Ultrafast Laser Cutting of Low Mass Superelastic Nitinol Parts
Ultrafast laser cutting is an effective tool for cutting precision low mass Nitinol parts (~0.5 mg). Low mass Nitinol parts have very low heat capacity making them susceptible to rapid temperature changes if the laser process allows substantial heat conduction to the bulk. Laser process conditions have been established that show a broad range of thermal transfer in parts cut from thin walled, small diameter SE508 Nitinol tubing. Parts cut show a range from highly annealed with large shifts in transformation temperatures (Af, Mf, etc) accompanied by elimination of cold work, to parts that exhibit no thermal effects: no change in base material properties from the starting tubing. A study of various laser energy densities (fluences) and repetition rates is presented, along with Differential Scanning Calorimetry measurements of material before and after laser-machining. Results are discussed with the relevant laser physics demonstrating how ultrafast lasers can be best utilized to deliver minimal thermal conduction to the bulk material.