封蓋的落料拉深沖孔復(fù)合模具設(shè)計(jì)-沖壓模含NX三維及18張CAD圖,落料拉深,沖孔,復(fù)合,模具設(shè)計(jì),沖壓,nx,三維,18,cad 中文翻譯 成形模具設(shè)計(jì)中的板料成形數(shù)值模擬與試制模具的比較 A. ANDERSSON? , ? , _ 當(dāng)今，金屬板料成形數(shù)值模擬是一種用于預(yù)測(cè)汽車零部件成形能力的強(qiáng)有力的技巧。與傳統(tǒng)的方法比如使用試制模具，金屬板料成形數(shù)值模擬在模具設(shè)計(jì)中應(yīng)用程度的巨大的增加使實(shí)體模具在制造之前被測(cè)試成為可能。另外一種金屬板料成形模擬的優(yōu)點(diǎn)在于其可利用于工藝設(shè)計(jì)早期階段，例如在最初的設(shè)計(jì)階段。如今，金屬板料成形數(shù)值模擬的結(jié)果的精確度在很大程度上已足夠高，以致于可代替試制模具的使用。在沃爾沃汽車公司，車身部件工廠，該項(xiàng)研究已經(jīng)被啟動(dòng)，金屬板料成形模擬以集成的模塊形式在模具設(shè)計(jì)與模具生產(chǎn)的工藝中被使用。 1 引言 傳統(tǒng)地，試制模具被用于驗(yàn)證某種模具設(shè)計(jì)能否生產(chǎn)滿足要求質(zhì)量的零件。試制模具通常由比生產(chǎn)用模具更便宜的材料制成。這是一種很省時(shí)且節(jié)約成本的方式。但是，如今另外一種更為行之有效的技術(shù)可以使用——金屬板料成形模擬。這種新技術(shù)基于成形工藝的數(shù)值模擬，并且對(duì)于每套實(shí)用模具可以降低10%的成本和15%的生產(chǎn)時(shí)間。金屬板料成形數(shù)值模擬技術(shù)不斷的發(fā)展，并且模擬的結(jié)果越來越精確。在將來，或許可以使用金屬板料成形數(shù)值模擬用于分析更多的工藝。如今，金屬板料成形數(shù)值模擬的結(jié)果的精確度在很大程度上已足夠高可代替試制模具的使用。 2 方法 該研究的目的在于分析和比較金屬板料成形數(shù)值模擬和試制模具在成形模具設(shè)計(jì)中的優(yōu)缺點(diǎn)。此研究中使用的方法基于專為該研究開發(fā)的產(chǎn)品可靠性模板（PSM) (Rundqvist and Sta°hl 2001年)和工藝一致性模板 (PCM)。PSM是一種把工藝中的不同因素（參數(shù)）按目錄編入不同因素組的模板。然后每種因素（參數(shù)）的影響被評(píng)定為0—3等級(jí)?；谀０宓慕Y(jié)果，對(duì)產(chǎn)品工藝有最大影響的參數(shù)可以被篩選出來，然后可以制作折中或是最小化這些影響的優(yōu)先表。PCM是通過高級(jí)專家測(cè)試在實(shí)際生產(chǎn)中對(duì)汽車元器件成形的連續(xù)測(cè)試來分析金屬板料成形數(shù)值模擬、試制模具的結(jié)果，生產(chǎn)零件的質(zhì)量 3 設(shè)計(jì)成形模具的工藝 圖1所示，一種在沃爾沃汽車公司車身部件工廠（VCBC）的開發(fā)一種成形模具的簡(jiǎn)化生產(chǎn)工藝流程。 一種成形模具設(shè)計(jì)的工藝包括試制階段，該階段各種不同的模具設(shè)計(jì)被測(cè)試。這是一個(gè)在模具設(shè)計(jì)工藝中很重要的階段，目的在于驗(yàn)證零件將會(huì)滿足所要求的質(zhì)量。預(yù)測(cè)一種成形操作的結(jié)果是很困難的，但是通過使用金屬板料成形數(shù)值模擬方法使得對(duì)成形操作的結(jié)果有價(jià)值的預(yù)測(cè)成為可能。 零件/工藝最初的設(shè)計(jì) 零件 設(shè)計(jì) 硬質(zhì)模具/工藝設(shè)計(jì) 試制 模具 金屬板料成形數(shù)值模擬 圖1 VCBC設(shè)計(jì)成形模具的工藝方法 3.1 金屬板料成形數(shù)值模擬的使用 金屬板料成形數(shù)值模擬可以被利用到模具設(shè)計(jì)工藝的幾個(gè)階段。 ● 起初設(shè)計(jì)的早期階段，能夠快速驗(yàn)證汽車元器件設(shè)計(jì)的不同的方案 ● 預(yù)測(cè)并且驗(yàn)證成形工藝 ● 改善現(xiàn)有的工藝 3.1.1 金屬板料成形數(shù)值模擬的需求 ● 數(shù)值模擬軟件 ● 零件布局的CAD模型或模具成形表面的CAD模型 ● 描述特定金屬板料材料的參數(shù) ● 工藝參數(shù) ● 工作站（現(xiàn)今個(gè)人計(jì)算機(jī)的發(fā)展快速的提升以致于個(gè)人計(jì)算機(jī)在將來會(huì)成為一種強(qiáng)有力的替代） ● 一名有能力可以操作該軟件并能夠分析數(shù)值模擬結(jié)果的員工 數(shù)值模擬軟件?，F(xiàn)今市場(chǎng)有各種各樣的商業(yè)軟件可供使用。為找到合適的軟件，必須分析所使用的領(lǐng)域。考慮到用戶界面友好性與軟件柔性，軟件包是不同的。 在進(jìn)行該項(xiàng)研究的VCBC，兩種不同的軟件包得以使用。一種是用戶友好的可快速提供結(jié)果的AUTOFORM（2001）。該軟件用于獲取合理的模具集合形狀的反復(fù)的分析工藝。另外一種軟件是LS—DYNA（2001），被用于驗(yàn)證AUTOFORM的結(jié)果。 ● CAD模型。為使用金屬板料成形數(shù)值模擬方法分析零件或者模具設(shè)計(jì)，就需要該零件或者模具的CAD模型。這種模型可以在大多數(shù)CAD軟件中構(gòu)造。例如，在VCBC使用的CATIA軟件。不同的數(shù)值模擬軟件需要不同類型的CAD模型。 ● 材料參數(shù)。單向拉深實(shí)驗(yàn)被用于描述材料參數(shù)。同樣有必要描述材料內(nèi)部斷裂的風(fēng)險(xiǎn)。描述斷裂的數(shù)據(jù)是通過創(chuàng)建成形極限曲線來獲取的。成形極限曲線是一種顯示在斷裂發(fā)生前最大許用應(yīng)力數(shù)值的描繪在基準(zhǔn)應(yīng)力平面上的曲線。更為透徹的描述由Pearce于1991年提出。 ● 工藝參數(shù)。金屬板料成形數(shù)值模擬需要核實(shí)的工藝參數(shù)。 ● 工作站。用于進(jìn)行金屬板料成形數(shù)值模擬的模型通常很大以致于為獲得核實(shí)的運(yùn)算時(shí)間而需要使用工作站。但是，個(gè)人計(jì)算機(jī)技術(shù)的發(fā)展使幾臺(tái)PC聯(lián)網(wǎng)成為可能，這有可能會(huì)是工作站的替代。 ● 有能力的員工。為讀懂金屬板料成形數(shù)值模擬的結(jié)果，能夠輸入正確的數(shù)據(jù)并且擁有理解結(jié)果的能力是狠必要的。這就需要有能力的員工。這種能力應(yīng)該包括成形知識(shí)和數(shù)值模擬知識(shí)這由于考慮到生產(chǎn)工藝與翻譯結(jié)果二者的聯(lián)系。 表1 V-1158.的材料數(shù)據(jù) 壁厚(mm) Rp0.2屈服強(qiáng)度(Mpa) Rm抗拉強(qiáng)度極限 (MPa) n 值 (平均值) R 值 (平均值) 0.8 140 320 0.243 1.76 3.2 金屬板料成形數(shù)值模擬的結(jié)果 金屬板料成形數(shù)值模擬式如下的研究成為可能： ● 壁厚的分配 ● 斷裂的幾率 ● 拉深線 ● 起皺 ● 拉深/沖孔的壓力 ● 表面缺陷 ● 表面的穩(wěn)定性 ● 彈性回復(fù) ● 材料行為 ● 工藝監(jiān)測(cè) ● 內(nèi)部拉深 ● 成形視窗 ● 力（凸模、沖孔） 圖2 壁厚的分配藍(lán)色區(qū)域顯示變薄20%，紅色10% 為驗(yàn)證可能的結(jié)果對(duì)VolvoS80的車身外側(cè)的數(shù)值模擬進(jìn)行了研究。用于該種汽車元器件的材料是一種有著良好成形能力的中碳鋼(V—1158)。材料的參數(shù)如表1所示。 3.2.1 壁厚的分配。 金屬板料成形數(shù)值模擬可以為部件壁厚的分配提供一個(gè)良好的近似值。在汽車工業(yè)對(duì)于考慮到壁厚減少的最大的許用量有要求，以確保在碰撞事故中的安全區(qū)域。 