Injection molding: Taking work in-house cuts reject rate to near zero

By moving silicone seal overmolding in-house, this injection molder was able to reduce its logistics effort and increase the yield of good parts it produces. Now it requires less effort to make more good parts—in this case, milk foaming nozzles for coffee machines.

The molder, Bernhard Kneifel Werkzeugbau GmbH (Bad Aibling, Germany), this spring added an all-electric EX 80-180 SilcoSetEX machine from KraussMaffei (Munich, also Germany) to its stable. The electric press is being used to overmold liquid silicone seals onto polyamide substrates for the foaming nozzles. Previously the molder had processed the substrates—which are formed from EMS-Grivory's HT1V with 40% glass fiber content—and then sent these to another processor for silicone overmolding.

"In this way, we are able to save substantial processing costs. We've eliminated the logistics effort and transport costs, and also the necessity for cleaning and reheating the substrates before applying the seal. Despite the extra effort involved, the yield of good parts never matched what we are now regularly achieving—our reject rate is now close to zero," according to Martin and Andreas Kneifel, managing directors of the processors and sons of its founder. They employ about 30 and since 1996 have added twelve injection molding machines from KM to their facility.  

The new EX machine, like others in the range, is equipped with a three-platen electric clamp unit and a 'Z'-toggle system. The plasticizing and injection units are direct drive systems with high-torque motors. The force of two coupled electric motors is transmitted directly to the screw. —[email protected]