購(gòu)買設(shè)計(jì)請(qǐng)充值后下載，，資源目錄下的文件所見(jiàn)即所得，都可以點(diǎn)開(kāi)預(yù)覽，，資料完整，充值下載可得到資源目錄里的所有文件。。?！咀ⅰ浚篸wg后綴為CAD圖紙，doc,docx為WORD文檔，原稿無(wú)水印，可編輯。。。具體請(qǐng)見(jiàn)文件預(yù)覽，有不明白之處，可咨詢QQ:12401814
河南機(jī)電高等?？茖W(xué)校
學(xué)生畢業(yè)設(shè)計(jì)（論文）中期檢查表
學(xué)生姓名
學(xué) 號(hào)
指導(dǎo)教師
選題情況
課題名稱
塑料蓋零件注塑成型工藝及注塑模具設(shè)計(jì)
難易程度
偏難
適中
偏易
工作量
較大
合理
較小
符合規(guī)范化的要求
任務(wù)書(shū)
有
無(wú)
開(kāi)題報(bào)告
有
無(wú)
外文翻譯質(zhì)量
優(yōu)
良
中
差
學(xué)習(xí)態(tài)度、出勤情況
好
一般
差
工作進(jìn)度
快
按計(jì)劃進(jìn)行
慢
中期工作匯報(bào)及解答問(wèn)題情況
優(yōu)
良
中
差
中期成績(jī)?cè)u(píng)定：
所在專業(yè)意見(jiàn)：
負(fù)責(zé)人：
年 月 日
河南機(jī)電高等?？茖W(xué)校畢業(yè)設(shè)計(jì)說(shuō)明書(shū)
塑料蓋注塑模具設(shè)計(jì)與制造
緒 論
大學(xué)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)實(shí)踐環(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(lái)愈廣泛的應(yīng)用。
隨著工業(yè)的發(fā)展，工業(yè)產(chǎn)品的品種和數(shù)量不斷增加。換型不斷加快。使模具的需要補(bǔ)斷增加。而對(duì)模具的質(zhì)量要求越來(lái)越高。模具技術(shù)在國(guó)民經(jīng)濟(jì)中的作用越來(lái)越顯得更為重要。
模具是制造業(yè)的重要工藝基礎(chǔ)，在我國(guó)，模具制造屬于專用設(shè)備制造業(yè)。中國(guó)雖然很早就開(kāi)始制造模具和使用模具，但長(zhǎng)期未形成產(chǎn)業(yè)。直到20世紀(jì)80年代后期，中國(guó)模具工業(yè)才駛?cè)氚l(fā)展的快車道。近年，不僅國(guó)有模具企業(yè)有了很大發(fā)展，三資企業(yè)、鄉(xiāng)鎮(zhèn)（個(gè)體）模具企業(yè)的發(fā)展也相當(dāng)迅速。雖然中國(guó)模具工業(yè)發(fā)展迅速，但與需求相比，顯然供不應(yīng)求，其主要缺口集中于精密、大型、復(fù)雜、長(zhǎng)壽命模具領(lǐng)域。由于在模具精度、壽命、制造周期及生產(chǎn)能力等方面，中國(guó)與國(guó)際平均水平和發(fā)達(dá)國(guó)家仍有較大差距，因此，每年需要大量進(jìn)口模具。中國(guó)模具產(chǎn)業(yè)除了要繼續(xù)提高生產(chǎn)能力，今后更要著重于行業(yè)內(nèi)部結(jié)構(gòu)的調(diào)整和技術(shù)發(fā)展水平的提高。結(jié)構(gòu)調(diào)整方面，主要是企業(yè)結(jié)構(gòu)向?qū)I(yè)化調(diào)整，產(chǎn)品結(jié)構(gòu)向著中高檔模具發(fā)展，向進(jìn)出口結(jié)構(gòu)的改進(jìn)，中高檔汽車覆蓋件模具成形分析及結(jié)構(gòu)改進(jìn)、多功能復(fù)合模具和復(fù)合加工及激光技術(shù)在模具設(shè)計(jì)制造上的應(yīng)用、高速切削、超精加工及拋光技術(shù)、信息化方向發(fā)展。近年，模具行業(yè)結(jié)構(gòu)調(diào)整和體制改革步伐加大，主要表現(xiàn)在，大型、精密、復(fù)雜、長(zhǎng)壽命、中高檔模具及模具標(biāo)準(zhǔn)件發(fā)展速度高于一般模具產(chǎn)品；塑料模和壓鑄模比例增大；專業(yè)模具廠數(shù)量及其生產(chǎn)能力增加；“三資”及私營(yíng)企業(yè)發(fā)展迅速；股份制改造步伐加快等。從地區(qū)分布來(lái)看，以珠江三角洲和長(zhǎng)江三角洲為中心的東南沿海地區(qū)發(fā)展快于中西部地區(qū)，南方的發(fā)展快于北方。目前發(fā)展最快、模具生產(chǎn)最為集中的省份是廣東和浙江，江蘇、上海、安徽和山東等地近幾年也有較大發(fā)展。
在完成大學(xué)三年的課程學(xué)習(xí)和課程、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)、機(jī)械原理等專業(yè)基礎(chǔ)課和專業(yè)課方面的知識(shí)，對(duì)機(jī)械制造、加工的工藝有了一個(gè)系統(tǒng)、全面的理解，達(dá)到了學(xué)習(xí)的目的。對(duì)于模具設(shè)計(jì)這個(gè)實(shí)踐性非常強(qiáng)的設(shè)計(jì)課題，我們進(jìn)行了大量的實(shí)習(xí)。經(jīng)過(guò)在新飛電器有限公司、洛陽(yáng)中國(guó)一拖的生產(chǎn)實(shí)習(xí)，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(guò)程方面的知識(shí)，而對(duì)于模具的制造工藝更是實(shí)現(xiàn)了零的突破。在指導(dǎo)老師的協(xié)助下和在工廠師傅的講解下，同時(shí)在現(xiàn)場(chǎng)查閱了很多相關(guān)資料并親手拆裝了一些典型的模具實(shí)體，明確了模具的一般工作原理、制造、加工工藝。并在圖書(shū)館借閱了許多相關(guān)手冊(cè)和書(shū)籍，設(shè)計(jì)中，將充分利用和查閱各種資料，并與同學(xué)進(jìn)行充分討論，盡最大努力搞好本次畢業(yè)設(shè)計(jì)。在設(shè)計(jì)的過(guò)程中，將有一定的困難，但有指導(dǎo)老師的悉心指導(dǎo)和自己的努力，相信會(huì)完滿的完成畢業(yè)設(shè)計(jì)任務(wù)。由于學(xué)生水平有限，而且缺乏經(jīng)驗(yàn)，設(shè)計(jì)中不妥之處在所難免，肯請(qǐng)各位老師指正.
