2.008 Metal Throwing.


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Green Sand Casting. Mechanical drawing of part. Center boxes. Center parts ... Adapt prepared for sand. Adapt in the wake of smashing to sand and evacuating example, sprue, and risers ...
Transcripts
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2.008 Metal Casting Reading: Kalpakjian pp. 239-316

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Outline Introduction Process Constraints Green Sand Casting Other Processes

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Some Facts First throwing: 5000-3000 BC Bronze, iron age, light metal age? Flexibility Many sorts of metals Rapid generation Wide scope of shapes and sizes Complex parts as a necessary unit

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Example – Sand Casting

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Example – Die Casting

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Example – Investment Casting

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Casting Process Physics and Constraints Phase Change Density Solubility Diffusion rates High softening temperature Chemical action High inert warmth Handling

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Analysis of Casting Processes Fluid mechanics for mold filling Heat exchange for hardening Thermodynamics, mass exchange and warmth exchange for nucleation and development Materials conduct for structure-property connections

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h Mold Filling Bernoulli\'s condition Reynold\'s number Turbulence Injection Molding : Re ~ 10 - 4

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MOLD LIQUID SOLID AIR T w TEMPERATURE METAL - MOLD INTERFACE T MOLD - AIR INTERFACE T T 0 DISTANCE Cooling for Sand Mold

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Conductivity/Diffusivity Conductivity (W/mK) Cu ~ 400, Al ~ 200 Sand ~ 0.5, PMMA ~ 0.2 Sand Casting a sand < a metal Die Casting a device metal ~ a metal Injection Molding an apparatus metal > a polymer

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Solidification Time : Sand Casting Transient 1-D heat exchange Solution Solidification time Chvorinov\'s standard

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

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Comparison: Sand Mold versus Metal Mold Sand Mold Sand throwing t s ~ (V/A) 2 Metal Mold Die throwing t s ~ (V/A) 1

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Microstructure Formation Schematic outline of three essential sorts of cast structures Columnar dendritic (b) equiaxed dendritic (c) equiaxed nondendritic

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Liquid T L L+S T S Liquidus Solid Temperature S + L Solidus Liquid Solid Mushy zone Alloying component Liquid Solid Mold divider Dendrites Formation of Dendrites

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SOLUTE ENRICHED LAYER IN FRONT OF LIQUID-SOLID INTERFACE C L * C L * T* C S * LIQUID COMPOSITION C  SOLID DISTANCE, x* (b) (a) T ACTUAL T LIQUIDS T ACTUAL T LIQUIDS TEMPERATURE CONSTITUTIONALLY SUPERCOOLED REGION T* DISTANCE, x* DISTANCE, x* (c) (d) Constitutional Supercooling

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Mechanical drawing of part Core parts stuck together Drag design plate Cope design plate Core boxes Cope subsequent to smashing with sand and expelling example, sprue, and risers Drag prepared for sand Drag in the wake of evacuating example Cope prepared for sand Casting prepared for shippement Casting as expelled from mold; heat treated Drag with center set up Cope and drag gathered prepared for pouring Green Sand Casting

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Green Sand Mold Dimensional, Thermal and Chemical steadiness at high T Size and shape Wettability by liquid metal Compatibility with fastener framework Availability and consistency

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Pattern Design Considerations (DFM) Shrinkage remittance Machining stipend Distortion recompense Parting line Draft edge

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Metal or compound Shrinkage stipends mm/m Aluminum combination … ...... 13 Aluminum bronze … ...… 21 Yellow metal (thick segments) … ...… ....… … 13 Yellow metal (slim segments) … ..… … ...… .… ...… 13 Gray cast press (a) … .... 8 - 13 White cast iron … ..… .. 21 Tin bronze … ..… … . 16 Gun metal … ...… 11 - 16 Lead … ..… ... 26 Magnesium … ..… … 21 Magnesium amalgams (25%) … ... 16 Manganese bronze … .… 21 Copper-nickel … .. 21 Nickel … … .... 21 Phosphor bronze … 11 - 16 Carbon steel … 16 - 21 Chromium steel … .… .. 21 Manganese steel … .… 26 Tin … … .… … . 21 Zinc … … .… ... 26 Typical Shrinkage Allowance

