Introduction
I use micro spot welds to make ultralight equipment for ultralight backpacking adventure equipment. The technique enables me to fabricate items out of flimsy paper-thin titanium and stainless steel foil.
For reference here is a professional description of spot welding/
With bending, folding and curving the foil can make a multitude of precise, rigid and strong functional shapes such as rings, tubes, cones, elbows, boxes, handles. doors, tabs, loops and brackets etc.
Much of what is in this post is sprinkled elsewhere in other posts, so I thought that a dedicated post on this would be useful for fellow tinkerers.
Note: Spot welding of ‘perversely dissimilar’ metal foils will be the subject of a future post, “Does the possibility of that get you excited? Probably not enough to wet your pants.”
Micro spot-welder
This funny ugly tool is key to nearly all my stove stuff so I have put it first. It was the first serious one that I made.
I think many fellow innovators would understand this: How I put off trying it for a while for fear of it failing to work after all the effort put in.
An ode to an innovators tensions between dreaming of success and putting the dream to the first test, to maybe just finding failure:
My plans easily hold my wondrous dreams of success,
Fear of failure by testing,,,,,, I delay,,,,,,,,,,,, I confess,
After reality is tested, after time invested,
A sensation, a lesson or just a little more mess.
The welder is made of wood (my carpenter fathers medium) a big garden gate hinge (scrap), copper bars (purchased tut-tut), MIG welding tips (made of beryllium copper alloy) and redundant arc welder transformer.
Thrown into the mix is a rope, levers, weights and a pulley system, that hangs from the ceiling (from yachting experience). It provides the required consistent closing force that is needed to form consistently good spot welds.
The mains power to the primary winding of the arc welder transformer is passed through a solid-state relay that is pulsed on for a short duration using a low voltage DC control signal from a 555 timer circuit. The pulse time can be adjusted between ~0.05 and ~3 seconds.
This welder is my baby and I have watched it grow in its capacity to flexibly weld in places that at first seemed impossible. I have a gaggle of alternative electrodes that can be quickly interchanged to weld in the most unusual places (some can be seen hanging in the bathroom in the top right-hand corner of the photo below).
It lives in my bathroom because that is where I first set up the experiment. I don’t dare shift it. Maybe being in this regularly visited place of meditation makes me a serial inventor?
“Together, we have made possible the making of many apparently impossible and ridiculously light backpacking component. So it probably deserves its prominent place in my bathroom!”
The weaknesses and virtues of a solo welds
The solo weak weld. A spot weld forms a small area, usually circular, where the two contacting faces of the metal melt and fuse together forming what is called a ‘nugget’. A single micro spot weld has a vulnerability to rotational forces around the centre of the nugget.
I exploit this vulnerability to make an easily broken nugget with sub-optimal welding dwell times during welding. This will result in a weld that can be broken without making a hole in either sheet. This means that for example a formed tube can be held together with a weak welded nugget and can be tested (gauged or calibrated) for a perfect fit with another component.
If a better fit is needed, the joint can be marked with a fine scribe, the nugget can easily be broken and welded again after adjusting for a better fit and anther test. When the fit is correct the weld can be supplemented with full strength welds.
An ode to the intrinsic weakness of single spot weld:
A lone spot weld nugget is intrinsically piss-weak,
Without good company so-as-to-speak,
Two welds make rotational stability and ends fragility,
And the strength found was what I did seek.
This little Instagram video can explain this better than my words can.
The solo strong weld. Even a strong nugget is vulnerable to breaking by the rotational forces. In this case, the breaking will be much more difficult and will probably result in a small ‘nugget sized hole’ being ripped from one side or the other.
Ganged strong welds. Because of the above vulnerability of solo spot welds, I never settle for less than two well-spaced welds. It means that the destructive rotation action will not be able to destroy the natural strength. Three or four welds in a two-dimensional array are even better for preventing this type of weld fatigue.
This little Instagram video shows strength is developed by ganged spot welds.
Just for fun, I did a 10mm wide foil band with six ganged welds and this easily supported my body weight (~65kg and holding).
Conclusion
Single tack spot weld nuggets can be used to make temporary joins that can be used to test the precise fit of a component before final welding with multiple strong spot welds. They can make extremely strong joints if ganged appropriately.
Tim
