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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]

An integrated method of micro-milling and micro electrical discharge machining (EDM) is proposed for micro-structures array manufacture in this paper. In order to obtain micro-cavity array with high accuracy and consistency, in situ machining on the same coordinate system ensures the positioning precision. After studying micro-milling graphite, the effect of parameters on the machining accuracy is found. Further, suitable mode is chosen for high-dimensional consistency and good surface quality array electrodes according to comparison of one-by-one and layer-by-layer milling tool trajectory. Workpiece lifting control is used to strengthen the debris clear; then, it is verified beneficial of lifting through flow simulation and adding discrete particles. In order to solve poor precision of the micro-cavity contour caused by electrode wear, a multi-step machining by group electrodes is proposed, rough machining for material removal and finishing machining for trimming. Finally, a micro-cavity with clear edge, small fillets, and high shape accuracy is obtained. This method improves the machining performance of the array micro-structures and shows good prospects in micro-fabrication. [ABSTRACT FROM AUTHOR]

Microwave-induced thermal-crack propagation (MITP) is an advanced processing technology for cutting ceramics introduced recently. However, due to the lack of methods to predict its machinability, its application has been limited. In order to evaluate the machinability of this method for different ceramic materials, in this paper, a simple method is presented to predict the machinability in microwave cutting ceramics. Firstly, the processing difficulty of microwave cutting ceramics using MITP is analyzed based on the fracture mechanics, and the concept of crack initiation factor is proposed. An experimental work demonstrates that crack initiation factor is effective to predict the machinability. However, the crack initiation factor is closely related to many process parameters in MITP, so its prediction process is complicated. To find a practical and straightforward method, the ceramic heated by the static point heat source is analyzed, and the crack initiation factor is simplified as the crack factor which is only related to the physical parameters of the material in this model. The theoretical calculation shows that there is a positive correlation between the crack factor and the crack initiation factor, so the machinability in MITP can be predicted by this simplified factor. By establishing a link with the processing parameters, the crack factor can be used to pre-select the processing parameters. The simulation results show that the crack factor can also be used to predict the relative magnitude of temperature gradient and maximum thermal stress of different ceramics under the same processing conditions. This study provides a simple and effective method for predicting the machinability of ceramics using MITP. [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]

This paper presents the manufacture of micro-rotating structure combining micro reciprocated wire electrical discharge machining (wire-EDM) and multi-cutting strategy. A novel rotating spindle is developed to achieve the rotation of cylindrical workpiece and the multi-cutting strategy including rough, semi-finish, and finish machining is attempted to improve the machining removal rate (MRR) and reduce the surface roughness (SR) of micro-rotating structure. To determine proper parameters for multi-cutting process, the effects of machining parameters such as open voltage, discharge capacitance, and rotation rate on MRR and SR are studied by systematically performing experiments planed by single factor design and central composite design (CCD) of response surface methodology (RSM). Analysis of variance (ANOVA) is conducted to identify the significant factor and confirm the adequacy of the established models of MRR and SR. The mathematical models are used to predict MRR and SR within 8.18 and 8.74% prediction error compared with the additivity tests, respectively. Desirability method in RSM technique is used to determine three sets of parametric combinations for multi-cutting process, which are verified by confirmation experiments with 1.75~7.76% prediction error for MRR and 2.77~8.59% prediction error for SR. Finally, a typical microballoon probe is successfully machined with 0.435 Ra and 98.7-μm diameter by the proposed method, which provides a feasible approach for the fabrication of micro-rotating structure with high efficiency and smooth surface. [ABSTRACT FROM AUTHOR]

