Ask HN: I don’t trust welding
I see so much quick welding on TV shows these days (cars, motorcycle shows) but not being an engineer I just can't trust the weld to hold.
What's the math?
What's the math?
Brazing is not as strong as it doesn’t melt 2 pieces of metal together. Instead, it more or less “glues” them together with a different, lower melting point metal/alloy.
It is easily possible to make bad welds so if you don’t know what you are doing, bolted construction would probably safer.
Example: suppose you wanted to add a roll bar to you car for track days. If you welded it in and didn’t know what you were doing, you could change the characteristics of the car metal close to the weld such that it would become brittle. In an accident, the roll bar would just punch through the sheet metal.
The PDF is an excerpt from Shingley's mechanical engineering design textbook. It's is considered to be one of the Mech E bibles. If you like buying random interesting books, buy it.
Food for thought: Most welding applications that "normal" people would do would experience forces that range from 1lb to 2000lbs. (This a bad assumption, but whatever) If you actually do the math, it's even a small weld bead would have the strength of several hundred pounds force.
Another general rule of thumb is that the base material will fail before the actual weld, if done properly.
The easiest way to mitigate the risk, is to weld the entire seam, but you risking warping your part.
The other thing is making sure you have full weld penetration when doing the weld. Penetration is affected by a multitude of parameters(amps, speed, technique), easy way to check is to look at the backside of the weld. Harder way is too cut a cross section at the weld. Or if you're going to ball hard. X-ray it.
You'll note in those calculations that he assumes that the weld is basically the same as the base metal. As long as the weld is performed properly, the assumptions should hold to within a factor of safety.
For the relatively thin material used in cars and motorcycles, it doesn't take very long for the metal to melt all the way through in a single spot, so very strong welds can be created quickly. Further, between the skill of the fabricators and editing for TV, it is hard for someone without familiarity with welding to know what all is going into a joint just by watching the footage after.
Do you have a specific show in mind?
But perhaps a talk with someone who is or has been a welder might best boost your confidence.