Due to special material properties, among others their two-way memory effect (TWME), shape memory alloys (SMA) are finding increasing attention in micro system technology. However, only slow and quite complicated training methods are available to induce the TWME. At the Laser Zentrum Hannover e.V., investigations are being carried out to realize the induction of the TWME into SMA components using laser radiation. By precisely heating SMA components with laser radiation, local tensions remain near the component surface. Concerning the shape memory effect (SME), these tensions can be used to make the components execute complicated movements. Compared to conventional training methods to induce the TWME, this procedure is faster and easier. Further, higher numbers of thermal cycling are expected because of the low dislocation density in the main part of the component. Results regarding the dependence of the laser induced TWME on material and machining parameters will be presented.
In the course of increasing miniaturization of components in minimal access surgery the superelastic properties of nickel titanium shape memory alloys (NiTi-SMA) find more and more attention. However, only a few processes are available for machining of miniaturized NiTi-components. Changes of the mechanical properties due to heat input or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are hardly to meet. Finding new methods for manufacturing micro-instruments of NiTi wires with high geometrical resolution and superelastic mechanical properties for applications in endoscopic surgery are the main goals of the investigations presented here. Because of the precise focussing properties and the possibility of an excellent non-tactile energy coupling, material processing by lasers is a suitable alternative to conventional machining-processes. Comparing investigations with laser systems with different wavelengths and pulse duration show the suitability of ultra-short pulse Ti:Sapphire lasers for this machining process. Only by the use of ultra-short laser pulses it is possible to structure micro-components of NiTi almost without thermal influence. Results of mechanical and metallographic examinations show that the special properties of miniaturized SMA-components can be maintained. Experimental results as well as example geometries produced with ultra-short pulse lasers are presented in the paper.
Due to special material properties, shape memory alloys (SMA) are finding increasing attention in micro system technology. However, only a few processes are available for the machining of miniaturized SMA-components. In this connection, laser material processing offers completely new possibilities. This paper describes the actual status of two projects that are being carried out to qualify new methods to machine SMA components by means of laser radiation. Within one project, the laser material ablation process of miniaturized SMA- components using ultra-short laser pulses (pulse duration: approx. 200 fs) in comparison to conventional laser material ablation is being investigated. Especially for SMA micro- sensors and actuators, it is important to minimize the heat affected zone (HAZ) to maintain the special mechanical properties. Light-microscopic investigations of the grain texture of SMA devices processed with ultra-short laser pulses show that the HAZ can be neglected. Presently, the main goal of the project is to qualify this new processing technique for the micro-structuring of complex SMA micro devices with high precision. Within a second project, investigations are being carried out to realize the induction of the two-way memory effect (TWME) into SMA components using laser radiation. By precisely heating SMA components with laser radiation, local tensions remain near the component surface. In connection with the shape memory effect, these tensions can be used to make the components execute complicated movements. Compared to conventional training methods to induce the TWME, this procedure is faster and easier. Furthermore, higher numbers of thermal cycling are expected because of the low dislocation density in the main part of the component.
The mechanical properties of shape memory alloys (SMAs) are finding more and more attention in micro-system technology. However, only a few processes are available for machining of miniaturized SMA-components. During the machining process, changes of the shape memory properties due to the extension of the heat effected zone or mechanical tensions have to be avoided. Especially for complex geometries with dimensions in the submillimeter-range, these requirements are difficult to fulfill.
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