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Up Topic Welding Industry / Inspection & Qualification / WPS Question
- - By electrode (***) Date 07-03-2016 17:12
Not really sure whether or not this is the right board for posting this question, but surely it's worth a try.
Basically this is addressed to those ones among you who have proved excellence (as I could learn by reading a high number of posts in here) in interpreting/producing Welding Procedure Specifications.

We are increasingly discussing issues in Europe as when it comes to advanced, i.e. 'waveform controlled' GMAW processes.
There's a - to me negatively - impressive rise to observe in the number of proprietary brand names of these processes.
Although quite often based upon similar process modes (for example: short circuit or dip transfer) they nonetheless can show different final welding results - although maybe the electrical parameters adjusted - and which I understand should be 'essential' variables in a WPS - prove comparatively similar.

That's an intricate subject to overcome or at least to appropriately consider in a WPS here at present and my question is: "How do you; i.e. the experienced US/AWS welding inspectors, welding technicians or engineers deal with these differences?"

Any response or thought shared is gratefully appreciated in advance.

Thanks and regards!
Parent - - By 803056 (*****) Date 07-03-2016 18:31 Edited 07-03-2016 18:34
As you noted, each manufacturer has their own idea of how to design a welding machine with the best operating characteristics while pulsing. The basic assumption is that there should be metal transfer while the pulsing parameters are their peak values and no metal transfer occurs when the parameters are not at the maximum. The means of producing the required pulsing wave form varies not only from one manufacturer to another, but also from one machine model to another.

Developing the optimum parameters is typically beyond the technical capability of the welder, so the manufacturers often provide "canned programs" based on the information provided by the end user, i.e., base metal to be welded and the thickness of the base metal, electrode diameter, electrode classification, position, shielding gas, etc. The welder is permitted some limited latitude in ranges of the welding parameters set by the manufacturer. The programs are tailored to provide acceptable results when using the particular model of welding machine with pulsing capability.

The problem is that no two welding machines are alike, each model uses a different approach to producing the pulsing characteristics. Thus the optimum parameters for one machine model rarely provide optimum results when used with a different welding machine. This complicates developing welding procedures that can be used with several different models of welding machines even when the machines are produced by the same manufacturer. Depending on one's basic philosophy of what a WPS is to accomplish, it may be nearly impossible to write a WPS that can be used with different welding machines with pulsing capability. The meters provided on the control panel do little in providing useful information to the individual collecting date while the WPS is qualified. There is little relevance in the information provided by the meters for the amperage and voltage used while welding. They provide no information regarding the wave form of the pulse, thus the conditions can not be replicated using a different welding machine model. Recording the instantaneous "power" while welding provides no information that allows the welding conditions to be replicated when setting up other machine models. What is the solution?

The only way I know of to record the welding parameters, i.e., the characteristics of the pulse, is to use a multichannel oscilloscope. This is no easy task, nor can the information be transfer to another welding machine that uses different characteristics to provide pulsing parameters. Basically, in my humble opinion, a WPS that utilizes pulsing is qualified for the particular welding machine and model used to qualify the WPS.

In my opinion the WPS functions as work instruction to the welders to ensure different welders produce welds that are consistent in their properties and if necessary, their appearance. That is, if the WPS is followed, the mechanical properties of the resulting weld should meet the minimum requirements of the applicable welding standard. However, the purpose of the WPS is much more than alluded to in the preceding sentence. The WPS should provide the welders with the parameters needed to set up the welding machine, the techniques to be used, and other information such as groove details, fit up tolerances, etc. When followed, the WPS should ensure a code compliant weld is produced. That entails much more that simply ensuring the weld produces the required mechanical properties. All of the preceding assumes the welders have the basic welding skills necessary to produce a sound welds and it assumes the welders follows the WPS.  

The bottom line is that the WPS is qualified only when used with the same model of pulsing welding machines produced by the same manufacturer that made the machine used to qualify the WPS. The information and thus the WPS is not transferable to a different pulsing welding machine model or to a machine produced by a different manufacturer. Pulsing isn't the same as conventional transfer modes.

Best regards - Al
Parent - - By electrode (***) Date 07-04-2016 12:52

Since noticeably driven by both long-term hands-on experience and theoretical expertise; I certainly count your response among the best statements that I have read in quite a number of years as when it comes to this particular subject.

Be assured that I deeply appreciate and will take this with me for further use - always of course correctly referring that to you!

Thanks very much and best regards!
Parent - By 803056 (*****) Date 07-04-2016 14:39
Remember there are individuals that have opinions that differ from mine. Having said that, I would like to see a welder set up and produce acceptable welds based on the WPS provided.

Happy 4th or July!!!!!

