Comparative study of CW, nanosecond- and femtosecond-pulsed laser microcutting of AZ31 magnesium alloy stents

Abstract

Magnesium alloys constitute an interesting solution for cardiovascular stents due to their biocompatibility and biodegradability in human body. Laser microcutting is the industrially accepted method for stent manufacturing. However, the laser-material interaction should be well investigated to control the quality characteristics of the microcutting process that concern the surface roughness, chemical composition, and microstructure of the final device. Despite the recent developments in industrial laser systems, a universal laser source that can be manipulated flexibly in terms of process parameters is far from reality. Therefore, comparative studies are required to demonstrate processing capabilities. In particular, the laser pulse duration is a key factor determining the processing regime. This work approaches the laser microcutting of AZ31 Mg alloy from the perspective of a comparative study to evaluate the machining capabilities in continuous wave (CW), ns- and fs-pulsed regimes. Three industrial grade machining systems were compared to reach a benchmark in machining quality, productivity, and ease of postprocessing. The results confirmed that moving toward the ultrashort pulse domain the machining quality increases, but the need for postprocessing remains. The real advantage of ultrashort pulsed machining was the ease in postprocessing and maintaining geometrical integrity of the stent mesh after chemical etching. Resultantly, the overall production cycle time was shortest for fs-pulsed laser system, despite the fact that CW laser system provided highest cutting speed

Novel Zn-based alloys for biodegradable stent applications: Design, development and in vitro degradation

“…The use of the ns-pulsed laser provides reduced thermal interaction compared to the continuous wave (CW) ones, commonly used in the cutting of permanent stents in stainless steel or Co-Cr alloys. Moreover, the use of CW lasers can induce larger amount of dross on materials with low melting point such as Mg alloys (Demir and Previtali, 2014). Going towards shorter pulse durations, namely fs-pulsed lasers the thermal interaction with cut material can be avoided completely.…”

Prototyping of biodegradable flat stents in pure zinc by laser microcutting and chemical etching

“…It can be expected that pure Zn is prone to generate high amount of dross and vapour due to very low melting and vaporization temperature. The dross amount after laser microcutting plays a critical role on the final quality achievable by the end of the finishing process [38]. A common approach in macro laser cutting is to manage the gas flow in terms of pressure and nozzle design [39].…”

Surface Finish and Back-Wall Dross Behavior during the Fiber Laser Cutting of AZ31 Magnesium Alloy

“…This chamber provided stability on laser cutting, by avoiding reactions between magnesium and oxygen and reducing the thermal effects. Whereas some researchers have used ultrashort-pulsed laser sources (i.e., nanoseconds, and femtoseconds) for reducing thermal effects and achieving average surface roughness below 1.4 μm [ 20 ]; our approach has achieved even lower roughness values while at the same time avoiding the high costs associated with using expensive ultra-short pulsed laser sources. For back-wall dross response, minimum values below 1.0% were observed on the central area of the cutting trajectory.…”