沖切製程參數對斷面品質之影響分析與模具設計之優化探討

Abstract

本論文以高階山用自行車變速器掛勾零件為研究對象，該零件為後變速系統與車架間之關鍵連接元件，需兼具高精度與耐衝擊性，其製造品質直接影響變速準確性與整體騎乘穩定性。此零件採用高強度7075鋁合金製成，並於製程末段進行刮光成形以修整輪廓，該道次成形後即為最終成品斷面，因此刮光製程之品質對產品性能與壽命具有決定性影響。 本論文專注於刮光成形階段之分析與優化，使用DEFORM-3D有限元素分析軟體，從材料特性、破壞行為、製程改善與模具設計等面向，進行分析與改善策略建構。首先透過單軸拉伸試驗取得材料參數，並導入Normalized Cockcroft & Latham延性破壞準則以推導臨界破壞值，作為初步破裂預測依據。然而模擬結果與實際成品斷面比較上有顯著差異，故進一步採用反推法，依據實際成品的斷面形貌，反求臨界破壞值以提升模擬可信度。於建模方面，建立符合實際尺寸與加工道次特徵之三維模型，針對多項製程參數進行系統性模擬分析。 模擬結果顯示，母模錐度為影響剪切穩定性與斷面品質之關鍵參數，能顯著提升剪切區比例並抑制模輥區生成。而為克服製程改善瓶頸，進一步提出道次分離策略，使原先之單一道次刮光加工改為「先刮光外輪廓、後刮光內孔」的雙道次設計，並加入拘束模具以穩定刮光量，進一步提升斷面品質與成品精度。此外，導入具有錐度設計之母模更可降低沖頭受力，兼顧模具壽命與切斷品質。整體研究結果對於高強度鋁合金與相關對應特徵零件之刮光製程具實務應用價值。

This thesis investigates the shaving process of a derailleur hanger used in high-performance mountain bikes, which serves as a critical structural component that connects the rear derailleur to the bicycle frame. The part must offer high dimensional precision and impact resistance, as its quality directly affects shifting accuracy and overall riding stability. Manufactured from high-strength 7075 aluminum alloy, the hanger undergoes a shaving process as the final stage of processing, which defines the product’s final sheared surface. As a result, the quality of this shaving process is essential to both functional performance and long-term durability. Finite element analysis(FEA) were carried out using DEFORM-3D software to analyze and optimize the stage of shaving process, with a focus on material behavior, damage evolution, process modification, and die design. Mechanical properties were obtained through uniaxial tensile test, and the Normalized Cockcroft & Latham ductile fracture criterion was implemented to estimate the initial critical damage value (CDV) for failure prediction. However, due to notable deviations between simulation and experimental results, an inverse calibration method was adopted, using actual fracture profiles to refine the CDV and enhance prediction accuracy. A 3D model incorporating real geometry and process features was established for parametric studies. The results reveal that introducing a taper-shaped die significantly improves shearing stability by increasing the proportion of the burnished zone while reducing the rollover area. To overcome issues in the original single-stage design, a two-stage forming strategy was proposed—shaving the outer contour before the inner hole—combined with the use of a restraining die to stabilize the shaving allowance and improve section precision. Incorporating taper-shaped die into this dual-stage approach further reduced punch force, contributing to better tool longevity and sheared surface quality. This thesis offers practical guidance for improving the shaving process of high-strength aluminum alloy components and other parts with comparable structural features.