The integration of shape memory (SM) wires in additive manufacturing (AM) processes and components, either as actuators or sensors, holds enormous potential for future developments. For example, a sensor or an actuator function could be integrated into a component already during the manufacturing process. This integration can eliminate downstream assembly steps and improve the flexibility of the component design. In addition to (complex) components, the AM process can also be used to attach connecting elements to the wire, ensuring an improved connection of the wire to other components like an actuators housing.The integration of shape memory alloys into the AM will be further investigated in the following and feasibility validated by initial trials. Selective laser melting with metal powder (PBF-LB/M) is used as an additive manufacturing process, thereby blocks are welded to the ends of the wire in the context of this work as proof of concept. By using a laser, the energy distribution on the materials can be adjusted very precisely, minimizing the thermal influence on the SM material and preventing damage due to overheating.In the experiments, the manufacturing process in the PBF-LB/M system produced a form-fitted connection between two blocks - each at the end of the wire - and the wire itself (0.7mm binary NiTi). To ensure an optimal connection of the materials in combination with a low influence on the functional properties of the wire, the parameters of the laser were adjusted in the test series. The most important varied laser parameters for the investigations are the scanning speed and the laser power. Subsequently, the specimens were tested at 150 MPa mechanical tension and cyclically activated. They were activated 10,000 times for 5 seconds at 5 V and then cooled for 40 seconds without applied electrical voltage. Compared to the reference samples, it was demonstrated, that the functional properties of the smart memory alloy (SMA) were still present after processing with the given process parameters, and the long-term behavior over 10,000 cycles were also not significantly different from those of untreated wires. Both, the reference tests and the tests with different welding parameters, were performed with three samples each.Furthermore, tensile tests determined the force up to which the generated joint would hold and a first sample was examined under the scanning electron microscope (SEM), to further roughly estimate the thermal influence of the laser on the microstructure of the SMA wire.

Integration of SMA Wires Into the Additive Manufacturing Process Using PBF-LB/M and Long-Term Tests of the Specimens to Validate the Functional Properties

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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