What is the Backstep Technique?
Basically, its when the direction of weld progression is in one direction, but the overall progression is in the opposite direction.
And for thin sheet metal, it can be a good way of limiting distortion.
The backstep technique uses a lot of stops and starts.
And stops and starts are where defects happen more often.
But the benefits of limiting distortion often outweigh the risks of a defect.
And as long as you taper amperage nice and slow on each stop, the risk of a defect can be lessened.
I am saying this as someone who has sent literally hundreds and maybe even thousands of backstepped test welds to X ray for welding certification on all types of alloys like 4130 chromoly, 15-7ph stainless, Inconel 7018, 6AL4V titanium, and Haynes 188 cobalt alloys.
These alloys are very crack sensitive but still passed X ray testing using the backstep technique because the welders were instructed to taper amperage slowly while continuing the torch movement on the stops.
Aluminum backing really helps to not only limit distortion by pulling so much heat out of a part...but also provides a way to trap argon on the back side to shield the weld almost as well as argon backing gas.
I welded 2 plates ...one with the aluminum chill plate in contact with the .043" thick cold rolled sheet.
and one with some spacer plates to lessen the chill factor.
The plate clamped directly to the thick aluminum chill block took 70 amps to penetrate and could have used 10 more amps.
Just by using some steel spacer plates, the amperage needed was only 55 amps.
that just goes to show that even though there is a rule of thumb that says one amp per thousandths of thickness will work on carbon steel butt joints, that goes out the window when chill blocks are used.
I used the Furick #8 pro clear cup for this video because it not only provides really good shielding , but also helps me to see better.
Being a clear cup, lights up like a light bulb and helps me to see where I am going. No BS here. you just have to try it and see for yourself.