Weld Stress Relief with Subharmonics 2

[jackboot]

Questions:

We are thinking of purchasing a subharmonic weld conditioner from Meta-Lax. The machine hooks up to your weldment and basically looks at the resonance frequencies (they change while you weld). The computer analyzes the signal and adjusts the "vibrations" to "stress relieve while you weld."

Does anyone use the Meta-Lax weld conditioning set-up or the equivalent?

Does anyone know of any information that explains the technology? Google doesn't yield much.

What type of test would one run to verify the amount of stress relief?

jackboot

 

[kenvlach]

For info, try this search:

http://www.mamma.com/powersearch.ht...indow=&domain_mode=1&domains=.&go.x=35&go.y=6

One site lists government jobs (NASA, Air Force, Navy,Army) that have used Meta-Lax Stress Relief and/or Weld Conditioning:

http://www.bonal.com/meta-lax/Home/Applications/Government_Jobs/government_jobs.html

I don't fully understand the details, but the basic idea is simple enough: impart some kinetic energy via a special transducer to the metal atoms to get them to vibrate more, as if at a higher temperature.
Metals can be induction heated, water-containing substances can be heated by microwave, and some ceramics can be sintered at specific microwave wavelengths, so why not this?

 

[TVP]

X-ray diffraction is the usual method used for analyzing components for residual stress. You can obtain more information using the following links:

http://www.tecstress.com/

http://www.protoxrd.com/xrdfacts.html

 

[Carburize]

There is no actual stress "relief" with this process, in order to relieve stresses there must be plastic flow within the material usually accomplished by creep at elevated temperatures - the normal form of thermal stress relief.
Mechanical techniques, such as the one you are considering,can be used to reduce the peak stresses by redistributing the stresses and can be useful in stabilizing large cast or fabricated parts prior to machining. Strain gage type residual stress determinations will show if the process has successfully reduced the peak residual stress levels.

 

[jackboot]

Carburize-

The Meta-Lax website is claiming all kinds of benefits:

Low distortion; Fewer cracking issues; and lower stresses- if we are not getting some type of "movement" then what would be happening?

And kenvlach made a good point about inputting kinetic energy into the part - be it by heat or by mechanical means. Why would this not be stress relief?

Again, I am asking because this seems slightly "to good to be true" to me as well.

jackboot

 

[Carburize]

I believe that the peak stresses will reduce but to balance this effect areas where the stresses were originally low increase in residual stress. In the case of large flimsy structures where thermal stress relief could cause major distortion problems mechanical vibration treatments have been used successfully to stabilize assemblies for machining.

 

[weldmete]

An important question to ask is: Does ASME allow this process to be used in lieu of thermal stress relieving in section VIII, division 1, UCS-56 of the pressure vessel code? As far as I know they don't. If ASME doesn't use the process then I would stay away from it if I were you.

 

[jackboot]

weldmete-

My weldment isn't a pressure vessel - and I know ASME probably wouldn't buy into this even if it whiten teeth. And I concur - if it was a pressure vessel or power piping- I'd never touch it.

But my problem is a complex, highly restrained weldment that is made from A514 (t-1 material). We are cracking welds - and I believe it is from distortion. The part is too large to weld and stress relieve in multiple steps. The part is later machined - so the dimensional stability is a must.

My hope is that it will solve our problems. I will write back to let everyone know. We are going to rent one to experiment with.

jackboot

 

[stanweld]

I've spoken with 8 users of the Meta-Lax system, including NASA, and all reported satisfaction. Two users actually performed x-ray diffraction or strain gauge measurements to confim stress relief when used after welding. NASA reported then that they used the conditioning mode only and always together with weld sequencing techniques to control distortion. NASA and others stated that weld puddle fluidity and welding efficiency was also improved when using the "Conditioning Mode".

FYI, IWI has recently evaluated similar "ultrasonic impact tratment" systems devolped in Russia and had info on their web site. Both Russian technical reports and data and IWI data are provided.

 

[jackboot]

Thanks stanweld - that is good news - I will let everyone know what benefits we see.

jackboot

 

[metman]

weldmete,
I don't know about ASME but I believe ASTM A-514 actually prohibits thermal PWHT of T1 because it causes cracking so that vibratory stress relief is the only option. As I recall it only applies to certain alloys in the so-called T1 family.

