铸造技术基础培训的英文资料课件.pptx

1、Fundamental of Materials Forming-Casting basic conceptMain contents1 1、铸造的概念及特点、铸造技术的发展；、铸造的概念及特点、铸造技术的发展；Fundamentals of Metal-Casting Fundamentals of Metal-Casting2 2、金属铸造工艺、金属铸造工艺 Metal-Casting Processes Metal-Casting Processes 砂型铸造及其工艺设计；砂型铸造及其工艺设计；特种铸造及其工艺；特种铸造及其工艺；3 3、铸件的结构设计、材料及经济性、铸件的结构设计、材料

2、及经济性 Metal Casting:Design,Materials,and EconomicsMetal Casting:Design,Materials,and Economics5 5、先进铸造技术。、先进铸造技术。Advanced CastingAdvanced CastingSand Casting Manufacturing,Engineering&Technology,Fifth Edition,by Serope Kalpakjian and Steven R.Schmid.ISBN 0-13-148965-8.2006 Pearson Education,Inc.,Uppe

3、r Saddle River,NJ.All rights reserved.Production Steps in Sand-CastingFigure 11.2 Outline of production steps in a typical sand-casting operation.Sand Casting processThe concept for Casting Schematic illustration of a typical riser-gated casting.Risers serve as reservoirs,supplying molten metal to t

4、he casting as it shrinks during solidification.See also Fig.11.4 Source:American Foundrymens Society.Why Sand Casting?In metal casting work,as with almost every In metal casting work,as with almost every kind of manufacture,high precision means high kind of manufacture,high precision means high cost

5、.In cost.In a a case we are making a small number of case we are making a small number of objects so we cant really afford to make a objects so we cant really afford to make a sophisticated metal mold(i.e.we cant do die sophisticated metal mold(i.e.we cant do die casting).The usual approach in this

6、case is to casting).The usual approach in this case is to make disposable molds out of sand or plaster.make disposable molds out of sand or plaster.The kind of disposable mold,and the The kind of disposable mold,and the techniques used to make the mold,are again techniques used to make the mold,are

7、again determined by questions of cost and quality.For determined by questions of cost and quality.For a very intricate,precise result,lost wax or a very intricate,precise result,lost wax or lost polystyrene foam casting is used.For less lost polystyrene foam casting is used.For less intricate workpi

8、eces,or lower precision intricate workpieces,or lower precision requirements,direct sand casting can be requirements,direct sand casting can be adequate.adequate.What is Sand Casting?All casting,not just sand casting,is about All casting,not just sand casting,is about pouring orpouring or squirting

9、a molten substance into a squirting a molten substance into a cavity.cavity.All casting methods require two basic things:All casting methods require two basic things:A cavity which is the shape of the desired final A cavity which is the shape of the desired final objectobject,and,and A way to put mo

10、lten substance into the cavity.A way to put molten substance into the cavity.In the sand casting process,the cavity is made In the sand casting process,the cavity is made of sand which is held together by a binder(a of sand which is held together by a binder(a substance that holds the sand grains to

11、gether).substance that holds the sand grains together).Sand casting is used to produce a wide variety of metal components with complex geometries.These parts can vary greatly in size and weight,ranging from a couple ounces to several tons.Some smaller sand cast parts include components as gears,pull

12、eys,crankshafts,connecting rods,and propellers.Larger applications include housings for large equipment and heavy machine bases.Sand casting is also common in producing automobile components,such as engine blocks,engine manifolds,cylinder heads,and transmission cases.Die-Casting Examples(a)(b)Figure

13、 11.1 (a)The Polaroid PDC-2000 digital camera with a AZ91D die-cast,high purity magnesium case.(b)Two-piece Polaroid camera case made by the hot-chamber die casting process.Source:Courtesy of Polaroid Corporation and Chicago White Metal Casting,Inc.Casting ExamplesFigure 11.2 Typical gray-iron casti

14、ngs used in automobiles,including transmission valve body(left)and hub rotor with disk-brake cylinder(front).Source:Courtesy of Central Foundry Division of General Motors Corporation.Figure 11.3 A cast transmission housing.Solidification ProcessesStarting work material is either a liquid or Starting

15、 work material is either a liquid or is in a highly plastic condition,and a is in a highly plastic condition,and a part is created through solidification of part is created through solidification of the materialthe material Solidification processes can be classified Solidification processes can be c

