1Fundam entalsofManufacturingAcuracyManufacturingcanbedefinedasthetransform ationofrawm aterialsintousefulproductsthroughteuseoftheasiestandleast-expensivem ethods.Itisnotenough,therfore,toprocessom erawm aterialsandobtainthedsiredproduct.Itis,infact,ofm ajorim portancetoachievthatgoalthroughem ployingtheasiest,fastest,andm osteficentm ethods.Ifleseficenttechniquesareused,theproductioncostofthem anufacturedpartwilbehig,andthepartwilnotbeascom petiveasim larpartsproducedbyotherm anufactures.Also,theproductiontim eshouldbeashortasposibletoenablecapturingalrgerm arketshare.Modernidustriescanbeclasifedindiferntways.Therincludeclasifcationbyproces,clasifcationbyproduct,andclasifcationbasedontheproductionvolum eandthediversityofproducts.Theclasifcationbyprocesisexm plifedbycastingindustries,tam pingindustries,andthelike.Whenclasifyingbyproduct,industriesm aybelongtotheautom tive,aerospace,andelctronicsgroups.Thethirdm ethod,i.e,clasifcationbasedonproductionvolum e,identifesthrem aindistinctypesofproduction,m as,jobshop,andm oerate.Letusbrieflydiscusthefaturesandcharcteristicsofeachtype.Masproductionischarcterizedbytheighproductionvolum eofthesam e(orverysim lar)partsforaprolngedperiodftim e.Ananual2productionvolum eoflesthan500piecscanotcertainlybeconsiderdasm asproduction.Asyoum ayexpect,theproductionvolum eisbaseduponaestablishedoranticpatedsalesvolum eandisnotdirectlyafectdbythedailyorm nthlyorders.Thetypicalexam pleofm as-producedgodsiautom biles.Job-shoproductionisbasedonsalesordersforavrietyofsm allots.Eachlotm ayconsitof20upto20orm resim larparts,depndiguponthecustom ersneds.Itisobviousthathistypeofproductionism ostsuitableforsubcontractorswhoproducevaryingcom pnetstosuplyvariousindustries.Them achinesem ployedm ustbeflexibletohandlevaritionsintheconfigurationftheorderdcom pnets,whicareusalyfrequent.Also,them ployedpersonelm ustbehiglyskiledinordertohandleavarietyoftask,whicdiferforthediferntpartsthatrem anufactured.Moderateproductionisaniterm diatephasebetwenthejob-shopandthem as-productiontypes.Theproductionvolum erangesbetwen100to200parts,andthem achinesem ployedareflexibleandm ultipurose.Thistypeofproductionisgaingpoularityinidustrybecauseofanicreasingm arketdem andforcustom izedproducts.Averyim portantfactofthem anufacturingscienceisthatitisalm ostim posibletobtainthedesirednom ialdim ensionwhenprocesingaworkpiec.Thisiactualycausedbytheinevitable,thoughveryslight,3inacuraciesinherntinthem achinetolaswelasbyvariouscom plicatedfactorslikethelasticdeform ationandrecoveryoftheworkpiecand/orthefixture,tem pratureefctsduringprocesing,andsom etim stheskiloftheoperator.Sinceitisverydificultoanlyzeandcom pletlyelim natethefectsofthesfactors,itism orefeasibletoestablishaperm isibledegreofinacuracyoraperm isibledeviationfrom thenom ialdim ensionthatwouldnotafectheproerfunctionigofthem anufacturedpartinadetrim entalway.AcordingtotheISO(InternationalStandarizationOrganization)sytem , thenom ialdim ensionisrefredtoasthebasicsizeofthepart.Thedeviationsfromthebasicsizetoeachside(i.e,positveornegative)detrm inetheighandthelowlim ts,respectively,andthediferncebetwenthosetwolim tsofsizeiscaledthetolerance.Thetoleranceisanabsolutevaluewithoutasign.Asyoum ayexpect,them agnitudeofthetoleranceisdepndentuponthebasicsizeandisdesignatedbyanalphanum ericsym bolcaledthegrade.TherareightenstandargradesoftoleranceintheISOsytem ,andthetolerancescanbeobtainedfrom theform ulasorthetablespublishedbytheISO.Itisobviousthatsm alertolerancesrequiretheuseofhig-precisonm achinetolsinm aufacturingthepartsandtherforeincreaseproductioncost.Beforetwocom pnetsareasem bldtogethr,therelationshipbetwenthedim ensionsofthem atingsurfacesm ustbespecifed.Inother4words,thelocationfthezrolinetowhicdeviationsarerferdm ustbestablishedforeachofthetwom atingsurfaces.Thisactualydetrm inesthedgreoftightnesorfedom forelativem otinbetwenthem atingsurfaces.Therarebasicalythretypesofits,nam ely,clearncefit,transitonfit,andinterfrencefit.Inalcaseofclearncefit,theuperlim toftheshaftisalwaysm alerthanthelowerlim tofthem atinghole.Thisinothecaseiniterfrencefit,wherthelowerlim toftheshaftisalwayslargerthantheuperlim tofthehole.Thetransitonfit,asthenam esugest,isaniterm diatefit.AcordingtoISO,theinternalenvelopedpartisalwaysrefredtoastheshaft,wherasthesuroundigsurfaceisrefredtoastheole.Acordingly,from thefitspointofview,akeyisrefredtoastheshaftandthekeywaystheole.Theraretwoaysforspecifyingandexpresingthevarioustypesoffits,theshaftbasiandtheholebasisytem s.Thelocationofthetolerancezonewithrespectothezrolineisindicatedbyaletr,whicisalwayscapitalforholesandlowercaseforshafts,wherasthetolerancegradeisindicatedbyanum ber,aspreviouslyexplained.Therfore,afitdesignationcanbeH7/h6,F6/g5,oranyothersim larform .Whenthesrvicelifeofanelctricbulisover,alyoudoisbuyanewoneandreplacethebul.Thiseasyoperation,whicdoesnotnedafiteroratechnican,wouldnotbeposiblewithoutwom ainconcepts,5interchangeabiltyandstandarization.Interchangeabiltym eansthatidenticalpartsm ustbeinterchangeable,i.e,abletoreplaceachother,whetrduringasem blyorsubsequentm ainteancework;withouthenedforanyfitingoperations.Asyoucaneasilyse,interchangeabiltyisachievdbyestablishingaperm isibletolerance,beyondwhicanyfurtherdeviationfrom thenom ialdim ensionofthepartisnotalowed.6影響加工精度的基本因素制造業(yè)可以看作是通過使用最簡便、最便宜的方法，把原材料轉化為有用的產(chǎn)品的方法，但這顯然還不夠準確,它應該是通過對原材料的加工,進而獲得所期望得到的產(chǎn)品。實際上，通過采用最簡單、最快捷和最有效的方法來達到目標是非常重要的。如果不能采用先進而有效的方法來加工，則產(chǎn)品的制造費用將增高，在與其他類似的產(chǎn)品制造商競爭時產(chǎn)品將會變得沒有競爭力。此外,為了獲取更大的市場份額，產(chǎn)品生產(chǎn)的時間也應盡可能短?，F(xiàn)代工業(yè)可以使用很多不同的方法來分類，包括按加工方式分類，按產(chǎn)品的類型分類，按產(chǎn)品生產(chǎn)的數(shù)量和產(chǎn)品的差異性分類。按產(chǎn)品的加工方式來分類，在鑄造行業(yè)及沖壓行業(yè)中被廣泛采用。而按產(chǎn)品的類型來分類的方法，則主要在汽車制造業(yè)、飛機制造業(yè)及電氣業(yè)中采用。第三種方法,即按產(chǎn)品的生產(chǎn)量來分類的方法，確定了三種主要的生產(chǎn)方法：大批量生產(chǎn)、單件小批量生產(chǎn)、中批量生產(chǎn)。下面讓我們來詳細的討論每種生產(chǎn)方式的特點。大批量生產(chǎn)的特點是長時間的生產(chǎn)同一種（或者非常類似的）產(chǎn)品，如果一件產(chǎn)品的年生產(chǎn)量小于500件則不能被視為大批量生產(chǎn)。正如你所能想到的，產(chǎn)品生產(chǎn)的數(shù)量是根據(jù)一個既定或預期的銷售數(shù)量來決定的，而不是由一天或一個月的訂單量來決定。一個典型的例子就是汽車的大規(guī)模生產(chǎn)。單件小批量生產(chǎn)主要是按種類多而批量小的銷售訂單來生產(chǎn)，每個批量在20件到20件或者更多，主要決定于客戶的需求。顯而易見，這種類型的生產(chǎn)最適合分包商，生產(chǎn)不同的零件來供應各類不同的行業(yè)需求。所采用的機器必須具有足夠的柔性，以適應按訂單生產(chǎn)的零件的外形變化，而這種變化是經(jīng)常發(fā)生的。另外，操作機器的工人也必須掌握比較高的技術水平，這樣才能成功的完成各種不同的任務，加工不同的零件。中批量生產(chǎn)是介于大批量生產(chǎn)和單件小批量生產(chǎn)之間的一種類型，生產(chǎn)量介于100至200件之間，而采用的機器也必須很靈活和多功能化。由于按客戶需求制造的產(chǎn)品的市場日益增長，這類類型的應用越來越多。在制造科學中，有一個非常重要的事實是：加工一個工件時要想獲得理想的名義尺寸幾乎是不可能的。其實，雖然誤差可能非常的小，但這是不可避免的，7因為很多復雜的因素造成機器上的刀具存在有固有的誤差。比如工件的彈性變形及其回彈，又或者工件的裝夾、加工過程中溫度的影響，有時還包括操作人員的操作技能。由于準確的分析并完全消除這些因素的影響是非常困難的，于是在名義尺寸之上建立一個允許的誤差或允許的偏差范圍更為可行，而這也不會影響工件的正常運作。按照ISO(國際標準化組織)體系，公稱尺寸被稱為零件的基本尺寸，從基本尺寸向每一側的偏差（正或負）分別決定了上限和下限，而二者之間的差值稱為公差。公差是一個沒有標志的絕對值