Numerous reports are available on the study of the characteristics of MIG arc. But they are some time not systematic, sometimes conflict with one another in certain points. To attain as rational selection of welding conditions as possible, the authors tried to collect the most systematic data on the state of burn-off with aluminum alloy filler wires of varied diameters.
In the present instalment, a welding source having a specified current-voltage characteristic curve was adopted to exclude the necessity of considering the influence of the characteristic of the source. The tested filler wires were the following six kinds : 43 S, 0.8mmφ, 3/64"φ. 1/16" φ, and 3/32"φ ; 2 S 1/16"φ ; and NP 5/6 1/16"φ.
The results are summarized with some comments :
1) Under less than 18V, 43 S and 2 S wires had the metal globules causing a short-circuit between electrodes ; under 18-19 V, such a short-circuit sometimes happened, sometimes not ; under more then 20V, it scarcely did. (The corresponding voltages for NP 5/6 are respectively 19, 19-20, and 21V.) A sharp rise of the burn-off rate of the filler wire with the drop of arc voltage might be related with this fact.
2) In the range 0.8mm-3/32"φ, the volume burn-off rate of 43 S wires is practically independent of diameter change. With same diameter (1/16"φ), 43 S and 2 S have same value of the rate ; NP 5/6 has a somewhat larger value.
3) There is a linear relation between the minimum current ensuring the favourable transfer of globu-les and the sectional area of filler wire, so far as same material (43 S) is concerned. With same diameter of wire, NP 5/6 gives a larger value than 43 S, and 2 S is rather small.
4) The size of globules under the current which is sufficienty larger than the minimum is generally constant and, for the measured range, approximately proportional to the sectiodal area of filler wire.
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