I am not sure why you say this is impossible to do with the SMAW process. During the welding operation you can get the amps and volts by using an AC/DC Clamp amp/volt Meter. For the travel speed you can time the welder to see how long he/she takes to weld. When he/she is done, measure the length of the weld. Since you now have a weld length and a time to complete that weld, you can determine the true travel speed for that weld. Now you have everything to plug into the equation and calculate heat input.
As far as how to incorporate this into the WPS for the welder to read and understand, not sure you need to do that. Once you have established a min and max heat input for the material/job you are qualifying, this gets entered into the WPS as parameter ranges. The WPS should contain a range for amps, travel speed etc. If the welder stays within these ranges he/she should produce a heat input that will be satisfactory for the job. Inform the welders of the heat input requirements for the job, list the max heat input on the WPS in kJ/in, educate the welders on how to calculate this and why it is required, what may happen if it is exceeded, then let them lose. If they are worth their weight in gold, the will rise to the challenge and produce welds that meet the requirements. An educated welder is an awesome asset.
I agree m-squared.
It may be near impossible without a clamp on ammeter! But with one it is pretty easy to set the perameters and incorporate the min. and max. on the wps. My experience is that most welders have no idea how to calculate heat input. The ones that know are invaluable with WPQ.
in Welding innovation vol XVI, no. 1, 1999 by R. Scott Funderbunk,
it was stated like ,
"The welding current is measured with either an inductance meter or a shunt with appropriate metering equipment. The current is never fixed with respect to time, especially on a microsecond level. with SMAW, the current is a also a function of the arc length, which is dependent on welder's skill. Therefore the current used in the heat input calculations should be the average value."
I think it is a bit risky to indicate exact min. and max values. It is better calculate according to average value and add +/- tolerances.
Regards,
T
The method of controlling heat input with SMAW that is allowed by ASME, AWS and MIL specs is this:
For each electrode diameter, there has to be a minimum length of weld for each inch of electrode consumed.
For instance, if in qualifying the WPS, the heat input used resulted in a 6" weld for each 10" of electrode consumed, then during production welding, there would have to be at least .6" of weld for each inch of electrode consumed. (assuming that the heat input obtained during the qualification is the maximum allowed during production). So if you see a welder depositing a weld, and when he/she stops, their rod stub is 5" shorter than when they started the weld, then the weld needs to be at least 3" long, or the heat input limits was violated.
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