Plastic Welding Revisited

Last time we talked about a video that purported to do plastic welding, we mentioned that the process wasn’t really plastic welding as we understood it. Judging by the comments, many people agreed, but it was still an interesting technique. Now [Inventor 101] has a video about plastic repair that also talks about welding, although — again, we aren’t sure all of the techniques qualify.

That’s not to say there aren’t some clever ideas, though. There are several variations on a theme, but the basic idea is to use a bolt or something similar in a soldering iron, metal reinforcement from things like wires and staples, and donor plastic from a zip tie. While we don’t think the nylon in a typical zip tie is the best way to repair anything other than nylon, if you were repairing something 3D printed, you could easily swap out the tie for filament of the same material, which — we think — would bond better.

The custom soldering iron tips made from copper wire probably have a few uses, too. Every time we see one of these videos, we think less about repairing plastic and more about reinforcing 3D prints, but maybe that’s just us.

If you want to grab the comments about the other post we saw someone using zip ties and a glue gun to “weld”, you’ll have a bit of reading to do. We think of proper welding as having a compatible kind of plastic and some form of heat, even if it is from friction.

27 thoughts on “Plastic Welding Revisited

  1. This is fantastic, I learned so much! It’d be amazing if someone did an equivalent video of ways to fix fabric for people who can’t sew, or can only sew very basic.

    1. A keyword you may want to search is “darning.” Darning is a technique to repair holes in fabric using only needle and thread (no patches). There are many great instructional videos on YouTube and I’m sure there’s at least one that will click with your particular learning style :)

  2. I feel this is almost at the level of a DIWHY but I guess it qualifies as a quick and dirty hack. For plastic repairs, I would think that the correct plastic epoxy/glue (for the specific plastic) would work better as they function by chemically dissolving then re-bonding to the polymer chains that make up the plastic. I guess the metal reinforcement is novel and a good idea, but when you overly/quickly melt plastic, especially in a non controlled manner it damages the polymer chains, especially on previously formed plastic. At least for 3d printing, the temperatures are generally controlled to be as low as what works. This method of fixing likely leads the resulting plastic to be overly brittle and prone to re-breaking, especially for plastics that aren’t generally considered a thermo-plastic. With the epoxy method, it would probably be easier to also fill in aesthetic side as well, similar to using woodfiller.

    1. I don’t know of any epoxy or polyester resin based glues, or any glue for that matter, that will make a servicable joint/repair in most plastics that I have had to repair. I know you can glue (chemically weld?) styrene, pvc, cpvc, and (barely) abs. Any of the polyethylenes or polypropylene and several others seem impervious and I have even tried heating solvents that are suposed to disolve some plastics to no avail. I have had good success with an old fashoined soldering copper heated with a torch with a scrap of the same type plastic for filler after cleaning or cutting a groove in the crack\break. Practice on scrap and dont get too hot (brittle). You have to sculpt it a bit but you can pretty it up with a file after. weed trimmer line worked a couple times. Mixing plastic types hasn’t worked for me, maybe if they had really close melting points? Last time I fixed the lower corner hole in a 5 gal fuel tank on a zero turn mower with a strip of the top cut out of a 55 gal plastic drum of same color and material, still working after 5+ years so ok

    2. I agree with Todd3465 that glues often don’t work. A trick I often use is drill a few holes in both sides and then sew them together with some rope soaked in epoxy. This will create a very strong composite. If you want you can poor some remaining epoxy in the crack.

  3. I have one of those soldering gun looking “welders” that melts staples into the plastic. I use it quite often in my shop to repair lawnmower hoods – especially the green John Deere crap. After using many different means of “welding” plastic over the years, this was one if the best gadgets I’ve ever come across.

    1. Years ago I bought Horror Fraught’s plastic welder. I was marginally successful fixing a couple of items. If I’d know these techniques, I probably wouldn’t have wasted my money on it.

  4. I sometimes chemically weld my ASA prints; lightly dissolve the contact sides with MEK, press them together, MEK dissipates: there you go, one continuous item of ASA!

  5. Inserting the metal reinforcments looks like a good idea. For example the handle of the protection glass is something I would say earlier impossible to fix. (Impossible meaning in this context: does not worth the effort.) The area where glue bonds is too small and it will break again in a minute. If the metal insert really fixes it permanently then the technique has its place in the quick hacks that actually work category. I will try it the next time the kids bring me something to fix.
    Besides being useful the video was also pleasing to watch. Thanks!

    1. It does seem logical to use the same filler as the base material. However, when you’re melting the plastic, the filler gets mixed in with the base material with the end result being an alloy of the different plastics, and this can give very good results. But it does of course depend a lot on the plastics that get alloyed.

  6. When we were kids, we had a toy set that you could weld plastic to make skyscrapers. Then you snap on the facia. And Walla!

    My brother had a plastic moulding machine that injected hot melted plastic in a mould. In the early 1970s, we had the most dangerous toys ever! Yes lawn darts and Super-elastic bubble plastic, too!

  7. Do this outside.
    With a fan.
    Or maybe a respirator.

    “Various nylons break down in fire and form hazardous smoke, and toxic fumes or ash, typically containing hydrogen cyanide.”

    Huh. That’s funny. When reading about 3d printing with Nylon the warning I remember reading many times was that overheated Nylon produces a neurotoxin. I was surprised not to see that word prominent in the results. Maybe that’s the hydrogen cyanide.

    “HCN is a systemic poison; toxicity is due to inhibition of cytochrome oxidase, which prevents cellular utilization of oxygen. Inhibition of the terminal step of electron transport in cells of the brain results in loss of consciousness, respiratory arrest, and ultimately, death.”

    Um.. ok. That’s bad enough.

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