The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining ...The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining （G-ECDM） is a promising technology for drilling advanced hard-to-ma- chine ceramics, glass, composites, and other brittle mate- rials. Edge-chipping at the entrance of the hole can be fully eliminated by optimizing the machining parameters of G-ECDM. However, edge-chipping at the exit of the hole is difficult to eliminate during the drilling of ceramics and glass. This investigation suggests some practical ways to reduce edge-chipping at the exit of the hole. For this pur- pose, a three-dimensional finite element model was developed, and a coupled field analysis was conducted to study the effect of four parameters, i.e., cutting depth, support length, applied voltage, and pulse-on time, on the maximum normal stress in the region where the edge- chipping initiates. The model is capable of predicting the edge-chipping thickness, and the results predicted by the model are in close agreement with the experiment results. This investigation recommends the use of a low voltage and low pulse-on time at the hole entrance and exit when applying G-ECDM to reduce the edge-chipping thickness. Moreover, the use of a full rigid support in the form of a base plate or sacrificial plate beneath the workpiece can postpone the initiation of chipping by providing support when the tool reaches the bottom layer of the workpiece, thereby reducing the edge-chipping thickness.展开更多
This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes...This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.展开更多
Electrochemical Discharge Machining(ECDM)is potentially applicable for the fabrication of film-cooling holes.However,It is extremely difficult for the holes to achieve higher precision and machining quality owing to t...Electrochemical Discharge Machining(ECDM)is potentially applicable for the fabrication of film-cooling holes.However,It is extremely difficult for the holes to achieve higher precision and machining quality owing to the working liquid diminish in the lateral machining gap.In this study,a non-metallic backing layer was proposed to overcome the diminish of working liquid,and the electrochemical reaming,as a post-processing method for ECDM,was used to further improve the machining accuracy and quality of the holes.First,the three-dimensional morphology of the melted pit of a paraffin backing layer was scanned to obtain the geometric parameters.Then,simulation analysis and experimental verification of auxiliary flushing by using the non-metallic backing layer were performed.The machining performance of the holes machined with electrochemical reaming based on non-metallic backing layer was confirmed by the observations of the surface topography of the hole wall and orifice,measurement of the orifice precision,and analysis of the element composition on the surface of the orifice wall.Finally,an optimum combination of machining parameters for electrochemical reaming is obtained through a process parameter optimization experiment.展开更多
Electric discharge is a common tool nowadays for machining of materials. It may be through a liquid medium or through air. Any metals, hard alloys, and nonmetals can be machined using the energy of electric discharge....Electric discharge is a common tool nowadays for machining of materials. It may be through a liquid medium or through air. Any metals, hard alloys, and nonmetals can be machined using the energy of electric discharge. In electric discharge machining (EDM), the discharge occurs between two electrodes through a liquid medium and it is applicable only for electrically con ducting materials and alloys. In electrochemical discharge machining (ECDM), the medium is an aqueous electrolyte and it is of two types. In the first type, the discharge occurs between two electrodes. One of the electrodes is the workpiece, and the other is the tool. In the second type, the discharge occurs between one electrode and an electrolyte. It is used for electrically nonconducting materials and the discharge energy is utilized maintaining the nonconducting workpiece in proximity of the discharge. All these electrical discharges are transient phenomena and do not result in a stable discharge in the form of arc. The output parameters depend on the discharge energy that requires precise control to maintain the accuracy of the machining. For micromachining, the control of the discharge is paramount both in terms of energy and pattern. Using various shaped tools, machining media with additives, different types of applied potentials, and supporting mechanical motions are some of the attempts made to improve the machining output. Optimization of these parameters for machining particular materials (or alloys) is a popular field of research. The present work is directed toward the investigation of discharge initiation and development by analyzing the cell current and discharge voltage relationship for both EDM and ECDM. The rectangular direct current (DC) pulse with different frequencies and the duty factor (on-off time ratio) are used for investigation. Observations on the voltage-current relationship are made for the external potential prior to discharge at discharge and above the discharge potential. Though the external poten tial above the discharge voltage is useful for machining, these observations elucidate the mechanism regarding the initiation of the electric discharge under different condi tions. The manner of discharge development in dielectrics and electrolytes is observed to be different. This understanding will aid in deciding the design of the discharge circuit including the external potential and its pattern for certain desired outputs in machining.展开更多
