SKD11硬切削锯齿形切屑形成机理试验研究

Experimental Study of Saw-tooth Chip Formation in Hard Cutting of SKD11

针对淬硬钢SKD11硬切削形成的锯齿形切屑,通过金相显微镜和扫描电子显微镜(SEM)观察了切屑的金相组织和微观形貌,分析了不同的切削速度下锯齿形切屑的特点,讨论了绝热剪切发生时剪切带内动态剪应力和温度的变化规律。研究结果表明:SKD11硬切削在低速和高速切削时均产生锯齿形切屑;提高切削速度有利于锯齿化程度的增加;锯齿形切屑的形成同时存在断裂和绝热剪切两种机制,并且随着切削速度的提高,切屑由周期断裂型向绝热剪切型转变;在绝热剪切过程中剪应力变化呈现二次曲线形式,且切削区温度对动态剪应力变化曲线具有较显著的影响;通过提高切削速度可以提高切削温度,抑制材料的硬化效应,引发剪切失稳,从而减小切削力。

Chips in hard cutting of hardened steel SKD11 were collected and observed by metallographic microscope and SEM;chip metallurgical textures and configuration under different cutting speeds were investigated.Dynamic shearing stress and temperature in adiabatic shear zones were discussed.Results show that in hard cutting of SKD11,saw-tooth chips are formed under both of low and high cutting speeds.Degree of segmentation increases with the increase of cutting speed.The saw-tooth chip formation could be due to fracture and adiabatic shearing;and with the increase of cutting speed,the chip formation mechanism changes from fracture to adiabatic shearing.During adiabatic shearing process,shearing stress develops as a quadratic curve,and cutting temperature shows distinct influence on the dynamic shearing stress.By increasing cutting speed,cutting temperature can be increased,which will weaken the hardening effect and reduce the maximum shear stress,cause occurrence of shearing instability and then reduce cutting force.