超声辅助混粉电火花加工7Cr13Mo钢试验研究

Experimental Study of 7Cr13Mo Steel by Ultrasonic-assisted Powder EDM

目的 利用超声辅助混粉电火花加工(Ultrasonic-assisted Powder Electrical Discharge Machining,US-PMEDM)对7Cr13Mo钢进行表面改性研究。方法用US-PMEDM和传统电火花加工(Electrical Discharge Machining,EDM)对7Cr13Mo钢分别进行表面改性研究。采用扫描电子显微镜(SEM)对试样表面的表面形貌和重凝层进行分析,用TR200粗糙度测量仪和FM800型显微硬度仪分别测量加工试样的粗糙度和表面硬度。结果和常规电火花加工相比,US-PMEDM加工表面更加平整,裂纹减少。随着脉冲宽度的增加,放电凹坑变得大而浅,当脉冲宽度增加到120μs时,裂纹数量增加。随着峰值电流的增加,US-PMEDM重凝层的连续均匀性变差,但随着脉冲宽度的增加,重凝层更加致密、均匀,与基体结合良好,厚度增加到10.30μm以上。US-PMEDM加工表面粗糙度随脉冲宽度和峰值电流的增加均增加,与电火花加工相比,相同放电参数下,其表面粗糙度降低,最大降低40%左右。随着峰值电流的增加,US-PMEDM的显微硬度增加,随脉冲宽度的增加,其显微硬度先增加后降低。与电火花加工相比,US-PMEDM的显微硬度提高约50%。结论用超声辅助混粉电火花复合加工改善了放电环境,使表面质量和表面硬度均得到提高。

In this study,the ultrasonic-assisted powder electrical discharge machining(US-PMEDM)process was applied to investigate the machining performance and surface modification of 7Cr13Mo steel.The machining parameter such as peak current and pulse duration was varied to explore their effects on surface morphology,surface roughness and micro hardness,compared with these of EDM process.The ultrasonic vibration adhered to the workpiece with TiC powder suspended in the dielectric.The surface morphology and the cross section morphology of the machined surfaces were observed by scanning electron microscope(SEM).Surface roughness was measured by TR200 roughness device with five different positions,and the FM800 vickers hardness tester was used to measure the micro hardness.The results showed that the US-PMEDM process has better surface quality with fewer micro cracks as compared with that of EDM process.As pulse duration increased,the discharge craters became shallower with larger diameters,more micro cracks formed on the US-PMEDMed surface when the pulse duration increased to 120μs.With the increase of peak current,the continuous uniformity of the recast layer thickness on US-PMEDMed surface got worse,the thickness of recast layer even increased to more than 10.30μm with the increasing pulse duration.The recast layer of US-PMEDMed surface was denser and more consistent and had a better combination with the matrix.The surface roughness of US-PMEDM process was increased with the increase of peak current and pulse duration.Compared with EDM process,the surface roughness of US-PMEDM process decreased by about 40%.The micro hardness was increased with the increase of peak current,and with the increase of pulse duration,the micro hardness increased firstly and then decreased.The micro hardness was increased by a maximum of about 50%as compared to that of EDM process.The results indicate that ultrasonic vibration combined with TiC powder in the dielectric improves the machining environment,thus the machining performance and the micro hardness are improved by US-PMEDM process.