This is an exercise I did at night school a couple of weeks ago. Since I want to build a motorbike chassis it is pretty relevant.
The material is 1.25″ Electro Resistance Welded steel tube, wall thickness about 0.060″ (32mm diameter, 1.6mm wall for the metric men). This is precisely the material you might choose for a home-built chassis.
The welding wire was 1.6mm ER70-S2, the electrode was 1.6mm thoriated tungsten, argon shielding gas at about 6 liters per minute (sorry imperial men, the regulator gauge was metric).
The welding machine was a little Lincoln inverter, I don’t know the model. This is a ferrous metal job so the work and ground leads are connected “DCEN” (or DC Electrode Negative) meaning the work lead is plugged into the negative terminal and the ground lead is plugged into the positive terminal.
I had the working current set to 60A (roughly 1 amp per thou of material thickness) with a current ramp down time of about 8 seconds, and a post flow gas time of about the same. The ramp down time was set so the end of the weld cooled in a controlled manner and didn’t shrink and cause a crater. If you have a foot pedal on your TIG you control the current directly with foot motion so you can ramp down (and up at the start of the weld) at whatever rate you like.
I was also using the pulse function, and I had the pulse set to about 2 Hz (cycles per second). Some people like the pulse really quick, some like it slow. I tend to set it pretty slow, it just seems to work ok for me with basic welds in ferrous materials. The idea of the pulse is to concentrate the heat of the arc and not heat soak your weld area, so the pulse function is just that – a pulse of current from the background level to the peak level, and back again, at the speed you set. The background current set to about 20% (of the peak value), which again, seems to work ok as a starting point for me.
Now I’m not suggesting these are perfect settings, but I managed an acceptable weld. Note you can adapt your welding technique if the setting are not great – if the arc is too hot, you can go a bit faster. Normally I err on the side of “slower” with my settings. And it is preferable to stop and adjust your machine before proceeding.
What I haven’t got photos of are my test welds. I ALWAYS test the machine settings on some scrap before I do the job, and where possible I record the settings when they work well.
So on this job, the instructor wanted me to notch out one tube to weld to the other at an acute angle. So for five minutes of welding, I did 40 minutes of filing to get a good tight joint. Obviously in a production environment you use a pipe notcher or even a ball nose mill in a milling machine to zap these joints out. But I’ll tell you, it was surprisingly therapeutic to hand fit that joint, no matter how long it took.
Anyway, the pictures show the fit up. I was aiming for NO GAP between the two at all. A half-round file with approximately the same radius as the tube helps to speed things up.
It’s not really evident in the photos, but I did file a bevel on the notched tube to facilitate the weld.
Now the instructor (after I was finished) suggested the joint welding should be started in the acute angle and run out around the tube to the obtuse angle. I did this on my second attempt. The benefits are obvious in hindsight, the crappy difficult weld in the tight angle is hidden and is the place to start and you should finish on the easy-to-access area.
So I tacked it up in four places to hold it and then proceeded to weld.
In the acute angle, obviously access is a problem. You need the smallest ceramic nozzle you can get (#4 for me) and you will have to extend the electrode out of the collet a lot more to get right into the root of the joint. I aim for normal exposed electrode of 6mm past the nozzle. In the back of the joint, I needed about 12mm. I asked our instructor whether the gas flow needed to be adjusted to provide adequate shielding but he didn’t believe it was necessary.
I did about 15mm of welding from the middle of the acute angle joint and out and around then I reset the electrode back into the collet and continued around to the front.
Then I flipped it over, pulled the electrode out, started back in the middle under the acute angle, welded out about 15mm, reset the electrode and continued to the front.
Finished! Not bad for my first acute angle tube joint in decent material.
I had to wire brush it as we dip all the work pieces in a water bath to cool them and it scaled up a bit.
For lots of really good welding info, don’t listen to me, go look at the websites for Lincoln or Miller, or my personal favorite which is weldingtipsandtricks.com.
Other than that, I was pretty happy with the results. Onto the next project!