Tool Cooling Simulation for Hot Forming II. Experiments and Simulations

To fulfill recent regulations for automobile fuel economy great demand on saving weight of automobiles is growing. Since making a lighter car with conventional material loses occupant safety, at least stiffer materials with the same weight are needed. For example, use of CFRP (Carbon Fiber Reinforced Plastics), Aluminum, Magnesium or Titanium is attracting our attention in these days. But technique to handle these materials is still under developmental stage. High-tensile steels made by hot forming is one of the most promising candidate since it can realize better balance between cost and weight saving. In hot forming technique, heated blank material is pressed by tools and then quenched by various methods to cause martensitic transition of the blank to obtain high tensile steel. It is not only stiff but also has good shape freezing property, causing smaller springback of the stamped materials. As an another advantage of hot forming, steels as raw materials can be easily obtained all over the world, compared with other materials listed above. On the other hand its disadvantages is relatively large investment in plant and equipment such as chiller or cooling tower and costs for prototyping production of tools with pipes to run cooling water. In order to cause the martensitic transition of the blank materials, one needs to quench it sufficiently fast. We, JSOL, think that a CAE tool to calculate and predict the stiffness of high-tensile materials contributes to ensure their strength in mass production stage. Important points in accurate prediction are following: (i) to calculate phase transition of the materials correctly (ii) to predict cooling performance of the tools to ensure (i). By making these uncertainties clear it is expected that CAE is capable of reducing trials-and-errors on prototyping, causing reduction of tool designing costs. LSTC, Dynamore and JSOL have been working on formulating a manufacturing CAE solution to the hot forming techniques. For example, development of phase transition material models (*MAT_244, *MAT_254) will overcome the uncertainty (i) described above. We also have been investigating simulation technique for thermal-structural-fluid coupling calculation to demonstrate the behavior of cooling water flowing in pipes of the tools, corresponding to item (ii) above. In this paper we report the results of recent solution developments on the latter point.