Finite element simulation and experimental validation of pulsed laser cutting of nitinol

Nitinol (NiTi) alloys are widely used in laser cutting of cardiovascular stents due to excellent biomechanical properties. However, laser cutting induces thermal damage, such as heat affected zone (HAZ), micro-cracks, and tensile residual stress, which detrimentally affect product performance. The key process features such as temperature distribution, stress development, and HAZ formation are difficult to measure experimentally due to the highly transient nature. In this study, a design-of-experiment (DOE) based 3-dimensional (3D) finite element simulation was developed to shed light on process mechanisms of laser cutting NiTi. The effects of cutting speed, peak pulse power, and pulse width on kerf width, temperature, stress, and HAZ were investigated. A DFLUX user subroutine was developed to model a moving volumetric (3D) heat flux of a pulsed laser. Also, a material user subroutine was used that incorporated superelasticity and shape memory of NiTi.