英文原文名《EnglishforDieMouldDesignandManufacturing》中文譯名《模具設(shè)計(jì)與制造專業(yè)英語》英文原文版出處：《模具設(shè)計(jì)與制造專業(yè)英語》，劉建雄王家惠廖丕博主編，北京大學(xué)出版社2006年3月第1版譯文：3．3壓鑄壓鑄是通過壓力作用下使熔融金屬進(jìn)入金屬模具，是快速生產(chǎn)精密產(chǎn)品的一局部。這個(gè)術(shù)語同時(shí)適用于所得的鑄件。壓鑄件因?yàn)榫哂杏辛己玫耐獗矶梢越?jīng)濟(jì)地應(yīng)用于批量和大批量生產(chǎn)中。只需要相對小的加工，就可以實(shí)現(xiàn)很好的公差保證，這些原那么在一些壓鑄操作中都得到了很好的檢驗(yàn)。壓鑄模具是永久性的，不會由于金屬的引入而影響到他們，除正常磨損或損耗。在相同的大小和形狀的條件下，壓鑄模通常比塑料模和永久鑄造更昂貴。這種快速成型依靠快速把金屬注入模具、冷卻、開模、鑄件取出和模具下次壓鑄的準(zhǔn)備。3．3．1模具壓鑄周期在鑄造周期里，首先模具閉合并且鎖緊，熔化的金屬在一個(gè)特定溫度的熔爐中，然后進(jìn)入注射缸，根據(jù)合金的類型，用于熱壓室或者冷壓室金屬澆注系統(tǒng)，這些將在后面描述。在注射階段的壓鑄過程中，熔融金屬在壓力的作用下，快速通過模具澆注系統(tǒng)進(jìn)入模具并排出模具里的空氣，金屬量必須足夠大以充滿型腔和溢流井，溢流井的設(shè)計(jì)是用來儲存接收溢流出來的融溶金屬液的，因?yàn)榻佑|到模具型腔的空氣容易氧化，同時(shí)也最先接觸到模具其也可以快速冷卻以便可以接下來進(jìn)行第二次的壓鑄。一旦這模具型腔填滿了，作用于金屬液的壓力會增大，保壓一定的時(shí)間以便金屬液凝固，模具的別離、工件的取出通常通過機(jī)器自動操作完成，翻開模具進(jìn)行必要的清理和潤滑，然后下一輪壓鑄繼續(xù)循環(huán)。從模具取下的工件冷卻后，操作工切除金屬澆注填充時(shí)產(chǎn)生的披鋒，同時(shí)去除溢流井和分型線，接著能進(jìn)行二次加工和外表后處理。3．3．2壓鑄合金四類主要的壓鑄模具合金為鋅、鋁、鎂和銅基合金，壓鑄工藝開展于19世紀(jì)鉛/錫合金零件的制作，然而，鉛和錫由于力學(xué)性能差，現(xiàn)在很少用來壓鑄。最常見的壓鑄合金是鋁合金，它們密度低，耐腐蝕性好，易于鑄造，并具有良好的力學(xué)性能和尺寸穩(wěn)定性。鋁合金的缺點(diǎn)是用冷壓室鑄造時(shí)比熱壓室鑄造需要更長的周期因?yàn)樾枰粋€(gè)別離澆注操作。鋅基合金是最容易鑄造的，它們也有很高的延展性和良好的抗沖擊強(qiáng)度，因此可廣泛用于產(chǎn)品上，鑄件可以制造得很薄，并且外表平滑性良好，使其易于電鍍和噴涂。然而，鋅基合金容易被腐蝕，需要在零件各局部涂上保護(hù)膜。因此，鋅合金的高比重導(dǎo)致每個(gè)單位體積的鋅合金比壓鑄鋁合金要更貴。鋅鋁合金的鋁含量〔82.7%〕比標(biāo)準(zhǔn)鋅合金高，類似于標(biāo)準(zhǔn)鋅合金，能獲得薄壁和耐久的壓鑄件，但與鋁合金，在冷壓室機(jī)器中必須每個(gè)周期都需要澆注熔融金屬，唯一例外的是ZA8〔8%鋁〕，這是鋁鋅系列中含鋁量最低的。鎂合金有較低的密度、高的強(qiáng)度重量比、優(yōu)越的阻尼能力和良好的機(jī)械加工性能。銅基合金、黃銅和青銅，比任何壓鑄合金的力學(xué)性能都要好，但是它們更貴。黃銅具有高的強(qiáng)度和韌性、好的耐磨性，并具有優(yōu)良的耐腐蝕性。銅基合金鑄造的一個(gè)主要缺點(diǎn)是在非常高的鑄造溫度下由熱疲勞引起模具壽命縮短，合金澆注溫度對模具壽命影響最為強(qiáng)烈，也正是因?yàn)檫@個(gè)原因模具壽命最長的是鋅合金，最短的是銅合金。然而，鑄件尺寸、壁厚和幾何復(fù)雜性同樣影響模具外表的磨損和最終的損壞也是差不多的。3．3．3壓鑄模具壓鑄模具由兩個(gè)主要局部組成——?jiǎng)幽＞植亢投＞植?，它們在分型線閉合，型腔和型芯通常加工后鑲嵌到這兩局部，定模固定在定模扳上，而動模固定在動模板上〔見圖3-10，3-11〕，型腔和型芯設(shè)計(jì)必須匹配以便能夠順利開模。壓鑄模具的結(jié)構(gòu)幾乎與注塑成型模具相似，在注射成型術(shù)語中，動模包括型芯和噴射器殼體，定模包括型腔和支撐板。壓鑄模鑄件側(cè)抽芯機(jī)構(gòu)與外部相交特征可以非常精準(zhǔn)地建立起來，這是壓鑄模和注塑模相同的特性。然而，熔模鑄造合金在模具接觸外表的粘性遠(yuǎn)遠(yuǎn)小于注射成型的。這種現(xiàn)象被稱為“噴射”，容易堵塞模具，正是因?yàn)檫@個(gè)原因，結(jié)合飛邊的高收縮力導(dǎo)致局部收縮非常困難，使得產(chǎn)品難以滿足內(nèi)部核心機(jī)制。因此，內(nèi)螺紋或其他內(nèi)部切削孔通常無法被鑄造，必須由昂貴的額外加工生產(chǎn)。澆注系統(tǒng)在壓鑄和注塑模具中的建立是相同的?！皣娚洹苯?jīng)常在定模和動模之間產(chǎn)生，在產(chǎn)品分型線上形成一些薄而不規(guī)那么的披鋒，有時(shí)，這些分型線會濺出合金，由于這個(gè)原因，壓鑄機(jī)必須安裝平安裝置以抑制這些濺出的材料。在壓鑄過程中的一個(gè)區(qū)別主要在于溢流井通常圍繞壓鑄型腔的周邊，如前面所提到的，在鑄造時(shí)它們可以減少氧化物的量，最先進(jìn)入模具的合金，通過排氣孔把型腔內(nèi)的空氣排出，隨后注射的合金和模具有更高的溫度，從而減少金屬凝固過早的時(shí)機(jī)，這種過早凝固形成的外表缺陷稱為冷料，是由于金屬流動時(shí)還沒有相遇熔接在一起就已經(jīng)凝固所致，當(dāng)壓鑄模較小時(shí)，溢流槽大幅增加熔融金屬也可以使模具保持一定的溫度。