Expandable Mold Castings

Expandable Mold Casting

A type of mold casting which is used once is broken to get the final product.

There are many types of expnadable mold casting which we discussed one by one.

1. Shell Molding:

Casting process in which the mold is a thin layer of sand held together by thermosetting resin binder.

Steps involved in this mold casting are:

• A match-plate of cope and drag pattern is first heated at 230-315℃ and is placed over a boz containing sand mixed with thermosetting resin.
• Bix is inverted so that sand and resin fall onto the hot pattern.
• It causes the sticking of layer on this hot pattern.
• Box is repositioned so to loose uncured particles.

2. Vaccum Molding or V-Process:

A type of molding process in which vaccum play the part of sand binder.

Steps involved in vaccum Molding are:

• A thin sheet of heat-softened plastic is drawn over a vented pattern which contains small holes to facilitate vaccum forming.
• Vaccum flask is then placed over it.
• 2nd sheet of plastic is placed over the mold.
• Molten metal is then poured.
• Pattern vaccum is released and the pattern is withdrawn.
• When vaccum is released, sand loose its bounded state and fall away.

3. Investment Casting (or Lost Wax Casting):

Sand Casting in which pattern is made by injection mold is called investment casting.

Steps involved in investment casting are:

• Produce master pattern which can produce master die and then wax pattern.
• Assemble the wax pattern onto a common sprue.
• Coat the cluster of tree with a thin layer of finely ground investment material called slurry.
• Coat the cluster of coarse particles from an additional investment called stuccoing upto 8 layers.
• Remove the wax pattern by heating and pour the molten metal.
• Remove the solidified casting from the mold.

4. Evaporative Polystyrene Process (EPS) (or Lost Foam or Fill Mold or Evaporative Foam Process):

The sand casting in which mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold.

Steps for EPS are:

• Polystyrene beads are pre-heated and then introduce into heated-die cavity.
• The foam pattern cluster is coated with a refractory material.
• Dry the coating and then placed into a vented flask.
• Molten metal is poured into the mold the pattern vapourizes and we get the final product.

Reference:

• University Notes 
• Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
• Videos from youtube and Google 
• Images from google images