Study On Surface/subsurface Damage Mechanism In The Ultrasonic Vibration Assisted Grinding Of Nanocomposite Ceramics

Because of the special characters of ceramics, such as,high strength, high wear resistance, heat resistance, and so on, it has attracted a lot of attention and would be widely used in the field of aerospace aviation and chemical industry. Grinding technique, as the most efficient method, was usually used in the machining of ceramics parts. But conventional grinding method usually leads to surface micro defects on finished surface, such as micro surface cracks, residual stress, etc. The existence of these damages will lower the reliability of ceramics parts. So it is necessary to develop precise machining technology to raise working efficiency and lower surface and subsurface damage. Ultrasonic Assisted Grinding (UAG), as a new technique in ceramic machining, can greatly improve the surface quality, but how UAG to reduce the surface/sub-surface damage isn't very clear. To this purpose, the surface/sub-surface damage mechanism of the UAG in grinding ceramics was mainly analyzed in this article. The main researches in this paper were listed as follow:1) Material removal mechanism was analyzed. And the surface and subsurface damage were also studied experimentally. The results show that UAG can realize ductile grinding in a large cutting depth. This will lower the surface damage and improve the machining efficiency. But micro-cracks can be observed in the conventional grinding method just in a low cutting depth.2) Based on indentation fracture mechanics, the stress field of UAG was established. From this stress filed we detailed discussed the crack generation mechanism when grinding with UAG.. The analyzing indicate that the stress field of UAG is a changing stress field, and this changing stress will accelerate the material fatigue damage, and it also can change the crack propagation direction to free surface, rather than propagate to the deep material which will happen in conventional grinding. And this will reduce the surface crack defects.3) The surface residual stress generating mechanism was analyzed, and the experiment on surface residual under the two grinding condition were carried out. Experimental results show that the surface residual stress with UAG is bigger than that of conventional method when grinding under the same parameters. The UAG has a large range of ductile cutting depth. So at the same grinding condition, material with UAG is easier being removed in ductile field than conventional method. And the ductile deformation will lead to compressive stress on the finished surface. The micro cracks occurred on the finished surface with conventional method will release some of compressive residual stress, and this will lower the compressive residual stress in conventional grinding surface.