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2.008 Metal Casting.

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Presentation on theme: "2.008 Metal Casting."— Presentation transcript:

1 2.008 Metal Casting

2 Outline Introduction Process Constraints Green Sand Casting
Other Processes

3 Some Facts First casting: 5000-3000 BC
Bronze, iron age, light metal age? Versatility • Many types of metals • Rapid production • Wide range of shapes and sizes • Complex parts as an integral unit

4 Example – Sand Casting

5 Example – Die Casting

6 Example – Investment Casting

7 Casting Process Physics and
Constraints Phase Change • Density • Solubility • Diffusion rates High melting temperature • Chemical activity • High latent heat • Handling

8 Analysis of Casting Processes
Fluid mechanics for mold filling Heat transfer for solidification Thermodynamics, mass transfer and heat transfer for nucleation and growth Materials behavior for structure-property relationships

9 Mold Filling Bernoulli’s equation Reynold’s number • Turbulence
• Injection Molding : Re ~ 10-4


11 Conductivity / Diffusivity
Conductivity (W/mK) Cu ~ 400, Al ~ 200 Sand ~ 0.5, PMMA Sand Casting αsand < αmetal Injection Molding αtool metal ~ αmetal Die Casting αtool metal > αpolymer

12 Solidification Time : Sand Casting
Transient 1-D heat transfer Solution Solidification time Chvorinov’s rule

13 Solidification Time : Die Casting
Transient 1-D heat transfer Solution Solidification time

14 Comparison: Sand Mold vs Metal Mold Sand Mold Metal Mold Sand casting
Die casting

15 Microstructure Formation
Schematic illustration of three basic types of cast structures (a) Columnar dendritic (b) equiaxed dendritic (c) equiaxed nondendritic

16 Formation of Dendrites
Liquid Liquidus Temperature Solid Solidus Solid Liquid Mushy zone Alloying element Solid Liquid Dendrites

17 Constitutional Supercooling

18 Green Sand Casting Mechanical drawing of part Core halves
pasted together Core boxes Cope pattern plate Drag pattern plate Cope after ramming with sand and removing pattern, sprue, and risers Drag ready for sand Cope ready for sand Drag after removing pattern Casting as removed from mold; heat treated Casting ready for shippement Drag with core set in place Cope and drag assembled ready for pouring

19 Green Sand Mold Dimensional, Thermal and Chemical stability at high T
Size and shape Wettability by molten metal Compatibility with binder system Availability and consistency

20 Pattern Design Considerations
(DFM) Shrinkage allowance Machining allowance Distortion allowance Parting line Draft angle

21 Typical Shrinkage Allowance
Metal or alloy Shrinkage allowances mm / m Aluminum alloy Aluminum bronze Yellow brass (thick sections) Yellow brass (thin sections) Gray cast iron (a) White cast iron Tin bronze Gun metal Lead Magnesium Magnesium alloys (25%) Manganese bronze Copper-nickel Nickel Phosphor bronze Carbon steel Chromium steel Manganese steel Tin Zinc

22 Typical Pattern Machining
Allowance Allowances,mm Pattern size, mm Bore Surface Cope side For cast irons For cast steels For nonferrous alloys

23 Gating System: Sprue, Runner, and Gate Rapid mold filling
Minimizing turbulence Avoiding erosion Removing inclusions Controlled flow and thermal conditions Minimizing scrap and secondary operations

24 Riser: Location and Size
Casting shrinkage Directional solidification Scrap and secondary operation

25 Progressive Solidification in
Riser Progressive solidification Intermediate rate Slow rate Fast rate Riser Temperature gradient rising toward riser Directional solidification

26 Draft in Pattern Patterns Mold

27 Investment Casting Wax pattern Injection wax or plastic patterns
Ejecting pattern Pattern assembly (Tree) Autoclaved Heat Heat Heat Heat Slurry coating Stucco coating Pattern meltout Completed mold

28 Investment Casting (cont.)
Casting Pattern Finished product Shakeout Pouring Pouring

29 Advantages of Investment Casting
Intricate geometry Close dimensional tolerance Superior surface finish High-melting point alloys

30 Advantages of Investment Casting
Platen Toggle clamp Gas/oil accumulator Piston Shot sleeve

31 Advantages of Die Casting
High production rates Closer dimensional tolerances Superior surface finish Improved mechanical properties

32 Lost Foam Casting Pottern molding Cluster Assemble Coating
Compacted in Sand Casting Shakeout

33 Lost Foam Casting Invest assembly in flask with backlip medium
Vibrate to compact medium Pour Shakeout castings Clean castings assembly Inspect castings Ship castings Receive raw polystyrene beads Expand beads Mold component pattern, including gating system Join patters (if multipiece) Coat pattern assembly Dry assembly

34 Advantages of Lost Foam Casting
No parting line No cores One-piece flask Freedom of design Minimum handling of sand Ease of cleaning and secondary operation

35 Semi-solid Casting Punch Die Induction furnace

36 Advantages of Semi-solid Casting

37 Produciotn rate (Pc/hr)
Casting Process Comparison Cost * Produciotn rate (Pc/hr) Process Die Equipment Labor Sand Shell-mold Plaster Investment Permancnt mold Die Centrifugal

38 Cost - Casting Sand casting Investment casting Die casting
‧Tooling and equipment costs are low ‧Direct labor costs are high ‧Material utilization is low ‧Finishing costs can be high Investment casting ‧Tooling costs are moderate depending on the complexity ‧Equipment costs are low ‧Material costs are low Die casting ‧Tooling and equipment costs are high ‧Direct labor costs are low to moderate ‧Material utilization is high

39 Quality - Casting Sand casting
‧Tolerance (0.7~2 mm) and defects are affected by shrinkage ‧Material property is inherently poor ‧Generally have a rough grainy surface Investment casting ‧Tolerance (0.08~0.2 mm) ‧Mechanical property and microstructure depends on the method ‧Good to excellent surface detail possible due to fine slurry  Die casting ‧Tolerance (0.02~0.6 mm) ‧Good mechanical property and microstructure due to high ‧pressure ‧Excellent surface detail

40 Rate - Casting Sand casting Investment casting Die casting
‧Development time is 2~10 weeks ‧Production rate is depending on the cooling time : t~(V/A)2 Investment casting ‧Development time is 5~16 weeks depending on the complexity ‧Production rate is depending on the cooling time : t~(V/A)2 Die casting ‧Development time is 12~20 weeks t~(V/A)1

41 Flexibility - Casting Sand casting Investment casting Die casting
‧High degree of shape complexity (limited by pattern) Investment casting ‧Ceramic and wax cores allow complex internal configuration but costs increase significantly Die casting ‧Low due to high die modification costs

42 New Developments in Casting
Computer-aided design Rapid (free-form) pattern making

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