Vacuum Casting is widely used for low volume 3d real models or prototypes. Typically with one soft tool 20-25 duplicates can be made out of polyurethane material.
The Vacuum casting process is a 5 step process that starts with the creation of an accurate and highly finished master model which can be created using various RP techniques such as Stereo lithography, FDM, SLS, CNC or an existing part.
The second step; this mother model is placed in a mould box and liquid silicon rubber is poured over the master.
Once the silicon is cured, the mould is cut as per split line established and master model is removed, leaving an accurately formed cavity.
Step 4: the mould cavity is used to cast large variety of polyurethane or epoxy materials available. This allows fast production of high quality parts in a short lead time
In the next chapter the advantaged and disadvantages will be elaborated.
The costs to create a silicone mould are much lower than steel moulds, the manufacturing of these moulds can be done in a short lead time. A lead time from 4-10 days is possible, but this depends on complexity and how the master model will be made.
There is a large variety of urethane materials available, which properties are very close to the injection molded materials ranging from soft rubber grades to hard plastics. Some polyurethane can be colored directly, It is also possible to sandblast or paint the finished parts. Because of the flexibility of the silicone moulds undercuts in the product can be made without sliders or cores. Also inserts can be placed in the moulds and even over-moulding 2 or more components is possible.
The tool life time of the silicone mould is limited; one cavity can only make 20-25 parts, than a new mould has to be created.Vacuum Cast parts are not identical to injection molded parts, because the conditions and method of manufacture are different. Very thin wall sections are not recommended and chances of cracking or warping.
The Minimum wall thicknesses are recommended not to be smaller than 0.8mm. Recommended size is above 1mm.Generally 20 pcs can be made from single mould so multiple of 20 can give you better pricing to cover up the silicon mould cost. E.G. Qty 20 or 40 has better pricing per piece than 30 or 50