Fraunhofer Institute for Material and Beam Technology IWS
Fraunhofer Institute for Material and Beam Technology IWS

CHIMERA

Functionalization of Laser-structured Fiber-reinforced Plastic Composites by Thermal Spraying (CHIMERA)

Mask-free coating of glass-fiber-reinforced thermoplastic using laser structuring before thermal spraying with copper.
© Fraunhofer IWS
Mask-free coating of glass-fiber-reinforced thermoplastic using laser structuring before thermal spraying with copper.

CHIMERA combines the strengths of metal with the lightweight potential of FRP in a highly flexible production line.
 

Motivation: Hybrid Materials with Multiple functions

Modern applications of functionally integrated components go hand in hand with new requirements for materials and manufacturing. In the field of promising mobility and transportation concepts, for example, various properties such as low weight, long-term durability, and electromagnetic shielding must be fulfilled simultaneously. One solution for this example is components made of plastic that are reinforced with fibers and coated with metal.

Objectives and Approach

The CHIMERA project further developed the functionalization of fiber-reinforced plastic components (glass fiber-reinforced thermoplastics) using metallic coatings (copper and zinc). The combination of two sub-processes, laser structuring and thermal spraying, resulted in weight-reduced metal-fiber composite hybrids with optimized composite strength and long-term durability. The demonstrator in the project is a housing component with an integrated electromagnetic shielding function. The long-term behavior of the hybrid materials was predicted based on computer models, and this prediction was compared with data collected over a long period of time under real operating conditions. This resulted in a digital test bench capable of generating long-term predictions.

Innovations and perspectives

The project offers a highly flexible process chain for imparting typical metal properties to plastic-based components over large or small areas, thereby generating functional added value with minimal additional weight. This significantly increases the marketability of hybrid materials and the associated manufacturing processes.

Microscopic image of a cross-section with APS copper coating; top: sandblasted, insufficient coating, yellow box: shows crack filled with copper and enclosed corundum particles from sandblasting; bottom: laser-structured, closed copper layer anchored in the CFRP.
Microscopic image of a cross-section with APS copper coating; top: sandblasted, insufficient coating, yellow box: shows crack filled with copper and enclosed corundum particles from sandblasting; bottom: laser-structured, closed copper layer anchored in the CFRP.
Demonstrator component (housing cover) with zinc coating for electromagnetic shielding.
© Fraunhofer IWS
Demonstrator component (housing cover) with zinc coating for electromagnetic shielding.

Results

As part of the project, the laser process for interface structuring of the CFRP component was successfully further developed and transferred to the thermally sensitive thermoplastic matrix material (PA6). Optimal and material-friendly laser structuring was achieved using an ultrashort pulse laser. A combination of (full) surface roughening and grid-shaped trench structures was found to be effective in ensuring high layer adhesion. In particular, the dimensioning of the trench structures can influence layer adhesion and the formation of a closed or interrupted layer (grid-shaped along the trench structures). Depending on the coating process, this can result in closed or grid-shaped coatings. The project also demonstrated that the process speed on the sensitive material can be increased many times over by parallel processing and the use of high laser powers. This enables economical production conditions.

Together with the project partners, two coating processes (atmospheric plasma spraying APS and arc wire spraying LDS) and two different coating materials (copper and zinc) were further developed and compared. With both processes and coating systems, adhesive coatings can be deposited after laser pretreatment, and their electromagnetic shielding effect has been characterized. The desired electromagnetic shielding function was achieved with both flat, closed spray coatings and grid-shaped spray coatings. At frequencies of 120 MHz, the desired attenuation of 60 dB was achieved.

The successful coating of the three-dimensional demonstrator geometry, a housing cover, was achieved through segmented and gap-free laser processing and an adapted multi-stage coating strategy.

The process chain (laser pretreatment and thermal spraying) was successfully transferred to another substrate material (glass fiber-reinforced sheet mold compound (SMC)). The results show that comparable coating results and thus functions can also be achieved on this widely used composite.

Another project goal was to investigate the possibility of mask-free, selective coating. Localized, sustainable coating was demonstrated through local laser roughening and APS coating. This saves additional process steps and masking material when coating less than the entire surface.

In addition to the manufacturing processes, another key project outcome within the consortium was the development of a virtual test bench for novel hybrid materials made of organic sheet metal and copper coating for static strength with micro-modeling. Shear strength was identified as a relevant critical variable for predicting the static strength of coated hybrid components made of different material combinations. The virtual test bench also shows plausible results for long-term strength. For this purpose, adapted methods for testing and characterizing the hybrid composite components under various load conditions were developed. The measured values show good agreement with the simulation results for the overall material model of the copper-coated CFRP substrate. This makes the resulting virtual test bench suitable for evaluating components under specific industrial load cases.