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1•DrillingandDrills钻削和钻头Drillinginvolvesproducingthroughorblindholesinaworkpiecebyforcingatool,whichrotatesarounditsaxis,againsttheworkpiece.钻削就是通过迫使绕自身轴线旋转的切削刀具进入工件而在其上生成通孔或盲孔。Consequently,therangeofcuttingfromthataxisofrotationisequaltotheradiusoftherequiredhole.Inpractice,twosymmetricalcuttingedgesthatrotateaboutthesameaxisareemployed.因此，从旋转轴线开始的切削范围等于所需孔的半径。实际上，使用的是两条围绕相同轴线旋转的对称切削刃。Drillingoperationscanbecarriedoutbyusingeitherhanddrillsordrillingmachines.Thelatterdifferinsizeandconstruction.Nevertheless,thetoolalwaysrotatesarounditsaxiswhiletheworkpieceiskeptfirmlyfixed.Thisiscontrarytodrillingonalathe.钻削作业既能采用手钻也能采用钻床来实现。钻床在尺寸和结构上虽有差别，然而始终都是切削刀具围绕自身轴线旋转、工件稳固定位的形式。这正好与在车床上钻孔相反。CuttingToolforDrillingOperationIndrillingoperations,acylindricalrotary-endcuttingtool,calledadrill,isemployed.Thedrillcanhaveeitheroneormorecuttingedgesandcorrespondingflutes,whichcanbestraightorhelical.用于钻削作业的切削刀具在钻削作业中，要用到被称为钻头的圆柱形回转端切削刀具。钻头可以有一条或多条直的或是螺旋状的切削刃以及相应的出屑槽。Thefunctionoftheflutesistoprovideoutletpassagesforthechipsgeneratedduringthedrillingoperationandalsotoallowlubricantsandcoolantstoreachthecuttingedgesandthesurfacebeingmachined.Followingisasurveyofthecommonlyuseddrills.出屑槽的功能是给钻削作业中产生的切屑提供排出通道，并允许润滑剂和冷却液到达切削刃和正在被加工的表面。下面是常用钻头的概述。Twistdrill.Thetwistdrillisthemostcommontypeofdrill.Ithastwocuttingedgesandtwohelicalflutesthatcontinueoverthelengthofthedrillbody,asshowninFig.12.1.Thedrillalsoconsistsofaneckandashankthatcanbeeitherstraightortapered.麻花钻：麻花钻是最常用的钻头类型。它有两条切削刃和两条沿钻头体全长连续的螺旋状出屑槽，如图12.1所示。麻花钻还包括钻颈和钻柄，钻柄可以是直的也可以是锥形的。Inthelattercase,theshankisfittedbythewedgeactionintothetaperedsocketofthespindleandhasatang,whichgoesintoaslotinthespindlesocket,thusactingasasolidmeansfortransmittingrotation.锥形钻柄通过楔入动作安装在主轴的锥形轴孔中，钻柄上还有柄舌插入主轴轴孔中的插槽，从而作为传递转动的可靠方法。Ontheotherhand,straight-shankdrillsareheldinadrillchuckthatis,inturn,fittedintothespindlesocketinthesamewayastaperedshankdrills.另一方面，直柄钻头用钻头卡盘夹住，接下来钻头卡盘则象锥形钻柄钻头一样安装在主轴轴孔内。AscanbeseeninFig.12.1,thetwocuttingedgesarereferredtoasthelips,2andareconnectedtogetherbyawedge,whichisachisel-likeedge.Thetwistdrillalsohastwomargins,whichenableproperguidanceandlocatingofthedrillwhileitisinoperation.如图12.1所示，两条切削刃就是钻唇，通过凿子状边缘的楔形体连在一起。麻花钻还有两条导向边，用于作业中钻头的正确导向和定位。Thetoolpointangle(TPA)isformedbythetwolipsandischosenbasedonthepropertiesofthematerialtobecut.TheusualTPAforcommercialdrillsis118°,whichisappropriatefordrillinglow-carbonsteelsandcastirons.两条钻唇形成钻顶角，并根据被钻削材料的性能来选取其大小。商品化钻头的钻顶角一般为118°，这适用于钻削低碳钢和铸铁。