Technology Knowledge

Comparison Between Injection Molding & Vacuum Casting


Injection molding  and vacuum casting are both popular manufacturing processes used to produce plastic parts . While they share some similarities, they differ in their techniques, applications, and cost considerations. Let’s compare them in several key aspects:

  1. Process Overview:

Injection Molding: In injection molding, molten plastic material is injected into a mold cavity under high pressure. The material solidifies inside the mold and takes the shape of the cavity. Once cooled, the mold is opened, and the part is ejected.

Vacuum Casting: Vacuum casting, also known as silicone molding or polyurethane casting, involves creating a master pattern or prototype part using various techniques. A silicone mold is then made around the master pattern, and a liquid resin is poured into the mold under vacuum to create the final part.

  1. Complexity and Detail:

Injection Molding: Injection molding is capable of producing highly complex parts with intricate details and fine features. It allows for precise control over dimensions and geometries.

Vacuum Casting: Vacuum casting is better suited for producing parts with relatively simpler geometries and moderate levels of detail. It may struggle with extremely fine features and intricate designs.


  1. Tooling and Lead Time:

Injection Molding: Injection molding requires the creation of expensive steel molds or tooling, which can take several weeks or even months to produce. However, once the molds are made, they can be used repeatedly, resulting in lower unit costs for large production runs.

Vacuum Casting: Vacuum casting utilizes less expensive silicone molds that can be produced relatively quickly, typically within a few days. This makes it more suitable for small production runs and prototyping, where fast turnaround times are crucia.



  1. Material Options:

Injection Molding: Injection molding supports a wide range of thermoplastics and engineering-grade materials, such as ABS, Polypropylene, Polycarbonate, and Nylon. The material selection is extensive, including options with varying properties like strength, flexibility, and temperature resistance.

Vacuum Casting: Vacuum casting primarily employs resins (eg: ABS-Like, PC-Like, PP-Like, POM-Like, PU-Like, Nylon-Like, Silicone-Like), which offer a limited but sufficient range of material properties, The material used for vacuum casting is not exactly same as that used for injection molding.


  1. Cost Considerations:

Injection Molding: While injection molding has higher initial setup costs due to tooling expenses, it becomes more cost-effective for large production volumes due to its high production speed and efficiency.

Vacuum Casting: Vacuum casting has lower initial setup costs since it relies on less expensive molds. However, it is generally more expensive per part and better suited for small production runs or prototyping.


  1. Surface Finish and Quality:

Injection Molding: Injection molding parts typically have excellent surface finish and dimensional accuracy. The process provides consistent results and high-quality finishes, requiring minimal post-processing.

Vacuum Casting: Vacuum casting parts can achieve good surface finishes, but they may not match the level of quality obtained through injection molding. Some post-processing, such as sanding or painting, might be necessary to achieve desired aesthetics.


In summary, injection molding is ideal for high-volume production of complex parts with precision and a wide range of material options. On the other hand, vacuum casting is better suited for low-volume production, prototyping, and simpler parts, offering faster turnaround times and lower initial costs. The choice between the two depends on the specific requirements of the project, including volume, complexity, lead time, and budget.