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Allowances, mm Pattern size, mm Bore Surface Cope side For cast irons Up to 152.… … .. 3.2 2.4 4.8 152 - 305… … 3.2 6.4 305 - 510.… … ... 4.8 4.0 6.4 510 - 915… … 6.4 4.8 6.4 915 - 1524… … .. 7.9 4.8 7.9 For cast steels Up to 152.… … .. 3.2 6.4 152 - 305… … 6.4 4.8 6.4 305 - 510.… … ... 6.4 7.9 510 - 915… … 7.1 6.4 9.6 915 - 1524… … .. 7.9 6.4 12.7 For nonferrous combinations Up to 76...… … .. 1.6 76 - 152..… … 2.4 1.6 2.4 152 - 305… … 2.4 1.6 3.2 305 - 510.… … ... 3.2 2.4 3.2 510 - 915… … 3.2 4.0 915 - 1524… … .. 4.0 3.2 4.8 Typical Pattern Machining Allowance

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Gating System: Sprue, Runner, and Gate Rapid mold filling Minimizing turbulence Avoiding disintegration Removing considerations Controlled stream and warm conditions Minimizing scrap and auxiliary operations

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Riser: Location and Size Casting shrinkage Directional cementing Scrap and optional operation

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Progressive hardening : Intermediate rate Fast rate Slow rate Riser Temperature angle ascending toward riser Directional cementing Progressive Solidification in Riser

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Patterns Mold Draft in Pattern

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Wax design Injection wax or plastic examples Ejecting design Pattern get together (Tree) Autoclaved Heat Stucco covering Completed mold Pattern meltout Slurry covering Investment Casting

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Casting Pattern Finished item Shakeout Pouring Investment Casting (cont.)

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Advantages of Investment Casting Intricate geometry Close dimensional resistance Superior surface complete High-softening point compounds

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Toggle clasp Platen Gas/oil gatherer Piston Shot sleeve Die Casting

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Advantages of Die Casting High generation rates Closer dimensional resiliences Superior surface completion Improved mechanical properties

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Lost Foam Casting

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Invest get together in carafe with backlip medium Expand dabs Vibrate to conservative medium Pour Mold segment design, including gating framework Shakeout castings Join patters (if multipiece) Clean castings get together Coat design get together Inspect castings Ship castings Dry get together Lost Foam Casting Receive crude polystyrene dabs

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Advantages of Lost Foam Casting No separating line No centers One-piece cup Freedom of outline Minimum treatment of sand Ease of cleaning and optional operation

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Punch Die Induction heater Semi-strong Casting

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Advantages of Semi-strong Casting

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Casting Process Comparison

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Cost - Casting Sand throwing Tooling and gear expenses are low Direct work expenses are high Material use is low Finishing expenses can be high Investment throwing Tooling expenses are moderate contingent upon the unpredictability Equipment expenses are low Direct work expenses are high Material expenses are low Die throwing Tooling and hardware expenses are high Direct work expenses are low to direct Material use is high

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Quality - Casting Sand throwing Tolerance (0.7~2 mm) and imperfections are influenced by shrinkage Material property is innately poor Generally have an unpleasant grainy surface Investment throwing Tolerance (0.08~0.2 mm) Mechanical property and microstructure relies on upon the technique Good to astounding surface subtle element conceivable because of fine slurry Die throwing Tolerance (0.02~0.6 mm) Good mechanical property and microstructure because of high weight Excellent surface subtle element

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Rate - Casting Sand throwing Development time is 2~10 weeks Production rate is relying upon the cooling time : t~(V/A) 2 Investment throwing Development time is 5~16 weeks relying upon the multifaceted nature Production rate is relying upon the cooling time : t~(V/A) 2 Die throwing Development time is 12~20 weeks Production rate is relying upon the cooling time : t~(V/A) 1

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Flexibility - Casting Sand throwing High level of shape many-sided quality (constrained by example) Investment throwing Ceramic and wax centers permit complex inte

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