文摘The problem of eliminating edge-chipping at the entrance and exit of the hole while drilling brittle materials is still a challenging task in different industries. Grinding- aided electrochemical discharge machining （G-ECDM） is a promising technology for drilling advanced hard-to-ma- chine ceramics, glass, composites, and other brittle mate- rials. Edge-chipping at the entrance of the hole can be fully eliminated by optimizing the machining parameters of G-ECDM. However, edge-chipping at the exit of the hole is difficult to eliminate during the drilling of ceramics and glass. This investigation suggests some practical ways to reduce edge-chipping at the exit of the hole. For this pur- pose, a three-dimensional finite element model was developed, and a coupled field analysis was conducted to study the effect of four parameters, i.e., cutting depth, support length, applied voltage, and pulse-on time, on the maximum normal stress in the region where the edge- chipping initiates. The model is capable of predicting the edge-chipping thickness, and the results predicted by the model are in close agreement with the experiment results. This investigation recommends the use of a low voltage and low pulse-on time at the hole entrance and exit when applying G-ECDM to reduce the edge-chipping thickness. Moreover, the use of a full rigid support in the form of a base plate or sacrificial plate beneath the workpiece can postpone the initiation of chipping by providing support when the tool reaches the bottom layer of the workpiece, thereby reducing the edge-chipping thickness.
文摘This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.
基金supported by the National Natural Science Foundation of China(No.51705239)。
文摘Electrochemical Discharge Machining(ECDM)is potentially applicable for the fabrication of film-cooling holes.However,It is extremely difficult for the holes to achieve higher precision and machining quality owing to the working liquid diminish in the lateral machining gap.In this study,a non-metallic backing layer was proposed to overcome the diminish of working liquid,and the electrochemical reaming,as a post-processing method for ECDM,was used to further improve the machining accuracy and quality of the holes.First,the three-dimensional morphology of the melted pit of a paraffin backing layer was scanned to obtain the geometric parameters.Then,simulation analysis and experimental verification of auxiliary flushing by using the non-metallic backing layer were performed.The machining performance of the holes machined with electrochemical reaming based on non-metallic backing layer was confirmed by the observations of the surface topography of the hole wall and orifice,measurement of the orifice precision,and analysis of the element composition on the surface of the orifice wall.Finally,an optimum combination of machining parameters for electrochemical reaming is obtained through a process parameter optimization experiment.
文摘Electric discharge is a common tool nowadays for machining of materials. It may be through a liquid medium or through air. Any metals, hard alloys, and nonmetals can be machined using the energy of electric discharge. In electric discharge machining (EDM), the discharge occurs between two electrodes through a liquid medium and it is applicable only for electrically con ducting materials and alloys. In electrochemical discharge machining (ECDM), the medium is an aqueous electrolyte and it is of two types. In the first type, the discharge occurs between two electrodes. One of the electrodes is the workpiece, and the other is the tool. In the second type, the discharge occurs between one electrode and an electrolyte. It is used for electrically nonconducting materials and the discharge energy is utilized maintaining the nonconducting workpiece in proximity of the discharge. All these electrical discharges are transient phenomena and do not result in a stable discharge in the form of arc. The output parameters depend on the discharge energy that requires precise control to maintain the accuracy of the machining. For micromachining, the control of the discharge is paramount both in terms of energy and pattern. Using various shaped tools, machining media with additives, different types of applied potentials, and supporting mechanical motions are some of the attempts made to improve the machining output. Optimization of these parameters for machining particular materials (or alloys) is a popular field of research. The present work is directed toward the investigation of discharge initiation and development by analyzing the cell current and discharge voltage relationship for both EDM and ECDM. The rectangular direct current (DC) pulse with different frequencies and the duty factor (on-off time ratio) are used for investigation. Observations on the voltage-current relationship are made for the external potential prior to discharge at discharge and above the discharge potential. Though the external poten tial above the discharge voltage is useful for machining, these observations elucidate the mechanism regarding the initiation of the electric discharge under different condi tions. The manner of discharge development in dielectrics and electrolytes is observed to be different. This understanding will aid in deciding the design of the discharge circuit including the external potential and its pattern for certain desired outputs in machining.
