The Influence of Edge Preparation Method on the Hole Expansion Performance of Automotive Sheet Steels

Edge stretching performance was assessed with the conical-punch hole expansion test for a variety of automotive sheet steels. Included were: an ultra-low carbon IF steel, a dual-phase advanced high strength steel (DP 980), an austenitic stainless steel (204), an annealed martensitic stainless steel (410 AN), and a ferritic stainless steel (429 MOD). Various hole fabrication methods were considered: conventional piercing (shearing), water-jet cutting and laser cutting. With pierced holes, no effect of shearing clearance on the hole expansion ratio (HER) was observed. The dual-phase steel and the austenitic stainless steel exhibited relatively low hole expansion performance in the pierced-hole condition (HER ≤ 50%). However, these materials demonstrated tremendous potential for improvement with alternative edge preparation methods, and both benefitted more from laser cutting than from water-jet cutting. The other materials showed relatively high hole expansion performance in the pierced-hole condition (HER ≥ 100%), and water-jet cutting and laser cutting provided only modest improvements.