Achieving Small Structures in Thin NiTi Sheets for Medical Applications with Water Jet and Micro Machining

Tuesday, May 18, 2010 - 4:00 PM

Achieving Small Structures in Thin NiTi Sheets for Medical Applications with Water Jet and Micro Machining – a Comparison

M. Frotscher, T. Simon, H. Gugel, K. Neuking, W. Theisen, Ruhr-University Bochum, Bochum, Germany; F. Kahleyß, D. Biermann, Technical University Dortmund, Dortmund, Germany; G. Eggeler, Ruhr University Bochum, Bochum, Germany

Small structures in NiTi shape memory alloys (SMA) are commonly manufactured by laser cutting. One disadvantage is the thermal interaction with the work piece. This is important, because in SMAs phase transformation temperatures can be changed and post processing may be required. We examine water jet machining and micro milling as two processes, where the thermal influence is minimal, to produce stent-like structures in NiTi sheets. The goal of this study was to compare key aspects between the two techniques, such as traverse speed, cutting width and cut quality. The influence on the surface roughness was examined using confocal laser scanning microscopy (CLSM). The microstructure was analysed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) before and after cutting. Due to small structure sizes, focused ion beam (FIB) was used to prepare samples. We used nanoindentation to examine differences in nanohardness and shape recovery before and after machining.

Summary: Our study compares the water jet machining and micro machining of small structures in thin NiTi sheets. We show that processing of stent-like geometries in these sheets is possible and we provide parameters and experimental results about the microstructure, surfaces and some mechanical properties.