Common Vacuum Casting Industry Terms

When you're considering vacuum casting services for prototype or small-batch production, understanding the industry terminology is crucial. Here, we’ve compiled a glossary of common vacuum casting terms to help you navigate the process and make more informed decisions when selecting a supplier.

1. Vacuum Casting (VC)

Vacuum casting is a rapid prototyping process in which a master pattern (usually made from 3D printing or CNC machining) is used to create silicone molds. These molds are then filled with liquid polyurethane resin (or other materials) under a vacuum to produce prototypes or small batches of parts. The vacuum ensures that air bubbles are removed during casting, leading to higher-quality parts.

2. Master Pattern

A master pattern is the original model or prototype from which the silicone mold is created. It is typically made using methods like CNC machining, 3D printing, or casting. The accuracy and quality of the master pattern significantly impact the final part's dimensions and surface finish.

3. Silicone Mold

A silicone mold is a flexible mold created by pouring liquid silicone over a master pattern. After curing, the mold becomes soft, allowing easy removal of the cast part. Silicone molds are ideal for small production runs due to their cost-effectiveness and ability to capture fine details.

4. Polyurethane Resin (PU Resin)

Polyurethane resin is a key material used in vacuum casting to create parts. It is a type of thermoset plastic that can be modified for different properties, such as rigidity, flexibility, and impact resistance. Different grades of PU resin can mimic various thermoplastics (like ABS, PC, or rubber).

5. Shore Hardness

Shore hardness is a measure of the material's resistance to indentation. It is used to define the rigidity of polyurethane resins and elastomers used in vacuum casting. Shore hardness is typically measured on a scale such as Shore A (for softer materials) or Shore D (for harder materials). Higher numbers indicate harder materials.

6. Dimensional Tolerance

Dimensional tolerance refers to the permissible variation in the size of a part during manufacturing. In vacuum casting, tolerances are typically expressed in millimeters (mm) or as a percentage of the part's nominal dimensions. Typical tolerances in vacuum casting range from ±0.1 mm for small parts to ±0.5 mm for larger parts, depending on geometry.

7. Shrinkage

Shrinkage refers to the reduction in size of a material as it cools and hardens. In vacuum casting, both the silicone mold and the resin can exhibit shrinkage. Typically, polyurethane resins shrink about 0.1–0.3% during curing. Understanding shrinkage is crucial when designing parts, especially for functional prototypes where dimensional accuracy is important.

8. Gating System

The gating system refers to the channels and entry points through which the resin flows into the mold. This system is crucial for controlling the flow of the material, preventing air bubbles, and ensuring the mold is filled evenly. Well-designed gating systems can improve the quality and consistency of the final cast parts.

9. Vacuum Process

The vacuum process is a technique used during casting to remove trapped air bubbles from the mold and resin. By applying a vacuum to the mold, the air inside is evacuated, reducing the likelihood of voids and imperfections in the final part. This process is critical for achieving high-quality parts with excellent surface finishes.

10. Curing Time

Curing time refers to the period required for the resin to harden after it has been poured into the mold. The curing process can vary depending on the type of resin and the curing conditions (temperature, humidity, etc.). Typical curing times for polyurethane resins range from 2–4 hours at room temperature, but some resins may require post-curing in an oven to achieve maximum strength and heat resistance.

11. Surface Finish

Surface finish refers to the texture or appearance of a part's surface after it has been cast. In vacuum casting, the surface finish can be influenced by the quality of the master pattern, the type of mold material used, and the curing process. Common surface finishes include smooth, matte, textured, or glossy. For critical aesthetic parts, additional post-processing like polishing or coating may be required.

12. Overmolding

Overmolding is the process of adding a second layer of material to an existing part. In vacuum casting, overmolding can be done by creating a part in one material (such as a rigid resin) and then adding a second layer (such as a soft-touch rubber-like material) to improve functionality or aesthetics. Overmolding is commonly used for producing handles, grips, or seals.

13. Casting Resin Types

There are various types of casting resins used in vacuum casting, each with unique properties suited for specific applications:

ABS-like Resin: Mimics the mechanical properties of ABS plas

tic, offering rigidity and impact resistance. Commonly used for functional prototypes.

PC-like Resin: Mimics polycarbonate, providing high impact strength and heat resistance. Suitable for more demanding applications.

Rubber-like Resin: Simulates rubber, offering flexibility and tear resistance. Ideal for parts requiring bending or compression.

Transparent Resin: Used for clear parts, such as light pipes, lenses, and enclosures, offering high optical clarity.

14. Post-Processing

Post-processing refers to the steps taken after the casting process to refine the part further. This can include trimming excess material, polishing surfaces, painting, coating, or even machining parts for tighter tolerances. Post-processing is often necessary to achieve the desired aesthetic appearance or functionality.

15. Short-Run Production

Short-run production refers to the manufacturing of small batches of parts, typically ranging from 5 to 50 units. Vacuum casting is ideal for short-run production, as it allows engineers to produce functional parts quickly and cost-effectively without the need for expensive molds or tooling. It is a perfect solution for prototype testing, low-volume production, and pre-production parts.

16. First Article Inspection (FAI)

First Article Inspection is the process of inspecting the first produced part or batch of parts to ensure they meet the specified tolerances, design, and quality standards. This step is critical for ensuring that parts produced in small batches are of consistent quality and meet the functional requirements.

Conclusion

Understanding the key terms in vacuum casting is essential for product engineers to effectively communicate with suppliers and ensure that the parts meet their design and performance needs. If you’re ready to start a project or need guidance on material selection, don’t hesitate to reach out to us. Our team is experienced in managing the full vacuum casting process from initial consultation to final delivery.