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 functionalised with fibre-reinforced plastics, combine high mechanical performance with low weight. The demand for manufacturing processes conducive to cost-effective mass-production is growing.

As part of 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 fibre-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 fibre-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.

“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 significantly increasing the component’s weight. 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 localised heating reduces distortion and residual stresses while joining the two materials. The laser texturing process, which has been developed at the FraunhoferILT, 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”
Fraunhofer ILT

The research partners have now finished a first demonstrator component made of high-strength steel and unidirectional fibre-reinforced thermoplastic tape to validate the applicability of the process in the form of a proof-of-concept. Two Fraunhofer researchers, Kira van der Straeten from the Fraunhofer ILT and Tido Peters from the Fraunhofer IPT, manufactured a hybrid lightweight rocker panel, a body component for the automotive industry, to test and prove the functionality of the process combination as part of the ComMUnion project. The project partners presented the component to visitors at the lightweight construction trade fair ‘JEC World’ from 12 - 14 March 2019 in Paris in the “Composites in Action Area”. 

The ComMUnion project is funded by the Horizon 2020 Research and Innovation Programme of the European Union under Grant Agreement No. 680567. European partners in the ComMUnion research project are Aimen Technology Centre, Spain (coordinator); Autotech Engineering; AIE, part of the Gestamp Group, Spain; AFPT GmbH, Germany; New Infrared Technologies SL, Spain; Tecnatom S.A., Spain; Motofil Robotics, S.A., Portugal; Philips Photonics GmbH, Germany; Laboratory for Manufacturing Systems and Automation (LMS) – University of Patras, Greece; Universidade de Coimbra, Portugal; Missler Software, France; Aciturri Engineering SL, Spain; CASP S.A., Greece; Lunovu GmbH, Germany and ESI Group, France. 

From ismr

By Amy Alford