镁合金低温切削性能及工艺参数优化

Optimization of process parameters and performances of cryogenic cutting of magnesium alloy

摘要:

为改善镁合金的切削加工性能及加工表面完整性,优化切削加工工艺参数,基于拟水平法设计了四因素四水平正交车削试验,研究切削三要素以及切削介质（常温干切、液态二氧化碳和液氮）对ZK61M镁合金车削加工表面完整性的影响规律。实验结果表明:切削深度对切削力的影响最显著,进给量次之,切削速度的影响较小,低温切削能降低切削力,但对切削力的影响不显著；进给量对表面粗糙度和残余应力具有显著影响,随着进给量增大,表面粗糙度增大,并引入表面残余拉应力；冷却介质对表面粗糙度和表面残余应力具有次显著影响,相比于常温切削,采用低温切削能有效降低加工表面粗糙度,细化表层晶粒,增大表面残余压应力,同时,采用液态二氧化碳作为冷却介质的效果优于液氮。基于灰色关联分析得到ZK61M镁合金低温切削的最优工艺参数:v_c=100 m/min,f=0.05 mm/r,a_p=0.4 mm,采用液态二氧化碳作为冷却介质。用关联分析结果建立了工艺参数与加工质量间的响应预测模型,平均误差为7.93%。

Abstract:

To improve the machinability and surface integrity of magnesium alloys, and optimize the machining parameters, a set of orthogonal experiment with four factors and four levels were carried out based on the method of pseudo-level. Comparative study involved in the influence of three different cooling strategies, namely, dry cutting, liquid carbon and liquid nitrogen coolants, as well as the cutting parameters on the surface integrity of ZK61M magnesium alloy during turning were conducted. The experimental results show that the effect of cutting depth on cutting force is the most significant factor, the feed quantity is the second significant factor, the effect of cutting speed on cutting force is ignorable. Although the effect of cryogenic cutting on cutting force is not significant, it can reduce the cutting force in some extents. The feed rate has a significant effect on the surface roughness and surface residual stress. As the feed rate increasing, the surface roughness increases and the residual stress is introduced on the machined surface. The cooling medium has a sub-significant effect on the surface roughness and surface residual stress. Compared with dry turning, The cryogenic coolants can effectively reduce the surface roughness, refine the surface grain and increase the surface compressive residual stress during cutting. As a cooling medium, the liquid carbon dioxide is more effective than liquid nitrogen in improving the machining-induced surface integrity. Grey relational analysis is used to obtain the optimal process parameters for cryogenic cutting of ZK61M magnesium alloy: v_c=100 m/min, f=0.05 mm/r, a_p=0.4 mm, liquid carbon dioxide is used as the cooling medium. The response prediction model between the process parameters and the machined surface quality was established through the results of the relational analysis, the average error was 7.93%.