Shot peening for metal improvement

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Not common

see

**LINK**

Robert G8RPI.

I know that they were doing this at Brooklands in the early '80s. Tornado taileron skill panels IIRC. I have checked my apprentice log book and have no notes on the subject, either on process or inspection/testing

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Maybe it is more practical to do flap peening rather than shot peening. There are flap peening kits you can buy - not so sure about shot peening to - you'll probably need a tool which would not be available to the home shop user.

At work we use flap peening often when reworking aircraft aluminium parts (especially on landing gear components). In theory it should improve the resistance of the material to resist crack propagation. This is achieved by inducing multiple small stress points on the material surface ( by the flap peen).

The flap peening kit should be easy to use i you have an air die grinder. I think the peens we use are from 3M - but I'm sure they are expensive. Maybe there are some other cheaper brands.

Shot peening aluminium alloys is used in the aero industry. The "shot" I saw being used at Metal Improvement Derby factory for peen forming wing panels was about 6mm diameter and projected with very little force, almost just dropping, to produce the curvature required.

I think shot peening in the home workshop would require a lot of effort to achieve good results, not impossible, just time consuming.

I think that you will find designs for peening guns and flap wheel shot projectors on the internet which could be made at home. The biggest problem as I see it is controlling the intensity of the the shot impact consistently.

MIL-S-13165C gives quite a bit of information on the process and measuring the intensity, but is more commercially based. The Metal Improvements website has some down loads which may help you.

The shot used in the peening process is not just steel, but can be glass or ceramic beads. I'm not sure were you would source the media, but you will need quite a lot of it. After the shot has been used it goes through a system that removes any broken or deformed shot, which would damage the work if used again, as well as sorting by shot size.

Shot peening is a messy process, years ago I attended the opening of Metal Improvements new factory at Newbury, I was told that this would be the only time that the floor would be free from shot! Do consider that the shot will go everywhere.

I hope this helps a little.

Neil

Just bray it with a hammer a few times and the jobs a good un

Just found a link to the Metal Improvements Applications green book.

**LINK**

Interesting reading if nothing else.

Neil

If you do try this idea, you need to use shot which is whole (no cracked pieces etc) and try to ensure that the impact s are all the same 'weight'. Cracked shot will cause sharp edged notches - just what you don't want for fatigue resistance, and uneven application will ensure that some of the dents are deeper and wider than others, and this is not the 'stretched evenly all over' condition you need.

An alternative - perhaps not as effective but it depends on your application - is to clean up the surface with abrasive working in line with the major stress (so the scratches are in line, not across, the main loads), and work up to a fine polish, always working along the scratches, not across them.

Hope this helps. Of course, fatigue depends on many other factors, including the crystalline nature of the material, and the presence (or not) of repeated shock loads in use.

Cheers, tim

I have used Oselli engines, when they were based in Oxford, to shot peen connecting rods. I was pleased to see they used Almen Strips to gauge the intensity (is that the correct word?) of the peening. Oddly enough, it made the rods very fragile until engine assembly was completed! The slightest mark on the rod completely nullified the advantageous effect, extreme care was needed on assembly.

I have considered using my blasting equipment for shot peening. I occasionally change the blast media from something aggressive to a more gentle media but have been advised by a supplier of peening media that A dedicated cabinet is vital so as to avoid contamination and therefore negating the advantages of shot peening.

John

Barrie.

Rather than try use a procedure critical process in home environment, have you considered changing the grade of Aluminium or changing features in the design to reduce any stress concentrations. Indeed has the component actually been stressed? If you are using say 6082-T6 you could change to 2024-T or T6. In this cases you get the double whammy of higher stress limits at yield and puts you further to right on the fatigue curves. Mil HNDBK 5 has the all the data you need and can be downloaded from the interweb.

Dave