RU2613247C2 - Method of mechanized arc welding with short circuit and in inert shielding gas - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method comprises forming an electric arc between the welding electrode and the welding structure periodically short-circuited by drops of melted from the electrode. Each cycle consists of a welding arc short-circuit period, in which an electrode is fed with high-current pulse, and the arc period, in which the electrode is fed with a high current pulse, which is followed by a low current pulse. In each welding cycle embedded energy during short-circuit is determined and set of the embedded energy of EHD in the arcing period, proper condition of ≥ EHD.

EFFECT: improving of the quality of the weld formation.

3 cl, 10 dwg

Description

The invention relates to the field of welding production, namely, to mechanized arc welding of root joints with a consumable electrode with separate control of parameters during periods of arc burning and short circuit in an inert and protective gas medium, and can be used for deep-fusion welding of structures or parts butt-to-face or with cutting their edges in any spatial positions, for example, for welding fixed joints of steel pipes in the construction of main pipelines.

Known methods of arc welding with short circuits (short circuit), containing in each cycle a short circuit period (TKZ) with a high current pulse and a period of arc burning (Tgd), which includes a stage of a high current pulse and the next small current stage after it, for example, patents:

US No. 4546234, IPC V23K 9/09, publ. 10/08/1985;

US No. 4866247, IPC V23K 9/09, publ. 09/12/1989;

US No. 5001326, IPC V23K 9/10, publ. 03/19/1991 g .;

US No. 6501049, IPC V23K 9/095, publ. 12/31/2002;

US No. 6995338, IPC V23K 9/10, publ. 02/07/2006;

US No. 8492678, IPC V23K 9/095, publ. 07/23/2013;

RF №2422255, IPC V23K 9/09, publ. 06/27/2011

In these patents, the current shape for the welding process corresponds to FIG. 1, which provides a solution to various problems associated with spraying, stabilization of the welding process, etc. However, they do not affect the influence of each period (TKZ and Tgd) on the shape of the weld pool and on the penetration depth of the welded parts.

The method of controlled droplet transfer, for example, the patented name STT, used in the mentioned patents, is widely used in welding various structures with a gap with the formation of a back roll, for example, in the construction of pipelines when welding fixed joints. The disadvantage of this type of welding during the formation of the root of the seam is lower strength characteristics compared with the characteristics of the root of the welded butt.

Closest to the proposed invention is a method of automatic welding with a consumable electrode (solid wire) in carbon dioxide using the STT method with separated periods of arc burning and short circuit (see "Operational flow sheet No. LGSS-STT + M300-2532", OJSC "LGSS" , pp. 1-2, issued in accordance with Recommendation "R Gazprom 2-2.2-8-824-2014" Automatic orbital welding of pipelines in a narrow gap ").

The method provides a root layer of the weld when welding fixed joints of steel pipes with cutting pipe edges and blunting up to 1.75 mm and can be implemented by welding machines of various companies, for example, Lincoln (USA) Power Wave 455 model.

The disadvantage of this method is the large number of rejects (up to 30%) when welding on butt pipes due to the difficulty of maintaining the required fluidity or accuracy of the temperature regime in the weld pool associated with the conversion of high-temperature arc energy to a lower melting temperature of the bath.

The objective of the invention is the reduction of rejects during welding by increasing the penetration depth, improving the regulation of the welding process, reducing the requirements for stability of welding parameters.

The technical result of the invention lies in the prompt qualitative formation of a welded root seam in any spatial positions by reducing the requirements for stability of arc burning and improving regulation of heat input.

The technical result is achieved by the fact that in the short arc welding method, comprising the formation of a periodically variable electric arc between the welding electrode and the structure to be welded, periodically short-circuited by means of a molten drop from the welding electrode, with the formation of at least one sequence of welding cycles consisting of a short circuit period said arc, in which a high-current pulse is supplied to the welding electrode, and an arc burning period, in which the welding electric ktrod fed high current pulse followed by a low current pulse in every welding cycle between short circuit energy determined nested copies, and the combustion period is set arc nested EHD energy corresponding Ekz≥Egd.

It is advisable to have a diameter of the welding electrode of at least 1.1 mm

In each welding cycle, the input energy during the short circuit period is preferably controlled by changing the magnitude of the initial short circuit current.

The essence of the invention is in higher accuracy of stabilizing the temperature of the weld pool, simplifying the regulation of the temperature of the bath due to the direct conversion of electric current energy into thermal energy during a short circuit and due to the separate controlled action of arc energy on the weld pool. The shift of the energy balance between the periods of the welding cycle towards the short circuit allows you to create a more efficient high-quality controlled welding process, which is less critical to the deviation of the parameters, especially in terms of mechanical movements of the welding head.

