Vibratory Stress Relief...Does it work?

Our shop is thinking of getting a Vibratory Stress Relief machine to use on our parts that tend to move during machining due to internal stress, things like big but thin heat treated wear rings with a .002 tol. that after parting off go .005 to .250 out of round!!! And for shafts that tend to move all over the place while you machining them and then getting runout again after keying them, anyone have any experience in this technology? http://www.vsrtechnology.net/

It sounds like hokum to me (and I am well educated in the mechanical engineering branch called solid mechanics), but I hear that some of the racing guys swear by vibratory stress relief. Did you check snopes.com? There was a discussion in the Deckel forum some time back. See near the bottom of the second page of this thread :http://www.practicalmachinist.com/vb/showthread.php/ill-doing-next-month-180692p2.html

I find it hard to believe you could get high enough stress to do anything except perhaps at a few vibrational "hot spots" in the structure, and if you managed to get high enough stresses everywhere, the hot spots would be overstressed.

VRS Technologies website says "Metal components fabricated in a cold-forming operation, e.g., cold-rolled steels, and highly tempered aluminum alloys, resist vibratory stress relief." In other words, metal components with lots of residual stress resist vibratory stress relief! Hmmmm....

Works well primarily for heat / contraction induced stresses rather than for heavy forming stresses. Effect is similar to tapping the hot area during cooling when welding cast iron under unfavourable conditions. Big fabrications tend to pull out of shape when welded due to heat contraction in the joints. The vibration allows the joints to relax so the weight of the casting or the effect of applied clamps lets the thing go back into shape.

Simple matter of injecting energy into the system so that it can find its lowest stress state. No different to heating up the joint again really except that with heat you still get left with contraction stresses. Hopefully less than you started with. I'd be unsurprised to discover that you have to be very careful with vibration nodes if the system is to work.

Clive

Yep i thought this was a load of rubbish too to start with but its been around a long time and i kinda agree that it should work in theory to some degree, I am doutfull if its as good as a proper annealing though!!

Oversimplifying Outrageously

Vibratory stress relief is a quite different thing to annealing where the energy input is sufficient to heal dislocations and / or change the basic "crystalline" structure of the material. Cold worked material mostly gets its extra strength from dislocations imposed by the working, steel becomes hard when quenched by changing the ratio of the various crystalline states in it. Both situations need lots of energy to change things which, essentially, is only readily available by heating.

Thermal contraction induced stresses are a much lower order of thing primarily due to the internal grains contracting so quickly during cooling that the grain boundaries can't shift fast enough to avoid being stressed once cooling is sufficiently complete. Vibrational energy can be enough to let the grain boundaries move and some of the internal crystalline structure shift to work out stressing. Similar effect to long period low temperature heat soak or repeated temperature cycling. Overall energy is lower but lots more cycles.

Clive

ten hours at 300 degrees F on an oil bath is pretty reliable for most tool steels.

In my old shop, I used to be the reluctant expert on vibratory stress relief. Once I had enough time on the gadget to assess its capabilities I concluded most of the claims made for it were deliberate frauds. Under strong management directive (whoever bought it had to justfy it somehow) I used to spend hours watching the gadget buzz and vibrate heavy compact fabrications on the rubber doughnuts that came with it. Vibratory stress relief is a scam as impressive sounding and in the end useless as magnet therapy, diet and exercise fads, and penis enhancement gimmicks.

By the time you get enough strain energy circulatng in a complex part to equalize stresses in the areas of interet you've over-stressed it in others possibly to the point of fatigue. The strain energy input by the vibrator concentrates at the flexural nodes while the rest of the energy merely circulates in the part's mass/compliance system at well below any level sufficient to resolve locked-in stresses -waving in the wind so to speak.

It does have its uses on structures and materials whose configration lend themselves to HARMONICS of the vibratory frequency available from the unit and whose resonances do not detructively concentrate strain energy at section changes of the part. So far as I can tell large rings are the safest bet.

Tell your boss for me to save their money and send their work to a controlled furnace for thermal cyclng. A VSR unit is a loser purchase sold by modern snake oil salesmen.

Have I said enough or should I get more specific?

I tested the vibratory stress machine at work by putting
a piece of flat bar on the table and supporting it at each
end with a 1/4 inch thick spacer.

I then
induced stress in the part by clamping it down to the
table in the middle with a C clamp.

I ran the machine through its stress relief cycle several
times with the part in this" bent" condition.