第一章模塑工藝規(guī)程的編制
該塑件是端蓋產(chǎn)品，其零件圖如圖1-1所示。本塑件的材料采用尼龍1010，生產(chǎn)類型為大批量生產(chǎn)。 1-1塑料蓋
1.1塑件的工藝性分析
1.1.1塑件的原材料分析
塑件的材料采用尼龍1010，屬熱塑性塑料。從使用性能上看，尼龍1010是半透明，吸水小，耐寒性較好，堅(jiān)韌﹑耐磨﹑耐油﹑耐水，抗霉菌，但吸水性大；從成型性能上看，塑件壁不宜取厚，并應(yīng)均勻，脫模度不宜取小，尤其對(duì)厚壁及深高塑件更應(yīng)取大。受熱時(shí)間不宜超過(guò)30min，料溫高則收縮大，易出飛邊，收縮小，取向性強(qiáng)，注射壓力低易發(fā)生凹痕，波紋。成型周期按塑件壁厚而定，厚則取長(zhǎng)，薄則取短，為了減少收縮，凹痕﹑縮孔，一般宜取低模溫﹑高注射壓力的成形條件，以及采用白油作脫模劑;尼龍1010的主要技術(shù)指標(biāo)：密度是1.04kg/dm﹑比體積是0.96dm/kg﹑吸水率是0.2～0.4﹑收縮率是1.3～2.3s﹑熔點(diǎn)是205t/c﹑熱變形溫度是55c﹑抗拉屈服強(qiáng)度是62Mpa﹑拉伸彈性模量1.8×10Mpa﹑抗彎強(qiáng)度88Mpa﹑硬度9.75HB﹑擊穿強(qiáng)度20KV/mm。
1.2.塑件的結(jié)構(gòu)和尺寸精度及表面質(zhì)量分析
1.2.1.1結(jié)構(gòu)分析
從塑料蓋圖1-1上分析，該零件總體形狀為圓形。在高度方向有兩個(gè)高度12mm,高度為5mm的凸起在塑料蓋的內(nèi)部.在高度為5m,長(zhǎng)為6mm、寬為12mm的凸臺(tái)上,一個(gè)帶有12mm×3mm的對(duì)稱分布,因此,模具設(shè)計(jì)時(shí)必須設(shè)置側(cè)向分型抽心機(jī)構(gòu),該零件屬于中等復(fù)雜程度.
1.2.1.2尺寸精度分析
該零件重要尺寸，如外徑Φ59mm,Φ53內(nèi)部形狀等尺寸精度為MT3級(jí)（GB/T14486—1993），次要尺寸，如高度12mm的尺寸精度為MT5級(jí)（GB/T14486—1993）。由以上分析可見(jiàn)，該零件的尺寸精度中等偏上，對(duì)應(yīng)的模具相關(guān)尺寸加工可以得到保證。
從塑件的壁厚上來(lái)看,壁厚最大處為3mm,壁厚均勻, 符合尼龍1010的最小壁厚原則，在制件的轉(zhuǎn)角處設(shè)計(jì)圓角，防止在此處出現(xiàn)缺陷，由于制件的尺寸較小，尼龍1010的強(qiáng)度較大不需增設(shè)加強(qiáng)
1.2.1表面質(zhì)量分析
該零件的表面除要求沒(méi)有缺陷﹑毛刺，保持表面的平滑，內(nèi)部不得有導(dǎo)電雜質(zhì)外，沒(méi)有什么特別的表面質(zhì)量要求，故比較容易實(shí)現(xiàn)。
綜上分析可以看出,注塑時(shí)在工藝控制得較好的情況下,零件的成型要求可以得到保證.
1.2.2計(jì)算塑件的體積和質(zhì)量
計(jì)算塑件的質(zhì)量是為了選用注塑機(jī)及確定模具型腔數(shù)。
計(jì)算塑件的體積：V=31.3cm
計(jì)算塑件的質(zhì)量：根據(jù)設(shè)計(jì)手冊(cè)可查得尼龍1010的密度為ρ=1.04kg/dm
塑件質(zhì)量：M=Vρ
=31.3×10×1.04×10
=32.552g
采用一模兩件的模具結(jié)構(gòu)，考慮其外形尺寸，注塑時(shí)所需壓力和工廠現(xiàn)有設(shè)備等情況，初步選用注塑機(jī)SZY—125型。
1.2.3塑件注塑工藝參數(shù)的確定
查找有關(guān)文獻(xiàn)和參考工廠時(shí)間應(yīng)用的情況，尼龍1010的成型工藝參數(shù)可作如下選擇：（試模時(shí)，可根據(jù)實(shí)際情況作適當(dāng)調(diào)整）
注塑溫度： 括料筒溫度和噴嘴溫度。
料筒溫度： 后段溫度t選用190～210c；
中段溫度t: 選用200～220c；
前段溫度t: 選用210～230c；
噴嘴溫度： 200～210c；
注塑壓力一： 選用40～100Mpa；
注塑時(shí)間： 選用20～90s；
保壓壓力： 選用 65Mpa；
高壓時(shí)間： 選用0～5s；
冷卻時(shí)間： 選用20～120s；
總周期： 選用45～220s；
后處理方法： 采用油﹑水﹑鹽水；
后處理溫度： 90～100t/c;
后處理時(shí)間： 4h。
說(shuō)明1：預(yù)熱和干燥均采用鼓風(fēng)烘箱。
2：凡潮濕環(huán)境使用的塑料，應(yīng)進(jìn)行調(diào)濕處理，在100～120c水中加熱2～18h。
1.2.4.塑料成型設(shè)備的選取
根據(jù)計(jì)算及原材料的注射成型參數(shù)初選注塑機(jī)為SZY-300查材料知：
標(biāo)稱注射量： 320cm
螺桿直徑/cm Ф60mm
注射容量/克： 125克
注射壓力/10Pa： 125Mpa
鎖模力10kN： 1400kN
最大注射面積/㎝: 645㎝
模具厚度/mm： 130～355mm
模板行程/mm: 340 mm
噴嘴 球半徑： 12mm
孔半徑： 4mm
定位孔直徑/㎜ 125
推出兩側(cè)孔徑/mm 50mm
孔距/mm 230mm
第2章 注塑模的結(jié)構(gòu)設(shè)計(jì)
注塑模結(jié)構(gòu)設(shè)計(jì)主要包括：分型面選擇﹑模具型腔數(shù)目的確定﹑型腔的排列方式﹑冷卻水道布局﹑澆口位置設(shè)置﹑模具工作零件的結(jié)構(gòu)設(shè)計(jì)﹑側(cè)向分型與抽芯機(jī)構(gòu)的設(shè)計(jì)﹑推出機(jī)構(gòu)的設(shè)計(jì)等內(nèi)容。
2.1分型面選擇
模具設(shè)計(jì)中，分型面的選擇很關(guān)鍵，它決定了模具的結(jié)構(gòu)。應(yīng)根據(jù)分型面選擇原則和塑件的成型要求來(lái)選擇分型面。
