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Guides for Vacuum Casting on Prototype Development

Vacuum casting, CNC machining, 3D printing and injection molding are common techs in prototype development, but the unique guides make it attractively and increasingly developing in China.


Posted on: Oct. 8th, 2018, | By Mandy, WayKen Project Manager

There are many prototype development solutions in China, vacuum casting, CNC machining, 3D printing, injection molding etc. But do you know when should you consider vacuum casting for your prototype development solution in China? Let’s go ahead.

History of Vacuum Casting

Vacuum casting was born in Europe and developed in the 1960s. Then sold to Japan for apply in the automotive industry, but soon spread to all European markets. With the development of vacuum casting system, from with manual and tilting device to more systematic and simplified equipment in today’s work.

Process of Vacuum Casting

Step 1: Make master pattern and place the prototype in a container.

Step 2: Pour the liquid silicone which vacuum is used to remove all air into the mold to cover the product.

Step 3: Bake the mold in the oven, and the silicone mold is cured.

Step 4: Once the silicone is cured, the silicone is cut along the separation plane and the master pattern is removed from the mold.

Step 5: According to the materials required by the product, vacuum the material and copy the finished product.

Cycles of Silicon Mould

The cycles of the silicon mould depends on the complexity of the parts. Typically, it outputs 12-15 parts before degradation. If the structure of the part is simple, one mould can cast 20 parts. If parts require high quality, such as clear and complex parts, one mold can only make 10 casting parts. There are other standards for the replacement of silicone moulds, like silicone mould is damaged somewhere; Silicone sticks to the product when the mould is opened; The quality of the product is not up to standard. Just as clear product transparency is obviously not as good as the previous transparency etc.

How Can I Get the Master Pattern?

The quality of the cast parts is determined by the quality of master pattern. There are two methods can get the master pattern. The main factor is the CNC can provide higher accuracy of parts, hold tight tolerance such as +/-0.05mm. But the processing time is longer than the SLA. SLA is another method to get the master pattern, SLA relative time faster, especially for some complex structure parts are easier to integrated, all internal features to be exactly per 3D CAD input.

How Many Parts Is Vacuum Casting More Financially Attractive Than CNC?

It is recommended to use the vacuum casting process to obtain higher economic benefits. The quantity of more than 10 pieces, 10 to 20 pieces is the best stage to use vacuum casting. From this figure, not only the cost of manufacturing silicone mold is rewarded, but also more attractive than CNC machining. The quantity which is more than 200, it is recommended to use aluminum or steel moulds.

CNC for low volume production may not be able to achieve the economic benefits of the vacuum casting. Because there are more processing time and manual post processing, this is an inevitable CNC processing cost.

COSTS: Silicon Mold vs. Injection Mold

Compared with the cost of silicone mold and injection mold, the cost of silicone mould is usually much lower than the aluminum or steel tools used in injection molding. Silicone mould costs can range from hundred to thousand dollars, while injection mold costs range from thousands to tens of thousands of dollars. Injection mold need to produce thousands to tens of thousands of parts to offset the cost of injection mold.

Tooling Lead Time

Lead time for vacuum casting is shorter than conventional injection molding time. Injection mold takes 1-3 weeks, injection mold parts take 3-5 weeks to complete, typically get injection molding manufactured in just 4 to 8 weeks. However, the silicone mold can be prepared in 1-2 weeks, and more complex parts can be obtained in a short time.

Types of Material

There are many options for materials, from opaque to transparent, the durometers range from 30A-90D, UL94-V0. Listed below are several commonly used materials.

Hei-Cast 8150

Its properties are similar to engineering production plastics ABS, such as, well-balanced physical properties, superior dimensional stability and sufficiently high practical strength. There are beige and black colors. Flexural modulus 1830Mpa, hardness shore D 84.

Axson PX-223/HT

It is high temperature resistance, good impact and flexural resistance. Application in prototype requiring for temperature resistance and mechanical properties are close to thermoplastic.

Axson PX-5210

Its properties are optical clear similar to engineering production acrylic, such as high transparency (water clear), good UV resistance, high reproduction accuracy and easy polishing.

Axson PX-527

Its properties are optical clear similar to engineering production PC. Good flexural impact resistance, good mechanical properties and can be easily colored.

Can I Get The Color Cast Parts?

Vacuum casting can also offer in a variety of color prototypes to meet customer demand. Silicone can be adjusted in color, for example, you want red, blue, and yellow. There is no problem with this and it also saves a lot of post processing time. But it is worth noting that the colorful cast parts may not match the international Pantone and RAL color. If you have strict color requirements, the best method is to manual paint finish for these cast parts. WayKen’s staff has extensive experience to meet your customization surface finish requirements.

Pros and Cons of Vacuum Casting vs. CNC Machining

Vacuum casting is no problem to make complicated parts, it can keep the complicated part in one piece. Not like CNC machining that the parts may need to split due to the structure or size.

Silicone rubber shrinkage is a normal phenomenon. Any silicone rubber after curing with shrink, the shrinkage is different due to the different molecules density of the Silicone liquid. Once the silicone rubber has cured, the product shrinks. The high quality silicone rubber shrinkage rate is 1%-3%. The poor quality of the silicone shrinkage rate will be higher. The result of the shrinkage of the silicone rubber is that the size of the cast parts is different, which affects the tolerance. In terms of high tolerances, CNC will be an option solution.

In Conclusion

Vacuum casting is used in many industries, such as plastic automotive parts, medical device as well as soft plastic transparent soft rubber, colored transparent soft rubber etc.

When you're planning on prototype development in China, you have to do a balanced analysis from all aspects of which process is the best solution. If you are still hesitating, please feel free to email WayKen and we are willing to share.

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