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Urethane Casting and Vacuum Casting
Urethane casting is a manufacturing process similar to injection molding where urethane resin is cast in a cavity between two silicone mold halves. The process replicates a master model by pouring a silicone mold around it. In a highly skilled procedure, the mold is sliced into two halves, the master model is removed, and then a gating and ventilation system is added. Subsequently, the model maker casts a urethane-based resin into the resulting cavity and cures it under a vacuum to prevent air bubble intrusion. Vacuum casting is better known as urethane casting or polyurethane casting in the US.
Step 1: Master Building
Masters represent 3D solids derived from your CAD designs. Typically crafted via CNC machining or 3D printing, they are meticulously fabricated under controlled conditions, often at 40°C. Once the masters are meticulously finished and thoroughly inspected, the next phase involves progressing to silicone mold creation.
Step 2: Mold Making
The creation of casting molds commences with liquid silicone. The casting box is partially filled with this liquid silicone, and then subjected to controlled heating until the silicone is fully cured. Following this, the mold undergoes a 16-hour curing process within an oven. Additional batches of heated silicone are poured to complete the mold, ensuring comprehensive coverage. Once fully dried, the mold is carefully cut open to extract the master component.
Step 3: Part Production
Production of parts begins by pouring casting resins into the emptied mold cavity. This process results in the creation of highly precise replicas of the original master. The flexibility extends to the possibility of overmolding with multiple materials. Typically, silicone molds maintain their effectiveness for approximately 20 reproductions of the initial pattern.
This structured approach ensures the replication of intricate designs with fidelity and efficiency, leveraging the precision of CAD designs and the versatility of silicone molding techniques.
| Typical lead time | Up to 20 parts in 15 days or less, depends on the part specification and volumes. |
| Accurate | ± 0.3% (with lower limit on ± 0.3 mm on dimensions smaller than 100 mm) |
| Minimum wall thickness | To ensure that the mold is filled properly, a wall thickness of at least 0.75 mm is necessary. For best results, we recommend a wall thickness of at least 1.5 mm |
| Maximum part dimensions | The size of the mold is limited by the dimensions of the vacuum chamber (1900 x 900 x 750 mm) and by the volume of the product (maximum volume: 10 liters) |
| Typical quantities | Up to 25 copies per mold (depending on the mold’s complexity and the casting materials) |
| Color & Finishing | Pigment is added to the liquid polyurethane prior to casting, custom painting and texture. |
* Fast turnaround
Typically to have 20 parts in 15 days or less, depending on part specification and volume.
* Affordability
Silicone molds are less expensive than the tooling used for injection molding, resulting in cost effectiveness.
* Capable of producing large parts
Depending on the type of equipment used, vacuum casting can create very large size parts.
* Color options
Coloring pigments can be added to the resin for a variety of color options.
* Repeatability
Silicone molds can be used around 20 times injections.
Low volume prototypes, low volume production, rubber parts, market testing, rapid iterations.
FAQ of Vacuum Casting
1. What is vacuum casting?
Vacuum casting is a manufacturing process used to produce small to medium batches of high-quality plastic parts. It involves creating a silicone mold from a master pattern and then using vacuum pressure to pull liquid resin into the mold cavity. This method is favored for its ability to replicate complex geometries and textures accurately.
2. How does vacuum casting work?
First, a master pattern (typically made from CNC machining or 3D printing) is created. A silicone mold is then cast around the master pattern. Once the silicone is cured, the mold is cut open, and the master pattern is removed. Liquid resin is poured into the mold cavity. The mold is placed in a vacuum chamber, and vacuum pressure is applied, which pulls the resin into all the details of the mold. After curing, the mold is opened, and the replica part is removed.
3. What are the advantages of vacuum casting?
- High-quality replicas: Vacuum casting produces parts with excellent surface finish and detail reproduction.
- Cost-effective for small batches: Ideal for producing small to medium batches of parts without the high upfront costs of injection molding.
- Material versatility: Can use a wide range of casting resins, including materials with specific mechanical or aesthetic properties.
- Quick turnaround: Faster than traditional molding processes, allowing for rapid prototyping and iterative design improvements.
4. What materials can be used in vacuum casting?
A variety of casting resins can be used, including polyurethanes, epoxies, and silicones. These materials can be formulated to simulate a wide range of properties, from rigid to flexible, transparent to opaque, and even colored or textured finishes.
5. What industries use vacuum casting?
Vacuum casting is widely used in industries such as product design, automotive prototyping, aerospace, consumer electronics, and medical devices. It is particularly valuable in applications where high-quality prototypes or low-volume production runs are required quickly and cost-effectively.
6. How durable are vacuum-cast parts?
The durability of vacuum-cast parts depends on the specific resin used. Generally, these parts exhibit good mechanical properties suitable for functional testing and visual prototypes. For applications requiring higher durability or heat resistance, specific resin formulations can be chosen.
7. Is vacuum casting suitable for overmolding or multi-material parts?
Yes, vacuum casting can accommodate overmolding and multi-material parts by sequentially casting different materials into the mold cavity. This capability allows for the creation of complex parts with varied textures and properties in a single manufacturing step.
8. What are the limitations of vacuum casting?
- Limited to small to medium production runs: While cost-effective for small batches, it may not be economical for large-scale production.
- Mold lifespan: Silicone molds have a limited lifespan and may wear out after approximately 20 reproductions, depending on the complexity of the mold and the casting materials used.
- Material properties: While versatile, the range of material properties available in vacuum casting may not match those achievable through injection molding or other advanced manufacturing processes.
9. Why would I choose vacuum casting over injection molding?
Vacuum casting is a more affordable alternative to IM, especially in low volumes. It also offers unique advantages like an excellent surface finish.
10. What happens to the silicone mold(s)? Can I keep them?
The silicone molds used in vacuum casting have a short lifespan, typically around 20 moldings, so we dispose of them after use.
Urethane Vacuum Casting
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