Navigator #11, April 2002

When you’re in need of prototype metal castings, you have options that may change from project to project. Under the circumstances, you could complete the same project three different ways that would lend itself apart by cost, lead-time, and quality. Here are the three main options you have in choosing metal casting. Each option has it’s own pros and cons depending on material, tolerance, cost, and lead-time.

Investment Casting

Investment casting is a casting technique used by taking an SLA Quickcast® or a wax pattern and dipping it in a ceramic slurry. The application is repeated until a strong shell coating surrounds the pattern for support. Once this process is completed, the shell with the pattern still in it is heated up in a furnace. At the proper or correct temperature, the Quickcast® pattern is flashed out or the wax pattern is melted out to leave a cavity in a ceramic mold. The mold is then ready to be used for casting metal.

Materials- Most metals (steel, stainless steel, aluminum, zinc, etc.)

Lead-time- 3-7 days depending on size and complexity

Quantity- 1 cast part for 1 pattern and ceramic mold
Tolerance- +/- .005" inch

Investment casting patterns being dipped into a ceramic slurry to build up the outer shell (mold).

Cost- low for small quantities

Pros- Great for low volume and smaller parts. Fast with low porosity issues. No upfront tooling and is good for checking the design early in development.

Cons- Limited in larger sizes, and if you need high quantities, then tooling is required.


Molten metal being poured into the ceramic shell.

Rubber Plaster Molding (RPM)

Rubber plaster molding is used by making a series of silicone rubber molds off of a pattern (usually SLA). Then off of the rubber mold a plaster mold is created. From the plaster mold, non-ferrous metals such as aluminum and zinc can be cast for your prototypes.


An SLA pattern used in the rubber plaster molding process to get a cast aluminum prototype.

Materials- Non-ferrous alloys (aluminum, zinc, etc.)

Lead-time- 7-10 days

Quantity- 5-100+ per one pattern and a one-time tooling charge

Tolerance- +/- .005" per inch

Cost- low for midsize quantities 5-30

Pros- The best application for thinner walls and surface finish.

Cons- Initial tooling charge. Cost is high for quantities of 4 or less.


Poured Aluminum castings sitting next to their patterns.
Top right pattern is SLA Quickcast® and bottom right pattern is from Wax.

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Sand Casting

Using a pattern, machined Ren board or an SLA, a sand core and cavity are made. The sand is packed tightly with a binder to create a sand mold. After the pattern is removed, metal is then cast in this sand mold. Green sand will give you a course finish while air set sand casting will give you a smooth finish.


Middle, is an SLA pattern used for sand casting. This prototype was poured w/grey iron and weighs around 75 pounds.

Materials- Most any (Steel, Iron, Aluminum, etc.)
Lead-time- 7-10 days

Quantities- 5-100+ per one pattern and a one-time tooling charge

Tolerance- +/-.006" per inch

Cost- low for high volume 20-100+

Pros- Wide variety of materials and lower in cost for higher volumes.

Cons- Difficulty in casting thinner walls and thinner areas.

All these applications are used daily and are great for functional prototypes. Each application has pros and cons depending on what the critical areas or your project needs are. Ask your Vista sales rep to assist you in picking the right metal casting application for your next project

SME Tour

Vista hosted the St. Paul Chapter SME for a tour with a great attendance over 25 people. Vista showed their rapid prototyping capabilities. Included in the tour were their three SLA5000’s, their new Viper SLA machine and their three options of resins. On-site, Urethane Castings, Metal Castings, and SLA models were displayed in a question and answer forum.

Vista also showed their new tooling division that highlights their high-speed milling machine. Dave Rathke, manager of the tooling division, demonstrated the machine’s capabilities at running 42,000 RPM, cutting aluminum to a .005" wall thickness. This division’s focus is on fast turn around aluminum tooling for injection molding.

Vista has an open door policy that encourages tours, and welcomes your on-site visit!

2002 Trade Show Schedule

April 12 - TCPUG
Twin Cities Pro/Engineer
User Group
St. Anthony Main Event Center

October 23-24 - MDM
Medical Design & Manufacturing
Minneapolis Convention Center

*MDM and the AMCOM show are running at the same time and location. Please call us for your FREE pass to visit Vista’s booth.

Quick Quip “Whether you think you can or you can’t-you are right” -Henry Ford