A numerically controlled shape memory alloy wire bending process using vat photopolymerization

The fabrication of shape memory alloy (SMA) based products requires the precise bending and high-temperature training of SMA wires to obtain desired two-dimensional (2D) and three-dimensional (3D) patterns. In the typical fabrication process, SMA wire is bent and fixed in a pre-built mold and is trained using a furnace. However, in the small batch production, the fabrication of a mold that can be put in a high-temperature oven is costly and requires a long time to fabricate. A novel SMA wire bending process using vat photopolymerization (VPP) is presented in this paper. A rotary wire extruding system was designed to control the feeding speed of the fed wire and the bending of the wire into the desired shape. The wire bending process was enabled by utilizing a VPP tool that was immersed in liquid resin to selectively cure the resin to firmly fix the extruded SMA wire on a substrate. An air bubble assisted separation process was developed to address the separation of the cured resin from the immersed VPP tool. After the bending of the SMA wire into the desired shape, the SMA wire was connected to an electric current to heat the wire to a high temperature required by the training process so the SMA wire can memorize the fabricated pattern. Finally, the photocured fixtures deposited by the VPP tool were dissolved by a chemical solution and the bent SMA wire was detached from the fixture that was ready to use. The developed numerically controlled wire bending process is flexible for designed patterns and can fabricate SMA wires into 2D/3D shapes without specific molds or tedious manual work. Several test cases were performed to demonstrate the effectiveness of the newly developed SMA wire bending process.