TC4钛合金纵扭超声磨削表面残余应力及其试验研究

Study on the Surface Residual Stress and Experimental of TC4 Titanium Alloy by Longitudinal-torsional Ultrasonic Grinding

目的探究纵扭超声磨削工艺参数对TC4钛合金加工表面残余应力状态的影响规律,提高TC4钛合金的抗疲劳性能。方法通过纵扭超声磨削力模型,对磨削过程中的机械应力和热应力展开理论分析,并进一步建立纵扭超声磨削表面残余应力模型,通过MATLAB仿真获取磨削加工残余应力分布状况。基于力-热耦合作用,建立纵扭超声单颗磨粒磨削有限元模型,分析磨削参数对残余应力的影响规律,并通过TC4钛合金纵扭超声磨削试验,对模型的合理性进行验证。结果 TC4钛合金超声磨削加工表面残余应力为残余压应力,且该应力沿工件深度方向的分布曲线与"对号"相似。工件表面残余压应力起初随磨削深度增加逐渐增大,当磨削深度增加到8μm时,残余压应力达到最大值,为–488 MPa,之后随磨削深度的增加,呈现减小趋势。随磨削线速度的增大,残余压应力整体呈现减小趋势,随纵扭超声振幅的增大,整体呈现增大趋势。加工表面残余应力仿真与试验结果的平均误差为9.8%,且变化趋势具有一致性。结论纵扭超声辅助磨削加工可有效消除加工表面的残余拉应力,并获得较为理想的残余压应力,进而显著提高TC4钛合金的抗疲劳性能。

The work aims to explore the influence of longitudinal-torsional ultrasonic grinding process parameters on the residual stress state of TC4 titanium alloy machining surface to improve the fatigue resistance of TC4 titanium alloy.The mechanical stress and thermal stress generated during the grinding process were analyzed based on the grinding force model of longitudinal-torsional ultrasonic grinding,the residual stress model of the longitudinal-torsional ultrasonic grinding surface was further established,and the residual stress distribution of the grinding process was obtained by MATLAB simulation.The finite element for a single abrasive particle under longitudinal-torsional ultrasonic grinding was established based on thermomechanical coupling,and the influence of grinding parameters on residual stress was analyzed,the rationality of the finite element model was verified by the longitudinal-torsional ultrasonic grinding experiment of TC4 titanium alloy.The residual stress of the TC4 titanium alloy ultrasonic grinding surface was the residual compressive stress,and the distribution curve of the stress along the depth of the workpiece was similar to the "tick".The residual compressive stress on the machined surface of the workpiece increased gradually with the increase of the grinding depth at first,when the grinding depth increased to 8 μm,the maximum value of the residual compressive stress was –488 MPa,and then decreased with the increase of the grinding depth.The residual compressive stress decreased with the increase of the grinding linear speed,and increased with the increase of the longitudinal-torsion ultrasonic amplitude.The average error between the simulation and experiment results of the residual stress on the machined surface was 9.8%,and changing trends of the residual stress were consistent.Longitudinal-torsion ultrasonic assisted grinding can effectively eliminate the residual tensile stress on the machined surface and obtain a more ideal residual compressive stress,which significantly improves the fatigue resistance of the TC4 titanium alloy.