該塑件為端蓋，表面無(wú)特殊的要求，其分型面選擇如下圖所示：
2-1所示取A-A向?yàn)榉中兔?，影響零件外觀質(zhì)量，抽芯在動(dòng)模構(gòu)簡(jiǎn)單。
如圖2-1所示取B-B向?yàn)榉中兔?，抽芯?dòng)模，抽芯機(jī)構(gòu)簡(jiǎn)單，可以設(shè)計(jì)簡(jiǎn)單的B--B抽芯機(jī)構(gòu)進(jìn)行側(cè)抽。從以上兩個(gè)分型如圖面的比較可以很容易的看出應(yīng)該選擇第二個(gè)分型方法，有利于模具成型。
2-1分型面示意圖
2.2確定型腔的數(shù)目及排列方式
2.2.1模腔數(shù)量的確定
塑件的生產(chǎn)屬大批量生產(chǎn)，宜采用多型腔注塑模具，其型腔個(gè)數(shù)與注塑機(jī)的塑化能力，最大注射量以及合模力等參數(shù)有關(guān)，此外還受制件精度和生產(chǎn)的經(jīng)濟(jì)性等因素影響，有上述參數(shù)和因素可按下列方法確定模腔數(shù)量；
2.2.1.1.按注射機(jī)的額定鎖模力確定型腔數(shù)量N1
N1=（F/PC）/A－B/A
其中： F 注塑機(jī)的鎖模力 N
PC 型腔內(nèi)的平均壓力MPa
A 每個(gè)制件在分型面上的面積（㎜）
B 流道和澆道在分型面上的投影面積（㎜）
B 在模具設(shè)計(jì)前為未知量，根據(jù)多型腔模具的流動(dòng)分析B為（0.2～0.5），常取B=0.35，熔體內(nèi)的平均壓力取決于注射壓力，一般為25～40MPa實(shí)際所需鎖模力應(yīng)小于選定注塑機(jī)的名義鎖模力，為保險(xiǎn)起見(jiàn)常用0.8F則
N1=0.6F/APC=500000×0.6/30×342=29.2 （個(gè)）
2.2.1.2.注射機(jī)注塑量確定型腔數(shù)目N2
N2=（G－C）/V
其中： G 注射機(jī)的公稱注塑量（㎜）
V 單個(gè)制件體積 （㎜）
C 流道和澆口的總體積（㎜）
生產(chǎn)中每次實(shí)際注塑量應(yīng)為公稱注塑量的0.75～0.45倍，取0.6倍計(jì)算，同時(shí)流道和澆道的體積為未知量，據(jù)統(tǒng)計(jì)每個(gè)制品所需澆注系統(tǒng)是體積的0.2～1倍，現(xiàn)取C=0.6則
N2=0.6G/1.6V=0.375G/V=60×0.375
=10.7（個(gè)）
從以上討論可以看到模具的型腔個(gè)數(shù)必須取N1，N2中的較小值，在這里可以選取的個(gè)數(shù)是2，4，6，8，10個(gè)，考慮的制件的取出和模具的開(kāi)模等情況，以及模具的主流道長(zhǎng)度最好小于60mm，以防止因?yàn)樽⑺軌毫Φ慕档投鴰?lái)的制件充型不足等缺陷。我們所設(shè)計(jì)的端蓋注塑模具采用一模兩腔的方案，即N=2
2.2.2型腔的排列方式
A B
2-2型腔的排列方式
本塑件在注塑時(shí)采用一模兩腔,綜合考慮澆注系統(tǒng)，模具結(jié)構(gòu)的復(fù)雜程度等因素采取如圖2-2A所示的型腔排列方式。采用2-2B的型腔排列方式的最大優(yōu)點(diǎn)是便于設(shè)置側(cè)向分型抽芯機(jī)構(gòu)，其缺點(diǎn)是熔料進(jìn)入型腔后到另一端的料流長(zhǎng)度較大，但因本塑件較小，故對(duì)成型沒(méi)有太大影響。
這個(gè)圖顯示的只是對(duì)應(yīng)裝配的位置的確定。2-2B對(duì)應(yīng)的裝配方法都比較方便。
2.3澆注系統(tǒng)設(shè)計(jì)
2.3.1 主流道設(shè)計(jì)
根據(jù)XS-ZY-125型注塑機(jī)噴嘴的有關(guān)尺寸
噴嘴前端孔徑： d0=Ф6mm
噴嘴前端球面半徑： R0=8mm
根據(jù)模具主流道與噴嘴的關(guān)系：
R=R0+（1～2）mm
D=d0+(0.5～1)mm
取主流道的球面半徑： R=10mm
取主流道的小端直徑d=Ф4.5mm
為了方便將凝料從主流道中拔出，將主流道設(shè)計(jì)為圓錐形式其斜度取1～3度經(jīng)換算得主流道大端直徑D=Ф8.5mm，為了使料能順利的進(jìn)入分流道，可在主流道的出料端設(shè)計(jì)半徑r=5mm的圓弧過(guò)渡。
2.3.2分流道設(shè)計(jì)
分流道的形式和尺寸應(yīng)根據(jù)塑件的體積，壁厚和形狀的復(fù)雜程度來(lái)確定分流道的長(zhǎng)度的。由于塑件的形狀比較簡(jiǎn)單，尼龍1010的流動(dòng)性好，充型能力比較好，因此可采取梯形分流道，便于加工。根據(jù)主流道大端直徑D=Ф8.5mm，則梯形可選用上底為b=5.5mm,高為h=8mm的截面。
截面形狀為U型，在流道設(shè)計(jì)中要減小壓力損失，則希望流道的面積大。要減少傳熱損失，又希望流道的面積小。因此可用流道的面積與周長(zhǎng)的比值來(lái)表示流道的效率。U型實(shí)質(zhì)上是一種雙梯形流道截面。
效率為0.195D
分流道的尺寸：
尼龍1010 分流道直徑/mm 3.8---7.5
選取6mm
分流道表面粗糙度：
分流道表面不要求太光潔，表面粗糙度常取1.25—2.5Rμm，這可增加對(duì)外層塑料熔體流動(dòng)阻力，使外層塑料冷卻皮層固定，形成絕熱層。有利于保溫。但表面不得凸凹不平，以免對(duì)分型不利。
2.3.3澆口設(shè)計(jì)
根據(jù)塑件的成型要求及型腔的排列方式，選用側(cè)澆口較為理想。設(shè)計(jì)時(shí)考慮選擇從塑件的表面進(jìn)料，而且在模具結(jié)構(gòu)上采取鑲拼型腔﹑型心，有利于填充﹑排氣。故采用截面為矩形的側(cè)澆口，查表初選尺寸為（b×l×h）1mm
×0.8mm×0.6mm,試模時(shí)修正.
