Documenting and/or verifying the amperage value for GTAW Al

Date 12-10-2012 00:24

When documenting and/or verifying the amperage value for GTAW Aluminum (D1.2) I always watch the ammeter on the power source to ensure/verify conformance to the WPS, I’ve been doing this for years.
The welders that use the variable amperage foot controls always complain that I’m being to picky. I always stick to my guns and site directly for the code the allowable range limitation.

Recently the question came to mind, should I be checking the preset amperage only?

The argument that I present is that the verbiage in D17.1 specifies controlling all of the other variables and not the actual weld amp/volts since the welder cannot see the machine while welding. (this makes ense to me)

So my question is, is using the machine’s preset amperage value an acceptable option, even when the foot control will allow for the welder to drop below the 20% limit, particularly after the weldment heats up and also for crater fill.

How do the rest of you handle it?

This question can flow over to GMAW as well, because of variations in the electrode extention can cause significant variation in the welding machine output.

By eekpod

Date 12-10-2012 11:45

Here's how I check a SMAW machine, which was the simplest method of arc welding at our shop.

Using my verified/ calibrated amp meter (tong type) I check for amps as close to the stinger as possible, I'm usually 2' behind the welder while he running a bead on some scrap. I check to see where he has the dial set on the machine and compare it to what I get on the amp probe.
So for example the welding machine dial is set at 100 amps, as he runs his bead I watch the display of the amp probe to see what the actual reading is. You'll need to wait a few seconds to let it "calm down" after he initially starts but after 5-10 seconds I can get a steady reading. If the machine is within the range allowed I know the dial is set to what the machine is putting out and can feel comfortable saying the machine is within it's range.

Now there are alot of variables that can mess this process up, and arc length is one that can't be easily controlled. You'll have to do the best you can.
The best technique is to have a load cell used to calibrate the machines, but I can't do that myself. I need an outside service to come in and hook it up to each machine and it puts a constant pre-determined draw on the machine. This way they know what the welding machine is puting out and what is being drawn from it.

Basically you need to confirm that your welding machine is putting out what it says it is, and if it isn't either get it serviced or create a little chart saying the difference.

By Mwccwi

Date 12-10-2012 22:52

eekpod,
Thanks for the response, but what you answered isn't what I asking about.
The shop's equipment is calibrated and when it is suspect, we have procedures for verifying (similar to what you described).

What I'm asking is asumming the equipment is functioning properly.

My concern is the actual apmerage, how to record. (Am I being too picky?)

For example when I proctor/witness WPS Qualification Tests or when doing a audit to verify that the welders are following the writen WPS.

Is using the preset amereage reading from the power source acceptable practice? (this sets the max. but the amperage can be lessened by letting presure off of the foot control.)
or
Is it required that I monitor the ammeter throught the welding to verify that the welding does not fall out of the +- 20% range.

By Stringer (***)

Date 12-11-2012 00:12

In the letter of the law, yes. Amperage is amperage and a foot control effects it absolutely and depending on how the base amperage is set, a welder could easily weld outside the prescribed amperage. Amperage would be read downstream for an accurate figure. All that said, 20% is quite an easy range to stay within, seems to me.

By Mwccwi

Date 12-15-2012 20:27

Thank you, Stringer,
Your response echoes what I've been preaching.
Recently, I've been feeling pressured and felt the need for conformation of my convictions.

By Kix

Date 12-19-2012 13:39

You are on the right path.. When they qualified the procedure they should have documented every amp reading they saw so the range would be correct. A procedure is a recipe and needs to be followed like one within the 20% tolerance. When qualifying with a remote you definitely want to get your range spot on. SMAW, GMAW, FCAW procedures amp ranges will be a lot tighter for individual passes than with GTAW "remote" on small aluminum parts. GTAW "scratch start" will be a tighter range because there is no variable control. Sounds like you might have a case of someone not documenting the amp range to the T on the PQR therefore limiting your range in the WPS to something that can't be replicated in production. If you only have one welder out of 5 barely going outside of the range on the WPS I'd say the WPS was documented correctly and you have a viable procedure. If no one is staying within the range, then I'd start Dick Tracey’ing the procedure. You might also just for sh!ts and giggles check the PQR and see what was actually recorded and check it against the WPS to see if anything sticks out.

Kix

By Mwccwi

Date 12-19-2012 22:50

Thanks for the reply.
I'm looking into qualifying more procedures for a broader range of thicknesses.
Currently we have only one qualified GTAW aluminum for 0.08" square-groove 1G (very limiting), but the job quotes I've seen are for mosty 0.125" and 0.250".
I will dig into the scratch paper for the PQTR (maybe I'll get lucky and squeez some wiggle room).
The good news is that all of the welders that I've passed welder testing on were in the wps range, it's the one that deviated out of range and I stopped the test and failed them, that started the pressure issues about the mean old CWI being too picky.

again thanks for the reply, sometime this forum is the only support that I feel.

By Stringer (***)

Date 12-20-2012 02:01

We apply codes. It's all designed to dispassionately quantify with black and white measurements and eliminate personal bias. So it's not possible to be mean or picky. :smile:

By Mwccwi

Date 12-20-2012 22:53

It seems that everyone around brags on the fair and equal black & white calls until they try to read gray.

