化妝品蓋子注射模具設(shè)計(jì)【一模十腔】【說明書+CAD】

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畢業(yè)答辯課件 設(shè)計(jì)題目：化裝品蓋 指導(dǎo)老師：高光亮 塑料摸設(shè)計(jì) 零件名稱：化妝品蓋 設(shè)計(jì)要求：表面無劃痕、裂紋、缺陷 生產(chǎn)批量：中批量。未注公差等級(jí)MT4級(jí)精度要求化妝品蓋摸具（如圖） 一．塑件的工藝性分析 1塑件的原材料分析 朔料品種 結(jié)構(gòu)特點(diǎn) 使用溫度 化學(xué)穩(wěn)定性 性能特點(diǎn) 成型特點(diǎn) 結(jié)論 ABS 曲面結(jié)構(gòu)表面精度要求較好，光滑，無痕跡 耐溫，耐腐蝕性能較好，耐氣候性較差 有一定的化學(xué)穩(wěn)定性，耐酸堿等 有良好的耐化學(xué)腐蝕及表面硬度，有良好的加工性能和染色性能 ，有良好的絕緣性，耐油性，和耐水性 流動(dòng)性好，ABS有一定的硬度和尺寸穩(wěn)定性，易于成型加工，連續(xù)工作溫度為70度左右，熱變形溫度為93度左右 控制模具溫度，一般在50-70度為宜，模具應(yīng)用耐磨鋼，并淬火； ABS易吸水，成型加工前應(yīng)進(jìn)行干燥處理； ABS易產(chǎn)生熔接痕，故模具設(shè)計(jì)時(shí)應(yīng)盡量減少澆注系統(tǒng)對(duì)流料的阻力； ABS在溫度升高時(shí)黏度升高，所以成型時(shí)壓力高，故脫模斜度宜稍大為2度。 2 塑件的尺寸精度分析 因塑件重要尺寸只有和，尺寸精度需與化裝品瓶的尺寸相配合，尺寸較小，公差未注，故取精度等級(jí)為一般精度MT3，其它塑件的尺寸精度要求不高，所有尺寸可以按MT4查取公差，在模具設(shè)計(jì)和制造過程中較容易控制這些尺寸。（參考《塑料模設(shè)計(jì)及制造》附錄E）且壁厚均為0.8mm，塑件成型性能良好，其主要尺寸公差計(jì)算結(jié)果如下： 型心尺寸： 型腔尺寸： 3塑件的表面質(zhì)量分析 該塑件要求外觀美觀，色澤鮮艷，外表面沒有斑點(diǎn)和印痕，而內(nèi)表面有較高的尺寸和粗糙度要求。 4塑件的結(jié)構(gòu)工藝性分析 該塑件的尺寸較小，整體結(jié)構(gòu)較簡(jiǎn)單，卻帶有曲面特征，根據(jù)塑件的工作要求和表面特征及材料性能，故選一般精度等級(jí)四級(jí)。 二．成型設(shè)備的選擇 1．計(jì)算塑件的體積和重量 塑件體積：V=2.388 cm 塑件質(zhì)量：根據(jù)有關(guān)手冊(cè)查得：ρ=1.05g/cm 所以，塑件的重量為： M=V×ρ=2.388×1.05=2.5074g 2．計(jì)算澆注系統(tǒng)的體積 V 根據(jù)塑件形狀及要求采用一模兩件的模具結(jié)構(gòu)，參考模具設(shè)計(jì)手冊(cè)初選注射機(jī)：XS-ZY-60 3.確定成型工藝參數(shù) （1）塑件模成型工藝參數(shù)的確定 查表得出工藝參數(shù)見下表，試模時(shí)可根據(jù)實(shí)際情況作適當(dāng)調(diào)整。 ABS 硬熱和干燥 溫度50~70 成型時(shí)間 注射時(shí)間 3~5 時(shí)間3~5S 保壓時(shí)間 15~30 料筒溫度 后段 210~240 冷卻時(shí)間 15~30 中段 230~280 總周期 33~65 前段 240~285 螺桿轉(zhuǎn)速 28 噴嘴溫度 240~250 后處理 方法 紅外線燈 模具溫度 50~170 溫度 鼓風(fēng)烘箱100~110 注射壓力p/Ha 70~90 時(shí)間r/h 8~12 三．注射模的結(jié)構(gòu)設(shè)計(jì) 1．分型面的選擇 在選擇分型面是，根據(jù)分型面的選擇原則，考慮不影響其外觀質(zhì)量以及成型后能順利脫模取出塑件，設(shè)計(jì)分型面如下圖所示： 2．型腔數(shù)目的確定及型腔的排列 該塑件采用一模十件的結(jié)構(gòu) 3．澆注系統(tǒng)的設(shè)計(jì) （1）主流道的設(shè)計(jì) 根據(jù)選用的XS-ZY-60型號(hào)注射即的相關(guān)尺寸得 噴嘴前端孔徑： 噴嘴前端球面半徑： 根據(jù)模具主流道與噴嘴的關(guān)系 取主流道球面半徑：R=10mm 取主流道小端直徑：4.98mm （2） 分流道的設(shè)計(jì) 分流道選用半圓形截面：半徑R=2mm 流道表面粗糙度3.2 （3）澆口的設(shè)計(jì) 根據(jù)澆口的位置選擇要求，盡量縮短流動(dòng)距離，避免熔體破裂現(xiàn)象引起塑件的缺陷，澆口應(yīng)開設(shè)在塑件壁厚出，不影響外觀質(zhì)量等要求，選用點(diǎn)澆口 4． 推出機(jī)構(gòu)的設(shè)計(jì) 結(jié)合制品的結(jié)構(gòu)特點(diǎn)，模具型腔的結(jié)構(gòu)采用了整體式型腔板，這種結(jié)構(gòu)工作過程中精度高，并且在此模具中容易加工得到， 在推出機(jī)構(gòu)中采用廠組合式推桿，如圖中零件頂桿，這種結(jié)構(gòu)主要是防止推桿在于作過程中受到彎曲力或側(cè)向壓力而折斷。這里采用設(shè)計(jì)30根推桿，全部與z形的拉料桿固定在頂桿固定板。 5、模具制造與裝配要點(diǎn) 模具采用龍記大水口系統(tǒng)標(biāo)準(zhǔn)模架2525規(guī)格，材料為45鋼，調(diào)質(zhì)到230~270HBS。整套模具零件均采用標(biāo)準(zhǔn)零件，定模板（A板）采用進(jìn)口淬火不銹鋼，由于型腔的尺寸較小，所以定模板在加工中心直接加工成型。導(dǎo)柱采用正裝形式。 2.4模具工作過程 開模時(shí)，定模板與動(dòng)模從分型面處分開，動(dòng)模向后運(yùn)動(dòng)，Z形拉料桿拉住澆注系統(tǒng)的冷凝料及塑料制品一起向后運(yùn)動(dòng)。當(dāng)主流道中的凝料完全拉出一段距離后， 注射機(jī)的頂桿作用在推板上，使得澆注系統(tǒng)中的的冷凝料和小長(zhǎng)桿制件在Z形拉料桿和推桿的作用下一起推出，完成脫模過程。合模時(shí)，注射機(jī)頂桿復(fù)位，推桿固定板在復(fù)位桿的作用下，回到初始狀態(tài)，動(dòng)、定模完全閉合。回到成型位置，進(jìn)入下一個(gè)工作循環(huán)。 金 華 職 業(yè) 技 術(shù) 學(xué) 院 JINHUA COLLEGE OF PROFESSION AND TECHNOLOGY 畢業(yè)教學(xué)環(huán)節(jié)成果 （2009 屆） 題 目 化妝盒蓋子注射模具設(shè)計(jì) 學(xué) 院 專 業(yè) 班 級(jí) 學(xué) 號(hào) 姓 名 指導(dǎo)教師 2010年 05月 10 日 化妝品蓋子注射模具設(shè)計(jì) 摘要：隨著人們生活水平的提高，市場(chǎng)上的化妝品越來越多，化妝品的增多帶來了化妝品蓋在市場(chǎng)上的需求空間，這就使得化妝品蓋的生產(chǎn)商們需要花更多的心思在蓋的設(shè)計(jì)上面。化妝品蓋的設(shè)計(jì)好壞間接的影響了化妝品的銷售； 因此，化妝品蓋的設(shè)計(jì)是否新奇獨(dú)特，美觀成了化妝品蓋生產(chǎn)者所首要考慮的問題。 關(guān)鍵詞： 化妝品蓋子 注射模具 設(shè)計(jì) Cosmetics cover injection mold desigFirst, abstract Summary:Along with the people living standard enhancement, in the market cosmetics are more and more many, the cosmetics increased bring the cosmetics to cover in the market the demand space, this caused the producers which the cosmetics covered to need flowered more thoughts in above the design which covered. The cosmetics cover design quality indirect influence cosmetics sale; Therefore, the cosmetics cover the design novel is whether unique, artisticly became the cosmetics to cover the producer most important consideration the question. Key word： Cosmetics cover Injects the mold Design 目錄 摘要 2 英文摘要 2 引言 2 一、正文 5 1. 分析設(shè)計(jì)任務(wù)書 5 2．分析塑件制品圖及實(shí)祥 5 3. 初步確定型腔數(shù)目 13 4. 注塑機(jī)的選擇 13 5. 澆注系統(tǒng)的設(shè)計(jì) 22 6. 確定主要零件結(jié)構(gòu)尺寸選模架 14 7. 成型零部件的設(shè)計(jì) 16 8. 導(dǎo)向機(jī)構(gòu)的設(shè)計(jì) 21 9. 冷卻系統(tǒng)的設(shè)計(jì) 27 10.模具排氣槽的設(shè)計(jì) 22 11.