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
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
BTW, what are you and Henry still doing up and on the forum? Don't you old guys ever sleep?
OOPPS. I resemble that remark.
BB
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
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