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Technical Information: One-Shot Casting Process

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What is One-Shot Casting?

Plaster mold casting is a method of producing aluminum, zinc or magnesium castings by pouring liquid metal into plaster (gypsum) molds. At Armstrong RM, there are two methods of plaster mold casting:

Rubber Plaster Molding (RPM): Patterns create foundry tooling that makes copes, drags and core boxes used to create the plaster molds.
One-Shot Casting: Plaster is poured directly on patterns, which are melted out in a furnace cycle.

Following is the process for the One-Shot method of making plaster mold castings.

Step 1: Model/Pattern

Constructed from customer drawing or CAD file.
Laser-sintered patterns are produced.
Model is engineered to include:
  A) Metal shrinkage.
  B) Mold taper (if required)
  C) Machine stock (if required).
We can "clone" or adapt customer supplied model if requested.

Step 2: Plaster Mold

A liquid plaster slurry is poured around the pattern.
The plaster mold is heated in a furnace to melt out the pattern and cure plaster.

Step 3: Pour Casting

Molten metal is prepared by degassing, and a spectrographic sample is taken to check the chemical analysis.
The molten metal is then poured into the plaster mold.
The plaster is removed by mechanical knock-out and high pressure waterjet.
When the casting has cooled, the gates and risers are then removed.

Step 4: Secondary Operations

The raw castings are inspected and serialized.
Castings may then require (per customer specifications):
  A) Heat treatment
  B) X-Ray
  C) Penetrant inspection
After finish inspection, casting is ready for:
  A) Machining
  B) Chemical film, chromate conversion, paint
      or special finishes
  C) Assembly
  D) Form-in-place gasketing.

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