Hybrid, thermoplastic fiber composites can meet the requirements for cost-effective, large-volume production of highly innovative lightweight applications. Decisive factors are the properties of thermoplastic polymers compared to thermoset variants. The advantages of thermoplastics include processability with short cycle times, meltability and recyclability. This opens up new ways of processing, including highly automated, economical injection molding processes.
Institute for Composite Materials (IVW) in Kaiserslautern has built up 30 years of know-how in the field of fiber composites and is consistently expanding the research portfolio. The development of organic sheet and forming technology, in-situ consolidation in thermoplastic tape laying and induction welding technology are some examples of IVW's long-term commitment. In order to cover existing gaps in the high-revenue automotive industry with its technologically and economically demanding framework conditions, the processing of hybrid injection molded parts for structural components is being pushed forward. For this purpose, IVW has expanded the machinery equipment by a new injection molding machine (Engel Victory 400, see Figure 1) with infrared heating oven and automation technology, such as multi-axis robots.
In the current research project pro-TPC-Structure, material selection and characterization, stress analysis, manufacturing and quality control of hybrid injection molded components are investigated, verified and validated. This includes the production of a demonstrator component, which is to replace 1:1 the conventionally produced structural component in automotive engineering. It’s a connection rod (see Figure 2), which is a widely used structural component in the chassis that directs steering movements into the wheel bearing seats or in/out movements into a stabilizer. The component is characterized by static and oscillating tension/compression loads.
Further targets of the pro-TPC structure project are, in addition to the engineering plastic polyamide 6 (PA6), to process high-performance plastics such as polyether ether ketone (PEEK) as well as to implement production without waste with short cycle times (< 1 min). In addition, a closed simulation chain with topology optimization can be integrated into production. Since the aim is to use the system in large series, a complete inline process control system must be developed to monitor upstream and downstream work steps. The data obtained can then be used for intelligent data analysis.
The amazing properties of fiber composite components result from the combination of fibers and matrix. Chopped fibers as well as endless fibers embedded in thermoplastic matrix are combined. Both materials exhibit the most diverse properties and demonstrate the potential of hybrid materials. Hybrid injection molding offers a unique opportunity to economically produce the most complicated structures in one step. The following process route is widely used:
Production of an insert in an upstream process. This insert is transported via automation technology into an infrared oven for heating. After melting the matrix, the insert is transported to the injection molding cavity where it is functionalized by injection molding.
The following challenges result from this process:
- Multiple transport routes and intermediate steps
- Handling of very hot and limp inserts
- Complex temperature control for complex insert geometries
- Critical cooling of the component during transport to the injection molding machine
- Moderate material closure between insert and injection molding compound
- Fixation of the flexible inserts in the injection molding cavity
In order to implement an innovative and more economical production, a novel strategy is being pursued in the pro-TPC structure project: During the production of the inserts (e.g. in thermoplastic tape laying), the surface is modified, so that a strong bond between insert and the injection molding material results during the injection molding process. A cold and thus stiff insert is created, which both eliminates the heating process and is very easy to transport. The higher stiffness in the injection molding cavity allows the inserts to be overmolded on all sides. Optically appealing surfaces are created, which provide additional support against buckling. The “pro-TPC structure” project represents an innovative and more economical way of producing hybrid injection-molded components and is funded for 3 years by the European Regional Development Fund and the Ministry of Agriculture, Forestry, Environment, and Water Management of Rhineland-Palatinate.
M.Sc. Alexander Nuhn/Dr.-Ing. Jens Schlimbach
Institut für Verbundwerkstoffe GmbH
Tel.: +49 631 2017 117 / +49 631 2017 312
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