Core Deflection for Pre-mold with Over-mold Injection Molding in Moldex-3D

Side door latches in an automotive play a major role in occupants’ safety. The latches consist of both retention assembly and actuator assembly. The actuator assembly majorly consists of motor, gear & other components and these are protected through a Plastic Lower case and Housing. The Lower case (over-mold) with the Electrical Component Carrier - ECC (pre-mold) plays an important role in providing electrical power supply to the latch system. Since these parts are manufactured with terminal traces & plastics, upfront mold flow simulations help the product teams to evaluate the short fills, warpage, and other quality aspects in the critical areas of these components.

In the part assembly station, the ECC (pre-mold) and the Lower case (over-mold) are connected to the Motor on one side and the Connector on the other. The proper alignment of the pre-mold pins is of great importance and the pre-mold must not be externally visible once the molding is complete. During the prototype build, the pins were offset/dislocated due to pre-mold shift. This in turn caused deformation of the Over-mold resulting in dimensional inconsistency leading to assembly & functional issues.

This issue was complex since the part couldn’t be modified structurally because of the constraints in packaging as these interfaces with the backplate & the child feature would affect its integrity. Here, overcoming the ‘pre-mold’ shift was an important aspect to keep the Lower-case pins within the location limits ensuring a proper part assembly. However, it was challenging to control the ‘pre-mold’ shift defect merely based upon the molding manufacturing knowledge. Hence, we had to utilize ‘core-deflection analysis’ method in Moldex-3D, an injection molding specialized software, to verify the cause of ‘pre-mold’ shift and correct the problem. Virtual simulation technique has helped to resolve the issue and same technic was used in production tool. This paper will provide an insight to both the methodologies used and the tooling changes required to achieve the product assembly requirements.