2.3.4排氣結(jié)構(gòu)的設(shè)計(jì)
在注塑模具的設(shè)計(jì)過(guò)程中，必須考慮排氣結(jié)構(gòu)的設(shè)計(jì)，否則，熔融的塑料流體進(jìn)入模具型腔內(nèi)，氣體如不能及時(shí)排出會(huì)使制件的內(nèi)部有氣泡，甚至?xí)a(chǎn)生很高的溫度使塑料燒焦，從而出現(xiàn)廢品。
排氣方式有兩種：開(kāi)排氣槽排氣和利用合模間隙排氣。
由于端蓋注塑模是小型鑲拼式模具，可直接利用分型面和鑲拼間隙進(jìn)行排氣，而不需在模具上開(kāi)設(shè)排氣槽。（尼龍1010塑料的最小不溢料間隙為0.03mm，間隙較小，再加上尼龍1010的流動(dòng)性較好，也不宜開(kāi)排氣槽.
2.3.5主流道襯套的選取
為了提高模具的壽命在模具與注塑機(jī)頻繁接觸的地方設(shè)計(jì)為可更換的主流道襯套形式，選取材料為T8A，熱處理以后的硬度為53～57HRC，主流道襯套和定模的配合形式為H7/m6的過(guò)渡配合。
2.4抽芯機(jī)構(gòu)設(shè)計(jì)
此設(shè)計(jì)的塑件側(cè)壁有兩個(gè)側(cè)凹,它們均垂直于脫模方向,阻礙成型后塑件從模具脫出.因此成型小側(cè)凹的零件必須做成活動(dòng)的型心,即必須設(shè)置抽芯機(jī)構(gòu).本模具采用斜銷抽芯機(jī)構(gòu).
2.4.1確定抽芯距
抽芯距一般大于側(cè)凹的深度本副模具設(shè)計(jì)中必須高于制件最小高度的一半
H1=B2/2=1.5/2=0.75mm
另加3～5mm的抽芯安全系數(shù)，可取抽芯距為3.5mm
2.4.2確定斜銷的傾角
斜銷的傾角a是斜銷機(jī)構(gòu)的主要技術(shù)參數(shù)，它與抽拔距和抽芯距有直接關(guān)系，一般取15°～25°本副模具取a=20°
2.4.3確定斜銷的尺寸
斜銷的寬度，長(zhǎng)度抽拔力及傾角還有制件的結(jié)構(gòu)可按設(shè)計(jì)資料有關(guān)公式進(jìn)行計(jì)算，本例可采用經(jīng)驗(yàn)估值，斜銷的長(zhǎng)度寬度分別為20mm，7mm
2.4.4斜銷長(zhǎng)度的確定
可根據(jù)抽拔距，固定端模板的厚度，斜銷直徑及斜角大小確定：
L=L1+L2+L3+L4+L5
=D/2×tana+h/cosa+d/2tana+H/sina+（10～15）
=109mm
?。? L=109mm
2.5 凹模的設(shè)計(jì)
本副模具采用整體式凹模結(jié)構(gòu)，由于制件結(jié)構(gòu)簡(jiǎn)單，模具牢固，不易變形，制件沒(méi)拼界逢，適用用于本制件的模具。如圖所示：
2-2凹模的結(jié)構(gòu)圖
材料選用T8A, 硬度在50HRC以上.
根據(jù)分流道與澆口的設(shè)計(jì)要求，分流道與澆口設(shè)在凹模型腔上其結(jié)構(gòu)見(jiàn)上2-2圖所示。
凹模板尺寸：根據(jù)矩形凹模最小壁厚經(jīng)驗(yàn)曲線知，此塑件的成型
壓力小于30MPA。
由經(jīng)驗(yàn)可知【3】：
長(zhǎng)為:355 mm. 寬為:250 mm.
凹模高為: h=40mm
件高為: 12mm
加工可以直接用銑刀銑出，也可以用成型電極。為了節(jié)約成本。在這里我選用銑刀銑。
第3章 端蓋注塑模具的有關(guān)計(jì)算
本例中成型零件工作尺寸計(jì)算時(shí)均采用平均尺寸，平均收縮率平均制造公差和平均磨損率來(lái)計(jì)算。
查常用塑料的收縮率塑料尼龍1010的成型收縮率為S=0.5～4.0％，故平均我們?nèi)镾cp=0.5％?？紤]到工廠模具制造的現(xiàn)有條件，模具制造公差取Б=Δ/3。
表一：凹模工作尺寸的計(jì)算：
塑件尺寸
計(jì)算公式
型腔工作尺寸
Φ59
Lm=(Ls+LsScp％－3/4Δ)+Б
Φ61.40+0.050
12
12.48+0.020
40
39.96+0.08
成型長(zhǎng)12mm寬3mm的型芯：
材料選用T8A, 硬度在50HRC以上.
成型零部件的制造誤差：
成型零部件的制造誤差包括成型零部件的加工誤差和安裝誤差，配合誤差等幾個(gè)方面。設(shè)計(jì)時(shí)一般應(yīng)將成型零部件的制造公差控制在塑件的1/3左右，通常取IT6—IT9級(jí)，綜合考慮取IT8級(jí)。
第4章 模具加熱和冷卻系統(tǒng)的設(shè)計(jì)
塑料在生產(chǎn)過(guò)程中由于需要對(duì)熔融的塑料流體進(jìn)行冷卻，塑料制件不能有太高的溫度（防止出模后制件發(fā)生翹曲，變形）冷卻系統(tǒng)設(shè)計(jì)可按下式進(jìn)行計(jì)算：
設(shè)該模具平均工作溫度為60°，用20°的常溫水作為模具的冷卻介質(zhì)，其出口溫度為30°，產(chǎn)量為（1分鐘2模）1000g/h。
① 求塑件在硬化時(shí)每小時(shí)釋放的熱量為Q3，查有關(guān)文獻(xiàn)得尼龍1010的單位熱流量為Q2=314.3～398.1J/g ,取Q2=350J/g：
Q3=WQ2=1008g/h×350J/h=352800J
② 求冷卻水的體積流量V
V=WQ1/Pc1(T1－T2)
=140cm3
溫度調(diào)節(jié)對(duì)塑件的質(zhì)量影響主要表現(xiàn)在以下幾個(gè)方面：
變形 尺寸精度 力學(xué)性能 表面質(zhì)量
在選擇模具溫度時(shí)，應(yīng)根據(jù)使用情況著重滿足制件的質(zhì)量要求。
在注射模具中溶體從200 C,左右降低到60C左右，所釋放的能量5％以輻射，對(duì)流的方式散發(fā)到大氣中，其余95％由冷卻介質(zhì)帶走，因此注射模的冷卻時(shí)間只要取決與冷卻系統(tǒng)的冷卻效果。模具的冷卻時(shí)間約占整個(gè)循環(huán)周期的2/3?？s短循環(huán)周期的冷卻時(shí)間是提高是提高生產(chǎn)效率的關(guān)鍵。在冷卻水冷卻過(guò)程中，在湍流下的熱傳遞是層流的10—20倍。在次我選擇湍流。 如圖表二：
冷卻水直徑d/（mm）
最低流量v（m/s）
流量qv/（m/min）
12
1.10
7.4×10
表二
第5章 模具閉合高度確定
在支撐板與固定零件的設(shè)計(jì)中根據(jù)經(jīng)驗(yàn)確定：定模板厚度H1=42mm，斜楔塊厚度為H2=34mm，腔板型芯固定板厚度為H3=28mm，推件板厚度為H4=16mm，墊塊厚度H5=73mm動(dòng)模板厚度H6=27mm(考慮模具的抽芯距)如下圖所示：
1計(jì)算模具的閉合高度：
H=H1＋H2＋H3＋H4＋H5
=25＋46＋23＋70＋25＋31
