Research On Machining Mechanism And Experiments Of High-speed WEDM In Atmosphere And Water Mist Media

The wire electrical discharge machining(WEDM)in atmosphere and water mist uses the atmosphere and water mist as the processing media.It replaces the traditional liquid media and conforms to the trend of green manufacturing.This kind of processing method has broad application prospects.As the WEDM in atmosphere and water mist improves the surface quality of workpiece and processing efficiency,it has received extensive attention,which opens up a new way for the wire-cutting process.However,there are great differences in the physical and chemical properties among the above working media.The discharge processing performance in atmosphere and water mist is also different from that in the conventional liquid.Therefore,it is necessary to study the discharge mechanism,inter-electrode discharge characteristics,material erosion mechanism and processing technology characteristics of WEDM in atmosphere and water mist media.The discharge mechanism and inter-electrode discharge characteristics of WEDM in atmosphere and water mist were analyzed in this thesis.The discharge in atmosphere begins with the breakdown of Thomson and gradually develops into the streamer breakdown.Due to the presence of mist droplet,it causes the distortion of the electric field between the poles in water mist,which leads to lower breakdown voltage and larger discharge gap in water mist than those in atmosphere.According to the different voltage and current characteristics corresponding to different discharge states,the discharge state detection technology of the particle swarm optimization support vector machine(PSO-SVM)was proposed to identify various types of discharge states in real time.The discharge state detection system was designed and built based on the LABVIEW platform,and the on-line detection of the discharge state in different media was realized on the high speed wire electrical discharge machine(HS-WEDM),which provides a new way for further research on the machining mechanism of HS-WEDM in atmosphere and water mist.The single-pulse discharge simulation and the material erosion model of WEDM in atmosphere were studied.The temperature field model of single-pulse discharge of WEDM in atmosphere was established.The finite element simulation software was used to simulate and analyze the temperature field of WEDM in atmosphere,which obtained the variation of the size and depth of electro-erosion pit under different pulse duration with fixed peak current and different peak current with fixed pulse duration.The analysis of melting field was performed based on the analysis of temperature field and the morphology of electro-erosion pit formed by single pulse discharge was obtained.The superposition of electro-erosion pits formed on the machined surface during continuous pulse discharge in atmosphere was analyzed.The calculation methods for the maximum surface roughness and the material erosion under even distributions of electric pits were obtained,which provides a theoretical basis for the research on the material erosion mechanism of continuous discharge machining in atmosphere.A new multiple cutting process of multi-media combination in WEDM was proposed in which the initial cutting stage is carried out in emulsion,the transitional cutting stage is in water mist(steam water mist or ultrasonic water mist)and the final cutting stage is in atmosphere.Compared with the multiple cutting in emulsion,the new process not only improves the quality of the machined surface,but also increases the cutting speed and material removal rate.It provides a new approach to improve the processing quality of WEDM.The finishing characteristics of HS-WEDM in atmosphere and water mist media were studied.The surface roughness,cutting speed,material removal rate,straightness,and micromorphology of the machined surface of finishing in different media were compared and analyzed.The single factor experiment studied the influence of processing parameters such as pulse duration,peak current and water mist on the surface roughness and other process indicators in water mist media,and analyzed the related influence mechanisms.Based on the multi-factor experiment,the regression models of various process indicators were established and the factors that influenced the process index significantly were obtained in water mist media.A comprehensive model was established by weighted comprehensive evaluation method.In order to find a combination of processing parameters that were suitable for the multiple process indexes in HS-WEDM,the composite desirability optimization technique was used to optimize the combination scheme,which improves the overall processing performance of HS-WEDM.