Presented by Chao Pu, AK Steel, at the 2018 Great Designs in Steel.
The elevated strength of advanced high-strength steels (AHSS) leads to great challenges for the sheet metal processing, one of which is hole punching operation. A comprehensive study was conducted to investigate the tool shape and punching configuration effects on force reduction, hole dimensional accuracy, edge qualities, etc. Three grades of AHSS (DP1180, DP980 and DP590) were tested using flat, conical and rooftop shaped punch respectively with three cutting clearances for each material. The punching force coefficient is calculated based on the experimental measured data, and it indicates a negative correlation with the material strength. The punching force was significantly reduced benefited from progressive cutting mechanism introduced by rooftop punch but such punch shape can lead to dimensional inaccuracy issues. Conical punch leads to the uniform diametrical enlargement according to the measurement. To uncover the mechanism of the hole dimensional change and various cutting modes, a series of finite element simulations were established for numerical investigation. The tooling effects on cutting edge quality and associated tool protection was also investigated.