Forharderandtoughermetals,suchashardenedsteel,brassandbronze,largerTPAs(130°or140°)givebetterperformance.Thehelixangleoftheflutesofthecommonlyusedtwistdrillsrangesbetween24°and30°.Whendrillingcopperorsoftplastics,highervaluesforthehelixanglearerecommended(between35°and45°).对于更硬更韧的金属，诸如淬火钢、黄铜和青铜，更大的钻顶角(130°或140°)才能有更好的效果。麻花钻常用的出屑槽螺旋角范围为24°到30°。钻削紫铜或软塑料时，推荐采用更大的螺旋角(35°到45°)。Twistdrillsareusuallymadeofhigh-speedsteel,althoughcarbide-tippeddrillsarealsoavailable.Thesizesoftwistdrillsusedinindustrialpracticerangefrom0.01upto3.25in.(i.e.,0.25upto80mm).虽然也有硬质合金刀尖的钻头，麻花钻一般用高速钢制成。工业实际中使用的麻花钻尺寸范围为0.01到3.25英寸(即0.25到80毫米)。Coredrills.Acoredrillconsistsofthechamfer,body,neck,andshank,asshowninFig.12.2.Thistypeofdrillmayhaveeitherthreeorfourflutesandequalnumberofmargins,whichensuresuperiorguidance,thusresultinginhighmachiningaccuracy.空心钻：空心钻包括斜面、钻头体、钻颈和钻柄，如图12.2所示。这类钻头可以有三条或四条出屑槽及相同数量的保证良好导向的导向边，这样使得加工有高精度。ItcanalsobeseeninFig.12.2thatacoredrillhasflatend.Thechamfercanhavethreeorfourcuttingedgesorlips,andthelipanglemayvarybetween90°and120°.在图12.2中同样能看到，空心钻具有平坦的端部。斜面可以有三或四条切削刃或钻唇，并且钻唇角可以在90°到120°之间变化。Coredrillsareemployedforenlargingpreviouslymadeholesandnotfororiginatingholes.Thistypeofdrillischaracterizedbygreaterproductivity,highmachiningaccuracy,andsuperiorqualityofthedrilledsurfaces.空心钻用于扩大已有的孔而不是打孔。这类钻头具有较大生产率、高加工精度和优良钻削表面质量的特性。Gundrills.Gundrillsareusedfordrillingdeepholes.Allgundrillsarestraight-fluted,andeachhasasinglecuttingedge.Aholeinthebodyactsasaconduittotransmitcoolantunderconsiderablepressuretothetipofthedrill.深孔钻：深孔钻用于钻深孔。所有深孔钻都是直出屑槽的，并且均为单切削刃。钻头体中有个孔作为导管在相当大的压力下将冷却液传送到钻头顶端。Therearetwokindsofgundrills,namely,thecenter-cutgundrillusedfordrillingblindholesandthetrepanningdrill.Thelatterhasacylindricalgrooveatitscenter,thusgeneratingasolidcore,whichguidesthetoolasitproceeds3duringthedrillingoperation.深孔钻有两种类型，即用于钻盲孔的中心切削深孔钻和套孔钻。后者在其中心有一圆柱形沟槽，这样能生成整体芯在钻孔作业过程中引导钻头。Spadedrills.Spadedrillsareusedfordrillinglargeholesof3.5in.(90mm)ormore.Theirdesignresultsinamarkedsavingincostofthetoolaswellasatangiblereductioninitsweight,whichfacilitatesitshandling.Moreover,thistypeofdrilliseasytogrind.扁平钻：扁平钻用于钻削3.5英寸(90毫米)或更大的大孔。其设计使得钻头成本明显节省、重量切实减轻，重量轻又使操作更方便。此外这种钻头容易磨利。•MillingandMillingCutter铣削和铣刀Millingisamachiningprocessthatiscarriedoutbymeansofamultiedgerotatingtoolknownasamillingcutter.铣削是采用被称为铣刀的多刃旋转刀具完成的机加工作业。Inthisprocess,metalremovalisachievedthroughcombiningtherotarymotionofthemillingcutterandlinearmotionsoftheworkpiecesimultaneously.Millingoperationsareemployedinproducingflat,contouredandhelicalsu