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Injection Molding Or Vacuum Casting: Which To Use? 2

Injection Molding Or Vacuum Casting: Which To Use?

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Two of today’s most common manufacturing methods are vacuum casting and injection molding. These two solutions are similar in many ways:


  • Both use a mould with a cavity to fabricate parts.
  • Both are ideal for creating plastic parts.
  • Colouring and texturing are conferred by the tooling.


Due to their shared similarities, it is often difficult to pick between the two processes. This article highlights key factors that one can consider to make an informed choice when deciding between the two processes.

What is Injection Molding?

Injection molding is one of the most often-used manufacturing processes for creating plastic parts. The method involves heating and mixing material (sometimes multiple materials). The melted material is then injected into a mould, where it cools and solidifies into the final plastic part. By repeating this process, the mold can be used to make hundreds to ten-thousands of identical parts effortlessly.



What is Vacuum (Urethane) Casting?

Vacuum casting or urethane casting is a process that begins with a master model, which, in HLH’s case, is CNC machined or 3D printed (via SLA or SLS). Liquid silicone is then poured into this master model and cured, then cut and separated from the master model. The resin part is cured and removed from the silicone mould, which can be reused around 25 times.

Although urethane casting is less widely known and used than injection moulding, it is a great alternative for creating small batches of production-like parts quickly and more affordably.



When is Vacuum Casting More Suitable Than Injection Molding and Vice Versa?


Speed creating molds for vacuum casting is a faster process than creating tooling for injection molding. At HLH, vacuum casting lead times typically range between 5-7 days, whereas rapid tooling takes a minimum of 2 weeks. For this reason, urethane casting is preferred for time-sensitive, low-volume projects.

It is worth noting that vacuum cast tools will only last between 10 to 25 runs — depending on the geometry of the part and the material choice — the tool will then need to be replaced. By comparison, a single injection mold tool can last between 100 to 100,000s of shots (depending on the tool material, maintenance and other factors). Hence, injection molding may be a faster solution when higher quantities are involved.

Cost & Quantity

At any stage, if a design needs to be amended, it is easier and cheaper to alter vacuum casting molds than it is to rework or remake tooling for injection molding. This makes vacuum casting ideal during the earlier stages of development, cost-wise.

While injection molding demands a higher front-end cost, it offers a significantly lower unit price. For high-volume production runs, you will simply not see the ROI with another process that you will with a steel mold. When it comes to producing higher volumes of plastic parts, injection molding is the perfect solution.


Commonly, businesses use urethane casting to develop early prototypes before creating their end-use injection molded parts. While this is recommended, bear in mind the specific needs of your individual prototype/project. Even if all the signs point to vacuum casting, for projects where you need parts in the production intent material, you’ll need to pick the appropriate plastic for your needs.


Vacuum Casting Materials Injection Molding Materials
PX5210, PX520, PX223, Hei-Cast 8150, etc.
Full Material List Full Material List

Which Solution Is Right For Your Project?

Between the two methods, there is no one “superior process.” Each one is, however, better suited for different product development stages. Unsure whether to use injection molding or vacuum casting for your next project? Contact us at or start your project review here. Our experts will advise you on the most suitable process for your project.

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