陳復國臺灣大學：機械工程學研究所廖建智Liao, Chien-ChihChien-ChihLiao2007-11-282018-06-282007-11-282018-06-282007http://ntur.lib.ntu.edu.tw//handle/246246/61431摘 要 近年來，因要求輕薄短小的3C產業快速發展，鎂合金逐漸受到產業界的重視，加速了鎂合金的應用，目前用於沖壓製程之鎂板以AZ31為主，然因其原子結構屬於六方最密堆積(HCP)，在常溫的成形性甚差，必須加溫至200℃以上方具備良好之成形性。但藉由鋰元素之添加，增加了體心立方(BCC)之原子結構，由於BCC可供滑移的系統眾多，因此鎂鋰合金之常溫成形性較佳，可採用一般塑性加工方式成形。 筆記型電腦外殼因為有兩個幾何特徵比較複雜的形狀，所以在沖壓過程中更增加其困難度。其中一個幾何特徵複雜部分是因為底部圓角半徑太小所造成，因而使衝壓過程中產生皺褶及底部圓角破裂情形，而影響此一參數設計有壓料板之力量、胚料板之尺寸大小及壓料阻條之所在位置，然而這個破裂問題是比較容易解決，從漸進式改變衝頭圓角大小、胚料板尺寸之最佳化設計及增加壓料力方式來解決。此外，另一個幾何特徵複雜部分是因為鉸鍊凸緣之位置太過靠近邊緣造成圓角之幾何半徑變化過於劇烈所造成，因此在沖壓過程中會產生鉸鍊凸緣部分有破裂情況，而影響此一設計參數有鉸鍊凸緣與邊緣之距離位置、母模之圓角半徑、衝頭角隅半徑、模擦係數及潤滑劑，此一問題可藉由成形過程中切割局部胚料板方式來解決，至於所切割位置則需使用有限元素分析來模擬。 本研究將進行實際開設模具來進行沖壓為以驗證有限元素之分析結果，因此共開設三組模具，板材使用鎂合金LZ91薄板，模具設計製作參數完全採用有限元素分析結果，並經實際沖壓結果證實使用有限元素分析軟體來進行鎂合金LZ91薄板沖壓之模具設計之正確性。Abstract Due to its lightweight and high specific strength, magnesium alloys have been widely used for structural components. However, because of the hexagonal closed-packed (HCP) crystal structures, magnesium alloys show low ductility at room temperature, and require thermal activation to increase their formability. It is well known that ductility of magnesium alloys can be improved with addition of lithium which develops the formation of body centered-cubic (BCC) crystal structures. The BCC crystal structure gives rise to high formability at room temperature. In the present study, the forming process was examined by the finite element simulations. According to finite element simulation analysis, two features in the notebook case were found to be relatively complex geometrically and were thus more difficult to form in the stamping forming. One of the complex features was caused by the small radius of the bottom, which would cause fracture and wrinkling during the stamping forming process. The process parameters resulting in the fracture defect were blank-holder force, blank size, and the location of draw-bead. However, this fracture defect could be easily removed by changing the punch comer radius, optimum blank size, and decreasing the blank-holder force. The other geometric complexity was caused by the dramatic change in the corner radius when the flange of hinge got too close to the edge of the notebook, which would easily cause the fracture defect around the flange of hinge during stamping forming process. Process parameters causing this defect includes the distance between the flange of hinge and the edge of the notebook, die corner radius, punch comer radius, friction coefficient, and lubricity. This fracture defect around the flange of hinge was eliminated through local trim of blank during the stamping forming process. As for the optimum position distance of local trim blank, it was determined based on the finite element simulation results. To validate the finite element simulation results, an actual stamping process for producing notebook cases was performed. Three sets of tooling were machined to the profiles according to the finite element simulation results. The LZ91 sheets were then stamped into the shapes of notebook cases with the process parameters determined above. The experiment results have validated the finite element analysis for the process design for stamping LZ91 magnesium alloy sheets.目錄 目錄-----------------------------------------------------Ⅰ 圖表目錄-------------------------------------------------Ⅳ 第一章 緒論 1.1 前言--------------------------------------------------1 1.2 研究動機與目的--------------------------------------3 1.3 文獻回顧--------------------------------------------6 1.4 研究方法與步驟--------------------------------------9 1.5 論文總覽-------------------------------------------13 第二章 材料機械性質實驗 2.1. 拉伸試驗------------------------------------------14 2.1.1 應力－應變曲線---------------------------------14 2.1.2 加工硬化指數(n 值)---------------------------21 2.1.3 塑性應變比值(r 值)---------------------------23 2.2 成形極限實驗---------------------------------------26 2.2.1 圓格分析法-----------------------------------26 2.2.2 成形極限曲線之判讀---------------------------27 第三章 筆記型電腦外殼之鉸鍊凸緣沖壓成形製程分析 3.1 載具決定-------------------------------------------29 3.2 CAE模擬方式之建立----------------------------------31 3.2.1有限元素模擬軟體PAM-STAMP簡介------------------31 3.3鉸鍊凸緣成形參數探討--------------------------------33 3.3.1模型幾何外形之建立-----------------------------33 3.2.2外框與成形性之關係-----------------------------36 3.2.3不同沖頭圓角半徑之模擬與探討-------------------37 3.2.4不同凸緣尺寸之模擬與探討-----------------------39 3.2.5不同凸緣R角之模擬與探討------------------------41 3.2.6凸緣R角與凸緣尺寸交互影響之模擬與探討----------43 3.4鉸鍊凸緣沖壓成形深度之探討--------------------------45 3.5鉸鍊凸緣距邊界距離對成形性之影響--------------------47 第四章 筆記型電腦外殼之CAE沖壓模具設計 4.1筆記型電腦外殼模擬模型之建立與初步模擬結果----------50 4.2 CAE沖壓模具設計--先沖側壁再成形凸緣----------------53 4.3 CAE沖壓模具設計--多道次預成形折邊模----------------55 4.3.1第一道次--預成形模具設計----------------------56 4.3.2第二道次--凸緣整形模具設計--------------------74 4.3.3第三道次--折邊模具設計------------------------75 4.3.4第四道次—整形模具設計------------------------80 4.3.5多道次預成形折邊模結論------------------------82 4.4 CAE沖壓模具設計--突破刃(Lancing)模具設計-----------83 4.4.1 Lancing時機之探討----------------------------85 4.4.2 Lancing流速之探討----------------------------90 4.4.3 第二道次整形製程探討-------------------------90 4.4.4 Lancing製程結論------------------------------93 第五章 有限元素模擬實驗驗證 5.1板材來源--------------------------------------------94 5.2簡易模實驗驗證--------------------------------------95 5.2.1 SPCEN模擬結果探討----------------------------98 5.2.2 LZ91模擬結果探討-----------------------------99 5.3多道次預成形折邊模實驗驗證-------------------------101 5.3.1實驗設備與模具-------------------------------101 5.3.2實驗結果探討---------------------------------104 5.3.3不同沖壓製程比較-----------------------------107 5.3.3實際產品外形沖壓試驗-------------------------109 第六章 結論---------------------------------------------111 參考文獻------------------------------------------------1135677373 bytesapplication/pdfen-US鎂合金LZ91有限元素法筆記型電腦外殼鉸鍊凸緣沖壓模具設計Magnesium Alloy LZ91Finite Element Methodnotebook caseflange of hingeDie Design for Stampingthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/61431/1/ntu-96-R94522511-1.pdf