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:

  1. Rubber Plaster Molding (RPM): Patterns create foundry tooling that makes copes, drags and core boxes used to create the plaster molds.
  2. 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.

One-Shot casting process diagram

Step 1:  Model/Pattern

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

Step 2:  Plaster Mold

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

Step 3:  Pour Casting

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

Step 4:  Secondary Operations

  1. The raw castings are inspected and serialized.
  2. Castings may then require (per customer specifications):
      A) Heat treatment
      B) X-Ray
      C) Penetrant inspection
  3. 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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