An Investigation of Process Parameters on Selective Laser Melting of Nitinol

Abstract

Nitinol’s superelastic and shape memory effects can be used in passive or active actuation systems. Often used in the aerospace industry, the use of Nitinol for actuation is also growing in the biomedical fields and elsewhere. However, the industry currently lacks the ability to produce complex Nitinol actuators, which is strictly limiting its potential. The extreme difficulty of machining Nitinol complicates manufacturing processes. Furthermore, the transformation temperatures which drive Nitinol’s unique behavior are extremely sensitive to the relative concentrations of nickel and titanium. Therefore, exceptionally tight compositional control during production is necessary to guarantee ideal material behavior. Additive manufacturing (AM) is a near-net-shaping technology which allows for the direct fabrication of complex metallic components. In this way, the (lack of) machinability of Nitinol is no longer an issue because no traditional machining is required during fabrication. Using AM also enables production of 3D geometries that are not possible using traditional techniques. Features such as engineered porosity, hollow parts, curved holes and filigree structures are suddenly realizable. Furthermore, direct CAD fabrication reduces the timescale of the concept-to-prototype transition. A major breakthrough in additive manufacturing came with the development of fiber laser technology in the mid-1990’s, which enables direct melting of manufacturing grade metals into fully dense parts. This technology became known as selective laser melting (SLM). Despite its huge potential, SLM of Nitinol has received little attention from the engineering world. In the present work, two different SLM machines (Realzier SLM 100 and Phenix Systems PXM) are used to develop Nitinol components directly from powder. Adjustment and optimization of the process parameters on the product are analyzed and compared.