Metal Casting -1 - IIT Bombay

1 1 Metal Casting -1ME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. ColtonME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton2 Outline Casting basics Patterns and molds Melting and pouring analysis Solidification analysis Casting defects and remedies3 Casting Basics A Casting is a Metal object obtained by pouringmoltenmetal into a moldand allowing it to solidify. Gearbox castingMagnesium castingAluminum manifoldCast wheelME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

2 Melkote / Dr. Colton4 Casting : Brief History 3200 Copper part (a frog!) cast in Mesopotamia. Oldest known Casting in existence 233 Cast iron plowshares (in China) 500 Cast crucible steel (in India) 1642 First American iron Casting at Saugus Iron Works, Lynn, MA 1818 First cast steel made in using crucible process 1919 First electric arc furnace used in the Early 1970 s Semi-solid metalworking process developed at MIT 1996 Cast Metal matrix composites first used in brake rotors of production automobile ME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh.

3 Notes by: Prof. Melkote / Dr. Colton5 Complex, 3-D shapes Near net shape Low scrap Relatively quick process Intricate shapes Large hollow shapes No limit to size Reasonable to good surface finishME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton6 Capabilities Dimensions sand Casting -as large as you like small -1 mm or so Tolerances in to in Surface finish die Casting 8-16 micro-inches (1-3 m) sand Casting -500 micro-inches ( m)ME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

4 Melkote / Dr. Colton7 Processes Sand Shell Plaster Ceramic Investment Lost foam Pressure Vacuum Die Centrifugal Squeeze Semi-solid Single crystal Directional solidification Slush ContinuousME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton8 Metals processed by Casting Sand Casting 60% Investment Casting 7% Die Casting 9% Permanent mold Casting 11% Centrifugal Casting 7% Shell mold Casting 6%ME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

5 Melkote / Dr. Colton9 Casting : Basic Steps Basic steps in Casting are: Preparation of pattern(s), core(s) and mold(s) Melting and pouring of liquefied Metal Solidification and cooling to room temperature Removal of Casting -shakeout Inspection (for possible defects )ME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton10 Pattern Making Pattern is a replica of the exterior surface of part to be cast used to create the mold cavity Pattern materials wood, Metal , plasterME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

6 Melkote / Dr. Colton11 Pattern Making Pattern usually larger than cast part Allowances made for: Shrinkage: to compensate for Metal shrinkage during cooling from freezing to room tempShrinkage allowance = aL(Tf T0)expressed as per unit length for a given materiala= coeff. of thermal expansion, Tf= freezing tempT0= room Cast iron allowance = 1/96 allowance = 3/192 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton12 Pattern Making Pattern allowances made for: Machining: excess dimension that is removed by machining; depends on part dimension and material to be iron, dimension 0-30 cm, allowance = mm; aluminum, allowance = mm Draft: taper on side of pattern parallel to direction of extraction from mold; for ease of pattern extraction; typically ~2 degreesME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

7 Melkote / Dr. Colton14 Mold Making: Sand CastingME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton15 Mold Making: Sand CastingME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton16 Mold Making: Sand CastingCasting video: 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton17 Sand Casting Green sand mold: sand + clay + water + additives Typical composition (by wt.)

8 : 70-85% sand, 10-20% clay, 3-6% water, 1-6% additives Important properties of molding sand: Strength Permeability Deformation Flowability RefractorinessME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton18 Melting For a pure Metal :total heat energy required, H= energy to raise temp of Metal to melting point, Tm+ heat of fusion, Hf+ energy to raise temp of liquid Metal to pouring temp, TpH = rV[cs(Tm T0) + Hf+ cl(Tp Tm)] Heat required for alloys more complex Gas fired, electric arc and induction furnaces used to melt metalME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

9 Melkote / Dr. Colton19 Melting Solubility of gases (hydrogen and nitrogen) in molten Metal an issue Solubility of H2, S: S = C exp [-Es/(kq)]Es= heat of solution of 1 mol ofH2q= absolute temp, C and kare 1 atm pressure, liquid solubility of H2in iron = 270 cc/kg; in aluminum = 7 cc/kgME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton20 Melting FurnacesInduction HeatingME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.

10 Melkote / Dr. Colton21 Pouring An important step in Casting since it impacts mold filling ability and Casting defectsME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof. Melkote / Dr. Colton22 Pouring Key aspects of pouring Pouring rate Too slow Metal freezes before complete mold filling Too fast inclusion of slag, aspiration of gas, etc. Reynolds number: Laminar versus turbulent flow Most steels reach mildly turbulent flow conditions easily (Re > 3500) Superheat ~ (Tp Tm); Tp= pouring temp Too high increased gas solubility porosity problemsReVDrh=r= density of liquid, V= mean flow velocity, D= tube diameter, h= dynamic viscosity of liquidME 206: Manufacturing Processes & EngineeringInstructor: Ramesh Singh; Notes by: Prof.