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

Abstract

Laser transmission welding (LTW) of thermoplastics is a direct bonding technique already used in different industrial applications sectors such as automobiles, microfluidics, electronics, and biomedicine. LTW evolves localized heating at the interface of two pieces of plastic to be joined. One of the plastic pieces needs to be optically transparent to the laser radiation whereas the other part has to be absorbent, being that the radiation produced by high power diode lasers is a good alternative for this process. As consequence, a tailored laser system has been designed and developed to obtain high quality weld seams with weld widths between 0.7 and 1.4 mm. The developed laser system consists of two diode laser bars (50 W per bar) coupled into an optical fiber using a nonimaging solution: equalization of the beam parameter product (BPP) in the slow and fast axes by a pair of step-mirrors. The power scaling was carried out by means of a multiplexing polarization technique. The analysis of energy balance and beam quality was performed considering ray tracing simulation (ZEMAX®) and experimental validation. The welding experiments were conducted on acrylonitrile/butadiene/styrene (ABS), a thermoplastic frequently used in automotive, electronics and aircraft applications, doped with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). Quality of the weld seams on ABS was analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. Mechanical properties of weld seams were analyzed by mechanical shear tests. High quality weld seams were produced in ABS, revealing the potential of the laser developed in this work for a wide range of plastic welding applications.

High brightness beam shaping and fiber coupling of laser-diode bars

“…where BPP total is the BPP of the laser beam in a diagonal direction and d fiber and NA denote the diameter and numerical aperture of the fiber, respectively [5][6][7][8][9]. Based on the BPP of single mini-bar after beam shaping, we can arrange two minibars in the y direction and four mini-bars in the x direction, as shown in Eq.…”

Recent Advances in Thermoplastic Microfluidic Bonding

“…The laser energy that is absorbed in this material causes vibration of the electron bonds, followed by heat transfer to the surroundings through convection and radiation. When heated to temperatures above the T g reaching melting temperature, a weld is formed while applying pressure to increase mating contact forces [ 114 ]. Laser welding requires a suitable combination of dissimilar materials with transparent and opaque properties; therefore, it is not suitable for the fabrication of fully transparent microfluidic devices [ 115 ].…”

Simultaneous polarization and wavelength merging for efficient fiber coupling system using a designed one-mirror prism

“…The heat dissipation method of the laser stack mostly adopts the microchannel water cooling method, because of the encapsulation, there is a certain spacing between the bars in the vertical direction, which leads to the beam fast-axis filling factor is low and the quality is poor, and at the same time, the BPP (Beam Parameter Product) in both directions of the stack has large differences and the value corresponding to the fiber does not match, which makes it difficult for the beam to be coupled into the fiber [5,6]. To solve these problems, efficient and simple shaping methods must be designed to improve and equalize the beam quality in both directions [7,8].…”