Cordula Regensburger, a product and technology management specialist at injection molding machinery producer KraussMaffei Technologies GmbH in Munich, Germany, described selection and development of a production cell to mold two‑component LSR/glass-fiber-reinforced nylon automotive engine compartment housings, such as one carrying a circuit board.
One such part that KM features is a fuse cover-box. The part represents a trend toward replacement of thermoplastic elastomer molded-on seals with LSR seals, which stand up better to rising engine compartment temperatures.
Regensburger reviewed means of producing such two-component parts, including using two molding machines, before showing the final preferred minimum footprint customer solution: using a reversibly rotating turntable table mold and two injection units mounted “piggyback” on KM's CXZ160‑750/180 Multinject 2-platen hydraulic drive molding machine.
The cell was also fitted with a KM LRX250 linear handling robot. Thermal separation of the injection units with insulation sleeves prevents premature LSR cure before the material reaches the mold cavity, Regensburger revealed.
As the housing is produced in different sizes, shot weight of the primary nylon thermoplastic component is in the 60 to 100 gram range, with 10 to 20 grams for the secondary red self‑adhesive LSR seal component. Four inserts are overmolded in the part, which also has been designed to optionally apply a membrane by ultrasonic welding.
The production cell includes a fully automatic test station with membrane seal pressure testing and a camera and 3D scanning system part inspection, controlling 175 different dimensions.
Regensburger said injection of the LSR at the higher (hot) position and nylon at the lower (cool) position is “preferred by mold makers, also as it means larger volume part being injected in the lower position.”
Michael Pühringer, technical and design manager at Wolfern, Austria-based mold maker Ebner‑Tec Solution GmbH, provided further details of the application, talking of the importance of a highly even surface for support of the circuit board, with deviation required to be
High demands set on the part made repeated mold filling and warping simulation essential for both the polyamide as well as the LSR prior to cutting tools, and the optimum injection point was also important to reach the objective of obtaining the best possible result on the first trial parts, without having to regrind the mold tool. Two independently adjustable needle valve nozzles for LSR injection were used to ensure even filling of the separate LSR areas on the part, involving volumes of 7.2 and 3.6 ccm.