Forming dies, while very simple in design and to make, often present difficulties, inasmuch as the metal being formed does not always form up to just the shape of the die or the desired shape. The forming punch and die can be made exactly the shape desired in the blank but the metal may crawl - the shop phrase for metal going where it is not intended to go - or the temper of the metal may play an important part, and even after the forming punch and die are made to produce the desired blanks the next shipment of metal may be of a different temper and the die must be altered.
There are no hard and fast rules to lay down for forming dies, except to allow for the double thickness of stock between the punch and the die. The making of forming dies is a cut-and-try method. One point must be borne in mind - if dies to produce a formed piece are to be made, the forming punch and die should be made first in order to determine the exact shape of the blank from which the blanking die is made.