Investigation of applying protective sheet metal die covers for hot forging dies on a cross-forging geometry

摘要

Improving tool life is one of the main challenges and research objectives in closed-die forging. One approach, first proposed in (Rosenstock et al. 2015) uses an inexpensive and easy-to-exchange sheet metal die cover, which is placed on the die surface during forging. By using this cover, die wear can be reduced since mechanical and thermal loads mostly affect the die cover instead of the die itself. Numerical and experimental investigations (Wolfgarten et al. 2015; Yu et al. 2016) have proven the general key features of the concept and the positive impact on the lifetime of the forging die. However, these studies have shown that the applicability of the concept and the corresponding lifetime of the die cover are strongly dependent on the investigated die and die cover geometries. For simple 2D die cover geometries, where the die cover can be produced by a simple bending operation, the maximum die cover lifetime of seven forging cycles was achieved. Since these geometries offer low structural stability, the die covers are prone to deformation or folding during forging. Hence, this work investigates the application of die covers in complex geometries. For this purpose, a 3D die cover geometry was proposed that offers higher structural stability and less challenging contact conditions regarding the material flow during forging. The die cover successfully experienced 40 forging cycles without visible distortions or folds. Regarding the thermal loads, the maximum temperature and the temperature amplitude measured in the forging die were reduced by 40 degrees C. Based on the experimental results, a numerical simulation model was built and validated regarding the temperature evolution and forging forces. The numerical model indicates a significant reduction in the mechanical loads on the dies through the application of the die cover.