Vacuum Casting

What Is Vacuum Casting

This is a casting process for elastomers that uses a vacuum to draw any liquid material into the mold. Vacuum casting is used when air entrapment is a problem with the mold.

Additionally, the process can be used when there are intricate details and undercuts on the mold. Also, it is applied if the material used to make the mold is fiber or a reinforced wire.

The process is sometimes called thermoforming because the manufacturing process involves rapid prototyping where the plastic sheets are preheated. The materials are preheated in an automated vacuum casting machine until they are soft and pliable.

The Vacuum Casting Process

The Vacuum Casting process begins with the creation of a master pattern using the Sterelithography process. The SLA model is then finished/painted to meet customer specified surface texture is achieved. Where the customer has supplied an existing component for casting, any part clean up is carried out at this stage.

The master pattern is then fitted with a casting gate and suspended upon the parting line in a mould casting frame

Silicone rubber is mixed, de-aerated and poured under vacuum into the mould casting frame, where it will flow around the master pattern, to create a silicon mould.

The mould is then cured within a heating chamber, and once set the mould is removed and cut along the parting line. The master pattern is removed before a casting funnel is placed and the mould sealed closed.

Customer specified casting resin is then measured and any colour pigment mixed, where specific colour requirements have been outlined. The mould is returned to the casting chamber and the resin is pour into the mould under vacuum to avoid any air pockets or voids.

When the resin has been cast, the mould is then placed in heating chamber to cure. Once cured the casting is removed from the mould, and any subsequent castings are produced (each mould can be reused with the number of castings greatly dependent on individual part complexity and casting resin selected).

At this stage the gate and risers are removed from the casting and any additional finishing is carried out.

Advantages and Disadvantages of Vacuum casting
Advantages of vacuum casting
Multiple components can be used from the master pattern within 24hrs which would reduce the product design prototyping stage cutting time and cost on new product development

Vacuum casting can be used to create small batches of high-quality injection moulding type parts for prototypes or low volume end-use parts for low stress, relatively benign environments

A wide range of vacuum casting resins are available to suit various applications such as clear, rubbery, flame retardant, food-grade and coloured to suit

Resin type can be changed easily without the need to retool to test various material types for a given application or part

Complex shapes and features can be accommodated by using multi-segment moulds & cores

Aluminium and brass in-mould inserts can also be used

Disadvantages of vacuum casting
Since the mould is manufactured using soft silicon, it wears out quickly and generally lasts for about 30 – 50 parts. Tool wear depends on the surface textures, features and size. Bigger parts, rough surface textures and lots of proud features would reduce mould life.

Similar to injection moulding, irregular, overly thin and thick features may deviate from normal tolerance due to shrinkage.

15% – 0.25 % shrinkage rate due to thermal expansion of the liquid and the flexible mould. Generally, the manufacturer would allow and add the shrinkage tolerance but worth talking to them before the order.

As the surface finish depends on the post-processing of the part, sometimes it is limited to only the outside as it’s difficult to access some internal features of the pattern

Sharp corners and texts will sometimes have rounded edges，You will also need plugs and cores for some features

WKproto is a professional rapid prototyping and low-volume production manufacture specializing in 3D printing, CNC machining, and Vacuum Casting. Our factory and parter factories enable rapid prototyping of designs from our customers and low volume production for market verification.

We have three factories. 3D printing factory meets the demands of most 3D printing services with 100 SLA machines, 10 SLS machines, 10 MJF machines, 10 SLM machines, and 20 FDM machines. CNC machining factories for processing metals, plastic and more materials with more than 200 machines for CNC milling/CNC lathes/EDM / Wire EDM and the Vacuum Casting factory is for low volume production for ABS、PC、PP、PE、PA、POM、PMMA、PVC.