Light and Strong: Hybrid Lightweight Components in Mass-Production

In recent years there has been a sharp increase in demand for lighter components for applications in mobility and transport in response to the need to save weight, and therefore energy and resources. Hybrid components made of steel, locally functionalized with fiber-reinforced plastics combine high mechanical performance with low weight. Demand for manufacturing processes conducive to cost-effective mass-production is burgeoning. In the EU research project ”ComMUnion”, the two Aachen-based Fraunhofer Institutes for Production Technology IPT and for Laser Technology ILT, in collaboration with 14 partners from industry, research and academia, are developing industrial processes and solutions for hybrid lightweight design by combining metal and polymer-matrix composites for automotive and aerospace applications.

The new hybrid manufacturing process is based on a combination of laser texturing and laser-assisted tape placement: For this purpose, components are first pre-processed using the laser to provide a specially developed, defined, rough surface structure. The textured surface allows the continuous fiber-reinforced thermoplastic lightweight materials, which will later be used for stiffening, to be bonded directly to the steel component. The bond is then mechanical, eliminating any need for additional pre-treatment measures or additional adhesion promoters, such as adhesives or bonding agents.

The stiffenings made of thermoplastic fiber-reinforced plastics, which are especially adapted to the expected loads, are joined to the component using a tape placement process. The laser heats the thermoplastic tapes locally in the joining zone to the steel. The matrix material melts and flows into the laser textured cavities. After solidification of the melt material, the tape with the embedded unidirectional fibers adheres to the roughened surface of the steel part.

Combined process, suitable for mass production

The advantage of combining these two laser processes comes to the fore precisely when the mechanical properties of the component need to be improved locally without increasing the component’s weight significantly. The process is particularly suitable for mass production, as no further post-processing steps, such as curing operations, are required to consolidate the material after tape placement. Additionally, precision localized heating reduces distortion and residual stresses while joining the two materials. The laser texturing process, which has been developed at the Fraunhofer ILT, can also be applied in a reproducible way to the metal surface, precisely at the locations where the textures are needed. Additionally, the laser is not subject to any tool wear.