During the semester and summer of 2025, I worked with a start-up developing a concrete 3D printer using robots that move and extrude wet concrete. I was a mechanical engineering intern, where I helped design, analyze, and manufacture crucial parts for the robot. I designed the full CAD assembly on SolidWorks and designed new parts such as the printhead mechanism and conveyor holder and manufactured them using 3D printers and welders with sheet metal and metal beams.
Joining an emerging start-up building construction 3D printers, the lack of mechanical engineers on the team meant that electrical engineers, civil engineers, and the business operations team handled the CAD design of the robot. I wanted to create an overarching CAD assembly for the robotic 3D concrete printer to manage changes, complete motion assemblies, and design more accurate parts for the future. Measuring existing parts in the prototype, I created an assembly with 60+ unique parts, ensuring accuracy using calipers. When designing and implementing new parts, the overall CAD assembly was used to verify fit.
For instance, the z-axis gantry with the threaded rods needed to be adjusted to reduce bending and shear stress as the chassis moves up and down in the z-direction. The holders for the threaded rod mounts were designed, and the dimensions were verified using the CAD. As a result, we eliminated friction and stresses on the rod and the chassis moved up and down, allowing for smooth layer height adjustments.
The tensioner idler position was set to create the ideal tension for the belt length we had available. We initially faced the problem of the driving wheel not being able to transfer the rotation effectively to the driven wheel with the threaded rods. I designed a tensioner idler mounting point and verified the belt length using the CAD assembly.
The helical screw within the printhead.
While testing the prototype of the robot, a problem we ran into was the slow print speed. The concrete would not extrude out of the printhead at the desired speed, causing problems forming and building the concrete layers properly. I identified the problems as being associated with the design of the printhead itself. There was not enough pressure being generated to rely solely on the gravitational force to push the concrete downwards and out. I tried to come up with a mechanical solution to push and extrude the concrete. Looking into several dispensing mechanism designs, I decided to use an Archimedes screw. A major reason for this is its ability to move concrete forward to extrude, but also mix and distribute concrete in the back of the printhead. This prevented concrete from solidifying too early, which greatly reduced extrusion speed.