Optical design and development of a fiber coupled high-power diode laser system for laser transmission welding of plastics

Eva Rodriguez-VidalIban QuintanaJon EtxarriUrko AzkorbebeitiaDeitze OtaduyIK4-TEKNIKERPolo Tecnologico de EibarCalle Inaki Goenaga, 520600 Eibar, Gipuzkoa, SpainE-mail: erodriguez@tekniker.esFrancisco GonzalezFernando MorenoUniversity of CantabriaGroup of OpticsApplied Physics DepartmentAvenida de los Castros, s/n39005, Santander, SpainAbstract. Laser transmission welding (LTW) of thermoplastics is a directbonding technique already used in different industrial applications sectorssuch as automobiles, microfluidics, electronics, and biomedicine. LTWevolves localized heating at the interface of two pieces of plastic to bejoined. One of the plastic pieces needs to be optically transparent tothe laser radiation whereas the other part has to be absorbent, beingthat the radiation produced by high power diode lasers is a good alterna-tive for this process. As consequence, a tailored laser system has beendesigned and developed to obtain high quality weld seams with weldwidths between 0.7 and 1.4 mm. The developed laser system consistsof two diode laser bars (50 W per bar) coupled into an optical fiberusing a nonimaging solution: equalization of the beam parameter product(BPP) in the slow and fast axes by a pair of step-mirrors. The powerscaling was carried out by means of a multiplexing polarization technique.The analysis of energy balance and beam quality was performed consid-ering ray tracing simulation (ZEMAX®) and experimental validation. Thewelding experiments were conducted on acrylonitrile/butadiene/styrene(ABS), a thermoplastic frequently used in automotive, electronics and air-craft applications, doped with two different concentrations of carbon nano-tubes (0.01% and 0.05% CNTs). Quality of the weld seams on ABS wasanalyzed in terms of the process parameters (welding speed, laser powerand clamping pressure) by visual and optical microscope inspections.Mechanical properties of weld seams were analyzed by mechanicalshear tests. High quality weld seams were produced in ABS, revealingthe potential of the laser developed in this work for a wide range of plasticwelding applications.