New 3D Printing Technique – Friction Welding

Even though 3D printers can fabricate complex shapes that would be nearly impossible to mill, they are not well suited to designs requiring bridging or with large empty spaces. To overcome this, [Scorch] has applied an easy plastic welding technique that works with both ABS and PLA. All you need is a rotary tool.

Friction welding” is the process of rubbing two surfaces together until the friction alone has created enough heat to join them. Industrially, the method is applied to joining large, metal workpieces that would otherwise require a time-consuming weld. In 2012, [Fran] reminded us of a toy from decades ago that allowed children to plastic weld styrene using friction. This modified method is similar to stick welding in that a consumable filler rod is added to the molten joint. Inspired by our coverage of [Fran], [Scorch] experimented and discovered that a stick of filament mounted into a Dremel works just as well for joining 3d prints.

That is all there is to it. Snip off a bit of filament, feed it into your rotary tool, and run a bead to join parts and shapes or do repairs. Friction welded plastic is shockingly strong, vastly superior to glued plastic for some joints. Another tool for the toolbox. See the videos below for [Scorch]’s demo.

34 thoughts on “New 3D Printing Technique – Friction Welding

    1. Actually friction stir welding (FSW) does not consume the tool, or bit, so when the procedure is done, you can usually reuse it on another FSW. It is technically a forging technique, not a welding technique. The tools spins up fast enough to melt and mix the material of the two pieces together which are held against each other at high pressures so they stay where they want them to stay. and the tool is then removed from the weld area. The procedure in the above video is more akin to extrusion without the melting head…the heat is generated instead by the spinning friction, and the melted material is deposited on or in the spaces between the parts more like a hot glue gun….

    1. Indeed. Fran Blanche’a said video is linked in the middle of this article where I mentioned her by name. According to [Scorch], seeing it on Hackaday from her was what inspired him to apply this to 3d printing.

  1. Not sure if I would call it new since friction welding has been around pretty much since plastics have been a thing. First time I remember hearing about it was a few years ago from someone who was trying to recreate a friction welding toy from the 70s(? it was somewhere around there)

    Definitely useful tho :)

    1. Yep, scroll up. “[Fran] reminded us of a toy from decades ago that allowed children to plastic weld styrene using friction.” Was the inspiration for trying it on 3d printing filament.

  2. Plastic friction welding is used all of the time, though it’s usually referred to as “ultrasonic welding” or something similar. The theory is the same, even if the method of getting there is different: plastic is rubbed together until it melts.

    1. I thought ultrasonic welding just heated plastic by vibration (invisible, uberfast, vibration), not rotary with a fill stick. I used one ten years ago but I honestly can’t remember anything about it. Ultrasonic welders are stupid expensive IIRC.

      Haven’t seen anyone use it for 3d printers yet.

      1. That’s the difference between ultrasonic friction welding and friction stir welding. The mechanism of operation is the same (rub plastic together until it melts), but the method to get there is different.

        At least that’s what I was taught, I could be wrong.

        1. Sorry to interfere, but frictionwelding can be done with or without materialfeed in both methods. The main difference is that of use: A friction-stir – welder has to touch (nearly) all the space where the connection will be. That means that for thick connections you have to use a broad head for reasons of stability (you cant make a thick connection that is slim). On the other hand stir-welders are cheap, and the stirred up connection is stronger esp. for connections between different materials. A ultrasonic welder can be set on the surface of materials and connect very thick pieces without destroing its surface. On the cons, they are quite expensive and since they do not stir connections between different materials may be weaker than those that are stirred. As an example I’d give you ‘”Stainless” steel’ and Iron.
          Sorry for the bad english (Austria).

    2. I built some (unrelated) machines for a small factory that made water filters some ten years ago, they friction welded some of their filter containers, a cylindrical tube with an endcap, spin the endcap while pressing them together, a nice watertight weld in a few seconds.

    1. [Scorch] claims it works equally well with both materials. I’d expect it’s superior to acetone if for no other reason than that it typically runs a bead and thus adds some buttressing. But that’s not apples-to-apples.

      1. For thin parts this may very well be, but the chemical weld with acetone gets better with more contact surface, while the bead will only contact along the outline. I suspect the point where acetone is better than this method is the point where the combined contact area of the bead is lower than the touching surfaces, or somewhere in that area.

    2. I would guess for a broad joint/fracture like the robot head, solvent welding would be stronger due to large internal surface area. On smaller joints, friction welding would be stronger since it builds up a bead. No reason the two couldn’t be combined, though.

      Joining the hexagons together into the Buckyball shows another aspect, where strength works against you. You would not want lay several hexagons flat, and fully solvent weld their outer faces together; as it wouldn’t be flexible enough to later shape. Instead it looks like [Scorch] is applying a thin friction weld to the inside edge of each face only, forming a flexible “living hinge”. Clever. Then once the ball is fully constructed, you can reinforce with more friction welds on the outside.

  3. This is a handy option. My kids had a toy helicopter years ago that was assembled with a spin welder tool, and special clip on plastic weld sticks. I never thought of using a Dremel and filament like this. A good idea :)

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