3.2.2 斷裂的幾率 成形工藝過程中可以使用成形極限曲線的方法評(píng)定斷裂的幾率，該幾率已在此部分的最初時(shí)間被描述好。 圖3 斷裂的幾率。 圖中，裂紋以紅色顯示。右側(cè)黑線代表成形極限曲線。同樣顯示數(shù)值模擬的結(jié)果（藍(lán)色點(diǎn)） 圖4 圖中的深藍(lán)色線顯示材料在成形操作時(shí)的流動(dòng)情況。 如果材料流過圓角，零件上就會(huì)出現(xiàn)拉深線。如果拉深線出現(xiàn)在外觀零件的可見表面，該零件就會(huì)因質(zhì)量原因而廢掉。 3.2.3 拉深線 拉深線發(fā)生于當(dāng)一個(gè)可見的零件外部區(qū)域通過圓角滑入當(dāng)成形時(shí)。零件表面一點(diǎn)流動(dòng)方式的曲線在數(shù)值模擬器件即出現(xiàn)這些線。拉深線在外部零件的可見表面是不應(yīng)該出現(xiàn)的。 在描述成形能力的圖5，有足夠應(yīng)變的表面可以看到。通過共同研究這些使預(yù)測(cè)這些表面的穩(wěn)定性成為可能。這是一種簡(jiǎn)化的分寫。一種更為細(xì)致分析將會(huì)包括最終零件的應(yīng)力與應(yīng)變的聯(lián)系。 圖5該圖顯示對(duì)工藝監(jiān)測(cè)的一個(gè)實(shí)例。很容易理解成形工藝期間起皺的擴(kuò)展情況 3.2.4 起皺 可見的起皺在零件上市不允許的。這些可以通過金屬板料成形數(shù)值模擬來監(jiān)測(cè)。 3.2.5 力 為以一種精確的方法測(cè)量工藝，必須要知道哪些力對(duì)成形該零件是必要的。這些力的數(shù)據(jù)可以從金屬板料成形數(shù)值模擬的結(jié)果中獲取。 3.2.6 表面缺陷 汽車外部零件對(duì)可能發(fā)生于成形期間的表面的翹曲很敏感。這些翹曲可能很小但是零件噴涂后仍然可見，這就意味著這個(gè)零件必須被廢棄。這種缺陷可以通過人工檢查到當(dāng)它在表面輕微移動(dòng)的時(shí)候。金屬板料成形數(shù)值模擬通過對(duì)盈利應(yīng)變分配的分析可以被用于監(jiān)測(cè)危險(xiǎn)區(qū)域 3.2.7 表面的穩(wěn)定性 穩(wěn)定的表面的獲得目的為增大零件的剛度以阻止零件的不穩(wěn)定和振動(dòng)。金屬板料成形數(shù)值模擬可以通過對(duì)應(yīng)變分配的分析用于監(jiān)測(cè)危險(xiǎn)區(qū)域。 圖6 上圖顯示成形能力。上圖中的灰色區(qū)域暗指不穩(wěn)定的區(qū)域，粉紅色區(qū)域則為起皺區(qū)域。 在下圖中指示受壓小約束表面標(biāo)記為藍(lán)色。如果這些區(qū)域位于外觀零件的可見表面，則存在產(chǎn)生不穩(wěn)定區(qū)域的可能性。 3.2.8 彈性回復(fù) 彈性回復(fù)可以被用于描述在制件被取出成形模具后發(fā)生的一種幾何形狀的變化。這種幾何形狀的變化導(dǎo)致該零件與其他零件進(jìn)行裝配式的不匹配。 3.2.9 工藝監(jiān)測(cè) 在金屬板料成形數(shù)值模擬中，這種工藝可以通過動(dòng)畫的方式細(xì)致地而執(zhí)行。 3.2.10 拉深 為使材料的消耗最小，優(yōu)化毛坯的外形是很重要的。金屬板料成形數(shù)值模擬可以通過分析內(nèi)拉深工藝最大程度的充分利用坯料。 3.2.11 成形視窗 成形視窗可以被描述為工藝參數(shù)的許用變動(dòng)范圍。目的在于保證生產(chǎn)零件的質(zhì)量。 3.3 試制模具的使用 試制模具當(dāng)工藝方法設(shè)計(jì)需要驗(yàn)證時(shí)被使用（如圖1）?；谶@種設(shè)計(jì)試制模具用鋅合金鑄造。例如，快速原型零件從這種試制模具中生產(chǎn)出來。試制模具與生產(chǎn)模具制件有幾點(diǎn)不同。因此，在試制模具中生產(chǎn)如此多的零件是不可能的。另外一點(diǎn)不同在于試制模具比生產(chǎn)模具要便宜更多。但是，由于兩種形式模具件的區(qū)別的存在，對(duì)于在這兩種形式模具中生產(chǎn)處的零件有同樣的質(zhì)量沒有保證。 圖7 藍(lán)綠色線顯示坯料閉合后的板料位置。拉深線即可以通過與底部區(qū)域的線的比較測(cè)量。 4 產(chǎn)品可靠性模板(PSM) PSM可以用于確定哪個(gè)參數(shù)對(duì)工藝的穩(wěn)定性有巨大的影響。同樣使確定某種影響的程度成為可能。這就為對(duì)大多數(shù)極其困難的問題提供了數(shù)值上的幫助。這些極困難的問題就特別的有趣當(dāng)他們被解決的時(shí)候因?yàn)樗麄兪亲罱档托实摹?duì)PSM更為細(xì)致的描述由Rundqvist 和 Sta°hl 于2001年提出。一個(gè)PSM被使用的例子由. Pettersson于1991年提出，在該例子中在VCBCPSM被用于分析不同的工藝。 5 結(jié)果 使用試制模具的技巧已經(jīng)與金屬板料成形數(shù)值模擬的技巧從兩個(gè)方面進(jìn)行了比較。第一方面是預(yù)測(cè)生產(chǎn)工藝不同的參數(shù)的能力，在第3部分已經(jīng)提到。第二方面是驗(yàn)證哪個(gè)工藝參數(shù)應(yīng)該加以研究的能力。 5.1 預(yù)測(cè)工藝與生產(chǎn)工藝一致性的研究 PCM提供試制模具與數(shù)值模擬考慮生產(chǎn)工藝的相關(guān)性透徹的比較。表2顯示應(yīng)用的不同領(lǐng)域不同的技巧與能力預(yù)測(cè)在生產(chǎn)工藝中的行為。表2 的數(shù)值已經(jīng)通過與高級(jí)成形專家深入的研究而確定。 表2中，使用到下面的等級(jí) 5 結(jié)果顯示與生產(chǎn)工藝非常一致。4 4 結(jié)果顯示與生產(chǎn)工藝良好的一致。個(gè)別地方可能有分歧。 3 結(jié)果顯示與生產(chǎn)工藝在大多數(shù)地方較好的一致。 2 結(jié)果顯示與生產(chǎn)工藝在某些地方較好的一致。需要對(duì)結(jié)果進(jìn)行間接地理解。 1 結(jié)果顯示與生產(chǎn)工藝完全沒有一致性。它不能被用于工藝預(yù)測(cè)或者是檢驗(yàn)。 對(duì)于表2的結(jié)論包括如下 ● 斷裂的幾率與實(shí)際斷裂間的差異在于斷裂幾率顯示區(qū)域沒有發(fā)生裂紋而是縮頸出現(xiàn)的地方。 ● 參數(shù)“材料特點(diǎn)”指的是預(yù)測(cè)零件質(zhì)量的能力依賴于材料質(zhì)量的波動(dòng)。 ● 工藝監(jiān)測(cè)使控制在工藝過程中不同參數(shù)的如何改變成為可能。 ● 成形視窗對(duì)于監(jiān)測(cè)工藝對(duì)波動(dòng)的敏感程度是一個(gè)輔助工具。 ● 模具沖裁力的數(shù)值基于可以測(cè)量試制模具中的成形力的假設(shè)。 表2 工藝一致性模板（PCM）：產(chǎn)品工藝的一致性 參數(shù) 工藝 壁厚分配 斷裂幾率 斷裂 拉深線 起皺 表面缺陷 表面的穩(wěn)定性 彈性回復(fù) 材料性能 工藝監(jiān)測(cè) 內(nèi)部拉深 凸模沖壓力 拉深量 沖裁力 成形視窗 數(shù)值模擬 4 4 4 4 4 2 2 2 4 4 4 3 2 2 4 試制模具 3 3 4 3 4 4 4 3 2 3 4 3 4 3 3 5.2 對(duì)于生產(chǎn)工藝中何種因素可以分析的研究 依據(jù)PSM模型，將對(duì)生產(chǎn)工藝有特殊性的不同因素分成不同因素組的放啊已經(jīng)被運(yùn)用在此次研究中。在先前的研究中(Andersson et al. 1999年)，關(guān)于這兩種鋁成形的技巧的不同因素已經(jīng)被研究了。在這項(xiàng)研究中為方便的比較這兩種技巧由于預(yù)測(cè)和驗(yàn)證被考慮這項(xiàng)工作得以修正。 在表3中，使用到下面的等級(jí) 3 結(jié)果顯示對(duì)生產(chǎn)工藝極好的預(yù)見性。 2 結(jié)果顯示對(duì)生產(chǎn)工藝直接的預(yù)見性。 