Pros & Cons of Vacuum Casting & Injection Molding

 

Vacuum casting and injection molding are two of the most popular methods used to process plastics in the rapid prototyping industry.  We thought that we would share a brief overview of both manufacturing processes as well as the advantages and disadvantages of both.

 

What is Vacuum Casting?

Simply put, vacuum casting is a casting process for elastomers using a vacuum to draw the liquid material into the mold. This process is used when air entrapment is a problem, there are intricate details or undercuts, or if the material is fiber or wire reinforced.

The Process- Vacuum casting also known as “thermoforming” is a rapid prototyping or manufacturing process in which plastic sheet goods are preheated in automated vacuum forming equipment until soft and pliable.  Next, the preheated sheet makes contact with a mold or form and a vacuum source is turned on, which “sucks” the sheet to the mold.  Once cooled, the sheet takes the shape of the mold.  It is then trimmed with either a 5 axis CNC router machine or simply die cut.  If additional detail is required, positive air pressure is used to assist the forming process, a technique commonly known as “pressure forming.”

 

What is Injection Molding?

Injection molding is a far more complex manufacturing technique than vacuum casting and requires a good deal of engineering.  The process of injection molding begins with either pellets or granules of polymer which are placed in a hopper and then dropped into a barrel.  A screw pushes the material into a heater where it melts.  Next, the liquid polymer is injected into a steel or aluminum split die through a gate being held in a press under extreme high pressure.  After cooling, the die opens and pins eject the finished parts.

A great amount of engineering time and cost is required to fabricate the parts and dies used in injection molding, making vacuum casting the preferred process for many applications where time-to-market and low cost is critical.  Still, each method has its own distinct merits and also unique drawbacks.

Pros of Vacuum Casting

Cons of Vacuum Casting

Pros of Injection Molding

Cons of Injection Molding

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