Silicone Molds Injection

‍Silicone moulding is mainly used to reproduce a fewparts up to a few dozens in polyurethane. The method is fast and inexpensive touse and also capable of exceptionally good reproduction of the surfacestructure of the master parts.

The function of the FFF master part is to representthe desired shape with the best possible precision. The FFF methods that havethe best precision are SLA and Sanders inkjet. The latter gives betterprecision than SLA, but masters built in the wax-like material can only be usedfor one silicon mould. For bigger than small and for massive parts the inkjetmethod also is too slow.

Usually the thermosetting plastic polyurethane isused. In rare cases epoxy is also used. Polyurethane can be provided inqualities with very varied material properties from soft rubber-like to veryhard or firm qualities.

Polyurethane for silicone moulding is often offered assimulating polypropylene, ABS, nylon or other thermoplastics. The simulation isstill not good enough to be recommended for functional testing where mechanicalproperties are essential.

The silicone mould is normally capable of lasting 15 -30 shots. It is however so easy to produce new moulds that the method could beused over again for up to 60 parts. The practical/economical limitation is thatthe cycle time for thermosetting plastic is considerably longer than thecorresponding cycle time for injection moulding, and often only 3-4 parts canbe made per day shift.

Conventional silicone moulding is such a simple method, thatit could easily be carried out even in a hobby workshop. When for example thereis a need for iterative product development, where tests and product modificationstake place at a fast pace, the production could be made locally in a simpletest workshop. The method is also suitable for the private inventor withlimited resources.

At companies and departments that work mainly withprototype manufacturing, conventional silicone moulding is hardly used anymore.Instead the further developed variant, vacuum casting, isused. At vacuum casting, vacuum is used to eliminate airfrom the silicone and also to make the plastic fill better in narrow slots.Vacuum casting doesn’t only have an outstanding capability to render thesurface structure, it could also reproduce fairly thin walls and small details.Machines for vacuum casting are rather expensive and are available for partsizes up to over 2 meters.