16、lassified according to engineering material according to engineering material processed:processed:Metals Ceramics,specifically glasses Polymers and polymer matrix composites(PMCs)Classification of solidification processesClassification of solidification processesCastingProcess in which molten metal

17、flows by Process in which molten metal flows by gravity or other force into a mold where gravity or other force into a mold where it solidifies in the shape of the mold it solidifies in the shape of the mold cavitycavity The term The term castingcasting also applies to the part also applies to the p

18、art made in the processmade in the process Steps in casting seem simple:Steps in casting seem simple:1.1.Melt the metalMelt the metal2.2.Pour it into a moldPour it into a mold3.3.Let it freezeLet it freezeCapabilities and Advantages of Casting Can create complex part geometriesCan create complex par

19、t geometries Can create both external and internal shapesCan create both external and internal shapes Some casting processes are Some casting processes are net shape;net shape;others are others are near net shapenear net shape Can produce very large parts Can produce very large parts Some casting me

20、thods are suited to mass Some casting methods are suited to mass productionproductionDisadvantages of Casting Different disadvantages for different Different disadvantages for different casting processes:casting processes:Limitations on mechanical properties Poor dimensional accuracy and surface fin

21、ish for some processes;e.g.,sand casting Safety hazards to workers due to hot molten metals Environmental problemsParts Made by Casting Big parts:engine blocks and heads for Big parts:engine blocks and heads for automotive vehicles,wood burning stoves,automotive vehicles,wood burning stoves,machine

22、frames,railway wheels,pipes,church machine frames,railway wheels,pipes,church bells,big statues,and pump housings bells,big statues,and pump housings Small parts:dental crowns,jewelry,small Small parts:dental crowns,jewelry,small statues,and frying pans statues,and frying pans All varieties of metal

23、s can be cast,ferrous and All varieties of metals can be cast,ferrous and nonferrous nonferrous Overview of Casting Technology Casting is usually performed in a foundry Casting is usually performed in a foundry FoundryFoundry=factory equipped for making molds,=factory equipped for making molds,melti

24、ng and handling molten metal,performing melting and handling molten metal,performing the casting process,and cleaning the finished the casting process,and cleaning the finished castingcasting Workers who perform casting are called Workers who perform casting are called foundrymenfoundrymenThe Mold i

25、n Casting Contains cavity whose geometry determines Contains cavity whose geometry determines part shape part shape Actual size and shape of cavity must be slightly oversized to allow for shrinkage of metal during solidification and cooling Molds are made of a variety of materials,including sand,pla

26、ster,ceramic,and metal Two forms of mold:(a)open mold,simply a container in Two forms of mold:(a)open mold,simply a container in the shape of the desired part;and(b)closed mold,in the shape of the desired part;and(b)closed mold,in which the mold geometry is more complex and requires a which the mold

27、 geometry is more complex and requires a gating system(passageway)leading into the cavity gating system(passageway)leading into the cavity Two Categories of Casting Process1.1.Expendable mold processesExpendable mold processes uses an uses an expendable expendable moldmold which must be destroyed to

28、 remove casting which must be destroyed to remove castingMold materials:sand,plaster,and similar materials,plus binders2.2.Permanent mold processesPermanent mold processes uses a uses a permanent permanent moldmold which can be used many times to produce which can be used many times to produce many

29、castingsmany castingsMade of metal(or,less commonly,a ceramic refractory materialAdvantages and Disadvantages More intricate geometries are possible More intricate geometries are possible with expendable mold processeswith expendable mold processes Part shapes in permanent mold processes Part shapes

30、 in permanent mold processes are limited by the need to open moldare limited by the need to open mold Permanent mold processes are more Permanent mold processes are more economic in high production operationseconomic in high production operationsWhy Do We Prefer Casting?Near net shape Low scrap Rela

31、tively quick process Large hollow shapes No limit to size Reasonable to good surface finishMetal Casting Processes Sand Centrifugal Shell Die Ceramic Investment Permanent mold Plaster mold Evoparative PatternMetals processed by casting Sand casting 60%Investment casting 7%Die casting 9%Permanent mol

32、d casting 11%Centrifugal casting 7%Shell mold casting 6%(b)Sand casting mold(b)Sand casting moldSand Casting Mold Terms Mold consists of two halves:Mold consists of two halves:Cope=upper half of moldDrag=bottom half Mold halves are contained in a box,called a Mold halves are contained in a box,calle

