Discrete Element Simulation Of Crack Propagation In Ultra Precision Cutting Of Single Crystal Silicon

As the results of the tool wear,the internal defects of the material,external processing conditions and other factors,brittle removal model often occurs in the process of ultraprecision cutting of single crystal silicon with diamond tools,and leads to the appearance of a large number of micro-cracks near the cutting edge.Once these cracks extend to the machined surface and subsurface,the surface quality of the workpiece will be seriously affected.It is of great significance to find out the mechanism of crack propagation and to control it effectively for improving the quality of the workpiece.However,the process,mechanism and influencing factors of crack propagation are still not clear up to now.In the paper,the propagation process of the surface and subsurface cracks of single crystal silicon and the influence of crystal defects and processing parameters on the crack propagation are studied using discrete element simulation method.The main content of the paper is as follows:Firstly,in order to describe and analyse the process of crack propagation on the surface and subsurface of single crystal silicon exactly and ensure the accuracy of the model,a discrete element simulation model for ultra-precision machining of single crystal silicon with cutting edge radius and the friction coefficient between cutting tool and workpiece is established.For the purpose of facilitating the observation of crack propagation degree,the above model is treated in layers,and then ultra-precision cutting process of single crystal silicon is simulated with suitable cutting parameters.The stress calculation method for PFC2 D software is presented,and the accuracy of the method is verified by the mechanism of residual stress in the cutting process.On the basis of the above work,the process and concomitant phenomenon of the surface and subsurface cracks propagation in the cutting process is analyzed from the point of energy and stress.Secondly,in order to analyze the influence of the micro-crack and the micro-void on the crack propagation,the discrete element simulation models of ultra-precision cutting with above two kinds of crystal defects are established separately.The effects of the two kinds of defects on the crack propagation are measured by using the parameters including the number of cracks and the average depth of the crack layer respectively.Furthermore,the effects of the above factors on the crack propagation process are described and analysed from the perspective of energy and stress in this paper.Finally,taking the parameters such as the number of cracks,the average depth of the crack layer and the cutting distance before the cracks propagate as the quantitative criteria,the effects of process parameters and tool parameters including cutting speed,cutting depth,cutting edge radius and tool rake angle on the crack propagation are measured and analyzed.And the most suitable cutting parameters are given from the perspective of controlling crack propagation.