Friction Welding: An Idea Worth Sharing

Here is the idea.

Instead of heating plastic through external temperature sources, you can generate heat through friction between pieces of plastic.
This isn't novel but its been over looked for some reason.

Here is the setup I'm currently using.
I have a speed controlled drill (a battery powered dremel hooked to a variable power supply), with a piece of 5/16th ABS plastic welding rod in the chuck. I then apply the plastic rod rotating at high speed to a plastic sheet I'm working with. Holding the drill in place creates friction at the tip until a blob of molten plastic begins to form. This blob remains at the critical melting temperature of the plastic. I can now move the blob of plastic around slowly. I can also control how much plastic I'm depositing by changing the pressure applied to the tip, and the angle of the drill.

I've used this technique, along with using acetone as a plastic solvent, to rebuild plastic hinges on toys and build structural parts for a robot.

My current project is to incorporate the drill into a robotic arm, with the goal of building 3D objects out of plastic using this technique as a proof of concept.

The downside of this technique is that it needs very good precision and patience to get a decent weld.

The benefits however are that there is no need for scaffolding because the
plastic cools very rapidly due to being held constantly near its melting point.

-There is little waist if you can control the speed properly and can go slowly (high speeds can mean plastic splatter).

-Because the plastic is held near the melting point, you can work vertically

-This is a truly additive process, were a previously made cup could have a handle added to it later.

-In conjunction with a drill, this becomes an additive and subtractive process, which turns a fabrication tool into a general purpose 3D processing tool (This would be hard but possible).

-You can easily change the resolution of the tool head by using smaller plastic rod stock.

-I have exclusively used ABS plastic, but I assume that all thermal plastics have similar properties.

About me:
I'm a University of Oklahoma undergraduate senior who came up with this idea when struck with the limitations of working with plastics for a Robotics Club project.

This is my Holiday gift to all of you for sharing a fascinating project with the world,
Lawrence Kincheloe

Hi Lawrence,

... nice idea, but i didn't think it's precise enough for automated fabbing.

Whereas it's possible to build manually every shape you want, you didn't have the control or feedback which will allow a precise additive fabbing over larger areas or volumes ...

Viktor

I would expect problems spinning a 5KG reel of ABS at high speeds but perhaps an oscillating motion (like use for cast-cutting saws) would also cause enough friction to melt the plastic.

I think that's a good idea for fusing two large printed plastic parts into one huge one that we couldn't print in one piece.

But this is not really a rapid process from what I've seen with commercial friction welders (that are working a little different though)
I'd guess it'll take more than a while to actually print one of our cornerblocks for example using this method.

But just tell us Lawrence, since you're the one with the experience, what do you think how many plstic can you deposite per minute using this technique?

'sid

Thank You all for looking over this idea, and for the feedback.

Viktor: I completely agree and I've run into similar problems due to a lack of stiffness in the RC servo powered robotic arm I'm currently testing with. I do however feel that this is a solvable problem with a better arm.

JohnWasser: I'm actually spinning small snips of reel ABS. I've thought of how to feed it in and at the moment it involves something very similar to a mechanical pencil. Feeding material isn't a solved problem yet.

sid: It would work for what your mentioning, although I'll get to what I think this would be useful for below.

I would estimate, from my experience and general fictitious number calculations, that to make a 5 cm solid cube would take approximately 4.6 hours using one drill. The beautiful part of this process is that I could use multiple arms and drills to linearly improve production speeds. Also, hollow parts are possible with this technique, although technically more challenging.

This process isn't very appropriate for scaled fabrication. It is however very appropriate for flexible prototyping that needs to be worked and reworked. I also believe that although its a much more complex precess, I see a lot of possibilities that are not possible with other techniques.

I would like to put in one disclaimer. I don't know a whole lot about industrial processes. I've just now finished banging my head against forward and inverse kinematics for mobile manipulators. My main goal is to point out another fabrication technique, show off some results of my own work that seems relevant, and to engage in discussion.

Lawrence

Hi Lawrence,

... we had in past some discussions about fabbing with a pick'n'place-head and prefabbed elements - maybe small spheres or bricks.

Imagine a magazine supporting an endless count of small plastic-balls (maybe 1mm in diameter), a dispenser-needle (~0,8mm OD) with vacuum as gripping element, and last a heating element (maybe with friction-heating) which melts the lower half of the ball, so the head can place and weld it to the desired position ...

Viktor