Study On Subsurface Damage And Material Removal In Single-grit Grinding Of Brittle Materials By Theoretical Analysis

In engineering practice,brittle materials such as engineering ceramics and optical glass are widely used in optics,medical and military products because of their unique physical and mechanical properties.However,brittle materials due to their high hardness,difficult to process,brittle fracture and other shortcomings,resulting in the processing of surface and subsurface damage easily,while processing efficiency is low.In order to achieve high efficiency and low subsurface damage grinding,the contact rule of single abrasive and workpiece in grinding brittle materials is studied systematically in this paper.The relationship between the maximum penetration depth of single abrasive grains and the size of the abrasive grains is analyzed based on the model of the single abrasive grain deformation chip.Based on the theoretical analysis of indentation fracture mechanics,the relationship between surface damage depth and grinding parameters and abrasive size is analyzed.Based on the grinding model of single abrasive particle vibration,the relationship between surface damage depth and grinding parameters and vibration parameters is analyzed.Based on the material removal model,the relationship between the brittle material removal and abrasive size was analyzed.The specific innovation points of this thesis are as follows:(1)Based on the theory of single abrasive particle grinding,the mode of the material removal in the grinding of brittle materials is analyzed,and a prediction model for the grinding force of single abrasive particle is established.The theoretical expression of the grinding force of single abrasive particle and grinding parameters in grinding process of brittle materials is proposed and the influences of grinding parameters on the grinding force of single abrasive particle are revealed.In addition,according to the contact relationship between abrasive particle and workpiece in ultrasonic vibration assisted grinding,the grinding modes of abrasive particle are analyzed.A prediction model for the grinding force of single abrasive grain in ultrasonic vibration assisted grinding is obtained and the effects of different vibration parameters on the grinding force of single abrasive grains are also discussed.The theoretical results indicate that increasing the grinding depth and the workpiece speed will increase the material removal volume per unit time,so that the grinding force of each abrasive particle increased in the grinding process of brittle materials.Increasing the grinding speed will increase the total amount of abrasive particle involved in the grinding process per unit time and reduce the penetration depth of the abrasive particle during grinding process,so that the grinding force of each abrasive particle decreased,which is also conducive to improve theefficiency of the grinding process of brittle materials.At the same time,increasing the amplitude and frequency of ultrasonic vibration,which is equivalent to increasing the trajectory length of the abrasive particle and reduces the penetration depth of the abrasive particle during the grinding process,resulting in the grinding force of the single abrasive particle decreased.(2)Based on the theoretical analysis model of indentation fracture mechanics,the influence of grinding parameters and abrasive size on sub surface damage was analyzed.The original theoretical model is modified,and the depth prediction model of the Tip fillet triangular section and the trapezoidal cross section abrasive crack system is proposed.The effect of the depth ratio on the medium diameter crack is also considered.Increasing the ratio of grinding speed to workpiece feed speed can reduce the surface damage of workpiece material by reducing the depth of middle diameter crack,which is advantageous to obtain low damage and high machined surface quality.In addition,the depth of the medium-diameter crack decreases with the increase of depth ratio.In order to obtain low damage and high processing quality of the machined surface in the actual processing to choose a higher grinding speed and workpiece speed ratio,the smaller grinding depth is more reasonable.(3)Based on the grinding model of single abrasive particle vibration,the depth prediction model of single abrasive grinding parameters and vibration parameters is presented.The influence of the initial grinding depth on the subsurface damage depth,it is found that ignoring the vibration in the prediction model can lead to the underestimated depth of subsurface damage.For the grinding process with a frequency ratio greater than 1,the subsurface damage depth first increases and then decreases with the increase of damping ratio.(4)Based on the material removal model,the theoretical analysis of material removal under ductile removal and brittle fracture removal was analyzed,and the prediction model of ductile removal volume and removal rate of brittle materials was proposed,as well as the material removal volume and removal rate of mixed toughness removal and brittle fracture removal method.In the process of brittle material removal,the size of abrasive grains is introduced into the calculation of material removal volume and material removal rate,taking into account the phase of material toughness removal in the early stage of grinding.The mixing toughness removal and the brittle fracture material removal volume of single abrasive grinding are decreased with the increase of fillet radius of abrasive tip at the same time,the material removal volume decreases with the increase of the grinding grains when the fillet radius is certain.