RU2736144C1 - Method of arc welding by consumable electrode in atmosphere of protective gases - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention relates to welding production, namely, to mechanized arc welding by consumable electrode in medium of protective gases, and can be used for welding of structures or parts butt-joint without a gap. In the proposed method of arc welding with a consumable electrode in the medium of protective gases an electric arc is formed with formation of a welding bath and formation of a sequence of welding cycles. Cycles consist of phase of arc burning and phase of short circuit between electrode and welding bath. At that, at the initial moment of the arc burning phase, a high-current energy pulse is supplied. It provides a mode of small-drop transfer, or jet transfer, or mode of transfer of electrode metal in the form of vapours. This provides drop-free transfer of electrode metal with formation of a welding bath. After that electrode end with bath is approached in arc burning maintenance mode and electrode is immersed into welding bath with energy pulse supplied to electrode.

EFFECT: technical result of claimed method is improvement of welding quality due to deep penetration of welding bath.

1 cl, 3 dwg

Description

The invention relates to the field of welding, namely to mechanized arc welding with a consumable electrode in a gas-shielded environment, and can be used for welding structures or parts butt-weld without a gap or with cutting edges, in any spatial positions, for example, for welding fixed joints of steel pipes when construction of main pipelines.

Known methods of arc welding with short circuits, containing in each cycle a short circuit (SC) phase with a high-current pulse and an arc burning phase, for example, described in patents: US 4546234, US 4866247, US 5001326, US 6501049, US 6995338, US 8492678 and others. In the methods of the listed patents, the short circuit phases and the arc phases alternate with each other, and the energy control of each phase occurs independently of each other.

This method is commonly referred to as the controlled droplet transfer method. Such advanced technologies as STT, Cold Arc are based on this method. Root, etc.

In practice, the patents listed above are widely used in welding various structures with and without a gap, with the formation of a back bead of the root of the seam.

The STT method has become a leader in this field, which ensured the effective transfer of a droplet of electrode metal mainly due to the action of surface tension forces when the short-circuit current is turned off.

The STT method, specially created for the formation of root welds, is rather complicated in hardware implementation, since it requires not only separate control of the arc-burning phase and the short-circuit phase, but also the provision of a pre-emptive reduction in the current before droplet separation and its transition into the bath under the action of surface tension forces. The main disadvantage of welding with drop transfer is the difficulty of welding in the overhead and vertical position, since the forces of surface tension and electrodynamic pressure of the arc, on the one hand, and gravitational forces, on the other, act on the drop simultaneously. Also, the disadvantage of this type of welding is a rather large percentage of rejects in the formation of the root of the seam when welding pipes in a "blind" gap, used in pipeline engineering, for example, in accordance with "Operational flow chart No. LGCC-STT + M300-2532", JSC "LGSS", from. 1-2, issued in accordance with the Recommendation “R Gazprom 2-2.2-824-2014“ Automatic orbital welding of main pipelines in a narrow gap. ”This is due to the fact that drip transfer fundamentally does not allow creating deep penetration without a significant increase in power, which is unacceptable when forming the root of the seam when welding fixed joints.

Various welding methods are known, the solutions of which are aimed at minimizing the fundamental disadvantages of drip transfer welding.

Closest to the proposed invention is a Method of mechanized arc welding with short circuits in an inert and shielding gas environment, described in patent RU 2613247, taken as a prototype. The prototype method includes forming an electric arc between the welding electrode and the structure being welded, periodically short-circuited by means of a molten drop from the electrode. In the phase of the short circuit of the arc, a high-current pulse is applied to the electrode, in the phase of the arc burning, a high-current pulse and the following low-current pulse are applied to the electrode. In each welding cycle, the energy input during the short-circuit period Ex is determined and the energy input during the arc burning Egd is set, corresponding to the condition Ex≥Egd. This energy ratio characterizes the welding process mainly as current, in which the formation of a weld pool occurs mainly due to the short-circuit current, and not due to the burning of the arc. This method provides a deeper penetration of structures in relation to the listed analogs.

