授章节教师杨宏智教授.ppt
Manufacturing Engineering Technology Metal Casting:Design,Materials and Economics,授課教師：楊宏智教授,1,【本著作除另有註明外，採取創用CC姓名標示非商業性相同方式分享台灣3.0版授權釋出】,【本著作除另有註明外，採取創用CC姓名標示非商業性相同方式分享台灣3.0版授權釋出】,【本著作除另有註明外，採取創用CC姓名標示非商業性相同方式分享台灣3.0版授權釋出】,Manufacturing Engineering Technology機械製造,楊宏智（台大機械系教授）,2,Chapter Outline,IntroductionDesign Considerations in CastingEconomics of Casting,Introduction,Successful casting practice requires proper control of a large 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 casting,Design Considerations in Casting,All casting operations share the characteristics of phase change and thermal 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 reproduce,Design Considerations in Casting:General Design Considerations for Castings,2 types of design issues in casting:Geometric features and tolerances incorporated into the partMold features that are needed to produce the desired casting,Design Considerations in Casting:General Design Considerations for Castings,Design of Cast PartsCorners,angles,and section thicknessFlat areasShrinkageDraftDimensional tolerancesLettering and markingsFinishing operations,Design Considerations in Casting:General Design Considerations for Castings,Locating 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 contouredLocation 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 metals,Design Considerations in Casting:General Design Considerations for Castings,Locating 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 gate length should be 3 to 5 times the gate diameterCurved gates should be avoided,Runner 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 Mold FeaturesGoal in designing a sprue is to achieve the required metal flow rates while preventing excessive dross formation,Design Considerations in Casting:General Design Considerations for Castings,Designing Other Mold FeaturesGoal 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 used to speed up solidification of the metal,Design Considerations in Casting:General Design Considerations for Castings,Establishing Good PracticesHigh-quality molten metal is essential for producing superior castingsPouring of metal should not be interruptedStress relieving necessary to avoid distortions of castings in critical applications,Design Considerations in Casting:General Design Considerations for Castings,Expendable-mold process cool much slower than die castingImportant design considerations are:Mold Layout-must be placed logically and compactly with gatesRiser Design-consideration in size and placement of risersMachining Allowance-require for additional finishing operations,Design Considerations in Casting:General Design Considerations for Castings,Design Considerations in Casting:Design for Permanent-mold Casting,Designs may be modified to eliminate the draft for better dimensional accuracyDie-cast parts are net shaped to remove gates and minor trimming to remove flashing and defectsThey do not require a machining allowance,Design Considerations in Casting:Computer Modeling of Casting Processes,Casting involves 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 structures,impingement of grains and movement of the liquidsolid interface during solidificationCommercial software programs are Magmasoft,ProCast,Solidia and AFSsolid,Economics of Casting,Cost of each cast part(unit cost)depends on several factors,including materials,equipment,and laborEach of individual factors affects the overall cost of a casting operation,Economics of Casting,Costs 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,