=220mm
2．校核注塑機(jī)的開(kāi)，合模空間
(1)：模具合模時(shí)校核：
110mm<220mm<277mm （模具符合注塑機(jī)的要求）
(2)：模具開(kāi)模時(shí)校核：
110mm<220mm＋15mm<200mm （模具符合注塑機(jī)的要求）
第6章 注塑機(jī)有關(guān)參數(shù)的校核
本模具的外形尺寸為300mm×300mm×220mm, XS-ZY-125型注塑機(jī)模板最大安裝尺寸是370mm×350mm。
由于上述計(jì)算的模具閉合高度為220mm，XS-ZY-125型注塑機(jī)的最小模具厚度為200mm，最大模具厚度為300mm
1：模具合模時(shí)校核：
200mm<220mm<300mm
2：模具開(kāi)模時(shí)校核：
200mm<220mm＋15mm<300mm
其中：15mm為模具的抽拔距
經(jīng)校核SZY-125型注塑機(jī)能滿足使用要求故可以采用。
第7章 繪制模具總裝圖和非標(biāo)零件工作圖
7.1本模具總裝圖如下圖所示：
7-1模具裝配圖
7.2本模具的工作原理：
模具安裝在注塑機(jī)上，定模部分固定在注塑機(jī)的定模板上，動(dòng)模固定在注塑機(jī)的動(dòng)模板上。合模后，注塑機(jī)通過(guò)噴嘴將熔料經(jīng)流道注入型腔，經(jīng)保壓，冷卻后塑件成型，注塑完成。開(kāi)模時(shí)動(dòng)模部分隨動(dòng)模板一起漸漸將分型面打開(kāi)，與此同時(shí)在斜導(dǎo)柱的作用下側(cè)抽芯滑塊從型腔中退出，完成側(cè)抽芯動(dòng)作
當(dāng)分型面打開(kāi)到23mm時(shí)動(dòng)模運(yùn)動(dòng)停止，在注塑機(jī)頂出作用下，推動(dòng)頂桿運(yùn)動(dòng)將塑件頂出。合模時(shí)，隨著分型面的閉合側(cè)型心滑塊，同時(shí)復(fù)位桿也對(duì)頂桿進(jìn)行復(fù)位。
結(jié)論
大學(xué)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)實(shí)踐環(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(lái)愈廣泛的應(yīng)用。在完成大學(xué)三年的課程學(xué)習(xí)和課程、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)、機(jī)械原理等專業(yè)基礎(chǔ)課和專業(yè)課方面的知識(shí)，對(duì)機(jī)械制造、加工的工藝有了一個(gè)系統(tǒng)、全面的理解，達(dá)到了學(xué)習(xí)的目的。對(duì)于模具設(shè)計(jì)這個(gè)實(shí)踐性非常強(qiáng)的設(shè)計(jì)課題，我們進(jìn)行了大量的實(shí)習(xí)。經(jīng)過(guò)在新飛電器有限公司、洛陽(yáng)中國(guó)一拖的生產(chǎn)實(shí)習(xí)，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(guò)程方面的知識(shí)，而對(duì)于模具的制造工藝更是實(shí)現(xiàn)了零的突破。在指導(dǎo)老師的協(xié)助下和在工廠師傅的講解下，同時(shí)在現(xiàn)場(chǎng)查閱了很多相關(guān)資料并親手拆裝了一些典型的模具實(shí)體，明確了模具的一般工作原理、制造、加工工藝。并在圖書(shū)館借閱了許多相關(guān)手冊(cè)和書(shū)籍，設(shè)計(jì)中，將充分利用和查閱各種資料，并與同學(xué)進(jìn)行充分討論，盡最大努力搞好本次畢業(yè)設(shè)計(jì)。
在設(shè)計(jì)的過(guò)程中，將有一定的困難，但有指導(dǎo)老師的悉心指導(dǎo)和自己的努力，相信會(huì)完滿的完成畢業(yè)設(shè)計(jì)任務(wù)。由于學(xué)生水平有限，而且缺乏經(jīng)驗(yàn)，設(shè)計(jì)中不妥之處在所難免，肯請(qǐng)各位老師指正。
致謝
時(shí)光如電，歲月如梭，三年的大學(xué)生活即將結(jié)束，而我也即將離開(kāi)可敬的老師和熟悉的同學(xué)踏入不是很熟悉的社會(huì)中去。在這畢業(yè)之際，作為一名工科院校的學(xué)生，做畢業(yè)設(shè)計(jì)是一件必不可少的事情。
畢業(yè)設(shè)計(jì)是一項(xiàng)非常繁雜的工作，它涉及的知識(shí)非常廣泛，很多都是書(shū)上沒(méi)有的東西，這就要靠自己去圖書(shū)館查找自己所需要的資料；還有很多設(shè)計(jì)計(jì)算，這些都要靠自己運(yùn)用自己的思維能力去解決，可以說(shuō)，沒(méi)有一定的毅力和耐心是很難完成這樣復(fù)雜的工作。
在學(xué)校中，我主要學(xué)的是理論性的知識(shí)，而實(shí)踐性很欠缺，而畢業(yè)設(shè)計(jì)就相當(dāng)于實(shí)戰(zhàn)前的一次總演練。畢業(yè)設(shè)計(jì)不但把我以前學(xué)的專業(yè)知識(shí)系統(tǒng)的連貫起來(lái)，也使我在溫習(xí)舊知識(shí)的同時(shí)也可以學(xué)習(xí)到很多新的知識(shí)；這不但提高了我們解決問(wèn)題的能力，開(kāi)闊了我們的視野，在一定程度上彌補(bǔ)我們實(shí)踐經(jīng)驗(yàn)的不足，為以后的工作打下堅(jiān)實(shí)的基礎(chǔ)。
由于本人資質(zhì)有限，很多知識(shí)掌握的不是很牢固，因此在設(shè)計(jì)中難免要遇到很多難題，在有課程設(shè)計(jì)的經(jīng)驗(yàn)及老師的不時(shí)指導(dǎo)和同學(xué)的熱心幫助下，克服了一個(gè)又一個(gè)的困難，使我的畢業(yè)設(shè)計(jì)日趨完善。畢業(yè)設(shè)計(jì)雖然很辛苦，但是在設(shè)計(jì)中不斷思考問(wèn)題，研究問(wèn)題，咨詢問(wèn)題，一步步提高了自己，一步步完善了自己。同時(shí)也汲取了更完整的專業(yè)知識(shí)，鍛煉了自己獨(dú)立設(shè)計(jì)的能力，使我受益匪淺，我相信這些經(jīng)驗(yàn)對(duì)我以后的工作一定有很大的幫助，而且也鍛煉我的吃苦耐勞的精神，讓我在這個(gè)競(jìng)爭(zhēng)的社會(huì)里有立足之地
參考文獻(xiàn)
［1］楊占堯主編. 塑料注塑模結(jié)構(gòu)與設(shè)計(jì). 清華大學(xué)出版社.
