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#107 - 11/10/09 12:28 PM how to measure shot peen dent diameter
Jack Champaigne Offline


Registered: 04/20/99
Posts: 317
Loc: Mishawaka, IN, USA
Dr. Kirk,
Do you know of anyone that offers the service or has the ability to measure shot peen dimple diameter and depth ?

Bill

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#108 - 11/10/09 12:34 PM Re: how to measure shot peen dent diameter
Jack Champaigne Offline


Registered: 04/20/99
Posts: 317
Loc: Mishawaka, IN, USA
Dear Bill,

I assume that you have received the Solver programs from Jack. If you encounter any problems using them do not hesitate to ask me for advice.

On the question of dimple diameter and depth measurement I also do not know of a commercial service. My advice is to do it yourself!! A simple procedure is to: (1) put your sample on a scanner together with a ruler, (2) scan at the highest resolution, (3) save as a jpeg, (4) open Word and INSERT the file as a PICTURE, (5) increase the size of the inserted picture using the 'grab handles', (6) increase the magnification of Word to the maximum (500% in my case), (7) use a ruler to measure the projected image of the ruler (in order to get 'real-time' magnification), (8) use the ruler to measure the on-screen dimple diameters and finally (9) convert these on-screen diameter measurements by dividing by the 'magnification factor'. All that may seem daunting but don't be put off - it is simple in practice and some fun.

The attached file is an example that I did a few minutes ago on a part-peened Almen strip that is not at all photogenic. Please try manipulating the image in Word - bear in mind that the strip is curved so that only part is in focus. I got to an on-screen linear magnification of 20 (the 1mm ruler divisions appear as 20mm on screen). Measuring individual indents with the same ruler gave me values averaging 2.5mm. Dividing 2.5mm by the magnification factor of 20 shows that the dimple diameters are arranged around 0.125mm. Dimple depth can be estimated using the shot size and dimple diameter.

Use of the scanning technique removes the problem of lighting effects influencing the character of the image produced using a camera.

Regards

David

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#109 - 11/10/09 12:35 PM Re: how to measure shot peen dent diameter
Jack Champaigne Offline


Registered: 04/20/99
Posts: 317
Loc: Mishawaka, IN, USA
David,



Thanks for the suggestion I did a sample test and it worked well. Rather than a scanner I took a picture thru our microscope which yielded a great resolution. , Do you think that there would be any merit to developing an automated vision system that could calculate the mean peen crater diameter, and number of craters in a given area of a specimen. Then be able to calculate percentage of coverage, and have the ability to compare from lot to lot, as well as differentiate under/over coverage.



Thanks



Bill

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#110 - 11/10/09 12:36 PM Re: how to measure shot peen dent diameter
Jack Champaigne Offline


Registered: 04/20/99
Posts: 317
Loc: Mishawaka, IN, USA
Bill,

How does microscopy compare with scanning in your experience? I have accumulated hundreds of pictures using microscope-mounted cameras but have never matched either the resolution or reproducibility that I get using a simple scanner. Optical pictures are so sensitive to surface condition and lighting that I sometimes dispair of getting reproducible results.
There would be great merit in developing an automated vision system having the properties that you mention - if it was possible! Image manipulation programs are readily available that calculate mean diameter and number of isolated craters in a given area. They start to fail as soon as craters overlap - are they treating a pair of overlapping indents as one or two objects? Treated as a pair, the 'diameter' and number results are obviously false. It is also virtually impossible to identify tiny areas of unpeened surface.
Scanning has the practical advantages of (1) being available in every shot peening plant (whereas it is exceptional to find microscopes and cameras) and (2) not requiring specific skills or training (virtually everyone knows how to use a scanner).

David

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