I want you to understand more of what has been presented to you in plain English concerning the pulse mode of transfer when welding steel. (GMAW-P). I will use The Lincoln Electric Company’s C4.200 document as a frame of reference. On page 10 it says, “GMAW-P was developed for two demanding reasons: control of weld spatter and the elimination of incomplete fusion defects common to globular and short-circuiting transfer (Frank Armao, 2006). Note it was not developed to be a better alternative to the spray transfer mode of GMAW and the known high deposition rates of FCAW. Short-circuit transfer (S/C) is known to be effective up to .250”, or simply thin material according to the un-numbered figure at the bottom of the same page (who edits these things). Consequently, GMAW-P was developed (in so far as steel is concerned) to weld thin steel (only). It is capable of welding thicker steel, but it is important to understand that is not its purpose or advantage.
1) Voltage reduction lends itself to the reduction of spatter for a given wire feed speed. A basic understanding of the relationship between an arc’s magnitude and its trajectory and level of control will bare that out. A good example is static electricity versus lighting. Prove to it yourself. Try to weld steel in the GMAW process with a qualified weld procedure but use voltage settings above the qualified range.
2) Don’t use Globular transfer. Globular transfer happens in the middle of the transition current of a given electrode size when too much CO2 is in the gas shielding mix. Excess CO2 requires more voltage by the way. See 1 above. This was common in Japan before they learned better. So, keep one’s settings safely within the S/C range and problem solved.
3) This one should be obvious based on 2 above, lower the CO2 content in one’s shielding gas. This much has been proven and deserves little discussion.
Increase the use of your power source’s induction knob, that you never use. The purpose of the induction feature is to manipulate the frequency of arc events in S/C. More induction causes less frequency. Less frequency prolongs each arc event. The prolonged arc event allows more heat input to each event, thereby increasing reliable fusion. Feel silly now?
GMAW-P is often praised for the low background current feature that controls heat input and reduces distortion and burn through. Ok, get ready to kick yourself again. Lesnewich demonstrated (way back in 1950 something for you youngins) that increasing the contact tip to work distance (CTTWD) proportionally lowered heat input. Add that to the reduction in CO2 above and viola, (my mom used to say Viye Olla! to make me chuckle) instant heat reduction. The bonus is that there will be no reduction in deposition rate. Again, proven, do your research.
One should strive to use the same electrode “stick out” beyond the GMAW gun nozzle, always. To do so (and so you won’t thing me daft about the CTTWD thing I said before), manage increased CTTWD by deepening the recess of the contact tip inside the nozzle. This will also allow you to increase you welder/robot run time and cut your welding consumables budget. Stop placing the tip flush with the nozzle.
Frank Armao, L. B. (2006). GMAW Welding Guide. Cleveland: The Lincoln Electric Company.
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