壓鑄機(jī)1.熱室壓鑄機(jī)一個(gè)典型的熱室注射系統(tǒng)如圖3-12所示，由氣缸、柱塞、流道和噴嘴組成，注塑周期開始時(shí)的柱塞在相應(yīng)的位置上，熔融金屬流入保溫爐內(nèi)，通過進(jìn)氣口并進(jìn)入壓力缸，然后，當(dāng)模具合模并鎖緊時(shí)，液壓柱塞移動到氣缸和密封進(jìn)氣口，熔融金屬通過流道和噴嘴到澆口、澆注系統(tǒng)和模具模腔，澆口是噴嘴通過進(jìn)料系統(tǒng)進(jìn)入定模的錐形擴(kuò)流通道，錐形狀提供從澆注點(diǎn)到澆注流道的平滑過渡，這使凝固后的產(chǎn)品容易脫出。在預(yù)設(shè)的金屬凝固時(shí)間里，液壓系統(tǒng)使柱塞返回，這個(gè)周期循環(huán)往復(fù)。2.冷室壓鑄機(jī)一個(gè)典型的冷室壓鑄機(jī)如圖3-13所示，由水冷式柱塞，一個(gè)壓射缸，和位于上方的水平式注射室和一個(gè)澆注孔組成。操作順序如下：當(dāng)模具關(guān)閉和鎖緊并且氣缸柱塞縮回，熔融金屬通過澆注孔被澆進(jìn)注射室，為了包緊型腔里的金屬液，金屬的澆注體積大于型腔和澆注系統(tǒng)、溢流井的體積，然后注射氣缸加壓，使活塞通過注射室，使熔融金屬進(jìn)入模具型腔，在金屬凝固后，模具翻開，柱塞返回到原來的位置。當(dāng)模具翻開，在注射筒端多余的金屬，被稱為料柄，是被逼出來的，因?yàn)樗沁B接到缸體鑄件。在壓鑄周期中料柄是需要的，用于保持液態(tài)金屬的壓力鑄造、凝固和收縮。第4章鍛造模具4.1簡介鍛造是一個(gè)通過各種模具和工具施加壓力到工件加工的方法，這是最古老的金屬加工方法，至少可以追溯到公元前4000年，也許早在公元前8000年，鍛造通過用石頭錘擊金屬用來制造珠寶、錢幣和各種器具。簡單的鍛造操作，傳統(tǒng)上由鐵匠用重錘子和砧進(jìn)行。然而，大多數(shù)鍛件需要一套模具和壓力機(jī)或鍛錘等設(shè)備完成。典型的鍛造產(chǎn)品有螺栓和鉚釘、連桿、渦輪機(jī)軸、齒輪、有手柄的工具、機(jī)械構(gòu)件、飛行器、鐵路和各種其它運(yùn)輸設(shè)備。通過控制金屬的流動和晶粒結(jié)構(gòu)，可以鍛造具有良好的強(qiáng)度和韌性的零件；它們能夠可靠地用于高強(qiáng)度工序〔如圖4-1〕。鍛造可在室溫〔冷鍛〕或在高溫〔熱鍛，取決于溫度〕進(jìn)行。由于該材料的強(qiáng)度較高，冷鍛需要更大的力量，工件的材料在室溫下必須具有足夠的延展性，冷鍛造件具有良好的外表光潔度和尺寸精度。熱鍛需要較小的力量，但它產(chǎn)生的尺寸精度和外表光潔度較差。鍛件通常需要額外的后處理操作，例如熱處理以修改其性能，然后加工以得到準(zhǔn)確的成品尺寸，這些操作可以通過精密鍛造，是一個(gè)趨向最終形狀或近終形狀成型過程的重要例子，這種顯著減少加工，降低產(chǎn)品制造本錢的方法，是今后開展的趨勢。有幾種形式的鍛造，但還是有一些差異識別過程與名字在不同的引用。4.2開式模鍛開式模鍛是最簡單的鍛造工藝，雖然大多數(shù)開放式模鍛一般重達(dá)15公斤?500公斤，但是也有鍛重300噸的，大小的范圍可以從非常小的零件到長達(dá)23米〔如螺旋槳〕。開模鍛過程可以描述為由固體工件放置在兩個(gè)平面之間通過壓縮它降低高度〔如圖4-2〕，這個(gè)過程也被稱為鐓粗或平鍛。模具外表在開式模鍛可以簡單鑄造，生產(chǎn)相對簡單的鍛件。在理想的條件下對工件的變形如圖4-2〔b〕所示，因?yàn)殄懠w積恒定，在高度方向減少，在直徑方向就會增加。需要注意的是，在圖4-2〔b〕中，所述工件是均勻地變形，而在實(shí)際操作中，工件變成桶形〔如圖4-2〔c〕〕，這種變形也被稱為鐓鍛。快速移動造成主要由摩擦力形成接口,反的材料在這些接口對流?？焖僖苿涌梢杂行Ю脻櫥瑒?。把加熱后的工件放在冷模之間鍛造同樣能變成圓桶形，在界面的局部迅速冷卻，而工件的其余局部仍然相對較熱，因此，在工件的端部的材料具有變形比在其中心處的材料高的阻力，所以在工件的中心局部沿橫向擴(kuò)展比端部大，可以通過熱效應(yīng)使用加熱的金屬模具減少或消除圓桶效應(yīng)，熱障如在模具和工件接觸面之間使用玻璃纖維也是可行的。引伸鍛造也稱為拔長，是一個(gè)基于開式模鍛并通過間隔連續(xù)鍛造工序減小棒料厚度的操作〔如圖4-3所示〕，因?yàn)槊看涡谐痰慕佑|面積較小，一條長的棒料不需要很大的力或者機(jī)器就能減小其厚度。鐵匠用錘子和砧加工加熱的金屬工件，各種設(shè)計(jì)的鐵柵欄通常用這種方法制成。4.3模鍛和閉式模鍛在模鍛里，工件通過在兩個(gè)有所需形狀的模具型腔〔鍛?！持谐尚巍踩鐖D4-4所示〕，需要注意的是一些材料向外流動，并形成一些飛邊。飛邊有一個(gè)顯著的作用在流動的材料進(jìn)入模鍛時(shí)：薄的飛邊快速冷卻，并且由于其摩擦力，這使得材料在模具型腔中受到高的壓力，從而促進(jìn)模具型腔的填充。坯件通過這些方法制備〔a〕切割或剪切一條擠壓或拉伸的棒料〔b〕粉末冶金制作型坯〔c〕鑄造或者〔d〕在鍛造前預(yù)先成形毛坯。坯件放在下模，然后上模開始下降，坯件的形狀逐漸改變，如圖4-5〔a〕所示為一個(gè)連桿鍛造。預(yù)制坯鍛造過程如拔長和滾壓〔如圖4-5〔b〕和〔c〕〕通常用于將材料分配到不同坯件區(qū)域，就像它們是面團(tuán)制作餡餅。