Cast from a single mold

Steinbeis contributes to the development of a novel battery holder made of a textile/plastic hybrid material

The demand for components in the automotive industry continues to grow: OEM strategies geared toward standardized parts, legal requirements related to recyclability, and current trends toward comfortable, high-performance, lightweight construction are raising the bar for component suppliers. With this in mind, the Steinbeis Research Center for Automation in Lightweight Design Processes (ALP) has teamed up with the polymer processing company Hugo Stiehl, the faculty chair of the Department of Lightweight Structures at Chemnitz Technical University, and Cetex, a private research institute based at the same university. Together, they have successfully implemented a new and innovative technology concept. Using a battery holder as the basis for their work, the project partners were able to develop a novel technical process for creating an assembly line for components made of textile/plastic hybrid materials.

The aim of the project was to manufacture a battery holder in a fully automated production process with quality controls in place for each step of production. The project’s key challenges included packaging, preparation for delivery, as well as mounting the inserted component on the tool and coupling the textile cord with the formed mold. To do this, process steps had to be devised that come before the actual injection molding process. The project team was able to demonstrate that it is possible to meet complex requirements for the production of components for the automobile sector. This can be done through the application of new and innovative textile/plastic hybrid technologies and the use of homogenous synthetic materials.

The battery holder can handle forces of up to 3,200 N, has a mass of 21g, and is made of hollow polypropylene (both the holder and the textile component). The cord material is a twisted, fi brillated polypropylene band sourced as a raw material. The material is pulled from a roll, fed through a guide channel, and then reformed with a heated molding unit. This allows the material to bind better with the injection molding unit. The cord is subsequently shortened to the right length using heat cutters. At the same time, the twisted ends are sealed. After this, a handling system positions the workpiece and transfers it to the singlecavity injection molding tool.

A particular challenge when working with textile/plastic hybrid materials is how to couple the plastic, and how to position and seal the components mounted on the injection molding tool. Additional parts on the molding tool hold the inserted workpiece in place when the tool is clamped in position and secure the alignment of the movable cord in the cavity during the fi lling process. In addition, it is important that the cavity is sealed despite undefi ned contours and production tolerances for the inserted textile component. To achieve this, the project team fixed the textile insert in the tool in two stages. To prevent the inserted cord from deforming due to intrinsic tension or external forces and to keep it in the right position in the cavity, clamp grips are used from and to the end effector on the robot. The insert’s position is secured with needles during the injection molding process. These needles are incorporated in the cavity and they hold and lock the end of the cord in place. The insert is sealed in the cavity through a crimping edge, which primarily shapes the inserted cord elastically without significantly damaging the fibers.

To ensure the battery holder can handle the necessary loads, the developers placed a lot of emphasis on the coupling of the textile cord in the injection molding process. If the undercut is not designed properly, or if the plastic and the cord are not coupled suffi ciently in the injection molding process, the holder will fail because the cord could be tugged out of the plastic component. This would not achieve the required composite strength.

The project partners developed and built a pilot facility for manufacturing the battery holders based on the process schematics. This facility helped to demonstrate the feasibility of the production process as well as the high performance of the finished component.

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