Amir Abdollahpoor

Advances in tailored hot stamping – innovations in material and local patchwork topology

Hot stamping is now commonplace in the automotive industry. The continuing need by automotive manufacturers to reduce weight while increasing crashworthiness has driven the industry to seek new hot stamping solutions. Tailored hot stamping can be thought to produce a part that has patchwork of hard and soft regions. In this context, patchwork means that there is a relational organization (topology) to the network of hard and soft regions. The next generation of tailored hot stamping will therefore combine new steel grades together into a single part, and secondly will be able to locally tailor material properties to meet detailed engineering targets. The key to meeting engineering demands will be how the patchwork material properties are organized on the part. This paper will briefly outline our latest research in tailoring parts.

A general approach on the modelling of incubation in ferrite transformation using non-isothermal kinetics data for 22MnB5 steel

Abstract The most challenging part, in modelling tailored hot stamping processes, is the variable cooling transformation that occurs in real industrial processes. In this study, analytical equations are first fitted to both experimental isothermal and continuous cooling transformation data. Then, an optimized fitting method with a weight coefficient is introduced that considers two transformation data to provide a more accurate transformation prediction. Finally, the generalized calculated result of incubation time using Rioss proposed method based on optimized continuous cooling transformation curves is contrasted against one calculated with a modified generalized calculated method. The results show that the consideration of the current temperature and cooling rate increases the accuracy of incubation time predictions as the gradient of cooling rate increases.

Experimental Investigation of Tailored Hot Stamping Parts

It is known that tailored hot stamped parts, which have locally graded properties, can improve car crashworthiness. In this experimental study, a heated tool was used to decrease the temperature difference between the hot blank and the tool which led to lower cooling rates and softer properties. First, a flat heated tool was used to investigate the effects of process parameters on metallurgical and mechanical properties. Based on the range of parameters examined, press force and quenching time did not have a significant effect on the post-formed mechanical properties. In the next step, a hatshaped channel tool with heating system was used to produce tailored hot stamping parts. The results show considerable differences between hardness values of the top and side faces in the soft section, while the hardness was almost uniform in the hard section. These experimental results generally compare well with the results of previous numerical parametric studies performed by the authors, which identified less robustness of the tailored hot stamping process compared to conventional hot stamping.

Understanding wear conditions during hot stamping

Wear and galling are significant issues during production hot stamping processes. This paper uses thermo-mechanical finite element analysis to study the contact pressure, sliding distance and temperature conditions that occur at the wearing interface during hot stamping. Several hot stamping processes are studied, representing the numerous methods that are used in industry to form a typical hat-shaped channel component. These process include crash forming (without blankholder), stamping with a blank holder with an applied blank holder pressure, and stamping with a clearance blank holder (i.e. with spacer blocks). This paper identifies the distinct contact pressure and temperature conditions that occur for each of these forming methods. The regions of the most severe contact conditions are notably different for each of the forming methods. The work from this paper will form the basis for the development of suitable temperature dependent wear models and low cost wear tests for industrial hot stamping applications.