A novel approach to the electromechanical integration of NiTi-SMA actuator wires

Shape memory alloy (SMA) actuators are attractive for a variety of applications in different fields due to several outstanding properties. In mobility, both ground and air, lightweight construction is an issue that can benefit from the high energy density of NiTi-SMA. Also, noiseless operation, high actuator performance, and good cyclic stability are reasons for the use of NiTi. Another important property is the high corrosion resistance of NiTi SMA. However, even if an actuator component can withstand a corrosive environment, it still has to be integrated into its surroundings. And today, that is mostly achieved with crimps that are made of malleable metals such as aluminum, which are not as corrosion resistant as NiTi. In this work, we present a novel approach for the integration of NiTi-SMA-actuators that eliminates the crimping process and hence, the use of different metals, by applying a force-fit connection made of the NiTi wire itself. To achieve a defined shape, laser melting is utilized, generating a sphere at the wire end. The electrical connection, required to activate the wire actuators, is ensured by welding copper wires to the spheres. Our results of both microstructural and mechanical characterization show that the form-fit connection is suitable for cyclic and high-force actuator applications. A side effect with a nonetheless important impact on costs is the reduction of complexity for automatization. Just the wire has to be handled, not the wire plus crimping. In our opinion, this technology might represent an important step towards the standardization of SMA.