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#975 - 05/28/13 10:58 AM Influence of Shot Size vs Surface Roughness
Neil Offline
Member

Registered: 05/28/13
Posts: 2
Loc: UK
Hi, I'm new to the forum.
I have a question regarding the control of Surface Roughness, Ra and Rz.
I am running some trials to determine the variables which have the most effect on the value of Rz/Ra.

The most obvious variable is Pressure/Velocity of shot. Increasing velocity gives a higher surface roughness measurement. However lowering the velocity reduces the intensity so it is not always an option.

So if I have to maintain a given Intensity (energy) then is the best way to increase the size of the shot and reduce the velocity to give an equivalent intensity (energy) and therefore produce a lower value for Rz/Ra?

I am interested if someone knows about the relationship between shot size and surface roughness for a given Intensity level (all other things being equal).

Any advice would be much appreciated.
Neil
_________________________
Neil

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#976 - 05/29/13 03:24 PM Re: Influence of Shot Size vs Surface Roughness [Re: Neil]
Jack Champaigne Offline


Registered: 04/20/99
Posts: 320
Loc: Mishawaka, IN, USA
I don't know of any definitive study other than "tribal lore" that says to use larger media for a smoother surface because the depth of the dent is much less. A small media impact must drive itself very deep in order to achieve the intensity level you desire. Substituting larger media (more mass, larger impact diameter) will create a shallow dent but with deep compression. You should experiment with scrap pieces until you get the size you need.
You should also search or library using various search terms such as dent, depth, shot size, surface roughness etc.

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#977 - 05/29/13 03:53 PM Re: Influence of Shot Size vs Surface Roughness [Re: Neil]
Socrates Offline


Registered: 02/20/06
Posts: 108
Much depends on the priorities attached to a given situation. For example: if fastest achievement of a specified coverage has top priority then the smallest shot size that will generate the required intensity would be an obvious choice. If, on the other hand, surface smoothness is the top priority then two-stage peening can be employed - with small shot being used in the second stage after a required depth of compressive residual stress has been achieved using larger shot.

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#978 - 05/30/13 04:36 AM Re: Influence of Shot Size vs Surface Roughness [Re: Neil]
Neil Offline
Member

Registered: 05/28/13
Posts: 2
Loc: UK
Thank you both for the swift replies.
I need to develop a process where I have been give a maximum value of Rz. Also for economical reasons I will target a one stage peening process (i.e. one size shot)
I have carried out trials in the last couple of days using S170 and S230 and will be trialling S330 within the next week.

Jack, your answer confirms some of my theoretical thinking that a larger peen size will lead to a lower Rz. Extending the peening time slightly shouldn't be an issue.

There is a lot of research out there on Intensity and Coverage but very little on Surface Roughness control.

Hopefully I'll have the results I need by the end of next week.
Many thanks for your help and guidance.
_________________________
Neil

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#979 - 05/30/13 09:27 AM Re: Influence of Shot Size vs Surface Roughness [Re: Neil]
Jack Champaigne Offline


Registered: 04/20/99
Posts: 320
Loc: Mishawaka, IN, USA
It would be great if you could share some of your experimental data. Although it wouldn't be massive like a thesis but it could be very helpful for someone else in the future. You (or I) could write a short paper and archive it at our web site. Thanks for your consideration.

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