I believe that is a BUMP in the clamp during the injection phase when molding rubber or silicone. The clamp is allowed to breathe (reduce tonnage) to expel the air trapped inside the mold. The clamp can be opened and closed ever so slightly (i.e. BUMPED) during the filling/pack phase of injection. This can also help to reduce molded in stress. The majority of press manufactures that have accurate control over their clamp movement can add this option to their control for a charge.

It should be capable of doing this on any standard injection molding machine, as long as you can do a multi-stage platen closing, i.e. close to first position (a few mm from final), inject full volume of material, close platen to final position. Most new machines with good controllers are capable of this. What’s more important is the injection mold design. You have to use a shear edge tool, and injection locations should either be a center top gate, or multiple hot drops away from the edges. Eliminate free-standing cores if possible too. This process really only works well for large thin parts that do not have a lot of projections from the nominal wall.

The compressional motion can be done by injection compression molding machine itself or separate mechanism linked with traditional injection molding machine. The mechanism is normally hydraulic-designed. It pushes mold plates or necessary cores to compress prior-filled melt then a finished part is made. To complete a process cycle, the mechanism is normally also integrated/programmed with injection molding machine so that its actuation/ending timing signal of compressional motion can be sent from/to injection molding machine.