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Up Topic Welding Industry / General Welding Discussion / GMAW-P procedure and test
- - By TALower Date 03-09-2016 05:10
I am trying to write a set of weld procedures for a shop for their miscellaneous welding area, i.e. handrail, stairs, etc.  It is most likely a GMAW Pulse process.  The wire is ER70S-6, 0.035" diameter using 75% argon and 25% CO2 shielding gas.  Per the manufacturer's recommendation, the volts are between 19 and 22, amperage is 130 to 150 with a wire speed of about 200 ipm.  Each of the welders were attempting a 3/8", 2G qualification test using the Optional Test Plate shown in figure 4.32.  However, every single test failed the root bend test due to lack of fusion on the root pass to the bottom (flat) plate.  All of the face bend tests passed.

Is this simply a case of lack of skill on the welders part?  Each test was between 40 and 50 degrees.  Should they have pre-heated first?  Should they have increased the wire speed and thus the amperage to achieve a greater heat input on their first pass?  Is this even a valid test for someone that will not use this process for a multi-pass weld in the future? Handrails do not usually require more than a single pass.

I am basing my earlier statement about it being a Pulse process on the fact that it certainly sounded like pulse arc while they were welding.  I know that pulse arc (short-circuit) is not prequalified and that I would need to do a weld procedure qualification test to use any procedures in structural applications.  Am I going about this all wrong?  Is this even the proper test for this application?

I apologize if my questions seem naive.  I came up through the detailing department, not the welding department.  I became an inspector and later a CWI because I could read drawings and showed aptitude, not because I would weld.

Thanks in advance,

Tom Lower
TAL Quality Consultants, LLC
CWI# 07041371
Parent - By welderbrent (*****) Date 03-09-2016 06:02
Not Pulse, it is Short Circuit Transfer.  Two different modes. 

GMAW has 4 according to the 'Experts': Spray, Pulse, Globular, and Short arc. 

The problem is the 'coldness' of your mode.  With the gas and the range you are running a 'warm' short arc but not warm enough for that root.  Lack of penetration. 

Spray, which the unit would go back and forth between with short arc for Pulse, requires 80% or more Argon.  With a change of gas and the correct machine you could achieve Pulse but I'm not sure you have the correct machine to get there.  You must be able to set a cycling rate for the pulse to be going back and forth from spray to short. 

It is the 'heat' of the spray that gives you your penetration to be able to pass that root bend test. 

Do they even need it?  Probably not in all reality. 

He Is In Control, Have a Great Day,  Brent
Parent - - By KBNY (**) Date 03-09-2016 13:09
You need a qualified procedure to test the welders to. It doesn't sound like you have that.
Parent - By KBNY (**) Date 03-09-2016 15:21
I realize you never stated to which code you were working to, so my comment may not apply
Parent - By Lawrence (*****) Date 03-09-2016 13:21
You seem to be asking all the right questions, that is what makes you a good CWI. Don't worry about being a welder in your past or not.

My advice would be to prepare several procedures.   One specifically for the Fig 4.32 test assembly and then procedures for production.

Tell us about the welding power supply you are using.  With the proper gas (as Brent mentioned) you *might* achieve spray transfer at 200 ipm with a pulse unit, but it's at the low end for sure. 

The voltage you mention (19-22) on a CV mig uint would produce short circuiting transfer.

Knowing the capabilities of your power supply are important/critical for your questions.  I say this because you can adjust your parameters and gas and do a Spray GMAW welder test.. But if your production work demands short circuit that presents a problem.  However, some GMAWP units can produce pulsed spray transfer at surprisingly low average current and voltage.

D1.1 does not differentiate between Traditional Spray and Pulsed Spray for performance or procedure qualifications.  So if you are actually pulsing, then it's a matter of getting an appropriate shield gas, writing a WPS for your performance qualification test that gives enough current to get the root pass in easily, and then prepare production WPS's for your hand rails that are pulse spray, but cool enough to get the job done.
Parent - By pipewelder_1999 (****) Date 03-10-2016 03:08 Edited 03-10-2016 03:16
Tom,

I'm not a big fan of the "optional" test unless that joint is to be used in production. Even myself knowing the fact that the lower piece is a big heat sink and prone to poor fusion, I still sometimes catch myself with a work angle pointing up. The 1st bead should almost be treated like a fillet weld (which can be a pain to pass by itself).

