FUNDAMENTALS OF METAL CASTING SME Video - Forming Processes Casting (vts_17) Overview of Casting Technology Heating and Pouring Solidification and Cooling In-class Assignment ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Solidification Processes ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Casting Molten metal Gravity or pressure Solidifies mold cavity Steps in casting seem simple: Melt the metal Pour it into a mold Let it freeze ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Open Molds and Closed Molds Closed mold requires a gating system Molds are made of sand, plaster, ceramic or metal ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Casting Advantages and Disadvantages External and internal geometries Net shape & Near net shape Produce very large parts Mass production Disadvantages Limitations on mechanical properties Dimensional accuracy and surface finish Hazards to workers due to hot molten metal Environmental problems ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Parts Made by Casting Big parts Engine blocks for automotive vehicles Wood burning stoves Machine frames Small parts Dental crowns Jewelry Frying pans Ferrous and nonferrous metals ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Overview of Casting Technology Foundry = factory equipped & foundrymen Making molds Melting and handling molten metal Performing the casting process & cleaning Expendable mold Intricate geometries possible Sand plus binders Permanent mold Metal molds Limited part geometry ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Sand Casting Mold Gating system ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Forming the Mold Cavity Pack sand around a pattern Remove pattern Oversized pattern to allow for shrinkage Shrinkage due to Solidification Cooling Sand for the mold is moist with binder Cores to create internal geometries ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Cooling Curve for a Pure Metal Pure metal solidifies at a constant temperature ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Solidification of Alloys Alloys freeze over a temperature range ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Copper‑nickel phase diagram Cooling curve for a 50%Ni‑50%Cu

Solidification of Metals Spiral mold test for fluidity ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Solidification of Pure Metals Skin form due to chilling action of mold wall Rate of freezing depends on heat transfer Grain structure Casting of pure metal Near mold wall Randomly oriented grains Small size Toward center of casting Large columnar grains Oriented toward the center ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Solidification of Alloys Segregation of alloying components in center of casting ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Shrinkage in Solidification and Cooling Pattern shrinkage allowance EXCEPTION: Cast iron with high C content Graphitization during freezing causes expansion Couteracts shrinkage ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

External Chills for Directional Solidification Desirable for regions of the casting most distant from the liquid metal supply to freeze first Solidification to progress from these remote regions toward the riser rapid freezing chill not used ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Solidification Time TST depends on size and shape of casting by relationship known as Chvorinov's Rule TST = total solidification time V = volume of the casting A = surface area of casting n = exponent with typical value = 2 Cm = mold constant Design the riser to have a larger volume‑to‑area ratio Cm for a given casting based on experimental data ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Example In the casting of steel under certain mold conditions, the mold constant in Chvorinov's Rule is known to be 4.0 min/cm2, based on previous experience. The casting is a flat plate whose length = 30 cm, width = 10 cm, and thickness = 20 mm. Determine how long it will take for the casting to solidify. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

SME Video ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Assignment A disk‑shaped part is to be cast out of aluminum. The diameter of the disk = 500 mm and its thickness = 20 mm. If the mold constant = 2.0 sec/mm2 in Chvorinov's Rule, how long will it take the casting to solidify? ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extra Credit – hand in before test 1 A steel casting has a cylindrical geometry with 4.0 in diameter and weighs 20 lb. This casting takes 6.0 min to completely solidify. Another cylindrical‑shaped casting with the same diameter‑to‑length ratio weighs 12 lb. This casting is made of the same steel and the same conditions of mold and pouring were used. Determine: (a) the mold constant in Chvorinov's Rule, (b) the dimensions, and (c) the total solidification time of the lighter casting. The density of steel = 490 lb/ft3. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Manufacturing Economics ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Time Permitting Content ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Riser Design Reservoir of liquid metal to compensate for shrinkage Shrinkage due to solidification Design risers to freeze after the main casting Riser is waste metal that is later separate Melt risers to make more castings Maximize the V/A ratio of riser ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Casting Process Heating the metal in a furnace Raise temperature to melting point Heat of fusion converts solid to liquid Pouring the molten metal Pouring temperature Pouring rate and turbulence Solidification of metals Transforms molten metal to solid state Pure element Alloy ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e