Frank and I came up with two slightly different designs for electrodes, but they both follow the same design principles. You must use thick copper, and any connection must have a solid copper-to-copper connection. I'm not saying that my electrodes are best, or that Franks are, but lets take a look at those electrodes from China.
The joint at "A" appears to have a silvery connection pressed against the copper flat-bar. I have used Cembre connectors that are pure annealed copper, but they have a thin plating of zinc to eliminate any corrosion and oxidation, so I will assume the connection at "A" is copper to copper. (The bolts appear to be brass, they can be steel which is cheaper and stronger, because the connecting bolt doesn't really perform any of the conductivity of the current)
At "B", the blocks that hold the electrode tips are clearly brass, which is common. Copper is soft, and difficult to drill to any appreciable depth. Brass is copper with 25% added zinc. It has roughly 28% the conductivity of copper, so it has a 3-1/2 times the resistance of copper. It does conduct electricity, but it will be much hotter than the copper parts of the system.
If you are thinking about using thicker copper conductors to reduce the heat from welding, be aware that any brass parts will be 3 times hotter. When copper is out in the weather, corrosion is a serious issue, but indoors it is not a problem. Copper may turn a little brown instead of bright reddish, but the conductivity of a solid connection is still MUCH better than brass.
The electrode tip holders that frank and I have used is C14500 "Tellurium" copper. It has 93% of the conductivity of pure copper (so they run cooler) but they have a tiny amount of alloy that makes them easy to machine/drill. I approve of
cylindrical electrode tips (the replaceable part) because we can find those in copper, tungsten, and carbon.
It is an STM32F103C6T6A.
.
