Additively manufactured temperature sensitive actuators made of shape memory wire reinforced polymer structures

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The aim of the project is to develop a manufacturing process for three-dimensional temperature-sensitive actuators and to generate a comprehensive understanding of the material based on the process-structure-property relationships. For the project, the Arburg plastic freeforming (APF) will be used, which has already been developed for the implementation of continuous glass fibers. Existing methods for the production of temperature sensitive actuators are based on the manual positioning and embedding of shape memory wires (SMW) made e.g. of nickel-titanium alloys. These manufacturing strategies are therefore comparatively complex to manufacture and do not offer the possibility of depositing wires in curved structures. The freedom in shaping opens up further possibilities, such as the electrical activation of an actuator consisting of a meandering SMW deposited in a thermoplastic matrix material. For this purpose, potential thermoplastic matrix materials which fulfil both the mechanical and thermal requirements are selected and qualified for the APF process. From a process-technical point of view, the composite is optimized with regard to the processability of the wire, whereby, on the one hand, limits of the minimum discharge radius are determined and, on the other hand, the minimization of porosities within the matrix material is aimed at. During the entire development process, the actuators are characterized and optimized with regard to their microstructure, quasi-static and cyclic mechanical properties. The focus is on the thermomechanical material properties to estimate the activation temperature and the deflection of the resulting actuators. Therefore, an analytical model is used for the design of the actuator with the help of the determined material properties. In addition, the interfacial strength between SMW and matrix material is measured and increased both by the previous material selection and by suitable surface treatment of the wire. The position of the wire along the pressure path is validated by computed tomographic analyses and adjusted if necessary. For an efficient use of the SMW, an optimization model is used which adjusts the filling content locally and fully automatically in order to achieve a given deformation. After successful development of the printing process and the mechanical models, a functional demonstrator in the form of a two-finger gripper is designed and manufactured to finalize the project.