Karışık metal döküm ( ingilizce ) 2.008 Metal Casting Outline Introduction Process Constraints Green Sand Casting Other Processes 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 Example – Sand CastingExample – Die Casting Example – Investment Casting Casting Process Physics and Constraints Phase Change •D e n s i ty • Solubility • Diffusion rates High melting temperature • Chemical activity • High latent heat • Handling 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 relationshipsMold Filling . 2 2 const g v g P h = + + ? 4 10 5 Re × ? = µ ? vD m/s 5 . 1 2 ? ? gh v Bernoulli’s equation Reynold’s number • Turbulence • Injection Molding : Re ~ 10 -4 h Cooling for Sand Mold ?T ?T METAL - MOLD INTERFACE MOLD - AIR INTERFACE DISTANCE T 0 T w TEMPERATUR E MOLD AIR SOLID LIQUID Conductivity / Diffusivity Sand Casting ? sand < ? metal Die Casting ? tool metal > ? polymer Injection Molding ? tool metal ~ ? metal Conductivity (W/mK) Cu ~ 400, Al ~ 200 Sand ~ 0.5, PMMA ~ 0.2 Solidification Time : Sand Casting Transient 1-D heat transfer 2 2 x T t T s ? ? = ? ? ? t x erf T T T T s M o M ? 2 - = - - Solution 2 ? ? ? ? ? ? = A V C t s Solidification time Chvorinov’s ruleSolidification Time : Die Casting Transient 1-D heat transfer ) ( o p T T Ah t T mC - - = ? ? ? ? ? ? ? ? ? ? - - ? + = mold eject mold sp inject p T T T T T Ah mC t ln Solution 1 ? ? ? ? ? ? = A V C t s Solidification time Comparison: Sand Mold vs Metal Mold Sand Mold Sand casting t s ~ (V/A) 2 Metal Mold Die casting t s ~ (V/A) 1 Microstructure Formation Schematic illustration of three basic types of cast structures (a) Columnar dendritic (b) equiaxed dendritic (c) equiaxed nondendritic Formation of Dendrites Temperature Alloying element Solid Liquid T S T L Solid Solid Liquid Liquid L+S S + L Mushy zone Dendrites Mold wall Solidus LiquidusConstitutional Supercooling SOLID LIQUID C S * C L * T* (a) (b) SOLUTE ENRICHED LAYER IN FRONT OF LIQUID-SOLID INTERFACE C ? C L * LIQUID COMPOSITION DISTANCE, x* T* TEMPERATURE DISTANCE, x* T ACTUAL T LIQUIDS (c) T* TEMPERATURE DISTANCE, x* T ACTUAL T LIQUIDS (d) CONSTITUTIONALLY SUPERCOOLED REGION Green Sand Casting Mechanical drawing of part Core boxes Core halves pasted together Cope pattern plate Drag pattern plate Cope ready for sand Cope after ramming with sand and removing pattern, sprue, and risers Drag ready for sand Drag after removing pattern Drag with core set in place Cope and drag assembled ready for pouring Casting as removed from mold; heat treated Casting ready for shippement 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 Pattern Design Considerations (DFM) Shrinkage allowance Machining allowance Distortion allowance Parting line Draft angleTypical Shrinkage Allowance Metal or alloy Shrinkage allowances mm / m Aluminum alloy ………………………………...... 13 Aluminum bronze ……………………………...… 21 Yellow brass (thick sections) ………...…....…… 13 Yellow brass (thin sections) …..……...….…...… 13 Gray cast iron (a) …………………………….... 8 - 13 White cast iron ………………………………..….. 21 Tin bronze …………………………………..……. 16 Gun metal …………………………………...… 11 - 16 Lead …………………………………………..…... 26 Magnesium …………………………………..…… 21 Magnesium alloys (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 Pattern Machining Allowance 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 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 3.2 6.4 152 - 305………………………………… 6.4 4.8 6.4 305 - 510.………………………………... 6.4 6.4 7.9 510 - 915………………………………… 7.1 6.4 9.6 915 - 1524……………………………….. 7.9 6.4 12.7 For nonferrous alloys Up to 76...……………………………….. 1.6 1.6 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 3.2 4.0 915 - 1524……………………………….. 4.0 3.2 4.8 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 Riser: Location and Size Casting shrinkage Directional solidification Scrap and secondary operationProgressive Solidification in Riser Temperature gradient rising toward riser Riser Slow rate Fast rate Intermediate rate Progressive solidification : Directional solidification Draft in Pattern Patterns Mold Investment Casting Injection wax or plastic patterns Ejecting pattern Wax pattern Pattern assembly (Tree) Slurry coating Stucco coating Completed mold Pattern meltout Autoclaved Heat Heat Heat Heat Investment Casting (cont.) Pouring Shakeout Casting Pattern Finished productAdvantages of Investment Casting Intricate geometry Close dimensional tolerance Superior surface finish High-melting point alloys Die Casting Gas/oil accumulator Piston Shot sleeve Die Toggle clamp Platen Advantages of Die Casting High production rates Closer dimensional tolerances Superior surface finish Improved mechanical properties Lost Foam CastingLost Foam Casting Receive raw polystyrene beads Expand beads Mold component pattern, including gating system Join patters (if multipiece) Coat pattern assembly Dry assembly Vibrate to compact medium Pour Shakeout castings Clean castings assembly Inspect castings Ship castings Invest assembly in flask with backlip medium 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 Semi-solid Casting Punch Die Induction furnace Advantages of Semi-solid CastingCasting Process Comparison Cost - Casting Sand 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 Direct labor costs are high Material costs are low Die casting Tooling and equipment costs are high Direct labor costs are low to moderate Material utilization is high 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 Rate - Casting Sand 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 Production rate is depending on the cooling time : t~(V/A) 1Flexibility - Casting Sand 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 New Developments in Casting Computer-aided design Rapid (free-form) pattern making