锻压emphasis.docx
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锻压emphasis.docx
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锻压emphasis
ReviewandQuestion
Chapter13RollingofMetals
1、Whatisthedefinitionoftherolling?
theprocessofreducingthethickness(orchangingthecross-section)ofalongworkpiecebycompressiveforcesappliedthroughasetofrolls(轧辊).
3、Whatistheflatrolling?
FlatrollingorRollingisdefinedasthereductionofthecross-sectionalareaofthemetalstock,orthegeneralshapingofthemetalproducts,throughtheuseoftherotatingrolls
Astrip(带料/条料)ofthicknesshoenterstherollgap(辊缝/辊隙/辊间距离)andisreducedtothicknesshfbyapairofrotatingrolls,eachrollbeingpoweredthroughitsownshaftbyelectricmotors(电动机).
4、Whatisthedifferencebetweenaplateandasheet?
Platearegenerallyregardedas
(1)havingathicknessgreaterthan6mm,are
(2)usedforstructuralapplications,suchasmachinestructures,shiphulls,boilers,bridgesandnuclearvessels.
Sheetsaregenerally
(1)lessthan6mmthick;theyareprovidedtomanufacturingfacilitiesasflatpiecesor
(2)asstripincoilsforfurtherprocessingintovariousproducts.
7、Explaintheadvantagesanddisadvantagesofthefrictionduringtherolling.
DisadvantageOfFriction
Althoughfrictionisnecessaryforrollingmaterials,
(1)energyisdissipatedinovercomingfriction;thus,increasingfrictionmeansincreasingforcesandpowerrequirements.
Furthermore,
(2)highfrictioncoulddamagethesurfaceoftherolledproduct.Acompromisehastobemade,onewhichincludeslowcoefficientsoffrictionbyusingeffectivelubrication(润滑).
9、Describethedifferencebetweenabloom,aslab,andabillet.
Slab
(1)usuallyrectangularincross-section.
(2)Slabsarerolledintoplatesandsheetslater.
Bloom
(1)usuallyhasasquarecross-section,atleast150mmontheside.
(2)Bloomsareprocessedfurther,byshapingrolling,intostructureshapes,suchasI-beamsandrailroadrails.
Billets
(1)areusuallysquare,withacross-sectionareasmallerthanblooms;
(2)theyarelaterrolledintovariousshapes,suchasroundrodsandbars,byetheuseofshapedrolls.
11、Whatisthehotrollingandcoldrolling?
Therollingpracticewhichisdoneabovetherecrystallization(再结晶)temperatureofthemetaliscalledhotrolling
coldrollingiscarriedoutatroomtemperature
12、Whatisthedifferencebetweencaststructureandwroughtstructure?
Thecharacteristicsofacaststructure(铸造结构):
(1)typicallydendritic(树枝状的),
(2)includescoarseandnonuniformgrains.
(3)usuallybrittle(易碎的)andporous(多孔的)
Thecharacteristicsofawroughtstructure(锻造结构):
(1)finergrainssize
(2)enhancedductility(柔韧性)
13、Whatisthedifferencebetweenhotrollingandcoldrolling?
?
AdvantagesofHotrolling
•reducegrainsize
•improvestrengthandductility(塑性/延展性/柔韧性)
–breakingupbrittlegrainboundaries(晶界)
–closingup(压合/压实)internaldefects(内部缺陷),especiallyporosity(多孔性)
Comparedtohotrolling,coldrollingproducessheetandstripwithmuchbetter:
(1)surfacefinish(becauseoflackofscale),
(2)dimensionaltolerances
(3)mechanicalproperties(becauseofstrainhardening).
14、Whatisscale?
Scaleisadefectoftherollingproductsdevelopedduringhotrolling.
16、Whatistheshaperolling?
Straightandlongstructureshapes,suchassolidbars(withvariouscross-section),channels,I-beams,andrailroadrails,arerolledbypassingthestock(原料)throughasetofspeciallydesignedrolls.
17、Makealistofsomepartsthatcanbemadebyshaperolling.
•Variousshapescanbeproducedbyshaperolling
–bars
–channels(槽钢)
–I-beams(工字梁)
–railroadrails
•VariousshapescanbeproducedbyRingRolling
largeringsforrockets(火箭)andturbines(涡轮)
-gearwheelrims(边缘带齿的轮子)
-ball-bearingandroller-bearingraces(滚珠轴承与滚柱轴承环)
-flanges(法兰盘)
-reinforcingrings(增强环/补强环)forpipes.
Chapter14ForgingofMetals
3、Whatdothetypicalforgedproductsinclude?
bolts(螺栓)andrivets(铆钉),connectingrods,shaftsforturbines(涡轮),gears(齿轮)、handtools,andstructuralcomponentsformachinery,aircraftrailroads,andavarietyofothertransportationequipment.
4、Whataretheadvantagesoftheforgingparts?
?
Metalflowandgrainstructurecanbecontrolled,soforgedpartshavegoodstrengthandtoughness;theycanbeusedreliablyforhighlystressedandcriticalapplications
5、Whatisthedifferencebetweencastparts,cuttingpartsandforgingparts?
铸造件(Casting)有inevitable缺陷,如晶粒粗大、结构疏松、具有多孔,其组织和性能均较差。
切削件(Machining)的内部晶粒大小和结构不改变,且其金属纤维组织被切断了,使得零件强度下降。
锻造件(Forging)在经受了塑性变形和再结晶,粗大的树枝状结晶组织被破碎,疏松和孔隙被压实、焊合,内部组织和性能都得到了提高
9、Whatistheopen-dieforging?