拔長時(shí)，材料從一個(gè)區(qū)域分配，滾壓時(shí)，材料聚集在一個(gè)局部區(qū)域里，然后將部件形成為連桿的粗糙形狀稱為預(yù)鍛過程，使用預(yù)鍛模，最后的操作是在鍛造金屬模具給予鍛造件最終形狀的精加工，飛邊通常通過修整操作去除〔如圖4-6所示〕。如圖4-4和4-5〔a〕所示的例子被稱為閉式模鍛。然而，真正的閉式模或者毛邊鍛造，飛邊不形成并且工件完全填充模腔〔如右圖4-7〔b〕所示〕。精確控制材料體積和適當(dāng)?shù)哪＞咴O(shè)計(jì)是為了閉式模鍛獲得所需尺寸和公差。尺寸缺乏的坯料阻礙完全填充模腔，相反尺寸有余的坯料產(chǎn)生過多的壓力并且可能引起模具過早地失效或者卡住。精密鍛造出于經(jīng)濟(jì)原因，當(dāng)今鍛造加工的趨勢是朝著更大的精確度開展，從而降低了額外精加工操作的數(shù)量。其中形成的局部接近于所需零件的最終尺寸稱為近凈形狀或者凈形鍛造，在這樣的過程中，有少量過量的材料在鍛造部件上，并且它隨后被去除〔通常通過修整或磨削〕。在精密鍛造，特別模具生產(chǎn)零件比模鍛精度更高并要求更少的加工，該方法需要更高性能的設(shè)備因?yàn)榈玫骄?xì)部件需要更大的力。由于它們需要相對低的鍛造負(fù)載和溫度，鋁和鎂的合金特別適用于精密鍛造，同時(shí)發(fā)生模具磨損小，外表光潔度好，鋼和鈦也可以精密鍛造。典型精密鍛造產(chǎn)品有齒輪、連桿、外殼和渦輪葉片。精密鍛造需要特殊和更復(fù)雜的模具，精密控制坯料的體積和形狀，坯料在模腔內(nèi)精確定位，因此投入較高。然而更少的材料被浪費(fèi)，并且需要更小后續(xù)加工，因?yàn)樵摴ぜ咏罱K所需的形狀。因此，以往的鍛造與精密鍛造之間的選擇需要一個(gè)經(jīng)濟(jì)分析，特別是在考慮到生產(chǎn)數(shù)量時(shí)。精壓精壓根本上是一個(gè)閉式模鍛過程，通常用來鑄造硬幣、獎(jiǎng)?wù)潞椭閷殹踩鐖D4-8〔a〕〔b〕所示〕，鍛造毛坯在一個(gè)完全封閉的模腔里精壓。為了生產(chǎn)精細(xì)所需的壓力可以是五或六倍的材料強(qiáng)度，例如，在新鑄幣的細(xì)致局部。對于某些工件可能需要幾個(gè)精壓操作，潤滑油不能用于精壓中，因?yàn)樗鼈兡芟萑肽＞咝颓恢?，并且是不能壓縮的，阻止充分再現(xiàn)模具外表細(xì)節(jié)。在精壓過程中也使用鍛件和其他的產(chǎn)品，以改善外表光潔度和賦予所需的尺寸精度，這一過程被稱為按尺寸加工，涉及高壓的同時(shí)在工件形狀按尺寸加工使用小的變形。制造帶有字母和數(shù)字的工件能夠類似于精壓過程快速完成。原文：3.3DieCastingDiecastingistheartofrapidlyproducingaccuratelydimensionedpartsbyforcingmoltenmetalunderpressureintometaldies.Thetermalsoappliestotheresultantcasting.Diecastingscanbeusedeconomicallyindesignshavingmoderatetolargeactivitybecausethecompletedpiecehasagoodsurface,requiresrelativelylittlemachining,andcanbeheldtoclosetolerances.Theprinciplesofdiecastingfollowthoseofgoodpracticeinanycastingoperation.Thesteeldiesarepermanentandshouldnotbeaffectedbythemetalintroducedintothem,exceptfornormalabrasionorwear.Die-castingdiesareusuallymoreexpensivethanthoseusedinplasticorpermanentmoldingofapartofsimilarsizeandshape.Therapidityofoperationdependsuponthespeedwithwhichthemetalcanbeforcedintothedie,cooled,andejected;thecastingremoved;andthediepreparedforthenextshot.TheDieCastingCycleInthecastingcycle,firstthedieisclosedandlocked.Themoltenmetal,whichismaintainedbyafurnaceataspecifiedtemperature,thenenterstheinjectioncylinder.Dependingonthetypeofalloy,eitherahot-chamberorcold-chambermetal-pumpingsystemisused.Thesewillbedescribedlater.Duringtheinjectionstageofthediecastingprocess,pressureisappliedtothemoltenmetal,whichisthendrivenquicklythroughthefeedsystemofthediewhileairescapesfromthediethroughvents.Thevolumeofmetalmustbelargeenoughtooverflowthediecavitiesandfilloverflowwells.Theseoverflowwellsaredesignedtoreceivetheleadportionofthemoltenmetal,whichtendstooxidizefromcontactwithairinthecavityandalsocoolstoorapidlyfrominitialdiecontacttoproducesoundcastings.Oncethecavitiesarefilled,pressureonthemetalisincreasedandheldforaspecifieddwelltimeduringwhichsolidificationtakesplace.Thediesarethenseparated,andthepartextracted,oftenbymeansofautomaticmachineoperation.Theopendiesarethencleanedandlubricatedasneeded,andthecastingcycleisrepeated.Followingextractionfromthedie,partsareoftenquenchedandthentrimmedtoremovetherunners,whichwerenecessaryformetalflowduringmoldfilling.Trimmingisalsonecessarytoremovetheoverflowwellsandanyparting-lineflashthatisproduced.Subsequently,secondarymachiningandsurfacefinishingoperationsmaybeperformed.DieCastingAlloysThefourmajortypesofalloysthataredie-castarezinc,aluminum,magnesium,andcopper-basedalloys.Thediecastingprocesswasdevelopedinthe19thcenturyforthemanu-factureoflead/tinalloyparts.However,leadandtinarenowveryrarelydie-castbecauseoftheirpoormechanicalproperties.Themostcommondiecastingalloysarethealuminumalloys.Theyhavelowdensity,goodcorrosionresistance,arerelativelyeasytocast,andhavegoodmechanicalpropertiesanddimensionalstability.Aluminumalloyshavethedisadvantageofrequiringtheuseofcold-chambermachines,whichusuallyhavelongercycletimesthanhot-chambermachinesowingtotheneedforaseparateladlingoperation.Zinc-basedalloysaretheeasiesttocast.Theyalsohavehighductilityandgoodimpactstrength,andthereforecanbeusedforawiderangeofproducts.Castingscanbemadewithverythinwalls,aswellaswithexcellentsurfacesmoothness,leadingtoeaseofpreparationforplatingandpainting.Zincalloycastings,however,areverysusceptibletocorrosionandmustusuallybecoated,addingsignificantlytothetotalcostofthecomponent.Also,thehighspecificgravityofzincalloysleadstoamuchhighercostperunitvolumethanforaluminumdiecastingalloys.Zinc-aluminum(ZA)alloyscontainahigheraluminumcontent(82.7%)thanthestandardzincalloys.Thinwallsandlongdielivescanbeobtained,similartostandardzincalloys,butaswithaluminumalloys,cold-chambermachines,whichrequirepouringofthemoltenmetalforeachcycle,mustusuallybeused.ThesingleexceptiontothisruleisZA8(8%Al),whichhasthelowestaluminumcontentofthezinc-aluminumfamily.Magnesiumalloyshaveverylowdensity,ahighstrength-to-weightratio,exceptionaldampingcapacity,andexcellentmachinabilityproperties.Copper-basedalloys,brassandbronze,providethebestmechanicalpropertiesofanyofthediecastingalloys;buttheyaremuchmoreexpensive.Brasseshavehighstrengthandtoughness,goodwearresistance,andexcellentcorrosionresistance.Onemajordisadvantageofcopper-basedalloycastingistheshortdielifecausedbythermalfatigueofthediesattheextremelyhighcastingtemperatures.Dielifeisinfluencedmoststronglybythecastingtemperatureofthealloys,andforthatreasonisgreatestforzincandshortestforcopperalloys.However,thisisonlyanapproximationsincecastingsize,wallthickness,andgeometricalcomplexityalsoinfluencethewearandeventualbreakdownofthediesurface.DieCastingDiesDiecastingdiesconsistoftwomajorsections——theejectordiehalfandthecoverdiehalf——whichmeetatthepartingline.Thecavitiesandcoresareusuallymachinedintoinsertsthatarefittedintoeachofthesehalves.Thecoverdiehalfissecuredtothestationaryplaten,whiletheejectordiehalfisfastenedtothemovableplaten(seeFigs.3-10,3-11).Thecavityandmatchingcoremustbedesignedsothatthediehalvescanbepulledawayfromthesolidifiedcasting.Theconstructionofdiecastingdiesisalmostidenticaltothatofmoldsforinjectionmolding.Ininjectionmoldingterminology,theejectordiehalfcomprisesthecoreplateandejectorhousing,andthecoverdiehalfcomprisesthecavityplateandbackingsupportplate.Side-pullmechanismsforcastingpartswithexternalcross-featurescanbefoundinexactlythesameformindiecastingdiesasinplasticinjectionmolds.However,moltendiecastingalloysaremuchlessviscousthanthepolymermeltininjectionmoldingandhaveagreattendencytoflowbetweenthecontactingsurfacesofthedie.Thisphenomenon,referredtoas“flashing”,tendstojammoldmechanisms,whichmust,forthisreason,berobust.Thecombinationofflashingwiththehighcoreretractionforcesduetopartshrinkagemakesitextremelydifficulttoproducesatisfactoryinternalcoremechanisms.Thus,internalscrewthreadsorotherinternalundercutscannotusuallybecastandmustbeproducedbyexpensiveadditionalmachiningoperations.Ejectionsystemsfoundindiecastingdiesareidenticaltotheonesfoundininjectionmolds.“Flashing”alwaysoccursbetweenthecoverdieandejectordiehalves,leadingtoathin,irregularbandofmetalaroundthepartingline.Occasionally,thispartinglineflashmayescapebetweenthediefaces.Forthisreason,fullsafetydoorsmustalwaysbefittedtomanualdiecastingmachinestocontainanysuchescapingflashmaterial.Onemaindifferenceinthediecastingprocessisthatoverflowwellsareusuallydesignedaroundtheperimeterofdiecastingcavities.Asmentionedearlier,theyreducetheamountofoxidesinthecasting,byallowingthefirstpartoftheshot,whichdisplacestheairthroughtheescapevents,topasscompletelythroughthecavity.Theremainingportionoftheshotandthediearethenatahighertemperature,therebyreducingthechanceofthemetalfreezingprematurely.Suchprematurefreezingleadstotheformationofsurfacedefectscalledcoldshuts,inwhichstreamsofmetaldonotweldtogetherproperlybecausetheyhavepartiallysolidifiedbythetimetheymeet.Overflowwellsarealsoneededtomaintainamoreuniformdietemperatureonsmallcastings,byaddingsubstantiallytothemassofmoltenmetal.DieCastingMachines1.Hot-ChamberMachinesAtypicalhot-chamberinjectionorshotsystem,asshowninFig.3-12,consistsofacylinder,aplunger,agooseneck,andanozzle.Theinjectioncyclebeginswiththeplungerintheupposition.Themoltenmetalflowsfromthemetal-holdingpotinthefurnace,throughtheintakeports,andintothepressurecylinder.Then,withthediesclosedandlocked,hydraulicpressuremovestheplungerdownintothepressurecylinderandsealsofftheintakeports.Themoltenmetalisforcedthroughthegooseneckchannelandthenozzleandintothesprue,feedsystem,anddiecavities.Thesprueisaconicallyexpandingflowchannelthatpassesthroughthecoverdiehalffromthenozzleintothefeedsystem.Theconicalshapeprovidesasmoothtransitionfromtheinjectionpointtothefeedchannelsandallowseasyextractionfromthedieaftersolidification.Afterapresetdwelltimeformetalsolidification,thehydraulicsystemisreversedandtheplungerispulledup.Thecyclethenrepeats.2.Cold-ChamberMachinesAtypicalcold-chambermachine,asshowninFig.3-13,consistsofahorizontalshotchamberwithapouringholeonthetop,awater-cooledplunger,andapressurizedinjectioncylinder.Thesequenceofoperationsisasfollows:whenthedieisclosedandlockedandthecylinderplungerisretracted,themoltenmetalisladledintotheshotchamberthroughthepouringhole.Inordertotightlypackthemetalinthecavity,thevolumeofmetalpouredintothechamberisgreaterthanthecombinedvolumeofthecavity,thefeedsystem,andtheoverflowwells.Theinjectioncylinderisthenenergized,movingtheplungerthroughthechamber,therebyforcingthemoltenmetalintothediecavity.Afterthemetalhassolidified,thedieopensandtheplungermovesbacktoitsoriginalposition.Asthedieopens,theexcessmetalattheendoftheinjectioncylinder,calledthebiscuit,isforcedoutofthecylinderbecauseitisattachedtothecasting.Materialinthebiscuitisrequiredduringthediecastingcycleinordertomaintainliquidmetalpressureonthecastingwhileitsolidifiesandshrinks.Chapter4ForgingDie4.1IntroductionForgingisaprocessinwhichtheworkpieceisshapedbycompressiveforcesappliedthroughvariousdiesandtools.Itisoneoftheoldestmetalworkingoperations,datingbackatleastto4000B.C.