Study On Ultra-precision Machining Of Copper Sheet With High Radius-thickness Ratio

In the study of extreme manufacturing of weak rigidity members,copper has become a typical research object because of its weak stiffness and excellent electrical conductivity,thermal conductivity and ductility.To meet the need of precise physical experiments,radius-thickness ratio（radius-thickness ratio≥25）with high surface precision,high surface quality,no scratch is often required.At present,diamond precise flying cutting and diamond precision turning technology are mainly used in the processing of pure copper sheet.However,the internal residual stress release in the later processing stage makes the surface shape of copper sheet always fail to meet the requirement of high precision surface shape control.To solve the problem of poor surface precision of copper sheet,the machining method of soft grinding pad based on CMP is put forward in this paper.The paper first analyzes the law of material homogeneity removal from the angle of kinematics.By establishing the motion equation of abrasive particle relative to copper sheet,the effects of different rotational speed ratio,abrasive particle position and the initial phase of abrasive particle on the motion trajectory of abrasive particle are analyzed.The simulation results show that the rotational speed ratio has a significant effect on the motion trajectory,which mainly affects the shape and the density degree of the motion trajectory.The relative position of the abrasive particle locus on the workpiece is mainly affected by the abrasive particle position.The initial phase had no effect on the shape of the motion trajectory,but it affects the angle of the trajectory turning.According to the uniform function of fixed eccentric grinding,when the rotational speed ratio is 1,the machined surface can be removed completely and uniformly.From the angle of cutting depth distribution of soft grinding pad abrasive particle group,the uniform removal rule of copper sheet surface material is analyzed.The influence of abrasive particle size on the cutting depth distribution of abrasive group is analyzed by establishing the cutting depth distribution model of abrasive particle group.The experimental and simulation results show that the standard deviation of cutting depth distribution decreased with the increase of abrasive particle size.The finer the abrasive particle size is,the better the consistency of the cutting depth distribution of the free abrasive pad is.The more uniform the copper surface material can be removed,the more accurate the surface shape can be.Based on the machining method of CMP aided soft grinding pad,the abrasive with different particle size was used for grinding experiment.Taking copper sheet of?100×2mm as the processing object,the optimum processing parameters under Al₂O₃ abrasive with particle size W14 were determined by orthogonal test,that is,the concentration of Al₂O₃ abrasive was chosen as 0.8%,the grinding pressure was chosen as 1.0psi and the rotational speed of grinding disc was chosen as 35rpm.The single factor analysis of Al₂O₃ abrasives with different particle sizes was carried out by using the determined process parameters,and the changing trend of each index of pure copper sheet with time was determined.Based on the processing method of CMP aided soft grinding pad,The polishing experiment of copper sheet was carried out.The surface quality and surface shape accuracy of polished copper sheet were improved by chemical mechanical polishing method.After polishing,the surface roughness of the copper sheet reaches 8.1nm and the planeness decreases to 3.841μm.In this paper,the uniform removal law of copper sheet surface material is analyzed from the angle of kinematics and the distribution of abrasive particle group cutting depth of free abrasive pad according to the processing method of CMP aided soft grinding pad.Then a group of processing parameters is determined by orthogonal test.Finally,the surface quality and surface precision of copper sheet are further improved by means of chemical mechanical polishing.