33、d a flaskflask The two halves separate at the The two halves separate at the parting lineparting lineForming the Mold CavityForming the Mold Cavity Mold cavity is formed by packing sand around a Mold cavity is formed by packing sand around a patternpattern,which has the shape of the part,which has t

34、he shape of the part When the pattern is removed,the remaining When the pattern is removed,the remaining cavity has desired shape of cast partcavity has desired shape of cast part The pattern is usually oversized to allow for The pattern is usually oversized to allow for shrinkage of metal as it sol

35、idifies and cools shrinkage of metal as it solidifies and cools Sand for the mold is moist and contains a binder Sand for the mold is moist and contains a binder to maintain shape to maintain shape Cores in the Mold Cavity The mold cavity provides the external The mold cavity provides the external s

36、urfaces of the cast partsurfaces of the cast part In addition,a casting may have internal In addition,a casting may have internal surfaces,determined by a surfaces,determined by a corecore,placed,placed inside the mold cavity to define the inside the mold cavity to define the interior geometry of pa

37、rtinterior geometry of part In sand casting,cores are generally made In sand casting,cores are generally made of sandof sandGating System Channel through which molten metal flows Channel through which molten metal flows into cavity from outside of mold into cavity from outside of mold Consists of a

38、Consists of a downspruedownsprue,through which,through which metal enters a metal enters a runnerrunner leading to the main leading to the main cavity cavity At top of downsprue,a At top of downsprue,a pouring cuppouring cup is is often used to minimize splash and often used to minimize splash and t

39、urbulence as the metal flows into turbulence as the metal flows into downspruedownsprueRiser Reservoir in the mold which is a source of Reservoir in the mold which is a source of liquid metal to compensate for shrinkage liquid metal to compensate for shrinkage during solidification during solidifica

40、tion The riser must be designed to freeze after The riser must be designed to freeze after the main casting in order to satisfy its the main casting in order to satisfy its functionfunction Heating the Metal Heating furnaces are used to heat the metal Heating furnaces are used to heat the metal to m

41、olten temperature sufficient for casting to molten temperature sufficient for casting The heat required is the sum of:The heat required is the sum of:1.Heat to raise temperature to melting point 2.Heat of fusion to convert from solid to liquid 3.Heat to raise molten metal to desired temperature for

42、pouring Pouring the Molten Metal For this step to be successful,metal must flow into For this step to be successful,metal must flow into all regions of the mold,most importantly the main all regions of the mold,most importantly the main cavity,before solidifying cavity,before solidifying Factors tha

43、t determine success:Factors that determine success:Pouring temperature Pouring rate Turbulence Transformation of molten metal back into solid Transformation of molten metal back into solid statestate Solidification differs depending on whether the metal is a Solidification differs depending on wheth

44、er the metal is a pure element or an alloypure element or an alloyFigure 10.4 Figure 10.4 Cooling curve for a pure metal during casting Cooling curve for a pure metal during castingA pure metal solidifies at a constant temperature equal to its freezing point(same as melting point)Solidification of P

45、ure Metals Solidification of Pure Metals Due to chilling action of mold wall,a Due to chilling action of mold wall,a thin skin of solid metal is formed at the thin skin of solid metal is formed at the interface immediately after pouringinterface immediately after pouring Skin thickness increases to

46、form a shell Skin thickness increases to form a shell around the molten metal as solidification around the molten metal as solidification progressesprogresses Rate of freezing depends on heat transfer Rate of freezing depends on heat transfer into mold,as well as thermal properties into mold,as well

47、 as thermal properties of the metalof the metal Characteristic grain structure in a casting of a pure Characteristic grain structure in a casting of a pure metal,showing randomly oriented grains of small size metal,showing randomly oriented grains of small size near the mold wall,and large columnar

48、grains oriented near the mold wall,and large columnar grains oriented toward the center of the castingtoward the center of the casting (a)Phase diagram for a copper (a)Phase diagram for a copper nickel alloy nickel alloy system and(b)associated cooling curve for a system and(b)associated cooling cur

49、ve for a 50%Ni50%Ni 50%Cu composition during casting50%Cu composition during castingMost alloys freeze over a temperature range rather than at a single temperature Characteristic grain structure in an alloy casting,Characteristic grain structure in an alloy casting,showing segregation of alloying co

50、mponents in center showing segregation of alloying components in center of castingof castingSolidification TimeSolidification Time Solidification takes timeSolidification takes time Total solidification time Total solidification time TSTTST=time =time required for casting to solidify after required