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1、授章节教师杨宏智教授 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望楊宏智（台大機械系教授）2Chapter OutlineChapter Outline1.Introduction2.Design Considerations in Casting3.Economics of CastingIntroductionIntroductionSuccessful casting practice requires proper control of a large
2、number of variablesFlow of the molten metal in the mold cavities,the gating systems,the rate of cooling,and the gases evolved would influence the quality of a castingDesign Considerations in CastingDesign Considerations in CastingAll casting operations share the characteristics of phase change and t
3、hermal shrinkage during the casting cycleBut each process will have its own design considerationsSand casting will require mold erosion and sand inclusions in the castingDie casting will not have this concernDefects frequently are random and difficult to reproduceDesign Considerations in Casting:Des
4、ign Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for Castings2 types of design issues in casting:1.Geometric features and tolerances incorporated into the part2.Mold features that are needed to produce the desired castingDesign Considerations in C
5、asting:Design Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsDesign of Cast PartsCorners,angles,and section thicknessFlat areasShrinkageDraftDimensional tolerancesLettering and markingsFinishing operationsDesign Considerations in Casting
6、:Design Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsLocating the Parting LineParting line is the line or plane separating the upper(cope)and lower(drag)halves of moldsParting line should be along a flat plane rather than be contouredL
7、ocation is important as it influences mold design,ease of molding,number and shape of cores required,method of support and the gating systemParting line should be low for less dense metals and located at mid-height for denser metalsDesign Considerations in Casting:Design Considerations in Casting:Ge
8、neral Design Considerations for CastingsGeneral Design Considerations for CastingsLocating and Designing GatesMultiple gates are preferableGates should feed into thick sections of castingsA fillet should be usedGate closest to the sprue should be placed sufficiently far away from the sprueMinimum ga
9、te length should be 3 to 5 times the gate diameterCurved gates should be avoidedRunner DesignRunner is a horizontal distribution channel that accepts molten metal from the sprue and delivers it to the gatesIt is used to trap dross and keep it from entering the gates and mold cavityDesigning Other Mo
10、ld FeaturesGoal in designing a sprue is to achieve the required metal flow rates while preventing excessive dross formationDesign Considerations in Casting:Design Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsDesigning Other Mold Featur
11、esGoal in designing a sprue is to achieve the required metal flow rates while preventing excessive dross formationTurbulent flow rates should be avoidedA pouring basin is used to ensure uninterrupted metal flow into the sprueFilters are used to trap large contaminants and more laminar flowChills use
12、d to speed up solidification of the metalDesign Considerations in Casting:Design Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsEstablishing Good PracticesHigh-quality molten metal is essential for producing superior castingsPouring of m
13、etal should not be interruptedStress relieving necessary to avoid distortions of castings in critical applicationsDesign Considerations in Casting:Design Considerations in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsExpendable-mold process cool much sl
14、ower than die castingImportant design considerations are:1.Mold Layout-must be placed logically and compactly with gates2.Riser Design-consideration in size and placement of risers3.Machining Allowance-require for additional finishing operationsDesign Considerations in Casting:Design Considerations
15、in Casting:General Design Considerations for CastingsGeneral Design Considerations for CastingsDesign Considerations in Casting:Design Considerations in Casting:Design for Permanent-mold CastingDesign for Permanent-mold CastingDesigns may be modified to eliminate the draft for better dimensional acc
16、uracyDie-cast parts are net shaped to remove gates and minor trimming to remove flashing and defectsThey do not require a machining allowanceDesign Considerations in Casting:Design Considerations in Casting:Computer Modeling of Casting ProcessesComputer Modeling of Casting ProcessesCasting involves
17、complex interactions among material and process variablesA quantitative study of these interactions is essential to the proper design and production of high-quality castingsStudies consist of heat flow,temperature gradients,nucleation and growth of crystals,formation of dendritic and equiaxed struct
18、ures,impingement of grains and movement of the liquidsolid interface during solidificationCommercial software programs are Magmasoft,ProCast,Solidia and AFSsolidEconomics of CastingEconomics of CastingCost of each cast part(unit cost)depends on several factors,including materials,equipment,and labor
19、Each of individual factors affects the overall cost of a casting operationEconomics of CastingEconomics of CastingCosts are involved in melting and pouring the molten metal into molds and in heat treating,cleaning,and inspecting the castingsLabor and skills required is also a considerationEquipment cost per casting will decrease as the number of parts cast increasesHigh production rate can justify the high cost of dies and machinery