Benefits of Vacuum Casting for Rapid Prototypes

If you’re wondering what the most cost-effective way to make any prototype is, it may be time to set your sights on vacuum casting. Vacuum casting—sometimes referred to as urethane casting or polyurethane casting—was first developed in Europe in the 1960s and has since become one of the most widely used techniques for the development of plastic prototypes. Vacuum casting is a flexible and effective method for making high-quality rapid prototypes and end-use parts in low volumes, and is considerably faster than other manufacturing processes. The process uses pourable casting resins and silicone molds ( which can be reused about 20 times) to make perfect copies of master patterns,Such copies are useful in many ways, including for functional testing, engineering testing, product development, as display models and for marketing and crowdfunding campaigns.

Let’s take a closer look at the benefits of vacuum casting for rapid prototypes and why you may want to consider it for your next prototyping project.

The Vacuum Casting Process in Rapid Prototyping

Master Patterns

Polyurethane vacuum casting begins with a master pattern, which itself is a prototype made from any durable, solid material. It’s common to use 3D printing or CNC machining to produce these patterns because these methods are fast, don’t require separate tooling and can easily be modified to accommodate design changes as needed.

Master pattern, sealing, Star Rapid blog
Sealing the surface of a master pattern before pouring the mold.

Once the patterns are made they need to be carefully prepared before they can be copied. This preparation usually involves sanding, polishing and painting to get the surface finish just right. For multiple parts that might fit together into an assembly, we also test fit the pieces and make minor adjustments to ensure a clean, tight appearance.

Making Molds

After the patterns are ready they are placed in a casting box that is then filled with liquid silicone. After curing in an oven for several hours, the silicone is solidified and the casting box can be taken apart.

Filling casting box with Silicone, Star Rapid
Filling the casting box with liquid silicone

We carefully cut this mold open along a predetermined seam line and remove the pattern. This leaves behind an empty cavity in the exact mirror image of the original.

Mold opening, Star Rapid vacuum casting
Carefully opening the silicone mold along the split line
Mold opening, surface texture, Star Rapid
Silicone molds can reproduce delicate surface texture

Vacuum Casting

To make copies of the master pattern the mold must be resealed, this time with a feed tube leading into the cavity. Liquid urethane resin is poured into the mold and then the mold put into a vacuum chamber.

Preparing to cast a mold, Star Rapid
Silicone molds can be used 20 or more times to make cast copies of the master patterns

The purpose of the vacuum is to draw air out of the cavity, removing any bubbles while forcing resin into the entire volume of space. Then the mold is heated in an oven where the resin is cured. Upon reopening the mold, a perfect copy of the original emerges.

Vacuum cast copy, Star Rapid
Vacuum pressure is used to remove air bubbles

Those are the basic steps. But, how does this set you up for success on your next project?

Standard Technical Specifications

  • Lead time—Ready in as little as 5 working days
  • Accuracy—Usually ±0.3% 
  • Minimum wall thickness—To ensure your mold is filled properly, a wall thickness of 0.75 mm is recommended. For best results, opt for a wall thickness of at least 1.5 mm.
  • Maximum part dimensions—The size of your mold is limited by the dimensions of the vacuum chamber, as well as the volume of the product.
  • Typical quantities—Between 15-25 parts per mold.

Key Benefits of Vacuum Casting for Rapid Prototypes

1. Quality

The quality of cast parts is excellent, easily reproducing even very fine surface details from the original. This is why it’s so important to prepare the master patterns carefully. Vacuum casting creates high quality copies with excellent surface details. Finished copies can be painted, printed, or machined as necessary to improve appearance and function. People who are new to this service are constantly surprised by the fidelity to the original, which can easily be mistaken for a plastic injection molded part.

2. Speed

Compared to the time it takes to make mass production hard tools out of steel – which could take a few weeks – parts can be prepared and delivered in a matter of days, depending on the size and quality of your parts. This can be a critical factor if you’re trying to meet a tight deadline, like getting display models ready for an upcoming trade show or crowdfunding campaign, for example.

3. Versatility

There are many casting resins available that reproduce the look, feel and mechanical performance of most standard thermoforming resins like nylon, ABS or polyethylene. This means you don’t need to sacrifice functionality for speed or convenience. And for even more options, urethanes of different types can be overmolded to create various surface textures and hardnesses in one unit.

4. Cost-Effectiveness

Once the master patterns have been prepared, vacuum casting is the most economical way to make high-quality replicas. This is because money is not being invested in making hard tools, as would be the case for plastic injection molding or pressure die casting. That savings, in turn, can be invested in further product development or alternate design iterations.

Further, the process uses much less electricity than injection molding, die casting or CNC machining.  That cost would otherwise be passed on to the customer. Taken together, the savings on tooling, materials, energy and labor costs can be significant.

Is Vacuum Casting Right for You?

With the wide array of benefits of vacuum casting for rapid prototypes, it might be wise to invest in a vacuum casting service. We have everything in-house to offer a great vacuum casting solution for rapid prototypes and end-use parts. With our experienced staff, finishing services and quality inspection, you’ll get production quality parts at a fraction of the production price. Upload your CAD files now for a free quotation.


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