| Short arc machining technology not only solves the problem of poor machining performance of super hard alloy,but also has the advantages of large current and high machining efficiency compared with the same type of EDM technology.In order to reveal the mechanism of short arc milling,the temperature field is one of the important research contents.In the short arc milling process,the previous temperature field model of short arc milling process assumes continuous,multiple and random arc discharge as continuous and uninterrupted arc discharge,and has achieved certain research results.However,the effect of voltage,current and duty ratio on material erosion and surface quality in short arc milling is not revealed.Therefore,this study will establish a temperature field model from the perspective of single arc discharge to analyze the influence of voltage,current and duty cycle on temperature field distribution and material erosion.Firstly,in order to distinguish single arc discharge from a continuous discharge waveform and determine its discharge duration,a mechanical motion arc breaking model was established to calculate the maximum theoretical duration of a single arc discharge channel at different electrode speeds,and the voltage and current waveforms of of short arc machining arc from breakdown to deionization were analyzed through the expansion law of discharge channel.The experimental results show that there are voltage and current waveforms of a single arc from breakdown to deionization in the maximum theoretical duration of a single arc discharge channel,which verifies the correctness of the calculation results and waveform analysis;moreover,the arc discharge time corresponds to a single pulse period,so changing the electrode speed does not affect the arc discharge.The correctness of the conclusion is further verified by the processing experiments under different electrode speeds.Secondly,the heat source radius is calculated according to the duration and current of a single arc discharge channel.Combined with the analysis of heat conduction,heat convection and material erosion on the workpiece,the energy distribution coefficient is introduced into the heat source function as an unknown number,and the temperature field model of the workpiece is established.The correctness of using Gauss surface heat source in the temperature field model is verified by the heat source shape of arc formed on the workpiece by thermal imager.In order to determine the energy distribution coefficient,the simulation results of recast layer thickness under different energy distribution coefficients are obtained through the established temperature field model;the thickness of recast layer under corresponding electrical parameters is obtained through metallographic preparation and microscopic observation;finally,the relative error between simulation results and experimental results is analyzed.The results show that the energy distribution coefficient of 0.3 can better reflect the distribution proportion of discharge energy on the workpiece.Finally,the energy distribution coefficient is introduced into the temperature field model,and the influence of voltage,current and duty ratio on the temperature field distribution of the workpiece,as well as the influence on the depth and radius of material erosion are simulated and analyzed by controlling variables.The change trend of material removal rate and surface quality with voltage and duty cycle is predicted through material erosion simulation.The experimental results show that the experimental erosion rate and the simulation erosion rate are in good agreement,and the variation trend of the surface roughness of the workpiece is consistent with the simulation prediction results,which proves the correctness of the temperature field model established,and the feasibility of improving the machining quality by reducing the voltage and increasing the duty cycle is verified by experiments,which lays a theoretical foundation for short arc milling. |
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