The disadvantage of this method, also based on drop transfer, is the difficulty of fulfilling the assigned energy ratio - the difficulty of increasing the SC energy, on the one hand, and the restrictions imposed on reducing the arc burning energy, on the other.

The ratio Ex≥Egd limits the scope of application, since the implementation of the method (specific technological modes) depends on the thicknesses of the parts to be welded on the diameter of the welding electrode.

To fulfill the ratio Ex> Egd when welding butts, a decrease in Egd is necessary, which can lead to instability of the process (cooling the pool), and an increase in Ex can lead to a violation of the welding process, since an excessive current will lead to a decrease in the duration of the short circuit and explosion of a drop.

Therefore, if it is necessary to increase Ex, while maintaining Egd, an increase in the diameter of the electrode will be required, which is not always acceptable

The invention is based on the technical problem of expanding the arsenal of tools and creating a new method of short arc welding, implemented in the drip-free transfer mode. The achieved technical result is an improvement in the quality of welding due to the provision of deep penetration of the weld pool.

In the context of this application, the term "drip-free transfer mode" means a short-circuit welding mode in which a detachable drop is not formed at the end of the electrode, which short-circuits the arc gap.

The problem is solved by the fact that in the method of arc welding with a consumable electrode in a shielded gas environment, each welding cycle consists of the arc burning phase and the short circuit phase of the electrode and the weld pool. In this case, in the arc burning phase, the mode of transfer of the electrode metal is provided by supplying a high-current pulse of energy, which provides the mode of fine-droplet transfer, or jet transfer, or the mode of transfer of the electrode metal in the form of vapor to the bath. In the process of approaching the end of the electrode melted by the arc (melting without the formation of a drop flowing into the bath, short-circuiting the arc gap and carrying out mass transfer), a low-energy mode of maintaining the arc is provided with the bath, and in the short-circuit phase, namely, when the end of the electrode is immersed in the bath, on the electrode is supplied with a pulse of energy stabilized by current or voltage, which ensures the maintenance of the bath-electrode end system in the molten state until the electrode is detached from the bath with the subsequent transition to the arc burning phase.

Depending on the selected technological parameters (diameter and brand of the electrode, short-circuit current, time of the short-circuit phase, speed of movement of the electrode, and, accordingly, the degree of its penetration into the bath, etc.), separation can occur at different times.If necessary, limiting the time of the short-circuit phase is possible forced separation of the electrode by supplying an additional high-current short-circuit pulse.

In order to better illustrate the features of the invention, by way of non-limiting example, a preferred embodiment with forced separation of the electrode from the bath is described below. An example of implementation is illustrated by the Figures of the drawings, which show:

Fig. 1. current oscillogram, combined with the physical position of the electrode relative to the bath in the phases of short circuit and arc burning (mode with forced separation of the electrode),

FIG. 2.photo of the root of the seam from the cutting side,

FIG. 3. Photo of the reverse roller.

Welding is carried out in a shielded gas environment with a consumable electrode, traditionally used for these purposes. The current and voltage waveforms and the parameters that influence them are generated by the welding source software in order to optimize the process. FIG. 1 is indicated: 1 - stabilized current of the first high-current short-circuit pulse (when the end of the electrode is immersed in the bath), 2 - current of an additional high-current short-circuit pulse for forced detachment of the electrode, 3 - current of a high-current pulse of arc burning, 4 - base current of arc burning.

Welding involves the alternation of an arc phase and a short circuit phase. In the process of approaching the end of the electrode with the bath, a low-energy mode of maintaining the arc is provided. In the operating mode, the arc between the electrode and the weld pool burns at the base current value 4. The value of the base current 4 is selected from the energy condition under which the melting of the electrode end does not lead to the formation of a drop flowing into the pool.

When the electrode is moved, its end is immersed in the bath. At this moment, an energy pulse is applied to the electrode, stabilized by current or voltage, which ensures the maintenance of the bath-electrode end system in a molten state. In the oscillogram of Fig. 1 section 1 corresponds to a current-stabilized pulse.