校核 31 二、結(jié)論 32 三、謝辭 33 四、參考文獻(xiàn) 33 引 言 隨著中國(guó)當(dāng)前的經(jīng)濟(jì)形勢(shì)的日趨好轉(zhuǎn)，在“實(shí)現(xiàn)中華民族的偉大復(fù)興”口號(hào)的倡引下，中國(guó)的制造業(yè)也日趨蓬勃發(fā)展；而模具技術(shù)已成為衡量一個(gè)國(guó)家制造業(yè)水平的重要標(biāo)志之一，模具工業(yè)能促進(jìn)工業(yè)產(chǎn)品生產(chǎn)的發(fā)展和質(zhì)量提高，并能獲得極大的經(jīng)濟(jì)效益，因而引起了各國(guó)的高度重視和贊賞。在日本，模具被譽(yù)為“進(jìn)入富裕的原動(dòng)力”，德國(guó)則冠之為“金屬加工業(yè)的帝王”，在羅馬尼亞則更為直接：“模具就是黃金”。可見模具工業(yè)在國(guó)民經(jīng)濟(jì)中重要地位。我國(guó)對(duì)模具工業(yè)的發(fā)展也十分重視，早在1989年3月頒布的《關(guān)于當(dāng)前國(guó)家產(chǎn)業(yè)政策要點(diǎn)的決定》中，就把模具技術(shù)的發(fā)展作為機(jī)械行業(yè)的首要任務(wù)。 近年來，塑料模具的產(chǎn)量和水平發(fā)展十分迅速，高效率、自動(dòng)化、大型、長(zhǎng)壽命、精密模具在模具產(chǎn)量中所戰(zhàn)比例越來越大。注塑成型模具就是將塑料先加在注塑機(jī)的加熱料筒內(nèi)，塑料受熱熔化后，在注塑機(jī)的螺桿或活塞的推動(dòng)下，經(jīng)過噴嘴和模具的澆注系統(tǒng)進(jìn)入模具型腔內(nèi)，塑料在其中固化成型。 本次畢業(yè)設(shè)計(jì)的主要任務(wù)是鎖蓋注塑模具的設(shè)計(jì)。也就是設(shè)計(jì)一副注塑模具來生產(chǎn)鎖蓋塑件產(chǎn)品，以實(shí)現(xiàn)自動(dòng)化提高產(chǎn)量。針對(duì)鎖蓋的具體結(jié)構(gòu)，通過此次設(shè)計(jì)，使我對(duì)點(diǎn)澆口單分型面模具的設(shè)計(jì)有了較深的認(rèn)識(shí)。同時(shí)，在設(shè)計(jì)過程中，通過查閱大量資料、手冊(cè)、標(biāo)準(zhǔn)、期刊等，結(jié)合教材上的知識(shí)也對(duì)注塑模具的組成結(jié)構(gòu)（成型零部件、澆注系統(tǒng)、導(dǎo)向部分、推出機(jī)構(gòu)、排氣系統(tǒng)、模溫調(diào)節(jié)系統(tǒng)）有了系統(tǒng)的認(rèn)識(shí)，拓寬了視野，豐富了知識(shí)，為將來獨(dú)立完成模具設(shè)計(jì)積累了一定的經(jīng)驗(yàn)。 一.正文 1. 分析設(shè)計(jì)任務(wù)書 任務(wù)書條理清晰，適合我們學(xué)生的設(shè)計(jì)步驟，引導(dǎo)學(xué)生合理的設(shè)計(jì)模具，為我們提供了良好的起步，按照任務(wù)書的要求，我們經(jīng)過幾天的分析與思考，說明書的技術(shù)要求，制品的生產(chǎn)批量及所用注射機(jī)的型號(hào)和規(guī)格已經(jīng)基本定型。 2. 分析塑件制品圖及實(shí)祥 2.1 產(chǎn)品技術(shù)要求和工藝分析 零件名稱：化妝盒蓋 圖號(hào)：01 材料：PE(聚乙烯) 生產(chǎn)批量：中批量 零件圖 2.1.1產(chǎn)品技術(shù)要求：表面無劃痕、裂紋、缺陷。 2.2塑件的工藝分析 朔料品種 結(jié)構(gòu)特點(diǎn) 使用溫度 化學(xué)穩(wěn)定性 性能特點(diǎn) 成型特點(diǎn) 結(jié)論 ABS 曲面結(jié)構(gòu)表面精度要求較好，光滑，無痕跡 耐溫，耐腐蝕性能較好，耐氣候性較差 有一定的化學(xué)穩(wěn)定性，耐酸堿等 有良好的耐化學(xué)腐蝕及表面硬度，有良好的加工性能和染色性能 ，有良好的絕緣性，耐油性，和耐水性 流動(dòng)性好，ABS有一定的硬度和尺寸穩(wěn)定性，易于成型加工，連續(xù)工作溫度為70度左右，熱變形溫度為93度左右 控制模具溫度，一般在50-70度為宜，模具應(yīng)用耐磨鋼，并淬火； ABS易吸水，成型加工前應(yīng)進(jìn)行干燥處理； ABS易產(chǎn)生熔接痕，故模具設(shè)計(jì)時(shí)應(yīng)盡量減少澆注系統(tǒng)對(duì)流料的阻力； ABS在溫度升高時(shí)黏度升高，所以成型時(shí)壓力高，故脫模斜度宜稍大為2度。 2.2.1分析塑件使用材料的種類及工藝特征 該塑件材料選用ABS（丙烯腈—丁二烯—苯乙烯共聚物）。ABS有良好的耐化學(xué)腐蝕及表面硬度 ，有良好的加工性和染色性能。 ABS無毒、無味、呈微黃色，成型的塑件有較好的光澤。密度為1.02~1.05g/cm3。ABS有良好的機(jī)械強(qiáng)度和一定的耐磨性、耐寒性、耐油性、耐水性、化學(xué)穩(wěn)定性和電氣性能。水、無機(jī)鹽、堿和酸類對(duì)ABS幾乎無影響。ABS不溶于大部分醇類及烴類溶劑，但與烴長(zhǎng)期接觸會(huì)軟化溶脹。ABS有一定的硬度和尺寸穩(wěn)定性，易與成型加工，經(jīng)過調(diào)色可配成任何顏色。ABS的缺點(diǎn)是耐熱性不高，連續(xù)工作溫度為70oC左右，熱變形溫度為93oC左右，且耐氣候性差，在紫外線作用下易發(fā)脆。ABS在升溫時(shí)粘度增高，所以成型壓力高，故塑件上的脫模斜度宜稍大；ABS易吸水，成型加工前應(yīng)進(jìn)行干燥處理；ABS易產(chǎn)生熔接痕，模具設(shè)計(jì)時(shí)應(yīng)注意盡量少澆注系統(tǒng)對(duì)料流的阻力；在正常的成型條件下，壁厚、熔料溫度對(duì)收縮率影響極小。 2.2.2分析塑件的結(jié)構(gòu)工藝性 該塑件尺寸中等，整體結(jié)構(gòu)較簡(jiǎn)單.多數(shù)都為曲面特征。除了配合尺寸要求精度較高外，其他尺寸精度要求相對(duì)較低，但表面粗糙度要求較高，再結(jié)合其材料性能，故選一般精度等級(jí)：IT5級(jí)。 2.2.3工藝性分析 為了滿足制品表面光滑的要求與提高成型效率采用潛伏式澆口。該澆口的分流道位于模具的分型面上，而澆口卻斜向開設(shè)在模具的隱蔽處。塑料熔體通過型腔的側(cè)面或推桿的端部注入型腔，因而塑件外表面不受損傷，不致因澆口痕跡而影響塑件的表面質(zhì)量與美觀效果。 塑件的工藝參數(shù)：模具溫度： 注射壓力： 保壓力： 注射時(shí)間： 保壓時(shí)間： 冷卻時(shí)間： 成型周期： 3.初步確定型腔數(shù)目 根據(jù)塑件的結(jié)構(gòu)及尺寸精度要求,該塑件在注射時(shí)采用一模十腔，綜合考慮澆注系統(tǒng)，模具結(jié)構(gòu)的復(fù)雜程度等因素考慮以下兩種型腔排列方式。 方案一 方案二 方案二分流道為非平衡式布置，加工難度大，需多次修模校正，方案一分流道為對(duì)稱式布置，較容易實(shí)現(xiàn)均衡地進(jìn)料，據(jù)以上原因，采用方案一。 4.注射機(jī)的選擇 4.1 塑件體積的計(jì)算 根據(jù)零件的三維模型，利用三維軟件直接可查詢到塑件的體積 V=2.388 cm 澆注系統(tǒng)的體積： V2=2.375cm 塑件與澆注系統(tǒng)的總體積為: V=2.388+2.375=4.763 cm 計(jì)算塑件的質(zhì)量：查手冊(cè)取密度ρ=1.05g/cm 塑件體積：V=2.388 cm 塑件質(zhì)量：根據(jù)有關(guān)手冊(cè)查得：ρ=1.05g/cm 所以，塑件的重量為： M=V×ρ=2.388×1.05=2.5074g 4.2按注射機(jī)的最大注射量確定型腔數(shù)目 根據(jù) （4-1） 得 (4-2) 注射機(jī)最大注射量的利用系數(shù)，一般取0.8; 注射機(jī)最大注射量，cmз或g; 澆注系統(tǒng)凝料量，cmз或g； 單個(gè)塑件體積或質(zhì)量，cmз或g； 4.3估算澆注系統(tǒng)的體積，其初步設(shè)定方案如下 10.1cmз 4.4 查表文獻(xiàn)4、2得選用 XS-ZY-125型號(hào)注射機(jī) 5.澆注系統(tǒng)的設(shè)計(jì) 澆注系統(tǒng)的設(shè)計(jì)原則：澆口位置應(yīng)盡量選擇在分型面上，以便于模具加工及使用時(shí)澆口的清理；澆口位置距型腔各個(gè)部位的距離應(yīng)盡量一致，并使其流程為最短；澆口的位置應(yīng)保證塑料流入型腔時(shí)，對(duì)著型腔中寬敞、壁厚位置，以便于塑料的流入;避免塑料在流入型腔時(shí)直沖型腔壁,型芯或嵌件,使塑料能盡快的流入到型腔各部位,并避免型芯或嵌件變形;盡量避免使制件產(chǎn)生熔接痕,或使其熔接痕產(chǎn)生在之間不重要的位置;澆口位置及其塑料流入方向,應(yīng)使塑料在流入型腔時(shí),能沿著型腔平行方向均勻的流入,并有利于型腔內(nèi)氣體的排出。 