Plaster Mold Casting

Production Metal Castings Processes




What is Plaster Mold Metal Casting?

Plaster Mold Casting  (Rubber Plaster Mold)  is the process of making cast metal parts using plaster molds as the “die”. Plaster mold casting is a metalworking casting process using processing methods as sand casting except the molding material is plaster instead of sand. Plaster mold casting is an expendable mold process, however, it can only be used with non-ferrous materials

Plaster mold castings
Sand Mold casting

What are the Benefits of Plaster Mold Casting?

  • 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.
  • 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.


Pros of Plaster Mold Castings 

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
CNC machining
Sand Mold casting

What Metals can be used in Plaster Mold Casting?

Precise Cast specializes in Aluminum, Magnesium, and Zinc alloys. Our engineering will work with your product designers to find the best metal for your project. We even look for design flaws before they happen and will help every way through the design process. 

Aluminum metal castings
magnesium alloy
zinc alloy

Plaster Mold Castings Process

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.

Why Precise Cast?

Our skilled engineers go to great lengths to make sure your castings and machining are done right the first time, thereby saving your time and money. Our engineers take strict measures to finalize the dimensions, tolerances, surface finishes, and shrink rates of each casting. We also do FEA simulations to ensure your castings will have no “trouble spots” due to the casting process.


Have questions? ALL CONSULTATION ARE FREE! We also offer secure file uploading so you can quickly send over any preliminary or finished items for us to review. We are happy to discuss any concerns and questions you have about the casting process. Our team is dedicated to proving exceptional customer service and an in-depth analysis of your project.

Get started on your next project and see why we are the #1 choice in  Custom Rapid Prototyping and Low Volume Manufacturing.