Welding ABS the easy way

[enlpck]

On occasion, the question comes up about fixing or joining plastic, so I thought I'd show the technique. A couple weeks ago, some $%^^%$#@ hit one of my bikes and I ended up with a bunch of cracked fairings and broken mounts. The common responses are buy new ones (about $2000 for this bike... not gonna happen), glue them up, screw/pop rivet them up with backers, or fiberglass them. The fairings are ABS, one of the most common structural plastics on vehicles,but the techniques work for a variety of other thermoplastics as well.

There are advantages and disadvantages to the various repair methods, but all have drawbacks. Glue up can be real messy and can leach out the plasticizers, making the material brittle, needs good fitup, and getting the parts clean enough can be tough. It is also not suitable if parts don't fit well or small pieces are missing (large pieces need to be made up from new material anyway). Also, the glues make a mess out of paint and can damage other plastics (like lenses on lights). Screws/pop rivets are suitable for an emergency, but look like crap and don't hold up. I use clear packing tape and stitch with stainless wire in cases where This would be appropriate. And fiberglass? I HATE working with it, and have moral reservations against using it to repair anything but fiberglass.

The best option is welding. This can be done by spending a couple hundred dollars on a hot air unit (even the harbor freight kit is about $150 with a coupon), using a soldering iron (results look like crap, and it is real easy to burn the material, which requires cutting it out and filling the void), or friction welding.

Friction welding is easiest and cheapest.

I use a Dremel tool to spin the filler. The filler is 1/8 ABS rod (from McMaster Carr, but the packages from Harbor Freight have are probably fine) held in the collet of the tool. Speed is low, and the extension is about 3/4" max.

The first set of pictures shows the setup: This is a sample since I didn't take good pics of the repair work

Prep of the samples: bevel about 30 degrees. Note the chuck key. That is used later as a follower for the weld material


Filler rod in the collet


First tack from the front


tack from the root side. Note that the penetration is not quite all the way through. This will be dealt with later (the tack is on the right end)


(several more posts to follow)

[enlpck]

Repositioned for the second tack (I like bench work for this. Large awkward part can be a real pain)


Second tack in place. parts are in plane and lined up. I used a straightedge while the first tack was hot and soft, then again while the second was


Repositioned to lay the first pass in flat. The technique is pretty easy: spin the rod (low speed on the dremel.... about 5000RPM) and apply GENTLE pressure. The frictional heat melts the base material and the filler. Work to both parts, as you need both parts to become plastic for fusion to occur. The chuck key handle is smooth and rounded on the end, and the end is used to follow the fusion point. It is used to form the material and smoosh it in to the joint. It can also be used on the bottom to control push through.


First half of the first pass. Consumed the first tack. The second (and the stop) will be ground with a small ball end cutter (3/32" engraving point) to allow for full fusion. ou can see the consumption on the base material (due to the spin, care needs to be taken so it isn't all one side). It actually goes in a lot like 6010 on steel


Ground out

[enlpck]

First pass is done. It is under flush so a second pass will be layed in


Second pass is in. This was run in one shot. I had to extend my filler to about 3/4", and ended just about on the collet nut.


The cover pass was done following with the chuck key handle layed across the joint. There was a little cold lap, but the fill is complete. The weld can be flushed down later.


This is the root side. Note the heavy push through over much of it. The prep edges were fully consumed. It isn't all the way through everywhere, so....


A little grind, and a cover pass will follow

[enlpck]

Root finished using same technique. Not as much filler was needed, since most of it was full fill to start with. Note, again, the cold lap where the material was smooshed out


Root side cleaned up. This was done with a 3/8"dia ball end cutter. It is nearly flat, and there are no stress risers left. It could be shaved smooth for paint.


Section through weld (hacksaw cut). Note that the fill is full, and the face side was not dressed down.


Another shot of the section cut. Different lighting.


I did bend and tension on several test pieces, and the weld material has similar properties to the ****** material used for the tests. It has better properties than the nearly 20 year old material on my bike.

[mikecwik]

the coupons look much softer than your work plastics would be. if so, was there a great deal of difference in how they welded?

[bandsawguy]

This thread is causing me to flash back to my childhood. I can remember one Christmas getting a plastic welding kit. Consisted of a bunch of plastic I-beams and flat panels. Also a small battery powered (welder) which spun little plastic rods that fit on the end. I can remember building a top fuel funny car model and then crashing and re-welding it repeatedly. Must have been the trigger of my welding hobby/career. Thanks Dad and Mom.

Doug

[whateg0]

Wow! This is great information!!! I have tried using a heat gun before to weld ABS and always had trouble controlling the heat. This looks much better. Gotta go to HF tonight and get some plastic rod. I have a hood from a John Deere mower that is cracked in a couple of places that I need to fix...

Thanks!!

[enlpck]

the coupons look much softer than your work plastics would be. if so, was there a great deal of difference in how they welded?

The material I was repairing (pics if I remember later) was not that different except for being somewhat brittle from age. It was black ABS (not the v*rg*n material I used for the demo, and it is easier to see what is going on.

Bandsaw: I had the same kits. That is why I went with this method. In fact, those kits were styrene structural and ABS filler

whateg0: Just be sure the material and filler match. The HF fillers come in assortment packs. I tried it, and found that the rods varied a lot in diameter, but it works. Went with the sized rod from McMaster Carr when I ran out of the HF stuff. More consistent. Be careful not to dig too hard, and you will need to follow to smoosh the hot material in to get a good bond.

[Pangea]

Friction Stir Welding? Sounds familiar.

[hockeyguynick]

Cool, always wanted to see how it was done, and how it turns out... Time for a harbor freight run

[Grebbler]

This thread is causing me to flash back to my childhood. I can remember one Christmas getting a plastic welding kit. Consisted of a bunch of plastic I-beams and flat panels. Also a small battery powered (welder) which spun little plastic rods that fit on the end. I can remember building a top fuel funny car model and then crashing and re-welding it repeatedly. Must have been the trigger of my welding hobby/career. Thanks Dad and Mom.

Doug

Spin Welder! I had a blast with that thing. I was always welding mom's hair brushes and barrettes together.

She never really forgave me for that...

Now I have a bit of free time, a Dremel and some HF rod leftovers from my burned up plastic welder (the crappy $40 model - don't get one) and I am off to cause some damage in the shop. BRB