5.1主流道的設(shè)計(jì) 主流道是指澆注系統(tǒng)中從注射機(jī)噴嘴與模具處到分流道為止 塑料熔體 流動(dòng)通道 根據(jù)選用的XS-ZY-125型號(hào)注射機(jī)的相關(guān)尺寸得 噴嘴前端孔徑：； 噴嘴前端球面半徑：； 根據(jù)模具主流道與噴嘴的關(guān)系 取主流道球面半徑：； 取主流道小端直徑：； 為了便于將凝料從主流道中取出，將主流道設(shè)計(jì)成圓錐形，起斜度為，取其值為，經(jīng)換算得主流道大端直徑為 圖5.1 主流道示意圖 5.2 分流道的設(shè)計(jì) 分流道選用圓形截面：直徑D=10mm 流道表面粗糙度 5.3分型面的選擇設(shè)計(jì)原則 1） 分型面應(yīng)選在塑件外形最大輪廓處； 2） 分型面的選擇應(yīng)有利于塑件的順利脫模； 3） 分型面的選擇應(yīng)保證塑件的精度要求； 4） 分型面的選擇應(yīng)滿足塑件的外觀質(zhì)量要求； 5） 分型面的選擇要便于模具的加工制造； 6） 分型面的選擇應(yīng)有利于排氣； 7） 分型面的選擇還要考慮到型腔在分型面上投影面積的大小。 其分型面如圖5.2 圖5 .2 分型面示意圖 5.4澆口的設(shè)計(jì) 根據(jù)澆口的位置選擇要求，盡量縮短流動(dòng)距離，避免熔體破裂現(xiàn)象引起塑件的缺陷，澆口應(yīng)開設(shè)在塑件壁厚處等要求 澆口設(shè)計(jì)如圖5.3 圖5.3 澆口示意圖 5.5冷料穴的設(shè)計(jì) 冷料穴是澆注系統(tǒng)的結(jié)構(gòu)組成之一。冷料穴的作用是容納澆注系統(tǒng)流道中料流的前鋒冷料，以免這些冷料注入型腔。這些冷料既影響熔體充填的速度，有影響成型塑件的質(zhì)量，另外還便于在該處設(shè)置主流道拉料桿的功能。注射結(jié)束模具分型時(shí)，在拉料桿的作用下，主流道凝料從定模澆口套中被拉出，最后推出機(jī)構(gòu)開始工作，將塑件和澆注系統(tǒng)凝料一起推出模外。 其設(shè)計(jì)如下圖（Z字型） 圖5.4 冷料穴示意圖 5.6排氣系統(tǒng)的設(shè)計(jì) 利用配合間隙排氣是最常見也是最經(jīng)濟(jì)的，更具有使用性。 6.確定主要零件結(jié)構(gòu)尺寸選模架 模架的選擇，圖6.1 圖6.1 模架模型圖 7.成型零部件的設(shè)計(jì) 型腔、型芯工作尺寸計(jì)算 ABS塑料的收縮率是0.3%--0.8% 平均收縮率: =（0.3%--0.8%）/2=0.55% 型腔內(nèi)徑： =30.15MM 型腔深度： =25.12MM 型芯外徑： =28.54MM 型芯深度： =24.32MM 型腔徑向尺寸（mm ）; - 塑件外形基本尺寸（mm）; -塑件平均收縮率； -塑件公差 -成形零件制造公差，一般取1/4—1/6； -塑件內(nèi)形基本尺寸（ mm）; -型芯徑向尺寸（mm）; -型腔深度（mm）； -塑件高度（mm） -型芯高度（mm）； -塑件孔深基本尺寸（mm）； 模架與型腔型芯的計(jì)算： 確定型腔尺寸：270*300*50，型腔為定模板直接加工中心加工成型 型芯鑲件尺寸：200*195*59 8.導(dǎo)向機(jī)構(gòu)的設(shè)計(jì) 導(dǎo)向機(jī)構(gòu)的作用：1）定位作用；2）導(dǎo)向作用；3）承受一定的側(cè)向壓力 8.1導(dǎo)柱的設(shè)計(jì) 長(zhǎng)度 導(dǎo)柱導(dǎo)向部分的長(zhǎng)度應(yīng)比凸模端面的高度高出8—12 cm，以免出現(xiàn)導(dǎo)柱末導(dǎo)正方向而型芯先進(jìn)入型腔的情況。 形狀 導(dǎo)柱前端應(yīng)做成錐臺(tái)形，以使導(dǎo)柱能順利地進(jìn)入導(dǎo)向孔。 材料 導(dǎo)柱應(yīng)具有硬而耐磨的表面和堅(jiān)韌而不易折斷的內(nèi)芯，因此多采用20鋼（經(jīng)表面滲碳淬火處理），硬度為50—55HRC。 8.2導(dǎo)套的結(jié)構(gòu)設(shè)計(jì) 材料 用與導(dǎo)柱相同的材料制造導(dǎo)套，其硬度應(yīng)略低與導(dǎo)柱硬度，這樣可以減輕磨損，一防止導(dǎo)柱或?qū)桌? 形狀 為使導(dǎo)柱順利進(jìn)入導(dǎo)套，導(dǎo)套的前端應(yīng)倒圓角。導(dǎo)向孔作成通孔，以利于排出孔內(nèi)的空氣。 8.3推出機(jī)構(gòu)的設(shè)計(jì) 根據(jù)塑件的形狀特點(diǎn)， 模具型腔在定模部分，型心在動(dòng)模部分。其推出機(jī)構(gòu)可采用推桿推出機(jī)構(gòu)、推件板推出機(jī)構(gòu)。由于分型面有臺(tái)階，為了便于加工，降低模具成本，我們采用推桿推出機(jī)構(gòu)，推桿推出機(jī)構(gòu)結(jié)構(gòu)簡(jiǎn)單，推出平穩(wěn)可靠，雖然推出時(shí)會(huì)在塑件上留下頂出痕跡，但塑件底部裝配后使用時(shí) 不影響外觀，設(shè)立五個(gè)推桿平衡布置，既達(dá)到了推出塑件的目的，又降低了加工成本。注：推桿推出塑件，推桿的前端應(yīng)比型腔或型心平面高出0.1-0.2mm 采用推桿推出，推桿截面為圓形，推桿推出動(dòng)作靈活可靠，推桿損壞后也便于更換。 推桿的位置選擇在脫模阻力最大的地方，塑件各處的脫模阻力相同時(shí)需均勻布 置，以保證塑件推出時(shí)受力均勻，塑件推出平穩(wěn)和不變形。根據(jù)推桿本身的剛度和 強(qiáng)度要求，采用四根推桿推出。推桿裝入模具后，起端面還應(yīng)與型腔底面平齊或搞 出型腔0.05—0.1cm. 推件力的計(jì)算: 對(duì)于一般塑件和通孔殼形塑件，按下式計(jì)算，并確定其脫模力（Q）： (8-1) 式中 --型芯或凸模被包緊部分的斷面周長(zhǎng)（cm）; --被包緊部分的深度（cm）; --由塑件收縮率產(chǎn)生的單位面積上的正壓力，一般取 ； --磨擦系數(shù)，一般??； --脫模斜度； L=240.12*2+280.15=520.27MM H=24.32MM Q=520.27MM*24.32MM*10MPA(0.1*COS0.5-SIN0.5) =113.877(KN) 推桿的設(shè)計(jì): ①推桿的強(qiáng)度計(jì)算 查《塑料模設(shè)計(jì)手冊(cè)之二》由式5-97得 d=（） (8-2) d——圓形推桿直徑cm ——推桿長(zhǎng)度系數(shù)≈0.7 l——推桿長(zhǎng)度cm n——推桿數(shù)量 E——推桿材料的彈性模量N/(鋼的彈性模量E=2.1107N/) Q——總脫模力 取 。 ②推桿壓力校核 查《塑料模設(shè)計(jì)手冊(cè)》式5-98 = (8-3) 取320N/mm2 < 推桿應(yīng)力合格，硬度HRC50～65 9.冷卻系統(tǒng)的設(shè)計(jì) 冷卻水回路布置的基本原則： a) 冷卻水道應(yīng)盡量多，b) 截面尺寸應(yīng)盡量大； c) 冷卻水道離模具型腔表面的距離應(yīng)適當(dāng)； d) 適當(dāng)布置水道的出入口； e) 冷卻水道應(yīng)暢通無阻； f) 冷卻水道的布置應(yīng)避開塑件易產(chǎn)生熔接痕的部位； 由以上原則我們可以確定冷卻水道的布置情況，以及冷卻水道的截面積 本塑件在注射成型機(jī)時(shí)不要求有太高的模溫因而在模具上可不設(shè)加熱系統(tǒng)。是否需要冷卻系統(tǒng)可作如下設(shè)計(jì)算計(jì)。 設(shè)定模具平均工作溫度為，用常溫的水作為模具冷卻介質(zhì)，其出口溫度為。 9.1 求塑件在硬化時(shí)每小時(shí)釋放的熱量 查表3-26得ABS的單位流量為 得 = 9.2 求冷卻水的體積流量V 由式3-41得： (9-1) 查表3-27可知所需的冷卻水管直徑較小。 由上述可知，設(shè)計(jì)冷卻水道直徑為8符合要求。 10.模具排氣槽的設(shè)計(jì) 當(dāng)塑料熔體充填型腔時(shí)，必須順序地排出型腔及澆注系統(tǒng)內(nèi)的空氣及塑料受熱而產(chǎn)生的氣體。如果氣體不能被順利排出，塑料會(huì)由于填充不足而出現(xiàn)氣泡、接縫或表面輪廓不清等缺陷，甚至氣體受壓而產(chǎn)生高溫，使塑料焦化。特別是對(duì)大型塑件、容器類和精密塑件，排氣槽將對(duì)它們的品質(zhì)帶來很大的影響，對(duì)于在高速成行中排氣槽的作用更為重要。我們的塑件并不是很大，而且不屬于深型腔類零件，因此本方案設(shè)計(jì)在分型面之間、推桿預(yù)模板之間及活動(dòng)型芯與模板之間的配合間隙進(jìn)行排氣，間隙值取0.04㎜。 11.校核 11.1整體式圓形型腔壁厚度的計(jì)算 按剛度條件計(jì)算: 設(shè)想用通過型腔軸線的兩平面截面取側(cè)壁，得到一個(gè)單位寬度長(zhǎng)條，該長(zhǎng)條可以看作一個(gè)一端固定、一端外伸的懸臂梁，。由于長(zhǎng)條的寬度取得很小，梁的截面可近似視為矩形。由于該梁承受均勻分布載荷，故最大饒度產(chǎn)生在外伸一端，起值為： (10-1) 式中 --型腔材料彈性模量； --梁的慣性矩，其中，； s—側(cè)壁厚度。 應(yīng)使，則取為一單位寬度，可求得： (10-2) 得 校核條件成立 11.2整體式圓形型腔底板厚度的計(jì)算 按剛度條件計(jì)算: 整體式圓形型腔底板可視為周邊固定的圓板，在型腔內(nèi)熔體壓力作用下，最大饒度亦產(chǎn)生在底板中心，其數(shù)值為： (10-3) 應(yīng)使，則 得 校核條件成立 11.3注射機(jī)有關(guān)工藝參數(shù)的校核 1）鎖模力與注射壓力的校核 (10-4) --注射時(shí)型腔壓力 查參考文獻(xiàn)得 30MPa --塑件在分型面上的投影面積（） --澆注系統(tǒng)在分型面上的投影面積（） --注射機(jī)額定鎖模力，按GB XS-ZY-125型注射機(jī)額定鎖模力為900 得 得 得 符合條件 故選 XS-ZF-125注射機(jī)成立 11.4模具厚度H與注射機(jī)閉和高度 注射機(jī)開模行程應(yīng)大于模具開模時(shí)，取出塑件（包括澆注系統(tǒng)）所需的開模距離 即滿足下式 (10-5) 式中 --注射機(jī)最大開模行程，mm； --推出距離（脫模聚居），mm； --包括澆注系統(tǒng)在內(nèi)的塑件高度，mm； Sk=72+45=117 條件成立 二．