Building the Ultimate 3D Print Welder

3D printing pens are pretty gimmicky. Some particularly talented people can make cool things with them, but the “3D doodling” idea really doesn’t work for the vast majority of us. Still, we can put 3D printing pens into service as plastic welders. The problem is that they aren’t particularly good at that, either. So, Alex from half-baked-research set out to build the ultimate 3D print welder.

As Alex explains, joining two plastic parts in this way is more like welding than it is like hot-gluing. With hot glue, you’re just sticking two parts together. The heat’s only purpose is to liquify the hot glue stick. When you weld metal, you’re actually making both the parts and the filler molten. That causes them to all flow together and become a single piece of material. That’s very strong (weld joints are typically stronger than the surrounding material) and that’s what we want when joining two pieces of plastic — either 3D-printed or injection-molded.

Alex’s plan was to make something akin to a MIG welding gun: it heats up the filler (the filament) and the pieces to join, while also feeding the filler. But extruded thermoplastic doesn’t flow like molten MIG wire does, so Alex’s design has some special provisions to help with joining.

The hardware is standard 3D printing stuff: basically everything from the extruder carriage jammed into a handheld tool. Most of the components are generic, but Alex did use a Bambu Lab hotend (which has an integrated nozzle and heat break). Alex’s intention is for the nozzle to melt both the filler filament and the thermoplastic on the parts being joined. But he also including a kind of aluminum “tamping” tool, which helps to really squish the molten plastic together and create a solid bond.

Alex even tested the strength of welds done with this tool compared to other methods and displayed the data, despite the fact that it doesn’t make his tool look amazing. Personally, I respect him for having the humility to do that. But while his tool doesn’t produce welds as strong as the hot air technique does, they are better than a regular 3D printing pen and they are cleaner, too. More importantly, this tool doesn’t damage and deform the surrounding plastic, which hot air tends to do.