Laser Irradiation Effect And Material Removal Mechanism In Hybrid Grinding Of Zirconia Ceramics

Advanced ceramics are typical brittle materials,with wear resistance,high hardness and stiffness to weight ratio.They can withstand harsh working environment where metal materials and organic polymer materials cannot sustain,and therefore they become significant material in lots of key fields,and have been widely used in processing machine,automotive industry,aerospace industry and other fields.However,the above excellent performances force the processing of advanced ceramics to face enormous challenges.Good wear resistance,difficulty in ensuring surface integrity,low processing efficiency and some other issues trouble the fabrication of structural ceramic parts.Confront these challenges,massive investigations have been conducted in grinding mechanism field to improve the efficiency of ceramic grinding.At present,two mechanisms of ductile mode and brittle mode have been widely recognized,and the mechanism of brittle-ductile transition has successfully led to the development of high-speed grinding.However,the application of another important conclusion to the grinding mechanism that the lateral crack control material removed and the median crack affects the sub-surface damage is still in its infancy.xIn this paper,a novel hybrid method of laser processing and grinding is proposed to process ceramics.Zirconia ceramic,a typical structural ceramic,is selected as the research object.The effects of laser irradiation on the mechanical properties,material removal mechanism,and surface damage formation of zirconia ceramics were analyzed by experiments and numerical simulation.The main research contents include:Firstly,investigations on the correlation between laser irradiation and surface damage of ceramic materials were conducted.In order to reveal the process of damage propagation caused by laser irradiation,a series of irradiation experiments were carried out.It was found that laser irradiation first induced the median cracks,and then the adjacent median cracks were deflected to form semi-coin-lateral cracks.Based on the above conclusion,combined with accurate laser heat source model,the numerical analysis method was used to analyze the process.The results show that defects on sepcimen surface resulting in the stress of the depth direction increased significantly,thus induced the deflection and connection of median cracks.Based on the above conclusions,a prediction model of semi-coin-lateral crack depth was established.Secondly,study on characteristic regularity of scratch process on ceramics with laser irradiation were performed.This part included two aspects: the effect of laser irradiation on the machinability of ceramic materials and the evolution of thermal cracks during scratch.The above two aspects are the basis of grinding efficiency improvement and grinding damage control.For the first aspect,the effect of laser irradiation on scratch load,force ratio(Ft/Fn),scratch hardness,morphology and material removal rate were studied by scratch experiments.The results can provide a microscopic interpretation of the grinding process.The results show that the laser irradiation significantly improves the machinability of zirconia ceramics: the reduction of scratch resistance and the increase of scratch force ratio,and the increase of material removal rate.For the second aspect,the propagation law of thermal cracks under mechanical force and the theoretical explanation based on stress field were obtained by scratch experiments and simulation.The results show that the thermal lateral cracks are with shielding effects on the expansion of median cracks caused by mechanical force.The stress fields show that the reason for forming the shielding effect is that the lateral crack cut off the stress field inducing the median crack.Thirdly,the effects of laser irradiation on the processability of zirconia ceramics with super-hard abrasive grinding wheel were investigated.The effects of irradiation on grinding force,energy consumption and grinding surface integrity were focused in this chapter.The results show that irradiation can significantly reduce the grinding force and grinding specific energy of zirconia ceramics.And the minimum values of the grinding force and energy were at the depth with the densest cracks.The grinding force decreases as the volume of the material removavl increases.The reason causing above phenomena is the number of cracks on the surface accumulating during grinding process.Besides,The results show that the irradiation has no effect on the roughness of final grinding surface with the removal of the irradiated layer.And the grinding cracks are usually confined by the preformed lateral cracks in the irradiated layer and cannot be extended inside the material.This is advantageous to limit subsurface damage depth of the zirconia ceramics grinding,while reducing the grinding resistance.At last,feasibility study of using silicon carbide grinding wheel to grind zirconia ceramics with laser irradiation were discussed.The grinding performance of zirconia ceramic with and without irradiation was compared in terms of grinding ratio,grinding force,grinding specific energy and grinding surface quality.The results show that the Gratio of zirconia ceramics grinding with silicon carbide grinding wheel is very small,but the irradiation is beneficial to improve G-ratio.And,the experimental results shown that after irradiated,the grinding force and specific energy can be decreased,while the grinding force ratio increases.Roughness and morphology of grinded surface shown that the grinding mechanism is mainly rubbing and the surface is smooth.The surface roughness was affected by grinding parameters and irradiation damage.Irradiation was helpful to reduce the thermal damage.In summary,this paper investigates the effect of laser irradiation on the material removal and subsurface damage propagation during zirconia ceramics grinding.The controllability of the damage caused by laser irradiation was confirmed by means of experiment and simulation.The effect of irradiation on the grinding was revealed by the micro-scale scratch.The effects of grinding parameters on grinding quality and grinding energy consumption were studied.The above research results show that the hybird process is with a significant improvement in the grinding performance of zirconia ceramics,effectively reducing the grinding resistance and energy consumption,and improving the processing efficiency.The method can provide one more efficient process for the industrial production of zirconia parts.