結(jié)論 歷經(jīng)近一個(gè)月的畢業(yè)設(shè)計(jì)即將結(jié)束，敬請(qǐng)各位老師對(duì)我的設(shè)計(jì)過程作最后檢查。 在這次畢業(yè)設(shè)計(jì)中通過參考、查閱各種有關(guān)模具方面的資料，請(qǐng)教各位老師有關(guān)模具方面的問題，特別是模具在實(shí)際中可能遇到的具體問題，使我在這短暫的時(shí)間里，對(duì)模具的認(rèn)識(shí)有了一個(gè)質(zhì)的飛躍。模具在當(dāng)今社會(huì)生活中運(yùn)用得非常廣泛，掌握模具的設(shè)計(jì)方法對(duì)我們以后的工作和發(fā)展有著十分重要的意義。 從陌生到開始接觸，從了解到熟悉，這是每個(gè)人學(xué)習(xí)事物所必經(jīng)的一般過程，我對(duì)模具的認(rèn)識(shí)過程亦是如此。經(jīng)過一個(gè)月的努力，我相信這次畢業(yè)設(shè)計(jì)一定能為三年的求學(xué)生涯劃上一個(gè)圓滿的句號(hào)，為將來的事業(yè)奠定堅(jiān)實(shí)的基礎(chǔ)。 在這次設(shè)計(jì)過程中得到了朱永強(qiáng)等指導(dǎo)老師以及許多同學(xué)的幫助，使我受益匪淺。在此，對(duì)關(guān)心和指導(dǎo)過我的各位老師和幫助過我的同學(xué)表示衷心的感謝! 三年的學(xué)習(xí)即將結(jié)束，畢業(yè)設(shè)計(jì)是其中最后一個(gè)環(huán)節(jié)，是對(duì)以前所學(xué)的知識(shí)及所掌握的技能的綜合運(yùn)用和檢驗(yàn)。隨著我國(guó)經(jīng)濟(jì)的迅速發(fā)展，采用模具的生產(chǎn)技術(shù)得到愈來愈廣泛的應(yīng)用。在完成三年的學(xué)習(xí)、生產(chǎn)實(shí)習(xí)，我熟練地掌握了機(jī)械制圖、機(jī)械設(shè)計(jì)、熱處理、計(jì)算機(jī)輔助設(shè)計(jì)等專業(yè)基礎(chǔ)課和專業(yè)課方面的知識(shí)，我對(duì)于模具特別是塑料模具的設(shè)計(jì)步驟有了一個(gè)全新的認(rèn)識(shí)，豐富了各種模具的結(jié)構(gòu)和動(dòng)作過程方面的知識(shí)，在指導(dǎo)老師的協(xié)助和講解下，同時(shí)查閱了很多相關(guān)資料并親手拆裝了一些典型的模具模型，明確了模具的一般工作原理、制造、加工工藝。并利用因特網(wǎng)查閱了大量設(shè)計(jì)資料，在設(shè)計(jì)過程中，本人運(yùn)用了大量的計(jì)算機(jī)輔助設(shè)計(jì)，通過對(duì)此塑件模具的設(shè)計(jì)，本人更加熟練了對(duì)UG和AutoCAD的運(yùn)用，同時(shí)，學(xué)習(xí)了軟件新的功能，如Moldflow Plastic Advisers和EMX插件。由于本人設(shè)計(jì)水平有限，在設(shè)計(jì)過程中難免有錯(cuò)誤之處，敬請(qǐng)各位老師批評(píng)指正。 三．謝辭 本次畢業(yè)設(shè)計(jì)是對(duì)我近三年來所學(xué)的專業(yè)知識(shí)的一次大檢驗(yàn)，使我能夠?qū)⒁郧八鶎W(xué)的知識(shí)更加融會(huì)貫通，加深了對(duì)專業(yè)知識(shí)的理解，為以后的工作打下了堅(jiān)實(shí)的基礎(chǔ)。通過這次畢業(yè)設(shè)計(jì)，我了解了注塑模具設(shè)計(jì)的全過程，對(duì)零件加工工藝分析的過程有了深刻的認(rèn)識(shí)，鍛煉了我分析問題和獨(dú)立思考解決問題的能力。 在朱永強(qiáng)老師的細(xì)心指導(dǎo)，這次的畢業(yè)設(shè)計(jì)非常順利，在畢業(yè)設(shè)計(jì)過程中幫我解答疑難問題，以及引導(dǎo)我的設(shè)計(jì)思路和方法，以及各位任課老師平時(shí)的教導(dǎo)，感謝模具實(shí)習(xí)期間各位老師的指點(diǎn)，，也感謝謝同學(xué)們平時(shí)的關(guān)懷與幫助，如果沒有你們的細(xì)心幫助，我的畢業(yè)設(shè)計(jì)也就不會(huì)那么成功。沒有你們的引導(dǎo)，我也許不會(huì)這么用功的學(xué)習(xí)，也不會(huì)有我今天的成績(jī)，在此，我表示忠心的感謝！謝謝大家！ 由于本人的能力有限，有不足的地方請(qǐng)各個(gè)老師評(píng)點(diǎn)。 四．參考文獻(xiàn) 《塑料模具設(shè)計(jì)與制造》 高等教育出版社 2004 齊衛(wèi)東 主編 《塑料成型工藝與模具設(shè)計(jì)》 機(jī)械工業(yè)出版社 2001屈華昌 主編 《型腔模具設(shè)計(jì)與制造》 化學(xué)工業(yè)出版社 2003章飛主編 《模具設(shè)計(jì)指導(dǎo)》 機(jī)械工業(yè)出版社 2003史鐵梁 主編 《塑料模具技術(shù)手冊(cè)》機(jī)械工業(yè)出版社（《塑料模具技術(shù)手冊(cè)》編委會(huì)編） 《塑料模具設(shè)計(jì)》 中國(guó)科學(xué)技術(shù)出版社 （馬金駿 編著） 《塑料注射模具設(shè)計(jì)實(shí)用手冊(cè)》 航空工業(yè)出版社 （宋玉恒 主編） 《數(shù)字化模具制造技術(shù)》 化學(xué)工業(yè)出版社 （許鶴峰 閆光榮 編著） 23 編號(hào)： 畢業(yè)設(shè)計(jì)(論文)外文翻譯 （原文） 學(xué) 院： 機(jī)電工程學(xué)院 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 韋良華 學(xué) 號(hào)： 1000110129 指導(dǎo)教師單位： 機(jī)電工程學(xué)院 姓 名： 陳虎城 職 稱： 助教 2014年 5 月 26 日  a r t i c l e i n f o Article history: Received 25 October 2010 Received in revised form 12 January 2011 Accepted 14 January 2011 Available online 21 January 2011 Keywords: Microcellular injection molding Plastic foaming Swirl-free surface a b s t r a c t Microcellular injection molding is the manufacturing method used for producing foamed plastic parts.Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability. l Introduction The commercially available microcellular injection molding process (a.k.a. the MuCell Process) consists of four distinctive steps, namely, gas dissolution, nucleation, cell growth, and shaping [1]. In the gas dissolution stage, polymer in the injection barrel is mixed with supercritical fluid (SCF) nitrogen, carbon dioxide, or another type of gas using a special screw which is designed to maximize the mixing and dissolving of the gas in the polymer melt. During injection, a large number of nucleation sites (orders of magnitude higher than conventional foaming processes) are formed by a rapid and substantial pressure drop as the polymer/gas solution is injected into the mold cavity, thus causing the formation of cells (bubbles). During the rest of the injection molding cycle, cells continue to grow to fill and pack out the mold and subsequently compensate for the polymer shrinkage as the material