Study On The Ultrasonic Assisted Grinding Process Of RBSiC

With the development of technology, space optical system requires larger diameter optical mirror. The mirror needs to be made of the lightweight material to reduce the transmission cost. Reaction Bonded Silicon Carbide (RBSiC) is the best choice for manufacturing large aperture mirror, for it has high stiffness, low thermal expansion coefficient, good thermal conducting performance, high hardness and other excellent property. Grinding is the main method to machine RBSiC because of its hardness and brittleness. Ultrasonic assisted grinding has good prospect in the field of machining hard and brittle materials, which combines traditional grinding process with ultrasonic machining process. In this paper grinding experiment was conducted on the ultrasonic assisted grinding test platform using RBSiC material. Surface morphology, subsurface damage and the grinding forces were compared between conventional grinding and ultrasonic assisted grinding. The material removal mechanism of ultrasonic assisted grinding process was analyzed. The main conclusions of this paper are illustrated as follows:(1) Surface morphology and the roughness were measured after experiment using 60# and 325# grinding wheels. The results show that the material has a lower surface quality in the ultrasonic assisted grinding process. The material is removed mainly by fracture process, scratch marks are also observed both in the ultrasonic assisted grinding and conventional grinding. There are less scratch marks on the surface, and the fracture area is more uniform in ultrasonic assisted grinding.(2) The characteristic of subsurface damage was investigated. The results showed that there was no obvious difference in damage type between ultrasonic assisted grinding and conventional grinding. The damage can classified as two types which are large fracture pits near to the surface and large crack going deep into materials. The statistical distribution of damage showed that most of the damage appeared on SiC particals. Vibration of grits induced more deeper and wider fracture pits in ultrasonic assisted grinding. But the depth of larger crack didn’t become larger.(3) Grinding force was also measured. Grinding force of ultrasonic assisted grinding and conventional grinding were measured respectively. The effect of grinding depth, feed speed and spindle speed on grinding process was investigated. The test results show that grinding force decline in ultrasonic assisted grinding greatly, and the decreasing amplitude could be 65%. Grinding force grows greatly with the increase of grinding depth. Feed speed and spindle speed has less effect on grinding force.