Experimental Research On The Mechanism Of High-speed Grinding For Hard And Brittle Materials

For its excellent performance of high strength,high hardness and good wear resistance,engineering ceramics and other hard and brittle materials has been widely used in high-tech fields.However,there are still a series of problems for the traditional grinding of engineering ceramics,such that the wear volume of grinding wheel is high and its associated high cost,the machined work-piece surface quality is hard to forecast and control,the poor processing performance leads to low productivity as well.During the high-speed and ultra-high speed grinding,hard and brittle materials could be removed in ductile mode,so as to achieve the high-quality grinding with improved surface integrity and controlled cracks.In this paper,a brief review of the techniques in hard and brittle materials grinding and finite element simulation applied in grinding is firstly presented.Based on the relevant concepts,a simulation model of a single abrasive grinding is developed and the proposed model is verified through experimental study.This paper focuses on the need for studying further high-speed grinding mechanism,providing effective solution for existing problems,and applying high-speed and ultra high-speed grinding process to hard and brittle materials processing effectively,which is based on the combined methods of theoretical analysis,simulation analysis and experimental research.The main contributions of this dissertation are as follows?Firstly,based on the ABAQUS finite element analysis software,a dynamic simulation model of a single diamond grit grinding silicon carbide is developed,while the work-piece is described with the widely used JH-2 material constitutive model.Through controlling the variable input parameters,the basic questions posed above are then discussed and conclusions are drawn.(1)It defined the critical value of maximum undeformed thickness for ductile grinding as well as the micro-crack generation of silicon carbide respectively.Therefore,the appropriate process parameters of actual grinding process could be selected to control the micro-cracks generation,so as to achieve the target varies from high material removal rate to high surface integrity of engineering ceramics.(2)It respectively revealed the affection of the maximum undeformed thickness and the wheel speed on grinding force,specific grinding energy and grinding temperature of silicon carbide under certain grinding conditions.It has been found that the grinding force and its force ratio as well as the grinding temperature increased with the maximum undeformed thickness while the specific grinding energy decreased due to the size effect.On the other hand,the grinding force and its force ratio decreased with the increasing wheel speed while the specific grinding energy increased for the transition to plastic removal.The grinding temperature firstly increased and then decreased,which is similar to the Salomon curve.(3)Compared to the static indentation fracture model,the dynamic high-speed grinding are more complex,considering the combined impact generated by the normal load and tangential load on the crack,it determined the critical load range of the micro-cracks generation.Then,based on the MGKS1332/H high-speed precision CNC cylindrical grinding machine,a grinding force test platform is established.Through the analysis of machined surface integrity and grinding force characteristics during high-speed grinding,the processing performance,mechanism and process issues of grinding silicon carbide are further studied.(1)Considered on the effects from single factor to the multiple factors of the grinding process parameters,it ultimately determined the optimal ratio between the process parameters.Under the experimental conditions of this study,maintaining a constant speed ratio of the grinding wheel speed and work-piece feed rate would improve the quality of the surface roughness and grinding efficiency,as well as reduce energy consumption in the grinding process.The increased wheel speed had no effect on the grinding efficiency,however,contributed to achieve ductile grinding so as to reduce the pits on machined surface,but the surface compressive stress gradually decreased,resulting in the trend of the transition to the tensile stress,this trend will reduce the surface integrity,therefore,further range of wheel speed need to be define(The wheel speed of 80 m/s in this study did not produce the phenomenon).(2)Debris collected from different wheel speed were observed,it could be concluded that the debris under high-speed grinding are more crushing,and there are obvious plastic buffing mark on the wear debris,which is not found under the low-speed and non-ductile grinding conditions.(3)Through comparative analysis between engineering experiments and simulation results,it comes to that the variation and magnitude of grinding force and its force ratio are basically the same trend,which also verifies the proposed material constitutive model,simulation tools are reasonable and effective in this paper(within the wheel speed of 80 n/s).