Fiber-reinforced thermoplastics (TP-FRPC) are characterized not only by their fast processability and lower weight but also by good recyclability, making them an important alternative to thermoset FRPC. These properties qualify TP-FRPC for a large number of lightweight applications, including the automotive industry. One way to optimize the properties of TP-FRPC components in terms of application is to combine them with metals. For example, metallic force introduction elements can be applied to TP-FRPC components by the use of suitable hybrid joining processes (Figure 1). In particular, hybrid joints that allow homogeneous force introduction lead to higher overall strenght of the component, which in turn can reduce the overall weight as a result of synergy effects.
HyBe is a current research project dedicated to the development of a fully automated joining process for the rapid and quality-assured joining of metallic fasteners to TP-FRPC components. The aim of the project is to develop an enabling technology that allows automated, digitized and energy-efficient inductive hybrid joining. By significantly reducing the cycle time using finite element methods to optimize energy input (Figure 2), in-line quality assurance, redundant process control and digital process chain modeling, the process will be taken to industrial maturity as a prototype. Metallic screw fasteners with a round connection surface are used as force introduction elements. The rotationally symmetrical geometry is particularly suitable for induction heating, whereby heating times of less than 5 seconds are achieved. After the fasteners have been picked up by the end effector (Figure 3), which can also be mounted on a robot, they are transported in a targeted manner to the joining position on the TP-FRPC component and joined. By using bonding agents (specifically developed for the project) on the joining surface of the fasteners, high joint strengths can be achieved even with matrix polymers such as polypropylene that are difficult to bond. In case of a hybrid joint of glass-fiber-reinforced polypropylene with steel, these are around 14 MPa (DIN1465) and thus exceed the strengths of conventional adhesives and TP-FRPC/metal joints. In addition, the fasteners coated with bonding agent are characterized by their uncomplicated processing and storage, e.g. in bulk form. Due to their industrial relevance, hybrid joints with fiber-reinforced ABS are also being investigated and optimized in the project.
In addition to process development, the characterization of the hybrid joints by means of material examples and studies on long-term durability is also an important part of HyBe project.
In the further course of the project, process time, energy input as well as bonding agents of the fasteners will be further optimized. Thanks to the close cooperation between the three industrial partners and Leibniz-Institut für Verbundwerkstoffe (IVW), a novel hybrid joining process that can be applied across all industries is being developed.
Dipl.-Ing. Stefan Weidmann
Scientific Staff Press & Joining Technologies
Phone: +49 631 2017 383