The easiest way to produce a moulded rubber part. Small series and where the mould cost is important.
You need to preform rubber parts (not cured). Sometime one per cavity.
You load a preformed rubber part directly into the cavity. Start the cycle. The rubber part cures in the pressure and heat. The machine open the mould and you take out the finished part. Same procedure as making waffles!
Rubber is a bad heat transfer-er so this means longer curing times compared to transfer or injection moulding.
The moulds are cheaper with this method.