Electric heating – Metal heating – By arc
Patent
1991-03-27
1994-05-31
Shaw, Clifford C.
Electric heating
Metal heating
By arc
21913031, B23K 909
Patent
active
053171160
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a pulse welding apparatus using a pulse discharge, and more particularly to a pulse welding apparatus in which phenomenon specific to welding such as the melting of a discharge electrode and separation thereof are controlled so as to obtain good quality of welding.
PRIOR ART
Examples of conventional pulse welding apparatus using the pulse discharge are a pulse arc welding apparatus disclosed by Japanese Patent Laid-Open No. 57-19177 and a short-circuit transfer arc welding apparatus disclosed by Japanese Patent Publication No. 62-54585.
In the pulse arc welding apparatus, a pulse arc current is run between the consuming welding wire electrode (hereinafter referred to as a wire electrode) and workpieces, and both the workpieces and the wire electrode are melted and then the wire electrode is cut by the electromagnetic pinch force produced by the pulse arc discharge, and the melted electrode or globule is then transferred to the workpieces (referred to a spray transfer). A pulse welding can be carried out even in a region where average current is less than that of a DC arc welding apparatus, and lends itself to the welding of thinner workpieces. The pulse welding has an advantage that the spray transfer serves to eliminate spatters produced during welding.
In the short circuit arc welding apparatus, short-circuiting is performed alternately with arcing in a periodic fashion so that the workpieces and the wire electrode are melted by the heat generated through the arc discharge developed by an arc current between the wire electrode and the workpieces and then the workpieces are short-circuited to the wire electrode so as to transfer the melted globules produced on the tip end of the wire electrode onto the workpieces. Periodically performing the short-circuiting alternately with arcing assures a stable welding operation.
In order to obtain the good quality of pulse arc welding, it is required that undercut, i.e., a defective shape of welding-bead, is prevented from being produced and the globules that separate from the electrode are held to substantially the same size. To prevent the spatters, the contact between the wire electrode and the workpieces should be prevented. To prevent undercut, the arc length should be short. In order to meet both of the requirements, it is important to ensure fine particles of globules (spray transfer) when the globules leave the electrode. For uniform size of globules, the uniform size of globules that separate from the electrode may be provided by periodically repeating pulse arc currents of the same pulse shapes.
In a shield gas of a mixture of argon gas and 20% CO.sub.2 gas, the arc size is large enough to enclose the globules produced on the electrode so that the periodic simple pulses as shown in FIG. 24 (.tau.:pulse width, I.sub.B :base current) will help the globules become particles and separate from the electrode in a regular manner. However, in a shield gas of 100% CO.sub.2 gas, the arc size is rather small to enclose the globules so that simple pulses causing phenomenon as depicted by (a) and (b) in FIG. 24, which does not ensure good welding results. Narrower pulse widths .tau. provided by high position of the base current I.sub.B as depicted by (a) in FIG. 24 will change the shape of globules produced on the tip end of electrode from Po state to Pa1 state and then to Pa2 state where the globules are large enough to be separated from the electrode. On the other hand, wider pulse widths r provided by low position of the base current I.sub.B will cause the electromagnetic force F due to pulse currents to be upward, which in turn causes the shape of globules on the tip end of wire electrode to become from Po state to Pb1 state where the globules are constricted and lifted. Then, the globules become as shown by Pb2 state so that the globules are separated by pulse currents. But the thus separated globules will spin at high speeds not to fall onto the workpieces but to be scattered as spatters to places other than the
REFERENCES:
patent: 4758707 (1988-07-01), Ogilvie et al.
patent: 4994646 (1991-02-01), Tabata et al.
Katou Yoshiaki
Mizuno Masanori
Nagano Osamu
Tabata Yoichiro
Ueda Yoshihiro
Mitsubishi Denki & Kabushiki Kaisha
Shaw Clifford C.
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