Research On Extrusion Cutting Mechanics Modeling And Surface Residual Stress Control

In the field of engineering applications,some extreme working conditions put forward high requirements on the surface contact performance of components.Surface residual stress is an important indicator of the surface quality of parts.Appropriate residual compressive stress can significantly improve the surface contact performance of parts such as wear resistance and fatigue resistance.Aiming at the surface quality requirements of high-contact parts,this thesis studies the blunt edge effect of extrusion cutting.Cutting force composition,cutting temperature and residual stress control methods by means of theoretical analysis,experimental research and numerical simulation.The main research contents are as follows:(1)The material flow forming mechanism in the first deformation region of the blunt edge of extrusion cutting is studied.The frozen chip root is obtained through the right-angle free cutting experiment and the emergency stop device,and the sample of the chip root is processed and observed,and the metallographic structure map of the blunt edge area is obtained.The flow forming law of the material in the blunt edge area is obtained through the grain shape of the metal in the metallographic diagram,the unique metal dead zone phenomenon of the blunt edge cutting is explained,and the cutting force form is analyzed.A finite element model of the extrusion cutting process is established,the material flow separation process inside and outside the metal dead zone and the material flow velocity law are studied,and the position of the material separation point is obtained.(2)An analytical model of extrusion cutting mechanics based on the instantaneous effective rake angle is established.The Merchant’s shear force calculation formula is expanded.The functional expressions of shear force,extrusion force and rebound force in extrusion cutting are derived based on the relationship between the instantaneous effective rake angle and the depth of cut,the radius of the blunt circle of the tool and other parameters by considering the relative relationship between the radius of the blunt edge and the depth of cut,according to the flow force process of the material.By numerical simulation,the variation law of shear force,extrusion force and rebound force with the radius of the blunt edge is analyzed.And the simulation results are compared and analyzed through cutting experiments.The results show that the average error of the mechanical analytical model compared with the test results is 6.01%for the tangential force and 5.13% for the radial force.(3)The average cutting temperature in extrusion cutting is obtained by numerical calculation,and the law of cutting fluid parameters to control surface residual stress is analyzed.According to the thermal-mechanical coupling effect of cutting,the generation mechanism of the residual stress on the surface of the extruded workpiece is analyzed,and the method of controlling the surface residual stress by cutting fluid is proposed.The thermal-fluid-solid coupled cutting finite element model is established,and the influence of the flow rate,cooling and lubricating effects of the cutting fluid on the residual stress on the workpiece surface is studied.The results show that the cutting fluid with higher friction coefficient and fast heat dissipation can effectively obtain the beneficial residual compressive stress on the workpiece surface.To sum up,the cutting fluid cooperates with the extrusion cutting process to obtain appropriate residual compressive stress on the surface.The application of the above research results to the machining of parts with high contact surface service requirements can significantly improve the surface quality of the parts and prolong the service life of the parts.