Investment Casting

Investment wax injection press

     Investment casting, also known as the lost wax process, starts with a wax pattern. It is created by injecting wax into a machined aluminum tool, a cast plastic mold, or by "printing" a CAD file in 3-D using a solid object modeler such as our Thermojet or SLA.  The tooling or CAD file can be supplied by the customer or created by DMI from customer drawings or specifications. DMI also accepts customer supplied wax patterns.

Wax pattern      This pattern is an exact copy of the as cast part. The wax pattern holds dimensional tolerances to within a few thousandths of an inch and incorporates allowances for the shrinkage of the cast metal. 
Wax assembly area      The wax patterns are assembled into "trees" by fusing the parts to be cast with gates, risers, vents, and pour cups as needed for casting. 
Wax tree ready for shelling      This tree is finished and ready for shelling. The pathways for the molten metal are laid out and attached to the part to accommodate both filling and feeding of each part. There are also vents at the highest point of the part to aid wax in escaping from the shell in dewax and to allow gasses to escape from the shell as it is poured. 
Shelling area      The finished trees are coated with a refractory ceramic shell. They are dipped into a colloidal silica slurry and then covered with a zircon and/or fused silica stucco (sand). This process starts with a fine slurry and zircon sand for a good surface finish and low reactivity. The dipping progresses through stages of coarser slurry and stucco until a thick shell  has formed around the wax tree.

     When the shelling process is finished and the shells have completely dried, the wax is removed under steam heat and pressure in an autoclave.

     After the shells have been dewaxed, they are cured at high temperatures. This process fuses the shell for higher strength at pouring temperatures and burns out any wax or liquid left from the shelling and dewax process.


Next Step: Melting and Pouring


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Diversified Metalsmiths, Inc.  2001