［2］中國(guó)模具設(shè)計(jì)大典.
［3］ 王孝陪主編. 塑料成型工藝及模具簡(jiǎn)明手冊(cè). 機(jī)械工業(yè)出版社. 2000
［4］ 模具制造手冊(cè)編寫(xiě)組. 模具制造手冊(cè). 機(jī)械工業(yè)出版社. 1996
［5］馮炳堯，韓泰榮，蔣文生主編. 模具設(shè)計(jì)與制造簡(jiǎn)明手冊(cè). 上海科學(xué)技術(shù)出版社，1998
［6］ 賈潤(rùn)禮，程志遠(yuǎn)主編. 實(shí)用注塑模設(shè)計(jì)手冊(cè). 中國(guó)輕工業(yè)出版社. 2000
［7］ 唐志玉主編. 模具設(shè)計(jì)師指南. 國(guó)防工業(yè)出版社. 1999
［8］屈華昌主編. 塑料成型工藝與模具設(shè)計(jì). 機(jī)械工業(yè)出版社. 1995
［9］ 黃毅宏主編. 模具制造工藝. 機(jī)械工業(yè)出版社. 1999
［10］ 彭建聲主編. 簡(jiǎn)明模具工實(shí)用技術(shù)手冊(cè). 機(jī)械工業(yè)出版社. 1993
目 錄
緒 論 1
第一章模塑工藝規(guī)程的編制 3
1.1塑件的工藝性分析 3
1.2.塑件的結(jié)構(gòu)和尺寸精度及表面質(zhì)量分析 4
第2章 注塑模的結(jié)構(gòu)設(shè)計(jì) 8
2.1分型面選擇 8
2.2確定型腔的數(shù)目及排列方式 9
2.3澆注系統(tǒng)設(shè)計(jì) 11
2.4抽芯機(jī)構(gòu)設(shè)計(jì) 13
2.5 凹模的設(shè)計(jì) 14
第3章 端蓋注塑模具的有關(guān)計(jì)算 16
第4章 模具加熱和冷卻系統(tǒng)的設(shè)計(jì) 18
第5章 模具閉合高度確定 20
第6章 注塑機(jī)有關(guān)參數(shù)的校核 21
第7章 繪制模具總裝圖和非標(biāo)零件工作圖 22
7.1本模具總裝圖如下圖所示： 22
7.2本模具的工作原理： 22
結(jié)論 23
致謝 24
參考文獻(xiàn) 25
27
河南機(jī)電高等?？茖W(xué)校
畢業(yè)設(shè)計(jì)說(shuō)明書(shū)
畢業(yè)設(shè)計(jì)題目：座塊蓋零件塑料成型工藝及注塑模具設(shè)計(jì)
系 部
專 業(yè)
班 級(jí)
學(xué)生姓名
學(xué) 號(hào)
指導(dǎo)教師
2007年 3月 20 日
插圖清單
1-1塑件的結(jié)構(gòu)形式
2-1分型面的選擇
2-2型腔的分布形式
2-3凹模的結(jié)構(gòu)
3-1側(cè)抽心型心
7-1模具裝配圖
1
目 錄
第一章 緒論…………………………………………………………………1
第二章 模塑工藝的編制 …………………………………………………4
1.1 塑件的工藝性分析 ………………………………………………5
1.2塑件的結(jié)構(gòu)和尺寸精度 ……………………………………………… 6
第二章塑料模的結(jié)構(gòu)設(shè)計(jì) ………………………………………………11
2.1分型面的選擇 ………………………………………………11
2.2確定型腔的數(shù)量及其分型面選擇 ………………………………… 12
2.3 澆鑄系統(tǒng)的設(shè)計(jì) …………………………………………………… 14
2.4抽心機(jī)構(gòu)的設(shè)計(jì) ………………………………………………14
2.5成型零件的結(jié)構(gòu)設(shè)計(jì) …………………………………………………14
第三章 端蓋注塑模的有關(guān)計(jì)算………………………………………16
第四章 模具加熱和冷卻系統(tǒng)的設(shè)計(jì)…………………………………… 19
第五章 模具閉合高度的確定…………………………………………… 24
第六章 注塑機(jī)有關(guān)技術(shù)參數(shù)的校核…………………………………… 25
第七章 繪制模具總裝圖和非標(biāo)零件圖………………………………26
第九章注塑機(jī)的安裝和校核………………………………………………27
9.1模具的安裝………………………………………………………27
9.2模具的試模 ……………………………………………………………27
第十章 總結(jié) ……………………………………………… 30
.致謝……………………………………………………… 31
參考文獻(xiàn)………………………………………………………………33
河南機(jī)電高等專科學(xué)校
畢業(yè)設(shè)計(jì)評(píng)語(yǔ)
學(xué)生姓名：王金艷 班級(jí): 模具042 學(xué)號(hào)： 0412228
題 目： 塑料蓋模具設(shè)計(jì)及其制造
綜合成績(jī)：
指導(dǎo)者評(píng)語(yǔ)：
指導(dǎo)者(簽字)：
年 月 日
畢業(yè)設(shè)計(jì)評(píng)語(yǔ)
評(píng)閱者評(píng)語(yǔ)：
評(píng)閱者(簽字)：
年 月 日
答辯委員會(huì)（小組）評(píng)語(yǔ)：
答辯委員會(huì)（小組）負(fù)責(zé)人(簽字)：
年 月 日
第 22 頁(yè) 共 23 頁(yè)
桂林電子科技大學(xué)畢業(yè)設(shè)計(jì)用紙
Automated Assembly Modelling for Plastic Injection Moulds
An injection mould is a mechanical assembly that consists of product-dependent parts and product-independent parts. This paper addresses the two key issues of assembly modelling for injection moulds, namely, representing an injection mould assembly in a computer and determining the position and orientation of a product-independent part in an assembly. A feature-based and object-oriented representation is proposed to represent the hierarchical assembly of injection moulds. This representation requires and permits a designer to think beyond the mere shape of a part and state explicitly what portions of a part are important and why. Thus, it provides an opportunity for designers to design for assembly (DFA). A simplified symbolic geometric approach is also presented to infer the configurations of assembly objects in an assembly according to the mating conditions. Based on the proposed representation and the simplified symbolic geometric approach, automatic assembly modelling is further discussed.
