熱沖壓裁縫式模具淬火製程之有限元素分析與模具加熱設計

Abstract

近年來環保意識抬頭，節能減碳已成為各國工業與製造業積極追求之目標，在汽車產業中亦以車體輕量化來節省油耗。高強度鋼以上之鋼種被大量使用於汽車結構件中，能在維持車體強度或剛性的同時減少材料使用量，達到車體輕量化目的。然而，強度越高的鋼種在常溫沖壓下越容易產生破裂、回彈與扭曲等缺陷，而熱沖壓成形技術則可克服上述缺點，且成品抗拉強度可高達1470MPa以上。熱沖壓件雖擁有高強度，但其延伸率較低，造成整體韌性不佳。為了改善以往熱沖壓件之缺點，各研究單位開始發展裁縫式熱沖壓件。裁縫式板件為在單件成品之各部位擁有不同強度，分為強區與弱區。其強區可避免車體嚴重變形，而弱區透過塑性變形吸收撞擊能量。其中，裁縫式淬火板件在製作方式上通常使用模內淬火，沖壓前的胚料無需焊接與滾軋成不同厚度，可進一步降低生產成本，但模具須進行加熱，且模具溫度與淬火時間等製程參數對部件強度分佈影響明顯。本研究藉由有限元素軟體PAM-STAMP建立製程模型，分析各項製程參數對弱區強度分佈的影響。此外，以卡式加熱棒作為模具加熱方式，並以另一套有限元素軟體ABAQUS建立模具加熱模型，探討模具隔熱與加熱棒排列方式對加熱功率以及模具溫度分佈之影響。最後將上述分析結果用於設計裁縫式A柱與B柱模具，在模擬中可在避免機台過熱的前提下，得到模面溫度均勻之模具加熱設計。透過上述分析結果，建立熱沖壓裁縫式模具淬火製程參數選擇及模具加熱設計方法。

In recent years, energy saving and carbon reduction have become the active pursuit of industries all over the world. In the automotive industry, fuel consumption is also reduced by car body weight reduction. Steel grades above high-strength steel are widely used in automotive structural parts, which can reduce the amount of material used while maintaining the strength or rigidity of the vehicle body. However, the steel with higher strength is more likely to cause forming defects such as cracking, rebound and distortion under cold stamping. Hot stamping forming technology can overcome the above disadvantages, and the tensile strength of the finished product can be as high as 1470 MPa. Although hot stamping parts have high strength, their elongation is low, resulting in poor overall toughness. In order to improve those shortcomings, various research units began to develop tailored property blanks, which have different strengths in a single part. Tailored property blanks were divided into strong and weak zone. When the car body is subjected to a side impact situation, its strong zone can avoid serious deformation while the weak zone absorbs the impact energy through plastic deformation. Among them, tailored die quenching blanks are manufactured usually by in-die heating technique.It doesn’t need to be welded and rolled into different thicknesses, which can further reduce the production cost. but the die heating is required and the process variables such as die temperature and quenching time have great influence on the part strength distribution. In this thesis, a process model was established by finite element software PAM-STAMP to analyze the influence of process variables on the part strength distribution. In addition, the cartridge heater was used as the die heating method, and another finite element software ABAQUS was used to establish the die heating model to investigate the influence of thermal insulation and cartridge heater arrangement on heating power and die temperature distribution. Finally, the above analysis results are used to design the A-pillar and B-pillar dies for hot stamping tailored die quenching process. In the simulation, the die heating design with uniform die surface temperature can be obtained under the premise of avoiding overheating of the machine. The subsequent experimental planning will be carried out with the A-pillar die to verify the influence of process variables on the strength distribution of the weak zone. The result of above analysis can be used to establish procsess variables chosen and die heating design for tailored die quenching process in the hot stamping process.