多孔穴鋁合金擠製成形模具設計之研究

Abstract

近年來隨著環保意識抬頭，自行車這類低汙染交通工具逐漸成為主流，其中以輕量化、高精度之自行車為主要發展方向，而隨著高階自行車的需求提高，對於自行車組件之品質也隨之提升，本論文以自行車輪圈作為研究載具，期望輪圈管件之擠製成品更能符合當今趨勢。 自行車輪圈的空心鋁合金管件一般使用Porthole Die進行擠製成形，Porthole Die由分流模具以及焊接模具組成，一般以單次擠製之管件數量定義為模具孔穴數。為了提升生產效率，減少人員開支以及避免因過多機台佔用廠房空間，進而達到降低成本之目的，使用多孔穴擠製模具(Multi-Porthole Die)有其必要性。然而，多孔穴模具擠製容易出現製品精度較低，良率較差進而提升成本等問題。本論文旨在透過CAE分析技術，探討多孔穴模具之變形機制，減緩自行車輪圈管件兩側厚度不均之現象，使後續輪圈彎管成形製程良率提升。在兼顧品質與提升生產效率下同時降低生產成本，增加台廠在自行車產業鏈之競爭力。 本論文使用DEFORM-3D有限元素分析軟體，建立自行車輪圈的單孔穴、雙孔穴以及四孔穴鋁合金擠製成形的CAE模擬模型，其中包括分流模具、焊接模具的幾何造型繪製、材料性質參數、製程參數、機台作動邊界條件以及模擬收斂性測試等，並將模擬結果與實際製程做模具的變形趨勢和管件的厚度分布等比較，藉以驗證模擬的正確性。 本論文統整不同孔穴數量之模具，在不同排列方式下的芯軸偏移趨勢，根據模擬結果，觀察單孔穴以及雙孔穴垂直排列之模具芯軸幾何對稱軸與模具對稱軸重疊，且芯軸支撐結構對稱，所以擠出管件並不會產生厚度不均之現象，相對地，雙孔穴水平排列與四孔穴模具無此特徵。 在管件兩側厚度不均方面，本論文透過CAE模型確認此現象，為擠製過程中芯軸之偏移造成出模間隙改變所致。在芯軸偏移的主要原因分成芯軸支撐結構強度分配不均與兩側分流孔填料速度差異兩種，其中結構的強度不均使胚料擠入瞬間即發生偏移現象，而填料速度的差異為芯軸受單一側胚料擠壓，造成偏移程度進一步增加。 在結構強度修正方面，本論文透過焊接模具的強度減損以及芯軸支撐樑斷面積增加兩種方式進行改善，透過此兩種方法有效調整各支撐樑在擠製過程的變形量，使結構變形趨近平衡，並大幅減少芯軸在胚料擠入時的偏移量。 在填料速度修正方面，本論文則以模具結構修正為基礎，進一步增加圓角造型結構、分流孔截面積的調整以及擋料結構設計，有效調整特定分流孔填料速度，減緩兩側填料速度不均之現象，進而改善芯軸因受胚料推擠，造成偏移量增加之趨勢。 透過CAE模型繪製各時間點之芯軸偏移趨勢圖，確認上述之修正方案均對芯軸偏移有明顯改善之趨勢，並量測其管件厚度分布，根據測量結果顯示，修正後之管件厚度差明顯優於業界廠商需求。 本論文之研究內容可提供相關模具廠商針對製品厚度缺陷，作為制定模具修正方案之參考依據。

In recent years, with the rise of environmental awareness, bicycles as low-pollution transportation have gradually become mainstream. Lightweight and high-precision bicycles have been the main development direction, and as the demand for high-end bicycles increases, the quality of bicycle components has also improved. This thesis focuses on bicycle wheel rims as the research subject, aiming to enhance the extrusion process of rim tube components to meet current trends.

Hollow aluminum alloy tubes for bicycle wheel rims are typically extruded using Porthole Dies, which consist of a Porthole Die and a Welding Chamber Die. The number of die holes is generally defined by the quantity of components extruded in a single operation. To improve production efficiency, reduce labor costs, and minimize the occupied space of multiple machines, the use of Multi-Porthole Dies becomes necessary. However, the use of multi-porthole dies often leads to lower product precision, poorer yield, and increased costs. This study aims to analyze and mitigate the issue of uneven thickness on both sides of bicycle wheel rim components during the extrusion process using CAE analysis techniques, thus enhancing the yield in subsequent rim bending processes. By simultaneously improving quality, production efficiency, and cost-effectiveness, this research contributes to the competitiveness of local manufacturers in the bicycle industry.

The DEFORM-3D finite element analysis software is employed in this study to establish CAE simulation models for single-hole, double-hole, and four-hole aluminum alloy extrusion of bicycle wheel rims. The models include the geometrical design of the Porthole Die and Welding Chamber Die, material properties, process parameters, machine boundary conditions, and convergence tests. The simulation results are compared with actual production processes to validate the accuracy of the simulations, including die deformation trends and thickness distribution of the components.

This thesis examines the displacement trends of the mandrel for different numbers and arrangements of die orifices. The simulation results show that the mandrel in the single-hole and vertically arranged double-hole dies exhibits geometric symmetry with the die's axis of symmetry, resulting in no thickness unevenness in the extruded components. In contrast, the horizontally arranged double-hole and four-hole dies lack this characteristic.

Regarding the issue of uneven thickness on both sides of the components, this study confirms through the CAE model that the phenomenon is caused by the displacement of the mandrel resulting in changes in the die clearance during the extrusion process. The main causes of mandrel displacement are attributed to uneven distribution of structural strength in the mandrel supports and differential filling speeds of the flow channels on both sides. Structural strength imbalance causes immediate displacement when the billet is extruded, while the differential filling speeds further increase the extent of displacement as the mandrel is subjected to the pressure from a single-side .

To address the structural strength issue, this study proposes improvements through weakening the Welding Die strength and increasing the cross-sectional area of the mandrel supports. These methods effectively adjust the deformation of each support beam during the extrusion process, leading to a more balanced structural deformation and significantly reducing the mandrel's displacement during billet extrusion.

For the correction of differential filling speeds, this study focuses on modifying the die structure by introducing rounded corners, adjusting the flow channel's cross-sectional area, and optimizing the design of material-blocking structures. These adjustments effectively regulate the filling speed of specific flow channels, mitigating the phenomenon of uneven filling speeds on both sides and improving the mandrel's displacement caused by billet extrusion.

By plotting the trends of mandrel displacement at various time points using the CAE model, it is confirmed that the proposed corrective measures exhibit a clear improvement in mitigating mandrel displacement. Furthermore, the thickness distribution of the components is measured, showing that the corrected components have a significantly better thickness uniformity than the industry's requirements.

The research findings of this study provide valuable insights for relevant die manufacturers as a reference for developing corrective measures to address product thickness defects