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河南機(jī)電高等?？茖W(xué)校
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塑料蓋零件注塑成型工藝及注塑模具設(shè)計(jì)
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塑料蓋模具的設(shè)計(jì)與制造
摘 要
本模具為連接套注射模具, 在設(shè)計(jì)時(shí):1 、接受任務(wù)書。2 、調(diào)研消化原始資料。3 、選擇成型設(shè)備。4 、擬定模具結(jié)構(gòu)方案。5 、方案的討論與論證。7 、繪制模具裝配圖。8 、繪制零件圖。9 、編寫設(shè)計(jì)說明書。10 、模具制造試模與圖紙修改。正確的確定模具成型零件的尺寸凸模、凹模等零件是確定制件形狀、尺寸和表面質(zhì)量的直接因素關(guān)系甚大，要特別注意。模具的設(shè)計(jì)應(yīng)制造方便, 盡量做道使設(shè)計(jì)的模具制造容易、造價(jià)便宜。特別是比較復(fù)雜的成型零件，必須考慮是采用一般的機(jī)械加工方法加工還是采用特殊的加工方法加工。模具的設(shè)計(jì)應(yīng)當(dāng)效率高、安全、可靠。模具零件應(yīng)耐磨耐用。
關(guān)鍵詞：模具、成型、凸模、凹模。
Plastic Fasteners Die Design and Manufacture
Abstract
This molding tool is a cup that the cover injects the mold, while designing:1, accept the mission book.2 , the investigation digests the primitive data.3 , choose to model the equipments.4 , draft the molding tool construction project.5 , the discussion of the project and argument.7 , drawing the molding tool assembles the diagram.8 , draw the spare parts diagram.9 , weave to write to design the manual.10 , the molding tool manufacturing tries the mold and diagram paper modification.The exactitude really settles size punch , die,etc. spare parts that molding tool model spare parts is a direct factor that certain system a shape, size relate to with the surface quantity very big, want to be specially attention.The design of the molding tool should make the convenience, doing a molding tool manufacturing that make design easy and build the price cheapness to the best.Model the spare parts especially more complicatedly, must consider is to adopt the general machine process the method processes to adopt still to process specially the method processes.The design of the molding tool shoulds the efficiency high, safety, dependable.The molding tool spare parts should bear to whet enduring.
Key words:Molding tool, model, punch , die .
河南機(jī)電高等專科學(xué)校畢業(yè)設(shè)計(jì)說明書
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。
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)量要求越來越高。模具技術(shù)在國民經(jīng)濟(jì)中的作用越來越顯得更為重要。
模具是制造業(yè)的重要工藝基礎(chǔ)，在我國，模具制造屬于專用設(shè)備制造業(yè)。中國雖然很早就開始制造模具和使用模具，但長期未形成產(chǎn)業(yè)。直到20世紀(jì)80年代后期，中國模具工業(yè)才駛?cè)氚l(fā)展的快車道。近年，不僅國有模具企業(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，中國與國際平均水平和發(fā)達(dá)國家仍有較大差距，因此，每年需要大量進(jìn)口模具。中國模具產(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)分布來看，以珠江三角洲和長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)過在新飛電器有限公司、洛陽中國一拖的生產(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。并在圖書館借閱了許多相關(guān)手冊和書籍，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，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，從零件圖上分析，該零件總體形狀為空心圓筒形，在下部帶有一圈內(nèi)凹，內(nèi)凹為外半徑為55mm、內(nèi)半徑53mm，高度為4mm的圓環(huán)，因此模具設(shè)計(jì)時(shí)必須設(shè)置側(cè)向分型抽芯機(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Φ118mm,Φ106內(nèi)部形狀等尺寸精度為MT3級(jí)（GB/T14486—1993），次要尺寸，如高度24mm的尺寸精度為MT5級(jí)（GB/T14486—1993）。由以上分析可見，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。
從塑件的壁厚上來看,壁厚最大處為6mm,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=60.3cm
計(jì)算塑件的質(zhì)量：根據(jù)設(shè)計(jì)手冊可查得尼龍1010的密度為ρ=1.04kg/dm
塑件質(zhì)量：M=Vρ
=31.3×10×1.04×10
=60.01g
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選擇分型面。
該塑件為端蓋，表面無特殊的要求，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)簡單。
如圖2-1所示取B-B向?yàn)榉中兔妫樾緞?dòng)模，抽芯機(jī)構(gòu)簡單，可以設(shè)計(jì)簡單的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
本塑件在注塑時(shí)采用一模一件，即模具只需一個(gè)型腔，故不需要設(shè)計(jì)分流道.
