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.
Laser transmission welding (LTW) of polymers is a direct bonding technique which is already used in different
industrial applications sectors such as automobile, microfluidic, electronic and biomedicine. This technique offers
several advantages over conventional methods, especially when a local deposition of energy and minimum thermal
distortions are required. In LTW one of the polymeric materials needs to be transparent to the laser wavelength and the
second part needs to be designed to be absorbed in IR spectrum. This report presents a study of laser weldability of ABS
(acrylonitrile/butadiene/styrene) filled with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs).
These additives are used as infrared absorbing components in the laser welding process, affecting the thermal and optical
properties of the material and, hence, the final quality of the weld seam.
A tailored laser system has been designed to obtain high quality weld seams with widths between 0.4 and 1.0mm. It
consists of two diode laser bars (50W per bar) coupled into an optical fiber using a non-imaging solution: equalization of
the beam quality factor (M2) in the slow and fast axes by a pair of micro step-mirrors. The beam quality factor has been
analyzed at different laser powers with the aim to guarantee a coupling efficiency to the multimode optical fiber. The
power scaling is carried out by means of multiplexing polarization technique. The analysis of energy balance and beam
quality is performed in two linked steps: first by means ray tracing simulations (ZEMAX®) and second, by validation.
Quality of the weld seams is analyzed in terms of the process parameters (welding speed, laser power and clamping
pressure) by visual and optical microscope inspections. The optimum laser power range for three different welding
speeds is determinate meanwhile the clamping pressure is held constant. Additionally, the corresponding mechanical
shear tests were carried out to analyze the mechanical properties of the weld seams. This work provides a detailed study
concerning the effect of the material microstructure and laser beam quality on the final weld formation and surface
integrity.
The use of optical fibers as sensing element is increasing in clinical, pharmaceutical and industrial applications.
Excellent light delivery, long interaction length, low cost and ability not only to excite the target molecules but also to
capture the emitted light from the targets are the hallmarks of optical fiber as biosensors. In biosensors based on fiber
optics the interaction with the analyte can occur within an element of the optical fiber. One of the techniques for this kind
of biosensors is to remove the fiber optic cladding and substitute it for biological coatings that will interact with the
parameter to sensorize. The deposition of these layers can be made by sol-gel technology.
The sol-gel technology is being increasingly used mainly due to the high versatility to tailor their optical features.
Incorporation of suitable chemical and biochemical sensing agents have allowed determining pH, gases, and biochemical
species, among others. Nonetheless, the relatively high processing temperatures and short lifetime values mean severe
drawbacks for a successful exploitation of sol-gel based coated optical fibres. With regard to the latter, herein we present
the design, preparation and characterization of novel sol-gel coated optical fibres. Low temperature and UV curable
coating formulations were optimized to achieve a good adhesion and optical performance. The UV photopolymerizable
formulation was comprised by glycidoxypropyltrimethoxysilane (GLYMO), Tetraethylorthosilicate (TEOS) and an
initiator. While the thermoset coating was prepared by using 3-aminopropyltrimethoxysilane, GLYMO, and TEOS as
main reagents. Both curable sol-gel coated fibres were analysed by FTIR, SEM and optical characterization.
Furthermore, in the present work a new technique for silica cladding removal has been developed by ultra-short pulses
laser processing, getting good dimensional accuracy and surface integrity.
We present a novel optical system for fiber coupling of a commercial high power diode laser stack and the application of
this laser system to transmission welding of engineering thermoplastics. The diode laser stack is made up of two 20% fill
factor bars, emitting at 808 nm and with a total maximum output power of 120W CW. The stack was collimated using
FSAC micro-optics lenses in the fast and slow axis, with a full angle divergence of <4mrad and <25mrad respectively.
The optical design and simulations were carried out using ZEMAX®. Based on the design we built an optical set up,
which is divided in two subsystems. The first one collimates the laser beam in order to achieve the best focus and couple
it into the 400μm core fiber with NA0.22 and 70% efficiency. The second subsystem is designed for beam conformation
after the fiber output, using collimation and beam shaping to have a Gaussian beam profile on the work piece. The laser
system was applied to study the welding of polycarbonate plastics, based on the effects of selected welding parameters
on the seam geometry and surface integrity. The quality of the spot welding has been analyzed obtaining welded seams
with a mean diameter about 500-600μm, preserving the good technological properties of the thermoplastic considered in
this work. The results show that we have successfully developed a novel laser system which is highly efficient for
thermoplastics processing.
Metallic glasses have been preferred to crystalline alloys for applications in microelectronics mechanical systems and die
components because of their ease of formability and excellent mechanical properties. This paper presents the machining
response of amorphous and polycrystalline Ni-based alloys (Ni78 B14 Si8) and Fe alloys (Fe81 B13.5 Si3.5 C2) when
subjected to micro-second and pico-second laser processing. The shape and topography of craters created with single
pulses as a function of laser energy together with holes drilled and laser milled areas in both materials were studied.
Focused ion beam (FIB) imaging and Energy Diffraction Spectroscopy (EDS) were used to analyse the single craters,
through holes and milled trenches in the amorphous and polycrystalline samples. The material microstructure analysis
revealed that processing both materials with micro-second and pico-second lasers does not lead to crystallisation and the
short-range atomic ordering of metallic glasses can be retained. When processing the amorphous sample the material
laser interactions resulted in a significant ejection of molten material from the bulk that was then followed by its partial
re-deposition around the craters. Additionally, there were no signs of crack formation that indicate a higher surface
integrity after laser machining. This integrity is closely related to the nature of the metallic glass. A conclusion is made
that laser processing both with short- and long-pulses is a promising technique for micromachining metallic glasses
because it does not lead to material crystallisation, preserving the good mechanical properties of these sort of materials.
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