外圆磨削18CrNiMo7-6表面完整性研究

Study on Surface Integrity of Cylindrical Grinding 18CrNiMo7-6

采用CBN砂轮对渗碳钢18CrNiMo7-6进行不同工艺参数下的外圆磨削,并借助三维形貌测量系统、残余应力测试仪以及显微硬度计分别对表面粗糙度、三维表面形貌、残余应力和显微硬度进行测量,探究不同外圆磨削工艺参数对表面完整性的影响规律。研究结果表明:在以砂轮线速度v_s为单因素变量研究时,v_s=16. 89 m/s(4 300 r/min)下表面粗糙度最优;在以工件速度v_w为单因素变量研究时,v_w=11. 12 m/min (150 r/min)下表面粗糙度值最大,v_w=22. 24 m/min (300 r/min)下表面粗糙度值最小;在以磨削深度a_p为单因素变量研究时,ap=0. 02 mm下表面粗糙度最小。不同磨削工艺参数下工件表面残余应力均呈现为残余压应力,且不同砂轮线速度和工件速度下,深度方向上周向残余应力σ_x和轴向残余应力σ_y也都呈现为残余压应力,残余压应力最大值都出现在表面,之后随深度逐渐减小并趋于稳定。同时结合原始试样的残余应力梯度分布可知,外圆磨削使得工件表层的残余压应力值变大,形成了30μm左右的残余应力变质层。不同砂轮线速度以及不同工件速度下的显微硬度梯度分布均呈现的是先下降后稳定的趋势,且结合原始试样的硬度梯度分布可知,磨削工艺使工件表层形成了约30~60μm的硬化层,显微硬度相对于原始试样有明显的提升。并采用单颗磨粒进行磨削仿真,获得了较为可靠的残余应力梯度分布,与试验结果相比整体趋势一致,具有一定的实际意义。

The cylindrical grinding experiment of the carburized steel 18CrNiMo7-6 under different process parameters was carried out by CBN grinding wheel,and the surface roughness,three dimensional surface topography,microhardness and residual stress were respectively determined by three-dimensional shape measurement system,residual stress tester and micro hardness testerto investigate the influence of different external grinding process parameters on surface integrity.The results show that the surface roughness is optimal at vs=16.89 m/s(4300 r/min)when the grinding wheel speed vs single-factor variation is used.When the workpiece speed vw is a single-factor variable,the surface roughness value is the largest at vw=11.12 m/min(150 r/min),and the surface roughness value is the smallest at vw=22.24 m/min(300 r/min).When the grinding depth ap is a single factor variable,the surface roughness value is smallest at ap=0.02 mm.The residual stress on the surface of the workpiece under different grinding process parameters is the residual compressive stress.Under the different grinding process parameters,the circumferential residual stressσx and the axial residual stressσy also appear as residual compressive stress.The maximum compressive stress appears on the surface and then gradually decreases with depth and tends to be stable.At the same time,combined with the residual stress gradient distribution of the original sample,it can be seen that the external cylindrical grinding makes the residual compressive stress value of the surface layer of the workpiece larger,and a residual stress metamorphic layer of about 30μm is formed.The microhardness gradient distribution under different grinding wheel speeds and workpiece speeds shows a trend of decreasing first and then stabilizing.Combined with the hardness gradient distribution of the original sample,the grinding process forms a hardened layer of about 30-60μm on the surface of the workpiece,and the microhardness is significantly improved relative to the original sample.Grinding simulation is carried out with a single abrasive grain,and a relatively reliable residual stress gradient distribution is obtained.The overall trend is consistent with the experimental results andthe simulation has certain practical significance.