Keywords: Assembly modelling; Feature-based; Injection moulds; Object-oriented
1. Introduction
Injection moulding is the most important process for manufacturing plastic moulded products. The necessary equipment consists of two main elements, the injection moulding machine and the injection mould. The injection moulding machines used today are so-called universal machines, onto which various moulds for plastic parts with different geometries can be mounted, within certain dimension limits, but the injection mould design has to change with plastic products. For different moulding geometries, different mould configurations are usually necessary. The primary task of an injection mould is to shape the molten material into the final shape of the plastic product. This task is fulfilled by the cavity system that consists of core, cavity, inserts, and slider/lifter heads. The geometrical shapes and sizes of a cavity system are determined directly by the plastic moulded product, so all components of a cavity system are called product-dependent parts. (Hereinafter, product refers to a plastic moulded product, part refers to the component of an injection mould.) Besides the primary task of shaping the product, an injection mould has also to fulfil a number oftasks such as the distribution of melt, cooling the molten material, ejection of the moulded product, transmitting motion, guiding, and aligning the mould halves. The functional parts to fulfil these tasks are usually similar in structure and geometrical shape for different injection moulds. Their structures and geometrical shapes are independent of the plastic moulded products, but their sizes can be changed according to the plastic products. Therefore, it can be concluded that an injection mould is actually a mechanical assembly that consists of product-dependent parts and product-independent parts. Figure 1 shows the assembly structure of an injection mould. The design of a product-dependent part is based on extracting the geometry from the plastic product. In recent years, CAD/CAM technology has been successfully used to help mould designers to design the product-dependent parts. The
Fig. 1. Assembly structure of an injection mould
automatic generation of the geometrical shape for a product-dependent part from the plastic product has also attracted a lot of research interest [1,2]. However, little work has been carried out on the assembly modelling of injection moulds, although it is as important as the design of product-dependent parts. The mould industry is facing the following two difficulties when use a CAD system to design product-independent parts and the whole assembly of an injection mould. First, there are usually around one hundred product-independent parts in a mould set, and these parts are associated with each other with different kinds of constraints. It is time-consuming for the designer to orient and position the components in an assembly. Secondly, while mould designers, most of the time, think on the level of real-world objects, such as screws, plates, and pins, the CAD system uses a totally different level of geometrical objects. As a result, high-level object-oriented ideas have to be translated to low-level CAD entities such as lines, surfaces, or solids. Therefore, it is necessary to develop an automatic assembly modelling system for injection moulds to solve these two problems. In this paper, we address the following two key issues for automatic assembly modelling: representing a product-independent part and a mould assembly in a computer; and determining the position and orientation of a component part in an assembly.
This paper gives a brief review of related research in assembly modelling, and presents an integrated representation for the injection mould assembly. A simplified geometric symbolic method is proposed to determine the position and orientation of a part in the mould assembly. An example of automatic assembly modelling of an injection mould is illustrated.
2. Related Research
Assembly modelling has been the subject of research in diverse fields, such as, kinematics, AI, and geometric modelling. Lib-ardi et al. [3] compiled a research review of assembly modelling. They reported that many researchers had used graph structures to model assembly topology. In this graph scheme, the components are represented by nodes, and transformation matrices are attached to arcs. However, the transformation matrices are not coupled together, which seriously affects the transformation procedure, i.e. if a subassembly is moved, all its constituent parts do not move correspondingly. Lee and Gossard [4] developed a system that supported a hierarchical assembly data structure containing more basic information about assemblies such as “mating feature” between the components. The transformation matrices are derived automatically from the associations of virtual links, but this hierarchical topology model represents only “part-of” relations effectively.
Automatically inferring the configuration of components in an assembly means that designers can avoid specifying the transformation matrices directly. Moreover, the position of a component will change whenever the size and position of its reference component are modified. There exist three techniques to infer the position and orientation of a component in the assembly: iterative numerical technique, symbolic algebraic technique, and symbolic geometric technique. Lee and Gossard [5] proposed an iterative numerical technique to compute the location and orientation of each component from the spatial relationships. Their method consists of three steps: generation of the constraint equations, reducing the number of equations, and solving the equations. There are 16 equations for “against” condition, 18 equations for “fit” condition, 6 property equations for each matrix, and 2 additional equations for a rotational part. Usually the number of equations exceeds the number of variables, so a method must be devised to remove the redundant equations. The Newton–Raphson iteration algorithm is used to solve the equations. This technique has two disadvantages: first, the solution is heavily dependent on the initial solution; secondly, the iterative numerical technique cannot distinguish between different roots in the solution space. Therefore, it is possible, in a purely spatial relationship problem, that a
mathematically valid, but physically unfeasible, solution can be obtained.
Ambler and Popplestone [6] suggested a method of computing the required rotation and translation for each component to satisfy the spatial relationships between the components in an assembly. Six variables (three translations and three rotations) for each component are solved to be consistent with the spatial relationships. This method requires a vast amount of programming and computation to rewrite related equations in a solvable format. Also, it does not guarantee a solution every time, especially when the equation cannot be rewritten in solvable forms.
Kramer [7] developed a symbolic geometric approach for determining the positions and orientations of rigid bodies that satisfy a set of geometric constraints. Reasoning about the geometric bodies is performed symbolically by generating a sequence of actions to satisfy each constraint incrementally, which results in the reduction of the object’s available degrees of freedom (DOF). The fundamental reference entity used by Kramer is called a “marker”, that is a point and two orthogonal axes. Seven constraints (coincident, in-line, in-plane, parallelFz, offsetFz, offsetFx and helical) between markers are defined. For a problem involving a single object and constraints between markers on that body, and markers which have invariant attributes, action analysis [7] is used to obtain a solution. Actionanalysis decides the final configuration of a geometric object, step by step. At each step in solving the object configuration, degrees of freedom analysis decides what action will satisfy one of the body’s as yet unsatisfied constraints, given the available degrees of freedom. It then calculates how that action further reduces the body’s degrees of freedom. At the end of each step, one appropriate action is added to the metaphorical assembly plan. According to Shah and Rogers [8], Kramer’s work represents the most significant development for assembly modelling. This symbolic geometric approach can locate all solutions to constraint conditions, and is computationally attractive compared to an iterative technique, but to implement this method, a large amount of programming is required.
Although many researchers have been actively involved in assembly modelling, little literature has been reported on feature based assembly modelling for injection mould design.Kruth et al. [9] developed a design support system for an injection mould. Their system supported the assembly design for injection moulds through high-level functional mould objects (components and features). Because their system was based on AutoCAD, it could only accommodate wire-frame and simple solid models.
3. Representation of Injection Mould
Assemblies The two key issues of automated assembly modelling for injection moulds are, representing a mould assembly in com- puters, and determining the position and orientation of a product-independent part in the assembly. In this section, we present an object-oriented and feature-based representation for assemblies of injection moulds.
