汽車板金熱成形製程特性之研究

Characterization of Sheet Metal Hot Forming Processes for Manufacturing Automotive Parts

陳奕寰(Yi-Huan chen)

指導教授 ： 陳復國

國立臺灣大學/工學院/機械工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903746

摘要

近年來，由於環保意識的提升，各大車廠皆致力於開發低耗能、輕量化汽車車輛，綜觀近幾年輕量化之趨勢，可概略分為兩大方向，其一是使用具高強度之材料，達到減輕車體體積與質量之目的，其二則是採用鋁、鎂等輕金屬作為車組件主要材料，在等體積與等剛性的條件下減小結構的重量。然而，常溫下的高強度鋼種與鋁合金等輕金屬，在一般沖壓成形過程中容易產生回彈及扭曲變形等缺陷，使得複雜造型之車組件成形不易。為了解決這些生產問題，熱沖壓成形技術應用於汽車結構件之開發逐漸受到重視。
熱沖壓技術最初以鋼材之應用為主，藉由高溫成形及模內淬火的方式，使板材在高溫下成形以抑制回彈與破裂缺陷，並於模內淬火階轉變為強度較高的麻田散鐵組織，其抗拉強度可達1400 MPa以上，熱沖壓成形技術已於目前汽車產業中被廣泛的運用。
然而，具麻田散鐵相之鋼材熱沖壓結構件雖然強度極高，但其延伸率較低，造成整體韌性不佳。為解決此問題，裁縫式淬火技術的概念因應而生，並開始被廣泛的研究，具裁縫性質之成品於不同的區域具有不同的強度，一般可分為強區與弱區，強區強度較高，以避免車體產生過大的變形，而弱區則能透過塑性形變吸收衝撞能量，保護乘客與駕駛的安全。
其他合金材料之熱成型沖壓技術近年來亦開始逐步發展，其中，針對可熱處理鋁合金所提出的HFQ(hot forming quenching)製程成為了日前熱門的新創製程，如同鋼材的熱沖壓製程，藉由模內淬火與時效處理，HFQ製程標榜其成品能達到與傳統經T6時效處理所能達到的高強度，且在高溫下成形，較不具高強度材料之成形性問題，此製程仍處於實驗階段，對於高溫下各種鋁材的成形特性與介面特性仍欠缺完整的資料，於分析方面亦不似鋼材熱沖壓具備較完整的數值分析模式可供參考。
本論文針對藉由常用數值分析軟體Pamstamp與Abaqus，分別針對錳硼鋼裁縫式淬火製程與鋁合金之熱沖壓製程進行分析模型建立與細部探討，最後藉由實驗對於所建立之分析模式進行驗證。
對於裁縫式淬火部份，藉由一實體A柱模型作為分析目標，分析製程參數對於成品之影響，並進一步探討模具加熱系統與模面溫度均勻性的關連性。
對於鋁合金熱成形部份，本論文注重於HFQ製程的淬火階段分析，針對基礎U型載具進行探討，討論不同板材材料的淬火特性與製程參數之影響，以及水路於HFQ製程的效益與循環淬火的影響性。
最後，本論文藉由基礎V型與U型載具針對分析結果進行驗證，由實驗結果與分析結果進行比對，其結果顯示，分析誤差約在10%以下，本論文所建立之分析方式與結論應具一定參考價値。
本論文藉由有限元素分析技術之輔助，針對鋼材與鋁材之熱沖壓技術之製程與模具設計進行分析流程建構，並進行細部設計與參數探討，期望可提供未來之研究人員與設計者作為設計之參考。

關鍵字

熱沖壓成形 ； 裁縫式模具淬火 ； 有限元素分析 ； HFQ製程

並列摘要

With the rise of environmental consciousness, automotive manufacturers are committed to developing fuel-efficient, lightweight automotive vehicles. The research on lightweight technology can be broadly divided into two major directions. One is using high-strength materials to reduce the overall vehicle weight and size. The other one is utilizing light-weight metal, such as magnesium-alloy or aluminum-alloy, as the main materials for automotive bodies to achieve weight reduction.
However, the forming of high-strength steel and light metals such as aluminum alloy in room temperature is more likely to produce defects such as cracks, wrinkles, or distortion during the forming process. To overcome these challenges, hot stamping technology has become widely used in the auto industry in recent years.
In the beginning, hot stamping technology was mainly applied to steel. Due to the characteristics of low flow stress in high temperature, products of hot stamping have fewer forming defects than conventionally formed products. In addition, by the quenching-in-die process in manufacturing, the tensile strength of the final product can reach nearly 1500 MPa.
Although hot stamping parts have high strength to resist deformation, their elongation is low, resulting in poor overall toughness. To solve this issue, researchers proposed the concept of tailor properties. The tailor properties suggests that the products have different strength in different areas. Generally, the areas can be divided into the strong zone and the weak zone. The material in the strong zone has high strength and is able to avoid serious deformation during impact, while the material in the weak zone can absorb the crash impact through plastic deformation. Therefore, products with tailor properties can achieve either high strength and high toughness.
The technology of hot stamping on other alloys is also growing in recent years. The HFQ(hot-forming-quenching) process on heat treatable aluminum alloys, in particular, has received considerable attention. Combining the heat treatment into the forming process, the process enables its products to achieve the strength as high as the traditional T6 aging treatment can reach and good formability. The technology is still under development; thus, there is still lack of data for the material properties and interface properties of aluminum alloys at high temperatures. Besides, a complete numerical analysis model is still yet to be established.
In this thesis, with the analysis software Pamstamp and Abaqus, two models for analyzing the hot stamping process are built, one is for tailor-die quenching of steel, and the other is for aluminum alloy. The characteristics of the commonly used materials in the forming process are analyzed by the model.
For hot stamping on steel, a tailor-die quenching process of an A-pillar is analyzed. The influence of process parameters on the final product, and the relationship between the design of the heating system and the distribution of the surface temperature of the die is further discussed.
For hot stamping on aluminum alloy, an analytical process for evaluating the quenching effect of the material by TTP curve and numerical simulation is established, and the effect of process parameters on different series of aluminum alloy is discussed.
Finally, a simple U-shape and a V-shape forming experiments are chosen to verify the accuracy of the analytical model. The results show that the estimation error between the model and the experiments is less than 10%; as a result, the accuracy of the models are verified.

並列關鍵字

Hot stamping ； tailor-die quenching ； finite element analysis ； HFQ process.

參考文獻

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