Open-dieforgingisthesimplestforgingprocess.Itcanbedepictedbyasolidworkpieceplacedbetweentwoflatdiesandreducedinheightbycompressingit.
10、Whatisthedifferencebetweenidealforgingandactualforging?
Uniformdeformationofthebilletunderidealconditions.Becauseconstancyofvolumeismaintained,anyreductioninheightincreasesthediameteroftheforgedpart.
Inactualoperations,thepartdevelopsabarrelshape;thisdeformationisalsoknownaspancaking(压扁)
causedbyfrictionalforcesatthedie-workpieceinterfaces
–canbeminimizedifaneffectivelubricantisused
–causedbythermaleffects(热效应)inhotforgingcanbe
minimizedbyusingheateddies
14、Whatisthedifferencebetweenopen-dieforgingandimpression-dieforging?
Inimpression-dieforging,theworkpieceacquirestheshapeofthediecavities(impressions)whilebeingforgedbetweentwoshapeddies.
15、Whatistheflash?
Howtoformtheflash?
Whatisthesignificanceoftheflash?
flash,whichisexcessmetalthatissubsequentlytrimmedoff.
thatsomeofthematerialflowsoutwardandformsaflash,
Becausethethinflashcoolsrapidlyandhashigherfrictionalresistancethandiecavity,itsubjectsthematerialinthediecavitytohighpressures,therebyencouragingthefillingofthediecavity.
22、Whatisthedifferencebetweenfulleringandedging?
Infullering,materialisdistributedawayfromanarea
Inedging,materialisgatheredintoalocalizedarea
33、Whatisthesignificanceoflubricationtotheforgingprocess?
1)Becauselubricantsgreatlyinfluencefrictionandwear,theyaffecttheforcesrequiredandtheflowofthemetalindiecavities;
2)Theycanactasathermalbarrierbetweenthehotworkpieceandtherelativelycooldies,slowingtherateofcoolingoftheworkpieceandimprovingmetalflow.
3)Lubricantsserveasapartingagentwhichinhibitstheforgingformstickingtothediesandhelpsinitsreleasefromthedie.
34、HowtoApplylubricantsinforging?
Inhotforging,thelubricantsisusuallyapplieddirectlytothedies;
Incoldforging,thelubricantsisusuallyappliedtotheworkpiece.
35、Whatistheforgeability?
Forgeabilityisgenerallydefinedasthecapabilityofamaterialtoundergodeformationwithoutcracking
Chapter15ExtrusionandDrawingofMetals
1、Whatistheextrusionprocess?
Intheextrusionprocess,abillet(generallyround)isforcedthroughadie,inamannersimilartosqueezingtoothpastefromatube.
2、Whatkindofproductscanbemadebyextrusion?
Almostanysolidorhollowcross-sectionmaybeproducedbyextrusion,whichcancreateessentiallysemifinishedparts
Typicalproductsmadebyextrusionarerailingsforslidingdoors,tubinghavingvariouscross-section,structuralandarchitecturalshapes,anddoorandwindowframes.
5、Whatisdrawing?
Drawingisanoperation,developedbetweenA.D.1000and1500,inwhichthecross-sectionofsolidrod,wire,ortubingisreducedorchangedinshapebypullingitthroughadie
6、Whatkindofproductscanbemadebydrawing?
Drawnrodsareusedforshafts,spindles,andsmallpistonsandasrawmaterialforfastenerssuchasrivets,bolts,andscrews.Inadditiontoroundrods,variousprofilescanalsobedrawn.
8、Whatisthedifferencebetweendirectextrusion,indirectextrusion,HydrostaticExtrusionandlateralExtrusion
Directextrusionalsoiscalledforwardextrusion,aroundbilletisplacedinachamber(container)andforcedthroughadieopeningbyahydraulically-drivenramorpressingstem.Themetalflowsinthesamewaythatthepressingstemmoves
Inindirectextrusion(reverse,inverted,orbackwardextrusion),thediemovestowardthebillet.
Thedirectionofthemetalflowsisoppositetothatthatthepressingstemmoves
Inhydrostaticextrusion,thebilletissmallerindiameterthanthechamber,whichisfilledwithafluid,andthepressureistransmittedtothebilletbyaram.Unlikeindirectextrusion,thereisnofrictiontoovercomealongthecontainerwalls.
Anothertypeofextrusionislateral,orside,extrusion
10、WhatisCCD?
Circumscribing-circlediameter,abbreviatedCCD,isaparameterdescribingtheshapeoftheextrudedproduct.Itisthediameterofthesmallestcircleintowhichtheextrudedcross-sectionwillfit
11、Whatistheshapefactor?
Thecomplexityofanextrusionisafunctionoftheratiooftheperimeteroftheextrudedproducttoitscross-sectionalarea,knownastheshapefactor.
13、Whatcausesthedeadzone?
wherethemetalatthecornersisessentiallystationary(静止的)
–mainlyduetofriction
Theparametersrelatedtothediezone
Ø
(1)dieangle,a:
a↑,diezone↑(a大,死区大,但制品表面质量好;a小,死区小,制品表
面质量差。
)
Ø
(2)friction:
externalfriction↑,diezone↑
Ø(3)R:
R↑,diezone↑
Ø(4)temperature:
T↑→externalfriction↑→diezone
15DescribeusualQuestionsinExtrusion
1、diewearcanbeexcessive;
2、coolingofthehotbilletinthechambercanbeaproblemwhichresultsinhighlynonuniformdeformation;
3、Thebilletmaydevelopanoxidefilmunlessheatedinaninert-atmosphere.
Thisfilmcanbeabrasive,anditcanaffecttheflowpatte
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