plaster mold casting

What is Plaster MOLD Casting?

Plaster Mold Casting and its benefits

Learn More About Plaster Mold Casting  and Why it Might be a Great Option for Your Next Project

What is Plaster Mold Casting?

Plaster mold casting also referred to as rubber plaster molding (RPM) is a method of pouring liquid metal into plaster molds which will produce aluminum or zinc castings.

Plaster Mold Casting works much like other castings processes where a heated liquid material is poured into a mold that contains a hollow cavity of the desired shape. This is then allowed to solidify. The solidified part is known as a casting.

Once it has molded and cooled the cast is broken out of the mold to complete the process.



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Plaster Mold Metal Casting Processes 

1) Tooling Engineering & Design: Precise Cast converts 3-D CAD data into a master pattern. Gating (rigging) and shrink compensation are factored into the CAD during this tooling design phase. Depending on part geometry, FEA solidification analysis is run to optimize the tooling design.

2) Tooling: A 3-D solid model is used to machine a master pattern.

3) Pour Silicone Tool: Tooling life depends on a number of factors including part geometry, draft, etc.

4) Form the Mold: A plaster mixture is poured into the tool to form the mold (die). After the mold is firm, the mold halves (cope and drag) are removed from the tool, carefully assembled into a complete mold, serialized, and dried.

5) Pour the Metal: A gravity pour method of filling the cavity is used. Variables that affect casting quality are carefully controlled. These variables include metal temperature, mold temperature, cooling rate, mold tilt, riser size and location, and metal filtering. We use rotary degassing, a continuous melt furnace, and employ a reduced atmospheric testing system to ensure optimal results.

6) Break Out: After the metal has solidified, the mold material is carefully broken away to reveal the metal casting.

7) Parts Cleaning: Next comes the removal of gates, chills, runners, and minor casting imperfections. The result is a “raw” casting.

8) Machining: Final machining is often used to create high-tolerance geometries that are either beyond the capabilities or not economical to incorporate into the casting process. We have a machining department dedicated to the machining of castings. Our technology includes multi-axis capability and probe technology to ensure consistent and accurate machining of each casting.

aluminum castings
Plaster mold castings

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Good To Know!

Precise Cast offers Sand Mold Castings and CNC machining as well. Learn more about these production processes for your next project.

Sand Mold Castings

CNC Machining

Benefits of Plaster Mold Castings


  • The tooling process is much quicker than permanent mold or die casting tooling processes.
  • Typical first article lead time is 1-2 weeks (expedited lead times are available)
  • Tooling costs are lower than permanent mold and die casting tools
  • Prototype to low-volume-production quantities is possible.
  •  Cost-effective manufacturing/prototyping solution for quantities of 5-1,000 EAU
  • For quantities under 5, our in-house CNC machining department could also be a good fit
  • Smooth surface finish – typical as-cast surface roughness of Ra 63 µinch (Ra 16 µm) – very comparable to a die-cast process surface finish.
  • Exceptional part detail is possible – this process can capture detail as fine as a fingerprint in the metal casting.


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    Plaster Mold Castings Capabilites

    Low volume manufacturing 2


    • Thin wall capabilities
    • The typical wall thickness of .080″- .100”
    • Capable of casting as thin as .030” (.75mm) wall thickness (depending on geometry)
    • Parts requiring cores (both simple and complex) are easily done. Many investment cast parts can be manufactured using the plaster casting process
    • Simple and very complex parts are achievable
    • Capable of manufacturing zero draft geometries (a minimum draft angle of 1-2 degrees is preferred)
    • Ability to accurately simulate mechanical, thermal, and corrosion properties typically associated with a die cast process

    Added Value Services

    Design analysis

    Product Development

    Our expert engineers are happy to review CAD models to help develop your products and check for design flaws prior to production.

    Design analysis

    Prototype Castings

    We provide one-off prototype castings and low-volume production castings. Most customers will use their prototype cast as final production parts.

    Design analysis

    Heat Tempering

    Our experts can recommend a heat-treating process for your castings, ensuring successful castings from start to finish.

    Our team of experts is ready to help you with your next plaster mold casting project. We can even offer a sample of your casting!

    ✔ FREE consultations

    ✔ FREE design assessment

    ✔ FREE, fast quotes!



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