An assembly is provided for induction welding. This induction welding assembly includes a fixture. The fixture includes a first support structure and a second support structure. The second support structure includes a frame and a plurality of trunks. Each of the trunks is connected to and repositionable on the frame. The fixture is configured to secure a workpiece vertically between the first support structure and the second support structure using the trunks during induction welding of the workpiece.