Study of die punching process for hot stamped high strength steel and its performance evaluation

Abstract. Using the hot stamping process to produce ultra-high strength steel parts has been regarded as a good option for lightweight of automotive parts. Hot stamped workpieces usually require post-stamping processes like hole machining before they can be utilized. Considering industrial production, die punching process is more attractive than other hole machining methods such as laser cutting due to its high efficiency and low cost. In this study, the die punching process for hot stamped steel Usibor 1500P was investigated, and the performance of the punched parts was also explored. Firstly, the influence of process parameters including punching velocity, die clearance, punch corner radius, punch diameter, etc. was studied through a specifically designed trimming tool. Corner radius at the punch edge significantly improves the sheared edge quality, and tapered punch and conical punch evidently reduce and raise blanking force respectively. Secondly, several finite element fracture models for die punching process of Usibor 1500P were constructed and validated, where the Oyane and MMC damage models are considered suitable for punching simulation. Thirdly, the service performances of hot stamped ultra-high strength steel after die punching were evaluated through some typical experiments, including tensile tests, bending tests, and hydrogen embrittlement tests.