Magnesium alloys constitute an attractive solution for cardiovascular stent applications due to their intrinsic properties of
biocompatibility and relatively low corrosion resistance in human-body fluids, which results in as a less intrusive
treatment. Laser micromachining is the conventional process used to cut the stent mesh, which plays the key role for the
accurate reproduction of the mesh design and the surface quality of the produced stent that are important factors in
ensuring the mechanical and corrosion resistance properties of such a kind of devices. Traditionally continuous or
pulsed laser systems working in microsecond pulse regime are employed for stent manufacturing. Pulsed fiber lasers on
the other hand, are a relatively new solution which could balance productivity and quality aspects with shorter ns pulse
durations and pulse energies in the order of mJ. This work reports the study of laser micromachining and of AZ31
magnesium alloy for the manufacturing of cardiovascular stents with a novel mesh design. A pulsed active fiber laser
system operating in nanosecond pulse regime was employed for the micromachining. Laser parameters were studied for
tubular cutting on a common stent material, AISI 316L tubes with 2 mm in diameter and 0.2 mm in thickness and on
AZ31 tubes with 2.5 mm in diameter and 0.2 in thickness. In both cases process parameters conditions were examined
for reactive and inert gas cutting solutions and the final stent quality is compared.
Thanks to the recent affirmation of the active fiber lasers, remote laser welding of zinc coated steels is under
investigation with a particular emphasis on the overlap joint geometry. Due to the high power and high beam quality
offered by these lasers, the remote laser welding process has become more practicable. However laser welding of lap
zinc coated steels is still problematic because of the violent vaporisation of zinc. The presence of a gap between the
plates allowing vapour degassing has been proven to avoid defects due to zinc vaporization. On the other hand variation
in the gap value can lead to the welding defect formation. Therefore constant gap values should be ensured and deviation
from the reference gap value has to be monitored during the execution of the welding process. Furthermore, the on-line
monitoring of the gap values between the plates can be helpful for the on-line quality control of the welding process.
The paper proposes a new monitoring solution for the measurement of the gap in remote fiber laser welding of
overlapped zinc coated steels. In this solution, referred as Through the Optical Combiner Monitoring (TOCM) , the
optical emissions from the welding process are directly observed through the optical combiner of the fiber laser source
with spectroscopic equipment.
The TOCM solution presented in the paper is integrated in an IPG YLS 3000 fiber laser source whose beam is deflected
and focused by means of an El.En. ScanFiber scanning system with an equivalent focal length of 300 mm.
After the definition of the right welding process conditions, spectroscopic tests are exploited to evaluate the optical
emission from the welding plasma/plume.
Acquired spectra are then analysed with multivariate data analysis approach in order to ensure gap monitoring. Results
showed that with the proposed method it is possible to evaluate not only the gap between the plates but also the location
inside the weld at which the variation occurs. Furthermore, the relationship between the gap variation and local changes
in the acquired spectra is given.