Laser transmission welding of polymer and wood composites: Material and joint mechanism related studies

Laser beam transmission welding is an innovative and promising technology for many industries such as the automotive, electronic, and medical industry. Extension to application of this technology to wood components makes it also interesting for the woodworking and furniture industry. Therefore, several investigations in the field of welding of fiber reinforced thermoplastic and wood composites with polymers have been carried out. Focus is given to the determination of the weldability and weld behavior of different thermoplastic and wooden materials in matrices relevant for recent industrial applications. Different laser sources with a variety of wavelengths are examined, e.g., high power diode lasers (810, 940 nm) and Nd Yttritium–aluminum–garnet (YAG) laser systems (1064 nm). New approaches using thermographic methods for an easy and fast evaluation of materials qualification regarding their weldability will also be presented. Different plastic and wood components taking into account properties like filling content are investigated. Results show that the thermographic transmission and heating rate are more or less different for Nd:YAG and diode laser radiation depending on the type of laser-transparent polymer material, production conditions, and on the presence of pigments and other filling materials. Investigating the absorbing materials, it has been shown clearly that a modification of the carbon content is observable very easily in the thermographic images recorded during the heating period. Since natural fiber composites have strong material inhomogenities and anisotropic structures, special process strategies for their application have been developed and are presented in this article.