By QATJones21 Date 01-16-2014 21:20

I have a question that is somewhat in this category of topic.

We just recently had a customer audit of our AWS D1.1 and D1.2 processes. The auditor had a finding that derived from his interpretation of AWS D1.1 Section 4.7: Preparation of WPS- The manufacturer or contractor shall prepare a written WPS that specifies all the applicable essential variables referenced in 4.8. The specific values for these WPS variables shall be obtained from the procedure qualification record (PQR), which shall serve as written confirmation of a successful WPS qualification.

His statement of the observed condition: "PQRs have a range documented for voltage and current. The current (Amps) is listed as 80-170 A and 21-24.6 V on the PQR and WPS. This should be a specified single current on the PQR, and a range of +/- 25% of the Amp value on the WPS."

My question is: On the PQR, do the amps and volts have to documented as an absolute value or can it be a range?

Explanation of what we do: We do document on the WQTR, the absolute values that were used during the test. Once the weld has passed all required tests for qualification, the WPS and PQR is established. On the PQR, we document a range for the amps and volts based on the actual values recorded on the WQTR and the +/- % of Table 4.5 in AWS D1.1. So...Our WPS's and PQR's have the exact same information for these two essential variables documented on the established forms.

By 803056

Date 01-17-2014 03:33

This is an interesting subject because everyone has a slightly different opinion on how to record the welding parameters during a test.

I will use GTAW as my example since it is the process cited in the original post.

When qualifying a WPS (one that does not meet the conditions of prequalification) we work with a preliminary WPS that lists all the welding parameters and the accepted or expected ranges we want to use for the qualification. Values for voltage, amperage, and travel speed are listed as ranges. The peak amperage is set at the machine and minor adjustments while welding are made with the foot pedal. Once the welder zeros in on the amperage he wants, the machine current at the machine is dialed in so that every successive bead is deposited with the foot pedal fully depressed. For all practical purposes, the test coupon is welded with the current, voltage, and travel speed that is fairly consistent. The "average" current, voltage, and travel speed is recorded for every weld bead. The travel speed is the parameter subject to the greatest amount of variation from one bead to the next, but it varies little for any one weld bead.

Unless the welding process is mechanized, it is crazy to think the welder is not going to vary current, voltage, and travel speed somewhat while welding the test assembly. By using the average value for each bead, a pretty accurate record of the parameters is achieved.

I use the statistical functions available with MS Excel to determine the median values for voltage, amperage, and travel speed. When the code permits a + or - value, it is the median that serves as the basis for those ranges.

The same holds true for the other process, except that there is no foot pedal to vary the current while welding. However, the approach is the same. The secret is writing a preliminary WPS that is reasonable. That where my experience comes into play. Over time, one develops a pretty good idea of what the welding parameters should be for a particular process and application. If the values prove wrong once welding begins, they can be adjusted and recorded on the PQR.

As is always the case, one must be there to watch the meters and to record the parameters and travel speed for each bead if the PQR is to be of any use.

By the way, current does not vary from one location to another along the welding leads. However, the voltage drop is proportional to the length of the welding leads, so when using long leads, it is necessary to record the arc voltage as close to the welding arc as practical. When welding with low currents, such as when welding thin sheet, the welding lead can be looped through the clamp tongs to multiply the amperage reading and get better consistency. In other words, if the cable is looped twice (two wraps) the amperage reading will be twice the actual amperage. This can be used to keep the amperage reading in mid scale of the tong meter where the readings are most accurate. Just remember to divide the amperage reading by the number of wraps.

Best regards - Al

By welderbrent (*****)

Date 01-17-2014 03:52

Hey Al,

Would you mind pasting this answer on his other post on the same topic down in 'Certification and Qualification'? I think it would fit a little nicer.

I was just looking some things up and was about to quote you from your recent response in IT when you did it for me. And much better too.

Have a Great Day, Brent

By welderbrent (*****)

Date 01-17-2014 03:55

BTW, what are you and Henry still doing up and on the forum? Don't you old guys ever sleep? :lol:

OOPPS. I resemble that remark.

BB

By ssbn727 (*****)

Date 01-17-2014 04:29

SLEEP???

We don't need no stinkin SLEEP!!! :yell:

By welderbrent (*****)

Date 01-17-2014 04:34

At least I have an excuse...I'm working a job on swing shift and it is only 9:30 here.

Hope you aren't up because of any problems. Been good seeing you back around more often.

Have a Great Day, Brent

By ssbn727 (*****)

Date 01-17-2014 04:42

Once the drugs kick in, I'll be catching enough zzz's to be deeply involved with studying my "harmonic distortion formula" with the robust model I use to to show an example of how harmonic distortion perpetuates by the frequency of movments! :yell:

Sweet dreams indeed!!! :twisted:

Respectfully,
Henry

By QATJones21 Date 01-17-2014 14:42

Thank you so much Al! I met with our 3rd party CWI earlier this week and he basically said the same thing about using the averages and although he did not agree with the auditor, he would revise our PQR's to be absolute values just to keep the customer happy. I just have not been able to let it go as easily and pretty much determined to argue this finding but I just needed a little more clarification of the standard as well as the opinions of others. So thank you, this has helped!

Traci