AUTOMATIC PULSED-ARC WELDING WITH FLUX-CORED WIRE

A. F. KNYAZKOV, R. I. DEDYUKH, V. I. KHIZHNYAKOV

(Presented by the Scientific and Technical Seminar of the Research Institute of Automation and Electromechanics)

Under the conditions of open shops and in field assembly, the most promising method for mechanizing welding operations is considered to be open-arc welding with flux-cored wire [1].

Practice in recent years has shown that the existing technology of welding with flux-cored wires without additional protection of the weld pool ensures good formation of seams only in the flat position, whereas in welding in positions other than flat it becomes unsatisfactory.

Free formation of vertical and overhead seams is limited by certain values of welding current, above which the volume of molten metal in the weld pool increases significantly and leads to its running off. The welding process at modes whose parameter values permit free formation of vertical and overhead seams proceeds unstably. Under these welding modes, the transfer of electrode-metal droplets is determined mainly by the action of gravity and proceeds stably only when welding in the flat position.

Reducing the welding current when welding vertical and overhead seams adversely affects the forming ability of flux-cored wires; insufficient heat does not make it possible for chemical reactions in the solid phases (the core) to proceed fully.

To a considerable extent, the difficulties in making vertical and overhead seams with flux-cored wire can be eliminated by using pulsed-arc welding with a consumable electrode, developed at the E. O. Paton Institute of Electric Welding [2].

In this connection, at the Research Institute of Automation and Electromechanics of the Tomsk Polytechnic Institute, studies were carried out on the development of pulsed-arc welding with flux-cored wire. The work was performed on an automatic machine with a constant electrode-wire feed speed. The source of direct current was a welding rectifier or converter. A specially developed current-pulse generator was connected in parallel, providing a wide range of adjustment of the parameters of the imposed pulses. Rapid processes in the arc were investigated by means of high-speed filming (up to 4800 frames per second), synchronized with oscillography. Welding was carried out—

were carried out with flux-cored wires of various diameters, of both rutile and carbonate-fluorite types.

As a result of studying high-speed motion-picture films and processing oscillograms, it was established that, in pulsed-arc welding with flux-cored wire, the optimal parameters of the current pulses are determined by the type of wire, its diameter, and the basic welding mode, taking into account the nonuniform distribution of the welding current over the cross section of the flux-cored wire and the heat expenditures required for the complete course of the interaction processes of the filler components at the droplet stage.

Fig. 1. Dependence of penetration depth, reinforcement, and bead width on the parameters of the current pulses: a—pulse frequency; b—pulse duration \((d_{\mathrm{e}}=2.3\ \mathrm{mm};\ V_{\mathrm{w}}=20\ \mathrm{m/h};\ V_{\mathrm{f.e.}}=188\ \mathrm{m/h})\)

The pulsed change in current has a considerable effect on the pool of liquid metal and on weld formation. It was therefore of interest to determine the influence of the current-pulse parameters on the geometric dimensions of the weld. For this purpose, beads were deposited in the flat position with PP-1DSK flux-cored wire containing a \(\mathrm{TiO_2—SiO_2—Al_2O_3}\) filler on a \(10\times100\times200\) plate of St. 3 steel. The dimensions of the deposited beads were determined as a function of the pulse duration and repetition frequency. Longitudinal and transverse macrosections were cut from the plate with the deposited bead. The dimensions on the macrosections were measured with a UIM-21 universal measuring microscope.

The influence of the pulse repetition frequency on the penetration depth, bead width, and reinforcement height is shown in Fig. 1,a. The weld shape and the character of penetration when the duration of the current pulses is varied are shown on transverse macrosections (Fig. 2).

Fig. 2. Weld shape and character of penetration with increasing pulse duration

With an increase in the duration of the current pulses, the penetration depth and the weld reinforcement initially increase. A further increase in duration leads to a decrease in penetration depth and weld reinforcement and to an increase in weld width (Fig. 1,b), which can be explained by redistribution of the energy of the pulsed arc.

The superposition of current pulses causes pulsation of the arc pressure, which improves weld formation. Pulsation of the arc pressure helps maintain the liquid pool and prevents it from flowing down when welding vertical, horizontal, and overhead seams [2].

The results obtained indicate that pulsed-arc welding with flux-cored wire has significant advantages over conventional arc welding. The most promising area for the introduction of automatic pulsed-arc welding with flux-cored wire is the automatic welding of fixed joints of main pipelines.

REFERENCES

1. I. K. Pokhodnya. Welding with flux-cored wire and prospects for its development. Svarochnoe proizvodstvo, 1967, No. 1.

2. B. E. Paton et al. Pulsed-arc welding with a consumable electrode with programmed control of the process. Avtomaticheskaya svarka, 1964, No. 1.