超弹镍钛记忆合金线切割加工工艺及形状恢复能力研究

Research on Wire-EDM Process and Shape Recovery Ability of Super-elastic Ni-Ti Memory Alloy

针对镍钛记忆合金传统机械加工成本高、表面完整性差等问题,采用电火花线切割工艺开展工艺参数对超弹镍钛合金Ni55.9Ti的材料去除率、表面完整性、形状恢复能力影响规律研究,基于记忆合金形状恢复理论分析了重铸层对形状恢复能力的影响机制。结果表明:脉冲宽度、峰值电压增加使材料去除率、表面粗糙度、表面残余应力及变形恢复偏移量增大,脉冲间隔比增加使材料去除率、表面残余应力与变形恢复偏移量降低,峰值电压与脉冲宽度分别为材料去除率与表面粗糙度的最大影响因素。加工过程中形成的镍钛氧化物及工作液电离分解的游离碳随电蚀物冷凝于工件表面,降低了记忆合金的形状恢复能力。

In view of the high cost of traditional machining of nickel-titanium memory alloy and poor surface integrity,the wire EDM technology is used to carry out the research on the influence of process parameters on the material removal rate,surface integrity and shape recovery ability of super-elastic nickel-titanium alloy Ni55.9Ti based on the shape recovery theory of shape memory alloy,the influence mechanism of the recast layer on the shape recovery ability is analyzed. The results show that the increase of pulse width and peak voltage increases the material removal rate,surface roughness,surface residual stress and deformation recovery offset,and the increase of pulse interval ratio reduces the material removal rate,surface residual stress and deformation recovery offset. Peak voltage and pulse width are the biggest influencing factors of material removal rate and surface roughness,respectively. The oxides of nickel and titanium formed during the processing and the free carbon that is ionized and decomposed by the working fluid are condensed on the surface of the workpiece along with the galvanic corrosion products,which reduces the shape recovery ability of the memory alloy.