Arc sensor sensitivity in short circuiting metal active gas welding with high speed torch oscillation

Abstract

The present paper describes the characteristics of the arc sensor, focusing on the sensitivity of the change in welding voltage and current to the torch oscillation frequency, in the low current and high speed torch oscillation metal active gas (MAG) process. First, a mathematical model of the short circuiting transfer welding is proposed, based on a previously reported model of spray transfer welding. Then, the relationship between the oscillation frequency and the rate of short circuiting was investigated using the proposed model. Numerical calculation results revealed that short circuiting regularly occurs at both oscillating edges at oscillation frequencies close to half the rate of short circuiting obtained under non-oscillating conditions. This finding agrees satisfactorily with the experimental results. Fast Fourier transformation analyses of the signals of welding voltage and current showed that the sensitivity of the change in the voltage and current is maximised at a frequency equal to about half the short circuiting rate obtained under nonoscillating conditions. It is considered that accurate seam tracking by arc sensors in short circuiting MAG welding can be achieved by setting the torch oscillation frequency to the above value.A arc heating coefficient of wire melting5 0 . 22 mm s 21 A 21 B Joule heating coefficient of wire melting5 6 . 3610 25 s 21 A 22 E a electric field intensity in arc column5 0 . 7 V mm 21 I welding current, A J z Joule heating weight at location z of wire extension, A 2 s K s slope of U-I characteristic of power source5 0 . 02 V[w5 L a arc length, mm L e wire extension length, mm L s inductance of circuit52 . 5610 24 H L t torch height (L e zL a ), mm P t ,P v ,P i peak strength at frequency of 2f for torch height, voltage, and current signals respectively R a electric resistance of arc column50 . 03 V R c resistance of welding power cable556 10 23 V R e resistance of wire extension, V r(J z ) resistance of unit length of wire extension as function of J z , r(J z )59610 28 J z z3 . 56 10 24 V mm 21 U a arc voltage, V U ao constant component of arc voltage516 V U e voltage drop across wire extension, V U s equivalent output voltage of power source in state when I50, V U t welding voltage (U a zU e ), V V f wire feeding rate, mm s 21 V m wire melting rate, mm s 21 z location of wire extension t time, s Symbols for short circuiting transfer condition B 1 Joule heating coefficient of wire melting at short circuiting53 . 8610 3 mm s 21 A 22 V 21 L em droplet length, mm L es wire extension length of unmelted part, mm N s rate of short circuiting with oscillation, s 21 N s0 rate of short circuiting without oscillation, s 21 R m radius of droplet having assumed spherical shape, mm S cross-sectional area of wire, mm 2 t ia time at start of droplet growth, s t is time at start of short circuiting, s a coefficient of droplet length53 b coefficient of short circuiting time5200

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