When I removed the C clamp, the part sprung back to
its previous straight condition , proving that the stress
had NOT been removed.

The machine was equipped with an accelerometer and a panel meter gage to allow one to adjust the vibration frequency, but the needle jumped around so much that I could never tell where the resonant frequency was , so I just used the "auto cycle" wherin the machine vibrated at one frequency for five minutes, a second frequency for five more minutes and then for five minutes at a third frequency.

I tried welding a part while vibrating but did not notice any effect in the weld pool behavior.

An old ex-girlfriend used to swear that it worked very well indeed.




OK, I'll get my coat....

On a cleaner note!

If it is such a good stress relieving technique

Why does the liberty bell have a dirty great crack in it?

Keith

For every size/shape material it make like somthing different. I have ground very long parts for the particle accelerator in illinois, I cant remember the name right now. the shop that did the machining on it told me they sent it out for the vibration stress relive. After grinding I was not impressed with how straight they stayed. The bard were approx 120" long.

Quite often we get grind jobs in and we can not keep them flat when grinding. I have found that if I throw the material in with a temper load of my own material, say a 1000 degree double temper this does the trick 99% of the time so when i go back to grind the parts stay flat for me.

Hello there!
This is a very old post and I don't know what your conclusion about VSR was back then, but I would like to share my opinion, and experience, with you, in case you haven't figured out yet whether it is good or not. Vibratory Stress Relief DOES work. I have been practicing it for about 9 years in Greece (!!) both in-store and in customers' premises. Either for Stress Relief or for Welding Conditioning. I have seen in practice the benefits and I am telling you it is remarkable. We imported the machine from the US and I am telling you it was one of the best buys we ever did. Due to the fact that I acquired experience on the matter I was also asked by the makers to train a few people around the country that had also bought it after us. I also had the opportunity to once demonstrate it to a Professor from the University of Sofia, Bulgaria. We run a few tests on VSR and on WC and he got a couple of specimens to examine them under the microscope regarding the molecular distribution of the welded material with and without the WC. The distribution on one without was fairly alright but on the one With the practice of WC the domain was practically even, smooth and "spread like butter". Even the thermal distribution was spread evenly helping to avoid thermal stress that you can normally have when you weld. The result was to buy one for themselves. Another test that I did for our own purposes, involved the machining of two shafts from exact the same material (proof with certificate). We had to machine a two meters shaft of 250 mm diameter. It required a lot of machining as there were quite a few diameter gradations along the shafts. After we machined the first one (with no VSR) it got bended for about 2,5 mm. It was practically ruined. We treated the second one with VSR and after the machining there was absolutely no deformation. We couldn't even believe it ourselves.
I have also tried it on molds of rotatory casting because after one use they were deformed but with no success. Although the evidence wasn't enough because I did it only in three specimens and for me it wasn't enough. It was not suggested by the makers, and it was only my choice. Like I said there wasn't any success on that project but I think with the proper experiments we could get some positive results.
I don't know if it is ok to suggest a name of a maker, and because I think it is going to be marketing and advertisement and I don't want to do that I will not provide any details. But I can tell you that we had such success with this equipment we were even interviewed by an American magazine of that field (again no name- but I can do that in a private message if you require me to). In general I was practicing it a lot ( I don't work for that company any more as I relocated my self in the UK) and for any purpose. Even the welders loved it and didn't want to do any job without it.
In conclusion, VSR and WC does work what it is recommended for. If you do require further information please do contact me and I will gladly help if I can.

Cuda i have to agree with Forrest seen it tried several times my opinion waste of time jsust don't make a difference don't think its gonna be very hepful on your parts suggest you buy htsrms on your shafting thats what we had to go to on hog shafts

Mechanest said:

Hello there!

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Do you have some peer reviewed literature to prove this? I would take a paper published in any journal. Otherwise, it is bull.

A few friends of mine did a college research project about this type of thing a few years ago. I really cant comment on the results or the testing methodology, but i do remember the people from the company. They were very short on evidence and got incredibly upset with even the slightest questioning of their claims or their results. Gave me the feeling that a. they were trying to hide something and b. it wasnt the first time their product was called snake oil in front of their faces.

I think the topic might be clarified by a bit of history.

Before modern methods of non destructive testing became practical, seasoned veterens of the foundry, rolling mill, and forge shops would gather late in the shift and "sound" the days's production by tapping them with hammesr. By listening to the ding or the clunk they could spot defective work items and even pinpoint the location of the defect.