Best regards - Al
Parent - - By js55 (*****) Date 07-05-2016 13:24
ASME has taken a decent stab at addressing this issue. You will find applicable variables sprinkled throughout the Code as well as a non mandatory appendix (H) with additional information. 
But don't feel like the lone ranger. Section IX set up a special task group to address this issue, a member of which participates in this forum from time to time, and it is a continuing and evolving issue.
Parent - By js55 (*****) Date 07-05-2016 13:29
It also may help to visit Walt Sperkos site. He has provided a tracking of Code changes some of which will be the very thing of which you are concerned. HSB provides the same service for its customers.
Parent - - By electrode (***) Date 07-05-2016 19:20

Thank you.

Honestly speaking; the results of this 'ASME task group' were and still are a main driver for the discussion that I was mentioning in my original post. As Al was both eloquently and competently describing the situation for 'regular' pulsed GMAW - the backbone of all further (and proprietary) advancements in waveform controlled GMAW - it gets even worse as when dealing with variants such as Lincoln STT^TM and others.

ISO has also - reasonably - begun in the meantime to lay particular focus on this by producing ISO/TR 18491 - released last year and taking very much into account the ASME recommendations on computing arc energy for finally obtaining greater accuracy in 'heat input' calculation.

However, the funny thing to me is that one needs to pay special attention to the final weld result. That is. Assume that you're taking two different - proprietary - welding systems using the same process mode (e.g. short circuit affected) varying though e.g. in the approach to electronically shape the waveform. It would be interesting to understand now whether there's a significant difference in e.g. the external parameters such as wetting behaviour; bead reinforcement etc. although the arc energy calculated proves the same - i.e. the metallurgical effects of both processes remains similar.

That was the background actually of my initial question. How does a WPS, or how do you inspectors in charge, cope with these phenomena?

Al has hit the nail, in my opinion at least, as he was saying: "The information and thus the WPS is not transferable to a different pulsing welding machine model or to a machine produced by a different manufacturer."

That gets it straight to the point. To me at least.

Thanks also for the 'Walter Sperko' advice. Very interesting(!) at the very least.
Parent - - By Lawrence (*****) Date 07-06-2016 14:07
Great conversation.

I'm involved in some GMAWP work, some procedures qualified by testing, others prequalified.

CWB W49 has actually published in 2013 that GMAWP is now a prequalified process, without much further guidance... D1.1 remains silent.

This rings back to a conversation with Js a week or so ago about how to govern our welding as an institution in a way :)

We use some wave forms developed in partnership with Lincoln,  Variants of "Rapid-Arc" and "Precision Pulse"  Both Spray GMAWP.   We developed specifically to produce a 3/16" horizontal fillet manually @ 28 IPM  and about 12.5 lbs per hour deposition, on moderate mill scale with .052 electrode.   There are several modifications to the stock electrical subroutines that we use to do this.   The procedures will do anything from 10ga. to unlimited thickness, but the "right sized" fillet is the moneymaker.

Those proprietary modifications are listed in detail on the PQR's,  But only the actual machine settings are listed on the WPS.. And of those details listed on the WPS, most are locked in.  The only thing the operator may adjust is the WFS (+30IPM) and voltage (+1.5)

The welding power supplies do have some capability for gathering current, voltage and overall energy averages per weld, as well as monitor "out of limit" conditions we have set for our own quality purposes,,, See attachment.

Our WPS's would be worthless as they stand today if we used a welding power supply that was from another maker... We have a covenant with Lincoln to have power supplies that can meet our criteria as they make various minor upgrades in the model.   This locks us in in some respect to a power supply... But that is not troubling as we did head to head trials up-front and nobody else could match what we were producing.  If such a time were to come that we needed a change... The WPS would require updating to reveal the machine settings for each type of power supply producing pulsed current... At least for us to keep our production the way we want it.. (I don't think D1 code drives such WPS details currently).

So Js... Competent weld management without an institutional governing body driving what we do, to keep our quality where we want it.  :)

I don't know how this speaks specifically to the many questions Al raised about energy input and that relationship to impacts, and PQR data gathering as far as "letter of the law" compliance issues.

The below snip is from one of the reports available in our cloud based data monitoring system for GMAWP.  We can look at individual weld data on each unit, or aggregate reports on groups of similar units by the weld, hour, day, week, or month...  It's a big help.

Electrode,  I'm not sure if this speaks to the ISO and other governing strategies.  But it is an example of how at least one GMAWP operator does things day to day... or at least a small fraction of how we operate, without giving up too much proprietary stuff.
Parent - - By electrode (***) Date 07-07-2016 07:05 Edited 08-28-2016 14:51
Parent - By 803056 (*****) Date 07-08-2016 00:58
Kind words -
thanks -

Up Topic Welding Industry / Inspection & Qualification / WPS Question

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