Vibration monitoring on machine tools

[manser]

Is anyone out there performing vibration monitoring/analysis on CNC and conventional machine tools? I've seen some information related to using vibration monitoring to monitor finish cut quality, but I'm interested in using it for overall machine condition monitoring/maintenance and troubleshooting. I'm not even sure if it's feasable since machine tools are so complex. Any tips gratefully accepted!

 

[tomirvine]

Machinery condition monitoring is very common. Machine failures are often signaled months in advance by changes in machine vibrations. Fourier transforms are used to monitor the baseline vibration of the machine, as well as any changes in the machine's vibration signature.

I recommend the following text:

Machinery Vibration: Measurement and Analysis
by Victor Wowk

Avialable from:

http://www.amazon.com/exec/obidos/ASIN/0070719365/qid=1010763806/sr=1-1/vibrationdata-20

Sincerely, Tom Irvine

 

[Viktor]

Although I would agree that the book by Wowk is useful for beginners to understand the nature of vibration analysis, I think it is of very small help in any analysis of vibration of machine tools.
There are a number of known attempts to study static and dynamic stability of machine tools. There are a number of different centers in the USA and Canada dealing with this problem. However, when one tries to use their results in practice he/she realizes: “Huston, we have a problem.” The problem is with understanding the sources of vibration in machining. This is a long story starting with Prof Tobias (S.A.Tobias, Machine Tool Vibration, Blackie, 1965. The history and state of the art on machine tool vibrations can be found in a book:
Y.Altintas, Manufacturing Automation: Metal Cutting Mechanics, Machine Tool Vibrations, and CNC Design, Cambridge Univ., 2000.
However, in my opinion, the real assessment, control and used of machine tool vibrations are not known. Ideally, it should be the DYNAMIC SIGNATURE of any machine tools which contains all the info on its quality. The results of any improvement, retrofitting, adding some fixtures, maintenance etc should compared against this signature to see what has been done in reality. Is it feasible? Oh yes, it is. Unfortunately, leading machine tool producers afraid this signature (by ignoring any further studies and blocking funds at any levels for this studies) because it will rank their machines so that they could not sell those really bad (70%). Because today, there is no any meaningful dynamic acceptance test during runoff of a machine tool, you still buy whatever they sell you. Apparent rigidity of the modern machine tools and excess of power do not guarantee their dynamic stability.

Regards
Viktor

http://viktorastakhov.tripod.com

 

Back when I had hair etc..... I did some work with vibration analysis to try and reduce the scrap rate of some cam grinders doing hot press ceramic inserts. By going through the machine one elemant at a time and reducing the vibrations to the lowest possible level at each point we were able to substancially improve grinding yields.

We were also able to prove at least to my satisfaction that when a freight train went by 1/2 mile away that it generated enough vibration to induce scrap (edge chipping visible at 50X)this was scrap. We decided not to produce this particual grade because of the "grinding" problems. But it sure did cut metal.

Note:

Once we got one of the grinders "tuned in" we were able to spot many problems through the use of the vibration analysis equiptment. If we had vibrations above a given level we could be sure that we were going to make scrap.

At a later date we were able to prove that the scrap that came off of an 8 spindle National Acme all came from one spindle that had a distintly worse vibration "signatiure" than the other seven. This company has used vibration analysis as a trouble shooting tool since.

PS I know of several manufactures who use this process to monator the health of some high power pumps.