1 結(jié)果顯示對(duì)生產(chǎn)工藝間接地預(yù)見性。 0 結(jié)果根本不能預(yù)測(cè)生產(chǎn)工藝。 5.3 測(cè)試能力的局限/擴(kuò)大 對(duì)表2和表3的分析顯示出在模具設(shè)計(jì)工藝過程中使用金屬板料成形數(shù)值模擬的幾個(gè)優(yōu)點(diǎn)。然而，金屬板料成形數(shù)值模擬的最大優(yōu)點(diǎn)之一在于其使對(duì)不同零件、模具或是工藝的設(shè)計(jì)的測(cè)試成為可能，從而潛在的節(jié)省了時(shí)間和金錢。在這個(gè)方面，試制模具更為局限和昂貴，這就意味著僅有極少數(shù)量的試制模具被生產(chǎn)出來。試制模具的使用對(duì)測(cè)試有助于可能性的局限，然而，金屬板料成形數(shù)值模擬的使用有助于測(cè)試可行性范圍的擴(kuò)大。 表3 利用PSM預(yù)測(cè)生產(chǎn)工藝中的不同因素（參數(shù)）的比較的可能性考慮試制模具中的測(cè)量力的可能性 因素分組 金屬板料成形數(shù)值模擬 試制模具 A 模具 A1 模具幾何外形 2 2 A2 微觀形狀/表面 0 1 A3 拉深筋 1 2 B 材料 B1 壁厚分配 2 2 B2 斷裂的幾率 2 2 B3 拉深線 2 2 B4 起皺 2 2 B5 表面缺陷 1 2 B7 表面穩(wěn)定性 1 2 B8 彈性回復(fù) 1 2 B9 材料性能 2 2 B10 內(nèi)部拉深 2 2 B11 表面粗糙度、擦損 0 2 C 工藝 C1 沖壓速度 1 2 C2 溫度 0 1 C3 潤(rùn)滑 1 2 C4 凸模沖壓力 2 2 C5 沖孔沖壓力 2 2 C8 成形視窗 2 2 D 人為因素 D1 控制 1 2 D2 變換頻率 1 2 E 維護(hù) E2 沖壓力維護(hù) 1 1 F 特殊因素 F1 模具潔凈成素 0 2 G 進(jìn)口設(shè)備 G1 操控設(shè)備 1 3 6 結(jié)論 金屬板料成形數(shù)值模擬的使用與試制模具的使用相比可極大地減少金錢和時(shí)間的花費(fèi)。要點(diǎn)在于研究的數(shù)值模擬與實(shí)際生產(chǎn)工藝參數(shù)之間的良好的一致性。金屬板料成形數(shù)值模擬對(duì)于預(yù)測(cè)和驗(yàn)證成形工藝也要比試制模具高級(jí)。 當(dāng)開始使用金屬板料成形數(shù)值模擬時(shí)，所需投入相對(duì)較小。投入工作站和軟件是很必要的，這些大概花費(fèi)500，000SEK。此外，擁有有能力勝任金屬板料成形模擬工作的員工同樣是比不可少的。與投資一套試制模具（每套50，000SEK）相比，如果在合適的時(shí)候使用金屬板料成形數(shù)值模擬在降低金錢和時(shí)間消耗方面的益處是很明顯的。 正如起初是所提到的，現(xiàn)今金屬板料成形數(shù)值模擬結(jié)果的精確性已足夠高可以在很大程度上代替試制模具的使用。模具設(shè)計(jì)工藝中試制模具的使用對(duì)于某些時(shí)候?qū)τ隍?yàn)證某些工藝參數(shù)可能是必要的，但是如下的優(yōu)點(diǎn)則很緊密的和金屬板料成形數(shù)值模擬聯(lián)系在一起。 對(duì)于極重要的最初階段工藝的更為深入的研究; 對(duì)于零件，模具和工藝設(shè)計(jì)測(cè)試的更高的柔性; 對(duì)于何時(shí)應(yīng)該采用試制模具，使試制模具更具成效的更為深入的理解; 對(duì)于更大膽的設(shè)計(jì)汽車提供更大的潛力; 對(duì)于應(yīng)用于汽車零部件的新材料的測(cè)試的更為可靠; 鑒于更前衛(wèi)的設(shè)計(jì)，更低的耗費(fèi)，和更短的交貨時(shí)間以得到更強(qiáng)的競(jìng)爭(zhēng)力。 7 總結(jié) 在該項(xiàng)研究得以進(jìn)行的VCBC，金屬板料成形數(shù)值模擬現(xiàn)今已經(jīng)是模具設(shè)計(jì)工藝的一個(gè)自然的部分。金屬板料成形數(shù)值模擬自從1995年起被使用，并且試驗(yàn)一直很好。現(xiàn)如今所有的工藝如此的復(fù)雜以致于基于數(shù)值模擬的試驗(yàn)選擇成形條件是困難的。在VolvoS80開發(fā)期間，該車是第一款全部使用數(shù)值模擬技術(shù)的汽車項(xiàng)目，當(dāng)?shù)谝淮伪煌度雽?shí)際生產(chǎn)時(shí)在工藝問題上有很大的降低得以完成。 致 謝 作者想要表達(dá)對(duì)VCBC的同事，此項(xiàng)工作期間提供大量的數(shù)據(jù)信息和有趣的討論。同樣的感謝他的導(dǎo)師Jan-Eric Sta°hl教授（產(chǎn)品與材料工程分院，蘭德大學(xué)），和他的合作導(dǎo)師Kjell Mattiasson教授（Chalmers University of Technology)，感謝他們的支持以及對(duì)該文章的修正。 57 英文資料 Comparison of sheet-metal-forming simulation and try-out tools in the design of a forming tool A. ANDERSSON Today, sheet-metal-forming simulation is a poAwerful technique for predicting the formability of automotive parts. Compared with traditional methods such as the use of try-out tools, sheet-metal-forming simulation enables a significant increase in the number of tool designs that can be tested before hard tools are manufactured. Another advantage of sheet-metal-forming simulation is the possibility to use it at an early stage of the design process, for example in the preliminary design phase.Today, the accuracy of the results in sheet-metal-forming simulation is high enough to replace the use of try-out tools to a great extent. At Volvo Car Corporation, Body Components, where this study has been carried out, sheet-metal-forming simulation is used as an integrated part in the process of tool design and tool production. 