CASE


04

2023

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12

Vacuum Casting


Used for prototypes, one-offs and low volumes, vacuum casting can replicate almost all the properties of injection molding. It is primarily used to mold twopart polyurethane (PUR), which is available in a vast range of grades, colours,transparencies and densities.

Vacuum Casting

Used for prototypes, one-offs and low volumes, vacuum casting can replicate almost all the properties of injection molding. It is primarily used to mold twopart polyurethane (PUR), which is available in a vast range of grades, colours,transparencies and densities.

Alternative and competing processes include:

Injection Molding

Rapid Prototyping

Reaction Injection Molding

What is Vacuum Casting?

In stage one, the liquid PUR is drawn into the mold which is held under vacuum. This ensures that the material has no porosity, will flow through the mold cavity and will not be restricted by air pressure. The PUR is held high above the mold, so as it is poured into the mold and runs underneath gravity forces it to rise upwards. The runner is designed to supply a curtain of liquid PUR. It flows through the mold and up the risers in part A. There are lots of risers to ensure that the mold is evenly and completely filled.

After a few minutes the mold cavity is filled and the vacuum equalized. The mold is left closed for the complete curing time, which is typically 45 minutes to four hours. In stage two, the part is ejected and the flash, risers and excess material are removed.

QUALITY Surface finish is excellent and will be an exact replica of the surface of the pattern used in the production of the mold

TYPICAL APPLICATIONS Prototyping applications include automotive parts, live hinges, keyboards and housings for mobile phones, televisions, cameras, MP3 players, sound systems and computers.

COST AND SPEED Tooling costs are generally low, but this is largely dependent on the size and complexity of the pattern.A mold will usually take between half a day to one day to make in silicone and will last 20-30 cycles. Cycle time is good.

MATERIALS PUR is available in water-clear grades and the full colour range. It can be very soft and flexible (shore A range 25-90) or rigid (shore D range).

ENVIRONMENTAL IMPACTS Accurately measuring the material reduces scrap, which cannot be recycled because it is a thermosetting plastic. The process is carried out in a vacuum chamber, so any fumes and gases can be extracted and filtered.

 

 

Translucent colour The PUR prototyping material range is designed to mimic injection molded plastics.Ribs, surface textures, snap fits, live hinges and other details that are usually associated with injection molding can be made.

Mimicking multishot injection molding The properties of different plastics can be incorporated as over-moldings. This is similar to multishot injection molding.In this case, rigid yellow acrylonitrile butadiene styrene(ABS) mimic has been over-molded with flexible black thermoplastic elastomer (TPE) mimic.

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