PRODUCTION OF SUBSTRATE FOR MEMORY DISK

PURPOSE:To form desired chamfered parts in a blank at the same time of pressing without degrading flatness of the blank by preliminarily forming chamfers 1 - 1.7 time as wide as the chamfers of the product and then pressing the blank at the thickness reduction rate of 1 - 4%. CONSTITUTION:The chamfers 2 of a memory disk substrate is formed on the outer and inner circumferences of the substrate during blanking a blank 1. The chamfer width W0 has generally + or -50% tolerance, that is, the chamfer width of 0.5 - 1.5W0 is allowed for the product. Usually, the chamfer width is narrowed in the process of pressing because of material flow accompanied with reduction of thickness, and the degree of decrease in chamfer width largely depends on the reduction rate of thickness. By considering these, the reduction rate of thickness of the plate is specified to 1 - 4%. The chamfer preliminarily formed on the blank is specified to 1 - 1.7 time as wide as the desired chamfer for the product in order to form the chamfer with + or -50% tolerance with considering the flow of the material during pressing. By this constitution, memory disk substrates having excellent productivity can be obtained by pressing.