1 Introduction Traditionally, try-out tools are used to verify that a certain tool design will produce parts of the required quality. The try-out tools are often made of a cheaper material (e.g. kirksite) than production tools in order to reduce the try-out costs. This is a very time-consuming and cost-consuming method. However, today another more efficient technique is available—sheet-metal-forming simulation. This new technique is based on the simulation of the forming process, and could result in a cost reduction of factor 10 and a time reduction of factor 15 for each hard tool. Sheet-metal-forming simulation technology is constantly developing and the results of the simulations are more and more accurate. In the future it will also be possible to analyse more processes using sheet-metal-forming simulations. Today, the accuracy of the results in sheetmetal- forming simulation is high enough to replace the use of try-out tools to a great extent. 2 Method The purpose of this study is to analyse and compare the benefits and drawbacks of the use of sheet-metal-forming simulation and try-out tools in the design of forming tools. The method employed in this study is based on the Production Reliability Matrix (PSM) (Rundqvist and Sta°hl 2001) together with a Process Correspondence Matrix (PCM) that has been developed especially for this study. The PSM is a matrix that categorizes the effects of different factors (parameters) in the process into different factor groups. The effect of each factor (parameter) is then assessed according to a scale of 0–3. Based on the results of the matrix, the parameters that have the most considerable effects on the production process can be extracted, and a priority list for neutralizing or minimizing these effects can be made. The PCM has been developed through extensive interviews of senior experts in automotive component forming to analyse the correspondence between the results of sheet-metalforming simulations, the try-out tool and the quality of produced parts in actual production. 3 Process for designing a forming tool Figure 1 shows a simplified flow of the production process of developing a forming tool at Volvo Car Corporation, Body Components (VCBC). The process of the design of a forming tool includes a try-out phase where different designs of the tool are tested. This is a very important stage in the tool design process,in order to verify that the part will fulfil the required quality. It is very difficult to predict the result of a forming operation, but by using sheet-metal-forming simulation there is a possibility to gain valuable insight into the outcome of the forming operation. 3.1 Use of sheet-metal-forming simulation Sheet-metal-forming simulation can be used in several stages of a tool design process: ●early in the preliminary design phase, to enable rapid verification of different proposals for the design of automotive components ●to improve an existing process. Preliminarydesign of part Part layout Hard forming tools/Process design Try-out tools Sheet metal forming simulation Figure 1. Process for designing a forming tool at VCBC. 3.1.1. Requirements for sheet-metal-forming simulation. Sheet-metal-forming simulation requires the following: ●Simulation software. ●A computer-aided design (CAD) model of the part layout or a CAD model of the forming surfaces of the tool. ●Parameters for description of the specified sheet-metal material. ●Process parameters. ●Workstations (today the development of the personal computer (PC) is rapidly advancing so that PCs will be a strong alternative in the future). ●A competent staff that can handle the software and analyse the results of the simulation. Simulation software. Today there is a variety of commercial software available on the market. In order to find suitable software, the area of use must be analysed. The software package is different with regard to user-friendliness and flexibility. At VCBC, where this study was performed, two different software packages are used. One is Autoform (2001), which is user-friendly and provides