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Plastic Welding

The subject of plastic welding has had my curiosity for some time. When I decided to "get into it" I spent days/weeks on the internet reading everything I could find and watching countless videos. I soon learned that plastic welding is a huge area with many techniques, materials, and tools.

In keeping with the nature of the site my focus here will stay with what the typical motorcyclist is likely to encounter. I'm not trying to be another scientific resource, just a non-informal resource intended to help you maintain your ride.

With that said we will talk about welding the most common plastic encountered by motorcyclist which is ABS. Most plastic motorcycle parts are made of ABS which is very easy to weld with inexpensive hand tools. With a single 40 watt soldering iron you can repair most ABS parts on your bike. On my Hondas most of the plastic parts I've looked at have the marker ABS molded into them.

As a college trained and very experienced Electric Welder I find little in common between the two and would describe plastic welding as shown here as a cross between wood burning arts and soldering. It is important to note the theory that our goal is to melt the base and filler materials together. In Electric welding this mixing of materials for the most part just happens as the liquid steel flows together with a little help from the flux and the small movement of the electrode. With plastic welding that mixing does not happen without mechanical intervention ie: you will need to mix the materials with the tip of the soldering iron in order to get a good weld. Just heating the materials and placing the tip on the welding rod will allow you to melt the rod and lay it over the weld but without the mixing of material the strength will be poor as the rod will just be laying on the surface.

For those who want to know more about other plastics check the web. There are numerous techniques to determining plastic material which is important when choosing a welding technique.


Tools

Airwelder. This tool has a heater and blower in it. It works by heating the tip and blowing hot air out of the tip. This tool is rated at 350 watts and is useful only with the thinnest of materials. Should you decide to buy one look at tools in the range of 1500 watts. This tool is not really needed for most motorcycle parts.




Soldering irons
. I use 2 irons for most of my work. A 40 watt and a 75 watt. On ABS the 40 watt is sufficient. For welding GTX (Harley-Davidson Fairings) the 40 watt was only capable of providing tack welds. Using a 75 watt iron on GTX was much more productive. NOTE: once you have used your iron for plastic welding no amount of cleaning will leave it usable for soldering again. When new the irons have a coating on the tip that is removed when plastic welding. Once removed the solder will not flow on the tip and applications of flux do nothing to help.




Harbor Freight Welding Iron.
This is a 70 watt iron from Harbor Freight packaged in the plastic welding kit. Like the reviews said the tip is soft and bends easily when hot. While the large triangular tip is handy for smoothing welds with the tip bending as easily as it does it spends most of its time in my tool box.  About the only time I use it is when embedding re-enforcing wire mesh into welds as the larger footprint makes the task easier.




Dremel variable speed motor tool.
I've had this tool forever and since working with plastics have used it more than I ever have. Useful for prepping the area, v grooving materials, or cleanup afterwards this is a must have tool.





XACTO knife. This is another tool I've had forever but have found a new use for. This handle allows you to change blade shapes and sizes. This wide blade is handy for weld cleanup and bathroom calking removal.





Supplies

Welding rods from the Harbor Freight welding kit. These are identified by color stating the material. While helpful in identifying the material the poor choice of colors is a limiting factor. There are multiple vendors on eBay and the internet selling welding rod. Note the rod material needs to be matched to the type of base material you are welding.




Reinforcing mesh.
This product came out of the Harbor Freight welding kit and is stainless steel screenwire. Embed this into joints where additional strength is needed.




Sheetstock
. These are some ABS shapes that I bought on the internet. The variety of shapes, colors,and sizes is limitless.





Projects


In this set of pictures we will walk through welding a filler piece into a Vetter Fairing. I've looked up Vetter products and Vetter states that their fairings produced in the late 70s and early 80s are made of ABS. This is an easy material to work with. This particular fairing is a Windjammer 5 which has holes cut in it behind the turn-signals for  the optional Vetter horn kit. The holes allowed the sound out and rain water in.




Remove the paint from the area to be welded. I used the Dremel with a stone and sander to remove the paint about 3/8" back from the weld. When you have the paint removed clean the area with Rubbing Alcohol.





Cut out some filler pieces. I used some ABS sheet stock that I bought for another project. Note this particular material has a textured and a shiny side. The textured side photographed better. marked the parts out then cut them with tin snips saving all the little pieces for later.





Tack weld a piece of rod or similar to the piece. Its hard to hold a flush piece if you can't access the backside. This also prevents you from loosing the filler piece into the fairing. This repair is a non-structural repair and therefore I wasn't real worried about fit. Filling gaps is no big deal with plastic.




Holding the iron tip at 90deg to the weld make a series of tack welds by gently forcing the iron into the material to approx the base/root of the weld. Move around the piece





With the piece tack welded in, turn the iron so that the tip is lengthwise with the seam and work around the piece forcing the tip to near the bottom of the seam. This action forces some material to the base of the weld and Vee's the opening so that the full depth can be filled.




Add filler. You can buy filler rods and you can also use the base material. The best filler is the same material that you are welding. These are the scraps from cutting the filler pieces which I use as filler rod.





Using the iron tip work the material that oozed up to the surface back into the weld at the same time depositing a little filler stock. You will need to "work" the weld a little with the iron tip to mix the different materials. Its possible to simply press down and get the material into the fill the void but there is not nearly as much strength gained as when mechanically mixing all the materials with the iron. Note: if an area becomes too hot it will become unstable so jump around a little. As the seam fills work the plastic with the tip similar to frosting a cake producing a smooth surface



That's all there is too it.







From here the part can be sanded and prepped as standard body prep. In my case these areas are behind the tun-signals so all I had to do was paint them flat back.


In this view, a 1/2" hole in the center of the dash and cracks extending 2" either side have been repaired. The hole was drilled for a Vetter Sound system and the cracks were stress cracks from the fairing flexing at the dash hole.




Hole plugging visible. Here is a Harley Davidson inner fairing that is now on my Honda. If you look you will see 3 holes that were plugged and welded from behind. In this case I used the part that covers the handlebar risers (not used on a Honda) as the filler material as its the same color, texture, and material as the inner fairing. Note that the filler plug shaping was more important and I spent a lot of time with the Dremel getting the plugs to fit tight.




Also on the HD fairing I added speakers to the large gauge openings. This required that I make some bosses for the mounting screws to anchor into. Here are the bosses that have been shaped from 3/8 ABS round stock. These were welded to the backs of the openings along with some bosses that I reclaimed from the discarded piece.




This picture is the back side of the inner fairing with the plugs and relocated lower bosses visible.




This is a closeup of the relocated bosses welded into place.



HD fairings are routinely identified as ABS and also Fiberglass. Both are incorrect. On mine I found a GTX identifier which is a proprietary product from DuPont made primarily from ABS and Nylon. It is much harder than ABS and welds at a higher temp. I fabricated a lower dash assembly under the stereo and found that welding ABS sheet stock to it required more heat and more mechanical mixing of materials to produce and reliable weld.

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