This process has many similarities to the classic Rubber Plaster Mold (RPM) technique. Their refinement of this process allows them to create parts with much thinner walls, better feature replication, and tighter tolerances. Prototype Casting, Inc.'s unique process also works extremely well with magnesium. Many foundries consider it difficult or dangerous to practice magnesium casting utilizing the RPM system. They can also generate tooling for cast parts by utilizing a variety of pattern types, such as wood or wax..

Creating the Pattern:

The first step in producing a prototype casting is to construct a physical model or pattern using 3D CAD data. The most commonly used pattern is an SLA. This process uses a Stereo Lithography Apparatus (SLA) machine to build a plastic part from the 3D file. A laser beam is fired into a resin bath that solidifies the resin in layers producing an SLA pattern. For producing larger quantities of parts, an aluminum master can be machined from stock, creating a stable and durable pattern.

Designing and Tooling:

One of the most critical steps in the casting process is the design of the tooling. Their expert engineering staff can quickly analyze parts to determine potential problem areas and casting difficulties. This allows them to effectively design tools that ensure even the most complex parts turn into high quality castings..

Tooling and Molds:

The SLA pattern is used to create a negative of your part. This is accomplished by surrounding the lower half of the SLA in clay and pouring liquid rubber onto the exposed portion. After the rubber has cured, the entire assembly is inverted. The clay is then removed and the SLA is revealed within the cured rubber. Rubber is then poured onto the exposed half of the SLA and left to cure. After the rubber has cured the two halves are separated and the SLA is removed, revealing an exact negative of the SLA geometry. It is during this process that the gates and risers required for metal pouring are built into the tooling.

From these negatives, a similar process is used to produce plastic patterns. The plastic patterns are positive images of the part, and cast a negative image into a plaster mold material. The plaster molds are then assembled and transferred to one of several ovens to bake. Depending on size, molds require anywhere from 1-3 days to dry completely.

The same construction principals are employed to produce complex geometry and cores.

Pouring the Part:

After the mold is dry and has reached temperature, it is removed from the oven and filled with molten metal. When it has cooled, the mold is broken open to reveal the part.