fast results. This software is used for the iterative process of finding the proper tool geometry. The other software is LS-DYNA (2001), which is used at VCBC to verify the results of Autoform. CAD model. In order to analyse a part or a tool design using sheet-metal-forming simulation, a CAD model of the part or tool is needed. This model can be created in most CAD programs, for instance CATIA, which is used at VCBC. Different simulation software demand different qualities of the CAD models. Material parameters. Uniaxial tensile tests are used to describe the material parameters. There is also a need for describing the risk of fracture in the material. Data regarding risk for fracture are obtained by creating a forming limit curve. The forming limit curve is a curve in the plane of principal strains that indicates the maximum allowed strain values before fracture occurs. A more thorough description is presented in Pearce (1991). Process parameters. Sheet-metal-forming simulation requires proper process parameters (e.g. drawbeads). Workstations. The simulation models that are used in sheet-metal-forming simulation are generally so large that they require a workstation in order to achieve reasonable calculation times. However, the development of PCs enables the clustering of several PCs, which can be an alternative to workstations. Competent personnel. In order to interpret the results of a sheet-metal-forming simulation, it is necessary to enter the correct input data and possess the ability to understand the results. This requires competent personnel. The competence should consist of both forming knowledge and simulation knowledge since that gives a natural connection between the production process and the interpretation of the results. Thickness(mm) Rp0.2yield strength(Mpa) Rm ultimate tensile strength (MPa) n value (average) R value (average) 0.8 140 320 0.243 1.76 Table 1 Material data for V-1158. 3.2. Results of a sheet-metal-forming simulation Sheet-metal-forming simulation enables the study of: ●Thickness distribution. ●Risk of fracture. ●Draw lines. ●Wrinkles. ●Drawbeads/ blankholder pressure. ●Surface defects. ●Stability of the surface. ●Springback. ●Material behaviour. ●Process surveillance. ●Draw in. ●Forming window. ●Forces (punch, blankholder). In order to demonstrate possible results, a simulation of a Body Side Outer from a Volvo S80 has been studied. The material used for this automotive component is a mild steel with good formability (V-1158). Material data are presented in table 1. 3.2.1. Thickness distribution. The sheet-metal-forming simulation can provide a good approximation of the thickness distribution for a part (see figure 2). In the automotive industry there are requirements concerning the maximum allowable reduction in thickness, in order to ensure safety margins in the event of a crash. Figure 2. Thickness distribution. The scale shows blue for 20% thinning and red for 10% thickening. 3.2.2. Risk for fracture. Risk for fracture during the forming process could be evaluated by means of a forming limit curve, which was described earlier in this section. Figure 3. Risk for fracture. In this image, cracks are shown in red. To the right is the forming limit curve represented by the black line. Shown also are the results of the simulations (blue points) 3.2.3. Draw lines. Draw lines occur when a visible section of an exterior part has been gliding over a radius during forming. A plot of how a point on the part surface moves during the simulation (see figure 4) illustrates these lines. Draw lines are not acceptable on a visible surface on an exterior part. In