How thick are the metal sections?

Thickness of base metal sections is an important consideration in selecting your metal joining method. If both sections are relatively thick – say .500" (12.7mml – either welding or brazing can produce a strong joint. But if you want to make a T-joint, bonding a .005" (.127mm) thick sheet metal section to half-inch stock for example, brazing is the better choice. The intense heat of welding is likely to

burn through, or at least warp, the thin section. The broader heat and lower temperature of brazing allows you to join the sections without warpage or metal distortion.

What's the joint configuration?

Is the joint a "spot" or a "line" 2 A spot joint made at one point can be accomplished as easily by welding as by brazing. But a linear joint – all other things being equal – is more easily brazed than welded. Brazing needs no manual tracing. The filler metal is drawn through the joint area by capillary action, which works with equal ease on any joint configuration.

What metals are you joining?

Suppose you’re planning a two- section metal assembly. You want high electrical conductivity in one section, high strength and corrosion resistance in the other. You want to þ se copper for conductive, and stainless for strength and corrosion resistance. Welding this assembly »ill present problems. As we've seen, you have to melt both metals to fuse them. But stainless melts at a much higher temperature than copper. The copper would completely melt and flow off before the stainless came anywhere close to its melting temperature. Brazing these dissimilar metals offers no such obstacle. All you have to do is select a brazing filler metal that is metallurgically compatible with both base metals and has a melting point lower than that of the two. You get a strong joint, with minimal alteration of the properties of the metals. The point to remember is that brazing joins metals without melting them, by metallurgically bonding at their interfaces. The integrity and properties of each metal in the brazed assembly are retained with minimal change. If you plan to join dissimilar metals – think brazing.

How many assemblies do you need?

For a single assembly, or a few assemblies, your choice between welding and brazing will depend largely on the factors discussed earlier – size of parts, thickness of sections, joint configurations, and nature of base metals. Whether you braze or weld, you'll probably do the job manually. But when your production needs run into the hundreds, or thousands (or hundreds of thousands), production techniques and cost factors become decisive. Which method is best – for production metal joining? Both methods can be automated. But they differ greatly in flexibility of automation. Welding tends to be an all-or-nothing proposition. You weld manually, one-at-a-time, or you install expensive, sophisticated equipment to handle very large runs of identical assemblies. There's seldom a practical in-between. Brazing is just the opposite. You can braze "one-at-a-time" manually, of course. But you can easily introduce simple production techniques to speed up the joining of several hundred assemblies. As an example, many assemblies, pre-fluxed and bearing pre-placed lengths of filler metal, can be simultaneously heated and brazed in a furnace. When you get into larger runs, it may become practical to rig up a conveyor which can run the assemblies past banks of heating torches and brazing filler metal can be applied to the joint in a pre- measured amount. And there are endless "in-between" possibilities, a good many of which you can accomplish with relatively inexpensive production devices. The point to keep in mind is that brazing is flexible. You can automate it on a step-by-step basis, at each step matching your automation investment to your production requirements.

Welding vs. Brazing considerations