Aluminium spot welding for the Homebuilder?

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AdrianS

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A quick search gives

Thermal conductivity:
Al 235
Steel 45
Stainless 15

Electrical conductivity:
Al 38
Steel 6
Stainless 1.4

So it's relying on the steel strips to provide enough resistance to get hot and melt the aluminium.
Stainless may work better with a low-voltage welder.
 

wsimpso1

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Spot welding has been around for about a century - if it was such a good idea, with all of the smart folks out there working on airplanes, we would see more of it in airplanes. At a minimum you will need to redesign around spot welding. Let's get into the why's a bit:

To weld anything, you must melt the base material local to the weld and warm up the metal near the weld to close to melting. The heat affected zone is soft, usually at or near annealed state. In most aluminum alloys annealed yield is around 5 kpsi, which is way lower than 6061-T6 at 35 kpsi or 2024-T3 at 42 kpsi. 6061 will naturally age to T3 or T4 with yield of around 16 kpsi. That is a big hit on strength. So we do not see much spot welding of aluminum structures.

Where we need the full strength of the materials, this drives us to rivet aluminum. Where we can tolerate substantially lower strengths, we can spot weld. Folks have already mentioned trailing edges of control surfaces as examples of where it has been done. Other places where we currently TIG or gas weld soft alloys. Drawback here is we usually use those alloys for tanks and other items - which means it has to seal the weld - seam welding with a rolling electrode and usually power driven rollers at that.

Billski
 

wktaylor

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Aluminum resistance [spot, seam, etc] is a lot more difficult than it appears. Primarily because aluminum is so conductive it bleeds-off electrical energy/heat needed to fuse the nugget at/around the spot between layers of materials. More than just electrical current, though, there has to be extraordinary squeeze-force-schedule applied to the SW point during the process thru the electrodes... all in under 1-second... to establish clean/fused SWs nuggets. Bare aluminum tends to produce better SWs than clad aluminum... simply because bare-fuses-to-bare with greater reliability ad higher native resistance... but generally poorer corrosion resistance [between sheets] than clad-to-clad. Repeatability and consistency is validated by on-going shear-testing to ensure the process is staying 'in specification'. Believe-me challenges of aluminum SW make professionals want to drink.

NOTE.
Arc-tack welding and small electrode poke-tack-welding have some value for low shear strength welds... typically joining foil and very thin/fragile parts.

Specs for spot [electrical resistance] welding.
MIL-W-6858 WELDING, RESISTANCE: SPOT AND SEAM was replaced by AMS-W-6858 which is not replaced by
AWS D17.2 Specification for Resistance Welding for Aerospace Applications. MIL-HDBK-5 and early MMPDS have published shear-allowables for SW... based on consistent equipment set-up/monitoring
 

Hot Wings

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Believe-me challenges of aluminum SW make professionals want to drink.
I can believe that.

I've done a lot of spot welding on steel sheet with the kind of tool being talked about. The weld quality can vary widely due to setup and procedure. The only real feed back is the intensity of the 60Hz hum and the rapidity of the little blue ring forming around the electrode tip..........and those tips need to be cleaned and shaped as they get used.

Using this for aluminum has some potential benefits for us but it won't replace rivets for everything.
 

Mad MAC

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There is story about spot welding that goes something like this.
Uni Lecture says spot welding is hard to make reliable and repeatable, Airforce personel on course point out they get good spot welds on J52 flame cans, lecture replys yes but you dim the local towns lights doing it.
 

AdrianS

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I'm actually interested in this for non-aviation use.
Fabricating bits & brackets for rally cars & boats, you're usually not working anywhere near the material's limits.
This looks an intesting alternative to the ubiquitous pop-rivet for non-structural parts.
 

cheapracer

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Using this for aluminum has some potential benefits for us but it won't replace rivets for everything.
Only because of the poor reach simply can not get to about 70~80% of the plane's surfaces, so rivets will still rule.

Of course very expensive machines will have large reach, usually a pedestal spot welder.


.... for rally cars
What rally cars would they be?
 

AdrianS

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I navigate a 1968 FIAT 1500 in historic (forest) rallying.
I was mainly thinking of a mate of mine who builds/preps mostly historic cars : thera are relay panels, catch tanks, reservoir mounts - quite a bit of bracketry.
His own cars are a 180B and a 120Y being built.
 

cheapracer

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I navigate a 1968 FIAT 1500 in historic (forest) rallying.
John E/Adrian S - Fiat 1500

I've been involve in Oz rallying since the 1960s, Dad was pretty good, sans the last 15 years overseas, but aiming at the Alpine 2021. Target car at this point in time is a Bolly Nagari.
 

AdrianS

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Thats us.
If you were competing in Victoria in the 80s, we've probably met.

I've done quite a few Alpines, but the performance gap between us pre-68 guys and the front of the field is getting too big, so we sat it out this year.

The Nagari sounds fun.
Edit2: memory failure. Forget it.
 
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cheapracer

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Thats us.
If you were competing in Victoria in the 80s, we've probably met.
I was living in Queensland by then, I went to school with Graham Wise, Hugh Bell is a family friend and i serviced, helped prep, ect for him a bit.


The Nagari sounds fun.
Hopefully scary, 302 Windsor in 1000kgs ... Building it from scratch, brand new 1970s original windscreen on it's way to me, most critical part to build the buck for the molds.

Bolly CAD.jpg


A few aluminium parts will be spot welded for it, and reported back to this thread, just to keep this post on topic :)
 

David H

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All,
I did a search for "welding" and this is the closest forum topic to my question. Has anyone tried this on low stress aluminum parts? Solution Welding Flux-Cored Rods Welding with a propane torch seems to fit the too good to be true category.
 

Riggerrob

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Look at all the thousands of spot welds inaluminium Republic RC-3 Seabee flying boats. The first were built in 1946 and a few have survived all the hazards or water-landings to this day.
Also look at the stainless steel Budd Conestoga airplanes and railway freight cars spot-welded since the 1930s.
Fleetwinds also spot-welded a few stainless steel airplanes during the 1930s and 1940s. Key patents cover timing devices.
 

cheapracer

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All,
I did a search for "welding" and this is the closest forum topic to my question. Has anyone tried this on low stress aluminum parts? Solution Welding Flux-Cored Rods Welding with a propane torch seems to fit the too good to be true category.
It's rubbish, period.

Many Shows have 'that guy' selling it while welding up holes in aluminium cans telling you how awesome it is, must be over 30 years since the first time I saw it.
 
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