2012 Volume 53 Issue 616 Pages 429-433
Backward extrusion is the most common method of forming bosses within product cases. However, backward extrusion requires a very large forming load, and has the disadvantage of producing dimple defects when forming thin sheets. To overcome this disadvantage, we developed a method of bottom compression drawing to replace backward extrusion. Bottom compression drawing is a technique in which, during normal drawing, back pressure from the counter punch that opposes the drawing punch applies a load on the blank, so that compressive force acts on the bottom face of the blank. Bosses are formed at the same time as the case is formed as a result of this drawing. Backward extrusion and bottom compression drawing were compared using both FEM analysis and experiment in the formation of solid bosses. The results showed that bottom compression drawing could form a piece with about 50% of the forming load used in backward extrusion because the radial compression stress in the bottom material is reduced by the tension in the bottom compression drawing.