金屬模具在高週期沖壓製程中承受重複循環負載，極易因幾何不連續或表面缺陷引發局部應力集中，進而導致疲勞裂紋起始與擴展，造成模具過早失效、生產線停機及高額維修成本。本研究針對沖裁 SUS304 不鏽鋼板材（厚度 1.0 mm）之沖壓模具，採用有限元素分析技術，系統探討上、下模具在高週期沖壓負載下的應力分佈與疲勞壽命預測。
研究方法分為三階段：首先利用 SolidWorks 建立三維沖壓模具並簡化成上沖模仁、下沖模仁、壓板以及 SUS304 不鏽鋼板，上、下沖模仁材質選用 SKD11 工具鋼（熱處理硬度 HRC 62.5，對應 773 K 回火後 HV 765），壓板採用 S45C 中碳鋼。接著將模型匯入 ANSYS，採用 LS-DYNA 顯式動態求解器模擬單次沖裁過程，設定表面對表面接觸（靜摩擦係數 0.15，動摩擦係數 0.1）、下模全固定、上模施加等效速度 200 mm/s，歷時 0.018 秒，並針對沖裁間隙以板厚 1 mm 之 5%、15% 二種條件進行參數比較分析。最後，將分析所得之應力歷程匯出至 nCode DesignLife，應力-壽命曲線依據 Fukaura【1】SKD11 工具鋼773 K 回火條件之實驗疲勞數據所建立（應力比 = −1，疲勞極限 550 MPa at 10⁷ cycles），預測上、下模具之循環壽命。
模擬結果顯示，二組沖壓間隙條件（5%、15%）之高應力區均集中於上沖模仁雙側邊圓角處及下沖模仁凹模開口圓角（R = 0.05 mm）附近。間隙 5% 條件下，上沖模仁 von Mises 應力峰值最高（1,247.3 MPa），下沖模仁最大應力為 1,116 MPa，對應疲勞壽命分別為 5,592 與 20,450 ；間隙 15% 條件下，上模最大應力降至 832.91 MPa、下模降至 647.25 MPa，疲勞壽命大幅提升至 2.373×10⁵ 與 2.337×10⁶ ，改善效果顯著。節點接觸力隨間隙增大呈單調遞減（195.26 → 125.14 N），符合沖裁理論預期。下沖模仁之疲勞壽命在二組間隙條件下均高於上沖模仁，主因凹模受力以壓縮為主，應力幅值本身較小，且上沖模仁直接承受每次沖程之衝擊反力，峰值應力持續時間較長。本研究結果可量化上、下模具之疲勞壽命差異，識別應力集中熱點，對汽車沖壓件與電子連接器製造業提升模具耐久性、降低總擁有成本具有重要參考價值。

Metal dies in high-cycle stamping processes are subjected to repetitive cyclic loads, making them highly susceptible to localized stress concentrations at geometric discontinuities or surface defects. This often triggers fatigue crack initiation and propagation, leading to premature die failure, production line downtime, and significant maintenance costs. This study employs finite element analysis (FEA) to systematically investigate the stress distribution and fatigue life prediction of punch and die sets during the blanking of SUS304 stainless steel sheets (1.0 mm thickness) under high-cycle stamping loads.
The research methodology is divided into three stages. First, a three-dimensional stamping die model—comprising the upper punch, lower die, stripper plate, and SUS304 sheet—was established in SolidWorks and simplified for simulation. SKD11 tool steel (HRC 62.5, HV 765 via 773 K tempering) was selected for the punch and die inserts, while S45C medium carbon steel was used for the stripper plate. Second, the models were imported into ANSYS, utilizing the LS-DYNA explicit dynamic solver to simulate a single blanking process. The simulation parameters included surface-to-surface contact with a static friction coefficient of 0.15 and a kinetic friction coefficient of 0.1, a fully constrained lower die, and an upper punch velocity of 200 mm/s for 0.018 s. A parametric analysis was conducted for two punch clearances: 5% and 15% of the sheet thickness. Third, the resulting stress histories were exported to nCode DesignLife. The Stress-Life (S-N) curves were established based on experimental fatigue data for SKD11 tempered at 773 K (Stress ratio R = −1, fatigue limit 550 MPa at 10⁷ cycles) as reported by Fukaura et al.【1】, to predict the cycle life of the punch and die.
Simulation results showed that under both clearance conditions (5% and 15%), high-stress regions were consistently concentrated at the bilateral cutting-edge radii on the upper punch body-to-cutting-edge section, and near the die opening edge radius (R = 0.05 mm) of the lower die insert. Under the 5% clearance condition, the peak von Mises stress of the upper punch insert reached 1,247.3 MPa, while the lower die insert exhibited a maximum stress of 1,116 MPa, corresponding to fatigue lives of 5,592 cycles and 20,450 cycles, respectively. Under the 15% clearance condition, the upper punch stress decreased to 832.91 MPa and the lower die stress to 647.25 MPa, significantly extending the fatigue life to 2.373×10⁵ cycles and 2.337×10⁶ cycles—a marked improvement. Nodal Contact Force decreased monotonically with increasing clearance (195.26 → 125.14 N), consistent with blanking theory. The fatigue life of the lower die was consistently higher than that of the upper punch across both clearance conditions. The lower die, subjected primarily to compressive loading, exhibited inherently smaller stress amplitudes, thereby accumulating fatigue damage at a slower rate compared to the upper punch, which experienced direct impact forces with longer peak stress durations at every stroke.
The results of this study quantify the fatigue life differences between upper and lower dies and identify stress concentration hotspots, providing a valuable reference for the automotive stamping and electronic connector industries to enhance die durability and reduce Total Cost of Ownership (TCO).

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