管件液壓成形模內彎管製程之研究

Abstract

汽車產業近年發展趨勢為輕量化以及高強度，汽車業界已廣泛使用管件液壓成形技術取代傳統沖壓技術，通常管件液壓成形道次包含彎管、預成形、液壓成形。本論文針對後副車架橫樑進行管件液壓成形製程之研究，使用模內彎管技術取代彎管機彎管。模內彎管為一種使用模具直接將管材彎曲之技術，相較於彎管機彎管有減薄率較低、製程速度較快、心線限制較小…等優勢，然此製程卻有易產生凹陷、截面變成橢圓狀以及截面周長減少之缺陷。 本論文透過蒐集常見液壓產品芯線種類，了解模內彎管缺陷之改善方向。首先，本論文利用有限元素法軟體建立一基礎載具以討論缺陷之發生機制，並透過探討幾何參數，如管材厚度、管徑以及彎管半徑等參數進行探討，得知當厚度增加時，管材的抗凹陷能力較好、彎管後成品截面橢圓度較低、截面周長減少量較低；當管徑增加時，管材的抗凹能力較差、彎管後成品截面橢圓度較高、截面周長減少量也較高，而當彎管半徑增加時，管材抗凹能力較好、彎管後成品截面橢圓度較低、截面周長減少量也較少。此外，本論文亦針對模具參數方面，如管材與模具間隙、下托塊(Holder)圓角進行優化設計，得知當管材與模具間隙越大，則凹陷越不容易產生，但是會造成截面橢圓度越高。於下模Holder設計方面，本論文透過改變Holder圓角得知，當圓角超過10mm時不會造成凹痕產生。本論文利用此些優化設計之結果建立模內彎管模具開發流程。 最後，本論文針對後副車架橫樑之成形道次進行模內彎管所產生之凹陷對於液壓的影響，經由觀察凹陷長度對應將凹陷脹出之液壓壓力，整理出可用液壓壓力脹出之凹陷長度。藉由上述研究成果，本論文建立了模內彎管製程之模具設計方法以及提供模內彎管缺陷改善之方式，可作為業界於模內彎管設計時之參考。

In recent years, the lightweight and high strength have become the development trends in the automotive industry. To achieve these goals, The tube-hydroforming technology has being applied to replace the traditional stamping-welding process in manufacturing automotive structural parts. Usually a tube-hydroforming process includes tube bending, pre-forming and hydroforming operations. In the present study, the research on the tube-hydroforming of a rear sub-frame beam was carried out, and the tube was bent in die instead of by a bending machine. The die bending is a technique in which the straight tube is bent with both the upper die and lower die which produces a lower rate of thinning with less restriction of the center line than that in draw bending. But this process is prone to producing depression, cross-section oval and reduced cross-section on tube. In this thesis, we collect the common types of center line of tube-hydroformed products to understand how to improve defects of die bending progress. First, the finite element analysis was employed to establish a basic model to examine the reason why defects occur. And then we take the geometrical parameters such as tube thickness, tube diameter and bending radius to analyze the reasons that cause the defects. It is found that when the thickness is increased, the anti-depressing ability of the tube is better, the ovality level of the section being lower and the reduction of the circumferential length being lower. When the diameter increases, the anti-depressing ability of the tube is poor, the cross section of the product having a higher ovality level and a decrease in the circumferential length of the section. When the radius of the tube increases, the anti-depressing ability of the tube is better, the ovality level of the section being lower and the reduction of the circumferential length being lower. In addition, this study also optimized the design of the corner of the down holder and the gap between die and tube. It is found as the gap gets greater the depression is smaller and the ovality level of the section becomes higher. In the design of down holder, this study changed the holder fillet and found when the fillet larger than 10mm would not cause dents. We use these research results to establish an optimal process for the die bending design. Finally, this thesis discusses the forming of the rear sub-frame beam. In the bending process, we researched the influence of the depression by varying hydroforming pressures and examine the relations between the length and pressure. Based on the above research, this thesis has established a die design method that offer a way to improve the defect of die bending process.