cools inside the mold. The cell growth is driven by the amount and spatial distribution of the dissolved gas. The cell growth is also controlled by processing conditions such as melt pressure and temperature as well as material properties such as melt strength and gas solubility. Finally, the shaping of the part takes place inside the mold until the mold opens allowing the part to be ejected. Since the microcellular injection molding process was invented, there have been numerous studies on process, material, and technical developments aimed at materializing the full process potential. According to previous studies [1-5], microcellular injection molding offers a number of advantages such as cost savings, weight reduction, ease in processing due to low viscosity, and outstanding dimensional accuracy. Due to these advantages, the microcellular injection molding process has been used in many industries such as automotive, electrical goods, and home appliances using a broad range of thermoplastics. Despite these advantages, however, the surface imperfections associated with microcellular injection molded partsdsuch as unique gas flow marks, referred to as swirl marks throughout this paper, and a lack of smoothnessdstill remain one of the main drawbacks surrounding microcellular injection molding. In order to eliminate or reduce these surface imperfections there have been several studies attempted, as reported in Refs. [6-14]. Some researchers have focused on temperature modification of the mold surface to improve the surface quality of microcellular injection molded parts [6-8]. With polymeric foam, it was found that bubbles forming at the advancing melt front are first stretched by the fountain flow behavior toward the mold surface and subsequently dragged against the mold wall causing swirl marks [9]. During the filling stage of polymer melts, keeping the mold wall temperature high enough for bubbles at the mold surface to beeliminated improves the surface quality of microcellular injection molded parts. By controlling the mold temperature rapidly and precisely using mold temperature control units or other kinds of thermal or surface heating devices, microcellular foamed plastics with glossy and swirl-free surfaces can be produced. There have also been efforts to eliminate the swirl marks on microcellular injection molded parts without any mold temperature controller. In particular, it was proposed that inserting an insulator onto the mold wall might help keeping the interface temperature between the mold and the polymer melt high. This technique basically yields the same result as temperature modification of the mold [10]. Thermal analysis and experimental results prove that the addition of an insulator layer on the mold can improve the surface quality of microcellular injection parts [11]. Another method of producing parts with an improved surface quality leads to a microcellular co-injection molding process [12]. In this technique, a proper amount of solid skin material is injected prior to the injection of a foaming core material. This can yield a sandwiched (solid skinefoamed coreesolid skin) structure with a surface finish similar to a conventionally molded component while partially maintaining the advantages of microcellular injection molding. Another approach for improving the surface quality of microcellular injection molded parts is the gas counter pressure process [13,14]. In this process, a high-pressure gas is injected into the mold prior to the polymer/gas solution to suppress cell nucleation and bubble growth while the polymer/gas solution is being injected into the mold cavity. Toward the end of injection, counter gas pressure is released and bubbles begin to form within the cavity. Since a majority of the part surface is already solidified, gas flow marks are eliminated. In spite of these efforts to improve the surface quality, there have been difficulties in applying the microcellular injection molding process in industries requiring parts with high surface qualities because these techniques entail additional equipment which results in high costs or maintenance. There have been no reported studies on improving the surface quality of microcellular injection molded parts without