# Case study efficiency arc welding

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Hi, As a student (european welding engineer), I'm doing a case study on determining the efficiency of some arc welding processes (Gas Metal Arc Welding =MIG/MAG; Gas Tungsten Arc Welding =TIG) in various positions (PA=1G; PC=2G; PF=3G; PG=3G). As can be found in NEN-EN 1011-1 (european standard) the efficiency suggests to be 80% for GMAW and 60% for GTAW. These values don't vary for different welding positions neither for base-metal (and fillermetals) used.

We think these effiencies have to be different when different base metals are used (Since heat transfer also depends on radiation and the radiation coefficient is characterized by the blackness degree. In such, there should be a difference in efficiency between e.g construction steel and Aluminium).

I have developed a Thermocouple-harpoon which shoots a thermocouple into a weld when the electrode has just passed the harpoon. With this thermocouple (which measures the temperature in the weld) I can determine the cooling time from 800 to 500 degrees (550 and 300 used when welding on Aluminium). Using the formula for the cooling time I can determine the heat-input in the weld.

Formula for cooling time: delta t8/5 = (4300-4,3*T0)*10E5 * [ (500-T0)E(-2) - (800-T0)E(-2) ] * QE2 / dE2 Comparing the heat-input Q from this formula with the heat input (measured at the machine) I can calculate the efficiency of all arc welding processes.

Of course, if it would be that simple I wouldn't post it over here... I've made a copper head surrounding the thermocouple so it can't melt when passing the arc (and creating multiple thermocouples when melting). The thermocouple itself is chosen as small as possible. I have done some tests and only became efficiencies between 40 and 50% for the GMAW process. I guess the copper surrounding is responsible for this heat loss. (I'll soon be trying a method only using a ceramic surrounding for the thermocouple.)

I was wondering whether there is somebody who knows how these effiencies have been measured before. Shouldn't there have been a procedure when they were determined for the European standard? I also have a book (heat effects of welding by Dieter Dadaj) in which I found values going from 0,65-0,90 for GMAW and 0,20-0,50 for GTAW. He got these data out of different books. I would like to make a table which concludes all these data so it can be seen that nobody really has found 1 value for the effiency. Unfortunately I'm just a student with a low budget and can't afford to buy all these books... It would be really helpfull if anyone could give me these data (with its reference)

Kind regards, Dries Vandezande Belgium

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My guess that previously experimenters would have done the process in an enclosed chamber then measured the increase in ambient air temp and the increase in temperature of a previously weighed sample. Knowing the mass of the the sample and the air in the chamber one could calculate the total calories produced and the relationship between the two. I can't figure out they would have calculated radiant energy other than insulate the interior of the chamber and line wiht reflective material? Randy

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The low efficiency with the Tig process can be found in the losses by heating up your non-melting electrode. And as an answer to you question: yes. When looking at your energy-cost (electricity) , it's cheaper to use a MIG. (But of course one can find so many reasons for using the TIG instead of a Mig. For instance the torch is more flexibel...)

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You can talk power cost and radiant energy all day long. The cost to repair welds that should have been TIG welded eats up the savings. It all looks good on paper, but in the field it can cost you a lot of money. Mig & Tig can both save money with the right application.

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