©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e Classification of solidification processes

Module 4a2 Casting Principle of the process Configuration / Structure Process modeling Defects Design For Manufacturing (DFM) Process variation

Module 4a Principle of the Casting Process

Module 4a4 Casting – Principle and process  Casting is a process in which the molten metal flows by gravity or other force into a mold and solidifies in the shape of the mold cavity.  Any material can be cast, as any material undergoes the liquid state and solid state.  Physics: 1. Fluid flow and interaction with solid 2. Thermal dynamics

Basic casting steps (very simplified): 1.Melt metal 2.Pour it into mold 3.Let it freeze Furnace Casting system

Module 4a6 Casting Principle of the process Configuration / Structure Process modeling Defects Design For Manufacturing (DFM) Process variation

Module 4a Casting system

Module 4a8 Basic components and their connections Make a cavity Casting System – (Generic) structure

Module 4a9 Casting Principle of the process Configuration / Structure Process modeling Defects Design For Manufacturing (DFM) Process variation

Module 4a Process modeling 1.Heat up metal to a certain temperature 2.Pour molten metal into mold cavity 3.Solidify molten metal

Module 4a11 -Heat metal above the melting point -Pour it into the mold cavity Heat 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 4a12 Heat up metal 3.1 Heating Period Thermal Analysis (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. Given T0, determine the total energy H, and then set up the furnace property

Module 4a Pour molten metal into mold cavity Flow rate at the base of a sprue (energy balance:

Module 4a14 Mass in = mass out Q=v1 A1 = V2 A2 Assumption: Fluid is incompressible. Pour molten metal into mold cavity Mass balance

Module 4a15 Time to fully fill the model cavity Assumption: not consider the transient process of molten metal in the cavity. Pour molten metal into mold cavity MFT is shorter than the actual time needed to fill up the mold cavity.

Module 4a Process modeling 1.Heat up metal to a certain temperature 2.Pour molten metal into mold cavity 3.Solidify molten metal

Module 4a17 Chvorinov’s rule: the time needed for the molten metal to completely solidify in the mold cavity TST:total solidification time, min V:volume of the casting, in. 3 (cm 3 ) A:surface area of the casting, in. 2 (cm 2 ) N:exponent, 2 C m :mold constant, min.in. 2 (min/cm 2 ) Solidify molten metal

Module 4a18 C m is a function of  mold material  thermal properties of the cast metal  pouring temperature relative to the melting point of the metal. Determination of C m can be done through experiment. The principle of such an experiment is to have a scenario that is the same as the casting and a known cavity geometry, to operate the process, and to record the Time TST.

Module 4a19 Implication 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 4a20 Casting Principle of the process Configuration / Structure Process modeling Defects/quality control Design For Manufacturing (DFM) Process variation

Module 4a 21 Basic Problems in Casting Processes - Incomplete filling of cavity - Gaps in casting Defects Incomplete 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.

handouts 322 Liquid Contraction 0.5% Further Contraction Lack of molten metal Different metal thermal expansion coefficients Shrinkage

Module 4a23 Riser: conducive to overcoming defects 1 and 2 Casting Riser Cup and Sprue to pour the molten metal Riser = Reservoir

Module 4a24 Summary of discussions so far  Principle of casting process (casting is liquid to fill up cavity)  Casting can be applied to any material  Three processes: heat up, pour, solidify  Defects (incomplete filling, )