any additional equipment or modification to existing equipment. This paper proposes a novel approach to improve the surface quality of microcellular injection molded parts by controlling the cell nucleation rate. In this study, the cell nucleation rate was dramatically lowered or delayed by controlling the degree of supersaturation so that cell nucleation was delayed during the filling stage. After the polymer/gas solution volumetrically filled the mold cavity, intentionally delayed nucleation occurred and bubbles formed in the polymer matrix, except on the surface where the material had already solidified upon touching the mold surface. Theoretical background and experimental results are described in this paper. Microstructure, surface profile, surface roughness,mechanical properties, and dimensional stability are also investigated in this study. 2. Theoretical 2.1. Nucleation theory for polymeric foams In polymeric foams, nucleation refers to the initial stage of the formation of gas bubbles in the polymeregas solution. For nucleation, gas bubbles must overcome the free energy barrier before they can survive and grow to macroscopic size [15]. According to classical nucleation theories [16-18], the nucleation rate is controlled by the macroscopic properties and states of the polymer and gas such as solubility, diffusivity, surface tension, gas concentration, temperature, and the degree of super saturation. One representative equation for the nucleation rate of polymeric foams was reported by Colton and Suh [19,20]. In addition to the mathematical representation, they also verified their nucleation theory experimentally for a batch foaming process using a high pressure vessel. The nucleation equation for microcellular foams dominated by the classical nucleation theory [16e18] can be expressed as N=fCex(-?G**/kT) where N is the nucleation rate, f is the frequency of atomic molecular lattice vibration, C is the concentration of gas molecules, k is the Boltzmann’s constant, T is the absolute temperature, and ?G**is the activation energy barrier for nucleation. According to previous studies [19,20], the nucleation rate of polymeric foams is composed of two components: a homogeneous term and a heterogeneous term. The activation energy for homogeneous nucleation is given by ?Ghom**?16πr33?P2 where g is the surface energy of the bubble interface and ?P.is assumed to be the gas saturation pressure. More precisely, ?P=|Pr'-Pr| where Pr` is the pressure that is exerted in a high pressure vessel and Pr is the pressure of the supersaturated vapor in the sample [16]. That is, DP is the pressure difference between the pressure that is applied to the sample and the pressure of the supersaturated vapor in the sample. When the pressure that saturates the gas in a high pressure vessel is suddenly released to trigger the so-called thermodynamic instability by rendering the sample into the supersaturated state, Pr` becomes 1 bardso low compared to Pr that DP can be approximated as Pr. On the other hand, the activation energy for heterogeneous nucleation is affected by a geometric factor that depends on the contact (wetting) angle between the polymer and the particle and can be expressed as ?Ghet**=?Ghom**×f(θ) (3a) fθ=12-34cosθ+14cosθ3 (3b) where f(q) is a geometric factor that is dependent upon the contact angle, θ, of the interface between the polymer and a second phase, and has values of less than or equal to 1. For a typical wetting angle of around 200 on the interface between a solid particle and the polymer melt, the geometric factor is 2.7X10-3, suggesting that the energy barrier for heterogeneous nucleation can be reduced by three orders of magnitude with the presence of an interface [20,21]. l 2.2. Nucleation theory for microcellular injection molding In the batch foaming process, the theory of Colton and Suh was verified by their experiments. Due to the large difference between the pressure exerted in a high pressure vessel and the pressure of the supersaturated vapor in the sample, the gas pressure dissolved in the polymer, the?P in the Gibbs free energy equation, can be approximately assumed to be the saturation gas pressure. The assumption that ?P is the gas saturation pressure is fairly reasonable