Beryllium copper alloys known as high-reliability engineered materials are widely used in many engineering fields. Micro-electrical discharge machining (micro-EDM) provides a safely and effectively machining process to machine beryllium copper alloys regardless of their toxicity and mechanical strength. During micro-EDM, the higher material removal rate and the lower electrode wear rate are observed when deionized water is used as a dielectric fluid. However, there are many stray-current corrosion pits on the end surface of holes which directly affect the performance and life span of parts. In this study, the method of auxiliary electrode was used to suppress the effects of stray-current corrosion on the end surfaces of holes on C17200 beryllium copper alloy. The end surfaces of holes were protected by sacrificing the auxiliary electrode. The feasibility of micro-EDM with an auxiliary electrode was verified by an experiment of a hole machined with half coved by the auxiliary electrode and the others without. The effects of the thickness of the auxiliary electrode on end surface quality and machining time were studied. The effects of the auxiliary electrode to suppress stray-current corrosion on C17200 beryllium copper alloy were proved under diffident pulse currents and pulse widths. Machining time and electrode wear were investigated. The results show that the electrode wear is scarcely affected by the auxiliary electrode. However, the machining time is slightly increased when the pulse current is lower than 0.55 A, and the pulse width is shorter than 20 μs. Beyond that level, the effect of the auxiliary electrode on machining time is not obvious. The end surface quality decreases when the pulse width is longer than 20 μs. In addition, the results also show that, when the thickness of the auxiliary electrode is 60 μm, a value of 0.34 A pulse current and 20 μs pulse width could be considered as ideal parameters for C17200 beryllium copper alloy machined by micro-EDM with an auxiliary electrode in deionized water. Furthermore, it is confirmed that the auxiliary electrode can be easily fixed on different radii of curvature surface and effectively protect the end surface of micro-holes from stray-current corrosion. [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]

Beryllium copper alloys with excellent features are widely used in many engineering fields, and their fabrication requires high machining speed. However, the fabrication of beryllium copper alloys by traditional processes has serious problems. In this study, high-speed electrochemical discharge drilling (HSECDD), a hybrid process containing electrical discharge machining (EDM) and electrochemical machining (ECM) in deionized water, was used to machine micro-holes on C17200 beryllium copper alloy. The material removal mechanism of HSECDD was studied and compared with traditional EDM. The performance of the process was investigated under different conductivities of peak current and pulse width. The results show that HSECDD is a high-efficiency method to machine C17200 beryllium copper alloy. During HSECDD, the material removal depends mainly on EDM. And, the ECM occurs at the entrance region of micro-holes machined by EDM. The function of ECM is to expand the gap between the electrode and the hole. The machining speed and average diameter of micro-holes increase with the increasing of peak current and pulse width. Increasing the pulse width will reduce the electrode wear. However, the taper angle will increase. In addition, the results also show that a value of 0.34-A peak current and 10-μs pulse width can be considered an ideal parameter for HSECDD to machine micro-holes on C17200 beryllium copper alloy. [ABSTRACT FROM AUTHOR]

This study aimed to develop software for multi-axis electrical discharge machining (EDM) computer numerical control (CNC) systems using open CNC technology and soft CNC technology and to then apply the software to the machining of rimmed turbine blisks. Through the analysis of functional requirements, this study established the hierarchy structure of the software. On the basis of this structure, three main modules and their communications were established with Linux and RT-Linux as the development platforms. The software architecture was also constructed. Through the construction of the modules and communications and the realization of the functions, the multi-axis EDM CNC system software was developed and installed into a five-axis EDM CNC machine to realize the machining of rimmed turbine blisks. Machining results show that the architecture of the software is correct, harmonious, and reasonable. The software is also stable and reliable and features strong real-time capability and accurate movement control. [ABSTRACT FROM AUTHOR]

Ni-AlO functionally graded materials (FGMs) have become important for high-temperature applications due to a continuous change in composition. However, the manufacturing of Ni-AlO FGMs with conventional machining methods is a long and costly process because of the insulating ceramic composition. This paper presents a new method of machining Ni-AlO FGMs by self-induced electrical discharge machining (EDM). Self-induced EDM uses the conductive compositions of Ni-AlO FGMs to trigger the discharges in the insulating composition. Machining characteristics of a four-layered Ni-AlO FGMs drilled by self-induced EDM have been investigated, which include the material removal mechanisms, discharge properties, surface characteristics, material removal rate, and electrode wear ratio. It has been found that graded layers, 70 % Ni-graded layer and 30 % Ni-graded layer, are removed by dislodgement of AlO particles, in addition to conventional melting and evaporation. Pure AlO layer is melted and evaporated by utilizing conductive layer-induced discharges. The discharge properties, surface characteristics, material removal rate, and electrode wear ratio are significantly influenced by the material removal mechanisms of graded compositions. These findings demonstrate that self-induced EDM is able to effectively machine Ni-AlO FGMs. [ABSTRACT FROM AUTHOR]