Tribology of drawing

Res tribological problems encountered in sheet metal forming are particularly difficult for at least two reasons:

• physical reasons. These problems concern the surface interactions of the sheet metal and tool surface materials, between which certain lubricant constituents and debris torn from the sheet metal and tool are interposed. These interactions result in friction, changes in the surface condition of the sheet metal, and damage and wear to the tool. The underlying phenomena, which occur on a scale of between ten nanometers and one micrometer, are complex and far from fully understood and mastered. However, even a purely qualitative understanding of these issues enables research and development work to be steered in the right direction, with a view to developing a cost-effective solution;

• industrial reasons. The success of the stamping operation depends on the know-how of at least three companies: the one that manufactures the sheet metal, the one that produces the lubricant and the one that carries out the stamping (or even the one that makes the tooling). Good cooperation and a good flow of information between these three obliged partners are therefore essential, but this is not always the case. Each is very concerned not to lose the advantage it believes it has over its competitors: for example, lubricant composition is generally confidential. Each party tries to leave the search for a solution to its partners. This can lead to long-lasting disputes, as in the 1980s between steelmakers and French carmakers over the shaping of body components in extra-soft sheet steel. This controversy, which came to an end thanks to a modification by the steelmaker of the sheet finishing operation by skin-pass rolling, clearly demonstrated the interweaving of responsibilities and possible courses of action.

The aim of this article is firstly to describe the friction problems encountered during sheet metal stamping operations and their consequences on the quality of the parts formed. After presenting the properties of the materials involved and recalling the deformation modes of sheet metal during stamping, which define their conditions of contact with the tools, we present the experimental methods used to simulate them and study their consequences on friction and the final surface finish of the part. We focus here on the scientific and analytical aspects of this issue, taking the case of steel sheets as our main example. The article [BM7536]...