Proceedings of the Visual-JW 2019 and WSE 2019

Study on Suppressing Bead-Meandering of Pure Ar-MIG Arc Welding
using External Magnetic Field
Noboru Sakurai *, Yasuyoshi Kaneko ***Saitama University, Graduate school of Science and Engineering
255 Shimo-Okubo, Sakura-ku, Saitama-shi, Saitama, 338-8570, Japan**
Saitama University, Graduate school of Science and Engineering
255 Shimo-Okubo, Sakura-ku, Saitama-shi, Saitama, 338-8570, Japan
KEY WORDS: GMA welding, MIG arc welding, Pure Ar shielding gas, Electromagnetic force, Beadmeandering

1. Introduction
Currently, in gas metal arc (GMA) welding using awidely used electrode wire, a minimal percentage of O2 isadded to the shielding gas to protect the arc. The arc isstabilized by the formation of iron oxide, which easily emits
electrons on the surface of the base metal to be welded by O2.
However, when O2 is mixed into the molten metal, thetoughness of the welded joint is lowered, which can beimproved by reducing the mixing ratio of O2 of the shield gas.
In particular, using pure argon as the shielding gas (pure ArMIG arc welding) is desirable. However, bead-meandering
is a challenge experienced in pure Ar-MIG welding. One of
the causes is the phenomenon whereby the cathode spot on
the base metal moves ahead of the molten pool in search of
O2 outside the shielding gas [1]. Conversely, research to
improve welding strength and quality is underway, such as
applying an external magnetic field to the current flowing in
the molten pool or arc, and consequently generating anelectromagnetic force. [2], [3] This study focuses on a methodof suppressing the bead-meandering by controlling thecathode spot using an electromagnetic force, without having
to change the electrode wire or the shielding gas. The
direction of the external magnetic field was perpendicular to
the welding direction, when both DC and AC external
magnetic field were used. Bead-on-plate welding
experiments were carried out by applying an external
magnetic field and using pure Ar shielding gas. The effect ofexternal magnetic field on arc stability, and bead shape wasevaluated from the obtained results, and the effectiveness ofpure Ar-MIG arc welding using external magnetic field wasexamined.

2. Bead-meandering suppression method using an
external magnetic field
We propose two methods of bead meandersuppression, one using a DC external magnetic field and theother using an AC external magnetic field. When a DC
external magnetic field of magnetic flux density BDC isapplied perpendicularly to the arc of welding current I,
electromagnetic force FDC per unit length is generated in theouter product direction. The bead-meandering is suppressedby the force FDC pressing the arc (cathode spot) backward.
When an AC external magnetic field of amplitude BAC andfrequency f is applied perpendicularly to the arc of welding

current I, electromagnetic force FAC per unit length isgenerated in the outer product direction. This allows the arc
to oscillate regularly at the frequency f as shown in Fig. 1.
In Fig. 1, an AC external magnetic field is applied in thedirection of welding progress and the arc is oscillated in a
left-right direction by the electromagnetic force, althoughoscillation in a front-back direction is still possible.

Fig. 1

Bead-meandering suppression by AC external
magnetic field.

3. Welding experiment
As shown in Fig. 2, a small electromagnet capable ofall-position welding was installed at the tip of the welding
torch, and an external magnetic field was applied to conduct
a bead-on-plate experiment.
To quantifiably evaluate the meandering of the obtained
beads, we measured the bead widths at multiple points for
one bead and obtained the average and standard deviation
values. Under similar conditions for all experiments, threevalues of the bead width, standard deviation and averagebead width each, were recorded and averaged. Table 1 showsthe experimental conditions.

Fig. 2

Overview of the experimental apparatus.

Study on Suppressing Bead-Meandering of Pure Ar-MIG Arc Welding using External Magnetic Field

Table 1

Experimental conditions.

Base metal (thickness [mm])SS400 (3.2)

Electrode wire (diameter [mm])DS1A (1.2)

Shielding gas

100%Ar

Gas flow [L / min]20

Welding speed v [m / min]0.8

Welding current I [A]300

DC magnetic flux density B [mT]AC magnetic flux density
root mean square value BRMS [mT]AC magnetic flux density
frequency f [Hz]0.5, 1.0, 1.5

Fig. 30.5, 1.0

Comparison of bead width standard deviation.
(O2 and AC magnetic field)

5, 10, 20, 50, 100

3.1 Experimental results
In the DC magnetic field, though there was a condition
that could suppress the bead-meandering, the width of thebead narrowed in all conditions. In the AC magnetic field,
bead-meandering could be suppressed under many
conditions, even when the arc was oscillated in the frontback or, right-left directions. The bead width became
narrower in front-back oscillation as well as in the DC
magnetic field application, but became thicker than the beadwithout magnetic field application in right-left oscillation.
Fig. 3 and Fig. 4 compare the bead obtained by adding O2
and the bead obtained by the proposed method when AC
external magnetic field was applied. The black dot line is thevalue at the time of adding O2. When front-back oscillation
properties were BRMS = 1.0 mT and f = 100 Hz, as shown in
Fig. 3, the standard deviation of the bead width was muchcloser to that in the case of O2 addition, and the beadmeandering could be effectively suppressed. However, asshown in Fig. 4, the average bead width was smaller and thebead became thinner. When left-right oscillation properties
were BRMS = 0.5 mT, f = 100 Hz, the bead width standard
deviation was larger than the previous condition, and thebead-meandering suppression performance somewhat
inferior. However, the average bead width was similar to thatof the case of O2 addition, and the bead width could bemaintained. Fig. 5 shows the appearance of the beads withgood meandering suppression. In the condition of front-backoscillation shown in Fig 5 (a), the bead-meandering waseffectively suppressed, although the bead was thin.
Additionally, the bead width was maintained under thecondition of right-left oscillation in Fig 5 (b). Thus, the beadmeandering of pure Ar-MIG welding can be suppressed byexternal magnetic field.
4. Conclusion
A method for suppressing the bead-meandering of pure
Ar-MIG arc welding using an external magnetic field wasproposed. The effectiveness of the proposed method wasverified by the bead on plate experiment by applying AC andDC external magnetic fields.

Fig. 4Comparison of bead width average value.
(O2 and AC magnetic field)(a) Conditions that suppressed bead-meandering the most.
(AC front-back oscillation, BRMS = 1.0mT, f = 100Hz)(b) Conditions for suppressing bead-meandering while
maintaining bead width.
(AC right-left oscillation, BRMS = 0.5mT, f = 100Hz)
Fig. 5

Bead appearance with good results.

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