When conducting patent research, no solutions were found that are identical to the claimed, and therefore, the proposed solution meets the criterion of "novelty." The invention does not follow explicitly from the known solutions, therefore, the proposed invention meets the criterion of "inventive step".

The invention is illustrated by the images in FIG. 1-10.

FIG. 1 shows the current shape of the STT welding process with separated periods of arc burning and short circuit.

FIG. 2 depicts the shapes of weld pools from a short-circuit current and an arc column with the same energy input.

FIG. 3 shows the ratio of the short-circuit and high-energy energies in the normal welding mode with separate control of the short-circuit and high-pressure periods.

FIG. 4 shows the energy ratio of short-circuit and high-pressure periods at high arc energy at an average welding current of 120 A.

FIG. 5 shows the energy ratio of the short-circuit and high-pressure periods at a low arc energy at an average welding current of 120 A.

FIG. 6 shows the energy ratio of the short-circuit and high-pressure periods for a consumable electrode (welding wire) with a diameter of 1.6 mm.

FIG. 7 explains the preparation for welding with cutting edges of the welded parts.

FIG. 8 shows a short-circuit pulse shape with an initial controlled current.

In FIG. Figure 9 shows the reverse roller when welding without a gap when optimizing the energy ratios in the periods of short-circuit and high pressure.

In FIG. 10 shows the welding seam from the side of the welding electrode in cutting parts that are welded without a gap (welding seam from the outside of the groove).

The proposed short-arc welding process with short circuits involves the formation of an electric arc 1 between the consumable welding electrode 2 (welding wire) and the welded structure 3, periodically short-circuited by means of a molten drop 4 from the welding electrode 2, with the formation of the sequence of welding cycles / Weld form 5 in the dependences of the short circuit current (SC) and the electric arc (arc column) for the same energy input are shown in FIG. 2. Each welding cycle consists of a short circuit period (TK3) of the aforementioned arc, in which a high current pulse is supplied to the welding electrode 2, and an arc burning period (Tgd), in which a high current pulse and a low current pulse follow it ( Fig. 1). At least one sequence of welding cycles is created, in which, in each cycle, during the short circuit period, the input short circuit energy (Ex) is calculated and the enclosed arc energy (Egd) is set during the arc burning period corresponding to the Ex з Egd condition.

To increase Ex, the diameter of the welding electrode must be at least 1.1 mm. In each welding cycle, the short circuit energy (Ex) is controlled by changing the value of the initial short circuit current (Fig. 8).

The proposed method can be implemented using commercially available devices FEB 555 PSP (Russia) or devices of other companies that have a separate control of the energy of the short-circuit and high-pressure periods for arc welding in a protective gas environment with a consumable welding electrode (without gap). This method can find application for welding structures from sheet steel and pipes with a thickness of 2 to 4 mm. With a larger thickness, it is necessary to groove the edges of welded structures with a blunting thickness D of up to 3 mm with an electrode with a diameter of 1.6 mm or 2.0 mm and with a large blunting thickness D with electrodes with a diameter of more than 2.0 mm (Fig. 7). This is especially true when welding butt pipes of pipelines end-to-end (without clearance), since the productivity and quality of the weld are increased.

The method has been experimentally tested for these purposes. Studies have shown that the penetration depth in the short circuit period is greater than in the period of arc burning. This is a consequence of different physical processes of heat transfer during short circuit and arc burning.

In short circuit, the release of thermal energy occurs due to the flow of current inside the weld pool, and the area of the contact spot for the passage of current is determined by the diameter of the electrode wire, more precisely, by the diameter of a drop of molten metal at its end. As is known, on average, the diameter of the droplet is approximately 20% larger than the diameter of the electrode wire, but taking into account the variable size of the diameter of the droplet during flowing, we can assume that the cross section of the energy source will have a cross section close to the diameter of the electrode. Thus, the source of heat during the passage of current is the element of increased resistance - a drop and a part of the volume of the bath under the drop. Since in this type of welding with drop transfer of metal the drop partially evaporates - the temperature of the heat source does not exceed the temperature of the boiling metal, the conversion of current energy into heat occurs without significant losses.