figure 5, which describes formability, surfaces with enough strains to be stable can be seen. By studying these images together it is possible to estimate the stability of the surfaces. This is a simplified analysis. A more detailed analysis would include the interaction between stresses and strains for the complete part. Figure 4. The blue dark line in the image shows how the material has flowed during the forming operation. If the material has flowed over a radius, a draw line will appear on the part. If the draw line appears on a visible surface of an exterior part, the part will be rejected for quality reasons. Figure 5. The images show an example of surveillance of the process. It is easy to follow how the wrinkles develop during the forming process. 3.2.4 Wrinkles. Visible wrinkles are not allowed on a part. These can be detected with sheet-metal-forming simulation (see figure 6). 3.2.5 Forces. In order to dimension the process in an accurate way, it is necessary to know which forces are necessary to form the part. The data for these forces can be obtained from the results of a sheet-metal-forming simulation. 3.2.6 Surface defects. Exterior automotive parts are sensitive to deflections of the surface that can occur during forming. These deflections can be very small but can still be visible after the part is painted, which means that the part must be scrapped.The defects can be detected by the human hand as it moves gently across the surface.Sheet-metal-forming simulation can be used for detecting risk areas through analysis of the stress strain distribution.。 3.2.7 Stability of the surface. Stable surfaces are required in order to increase the stiffness of the part to prevent the part from becoming unstable and vibrating. Sheet-metal-forming simulation can be used for detecting risk areas through analysis of the strain distribution. Figure 6 describes a simplified analysis. A more detailed analysis would include the interaction between stresses and strains for the complete part.。 Figure 6. The upper image shows the formability. The grey areas in the upper image indicate unstable surfaces and the pink area indicates wrinkles. In the lower image the surfaces with small strains are marked blue, which indicates compression. If these areas are located on a visible surface of an exterior part, there is a risk for unstable areas. 3.2.8 Springback. Springback is a phenomenon that could be described as a change in geometry that occurs after the parts have been removed from the forming tool. This g eometry change causes mismatch for the part when it is assembled with other parts. 3.2.9 Process surveillance. In sheet-metal-forming simulation, the process can be followed in detail by means of animations. Figure 5 illustrates this. 3.2.10 Draw in. To minimize material consumption, it is important to optimize the shape of the blank. Sheet-metal-forming simulation can facilitate optimization of the blank by analysing the draw in (see figure 7). 3.2.11 Forming window. A forming window could be described as the allowable variation of the process parameters in order to keep the quality of the produced parts. 