AN ENTRY BOARD FOR DRILLING SMALL HOLES, A METHOD OF MAKING THE SAME AND A METHOD FOR DRILLING SMALL HOLES

摘要

An entry board for drilling small holes having a front surface layer made of aluminum or aluminum alloy to be disposed at the drilling inlet side and a back surface layer made of aluminum or aluminum alloy to be disposed at the drilling outlet side. The back surface layer is adhered or joined by clad rolling to said front surface layer. The hardness of the front surface layer is smaller than that of the back surface layer.