Thermal Fatigue Analysis of Hot Forging Closed Dies

Abstract The aim of this work is to develop a numerical subroutine for the commercial finite element method software QFORM VX 8.1.4 capable of predicting, simultaneously, regions of closed dies which are prone to thermal fatigue as well as the number of cycles required for thermal fatigue cracking. The numerical subroutine was based on Manson (thermal fatigue) and Coffin-Manson (number of cycles) equations. Hot forging of AISI 1045 grinding balls using AISI H13 closed dies was performed and the numerical and experimental results were compared. The findings indicated that after forging 66 grinding balls, the numerical model achieved steady state for the temperature inside the die. After forging 600 grinding balls, both the experimental and numerical results showed that the regions of the dies subjected to the highest thermal gradient were prone to thermal fatigue. In addition to that, the numerically predicted values for the onset of thermal cracking were consistent with the experimental results: 517 and 600 cycles, respectively.摘要 本研究旨在为商用有限元软件QFORM VX 8.1.4开发一套数值子程序，使其能够同时预测闭式模具中易发生热疲劳的区域，以及热疲劳裂纹产生所需的循环次数。该数值子程序基于曼森（Manson）热疲劳方程与科菲因-曼森（Coffin-Manson）循环次数方程构建。实验采用AISI H13闭式模具对AISI 1045钢研磨球进行热锻加工，并将数值模拟结果与实验结果进行对比。研究结果表明：在完成66个研磨球的锻造后，模具内部温度场达到稳态；在完成600个研磨球的锻造后，实验与数值模拟结果均显示，模具中热梯度最高的区域易发生热疲劳。此外，数值模拟预测的热裂纹萌生循环次数与实验结果一致，分别为517次与600次。