3.3. Use of try-out tools Try-out tools are used when the design of the process is to be verified (see figure 1).Based on this design the try-out tools are then cast in kirksite, for example. Prototype parts are then produced from this try-out tool. There are several differences between a try-out tool and a production tool. One is that the try-out tool wears out much faster than a production tool. Therefore, it is not possible to produce so many parts in a try-out tool. Another difference is that a try-out tool is much cheaper than a production tool. However, since there are differences between the two types of tools, there is no guarantee that the parts produced in the two types of tools will have the same quality.. The PSM can be used to determine which parameters have significant effects on the stability of the process. It is also possible to determine the extent of an effect. This provides valuable help in the identification of the most severe problems. These severe problems are especially interesting since they are the most cost-effective when solved. A more detailed description of the PSM is presented by Rundqvist and Sta°hl (2001). An example where the PSM is applied is presented in Pettersson (1991), where the PSM is used to analyse different processes at VCBC. Figure 7. The cyan line shows the sheet position after blankholder closing. The draw in can then easily be measured by a comparison with the line in the bottom position. 5 Result The technique of using try-out tools has been compared with the technique of using sheet-metal-forming simulation from two aspects. The first aspect is a comparison of the ability to predict the different parameters of the production process, mentioned in section 3. The second aspect is the ability to verify which process parameters should be studied. 5.1 Study of agreement of predicted process with production process The PCM allows a clear comparison between try-out tools and simulation regarding correspondence with the production process. Table 2 presents the different fields of applications for the different techniques together with the ability to predict behaviour in the production process. The values in table 2 have been determined through extensive interviews with senior forming experts. In table 2 the following scale is used: 5 The results show perfect agreement with the production process. 4 The results show good agreement with the production process. Special cases can deviate. 3 The results show good agreement in most cases with the production process. 2 The results show good agreement in certain cases with the production process. Indirect interpretation of the results is needed. 1 The results show no agreement with the production process. It cannot be used for process prediction or verification. Comments on table 2 include the following: ● The difference between risk for fracture and actual fracture is that risk for fracture shows areas that have not cracked but where necking has appeared. ●The parameter ‘Material characteristics’ refers to the ability to predict the quality of the part depending on variation in the material quality. ● Process surveillance enables the monitoring of how different parameters change during the process. ●The forming window is an aid for detecting how sensitive the process is to disturbances. ●The values for the tool forces are based on the assumption that it is possible to measure the forces in the try-out press. process Thickness distribution Risk for fracture Fracture Draw lines Wrinkles Surface defects Stability of the surface springback Material properties Process surveillance Draw in Force-punch Draw beads Blankholder force Forming window simulation 4 4 4 4 4 2 2 2 4 4 4 3 2 2 4 Try-out tool 3 3 4 3 4 4 4 3 2 3 4 3 4 3 3 Table 2. Process Correspondence Matrix (PCM): correspondence with the production process. 