I qualified a procedure for open root fill and cap with 75/25 and short circuit so it is capable of producing quality welds. I suggest that you use the regular test coupon. But...

I also try to make companies aware that there is more to code compliance than having a qualified procedure and welders.

Consider the joints to be welded, do they comply with the range of qualification for the procedure and performance.
Are the joints as designed fillet welded or groove welded. If groove welded are they CJP or PJP. If groove welded, diameter restrictions may apply.
Are the dihedral angles on the handrails in need of consideration.
Are there jurisdictional requirements for code compliance?
Are the materials listed in the code and procedure qualified.
Is inspection performed in-process and finals.

You have already been straightened out on the pulse/short circuit deal so I won't comment ion that but understand that knowing what you don't know is sometimes as important as knowing what you don't. The ability to weld has nothing to do with the ability to perform duties as a welding inspector however a strong understanding of many things welding related is needed.

ALSO. The ability to obtain suitable results with 75/25 and conventional (non-pulsed) transfer modes . The bend being performed in this video is from a 2G weld done last night in class. 1/2" plate with open root.  https://youtu.be/q6b0Lp-pqbM
Parent - By kcd616 (***) Date 04-12-2016 09:54
Tom,
100% co2
lack of skill with the welders
if a welder can not pass this simple test
no go
to help you and the welders
the root is failing from not enough heat, penetration
co2 will fix it
this just imho
sincerely,
Kent
- By ashok Date 04-09-2016 15:19
Plz send me details about preheating nd post heating temp nd thkness range for CS nd Alloy steel
- By mwmw (**) Date 04-09-2016 23:10
90/10 for carbon and 1025 gas for SS willmake a world of difference
- - By 803056 (*****) Date 04-10-2016 15:11
The possible causes of the incomplete fusion in the root, where where the lower plate and backing meet, well, let's just say there are many. The two factors I would consider as primary suspects are the welder technique [pushing the arc (forehand), rather than pulling (backhand)] and incorrect machine settings (insufficient heat input).

AWS D1.1 does not consider short circuiting transfer to be prequalified, whether one is using a conventional machine or one capable of pulsing. One condition necessary for pulsed spray transfer is the use of the proper shielding gas. The gas must be capable of spray transfer, thus my recommendation is to use a mix comprised of no less than 80% argon. Personally, when there is a question with the type of shielding gas, I opt for 98% argon with 2% oxygen. This gas is my fall back whenever the contractor is experiencing problems with getting a true spray. Once the issue of gas is rectified, one can always experiment with other options such as 85% argon, 12% carbon dioxide, and 3% oxygen. There are many mixed gas combinations, but a mix with a minimum of 80% argon usually gets the job done.

One of the problems with pulsing is understanding how the machine pulses, i.e., the waveform and the manufacturer's terminology used to describe the waveform. Terms such as slope, upslope, downslope, frequency, duration, peak voltage, background voltage, peak current, background current, etc. are used to describe the pulsing parameters.  A number of manufacturers take the guess work out of the equation by preprograming the machine so that the welder dials in the correct program based on the base metal, electrode, diameter, and shielding gas used. If that is the case, the amount of "tweaking" permitted by the welder is limited. The parameters may not be optimum for the application, but they are close enough for most welding applications.     

Remember the meters on the welding machine control panel are averages, usually root mean square values for both amperage and voltage. That being the case, the voltage read is not the peak voltage, nor is the amperage the peak value, nor are they the back ground values. The meters usually do not have the ability to display either the peak or back ground values.

When welding carbon and low alloy steels, my personal experience has been the contractors often use a gas that is not optimum for pulsed spray transfer and the parameters set by the welder are such that the heat input is too low to obtain good fusion on materials used for welder qualification, i.e., 3/8 inch or 1 inch thick material. 

I would suggest the proper parameters be established by welding a series of single pass fillet welds. Once the parameters have been tweaked to produce proper fusion in the root, use them when qualifying the welder or if necessary the WPS.

Best regards - Al
Parent - By Stringer (***) Date 04-12-2016 03:43
I'm an 85/15 guy running L56 or L59.
Up Topic Welding Industry / General Welding Discussion / GMAW-P procedure and test

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