Sheet metal stamping - Importance of deformation modes

Sheet metal stamping is an operation that produces complex, non-developable parts, unlike the simpler operations of bending, rolling or cold forming. This widely-used process is used to manufacture car body parts, household appliances, kitchen utensils, metal packaging, mechanical parts, etc.

In addition to the shape of the tool, which depends on the complexity of the part to be obtained, many other parameters determine the success of the operation: those linked to the process, such as press settings, stamping speed and lubrication, and those linked to the qualities of the sheet itself and its capacity for forming, also known as formability, which is the subject of this article. Great progress has been made in measuring the mechanical characteristics of sheet metal and interpreting their relationship to formability. The same applies to the understanding of the stamping operation, among other things through numerical simulation, which now enables us to virtually visualize the behavior of the metal in the tool. Deformation measurement systems are also a tool that enables quasi-quantitative analysis of real parts.

Nevertheless, tool design and stamping are still partly an art based on experience. We can predict, however, that within the next five to ten years or so, automatic tool design and manufacturing methods will have taken over from those currently in use.

What follows focuses on the material. We will try to show which characteristics of metal sheets are influential with regard to shaping, particularly in relation to local modes of deformation, which play a major role here.

This text deals mainly with thin plates, i.e. in practice, plates with a thickness of between 0.2 and 3 or 4 mm. For thick sheet metal forming, please refer to the article "Heavy sheet metal forming".

The materials considered are essentially steel and aluminum alloys. Mention will be made of copper alloys, whose use is declining for reasons of price. Sandwich sheets" and "welded blanks" are relatively new materials that would require an article of their own. They are therefore not considered.