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CONTROL OF
MOLTEN DROPLET SHAPE IN
SHORT-CIRCUIT
CO2 ARC WELDING
ZHU Zhiming WU Wenkai CHEN Qiang
(Department of Mechanical
Engineering,Tsinghua University, Beijing 100084)
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Abstract: To
improve the welding process behavior and quality of short-circuit CO2
arc welding further, the effects of molten droplet shape just before
short-circuit on the short-circuit of molten droplet with weld pool, the
spread of molten droplet in weld pool and the formation of liquid bridge
neck are analyzed through the images of molten droplet and its
short-circuit transfer photographed by a high-speed CCD camera. By using
a static force balance model of molten droplet, the relationships
between molten droplet shape and electromagnetic force (arc current),
surface tensile force, gravity is studied. And then the molten droplet
shape is controlled effectively via precise adjusting of arc current.
When the molten droplet shape just before short-circuit is columned, the
short-circuit transfer process is stable and gentle. But the flat-shaped
molten droplet makes the short-circuit transfer unfavorable, generates
transient short-circuit even. The molten droplet shape during arc phase
embodies the action of various forces on the molten droplet, in which
the electromagnetic force (arc current) is the dominative factor to
determine the molten droplet shape. To obtain appropriate molten droplet
shape during different stages of arc phase, a control principle by
adopting a large arc current in prophase and a small current in anaphase
during the arc phase is proposed according to the influence regulation
of arc current on the molten droplet shape. The experimental results
show that a favorable molten droplet shape just before short-circuit is
achieved with this control approach, which is adapt to short-circuit
transfer. The short-circuit transfer is stable and gentle, the transient
short-circuits and the metal spatter induced by them are eliminated, the
short-circuit behavior of molten droplet is improved and the residual
liquid metal quantity at the end of wire electrode after the completion
of short-circuit transfer has a good equality.
Key words:Droplet
shape Short-circuit transfer Numerical simulation Residual
liquid metal
CLC No: TG403
国家自然科学基金资助项目(59975050).
Received 20050221, received in revised form 20060210
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