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Polyurethane vacuum casting delivers rapid turnaround prototypes efficiently. The process uses a solid master to cast soft silicone rubber molds.
These molds produce up to 20 high-quality prototype parts. The parts have excellent surface finishes and require minimal investment in raw materials.
Vacuum casting also supports multi-material overmolding. This is an additional advantage that many people overlook.
Our company is one of the few in the industry offering overmolding for vacuum-cast parts. Overmolding combines two or more resins step by step.
This process creates a uniform finished part. Below is an explanation of how overmolding works and why it suits product development.
Advantages of Overmolding
Overmolding creates parts with a wide range of textures, hardnesses, and mechanical properties. Manufacturers commonly use this technique to make plastic injection-molded parts.
For example, they use it to add soft grips to power tool handles. Few people realize that polyurethane vacuum casting can achieve similar results. Proper methods make this possible.
Detailed Process Flow for Overmolding
1. Modeling
You need at least two slightly different models for overmolding.
The first model shows the complete appearance of the finished part.
The second model removes the details in the area that will be overmolded.
Modern CAD software simplifies this process. You can erase the overmolding area directly in the software. Then, send the modified model to a 3D printer to create two master models.
2. Creating Silicone Molds
Use the two models to create two separate silicone molds.
The first set of molds produces the base parts. These molds use hard resin to provide structural strength.
The second set of molds is slightly larger. It holds the base part and creates space for the overmolded material.
After casting, remove the base part from the first mold. Place the base part in the second mold. The second mold leaves a small gap between the base part and the cavity wall. This gap defines the overmolding area.
3. Secondary Molding
Design a feed line that connects to the overmolding area.
Inject a softer elastomeric resin into the gap to fill the feed line.
Place the mold in a vacuum chamber. Heat it until the resin fully cures.
This process creates a permanent bond between the two materials. Theoretically, you can use multiple secondary molding resins. In practice, limit the process to two resins. This simplifies the operation and extends the silicone mold’s lifespan.
Applications and Advantages
Overmolding works well for parts requiring different properties. Examples include:
Electronics housings: Use hard material for protection and soft material for comfort.
Industrial equipment parts: Combine durable shells with soft-touch surfaces for a better user experience.
We provide overmolding services that address diverse design needs. Our solutions ensure fast and effective prototyping. If vacuum casting fits your project, upload your CAD drawings. We will provide a free professional quote!
FAQ:
Polyurethane vacuum casting is a rapid prototyping method that uses a solid master model to create silicone molds, which then produce up to 20 high-quality plastic parts with excellent surface finishes.
Overmolding is a process where two or more materials are molded together in layers. In vacuum casting, a hard base part is produced first, then placed into a second mold where a softer resin is added to overmold specific areas.
Vacuum casting delivers fast turnaround times, high-quality surface finishes, low material costs, and supports limited production volumes (up to ~20 parts per mold).
Overmolding allows designers to create parts with multiple textures, hardness levels, and material properties in one component — ideal for prototyping consumer and industrial products.
Yes. With proper process control, polyurethane vacuum casting can replicate multi-material overmolding effects similar to those in traditional plastic injection molding.
It involves creating two master models (one full, one with the overmold area removed), casting a base part, placing it into a second mold, and injecting a second material (usually softer) to fill the gap defined for overmolding.
Typically, polyurethane resins with varying hardness and elasticity are used — including rigid plastics for the base and elastomers for soft-touch or grip areas.
Examples include power tool grips, electronics housings with shock-absorbing layers, and industrial components that combine rigid structures with ergonomic surfaces.
While it’s theoretically possible to use multiple materials, it’s best to limit the process to two resins to keep operations manageable and extend the silicone mold’s life.
You can upload your CAD designs to the service provider’s platform. They will analyze your project and offer a free quote based on your part requirements and desired materials.
