Weld Like a Pro
This photo illustrates a lot of anatomical weld information.
First off, this photo shows two thick sheets of steel in a T-shaped butt joint, which are double fillet welded with partial penetration. In this example, the welds are created through TIG welding. As noted in Weld Like a Pro, a fillet weld is a triangular shaped weld, usually only achieving partial penetration. In this case, this is a double fillet weld because it's made on two sides of the butted joint. If the welds had penetrated into one another, this would be called a full weld rather than a partial.
Second, we have the most obvious: the numbers. Those are the temperatures reached in the two weld areas of the weld: the weld, itself and the HAZ, or Heat Affected Zone.
Third, the weld anatomy is only partially made up of the molten puddle created during welding. The HAZ is also an important area of the weld and relates directly to weld quality. The HAZ is actually the area of the base materials that heats up during welding, but doesn't melt. In the photo, the weld, itself, reaches 2500° while the HAZ gets up to 1300° as the weld heat dissipates through the base material. The roll the HAZ plays has a great deal to do with the strength of the finished weld joint and is a very complex subject, which Jerry Uttrachi covers throughout Weld Like a Pro.
In the case of my own car projects, the importance of the finished weld strength depends on the application of the weld. For the exhaust on the El Camino, a good, clean weld with sufficient penetration to seal the joint and keep the system together over its service life is all that's required. However, in the case of replacing body panels like the trunk floor of my '66 Mustang, the 351, those are structural and the welds have to be able to withstand the kinds of forces seen in both regular use of the car and in the case of an accident. In fact, you'll find that depending on the application, there are very precise specifications for weld materials and joints in auto body repair — in those situations you can't just make a weld puddle that joins a couple of pieces of metal together and call it good. Photo: Jerry Uttrachi.
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