Study On Material Removal And Subsurface Damage In Grinding Process Of Brittle Materials Utilizing Theoretical Analysis And Numerical Simulation

Due to the unique physical and mechanical properties of brittle materials, such as engineering ceramic, optical glasses, they have been used in the domains of aerospace, micro-electrical mechanical and so on. However, because of the hard-brittle characteristic, the brittle materials have poor machining efficiency and bad machining feature. In present, grinding is considered as one of the most efficient techniques in machining brittle materials. In grinding process of brittle materials, the long processing cycle results in the high processing cost due to the poor machining efficiency. Meanwhile, the ground specimen often contains surface and subsurface cracks affecting the surface integrity, which reduces the using performance and life of related components.In order to obtain a good machined quality with high efficient and low damage, the thesis aims to study the action relationship between the abrasive grain and workpiece in grinding of brittle materials. The theoretical analysis model of single abrasive grain grinding is established and obtained the relationship of material removal volume/material removal rate, subsurface damage and grinding parameters(wheel speed, grinding depth, apex angle of abrasive grain and workpiece speed). Based on the finite element method, the finite element model of brittle material grinding is established and also obtained the relationship of material removal volume/material removal rate, subsurface damage and grinding parameters. There are some main results and innovations of this thesis as follows:(1) Considering the kinematic characteristics of the grinding process, the theoretical analysis model of single abrasive grain grinding is established and obtained the mathematical expressions of the relationship between material removal volume/material removal rate, subsurface damage and grinding parameters. The theoretical analysis indicates that material removal volume decreases with the increasing wheel speed, while the material removal rate increase with the increasing wheel speed. Moreover, when wheel speed is up to the ultra high speed, the change of material removal volume/material removal rate with wheel speed is gradual indicating that the ultra high wheel speed is not helpful in enhancing material removal rate. Both material removal volume and material removal rate increase with increasing grinding depth or apex angle of abrasive grain. The workpiece speed has a little influence on material removal and is weaker than wheel speed, grinding depth and apex angle of abrasive grain. In addition, the bigger abrasive grain size is able to add the material removal rate.(2) When wheel speed is a fixed value, as a little grinding depth, the depth of median crack below grinding surface plane is increment with increasing rotation of abrasive grain and up to the maximum at maximal rotation. However, with grinding depth increasing, the depth of median crack below grinding surface plane is first increase with grinding depth and then decrease showing that the change of subsurface damage with grinding depth is gradual. When grinding depth is a fixed value, subsurface damage decreases with increasing wheel speed, which indicates a higher wheel speed is beneficial to obtain the workpiece with good subsurface quality. However, an ultra high wheel speed with a very small grinding depth is not helpful in control subsurface damage.(3) The finite element model of brittle material grinding is established and analyzed the relationship of material removal volume/material removal rate, grinding force, subsurface damage and grinding parameters. In grinding of brittle materials, when penetrating depth of abrasive grain and workpiece is greater than critical depth of brittle fracture, the material removal is mainly in brittle fracture mode. Material removal volume decreases with increasing wheel speed. While material removal rate increases with wheel speed, which showing a higher wheel speed is beneficial to obtain higher material removal rate. However, when wheel speed is up to ultra high speed, wheel speed is not helpful in enhancing material removal rate. Both material removal volume and material removal rate increase with increasing grinding depth or apex angle of abrasive grain. Workpiece speed has a little influence on material removal and is weaker than wheel speed, grinding depth and apex angle of abrasive grain. In addition, the grinding force is one of the main factors influencing brittle material removal.(4) At the beginning of grinding, the crack is initiated at the front and underside of the abrasive grain. With the constantly moving of grain towards the scratch direction, the crack at the front of the grain is removed by the grinding action, while the crack under the grain can not be removed but forms the surface and subsurface defects. Wheel speed plays an important role in brittle material grinding and a higher wheel speed is beneficial to obtain a good subsurface quality. Considering the kinematic characteristics of the grinding process, grinding depth has a little influence on subsurface damage and is weaker than wheel speed. Subsurface damage is increment with increasing apex angle of abrasive grain, which showing a small abrasive grain is beneficial to obtain good subsurface quality. Grinding force is also one of main factors influencing subsurface damage.