A car build I’m following that a neighbor is doing has a 3D printer for mocking up parts and they showed using the filament with a soldering point to fill voids on a joint. Check the video between 8:05 and 8:28.
Hollywood, I do something similar using a 3D pen. It uses the same filament as the printer and welds the parts together.
I’ve been using use bits of filament and a soldering/wood burning iron for years to join parts from the inside. Most recently to attach the 3 main sections of my 3281 hoppers. Sometimes I also lightly drag the iron over parts to smooth “stepping”
I do the same thing, I’ve added panes to windows I print using a soldering iron on the back side to weld things together.
That’s quite interesting.
The fellow who runs our local industrial 3D print shop demonstrated how he uses a Dremel when he is worried about potential heat distorting a print he wants to weld. He was using it to make masks and helmets.
He mounts the filament in the Dremel chuck and spins it up, then lets the friction created by applying the filament to the area needing welding create its own very localised heat to connect both surfaces and adding plastic to the weld.
I think the Dremel might have some advantages in tight spots but I suspect it takes longer than the 3d pen and wood burning set.