Construction of Process Window to Predict Hardness in Tailored Tool Thermomechanical Treatment and its Application

Abstract

Recently, in order to improve crashworthiness and achieve weight reduction of car body, a hot stamping process has been applied to the production of the part with tailored properties using tailored tool thermomechanical treatment. In the tailored tool thermomechanical treatment process, process parameters influence the mechanical properties of final product such as strength and hardness. Therefore, the prediction of hardness for final product is very important to manufacture hot-stamped part considering various process parameters. The purpose of this study is to propose a process window, which can predict hardness for various process parameters in tailored tool thermomechanical treatment. To determine the process window, finite element (FE) simulation coupled with quench factor analysis (QFA) has been performed for combinations of various process parameters. Subsequently, the process window was constructed through the training of artificial neural network (ANN) and experiment of tailored tool thermomechanical treatment for hat-shaped part was performed to verify effectiveness of hardness prediction. Then, the process parameters were determined from process window for hot stamping of the hat-shaped part with the required distribution of hardness. Hardness predicted by process window was in good agreement with measured one within 3.1% error in additional experiment. Therefore, the suggested process window can be used efficiently for hardness prediction and determination of process parameters in tailored tool thermomechanical treatment of hot-stamping parts.

Process Window Definition to Predict Mechanical Properties of Press Hardened Parts of Boron Steel with Tailored Properties

“…Figures 8a, 8b and 8c show, respectively, the process window to predict hardness, tensile strength and rupture deformability of low strength region for investigated quenching parameters. It has been found that the hardness decreases as the quenching time increases, in agreement to the results of Palmieri et al [15] and Kim et al [14]. Moreover, for low values of the quenching time, the hardness decreases as the temperature of the heated tools increases.…”

“…They exploited the theoretical model to estimate the martensite fraction on the formed part at the end of Press-Hardening process, which was numerically simulated in DYNAFORM. Kim et al [14] used FE simulation coupled with quench factor analysis to determine the process window adopted to predict hardness for different quenching time and tool temperature. In general, current scientific research aims at improving the prediction of mechanical properties by combining numerical simulations with experimental investigations.…”

Medium-Mn steels for hot forming application in the automotive industry

“…Moreover, the low resistance force and the high formability of steel during hot forming can solve the problems of severe wearing and short life of die mold, which are common in the cold forming of high-strength steels [6]. To further improve crashworthiness and lightweight, hot-formed parts with tailored properties can be synthesized using different process control strategies, such as using a furnace with areas maintained at different temperatures and using tools with different temperatures or with different materials having different thermal conductivities [20,[37][38][39].…”