Cooling channel design of hot stamping tools for uniform high-strength components in hot stamping process

Although high strengths up to 1,500 MPa can be obtained by means of hot stamping, the strength and uniformity of components cannot be guaranteed during mass production if the cooling channel is not properly designed. In this paper, we propose a method for designing the cooling channel by means of the energy balance principle and arrangement methods such as the triangular method, tool split, and the connection rule for 2D sections to improve the strength and uniformity of hot stamped components. Two separate approaches for designing the cooling channel are suggested. One is to reduce facility and maintenance costs, and the other is to reduce the cooling cycle time, which critically affects productivity. These approaches were applied to hot stamping tools for manufacturing a roof side that is used as part of the structure of an automobile. Cooling performance and cooling uniformity of the designed cooling channel were verified with finite element simulation. Finally, hot stamping tools for manufacturing a roof side were designed to reduce cooling cycle time and were then manufactured to verify the proposed design methods. A roof side was manufactured by means of the hot stamping tools with the designed cooling channel, and the strength and the uniformity of the component were evaluated by means of a tensile test, observation of the microstructure, and measurement of the micro-Vickers hardness.