| Due to the limitation of machining efficiency and cost,it is difficult to machine millimeter-scale narrow slots by traditional machining methods.These structures are usually machined by electrical discharge machining(EDM)with sheet electrode.However,there are still some problems in the machining process such as accumulation of debris and over-cutting caused by carbon deposition on the electrode.In order to solve these problems,this paper tries to modulate the water-based dielectrics suitable for this processing.The processing performance of different dielectrics were compared.The influence of the dielectric characteristics was studied.The waveforms of different working fluids were analyzed.The processing experiment in the optimized dielectric was completed and the processing efficiency of the slots was improved.Typical water-based working fluids such as WEDM working fluid,tap water,deionized water,emulsion and polyethylene glycol solution were studied.Experimental equipment was set up for the processing in water-based working fluids.Electrode materials and processing polarity were determined.The material removal rate and tool wear in different working fluids were compared by single factor experiments and deep slot machining experiments.It was found that the electrode wear was serious in WEDM working fluid,tap water and deionized water,and the processing efficiency was low in emulsions.Better machining efficiency were obtained by using polyethylene glycol solution compared with EDM oil.Based on the experiment results,the influence of dielectric characteristics on machining performance was analyzed.In the aspect of material removal rate,the influence of working liquid viscosity was analyzed by simulation and analysis of experimental results.The results show that increasing the viscosity of working liquid can improve the debris evacuation caused by tool lifting,and therefore improve the processing efficiency.By comparing different conductivity working fluids,it was found that the increase of conductivity had a negative effect on the processing efficiency.The influence of conductivity and carbon content of working fluid on electrode wear was studied.Based on the results of machining experiment and electrolysis experiment,it was found that the increase of conductivity of working liquid would lead to electrode electrolysis,which together with discharge explosion lead to serious electrode loss in high conductivity solution.The increase of carbon content in the working fluid was helpful to greatly reduce electrode loss in the water-based dielectrics by means of carbon deposition.Matlab programs were written to analyze processing waveforms of deionized water,emulsion,EDM oil and polyethylene glycol solution.The proportion of different discharge types,discharge maintenance voltage distribution and the distribution of average voltage were studied.With these results,this paper further explains the reasons that lead to the difference in the processing performance of different working fluids and provides reference for the design of electronic control system.Finally,based on the optimized polyethylene glycol solution,the influence of electrical parameters such as pulse width,pulse interval,peak current and servo reference voltage on the processing efficiency was studied.The optimal processing parameters were obtained by response surface analysis method,and the verification experiments were carried out.The results show that the machining efficiency of the slots can be greatly improved by applying the water-based working fluid and appropriate machining parameters. |
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