Vacuum casting plastic

What Is Vacuum Casting For Rapid Prototyping

If you think of the most inexpensive way of creating any prototyping, then vacuum casting is your answer. Vacuum casting is a rapid prototyping method suitable for pre-testing and validation, pre-series prototyping, and low-volume production for early market launch.

Vacuum casting, also known as urethane casting or polyurethane casting, is a pliable and efficient method for creating high-quality prototypes and faster manufacturing.

This process uses silicone molds and casting resins to create plastic and rubber elements under the vacuum. This effective manufacturing process can copy the master patterns of injection molding to construct complex parts on cast nylon and polyurethane resins.

Such copies are usable in many ways, such as engineering testing, functional testing, display models, product development, and many more.

It creates a blemish-free smooth surface texture without bubble casting as the process stays under the vacuum.

How Does The Vacuum Casting Process Work?

Vacuum casting is a similar process to injection molding. Still, it uses a molding tool made out of soft silicon, whereas injection molding requires tools made from metal like steel or aluminum. Let’s dig deep into the vacuum casting process.

1. High-quality Model 3d Part

Vacuum casting requires high-quality master models of the desired product. In addition, you must follow the injection molding guidelines to achieve a better result through vacuum casting.

However, you can get your model created with 3D printing methods such as SLS or SLA, the most effective and cost-efficient additive manufacturing process. You can also turn to traditional methods like CNC machining or get your model handcrafted.

Make sure the master model is used correctly for dimension and look. This ensures no flaws in the model prototype after finishing the process.

2. Creating Silicone Rubber Mold

After the creation process, the model is placed in a casting box filled with liquid silicon, where the liquid silicon flows around the master pattern filling every detail.

The model is encapsulated into a two-part silicone rubber mold. Later, the mold is cured inside an oven under a high temperature of around 40℃ for about 8-16 hours. The time and temperature may vary depending on the size of the silicon mold. This process is to make the mold more durable and robust.

When the curing process is over and the silicon rubber has solidified, the casting box is removed from the mold.

Then, the mold is cut in half into two and placed in a vacuum chamber. Later, the mold is filled with designated materials.

3. Mixing The Resins

For achieving specific functional properties, polyurethane resins are heated to 40°C before mixing with metallic powder or any color pigments. As a result, the resins mimic the attributes of industrial materials.

Generally, a two-component casting resin is mixed with the exact proportion of colored pigment, poured into a bowl, and placed in a vacuum. During the pouring process, the mixture of casting resins and color pigment is stirred and deaerated for a minute under a vacuum. Then, it is placed in the vacuum chamber to ensure no air bubbles in the mold.

4. Demould The Resins

After the resin has been cast, it is placed in a heating chamber for a final cure process. The mold is processed under high temperatures to make it durable and robust.

After the cured prototype is removed from the mold, it is painted and decorated to give a final touch and look more brilliant.

Application Of Vacuum Casting For Rapid Prototypes In The Industry

  • Vacuum casting is used to make commercial products for packaging. Mobile cases, sunglasses, pens, food, and drinking packages are some products made from this process.
  • Household products such as washing detergents, food processing, and cosmetics are made using vacuum casting.
  • The vacuum casting process can be used to make Aerospace and Automotive parts.
  • Decorative objects like custom ornaments, showpieces, jewelry, and wall plaques are made with this process.
  • The food and beverage industry uses vacuum-casting products to package their final products. Vacuum casting is ideal for making plastic bottles and tins.
  • Function Testing and Part Integration.

Benefits Of Using Vacuum Casting For Rapid Prototype

  • This process makes the shading color added to the vacuum chamber abreast of the particles of resin so that the final part will be a perfect shading match with the client’s requirements.
  • Many casting resins are available to fit different applications like rubbery, flame retardant, clear and food-grade, etc.
  • Many casting resins can mimic standard thermoforming resins’ look and mechanical performance, such as plexiglass, polycarbonate, nylon, ABS, or polyethylene.
  • Complex geometrical shapes and features can be accommodated through multi-segment molds & cores.
  • Compared to other manufacturing processes, parts can be created and delivered in a matter of days, depending on the size and quality of the parts. So you can go through this process if you are on a tight deadline.
  • Multiple materials can be used from the master pattern within 24 hours, reducing the time and cost of new product development.
  • Vacuum casting can construct high-quality copies with an excellent surface finish.
  • Aluminum and brass in-mold inserts are usable in this process.

Drawbacks Of Using Vacuum Casting For Rapid Prototype

You will face some drawbacks while using this method for rapid prototyping. Those are given below-

  • The mold is manufactured with soft silicon. It deteriorates quickly, probably lasting 30-50 parts at max. Tool wear depends on product size, surface texture, and features. The bigger the size, the more it wears off. Moreover, more features and rough surface texture will reduce the mold’s life.
  • As the process is similar to injection molding, irregularity and feature deviation from standard tolerance may occur due to shrinkage.
  • Surface finish mainly depends on the post-processing of a part. In this case, the post-processing of a piece is sometimes limited only to the outside. This is because it is tough to penetrate some internal features of the pattern.
  • Some features need plugs and cores.
  • Sharp corners and texts may have rounded edges sometimes.
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