5.2 Study of which factors in the production process are possible to analyse The concept of grouping different factors that are typical for the production process into different factor groups has been used in this study according to the PSM model. In a previous study (Andersson et al. 1999), different factors concerning the forming of aluminium were studied. This work has been modified in order to facilitate a comparison between the two techniques for prediction and verification considered in this study; namely, sheet-metal-forming simulation and try-out tools. See table 3 for the results. In table 3 the following scale is used: 3 The results show perfect prediction of production process. 2 The results show direct prediction of production process. 1 The results show indirect prediction of production process. 0 The results cannot predict production process at all. 5.3. Restriction /expansion of test possibilities An analysis of tables 2 and 3 shows several advantages of using sheet-metal-simulation in the tool design process. However, one of the biggest advantages of sheetmetal- forming simulation is that it enables the testing of many different designs of the part, tool or process, which generates substantial savings in costs and time. In this respect, try-out tools are more limited and expensive, which means that only a minimum number of try-out tools are produced. The use of try-out tools contributes to a restriction of test possibilities while the use of sheet-metal-forming simulation contributes to an expansion in test possibilitie 6. Conclusions The use of sheet-metal-forming simulation leads to a significant reduction in both cost and time compared with the use of try-out tools. The requirement is that the respective parameter for study (see section 3.1.2) demonstrates good correspondence between simulation and actual production processes. Sheet-metal-forming simulation is also superior to try-out tools with regard to predicting and verifying the forming process. The investment requirements are relatively small when starting to implement sheet-metal-forming simulation. It is necessary to invest in a workstation and software, which cost about SEK 500,000. In addition, it is necessary to have competent personal for handling the sheet-metal-forming simulation. Compared with the investment for one try-out tool (.SEK 500,000 per tool), it is clear that there is a lot to gain in reducing cost and time if sheet-metal-forming simulation is used when it is suitable. Factor gruups Sheet-metal-forming simulation Thy-out tools A Tooling A1 Tool geometry 2 2 A2 Microgeomertril/Surface 0 1 A3 Drawbeads 1 2 B Material B1 Thickness distribution 2 2 B2 Risk for fraction 2 2 B3 Draw lines 2 2 B4 Wrinkles 2 2 B5 Surface defects 1 2 B7 Surface stability 1 2 B8 Springback 1 2 B9 Material properities 2 2 B10 Draw in 2 2 B11 Surface roughness/galling 0 2 C Process C1 Press velocity 1 2 C2 Temperature 0 1 C3 Lubrication 1 2 C4 Forces-punch 2 2 C5 Forces-blankholder 2 2 C8 Forming-window 2 2 D Human factor D1 Control 1 2 D2 Change frequency 1 2 E Maintenace E2 Press maintenace 1 1 F Special factors F1 Tool cleaning 0 2 G Misc equipment G1 Handling equipment 1 3 Table 3. The possibilities to predict different factors (parameters) in the production process compared in a Production Reliability Matrix (PSM) Assuming the possibility of measuring forces in the try-out tool. As stated earlier, today the accuracy of the results in sheet-metal-forming simulation is high enough to replace the use of try-out tools to a great extent. The use of try-out tools in the tool design process may be necessary for some time to come to verify some process parameters, but the following advantages are closely associated with sheet-metal-forming simulation: ● Deeper insight into the process at significantly earlier stages. ● Greater flexibility in testing designs for the part, the