Design and application of low-cost polymer composite shell and backfill tooling for stamping of HSS 590 sheets

Sheet metal stamping uses hardened steel tools, due to their advantages in hardness, resistance to deformation, and resistance to abrasion. However, these tools have limitations when it comes to prototype production volumes, due to the high cost and time required for tool fabrication. Forming tools fabricated with polymers using additive manufacturing (AM) offer an inexpensive alternative suitable for low volume production and prototyping. For successful implementation of polymer AM tooling in sheet metal forming, tool cost, tool life, and part accuracy are important metrics. A composite tool design concept consisting of two distinct components-an outer polymer AM shell, and inner backfill-to make up the composite tool is proposed. Experimental and numerical investigation of stamping of high strength steel sheets with the new tool design is presented. It is shown that the new composite tool design concept improves performance and is more economical compared to fully dense or solid AM polymer tools. The interface between the shell and backfill has a significant impact on the tool performance in terms of tool longevity and stamped part geometry. Proper bonding at the interface is essential for preventing buckling or bulging of the shell away from the backfill, which may lead to tool failure as well as part wrinkling due to uneven blank holding force distribution.