A Comparative Study on Fatigue Damage of Caldie™ from Different Manufacturing Routes

In automotive body manufacturing the dies for blanking/trimming/piercing are under most severe loading condition involving high contact stress at high impact loading and large number of cycles. With continuous increase in sheet metal strength, the trim die service life becomes a great concern for industries. In this study, competing trim die manufacturing routes were compared, including die raw materials produced by hot-working (wrought) vs. casting, edge-welding (as repaired condition) vs. bulk base metals (representing new tools), and the heat treatment method by induction hardening vs. furnace through-heating. Caldie^TM, a Uddeholm trademarked grade was used as trim die material. The mechanical tests are performed using a WSU developed trimming simulator, with fatigue loading applied at cubic die specimen’s cutting edges through a tungsten carbide rod to accelerate the trim edge damage. The tests are periodically interrupted at specified cycles for measurement of die edge damage. The microstructures from different routes are examined by laser 3D confocal microscopy. The evolution of edge damage projected areas and converted volumes are used, and the fatigue performances of manufacturing routes are compared and ranked. Microstructures from different routes are analyzed for providing metallurgical explanations of mechanical testing results. Directions of further study and trim die reconditioning method for fatigue property improvement are discussed.