2.2.1模腔數(shù)量的確定
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=Ф3.5mm
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的圓弧過渡。
2.3.2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.
2.3.3排氣結(jié)構(gòu)的設(shè)計(jì)
在注塑模具的設(shè)計(jì)過程中，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，也不宜開排氣槽.
2.3.4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=22.5/2=11.25mm
另加3～5mm的抽芯安全系數(shù)，可取抽芯距為15mm
2.4.2確定斜銷的傾角
斜導(dǎo)柱的傾角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
斜導(dǎo)柱的直徑取決于抽拔力及傾角可按設(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，取斜導(dǎo)柱的直徑d=Ф12mm
2.4.4斜導(dǎo)柱的長度
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）
=69.6mm
取： L=70mm
2.4.5 滑塊和導(dǎo)滑槽設(shè)計(jì)
由于側(cè)凹的尺寸較小型芯滑塊可采用整體式加工增加強(qiáng)度，導(dǎo)滑槽的導(dǎo)滑長度和定位裝置的設(shè)計(jì)可采用經(jīng)驗(yàn)法，側(cè)向抽芯的抽拔距較小，也無須滑塊的定位裝置。
2-2 抽芯機(jī)構(gòu)示意圖
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)簡單，模具牢固，不易變形，制件沒拼界逢，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】：
長為:300 mm. 寬為:230 mm.
凹模高為: h=25mm
件高為: 6mm
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％。考慮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
Φ118
Lm=(Ls+LsScp％－3/4Δ)+Б
Φ118.40+0.050
24
24.48+0.020
80
79.96+0.08
表一
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，合?？臻g
(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。開模時(shí)動(dòng)模部分隨動(dòng)模板一起漸漸將分型面打開，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)過在新飛電器有限公司、洛陽中國一拖的生產(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。并在圖書館借閱了許多相關(guān)手冊和書籍，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)。
致謝
首先感謝本人的導(dǎo)師于智宏老師，他對(duì)我的仔細(xì)審閱了本文的全部內(nèi)容并對(duì)我的畢業(yè)設(shè)計(jì)內(nèi)容提出了許多建設(shè)性建議。于智宏老師淵博的知識(shí)，誠懇的為人，使我受益匪淺，在畢業(yè)設(shè)計(jì)的過程中，特別是遇到困難時(shí)，他給了我鼓勵(lì)和幫助，在這里我向他表示真誠的感謝！
感謝母?！幽蠙C(jī)電高等?？茖W(xué)校的辛勤培育之恩！感謝材料工程系給我提供的良好學(xué)習(xí)及實(shí)踐環(huán)境，使我學(xué)到了許多新的知識(shí)，掌握了一定的操作技能。
感謝和我在一起進(jìn)行課題研究的同窗司永富同學(xué)，和他在一起討論、研究使我受益非淺。
最后，我非常慶幸在三年的的學(xué)習(xí)、生活中認(rèn)識(shí)了很多可敬的老師和可親的同學(xué)，并感激師友的教誨和幫助！
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］ 中國模具設(shè)計(jì)大典.
