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Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

(OP)
During the assembly of one of our machinery products that has a cast iron housing, occasionally one of the hidden internal components is accidentally omitted.  The sub-assembly at this point in the manufacturing process is already bolted to a larger assembly, all of which is suspended vertically, has a vertical length of 18 inches and a total weight of 93 lb. (+ or - 2 lb.)  We would like to detect any ommission of this component and then rework the sub-assembly if required.  
     Should I be able to check the resonant frequency of a known good assembly and use it as a standard for checking the resonant frequencies of other production assemblies, in order to confirm that they do not have this component missing?  (I might add that the resonant frequency of the 93 lb. assembly is in the neighborhood of 500 hertz, and the weight of the sometimes missing steel component is 1.4 lb. (+ or - .05 lb.).  If this is feasible, and for a production quantity of 7,000 units annually, what types of vibration testing equipment do I need?

RE: Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

That seems an odd way of going about it. I think you'll need to do some experiments, there is no general answer, but I tend towards the opinion that it won't work.
You need a force gauge, a hammer, an accelerometer, conditioning amps and an FFT analyser of some sort.

Take a wander over to the FAQs for this forum to learn more about that lot.

Cheers

Greg Locock

RE: Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

Additionally, I think that there is a serious philosophical flaw in this concept.  

I don't know how much investment you put into the assembly, but don't you think that accepting the wasting of that investment is a poor business concept?  

The correct approach should be to catch the problem much earlier, so that you don't wind up scrapping a built-up assembly or ahve to disassemble and reassemble a complex assembly.

TTFN

RE: Checking Natural Freq. of a Unit to Detect Missing (hidden) Component

Additionally, your miss rate should/ought to be very, very low.  Is it economically plausible to test 7000 units to find a few errors?

TTFN

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