Fusion Message Board

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Subject: Re: Novice Questions (Spot Welder)
Date: Jan 31, 9:20 pm
Poster: Richard Hull

On Jan 31, 9:20 pm, Richard Hull wrote:

>I think I may be missing a really basic point. Are we supposed to be melting the SS/tungsten/etc. wire so that it bonds directly, or are we using some other metal for bonding?

Silver solder (other metalfor bonding) or resistance welding only (Spot welding). RH

>I hooked up a 24v power supply to a single 3000 MFD capacitor, and connected the leads to a pair of general purpose arc welding electrodes. Nice little spark but the only thing that bonded was the electrodes, to each other. It seems that I should use these electrodes if I want to bond using the electrode material, but something else if I want to actually melt the wires together. (I've only done silver soldering with a torch, never used an electric rig, so even the nomenclature is unfamiliar.)

Spot welding or resistance welding is ancient in its origin (before 1900). The secret is to use real spot welding electrodes. They contain special copper alloys including beryllium, etc.

Second, the key word is "resistance". The copper electrodes are fouled and spalded, but they do not melt before the tungsten or SS due to their low resistance. Thus, to resistance weld you must be joining materials of higher resistance or lower conductivity than the electrodes. Remember the voltages sum around a closed circuit.... All voltage appears across the HIGHEST resistance. SO.... The SS or tungsten round wires are terrible conductors, plus the point of contact is virtually a true point. The resistance is incredible there. As the pulse of energy is applied, the greatest voltage appears right at the joints of the two tungsten or SS pieces. As the current is the same throughout a series circuit, all the major power is disappated and focused at the junction of the wires to be fused. They melt and the applied pressure (pinch) merges the two wires at a tiny molten point.

Ideally, the joule energy delivered is just enough so that the wires melt together just as the sauce runs out of steam. Good, high end, professional, micro resistance welders allow you to control the joule delivery in each pulse.

They would be a snap to make with a small ignitron, a capacitor and small DC supply. Don't forget the real honest to goodness spot weld electrodes. (welding supply house.)

Richard Hull