［3］ 王孝陪主編. 塑料成型工藝及模具簡明手冊. 機(jī)械工業(yè)出版社. 2000
［4］ 模具制造手冊編寫組. 模具制造手冊. 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)與制造簡明手冊. 上海科學(xué)技術(shù)出版社，1998
［6］ 賈潤禮，程志遠(yuǎn)主編. 實(shí)用注塑模設(shè)計(jì)手冊. 中國輕工業(yè)出版社. 2000
［7］ 唐志玉主編. 模具設(shè)計(jì)師指南. 國防工業(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. 簡明模具工實(shí)用技術(shù)手冊. 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
塑料概模具的設(shè)計(jì)與制造
摘 要
本模具為連接套注射模具, 在設(shè)計(jì)時(shí):1 、接受任務(wù)書。2 、調(diào)研消化原始資料。3 、選擇成型設(shè)備。4 、擬定模具結(jié)構(gòu)方案。5 、方案的討論與論證。7 、繪制模具裝配圖。8 、繪制零件圖。9 、編寫設(shè)計(jì)說明書。10 、模具制造試模與圖紙修改。正確的確定模具成型零件的尺寸凸模、凹模等零件是確定制件形狀、尺寸和表面質(zhì)量的直接因素關(guān)系甚大，要特別注意。模具的設(shè)計(jì)應(yīng)制造方便, 盡量做道使設(shè)計(jì)的模具制造容易、造價(jià)便宜。特別是比較復(fù)雜的成型零件，必須考慮是采用一般的機(jī)械加工方法加工還是采用特殊的加工方法加工。模具的設(shè)計(jì)應(yīng)當(dāng)效率高、安全、可靠。模具零件應(yīng)耐磨耐用。
關(guān)鍵詞：模具、成型、凸模、凹模。
Plastic Fasteners Die Design and Manufacture
Abstract
This molding tool is a cup that the cover injects the mold, while designing:1, accept the mission book.2 , the investigation digests the primitive data.3 , choose to model the equipments.4 , draft the molding tool construction project.5 , the discussion of the project and argument.7 , drawing the molding tool assembles the diagram.8 , draw the spare parts diagram.9 , weave to write to design the manual.10 , the molding tool manufacturing tries the mold and diagram paper modification.The exactitude really settles size punch , die,etc. spare parts that molding tool model spare parts is a direct factor that certain system a shape, size relate to with the surface quantity very big, want to be specially attention.The design of the molding tool should make the convenience, doing a molding tool manufacturing that make design easy and build the price cheapness to the best.Model the spare parts especially more complicatedly, must consider is to adopt the general machine process the method processes to adopt still to process specially the method processes.The design of the molding tool shoulds the efficiency high, safety, dependable.The molding tool spare parts should bear to whet enduring.
Key words:Molding tool, model, punch , die .
26
河南機(jī)電高等?？茖W(xué)校
畢業(yè)設(shè)計(jì)說明書
畢業(yè)設(shè)計(jì)題目：塑料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 6月 05 日
河南機(jī)電高等專科學(xué)校
畢業(yè)設(shè)計(jì)評(píng)語
學(xué)生姓名： 班級(jí): 學(xué)號(hào)：
題 目： 塑料蓋產(chǎn)品注塑模設(shè)計(jì)
綜合成績：
指導(dǎo)者評(píng)語：
1）該同學(xué)工作態(tài)度較認(rèn)真，能較好的完成畢業(yè)設(shè)計(jì)任務(wù)；
2）該同學(xué)查閱了國內(nèi)有關(guān)沖壓模具設(shè)計(jì)與制造方面的大量資料，制訂出了較合理的沖壓成形工藝及模具結(jié)構(gòu)，設(shè)計(jì)中不存在創(chuàng)新；
3）該同學(xué)設(shè)計(jì)說明書內(nèi)容較完整，計(jì)算基本正確，書寫較規(guī)范，圖紙符合要求且質(zhì)量較高；
4）該同學(xué)裝配圖、零件圖上有少許不合理之處；
5）建議該同學(xué)成績評(píng)定：良好；
6）可以提交答辯。
指導(dǎo)者(簽字)：
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畢業(yè)設(shè)計(jì)評(píng)語
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第 22 頁 共 23 頁
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