The representation of assemblies in a computer involves structural and spatial relationships between individual parts. Such a representation must support the construction of an assembly from all the given parts, changes in the relative positioning of parts, and manipulation of the assembly as a whole. Moreover, the representations of assemblies must meet the following requirements from designers:
1. It should be possible to have high-level objects ready to use while mould designers think on the level of real-world objects.
2. The representation of assemblies should encapsulate operational functions to automate routine processes such as pocketing and interference checks.
To meet these requirements, a feature-based and object-oriented hierarchical model is proposed to represent injection moulds. An assembly may be divided into subassemblies, which in turn consists of subassemblies and/or individual components. Thus, a hierarchical model is most appropriate for representing the structural relations between components. A hierarchy implies a definite assembly sequence. In addition, a hierarchical model can provide an explicit representation of the dependency of the position of one part on another.
Feature-based design [10] allows designers to work at a somewhat higher level of abstraction than that possible with the direct use of solid modellers. Geometric features are instanced, sized, and located quickly by the user by specifying a minimum set of parameters, while the feature modeller works out the details. Also, it is easy to make design changes because of the associativities between geometric entities maintained in the data structure of feature modellers. Without features, designers have to be concerned with all the details of geometric construction procedures required by solid modellers, and design changes have to be strictly specified for every entity affected by the change. Moreover, the feature-based representation will provide high-level assembly objects for designers to use. For example, while mould designers think on the level of a real- world object, e.g. a counterbore hole, a feature object of a counterbore hole will be ready in the computer for use.
Object-oriented modelling [11,12] is a new way of thinking about problems using models organised around real-world concepts. The fundamental entity is the object, which combines both data structures and behaviour in a single entity. Object-
oriented models are useful for understanding problems and designing programs and databases. In addition, the object- oriented representation of assemblies makes it easy for a“child” object to inherit information from its “parent”.
Figure 2 shows the feature-based and object-oriented hier- archical representation of an injection mould. The representation is a hierarchical structure at multiple levels of abstraction, from low-level geometric entities (form feature) to high-level subassemblies. The items enclosed in the boxes represent “assembly objects” (SUBFAs, PARTs and FFs); the solid lines represent “part-of” relation; and the dashed lines represent other relationships. Subassembly (SUBFA) consists of parts (PARTs). A part can be thought of as an “assembly” of form features (FFs). The representation combines the strengths of a feature-based geometric model with those of object-oriented models. It not only contains the “part-of” relations between the parent object and the child object, but also includes a richer set of structural relations and a group of operational functions for assembly objects. In Section 3.1, there is further discussion on the definition of an assembly object, and detailed relations between assembly objects are presented in Section 3.2
Fig. 2. Feature-based, object-oriented hierarchical representation
3.1 Definition of Assembly Objects
In our work, an assembly object, O, is defined as a unique, identifiable entity in the following form:
O = (Oid, A, M, R) (1)
Where:
Oid is a unique identifier of an assembly object (O). A is a set of three-tuples, (t, a, v). Each a is called an attribute of O, associated with each attribute is a type,
t, and a value, v. M is a set of tuples, (m, tc1, tc2, %, tcn, tc). Each element of M is a function that uniquely identifies a method. The symbol m represents a method name; and methods define operations on objects. The symbol tci(i= 1, 2, %, n) specifies the argument type and tc specifies the returned value type.
R is a set of relationships among O and other assembly objects. There are six types of basic relationships between assembly objects, i.e. Part-of, SR, SC, DOF, Lts, and Fit.
Table 1 shows an assembly object of injection moulds, e.g. ejector. The ejector in Table 1 is formally specified as:
(ejector-pinF1, {(string, purpose, ‘ejecting moulding’), (string, material, ‘nitride steel’), (string, catalogFno, ‘THX’)},
{(checkFinterference(), boolean), (pocketFplate(), boolean)}, {(part-of ejectionFsys), (SR Align EBFplate), (DOF Tx, Ty)}).
In this example, purpose, material and catalogFno are attributes with a data type of string; checkFinterference and pocketFplate are member functions; and Part-of, SR and DOF are relationships.
3.2 Assembly Relationships
There are six types of basic relationships between assembly objects, Part-of, SR, SC, DOF, Lts, and Fit.
Part-of An assembly object belongs to its ancestor object.
SR Spatial relations: explicitly specify the positions and orientations of assembly objects in an assembly. For a component part, its spatial relationship is derived from spatial constraints (SC).
SC Spatial constraints: implicitly locate a component part with respect to the other parts.
DOF Degrees of freedom: are allowable translational/ rotational directions of motion after assembly, with or without limits.
Lts Motion limits: because of obstructions/interferences, the DOF may have unilateral or bilateral limits.
Fit Size constraint: is applied to dimensions, in order to maintain a given class of fit.
Among all the elements of an assembly object, the relation-ships are most important for assembly design. The relationships between assembly objects will not only determine the position of objects in an assembly, but also maintain the associativities between assembly objects. In the following sub-sections, we will illustrate the relationships at the same assembly level with the help of examples.
3.2.1 Relationships Between Form Features
Mould design, in essence, is a mental process; mould designers most of the time think on the level of real-world objects such as plates, screws, grooves, chamfers, and counter-bore holes. Therefore, it is necessary to build the geometric models of all product-independent parts from form features. The mould designer can easily change the size and shape of a part, because of the relations between form features maintained in the part representation. Figure 3(a) shows a plate with a counter-bore hole. This part is defined by two form features, i.e. a block and a counter-bore hole. The counter-bore hole (FF2) is placed with reference to the block feature FF1, using their local coordinates F2and F1, respectively. Equations (2)–(5) show the spatial relationships between the counter-bore hole (FF2) and the block feature (FF1). For form features, there is no spatial constraint between them, so the spatial relationships are specified directly by the designer. The detailed assembly relationships between two form features are defined as follows:
Fig. 3. Assembly relationships.
F2k= F1k (4)
r2F= r1F+ b22*F1j+ AF1*F1i (5)
DOF:
ObjFhasF1FRDOF(FF2, F2j)
The counter-bore feature can rotate about axis F2j.
LTs(FF2, FF1):
AF1, b11? 0.5*b21 (6)
Fit (FF2, FF1):
b22= b12 (7)
Where
F and r are the orientation and position vectors of features.
F1= (F1i, F1j, F1k), F2= (F2i, F2j, F2k).
bij is the dimension of form features, Subscript i ifeature number, j is dimension number.
AF1is the dimension between form features.
Equations (2)–(7) present the relationships between the form feature FF1 and FF2. These relationships thus determine the position and orientation of a form feature in the part. Taking the part as an assembly, the form feature can be considered as “components” of the assembly.
The choice of form features is based on the shape characteristics of product-independent parts. Because the form features provided by the Unigraphics CAD/CAM system [13] can meet the shape requirements of parts for injection moulds and the spatial relationships between form features are also maintained, we choose them to build the required part models. In addition to the spatial relationships, we must record LTs, Fits relationships for form features, which are essential to c