OVERVIEW

DPT offers two different casting technologies to produce metal castings.

Investment Casting is used for lower quantities (1 - 5) or when the desired material is steel, stainless steel, or Iron.

Metal Casting using Plaster/Sand Tooling is generally used for higher quantities (5 or greater) including short run production. The mechanical properties of Plaster Cast parts are very similar to Die Cast parts. Additional material will need to be added to all critical tolerance surfaces to account for dimensional error introduced in the plaster cast process. Secondary machining is used to machine the part to meet critical dimensions.

Metal parts produced by this method have been successfully used for design verification, life testing, pre-production, and even production when required.

 

PROCESS 1: INVESTMENT CASTING

Step 1

Wax Patterns are built directly from your 3D CAD file to eliminate the need for tooling. Several parts are wax welded to a single sprue and prepped for shell coating. The assembled sprue is then dipped into a ceramic slurry.

Step 2

After draining, the sprue is then coated or stuccoed with a fine ceramic sand. This process is repeated several times using progressively coarser grades of ceramic material to build sufficient shell strength.

Step 3

The shell encased sprue is then de-waxed by rapidly heating in a furnace or autoclave leaving behind the perfect shell cavity. The shells are then fired to make the cavity interior into a smooth, hard, and strong ceramic material. The hot shells are then removed from the furnace and the metal alloy is immediately poured into the shell cavity.

Step 4

The poured shells are set aside to cool. When cool, the shell material is stripped away and parts are then cut from the sprue and finished accordingly.

 

PROCESS 2: METAL CASTING USING PLASTER/SAND TOOLING

The process of metal casting using plaster/sand tooling is capable of prototyping parts that are typically produced using die-casting, permanent-mold, investment casting, or sand casting methods and is excellent for rapid prototyping and short-run production.

Step 1

A master model is created of the finished part via a rapid prototyping technology. This master model looks just like the eventual casting, but it is slightly larger to allow for material shrinkage during the metal casting process.

Step 2

Using the master pattern, a negative cavity of the geometry is produced by pouring silicone rubber around the master pattern. This is where the parting lines for mold halves and cores/slides are generated.

Urethane is poured over the Silicone negative, creating positive geometry of the part. The resulting urethane tool is used repeatedly to produce each plaster mold.

Step 3

The plaster slurry is poured into the urethane tooling and the plaster is given time to set-up. After the plaster is firm, the mold is removed from the tooling. The plaster molds contain the negative part geometry.

The mold halves are assembled into a complete mold. They are then baked to remove all moisture content. Once the mold halves are fully dried and hardened, they are rejoined to create the complete mold. Molten material is then poured into the assembled tool.

Step 4

After solidification of the cast metal, the plaster mold is broken away from the solidified metal part. Remaining plaster is removed via pressure washing and the part is then hand cleaned and detailed.

Final machining is often used to create high-tolerance geometries that are beyond the capabilities of the casting process.