——perhapsasfarbackas8000B.C.Forgingwasfirstusedtomakejewelry,coins,andvariousimplementsbyhammeringmetalwithtoolsmadeofstone.Simpleforgingoperationscanbeperformedwithaheavyhandhammerandananvil,aswastraditionallydonebyblacksmiths.Mostforgings,however,requireasetofdiesandsuchequipmentasapressoraforginghammer.Typicalforgedproductsareboltsandrivets,connectingrods,shaftsforturbines,gears,handtools,andstructuralcomponentsformachinery,aircraft,railroads,andavarietyofothertransportationequipment.Metalflowandgrainstructurecanbecontrolled,soforgedpartshavegoodstrengthandtoughness;theycanbeusedreliablyforhighlystressedandcriticalapplications(Fig.4-1).Forg-ingmaybedoneatroomtemperature(coldforging)oratelevatedtemperatures(warmorhotforging,dependingonthetemperature).Becauseofthehigherstrengthofthematerial,coldforgingrequiresgreaterforces,andtheworkpiecematerialsmusthavesufficientductilityatroomtemperature.Cold-forgedpartshavegoodsurfacefinishanddimensionalaccuracy.Hotforgingrequiressmallerforces,butitproducesdimensionalaccuracyandsurfacefinishthatarenotasgood.Forgingsgenerallyrequireadditionalfinishingoperations,suchasheattreating,tomodifyproperties,andthenmachiningtoobtainaccuratefinisheddimensions.Theseoperationscanbeminimizedbyprecisionforging,whichisanimportantexampleofthetrendtowardnet-shapeornear-netshapeformingprocesses.Thistrendsignificantlyreducesthenumberofoperationsrequired,andhencethemanufacturingcosttomakethefinalproduct.Thereareseveralformsofforging,butthereissomedisparityidentifyingprocesseswithnamesindifferentreferences.4.2Open-DieForgingOpen-dieforgingisthesimplestforgingprocess.Althoughmostopen-dieforginggenerallyweighs15kg~500kg,forgingasheavyas300tonshavebeenmade.Sizesmayrangefromverysmallpartsuptoshaftssome23mlong(inthecaseofshippropellers).Theopen-dieforgingprocesscanbedepictedbyasolidworkpieceplacedbetweentwoflatdiesandreducedinheightbycompressingit(Fig.4-2).Thisprocessisalsocalledupsettingorflat-dieforging.Thediesurfacesinopen-dieforgingmayhavesimplecavities,toproducerelativelysimpleforgings.ThedeformationoftheworkpieceunderidealconditionsisshowninFig.4-2(b).Becauseconstancyofvolumeismaintained,anyreductioninheightincreasesthediameteroftheforgedpart.Notethat,inFig.4-2(b),theworkpieceisdeformeduniformly.Inactualoperations,thepartdevelopsabarrelshape(Fig.4-2(c));thisdeformationisalsoknownaspancaking.Barrelingiscausedprimarilybyfrictionalforcesatthedie-workpieceinterfacesthatopposetheoutwardflowofthematerialsattheseinterfaces.Barrelingcanbeminimizedifaneffectivelubricantisused.Barrelingcanalsooccurinupsettinghotworkpiecesbetweencolddies.Thematerialatandneartheinterfacescoolsrapidly,whiletherestoftheworkpieceremainsrelativelyhot.Thus,thematerialattheendsoftheworkpiecehashigherresistancetodeformationthanthematerialatitscenter