in a batch foaming process although the ?Pcan still have an error of about 30-40% due to overestimation as reported in a previous study [15]. The nucleation theory by Colton and Suh is a simplified form derived and modified from classic nucleation theories [16-18] and is generally adequate for the batch foaming process. However, there is a need for this theory to be modified in cases of microcellular injection molding and extrusion systems because ?P cannot be directly controlled and measured. To predict nucleation in microcellular injection molding and extrusion processes more precisely, this paper proposes a cell nucleation theory of a different form, which includes a term for the degree of supersaturation because it is a directly controllable factor. To avoid misestimating ?P, and to consider the degree of supersaturation, a more proper activation energy equation for nucleation can be derived from the following equation [16,17] ?P=|Pr'-Pr|=2rrc （4） where rc is the radius of a characteristic droplet, and the W. Thomson equation RTlnPrP∞=2r?Mr?p （5） where P∞ is the pressure of the saturated vapor (i.e., the equilibrium pressure), R is the universal gas constant, M is the molar mass, and p is the density. These equations yield ?P=RTρlnPrP∞M （6） which can be alternatively expressed as ?P=ktρ1lnS (7) whereρ1is the molecular density of the bulk liquid, and S(=PrP∞) is defined as the degree of supersaturation. Thus, the activation energy equation (cf. Equation (2)) for nucleation in the microcellular injection molding process can be given by ?G**=16πr33(kTρ1lnS)2 （8） Hence it can be stated that the activation energy for nucleation is inversely proportional to the square of the natural logarithm of the supersaturation degree. In the microcellular injection molding process, the polymer/gas solution becomes a metastable supersaturation solution when it is injected into the mold cavity. This is because the amount of gas able to be dissolved in the polymer in the presence of a rapid pressure drop is less than the gas amount originally dissolved in polymer melts. In particular, assuming the air in the cavity is properly vented, the pressure at the advancing melt front is at the atmospheric pressure. The solubility of a gas in a polymer at atmospheric pressure and processing temperature can be obtained by an Arrhenius-type expression with regard to temperature [22] S@1 atm; melt temperature=S@STPexp?(-?HsR(1Tmelt-1298)) (9) where S@STP is the solubility of the gas in the polymer at standard temperature and pressure conditions (298 K and 1 atm). The parameter DHs is the molar heat of sorption, and Tmelt is the polymer melt temperature. Thus, the degree of supersaturation is given by S=mgS@STPexp?(-?HsR(1Tmelt-1298)) (10) where mg is the gas dosage which can be controlled by the supercritical fluid (SCF) supply system. The heat of sorption, ?HsRg, of various polymer/gas systems at standard temperature has been studied and summarized in many previously published studies. In order to obtain the degree of supersaturation for a polymer/gas solution in the microcellular injection molding process, one has to either measure the solubility of the gas in the polymer at standard temperature and pressure or consult published data on the solubility of the gas in the polymer. Then, the activation energy barrier for nucleation in Equation (8), ?G**, can be obtained based on the calculated degree of supersaturation and the surface energy of the bubble interface, γ. Given the activation energy barrier and the frequency factor, f, the nucleation rate (expressed in Equation (1)) can then be calculated.The estimate of the surface energy of the bubble interface and the frequency factor is discussed below. In microcellular injection molding, the polymer/gas solution can be treated as a liquid mixture. Thus, the surface energy of the bubble interface, g, can be expressed as [23,24] γmix=γpolymerρmixρpolymer4(1-wgas) （11） where γpolymer is the surface energy of the polymer, P′S are the densities, and wgas is the weight fraction of gas. In addition, a frequency factor for a gas molecule, f, in Eq. (1) can be expressed as [24-26] f=Zβ(4πrc2) (12) where z is the Zeldovich factor, which accounts for the many clusters that have reached the critical size, rc., but are still unable to grow to sustainable bubbles. The parameter b is the impingement rate at which gas molecules collide with the wall of a cluster. The parameter Zβcan be used as a correction factor and is determined experimentally. Once the nucleation rate as a function of the degree of supersaturation is obtained, one can control the gas (SCF) content in the polymer melt to control or delay the onset of cell nucleation so that no bubble will form at the advancing melt front during the injection filling stage, thus, allowing microcellular parts with solid, swirl-free surface to be injection molded. 