If the work was suspended or damped in various ways, struck in miltiple locations, compared in riing to identical items a very thorough examinatio was possible. Thus railroad wheels and axles, steam engine cylinders, anchor chains, shafting, and structural beams could be rejected for cold shuts, pipes, laminations, shrinks, voids, cracks, and a dozens other metallurgical and manufacturing defect based in the asessment of wise old ears.

I'm not suggesting vibration stress relief is all BS. I'm only saying I've seen no - zero - unqualified successes. I suspect it has to be intelligently applied amd for that the people specifying its use and the techs using it need to be schooled just as a man with a hemmer.

This makes sense as the ear is an incredibly sophisticated sound analysis device that unfortunately cannot be calibrated or included into an enginerred quality assurance program.

Many times when work was suspended and vigorously rung it would change shape or demsnsion slightly indicating a change in the material possibly from a resolution or re-distribution of locked in stresses. It was ony a srep to conclude that by circulating strain enegy through a raw casting, forging, fabricating, whatever stresses could be relaxed somehow. In the 1970 a number of well intended but over-sold vibration stress relieving gimmicks were touted in the manufacturing shows around the country and since senior executives and shop managers are no less gullible to flashy presentation than persons with penile perfprmance problems many systems were sold only to be misapplied.

Shocks from hammer blows shrewdly applied to items having locked in stresses may result in stress reduction because the energy rate and location of shock can be precisely controlled. Vibration stress relief is limited in energy rate and magnitude to nodes where resonance stress circulates to a greater degree, section changes, intersections, corners etc ie: places where fatigue could be expected.

I submit a skilled man with a hammer and keen ears selected for his intuition could resolve more stress in a metal item in about 1/10 the time and 1% of the surgical risk as a vibration stress system run by factrory trained techs.

Hell, I've done it. I used to run a big plate planer in the ship fitter shop cutting weld preps in the edge of 20 ft long bars burned from plate to be welded into elevator rails. Remove a double J-weld prep from the edge of burned plate and the result is a 3" to 7" of banana shape. During machining, the bars would slip and twist in the weenie ar cylinder clamps of the plate planer.. You have to send it to the bumper for straightening 3 time for some bars.

If I gave the ends of the bars a dozen mighty whacks with a 16 lb sledge and a healthy bash on about one foot centers down each of the burned edges, the bars needed no straightening for machining and only a little prior to weld.

vettedude said:

Do you have some peer reviewed literature to prove this? I would take a paper published in any journal. Otherwise, it is bull.

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Yeah, it is called physics and mathematics. Also 9 years of practice of this particular method.

Mechanest said:

Yeah, it is called physics and mathematics. Also 9 years of practice of this particular method.

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With that response I know you have no science and math to back it up. I am sure a snake oil dealer has 9 years of practice with snake oil.

There is no physical mechanism for stress relief by vibrating the part. If anything you would impart stress onto the part, like shot peening, that implies some compressive stress to the top layer of material, it does not stress relieve.

http://en.wikipedia.org/wiki/Shot_peening

In order to relax a part we apply heat to change the microstructure/chemistry by unlock bonds. Micro structure change comes about as the electrons are excited in the material and thus some bonds release. When parts cool in a specific way bonds are re-applied sometimes forming different compounds and other forming new crystal structures of the same compounds.

I submit a skilled man with a hammer and keen ears selected for his intuition could resolve more stress in a metal item in about 1/10 the time and 1% of the surgical risk as a vibration stress system run by factrory trained techs.

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But I doubt he can relieve stress just by listening. He can't!

Vibratory stress relief is 90…95% BS.
The source of internal stress is know. But what does it mean? The material is locally compressed or expanded up to to its yield strength. If there is stress above yield strength, the material gives in and the stress is reduced to yield strength.

Thermal stress relief works this way: Mat'l is heated, so its yield strength goes down to about 10% of that at room temperature. That means, thermal stress relief can reduce internal stress up to 90%.

For vibratory stress relief, there should be local stress increased by the hammering and shaking that is near the yield strength. Won't happen, as you can imagine. For welding structures that do bend a lot, you get better results. But still, you will relief the stress by just 5…10%.

Wasted money, wasted time.


Nick

Vibratory stress relief. Ask a woman if it's works and IM sure she will say hell ya. He he har har