.Consequently,thecentralportionoftheworkpieceexpandslaterallytoagreaterextentthandoitsends.Barrelingfromthermaleffectscanbereducedoreliminatedbyusingheateddies;thermalbarrierssuchasglassclothatthedie-workpieceinterfacesarealsoused.Cogging,alsocalleddrawingout,isbasicallyanopen-dieforgingoperationinwhichthethicknessofabarisreducedbysuccessiveforgingstepsatspecificintervals(Fig.4-3).Becausethecontactareaperstrokeissmall,alongsectionofabarcanbereducedinthicknesswithoutrequiringlargeforcesormachinery.Blacksmithsperformsuchoperationswithahammerandananvilusinghotpiecesofmetal;ironfencesofvariousdesignsareoftenmadebythisprocess.4.3Impression-DieandClosed-DieForgingInimpression-dieforging,theworkpieceacquirestheshapeofthediecavities(impressions)whilebeingforgedbetweentwoshapeddies(Fig.4-4).Notethatsomeofthematerialflowsoutwardandformsaflash.Theflashhasasignificantroleinflowofmaterialinimpression-dieforging:Thethinflashcoolsrapidly,and,becauseofitsfrictionalresistance,itsubjectsthematerialinthediecavitytohighpressures,therebyencouragingthefillingofthediecavity.Theblanktobeforgedispreparedbysuchmeansas(a)cuttingorcroppingfromanextrudedordrawnbarstock,(b)apreforminoperationssuchaspowdermetallurgy,(c)casting,or(d)apreformblankinapriorforgingoperation.Theblankisplacedonthelowerdieand,astheupperdiebeginstodescend,theblank’sshapegraduallychanges,asisshownfortheforgingofaconnectingrodinFig.4-5(a).Preformingprocesses,suchasfulleringandedging(Figs.4-5(b)and(c)),areusedtodistributethematerialintovariousregionsoftheblank,muchastheyareinshapingdoughtomakepastry.Infullering,materialisdistributedawayfromanarea;inedging,itisgatheredintoalocalizedarea.Thepartisthenformedintotheroughshapeofaconnectingrodbyaprocesscalledblocking,usingblockerdies.Thefinaloperationisthefinishingoftheforginginimpressiondiesthatgivetheforgingitsfinalshape.Theflashisremovedusuallybyatrimmingoperation(Fig.4-6).TheexamplesshowninFigs.4-4and4-5(a)arealsoreferredtoasclosed-dieforgings.However,intrueclosed-dieorflashlessforging,flashdoesnotformandtheworkpiececompletelyfillsthediecavity(rightsideofFig.4-7(b)).Accuratecontrolofthevolumeofmaterialandproperdiedesignareessentialinordertoobtainaclosed-dieforgingofthedesireddimensionsandtolerances.Undersizeblankspreventthecompletefillingofthediecavity;conversely,oversizeblanksgenerateexcessivepressuresandmaycausediestofailprematurelyortojam.4.3.1PrecisionForgingForeconomicreasonsthetrendinforgingoperationstodayistowardgreaterprecision,whichreducesthenumberofadd