Design Basics for Vacuum Casting

When tackling a project that requires the production of high-quality, detailed, and repeatable parts, vacuum casting is often the go-to method. Various industries favor this manufacturing technology for low-cost, small-batch production, making it one of the most efficient casting processes.

However, you must approach your design process thoughtfully to take full advantage of vacuum casting. This guide gives you the essential design basics you need to succeed.

Understanding Vacuum Casting

We wrote a guide giving a complete overview of vacuum casting, but here’s the short version: It’s a precise metal casting process used to create high-fidelity replicas of a master model, typically crafted using a CNC machine or 3D printer.

The model is placed inside a two-part silicone mold, and a chosen material – often a two-component polyurethane – is poured in. A vacuum is then applied to remove air bubbles and ensure the material fills every nook and cranny of the mold. The parts are then removed and finished as needed.

Materials used in vacuum casting are usually chosen for their plastic-like properties, though various materials can mimic various characteristics like flexibility, rigidity, color, and transparency. Ultimately, the choice of material depends on the intended use of your finished parts.

Now, let’s move on to the design basics.

Draft Angles

The concept of draft angles is vital in vacuum casting. A draft angle is a slight taper implemented on the vertical walls of your part design, making the mold opening slightly larger than its base.

But why is this important? The answer lies in the part removal process. When your design includes draft angles, the cast part can be removed more easily from the mold, reducing the risk of damage.

Ideally, your design should include draft angles of at least 1 to 2 degrees. However, the optimal draft angle may depend on the geometry of your part and the material used. This simple yet effective element can significantly improve the longevity of your molds and the overall quality of your cast parts.

Wall Thickness 

Maintaining a consistent wall thickness in your design is crucial for successful vacuum casting. When wall thickness varies significantly, some sections of the part might cool and cure at different rates, leading to deformities or weak spots.

Generally, we recommend a minimum wall thickness of 0.75mm to 1.5mm for small to medium-sized parts, with larger parts requiring greater thickness. However, the optimal thickness may depend on your project and material.

Incorporating Undercuts, Overhangs, and Complex Shapes

Undercuts and overhangs refer to features of a part that are hidden or extend over a cavity, making them challenging to mold and cast. Yet, one of the advantages of vacuum casting is its ability to handle undercuts and overhangs more efficiently than other manufacturing methods.

When designing parts with undercuts or overhangs for vacuum casting, these features will impact the complexity of the mold and may require additional considerations or modifications. It’s best to consult with your manufacturing partner to ensure these design features can be accurately and efficiently produced. At MakerVerse, we’re happy to help.

Designing for Mechanical Properties

The choice of material can significantly impact your design in vacuum casting. Different materials have varying levels of flexibility, strength, and temperature resistance, so consider these factors when designing your part.

For instance, if you’re working with a material that is highly flexible, consider whether your design can accommodate potential flexing without compromising the part’s functionality. On the other hand, if your material has a high rigidity level, ensure your design isn’t subject to stress concentrations that could lead to cracking or failure.

Remember, a successful design isn’t just about the geometry of the part but also how that geometry interacts with the properties of your chosen material.

Post-processing Considerations

Once your part is cast, it’s not always ready to go.

Post-processing methods, such as cleaning, painting, or applying a protective coating, may be necessary to achieve the desired appearance or functionality. It’s essential to plan for these steps in your design.

For example, if your part needs to be painted, you may want to include some allowance in your design for the added thickness of the paint layer. Similarly, if your part will be cleaned with a particular method, you must ensure that your design can withstand this process without damage.

Troubleshooting Common Issues

Despite its advantages, vacuum casting can encounter some common issues. Understanding and addressing these problems can help ensure a smooth casting process:

1. Porosity: Porosity occurs when air or gases are trapped in the mold cavity, leading to voids in the casting. To prevent porosity, ensure the mold is properly evacuated and pour the molten metal slowly and carefully to avoid trapping air.

2. Shrinkage: Shrinkage happens as the molten metal cools and solidifies, potentially causing dimensional inaccuracies. Design the mold with appropriate allowances to mitigate shrinkage and pour the molten metal at the correct temperature.

3. Surface Finish: The quality of the surface finish can be affected by the mold’s condition and the pouring process. To achieve a high-quality surface finish, ensure the mold is well-prepared and pour the molten metal steadily to avoid surface defects.

By understanding the vacuum casting process and troubleshooting common issues, manufacturers can produce high-quality castings with complex shapes and intricate designs, while minimizing defects and improving overall efficiency.

Bring Your Vacuum Casting Designs to Life

Designing for vacuum casting is about more than just coming up with a great idea; it’s about creating a design that is practical, manufacturable, and aligned with your project’s goals.

At MakerVerse, we’re ready to help. Upload your vacuum casting designs and get a quote within 24 hours. We’ll handle the production and quality control process and provide design insights as needed.