Vacuum casting: the knowledge series Industrial Design

Part 6 – vacuum casting

In Part 5, SLS Printing, we looked at each step in the process step by step. In this edition of our knowledge series, we will discuss the considerations that are required for vacuum casting.

Vacuum casting (vacuum casting) is a plastic molding process for the production of high-quality product prototypes. In vacuum casting, a silicone rubber mold is created using a product master pattern. After the silicone mold is cured at high temperatures, it is cut into sections using a zigzag cutting technique. The cut is zigzag to ensure that the mold cavity is correctly aligned when the sections are joined. Plastic resin is poured into the silicone mold. The entire mold is then placed in a vacuum chamber to ensure that no air is trapped.


If you want to create a complex design, a soft plastic product or multiple prototypes, Vac-Casting is the best choice. Compared to any 3D printing process, vacuum casting prototypes are of higher quality, and compared to CNC prototypes, vacuum casting prototypes are less limited to which molds can be made. In addition, the molds can usually be reused up to 5 or 10 times, and sometimes up to 20 or 25 times.


Vacuum casting prototypes have physical properties that are comparable to those of injection molding products. They are not as good, but closer than CNC or 3D printed ones. This makes them ideal for functional user or basic mechanical testing and even for marketing or display purposes.

Because the shapes are reusable, you can repeat fine details like patterns, dimensions, and even textures. However, you will find that the quality decreases slightly from the first to the last sample until it decreases so much that a new silicone mold is required.


Depending on the complexity of the product and its size, the production of vacuum casting molds can be a manually intensive and time-consuming process. Furthermore, the size of the product directly affects the curing time required for the pattern to sit in the mold. As a result, prototypes in vacuum casting have a longer lead time – production usually takes about 1 to 2 weeks.

Material costs

Depending on the resin used or if you are using metal powder or pigment additives, different aesthetic or functional properties can be achieved, including:

  • Heat resistance
  • Fire retardant
  • UV stability
  • Flexibility / rigidity
  • Softness / hardness
  • Clear (can use transparent plastic resin)
  • Paints (can tint / color the resin before molding – or the prototype can be painted once the resin is cured)
  • Matt, satin or glossy surface

Sometimes the material from which you inject your final product cannot be used in the vacuum casting process. In this case, the cabinet material is used instead. This happens with polypropylene products.

Vacuum casting is the most expensive compared to 3D printing or CNC. This is because you need to create a prototype pattern that will be sacrificed to make the shape yourself, which means that the whole process takes more time and work. However, because the shapes can be reused to create multiple patterns, the more patterns you create, the lower the cost per prototype.

At this point in the knowledge series, you begin to understand the world of product prototyping. Look forward to the next issue, in which we are dealing with SLA & FDM 3D printing!

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