Manufacturing technologies
Digital Manufacturing

Joint strength and numerical modelling of laser welding for CFRP/Steeland resistance spot welding for CFRP/Aluminum
Research Division of Materials Joining Assessment, Joining and Welding Research InstituteProfessor Ninshu Ma
https://researchmap.jp/ma.ninshu?lang=en

Abstract
An advanced numerical analyzing model was developed to reproduce the thermal and mechanical phenomena during directly
joining CFRP (carbon fiber reinforced resin material) and metals(high-strength steel plate, aluminum alloy) using the laser or electric resistance joule heat as heat sources. Based on analyzed
results, the temperature distribution on the joining interface, themelting region and decomposition region of CFRP were quantified,
which cannot be observed experimentally. The bonding mechanism was elucidated. It was found that controlling the joining interface temperature to the range between the melting and decomposition temperatures of CFRP is a necessary condition for joining
CFRP and metals. The wider of this temperature range zone, thehigher the strength of the joints. Through more detailed research,
we clarified the correlation between laser welding conditions (laserpower) and CFRP/Steel joint strength, and resistance spot welding
current (Joule heat) and CFRP/Aluminum joint strength.

Manufacturing technologies▍ Background & Results

Fig.1: (a) CFRP/Steel laser welding setup, (b) Interface temperature history,(c) Force-displacement curve in tensile-shear test, (d) Joint Strength

At manufacturing sites, digital control and visualization are essential to improve productivity and ensure product quality. DT (digital twin) and DX (digital transformation) are paid great attentions as
digital systems.
Firstly, a DT of resistance spot welding of CFRP/Aluminum wasdeveloped, which quantified and visualized the temperature field,weld dimensions, and tensile shear strength. The welding conditions with changes in dimensions of CFRP plates and aluminum
plates used at production sites can be given using this DT system.
It is expected that this DT system will propose optimized welding
conditions and predict associated results in real time.
In order to put the research results of laser welding of CFRP/
Steel into practical use, it is necessary to accumulate experimentaland analytical datasets and build prediction technology using ML(machine learning) algorithm.

▍ Significance of the research and Future perspective

Fig.2: (a) CFRP/Aluminum resistance spot welding, (b) Finite element
modelling, (c) Force-displacement curves in tensile-shear tests

To save energy and reduce CO2 emissions of vehicles, how toreduce the weight of automobile bodies is also necessary besides
to improve engine efficiency and battery performance. Therefore,
it is essential to design vehicle body using multi-materials and join/
assembly various parts made of lightweight materials such as composite resin (CFRP), light metals (aluminum, magnesium, etc.) andhigh-strength steel. In this study, we focused on resistance spot
welding technology for joining CFRP/Aluminum and laser welding
technology for joining CFRP/Steel. Through clarifying the joining
mechanism, it can be known interface temperature distribution
governs the joint strength and the size of joining zone. Throughnumerical simulations, guidelines for optimizing welding conditions can be proposed. Furthermore, through developing a digitalsystem such as DT/DX, the research achievement can make great
contribution to realize the GX (green transformation).

P a t e n t
Xia, Hongbo; Ma, Ninshu et al. Influence of laser welding power on steel/CFRP lap joint fracture behaviors. Composite Structures. 2022, 285 (115247),
1-12. doi: 10.1016/j.compstruct.2022.115247
Ren, Sendong; Ma, Ninshu et al. Numerical analysis on coaxial one-side resistance spot welding of Al5052 and CFRP dissimilar materials. Materials andDesign. 2020, 188 (108442), 1-14. doi: 10.1016/j.matdes.2019.108442UR
L http://www.jwri.osaka-u.ac.jp/en/research/research03_1.html
K e y w o r d Steel/CFRP laser welding, Al/CFRP resistance spot welding, RSW digital twin
Tr e a t i s e