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Vacuum Casting

The silicone mould is one of the prototype casting methods. It has advantages of short time, little cost, small probability of processing failure and so on. It is able to manufacture more than 20 same products with just one silicone mould. Materials of this product include: ABS, PP, PC, PMMA, high-temperature resistant material, flexible glue and silicone rubber.

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 two-part polyurethane(PUR), which is available in a vast range of grades, colours, transparencies and densities.

vacuum casting workshop




What is Vacuum Casting?

vacuum casting product

In stage one, the liquid PUR is drawn into the mold which is held under vacuum. This ensures that the material has 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 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 for the mold.

opening mould

Typical Applications

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

Cost and Speed

Tooling costs are generally low, but they largely depend 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

vacuum casting machine

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 Drange).

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.

Three Steps of Processing Prototype Casting:

Before manufacturing silicone mould, it needs to manufacture the prototype first. The prototype can adopt more common ABS material, for example CNC processing is ok.

VC machine

Silicone Mould

After preparing the prototype, it’s time to start manufacturing silicone mould.

After drying for eight hours, cut up the silicone mould and take out the prototype. At this point, the silicone mould is ready.
The above are processing steps of casting. You can quickly make batch of prototypes through the three steps.

Definition: The vacuum injection, that is vacuum casting, is to make use of the original sample to manufacture the de-aeration, stirring, preheating and injection for cast ables under the vacuum state, in order to clone the copies the same as the original samples. This technology has a high speed and a low-cost, and it can also greatly reduce cost, cycle and risk of developing product.

The materials firstly need to be made prototype before manufacturing a silicone mould. After preparing the prototype, it can start manufacturing the silicone mould. After drying for several hours, cut up the silicone mould and take out the prototype. At this point, the silicone mould is ready. Inject the liquid gum material into the silicone mould, and it will be ok just after drying. Both the poured liquid material and the silicone material of silicone mould are called by a joint name as vacuum injection material, also called casting material!


 
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