Achieving small structures in thin NiTi sheets for medical applications with water jet and micro machining – a comparison

Frotscher, M.1, a; Gugel, H.1; Simon, T.1; Theisen, W.1; Eggeler, G.1; Kahleyß, F.2, b; Biermann, D.2, c

1)
Institut für Werkstoffe, Ruhr-Universität Bochum, 44801 Bochum
2)
Institut für Spanende Fertigung, Technische Universität Dortmund, Baroper Str. 301, 44227 Dortmund

a) matthias.frotscher@rub.de; b) kahleyss@isf.de; c) biermann@isf.de

Kurzfassung

Small structures in NiTi shape memory alloys (SMA) are commonly manufactured by laser cutting techniques. Unfortunately, one of the key disadvantages of these methods is the thermal interaction with the work piece through the formation of heat affected zones (HAZ). SMAs are especially sensitive to this kind of interactions, because phase transformation temperatures can be changed and extensive and costly post processing may be required. We examine two alternative processing methods, where the thermal influence on the material is negligible or not existent. In this paper first results on water jet machining and micro milling of a thin sheet of binary austenitic NiTi-SMA are presented and compared. Water jet machining can be used to economically cut structures in hard-to-machine materials. We used abrasive- and non-abrasive precision water jet machining to cut small stent-like structures. Micro milling is an appropriate machining technique for producing complex and filigree parts. But the high ductility and the strong work hardening of NiTi alloys during cutting lead to very difficult machining conditions. This is especially true for the machining of thin sheets. TiAlN-coated end mills with a diameter of 0.4 mm were applied to machine simple structures. The goal of this study was to compare key aspects of the two processing techniques, such as traverse speed and cutting width. The work piece quality was analyzed by scanning electron microscopy (SEM).

Schlüsselwörter

NiTi shape memory alloys, water jet machining, micro milling, microstructure, pseudoelasticity, stents

Veröffentlichung

In: SMST Extended Abstracts 2010, SMST 2010 – International Conference on Shape Memory and Superelastic Technologies, 16.5.-20.5. 2010, Asilomar Conference Center, Pacific Grove, USA, D. S. Grummon; X. Fei; M. R. Mitchell; M. Mertmann (Hrsg.), S. 174-175