Types of Casting Process

Casting is an metal manufacturing process generally used for mass production in which materials in a molten state are poured into a mold where they solidify. In this process, complex parts can be manufactured economically and rapidly that otherwise would involve a lot of time if produced by other methods like shaping or cutting. Casting process can be utilized to produce a large variety of parts that are used in different industries.

Investment Casting

Investment casting is an ancient manufacturing process used for metals that are difficult to be machined or fabricated. It is also used for the manufacture of parts that cannot be formed by usual manufacturing techniques like turbine blades or components of airplane that are subjected to high temperatures. This process provides an excellent dimensional accuracy and surface finish. The pattern is made of wax or other substance that is melted, leaving behind a cavity which is filled with the material of the part being produced.

Sand casting

Sand casting is normally used for the production of large parts, by filling a molten metal into the mold cavity that has been shaped from natural or synthetic sand. The cavity is created by the utilization of a pattern, generally made of wood or metal that is of the same shape and dimensions as the actual part. The pattern is prepared slightly oversize due to which the cavity is also a little larger and compensates for the contraction of molten metal during cooling. Surface of the sand castings is normally rough with surface impurities for which a machining allowance is included.

Die Casting

In this process metal is forced into the mold at a high pressure that ensures production of identical parts, a better surface finish, and an increased dimensional accuracy. Some parts produced by die casting even do not require machining after casting, or may require only a light machining to achieve the desired dimensions. Defects of porosity are found more often in large castings because of entrapped air and the solidification of melt before it reaches the boundaries of the cavity. Parts with a uniform wall thickness can be more accurately produced by die casting. Die casting molds are expensive since these are made from hardened steel and because a longer time duration is required for their production.

Types  The Process Advantages Limitations
Investment Casting Refractory slurry is cast around (or dipped on)
a pattern formed from wax or plastic; when slurry hardens, pattern is melted out and mold is baked. When poured metal solidifes, mold is broken away from casting.
  • High dimensional accuracy
  • Excellent surface finish
  • Almost unlimited intricacy
  • Almost any metal can be used
  • No flash to remove 
  • No parting line tolerances.       
  • Size of part limited;   
  • Requires expensive
    patterns and molds;        
  • High labor costs.                                                                            
Sand Casting Green sand. Moist, bonded sand is packed around a wood or metal patterns, the pattern removed, and molten metal
poured into the cavity;
when metal solidifes, mold is brokenand casting removedDry sand. Same as above except; core boxes used instead of patterns, sand bonded with a setting binder, and core baked in an oven
  • Almost any metal can be used
  • Almost no limit on size and shape of part        
  • Extreme complexity possible 
  • Low tool cost 
  • Most direct route from pattern to casting.
  • Some machining always necessary;
  • Large castings have rough surface fnish;
  • Close tolerances diffcult to achieve;
  • Long, thin projections not practical;
  • Some alloys develop defects;   
  • Usually limited to smaller parts than possible with green sand
Die Casting Molten metal is poured into
closed steel die under pressures varying from 1500 to 25,000 psi; when the metal solidifes, the die is opened and the casting ejected.
  • Extremely smooth surfaces 
  • Excellent dimensional accuracy
  • Rapid production rate
  • High initial die costs;   
  • Limited to nonferrous metals; 
  • Size of part limited


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