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Shell Molding and Investment Casting ( (Shell Molding shell-mold-casting …
Shell Molding and Investment Casting
Shell Molding
Definition
A metal casting process similar to sand casting, in that molten metal is poured into an expendable mold. However, in shell mold casting, the mold is a thin-walled shell created from applying a sand-resin mixture around a pattern.
Allows the use of both ferrous and non-ferrous metals, most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys.
Steps of Shell Molding Casting Process :
Mold Assembly
Pouring
Mold Creation
Cooling
Pattern Creation
Casting Removal
Advantages and Disadvantages
Advantages
Low labor cost
The high productivity and good surface finishes
Little scrap generated
Shell molding can be completely automated for mass production.
Low tooling cost
Disadvantages
Poor material strength
High porosity possible.
High equipment cost
Secondary machining often required.
High labor cost if done manually.
Investment Casting
Definiton
One of the oldest manufacturing processes in which molten metal is poured into an expendable ceramic mold. The mold is formed by using a wax pattern - a disposable piece in the shape of the desired part. The pattern is surrounded, or "invested", into ceramic slurry that hardens into the mold.
Steps of Investment Casting Process:
Assemble wax patterns
Apply investment materials
Produce wax patterns
Dewax
Create a mould
Burnout preheating
Produce a master plan
Pouring
Divesting
Finishing
Can make use of most metals, most commonly using aluminum alloys, bronze alloys, magnesium alloys, cast iron, stainless steel, and tool steel.
Advantages and Disadvantages
Advantages
High strength parts
Very good surface finish and accuracy
Many material options
Little need for secondary machining
Can form complex shapes and fine details
Disadvantages
High labor cost
Time-consuming process
High tooling cost
Long lead time possible
