Vacuum Casting

Vacuum casting (polyurethane casting) is the perfect solution for rapid prototyping and low-cost low-volume manufacturing of plastic parts. The master mold is cheap to make and so finely crafted that the resulting plastic parts require little to no post-production. Each master mold can produce about 25-30 copies, which can be quickly produced in a short time. For low-volume manufacturing of plastic parts, polyurethane casting is more economical than injection molding. Vacuum casting contrasts with the hard molds required for injection molding. While injection molding requires expensive, laborious tooling, polyurethane casting uses flexible silicone master molds, which allows manufacturers to produce high-quality end-use plastic parts with shorter lead times and lower costs. This is why vacuum casting is commonly used for bridge molds, low-volume manufacturing, rapid prototyping, making joints, and making plastic parts with fine details.

What Is Vacuum Casting Or Polyurethane Casting?

The process of polyurethane casting first involves creating a master model – essentially a replica of the final part (usually 3D printed or CNC machined). Vacuum casting is a manufacturing process similar to injection molding in which polyurethane resin is cast into a cavity between two silicone mold halves. In a highly skilled procedure, the master model is replicated by pouring a silicone mold around it. The main mold is cut in half and after the main form is removed the pouring and ventilation systems are then added. The rapid fabricator then pours a polyurethane-based resin into the resulting cavity and cures it under vacuum to prevent the intrusion of air bubbles.

Making a polyurethane vacuum cast prototype involves 3 key steps: creating the master model, creating the mold, and casting the part:

Step 1. Main model or main pattern

The master pattern is the physical entity of the CAD design. They must be able to withstand temperatures up to 40°C. They are typically manufactured using CNC machining or 3D printing technologies such as SLA/SLS. Because these technologies create high-resolution and naturally smooth products.

Step 2. Make the mold

Liquid silicone is used to make casting molds. Pour this silicone into the casting box around the main model. Silicone encapsulates all features of the master model and cures in the oven for 16 hours. When the mold has cured, it is cut open and the master mold is removed, leaving a negative-shaped cavity that is exactly the same as the original.

Step 3. Cast copy

In the final stage of the process, liquid polyurethane is poured into the silicone mold. The mold is then placed into the chamber to eliminate air bubbles in the liquid mass. For opaque parts, the chamber is usually pressurized. For clear parts, the chamber is often evacuated to reduce air bubbles and improve transparency. The silicone halves are separated and the newly created section is removed after hardening. Continue this process until you reach the desired amount. Silicone molds can typically produce approximately 25 replicas of the master model.

Vacuum Casting Applications

Vacuum casting is an ideal process for manufacturing plastic parts for low-volume products that require near production-grade quality. This process creates highly detailed master models that are virtually indistinguishable from the final product. This makes polyurethane cast models ideal for investor pitch presentations, trade shows, and commercial photography. Since one silicone mold can produce approximately 25 castings, vacuum casting also allows the company to launch a first series of products for early market testing.

If a project requires a higher quantity of plastic parts, there are a few different options:

With a lead time of only about 10 days from the making of the master model to the receipt of the cast plastic product, vacuum casting is not only suitable for rapid prototyping but also for bridge production without the large upfront investment that comes with industrial-grade manufacturing processes such as injection molding. , thermoforming and rotation casting.

Because vacuum casting can create extremely detailed plastic parts with a perfect surface finish using a variety of materials with a wide range of mechanical properties, it is suitable for low-volume end-use products such as:

In addition to its cost-effectiveness and efficiency, vacuum casting also offers versatility in material selection. Manufacturers can choose from a wide range of polyurethane resins that can mimic various properties of thermoplastics, such as ABS, polycarbonate, or nylon. This flexibility allows designers and engineers to tailor the material characteristics to meet specific application requirements, including strength, flexibility, temperature resistance, and even color. Furthermore, the ability to incorporate additives such as fillers, pigments, or flame retardants enhances the functionality of the final product. This is particularly beneficial in industries such as automotive, aerospace, and consumer goods, where the performance and aesthetic appeal of plastic components are critical. Additionally, vacuum casting is not limited to simple shapes; it can accommodate complex geometries and intricate details that are often challenging to achieve with traditional injection molding techniques. As a result, this method is ideal for creating prototypes that closely resemble the final production parts, allowing for thorough testing and validation before moving into full-scale manufacturing. Ultimately, the combination of rapid turnaround, high-quality output, and customization options makes vacuum casting an invaluable tool for businesses looking to innovate and streamline their product development processes.

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