MFN Trainer Column

in Vol. 19 - March Issue - Year 2018
Shot-peening Efficiency

Marco Klijsen

As a shot-peen machine designer and manufacturer, we have seen many revolutions over the years.
Where the process originally was performed as a manual process without any control system besides the operator, it developed over the years to a more and more controllable process.
With the introduction of personal computers, PLC’s and robotic solutions, today’s shot-peen machines are state-of-the-art machines with high precision controls.
These developments into more high-end controlled machines have brought the process to the next level; assuring new part manufacturing facilities as well as MRO shops a completely controlled, repeatable and reliable output of shot-peened components.
To measure and quantify the effects of the peening process, an Almen test has to be performed.
An Almen test is a crucial component of a controlled shot peening process because it measures intensity.
Intensity is the measure of the energy of the shot stream, and the energy of the shot stream is directly related to the compressive stress that is peened into a part. Therefore, assessing intensity is one of the essential means of ensuring process repeatability.
The kinetic energy from the media stream depends on the key process variables (KPV's) from the process. Some of them are:
• media hardness and size
• peening pressure
• media flow rate
• media velocity
All these parameters are nowadays measurable and some of them are also real-time controllable in-process, assuring the required controlled, repeatable and reliable output.
As where developments into machines have brought the process to the next level, the Almen test as frequently run during production is still performed as when during its introduction in the 1940’s.
If we compare the developments on the shot-peen machine side with the developments of the intensity measurement techniques, we see two completely different worlds: high tech versus antique.
After 75 years of use and consequently recognized weak points, it needs to be asked if intensity measurement based on the standard spring steel strip curvature measurement is still state-of-the-art.
Especially if one has to peen complicated geometries, the intensity measurement using Almen strips is a time-demanding process, resulting often in machine-occupation of 50% of its full availability.
Multi-million Euro investments with machine availabilities for production of less than 50% is a quite common situation for today’s shot-peen machines. With the Almen strip intensity measurement as developed in the 1940’s and still described in all latest SAE-AMS specifications, one does not allow much better machine availabilities for production.
It is only a matter of time before cognizant organizations and/or committees have to accept alternative intensity measurement methods.
Said alternatives are already available and have proven themselves as highly reliable and repeatable.
The major savings besides the proven reliability and repeatability is time. Once the new measurement of shot velocity is widely accepted, it can be easily integrated into today’s high-end controls. Machine availabilities for parts production will easily increase to availability figures we know from the machining industry, which will support more investments in this direction.
"Who stands still will fall behind". When do we make the next step?

For questions contact marco@mfn.li

Author: Marco Klijsen

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