“We thought, ‘Why not get an industrial robot, attach an advanced welding machine to it, and see what it does?’” says Tim Geurtjens, chief technology officer of Joris Laarman Lab and its spinoff R&D company, also called MX3D. First, the team developed software to control the industrial robotic arm. Then they attached extruders—the parts of printers that push out material—to it and started printing with copper and aluminum. Most 3-D printers attach the extruding tools to a frame, which gives them three axes of movement. The MX3D has six: It is a mobile, freely moving robot that can travel with and around the printed structure to build an object of nearly any size or shape.