The energy source created by the arc gap is actually an external high-temperature emitter in the form of a plasma column, the diameter of which (in the zone of the weld pool) is several times the diameter of the melting electrode, respectively, the surface area of the surface of the bath is much wider compared to the short-circuit current and has a smaller depth penetration due to surface exposure by the high-frequency spectrum of arc radiation due to and because of a lower current density at the arc-bath transition. Due to the high temperature of the arc, significant radiation losses occur, which with various gases can reach 50%. Conventionally, the temperature distributions of heat during the short-circuit period and during the period of arc burning with a cross section of the weld pool are shown in FIG. 2.

The energy ratio of short circuit current and arc is shown in Fig. 3. Calculation of power and energy from current and voltage waveforms shows that during welding, the typical ratio of energy during arc burning (Edg) and energy during short-circuit (Ex) is more than 10: 1. The energy during short-circuit and in the arc was estimated using the current and voltage waveforms generated by a source of the FEB 555 PSP brand, which makes it possible to control the welding process in real time.

Investigations of the welding process showed that when the arc energy is reduced under the same conditions (the same welding current and wire feed speed), the energy balance moves during the short-circuit period, which is illustrated in FIG. 4 and 5. Under the same conditions of welding current and wire feed speed and with a decrease in arc energy, an absolute increase in short circuit energy occurs. It can be seen from the oscillograms that under the same welding conditions, there is an absolute increase in energy during the short-circuit period with a decrease in the arc burning energy, despite a decrease in the frequency of short circuits.

With an increase in the diameter of the electrode wire, the regularity of the process of shifting the energy balance of the short-circuit and high-pressure periods is preserved, but the energy of the short-circuit period absolutely increases when switching to a welding wire with a diameter of 1.6 mm (Fig. 6). In addition, an increase in Ex is possible due to an increase in the initial short-circuit current (Fig. 8).

Since energy during short-circuiting goes into the depth of the bath, depending on the thickness of the parts to be welded, the shape of the groove, it becomes necessary to regulate the heat input to the surface of the bath during welding to melt the edges and adjust the viscosity of the weld pool, for which an additional stepless temperature control is made by adding a welding process in which short circuit energy (Ex) predominates, a certain number of cycles with a predominance of arc energy (Edg). Thus, it is possible, while maintaining current deep penetration, to obtain an adjustable surface melt of the weld root, slightly affecting the viscosity of the weld root.

Experimentally confirmed:

- under approximately equal conditions, with a decrease in energy in the period of DG (Edg), the value of energy in the period of short circuit (Ex) increases;

- with an increase in the diameter of the electrode, the absolute value of energy in the short-circuit period (Ex) increases.

The diameter of the welding electrode is chosen to be at least 1.1 mm (i.e. equal to or greater than 1.1 mm), since with a smaller diameter the absolute value of the energy in the short-circuit period decreases.

In FIG. 9 shows a weld with added arc energy. While maintaining the energy of the short circuit, several welding cycles were introduced with the predominance of the energy of the main engine. The weld seam from the butcher side is shown in FIG. 10.

The proposed method of arc welding contributes to reproducible operational uniform high-quality formation of the weld, reducing the complexity of preparatory work by reducing the amount of metal sample during the cutting operation (increasing the thickness of the blunting), reducing welding time and saving welding materials. The method compares favorably with the prototype and analogues, as it allows:

- reduce the percentage of defects to almost zero during automatic welding;

- make the process of welding pipes without a gap less critical to deviations of welding parameters, more stable due to direct conversion of current into heat inside the bath itself;

- go to the blunting of the edges greater than 1.7 mm, which increases the reliability of the root of the seam;

- to improve the strength characteristics of the welded joint due to a decrease in the cross section of the deep part of the bath, which increases the depth of the bath and reduces the zone of thermal influence of welding (HAZ);

- reduce the proportion of high-temperature energy of the arc, which reduces the HAZ;

- to perform butt welding with the proposed current penetration manually semi-automatic.

Claims (3)

1. A short arc welding method in an inert and shielding gas medium, comprising forming an electric arc between the welding electrode and the structure to be welded, periodically short-circuited by means of a molten drop from the welding electrode, with the formation of at least one sequence of welding cycles consisting of the short-circuit period mentioned arc, in which a high-current pulse is supplied to the welding electrode, and the arc burning period, in which a high-current pulse is fed to the electrode, and the following followed by a low-current impulse, characterized in that in each welding cycle during short circuit is determined Specimen expended energy, and the combustion period is set arc nested EHD energy corresponding Ekz≥Egd condition. 2. The method according to claim 1, characterized in that a welding electrode with a diameter of at least 1.1 mm is used. 3. The method according to claim 1, characterized in that in each welding cycle, the energy input during the short circuit period is controlled by changing the magnitude of the initial short circuit current.

Images