S. Blümel
V. Wippo
S. Hirt
R. Stähr
P. Jäschke
S. Kaierle
L. Overmeyer

Joining of thermoplastic carbon fiber reinforced plastic laminates by selective heat input during laser cutting

J. Laser Appl.
33
022011
2021
Type: Zeitschriftenaufsatz (reviewed)
Abstract
The drilling of carbon fiber reinforced plastic (CFRP) components is a preliminary step within the assembly of airplanes or cars. The usage of CFRP brings along different challenges and opportunities due to the heterogeneous material characteristics. Laser cutting of thermoplastic composites can lead to distinctive heat affected zones (HAZs) if the process parameters are not optimized regarding the specific boundary conditions and material characteristics. During cutting, the matrix material gets molten and solidifies again. Further heat input beyond what is needed for cutting can lead to the deterioration of the matrix material. As a result, process strategies are normally developed to reduce the HAZ to a minimum. Such strategies can be used for adapting the process and generating a selective heat input in the interaction zone of two components during the drilling process. Adapting the process can also be used to weld components together. Unlike other more common efforts to reduce the HAZ, this study’s goal was to adapt the process so that two thermoplastic CFRP plates lying upon another can be welded during the cutting process. The developed process shows potential for the preliminary fixation of components in assembly processes by finding an optimum between reachable tensile force and resulting HAZ. The investigations were performed with CFRP plates with a thickness of h = 2.4mm and a drilled hole with a diameter of d = 5 mm. The results demonstrate the possibility of welding the laminates while reducing the HAZ width to values below b = 300 μm. Tensile tests were performed with the joined specimens to determine the resulting tensile load. Cutting the hole with parameters typically used to minimize the HAZ result either in no weld seam or in a weak weld seam, which breaks at minimum force before tensile testing. Cutting parameters resulting in a distinctive HAZ generate tensile forces of up to F = 5.82 kN within the observed process window. Furthermore, strategies were investigated allowing a defined heat input only within the transition between the two plates. With this adapted strategy, tensile forces in the range of F = 1 kN could be realized. For these samples, the major HAZ width was located in the welding area with decreasing HAZ width for the upper and lower plates.