With the passage of time, the SC temperature of the melt in the bath increases and when the critical temperature is reached in the local zone of the electrode end face, conditions arise that lead to the separation of the electrode from the bath. The higher the value of the short-circuit current (pulse 1 in Fig. 1), the faster the separation occurs. However, there are technological conditions for the formation of a weld, in which it is undesirable to increase the temperature to a critical one and bring the process to spontaneous separation of the electrode from the bath. In such modes, the duration of the short-circuit phase is limited by supplying an additional short-term high-current pulse (pulse 2 in Fig. 1) with an energy significantly exceeding the energy of the first stabilized pulse. Under the influence of this impulse, there is a forced separation of the electrode from the bath and transition to the arc burning phase. The short-circuit current in the stabilized mode (1) can be from 200A to 350 A for an electrode diameter of 1.2 mm, the pulse duration varies from 2 to 5 ms. The duration of pulse 2 can be set from 0.5 to 2 ms. The peak value of the short-circuit current can be 1.5-2 times higher than the current of the stabilized pulse.

After the electrode is detached at the initial moment of the arc burning phase, a high-current pulse of energy is applied, which in FIG. 1 corresponds to a short-term (0.5-3.0 ms) current pulse 3. This pulse provides a mode of fine-droplet transfer, or jet transfer, or a mode of transfer of electrode metal in the form of vapors to a bath. The magnitude of the current pulse 3, its duration, the transfer mode is determined by many factors: how exactly welding is carried out (overlapping, butt-joint or with a gap of parts), the thickness of the parts to be welded, the thickness of the electrode, the speed of its movement, etc. These parameters are determined experimentally. The main condition is to ensure the formation of a weld pool without the formation of a drop at the end of the electrode that can short-circuit the arc gap, i.e. providing a regime of drip-free transfer of electrode metal. After the end of the pulse 3, the arc current corresponds to the base value (section 4 in the graph of Fig. 1) until the end of the electrode is immersed in the bath (SC). Then the cycle is repeated.

These modes are not the subject of the present invention and are determined experimentally for specific welding conditions.

The proposed method can be implemented using software-controlled devices that have the ability to separately control the energy of the short-circuit phase and the phase of arc burning for arc welding in a shielded gas environment with a consumable electrode.

Thus, since the process is carried out without droplet transfer, it is possible to simplify the energy control of the welding process by eliminating the need to monitor the formation of the droplet. Direct transfer of the electrode material into the bath when its end is immersed minimizes the effect of gravity on mass transfer and does not lead to material loss, because practically eliminates splashing. In addition, since the seam is formed when the end of the electrode is immersed in the bath, deeper penetration is carried out, stabilizing the bath temperature throughout the volume, which leads to a high-quality formation of the reverse bead and the possibility of adjusting its gain both in height and width. The welding process itself is greatly simplified, since the welder does not need to maintain certain angles of inclination of the electrode when welding fixed joints, the effect of the electrode stickout length is reduced, in contrast to welding with drop transfer.

Claims (2)

1. A method of arc welding with a consumable electrode in a shielded gas environment, including the formation of an electric arc with the formation of a weld pool and with the formation of a sequence of welding cycles consisting of a phase of arc burning and a phase of a short circuit between the electrode and the weld pool, characterized in that at the initial moment of the phase of arc burning, a high-current pulse of energy is supplied, providing a mode of fine-droplet transfer, or jet transfer, or a mode of transfer of electrode metal in the form of vapors, providing a drip-free transfer of electrode metal with the formation of a weld pool without the formation of a drop at the end of the electrode capable of short-circuiting the arc gap, after which approaching the end of the electrode with the bath in the mode of maintaining the burning of the arc, immerse the electrode in the weld pool with the supply of an energy pulse to the electrode, stabilized by current or voltage, ensuring the maintenance of the bath-electrode end system in the molten state and until the moment of separation of the electrode from the bath with the subsequent transition to the phase of arc burning. 2. The method according to claim 1, characterized in that the separation of the electrode from the bath is carried out forcibly by supplying an additional high-current pulse.

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