Impact of Flow Conditions in Cooling Channels on Thermal Cycling

Abstract

In order to improve the set-up of industrial press hardening processes, companies and researchers are spending considerable efforts in the design and positioning of cooling channels. Following the increasing demands for modelling options, FEA software vendors have implemented corresponding features in their codes. Modeling cooling channels in FEA simulation facilitates a more accurate prediction of the location and dimensions of hot spots on the tool surface.The present simulation case study is based on a complete tool set up for a typical part. The FE-model of tool set-up, including a suitable cooling channel design, has been utilized for a study on press hardening of 22MnB5. The effectiveness of cooling channel design is determined by the flow conditions of the cooling media - here water. The flow rate and cooling media temperatures are the parameters with most influence on the thermal behavior of the tool. The impact of variations in these parameters on the final surface temperature distribution on tools, and the ramp-up of this distribution to thermal steady state, are the subject of this study. Beyond tool temperature distribution, the impact of the above parameters on the quality of produced parts is assessed by evaluating typical part quality metrics: hardness, martensite volume fraction in the part’s microstructure, and thermal distortion.It is observed that due to the complexity of the press hardening process, the details of cooling channel flow conditions do not carry a direct and proportional impact on part quality outcomes. This observation clearly indicates that engineers can derive descriptions of the cooling channel flow conditions from easy-to-use analysis tools that are fully integrated with the simulation of the forming process, rather than resort to extended, time consuming “offline” flow computations. An analytical method for calculation of cooling channel flow conditions is also introduced by the authors.