Casting & its types in metals


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main types of metal castings

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Casting & its types in metals

  1. 1. • Casting is the process of producing metal/alloy component parts of desired shapes by pouring the molten metal/alloy into a prepared mold (of that shape) and then allowing the metal/alloy to cool and solidify. The solidified piece of metal/alloy is known as a CASTING or FOUNDRY”.
  2. 2. EXAMPLES OF CAST PARTS Crank handle formed by casting; some areas were machined and assembled after casting
  3. 3. EXAMPLES OF CAST PARTS Complex part formed by casting
  4. 4. CASTING TERMINOLOGY Flask The box containing the mold Cope The top half of any part of a 2-part mold Drag The bottom half of any part of a 2-part mold Core A shape inserted into the mold to form internal cavities Mold Cavity Hollow mold area in which metal solidifies Riser Extra cavity to store additional metal to prevent shrinkage
  5. 5. Gating System Channels used to deliver metal into the mold cavity Pouring Cup The part of the gating system that receives poured metal Sprue Vertical channel Runners Horizontal channels Parting Line / Parting Surface Separate the cope and drag of a 2-part mold Draft Taper on a pattern that allows removal from the mold Casting The process and product of solidifying metal in a mold
  6. 6. CATEGORIES OF METAL CASTING PROCESSES 1. Expendable mold processes - mold is sacrificed to remove part TYPES: Sand Casting, Shell mold Casting,, Mold Casting, Investment Casting • • 2. Advantage: more complex shapes possible Disadvantage: production rates often limited by time to make mold rather than casting itself Permanent mold processes - mold is made of metal and can be used to make many castings TYPES:Die Casting, Permanent Mold Casting, Centrifugal Casting • Advantage: higher production rates • Disadvantage: geometries limited by need to open mold
  7. 7. Process Advantages Sand Wide range of metals, poor finish, sizes, shapes, low cost tolerance Shell mold better accuracy, finish, limited part size higher production rate Expendable pattern Plaster mold Wide range of metals, sizes, shapes complex shapes, good surface finish complex shapes, high accuracy, good finish complex shapes, excellent finish good finish, low porosity, high production rate Ceramic mold Investment Permanent mold Die Centrifugal Disadvantages Examples wide engine blocks, cylinder heads connecting housings rods, gear patterns have low cylinder heads, brake strength components non-ferrous metals, low prototypes of mechanical production rate parts small sizes impellers, injection mold tooling small parts, expensive jewellery Costly mold, shapes only simpler gears, gear housings Excellent dimensional costly dies, small parts, precision gears, camera accuracy, high production non-ferrous metals bodies, car wheels rate Large cylindrical parts, Expensive, limited shapes pipes, boilers, flywheels good quality
  8. 8. IMPORTANT METAL CASTING METHODS • Sand Casting • Investment Casting High Temperature Alloy, Complex Geometry, Rough Surface Finish High Temperature Alloy, Complex Geometry, Moderately Smooth Surface Finish • Die Casting High Temperature Alloy, Moderate Geometry, Smooth Surface
  9. 9. SAND CASTING • The most ancient , useful casting process • Nearly all alloys can be sand casted , e.g. steel, nickel, titanium • Mold can be used only one time • Parts ranging in size from small to very large • Production quantities from one to millions
  10. 10. • Sand casting typically has a low production rate. • Use of a furnace, metal, pattern, and sand mold in this process
  11. 11. Sand Casting process cycle • Mold-making A sand mold is formed by packing sand into each half of the mold. • Clamping Binding of the both halves of molds • Pouring Molten metal ladled and poured into the mold. • Cooling The solidification and cooling of molten metal for a predetermined solidification time • Removal/Shakeout After predetermined time has passed, breaking the mold • Trimming Removing the extra parts called flash by cutting from casting
  12. 12. Factors effecting the quality of sand cast :  Strength - Ability of the sand to maintain its shape.  Permeability - Ability to allow venting of trapped gases through the sand .Permeability is determined by the size and shape of the sand grains.  Thermal stability - Ability to resist damage, such as cracking, from the heat of the molten metal.  Collapsibility - Ability of the sand to collapse, or more accurately compress, .  Reusability - Ability of the sand to be reused for future sand molds.
  13. 13. • Advantages :  Can produce very large parts.  Many material options.  Low tooling and equipment cost.  Scrap can be recycled.  Short lead time possible. • Disadvantages:  Poor material strength.  Poor surface finish and tolerance.  Secondary machining often required.  Low production rate. Aluminum piston for an internal combustion engine: as-cast and after machining.  High labor cost. • Applications: Engine blocks and manifolds, machine bases, gears, pulleys
  14. 14. INVESTMENT CASTING • Investment casting is one of the oldest manufacturing processes • molten metal is poured into an expendable ceramic mold • The mold is formed by using a wax pattern • Using ceramic slurry that hardens into the mold • Investment casting also called "lost-wax casting" • Lost -wax processes increases production time and cost
  15. 15. Investment Casting Process Cycle • Pattern creation (a) Wax pattern (pattern creation) • Mold creation (b) Multiple patterns assembled to wax sprue • Immersing - (c) Shell built  immerse into ceramic slurry  immerse into fine sand (few layers)
  16. 16. • Wax removal (d) dry ceramic melt out the wax fire ceramic (burn wax) • Pouring (e) Pour molten metal (gravity)  cool, solidify [Hollow casting: pouring excess metal before solidification • Casting removal (f) Break ceramic shell (vibration or water blasting)
  17. 17. • Advantages:  Can form complex shapes  Many material options  High strength parts  Excellent surface finish and accuracy  Little need for secondary machining • Disadvantages:  Time Consuming process  High labor cost  High tooling cost  Long lead time possible • Applications: Turbine blades, pipe fittings, lock parts, hand tools, jewelry.
  18. 18. DIE CASTING • Produces geometrically complex metal parts • Reusable molds used, called dies. • A furnace, metal, die casting machine, and die is used • The metal, typically a non-ferrous alloy such as aluminum or zinc, . • After the molten metal is injected into the dies, it rapidly cools and solidifies into the final part, called the casting.
  19. 19. Die casting process cycle • Clamping - Preparation, binding and clamping of mold • Injection Molten metal is transferred to the die • Cooling Solidification and cooling of molten metal • Ejection The removing of cast by hydraulic mechanism • Trimming -. Cutting the extra metal by sawing
  21. 21. DIE CASTING EQUIPMENT • Two types of die casting machines are :• Hot chamber die casting machine • Cold chamber die casting machine • PARTS FORMED BY DIE CASTING
  22. 22. HOT-CHAMBER DIE CASTING • Used for metal/alloys with low melting temperatures, such as zinc, tin, and lead. • Clamping of the die • Molten metal poured in a chamber • Injecting the metal by forcing plunger • Metal flows through a goose neck • Low pressure required around 1000 - 5000 psi • After the solidification , ejection of cast part by hydraulic system .
  23. 23. Hot chamber die casting process 1)Clamping. 2)Injection 3) Cooling 4) Ejection
  24. 24. Cold Chamber Die Casting • Used for alloys with high melting temperatures e.g. aluminum • Clamping the die • Horizontally injection.. • High Pressure is required around 2000 - 20000 psi. • Solidification for predetermined time • After solidification, the part can be ejected by the clamping unit.
  25. 25. Cold chamber die casting process