.25 x .25 x 500 = 31.25, true true. Lets try another leg size like 1/2 inch or .5, .5 x .5 x 500 = 125, true. How about a 3/8 inch leg, .375 x .375 x 500 = 70.31, true. But do these heat inputs look or even sound correct? don't think so. Heat input is calculated using the following formula:
Amps X volts X 60 / 1000 X travel speed(inches per minute)
Given this for the stated 26 volts and 190 amps you get 190 x 26 x 60 / 1000TS = kJ/in Inserting the advertised travel speed the actual heat input would be...31.26 wow! pretty close.
Lets try another, .375 x .375 x 500 = 70.31 so 190 x 26 X .06 / 70.31 = 4.22 inches per minute, wow! pretty slow. Now the right way; 190 x 26 x 60 / 1000 x 4.22 = 70.24, wow! pretty close again, but whoever heard of welding with the mig process as 4.22 inches per minute. I would fire that guy for being to slow.
Remember that heat input is a function of the heat put into the metal, and where does this heat come from? That's right amps, volts, and dwell time or as we call it travel speed. You cannot just take the leg size and square it then multiply it by 500. What happens when you turn up the amps? Let me show you.
lets say we are using .045 dual shield running 100% CO2 with say 250 amps and 26 volts. 250 x 26 x 60 / 1000 x 9.48 (I am taking liberty with the travel speed) we get a heat input of 41.13
So how do we calculate actual travel speed? Easy, we use our experience gained through years of welding practice to estimate the travel speed, what! you say? Thats right we use our judgement because this is a pre-qualified procedure. If it were a procedure you were testing you would still use your judgement but adjust it accordingly as your test results dictated.
Ok, so what would I guess the travel speed to be for the above stated parameters, probably around 12 ipm. But just to be sure I would go out in the shop and have a welder weld at said parameters and time how long it takes him to weld a piece of material 12 inches long. Really simple.
In the end even so called pre-qualified procedures sometimes should be tested, without actually doing all the bend tests, tensile tests etc., in order to ensure a sound weld. Not all welds are equal!
Thank you for making my point. When you increased the amps to 250 and increased the travel speed to 12 you hit 32.5 kJin again close enough to the 31.25 kJin ΒΌ inch fillet target. Remember it is just a target that must be checked later in the shop with reality. When the material has less mass I reduce the kJin if it has a lot of mass I can increase the kJin. In this way I can help control the cooling rate. I have been using this method for 11 years it has never let me down.
Also if you check the Lincoln recommended parameters you should use 29 volts (+or-) with the 250 amps, that lets you increase the travel speed to 14 and still get 31.1 kJin. I never start making a procedure in the shop. I "Do the Math" first to predict the outcome, then do the +or - 10% Amps 7% Volts to see if those min max parameters will also work, if not adjust the optimum so the entire WPS spread is usable. When making a PQR I set the machine not the weldor.
Sense I have been asked off board and for the rest of you who read this when using the LxLx500 calc, let's review; this calculation will predict the total heat input needed for a given fillet (perfect triangle). It does not mean you go as slow as you need to (see D1.1-table 4.5 #18) get the 1/2" fillet with the procedure you have, something else must change.
If your WPS (Supported by the filler manufacturer's recommendations) will not support your weld size in one pass you do it 2 or 3 or 6 what ever it takes to equal the fillet heat input calc. Let's say your weld size is 1/2 inch or .5 x .5 x 500 = 125 and your WPS heat input is 29V x 250A x .06 divided by 14 that would equal 31.1 -- 125 divided by 31.1 would give you 4.01 that means it will take 4 passes to fill this 1/2 inch fillet with the above WPS "all things being equal".
If you do not like the 4 passes change your WPS to 30V x 275A x .06 divided by 12 ipm with equals 41.3. The 125 divided 41.3 would give you 3.02 or 3 passes, again "all things being equal."
The math works and is a great predictor. Once you "Do the Math" check the prediction in your shop. It does not replace good welding practice. If your weldor slows down or speeds up beyond the WPS ipm, the predicted size will change. Even gun angle and ESO will affect the outcome. No WPS will work if the weldor does what ever he/she wants to, it must be followed. The whole idea is doing what we know works (a PQR) and not changing it much (D1.1 - Table 4.5) to predict a good outcome. It does not mean you can put a 1/2" fillet weld on a 1/4" plate without paying a penalty, see D1.1 - 5.21 and good design practice.
Weldor's running-a-muck WILL give consistent outcomes, its called "crap."
I don't know if its "old school" or not, but I usually do as Chet suggested, i.e., the WPS and parameters used for welder qualification are somewhat broad. Based on the actual parameters used by those welders that "pass" the test, the WPS used for production is "tweaked" or tightened up to provide more consistency on the production floor. This is intended to imply that I do monitor the welder qualifications and I do record the actual welding parameters. That data is not listed on the performance qualification report.
I also concur with those that use the manufacturer's data published on their websites as a starting point. Most of the data they post is on the mark and backed up by testing.
Best regards - Al
Goose-em's comment regarding "even so called pre-qualified procedures sometimes should be tested, without actually doing all the bend tests, tensile tests etc., in order to ensure a sound weld" is well said.
Sometimes a pre-qualified WPS is created, issued to production and forgotten about. The limitations of the WPS variables (Section 3.6 - Amp, Volt, Travel Speed, and Shielding Gas Flow Rate) may never be periodically checked for conformance against Table 4.5 Essential Variables.
In the D1.1:2006 section 6.3.3 requires the contractor's inspector to "make certain that all welding operations are performed in conformance with WPSs that meet the requirements of this code."
This might be fun to try -
1. randomly check at least 25% of the machines in production against the written pre-qualified WPS for the welding being performed on the shop floor.
2. Without making ANY adjustments to machine, gas flow or personnel, record your results.
3. What percentage of each of the four variables make it past the verification the first time?
Has anyone tried this? If so, what were your results?