| The demand for rapid, low-cost die fabrication and modification technology is greater than ever in sheet metal forming industry. One category of rapid tooling technology involves the application of advanced polymers and composites to fabricate metal forming dies. Despite their advantages in lead time and cost reductions, polymer dies for sheet metal forming applications have several drawbacks. Due to their lack of strength as compared to conventional die materials, the use of polymer dies is often limited to prototype or short-run production. In addition, because the mechanisms by which they fail are not fully understood, the dies are designed on the basis of experience and intuition.; The research (1) characterized the mechanical behavior of an advanced polymer composite tooling material, (2) developed a method to predict the failure mode and the life of a polymer die, and (3) established optimal die design guidelines. The focus was on rapid prototyped, aluminum trihydrate(ATH)-filled, polyurethane-based dies in sheet metal forming. The study involved the determination of dominant process parameters based on the finite element analyses of 90° V-die bending and cylindrical cup drawing processes. The effects of process parameters on stress distribution in the die provided guidelines to the modification of die design for achieving the desired die life. The presented parametric study lays the groundwork for providing reliable tool failure prediction and design optimization guidelines for advanced polymer tooling materials in metal forming.; In addition, the failure mechanisms were investigated to predict the failure mode and the fatigue life of the die. To establish a fundamental understanding of the fatigue behavior of the polyurethane-based die material, extensive material tests were performed, the microstructure was studied, and the fatigue properties were identified experimentally. The test data were incorporated into the local stress-based fatigue analysis to obtain the number of cycles to crack initiation. The analysis results were validated by comparison with experimental data. The research provides a new set of engineering material data for the advanced polymer as well as potential applications in the design technology of rapid prototyped tools. |