Jesus is THE life,
Leonard

 

[jackboot]

Stress relief is not recommended except in some cases - one of these being dimensional stability. Since we machine the fabrication - it is a must - otherwise the part would move/relax with each machine cut.

http://www.ussteel.com/corp/Plate/weld/weld-app4.htm

This link talks a little about it.

jackboot

 

[kenvlach]

I found references to 2 journal articles which lend some more credibility to subresonant stress relief processing.

T. E. Hebel, Heat Treat., vol. 21, no. 9, pp. 29-31 (1989), cited in the process description given in Physical Metallurgy Handbook, p. 17.48 (2003).

From a computer search of ASM journals:
P A Hassell, ‘Opportunities in Applied-Energy Metal Treating,’ Advanced Materials & Processes, 141, (2) pp. 43-49 (February 1992). abstract:
“In general, applied-energy metal-treating processes are those in which energy is selectively applied to specific areas of a part for the purpose of altering such properties as hardness, strength, ductility, machinability, or corrosion resistance. Conventional induction heating is by far the best known and most widely used applied-energy method. Several lesser known (and often underutilized) applied-energy techniques are discussed, including: impulse induction heating, contact and high-frequency resistance heating, electron-beam and laser heating, and two nonthermal methods, magnetostriction and subresonant vibration.”

So, the process has been around for a while.

 

[bklauba]

Jackboot,

How did you ever make out with your sub-harmonic stress relief system?? Have you found the instrumentation honest, such as by doing the same part on successive mornings, to see if the data indicates a stress relief response again?? How about dimensional stability?

 

[jackboot]

I have not checked with our department as of yet - but we were going to rent a unit to experiment.

So, far we have not done the experiment.

jackboot

 

[MOB1]

I would refer you to a TWI publication "Vibrational Stress Relief" The Welding Institute Research Bulletin, Dec 1977.
More recent information (1994) from TWI reaffirmed their opinion that dimensional stability is improved but no "stress relief" as such occurs. In fact it has been suggested that the machines are introducing a large number of tensile stress cycles and could initiate fatigue cracking.
The advantages of thermal stress relief are, of course, not achieved eg hydrogen diffusion, HAZ softening.
I would have thought that weld cracking problems (weld metal or HAZ?) would be solved by welding parameters as part of the overall weld procedure. The use of lower strength weld metal, stringer bead, peening and temper bead techniques are all designed to prevent residual stress and cracking.

 

[bklauba]

Probably the firm and personnel most experienced with using vibratory stress relief on this material (or similar, such as HY 80 and HY 100) are the submarine folks. Try e-mailing jazzinar@ebmail.gdeb.com, who manages the machine shop at EB/GD. He might shed some lite on how to do this.

 

[jackboot]

OK- I emailed the gentlemen in the address - I will post the information if he replies back.

MOB1 - the article you listed requires a membership to TWI. I wasn't able to get the article.

jackboot

 

[VeryPicky]

Hi everyone.

I have been following this discussion with a lot of interest.

I understand that vibration stress relief has influence on surface and possible near surface stress distribution.
Compression stresses introduced by this method act against the shrinkage tension stress in the weld.(in the macro scale).
I would not recommend the method for thick components. However if the cracking is typically a toe initiated problem the vibration method might be a solution.

I would also try to provide smooth toe transitions and try to reduce the volume of weld metal.

In the case of pressure vessels the vibration stress relief method is not a recognised practice by ASME.
In ASME VIII Div 1 requirement for PWHT is a DEFAULT and than exemptions follow.

jaceksan

 

[jzanter]

We have a meta-lax system. We proved the effectiveness to ourselves and presented results at an ASM fall meeting a few years back.

We had an aluminum casting that was cracking when a certain bore was machined. Neutron diffraction studies of an uncracked casting before and after a meta-lax stress relief cycle showed a dramatic change in the stress state.

Since that time, I've used our machine to diagnose cracking problems in thermal sprayed coatings and distortion issues.

For reference, neutron diffraction, as I understand it, is the only way to do internal stress state measurements. It's not simple and access to reactors is naturally difficult.