The Interactions of Coated Steels, Die Materials, and Forming Lubricants

Sheet metal automotive components are developed in several stages, including “soft tool” (zinc alloy) prototype development and “hard” final tool tryout. Increased use of zinc and zinc-alloy coated steels for these stampings has raised concern about the reaction of metallic coatings on steels with the “soft” prototype die materials. Choice of forming lubricant adds further complications. To investigate this, a variety of hot-dip and electro-galvanized zinc and zinc-alloy coated mild steels were tested in several forming modes using both “hard” steel and “soft” prototype tools and several different lubricants. The zinc coating interaction with the prototype tooling depends on the nature of the coating on the steel, the deformation mode, and the lubricant. Therefore, proper selection of lubricant for soft tool tryout may be difficult. Hot-dip, alloy-coated steels pose special problems in this respect.