Springback as a Function of Strength and Thickness Variability in High Strength Sheet Steels

Springback in sheet metal forming is becoming a very troublesome issue with the increased use of high strength steels in automobiles. The current trend for many applications is to reduce vehicle weight by downgaging, that is, substituting higher strength, thinner steels for lower strength, thicker steels. The primary springback concern in sheet metal forming is variation in springback, rather than the magnitude of the springback. Even large springback can be accommodated if it can be consistently predicted. Variations in springback are caused by variations in mechanical properties and gage, and by fluctuations in the conditions of the forming process. This paper addresses the expected springback issues associated with the application of high strength sheet steels in light of strength and thickness uniformity. A simple expression is used to show how variations in yield strength and gage may be expected to influence springback in sheet metal forming. Also, the implications of down-gaging are discussed in the context of mechanical property and thickness variability data tabulated for actual production materials.