1. Field of the Invention
The present invention relates to metal stamping dies, and, more particularly, to a method for improving the release and finish characteristics of metal stamping dies through shot peening.
2. Description of the Prior Art
The use of metal stamping to produce a wide variety of metal parts is widespread. While there are variations of the metal stamping process, such as forming, piercing, deep drawing and the like and combinations thereof, and different types of dies, such as single and multiple cavity dies and progressive dies, most of the principles and techniques are the same. The problems are also often the same. One of the major problems which is common to virtually all metal stamping operations involving drawing or deformation of the workpiece,whereby the workpiece contacts the interior die cavity walls during the stamping operation, is a poor release characteristic between the workpiece and the die cavity walls. Poor release characteristics, which causes problems both during the stamping downstroke and the upstroke and workpiece removal stage, invariably leads to problems such as machine jams or smashups, misformed and non-uniform parts and poor finish characteristics on the workpiece surface proximal to the die cavity walls, such as scratches, galling, scoring, random shiny spots and the like. Although a poor release characteristic is most often the cause of a poor finish, poor finish can also be caused by other factors, such as heat buildup, improper lubrication, surface flaws and the like.
Because of the high cost of rejected parts and the down time due to die maintenance and reconditioning, as well as the potential very high cost occasioned by a machine or die jam or smashup, constant efforts are being made to improve the release and finish characteristics of metal stamping dies. These efforts range from varying the composition of the die material to coating the interior die cavity walls with release agents, plating and the like. Even the die designer continually attempt to improve the release and finish characteristics of dies by experimenting with variations of draft angles and the like.
While there has been steady improvement over the years, there is a continuing need for further improvements, especially improvements that are economical, reliable and durable.