MFN Trainer Column
in Vol. 9 - September Issue - Year 2008
A Case For The Art Of Manual Peening
MFN Trainer Shlomo Ramati
This column is a regular feature and is written by one of our MFN trainers or the Editorial Office. Readers are invited to send comments or questions to firstname.lastname@example.org. For more information about the trainers, see our website www.mfn.li/trainers.
In the long history of man, metal working has been viewed as an art form.
In our modern world we have automated many processes to enhance the rate and precision of the work we produce. The machines we have do the job of many workmen at faster, higher forces than could be achieved by manual hand, yet should we do away with manual processing all together?
In my opinion that would be a bad mistake. It is still an art form today.
I have had the fortune to know a few exceptional metal-workers, in France they were referred to as "Masters", they are those that could make the shape that the specifications said could not be done. None the less when an immediate corrective action must be taken these “masters” will make the correction and it will work.
Let us look at the peening world. It has changed dramatically in the last few years. Today one can purchase robotic peening machines of many types with many degrees of freedom. We have lances that can reach non direct line of sight areas for the shot to be propelled and achieve the desired intensity and coverage. These machines are fully computer controlled or partially so. The Laser peening is a very sophisticated computer controlled process used mostly for very high "add on value" procedures such as aircraft engine parts.
The new ultrasonic excitation peening machines can be run by controller or manually.
So where is there room for manual peening? Well consider a large aircraft landing gear fitting. These parts are normally machined out of a large forging, the stiffeners are strong and due to stiffness considerations the pockets are small and deep. So should we peen by lances? The robotic arms are normally large and would have a problem getting into the deeper areas. It could be done, but the cost? A manual operator can manipulate a single nozzle with great ease any time the depth creates an area that is shaded when peened at normal 45º. That is, that the angle of incidence to the work piece must be above 45º, otherwise we would get streaking with material being pushed sideways rather than the energy of peening going into the work-piece. This is but one case.
MIL, AMS 13165 now cancelled, did not define manual peening but also did not rule it out, so 13165 was referred to even in manual jobs.
The AMS 2430 which is meant to replace 13165, by the very name Automated Peening precludes manual peening, and yet most of the OEM’s not only allow manual peening but would resist taking it out of the peening world.
Simple economics will always have its say. Teaching a computer to copy a wing panel forming procedure is not trivial and so far can be done only up to a point.
Difficult "saddle" shapes are still done manually. I recently witnessed a test to compare ball peening with Ultrasonic spherils peening. This was for a difficult geometry that required a very high intensity. The manual U/S showed a smoother surface while achieving a very high intensity and forming capability, it has since been incorporated into our straightening and forming specs.
In summation some jobs would be far too expensive or not possible if not done manually. As long as we train the operators well we will benefit from their expertise.