A predictive model and validation of laser cutting of nitinol with a novel moving volumetric pulsed heat flux

Nitinol alloys are widely used in manufacturing of cardiovascular stents due to excellent biomechanical properties. Laser cutting is the predominant process for stent manufacturing. However, laser cutting induces thermal damage such as heat affected zone (HAZ), micro cracks, and tensile residual stress, which detrimentally affect product performance. Laser cutting induced temperature distribution, stress development, and HAZ formation are critical process characteristics. However, they are difficult to measure experimentally due to the highly transient process. To better understand the process mechanics in laser cutting of nitinol, a three-dimensional finite element model of pulsed laser cutting was developed to incorporate a novel moving volumetric pulsed heat flux model with high spatial accuracy. A material subroutine was also incorporated to model superelasticity and shape memory of nitinol. The predicted kerf geometry and dimensions agreed well with the experimental data. Also, the effects of cutting speed, pulse power, and pulse width on kerf profile, temperature, and heat affected zone (HAZ) were investigated.