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Ask the Engineer

Ask the Engineer

Weld inspection ... Generator power output ... Thin soft solder ...

Dear Search Engineer: I have a high-volume automotive welding process coming online. I would like to know if there are new ways that we could 100-percent inspect weld quality. Current practice would be inspection and/or arc data monitoring, which have not been 100 percent perfect in the past and can't supplant the teardowns we need to do weekly or more often for penetration, etc. Are there other new methods that could do more checks, better and faster (i.e., up to 70 long welds in under minute)? A teardown for cut and etch would take six days-a non-destructive test that meets AWI requirements would be helpful there, too. Any suggestions? -A.W. in Ontario, Canada

Dear A.W.: Digital flat panel technology has made x-ray inspection practical and flexible. It allows inspection of the underlying bond area rather than just the surface of the weld, as well as real-time imaging, and image storage for archival and rapid image retrieval. You can find an interesting article on the topic at

Dear Search Engineer: I am working on a permanent magnet generator and need to calculate the rated power output of the generator. The result for no load voltage is 27V at 2,000 rpm, and the result for short circuit current is 1.9A. Can we estimate the maximum power that the generator can transfer to a 12V battery? While attempting to charge a battery, it transfers just 7W of power. -P.G., DN reader

Dear P.G.: If you are looking for the maximum power at 2,000 rpm, the answer is certainly calculable. If you want the maximum power the generator can produce overall, that is more complex. The overall maximum power you can produce may be limited by any one of a number of factors. These include the maximum rotational speed allowed by the machinery, the resistance of the coils, and your ability to get the heat out of the system. Now if you want to know the maximum power at 2,000 rpm, first calculate your internal source impedance, 27V/1.9A=14.2O, in this case. We know that matching source and load impedance yields maximum power; so to calculate the maximum power in the load, use the relationship, P=I2*R, where I=V/(Rsource + Rload). For your case, it's about 12.8W. Based on your numbers, I would say your battery impedance is about 2.8O -far from ideal.

Dear Search Engineer: We are looking for a thin (0.05) soft solder in a wafer or sheet form to automate the fabrication of a retail product, including soldering two brass sheet parts (0.0625) thick with a flame. At this time our option is to roll conventional wire solder to get the thin profile required. Please let me know if I can source this configuration of solder.-N.C., Vancouver, BC

Dear N.C.: I know of one company that was making a foil that you can light with a match and it would braze heat sinks to devices. Check out this link and you may find something: .

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