Generation of Parabolic and Toroidal Surfaces on Silicon and Silicon-Based Compounds Using Diamond Cup Grinding Wheels

Abstract

This paper presents the methods and experimental results using diamond cup wheels and CNC machining centers for grinding parabolic and toroidal surfaces made of Si and SiC, the former for use as a thermal imaging lens and the latter for synchrotron radiation facilities. Generation of aspheric surfaces, by zonal material removal, on Si using cup grinding wheels and a 5-axis machining center was investigated. Theoretical and experimental investigation of the grinding and material parameters that influence ductile grinding are discussed. Ductile grinding is possible with wheels having small grit size and with proper combination of feed and unit normal load; a resinoid bonded wheel promotes this more easily than a metal bonded wheel, though at the expense of profile accuracy. Profile analysis, surface integrity, and examination of grinding swarf using digital imaging are discussed. Also, generation of toroidal surfaces on SiC using metal-bonded cup wheels, a 3-axis machining center and a micro-displacement table with piezoelectric actuators was studied. Toroidal SiC mirrors were ground with good shape accuracy, mirror finish, and low surface roughness. The time consumed in the process is very short. The machines used are inexpensive and not specially designed for ultra-precision grinding.