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Weld, Solder, and Braze

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Absolutely beautiful welds
They are not machine-made!

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Word count/read time: 677 words; 2-1/2 minutes

Entire books are devoted to a miniscule aspect of one category so this is clearly an introduction. Taken out of context, one could easily dispute the generalizations.

Excluded are Mother Nature's tricks like galvanic or oxidative welding. Even stranger, some metals will immediately fuse together. Pure titanium is notorious for this. Pure silver does so when red hot. Hammer-forged metals, too - look at how a traditional Japanese samurai sword is manufactured. Though no metal is melted and no solder is used, good luck separating the layers of metal.

In jewelry, soldering is technically brazing but no one quibbles about it. The base metals are heated, not melted, until the solder liquefies and flows into the joint. It is mostly for a localized area.

True brazing usually requires a torch and may cause heat-related issues similar to welding. Brazing can be used on long stretches of metal as easily as it can be localized for small spots.

Welding melts the base metals at the joining area. Thanks to flux, shielding gases, and a clean surface, the metals will join together. Most welding uses filler metal which is added to the molten weld pool; welds without filler are called fusion welds. High heat is guaranteed to cause chemical or physical transformations: weak welds or surrounding metal, annealing, brittleness, oxidation, porosity, metals coming out of alloy or making new ones, oh my!

TIG and plasma are not the fastest but they are more versatile and the most difficult to learn. They are essentially the only methods which consistently produce aerospace- and museum-quality welds (sometimes laser welding does). Plasma probably has a slight edge in overall performance and precision because the arc on TIG welding can wander. With TIG, electricity flows through an electrode and shielding gas to melt the metals. Plasma uses a stream of super-heated gas. Filler metal, if used, is added as needed.

Laser welding is definitely Buck Rogers in the 25th Century. In theory, it should weld just about as many metals as TIG or plasma. It can do fusion welds and is best for tiny areas (but it can run beads, too).

MIG and arc are similar, the major difference being how the metal is shielded. MIG uses gas, arc welding uses flux. Secondary is how the filler material is added. MIG welders have an automatic feed whereas arc welders have an electrode that must be held in contact with the metal (the electrode is the filler metal). MIG is cleaner. Arc welding can produce a solid weld but it's not for detailed work, thin metals, or aesthetic purposes.

Gas welding uses a flame. How that flame is generated, i.e. what gases are being burned, can affect the base and filler metals. Few alloys have the molecular stability to tolerate (unshielded) high heat without throwing a nutty. Fusion welds are possible on just a handful of metals, notably pure silver and pure gold.

Resistance welding sends an electrical current through two or more touching pieces. The heat created is enough to weld them together. It works great on steel alloys and takes virtually no training. Metals with low electrical resistance (gold, silver, and others) cannot be welded this way.

Flux core (wire) welding shares similarities to the MIG, arc, and soldering. The solder or flux is contained within the feeder wire so as it melts, it shields. Because it uses an actual physical substance as opposed to a shielding gas, it is like soldering. Due to the flux on/in it, it is like an arc welding electrode.

The metal often dictates how it must be joined. Sometimes dissimilar metals can be joined. Physical characteristics and chemical properties make some metals notoriously difficult to weld. Silver is considerably more difficult, no question about it, because it has the highest thermal and electrical conductivity and lowest electrical resistance. Its melting and fusion-ready temperatures are so close that at any time it can turn into a molten blob. But nothing makes jewelry as beautiful as pure silver so it's well worth the profanity that often accompanies ambitious projects.

Posted by M: July 25, 2019

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