 μm offset distance, and 20 μm layer thickness. Finally, the laminated 3D microelectrodes without stair steps on the surfaces were applied to micro-EDM to process microcavities. Two typical microcavities without the stair steps were obtained. [ABSTRACT FROM AUTHOR]

The ZrB-SiC-graphite composite is a promising engineering material for ultra-high temperature applications. However, the fabrication of micro-hole in this ceramic composite is difficult due to the high hardness. This paper presents micro-electrical discharge machining (EDM) drilling of the ZrB-SiC-graphite composite using the micro sheet-cylinder tool electrode to improve the machining efficiency and quality of micro-hole. The micro-hole is firstly drilled by the sheet segment of electrode under the high capacitance, and then finish drilling is conducted using the cylinder segment of electrode under the low capacitance. The material removal rate, surface roughness, surface microcracks, debris, and material removal mechanisms are investigated. It is found that the material is removed by melting/evaporation and thermal spalling during micro-EDM of the ZrB-SiC-graphite composite, and the thermal spalling effect produces the large size irregular debris. The electrode with the sheet shape can significantly increase the machining efficiency compared with the electrode with the cylinder shape. Furthermore, the surface roughness is reduced in finish drilling with the low capacitance. The experiment results of micro-holes machined by the sheet-cylinder electrode demonstrate that the presented method can improve the machining efficiency, surface quality, and machining accuracy. [ABSTRACT FROM AUTHOR]

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical methods for the machining of metal matrix composites and conducting ceramic blanks. However, the machining process of Ni-AlO functionally graded materials (FGMs) is extremely difficult because the insulating ceramic layer cannot be machined directly by EDM. In this paper, the pure AlO layer has been machined by self-induced EDM, using the conductive layers of Ni-AlO FGMs to trigger the discharges in the insulating ceramic layer. Machining experiments have been performed to investigate the effects of discharge capacitance, pulse off-time, and charging resistance on the process performance of the pure AlO layer using RC-type pulse generator. From the experimental results, the discharge waveform of pure AlO layer includes long pulse discharge waveform, in addition to conventional normal discharge of conductive layers. The shape of long pulse discharge waveform can be changed by pulse off-time. The appropriate pulse off-time not only improves the stability of EDM but also increases the material removal rate (MRR). Moreover, it was observed that the MRR increases with increasing discharge capacitance and decreasing charging resistance. The surface roughness increases with increasing discharge capacitance. Finally, a small hole with a depth-diameter ratio of 5, little tapper is machined based on the experimental analysis. [ABSTRACT FROM AUTHOR]