3. Experimental 3.1. Materials The material used in this study was an injection molding grade low density polyethylene, LDPE (Chevron Phillips Chemical Company, Texas, USA). It has a melt index of 25 g/10 min and a density of 0.925 g/cm3. To confirm the theory for improving surface quality by controlling the degree of supersaturation, a random copolymer polypropylene (PP)was also used in this study. The PP used in this study was Titanpro SM668 (Titan Chemicals Corp., Malaysia), with a melt flow index of 20 g/10 min and a density of 0.9 g/cm3. Both materials were used as received without any colorant, fillers, or additives. Commercial grade nitrogen was used as a physical blowing agent for the microcellular injection molding trials. 3.2. Microcellular injection molding In this study, an Arburg 320S injection molding machine (Arburg,Germany) was used for both the solid conventional and microcellular injection molding experiments. The supercritical fluid (SCF) supply system used in this study was the S11-TR3 model (Trexel, Woburn,MA, USA). The total gas dosagewas controlled by adjusting the gas injection time, t, and the gas injection flowrate,m_ g. A tensile test mold, which produces tensile test specimens that meet the ASTM D638 Type I standards, was used for this experiment. For injectionmolding of both LDPE and PP tensile test specimens, nozzle and mold temperatures were set at 221 。C and 25 。C, respectively. The cycle time was 40 s. An injection speed of 80 cm3/s was employed. In this study, six different gas dosages (concentrations) were used for injection molding of LDPE as shown in Table 1. Also, four different gas dosages were employed for microcellular injection molding of PP. The supercritical fluid was injected into the injection barrel at 140 bar pressure to be mixed with the polymer melts in this experiment. The weight reduction of foamed versus solid plastic partswas targeted at 8 _ 0.5% for each specimen. For the conventional injectionmolding experiment, the shot size of 20.2 cm3 and a packing pressure of 800 bars were employed for 6 s. For the microcellular injection molding experiments, the shot size of the polymer melt was 19.2 cm3 and the packing stage was eliminated. 3.3. Analysis methods To analyze the surface roughness of the molded tensile bar specimens, a Federal Surfanalyzer 4000 (Federal Product Corporation, RI, USA)was used. The surface roughnesses of conventional and microcellular injection molded parts were evaluated at three locations shown in Fig. 1 and the averaged surface roughness based on measurementsdone at all three locationswas recordedandreported. The cutoff, drive speed, and drive length for the test were 0.75 mm, 2.5 mm/s, and 25 mm, respectively. For each process condition, ten specimens and three points on each specimen were tested. In addition to the surface roughness, swirl marks commonly observed in microcellular injection molded samples can also be clearly revealed by a 3-D surface profiler. Zygo NewView (Zygo Corporation, CT, USA), a non-contact 3-D surface profiler, was employed to examine the surface profile of injection molded parts in this study using a scan distance of ±10 mm. A JEOL JSM-6100 scanning electron microscope with an accelerating voltage of 15 kV was employed for observing the microstructures of the foamed parts. To observe the cross section of the microcellular injection molded parts, test specimens were frozen by liquid nitrogen and subsequently fractured. Representative images of each process condition were selected and cell sizes and densities were analyzed. A UTHSCSA Image Tool was employed as the ima