Research On The Residual Stress Simulation And Process Of Polycrystalline Magnesium Fluoride Ultra-precision Ground Surface

Polycrystalline magnesium fluoride(MgF2)is a kind of typical infrared optical material which has high mechanical strength,strong heat resistance,strong chemical resistance and isotropy with small permittivity and low dielectric loss.However,due to its hardness and brittleness,MgF2 is difficult to be machined with high precision.The surface quality and performance is restricted by the residual stress.Therefore,this paper mainly studies residual stress of ground MgF2 surface and corresponding grinding process.The aims of this paper are to study the residual stress and improve the quality of ground surface.In order to realize the aim,simulations and experiments are carried out.And then analyze the results to find out what are the key factors for ground surface quality.On this basis,the grinding parameters can be optimized.Finally,machining of polycrystalline MgF2 surface by ultra-precision grinding can be realized.Based on micro-indentation experiment and nano-indentation experiment,polycrystalline MgF2's force performance can be known,and its constitutive model can be built at the same time.The micro-indentation experiment provides polycrystalline MgF2's hardness and indentation.Analyze the material removal mechanism through the indentation morphology.Study how indentation cracks propagate and how crystalline grains break.Establish the relationship between load and displacement through nano-indentation experiment.Then calculate the function stress-strain.Then established polycrystalline MgF2's constitutive model which would provide the basis of grinding simulation.Analyze how grinding parameters influence the ground surface quality by finite element analyzing software AdvantEdge.Explore the relationship among rotate speed of grinding wheel,grinding depth,grain size,grinding force and grinding power.The residual stresses are changed with different grinding parameters.Find out the trend of the changes and select a group of parameters which can obtain the smallest residual stress.According to the practical grinding process,it is necessary to explore how multiple grinding and flaws such as concaves influence the residual stress and grinding force.Based on these,grinding parameters can be chosen easier.Explore which grinding parameters are related to the locus of grinding point.And chose the most suitable rotate speed of workpiece accordingly.Set up the ultra-precision grinding experimental platform.Then dress the grinding wheel to reduce its circular run-out error.Complete two groups of ultra-precision grinding experiments of which feed speed and grinding depth are different.Record the variation of grinding force with time.It is found that the simulations and experiments have common trend.Then measure residual stress,roughness and infrared transmittance of the ground surfaces produced with different grinding parameters.The results show with grinding depth or feed speed is bigger,the roughness is oppositely smaller.With grinding parameters changed,however,the infrared transmittance is not obviously influenced.Eventually,considering all the factors,a group of grinding parameters that fit to grinding polycrystalline MgF2 can be chosen.