Module 4a -casting full 2024 (3)
.pdf
School
University of Saskatchewan**We aren't endorsed by this school
Course
ME 330
Subject
Mechanical Engineering
Date
Dec 17, 2024
Pages
29
Uploaded by CoachResolve12647
Casting processModule 4a
Module 4a
Casting processModule 4a
Module 4aClassification of solidification processesPolymer modified cement
Module 4a5CastingPrinciple of the processConfiguration / StructureProcess modelingDefectsDesign For Manufacturing (DFM)Process variation
Module 4aPrinciple of the Casting Process6
Module 4a7Casting –Principle of the process❑Casting is a process in which the molten metal flows by gravity or other forces into a mold and solidifies in the shape of the mold cavity❑Any material can be cast, because any material has a liquid state❑Physics: 1. Fluid flow and interaction with solid 2. Thermal dynamics
Basic casting steps (very simplified):1.Melt metal2.Pour molten metal into mold cavity3. Let it solidifyFurnaceCasting systemModule 4a8
Module 4a9CastingPrinciple of the processConfiguration / StructureProcess modelingDefectsDesign For Manufacturing (DFM)Process variation
Module 4aCasting system10
Module 4a11Basic components and their connectionsMake a cavityCasting System –(Generic) structure
Module 4aAnimationhttps://www.youtube.com/watch?v=EIBDp6U8bHo12
Module 4a13CastingPrinciple of the processConfiguration / StructureProcess modelingDefectsDesign For Manufacturing (DFM)Process variation
Module 4aProcess modeling1.Heat up metal to a certain temperature2.Pour molten metal into mold cavity3.Molten metal solidifies14
Module 4a15- Heat metal above the melting point- Pour it into the mold cavityHeat energy required for (1) heat for raising the temperature to the melting point, (2) heat of fusion to convert the solid to the liquid, (3) heat for raising the molten metal to the metal at the desired temperature ready to pour it into a cavity.Heat up metal
Module 4a16Heat up metal3.1 Heating Period Thermal Analysis)}()({0mplfmsTTCHTTCVH−++−=(1) heat for raising the temperature to the melting point(2) heat of fusion to convert the solid to the liquid(3) heat for raising the molten metal to the metal at the desired temperature ready to pour it into a cavityGiven T0, determine the total energy H, and then set up the furnace property
Module 4aPour molten metal into mold cavity221222222111FgvPhFgvPh+++=+++Flow rate at the base of a sprue (energy balance):ghv2=17
Module 4a18Mass in = mass out Q=V1 ×A1 = V2 ×A2❑Assumption: Fluid is incompressiblePour molten metal into mold cavityMass balancev2>v1, so A2<A1, so the sprue must be designed as tapered,where V: velocity; A: cross section area
Module 4a19Time to fully fill the mold cavityQVMFT=Assumption: not consider the transient process of molten metal in the cavity.Pour molten metal into mold cavityMFT is shorter than the actual time needed to fill up the mold cavity because of the assumption.
Module 4aProcess modeling1.Heat up metal to a certain temperature2.Pour molten metal into mold cavity3.Solidification of molten metal20
Module 4a21Chvorinov’s rule: the time needed for the molten metal to completely solidify in the mold cavitynmAVCTST)(=TST: total solidification time, min.V: volume of the casting, in.3(cm3).A: surface area of the casting, in.2(cm2).n: exponent, 2.Cm: mold constant, min.in.2(min/cm2).Solidification of molten metal
Module 4a22Cmis a function of ❑mold material❑thermal properties of the cast metal❑pouring temperature relative to the melting point of the metal.Determination of Cmcan be done through experiment.The principle of such an experimentis to have the same system (e.g., mold material, etc.) as that for the casting but for a simple and known cavity geometry or casting (e.g., rectangular shape), to run the process, and to record the Time TST for this test casting.nmAVCTST)(=
Module 4a23Implication of Chvorinov’s Rule:A casting with a higher volume-to-surface area ratio will cool and solidify more slowly than one with a lower ratio.
Module 4a24CastingPrinciple of the processConfiguration / StructureProcess modelingDefects/quality controlDesign For Manufacturing (DFM)Process variation
Module 4a25❑Defect 1: incomplete filling of cavity ❑Defect 2: gaps in castingDefectsIncomplete filling is caused by too fast solidification and flow blockage. Solutions: multiple pouring cups, riser, etc.Gaps in casting is caused by a phenomenon called shrinkage. Solutions: riser, pattern allowance, etc.
Module 4a26Shrinkage -- the source of problems in any process involving the heat transfer
27Liquid Contraction0.5%Further ContractionLack of molten metalDifferent metal thermal expansion coefficientsShrinkage →gaps and voids
28Riser: overcoming the two defectsCastingRiserCup and Sprue to pour the molten metalRiser = Reservoirhttps://www.youtube.com/watch?v=eLiJLz2qhIA
Module 4a29Summary of discussions so far:❑Principle of casting process (liquid fills up cavity, and then cool down to solid).❑Casting can be applied to any material.❑Three processes: heat up, pour, solidify.❑Defects (incomplete filling, gap).