RU2697756C1 - Method of defect-free hybrid laser-arc welding of thin-wall butt joints - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to hybrid laser-arc welding of metal structures with wall thickness from 8 to 12 mm. Method of hybrid laser-arc welding of thin-wall butt joints involves making of root seam by electric arc welding with consumable electrode in protective gas medium together with laser welding in single weld pool. A laser beam is used to influence the value of edge blunting. Root seam top defects are detected at a depth limited by half the height of the root seam, elimination of root seam defects by making outer facing suture using defocused laser beam with focal spot diameter from 1 to 8 mm. Defects are detected using a sample.

EFFECT: providing quality of welded joint and improving operational characteristics of article with welded seam due to simultaneous elimination of main defects of butt joint weld seam, reduction of material consumption along the way of elimination of equipment providing for suppression of defects in the form of pores.

1 cl, 1 ex, 1 dwg

Description

The invention relates to a hybrid laser-arc welding of metal structures with a wall thickness of 8 to 12 mm

When laser-hybrid welding of thin-walled structures with a wall thickness of 8 to 12 mm, the technical problem is to obtain a product with a high-quality weld, devoid of the most probable defects of the welded joint:

- gas pores that inevitably appear at the top of the weld during through penetration by a laser beam due to the crystallization of the weld metal;

- undercuts and sagging of the weld.

Thus, in hybrid laser-arc welding of butt joints, including thin-walled joints, metal vapors are intensely released in the upper part of the weld pool, they boil and spatter the liquid phase, which leads to the penetration of the protective gas from deeper into the weld pool. In addition, the type of welding under analysis is characterized by unstable and cyclic processes: the vapor-gas channel becomes extended, the laser beam passing through it experiences repeated reflections, so the root of the welding cavity reaches the beam with a significant loss of power, no longer able to further melt the metal deeper, then molten metal enters the back of the bath and a “step” is formed. The figure schematically shows a vapor-gas channel in the direction of welding, illustrating the presence of such a "step" (the position is not indicated by virtue of evidence). In addition, the process of crystallization of the metal is characterized as an uneven process, since the metal periodically melts and evaporates, a shielding plasma appears, the metal goes to the back of the bath and the above process repeats as the beam moves. Due to the above processes (the release of metal vapor, boiling and spraying), which are negative, the exit of gas bubbles to the surface is difficult: gas bubbles do not have time to leave the weld pool and solidify, forming pores. Thus, the crystallization of the weld pool metal occurs from the walls of the weld pool to the center of the weld pool, because from the side of the walls of the weld pool, the heat transfer rate is higher, therefore, due to this, the weld seams up gradually from the bottom of the bath to its center, therefore gas pores are formed in the area where the metal solidifies last, at the top of the weld.

The prior art contains solutions aimed at suppressing pores as characteristic defects of a butt welded joint obtained by hybrid laser-arc welding.

So, for example, a technical solution is known from patent document CN No. 106271139 - a method for hybrid laser-arc welding of a butt joint using an arc torch with an electrode and a laser beam. Pore suppression as a possible defect of the weld is carried out by adjusting the angle of inclination of the electrode of the welding torch and the laser beam, as well as the distance between the focal spot of the laser on the surface being welded and the point of arc contact of the welding torch by installing the arc torch at an angle to the welded surface.

Controlling the position of the distance between the arc and the laser beam together with the angle of inclination of the arc and the laser does not guarantee the elimination of pores.

As the closest analogue, the technical solution “Method of laser-arc welding of the joint of carbon steel workpieces” was selected from the patent description RU No. 2660791. According to this method, the first laser beam is applied to the surface to be welded, which is set perpendicular to the surface to be welded, and the effect is hybrid laser-arc welding with a consumable electrode. During the welding process, to suppress defects, defocusing of the first laser beam is carried out, the welding torch is placed in front of the second focused laser beam, in addition, the distance between the arc contact point and the center of the focused spot of the second laser beam is adjusted, the second laser beam and the arc torch are deflected by a certain angle .

In the above fragment, the same terms are used as in the patent description RU No. 2660791, while the general features of the known technical and proposed method are as follows: the implementation of hybrid laser-arc welding with simultaneous exposure to a laser beam (sign "second laser beam" in the specified patent description ) and a welding torch with a consumable electrode, as well as the use of a defocused laser beam ("first laser beam" in the specified patent description).

Despite the fact that all considered similar technical solutions are aimed at suppressing defects, the use of these methods reveals the inability to obtain a high-quality (defect-free) weld due to the fact that the probability of formation of defects remains. So, for a weld of butt joints of small thicknesses up to 12 mm, this occurs due to the indicated reasons: penetration of the protective gas into the bath due to the intense release of metal vapors from negative cyclic and unstable processes.

For thin-walled structures, as a rule, no facing seam is applied, but the seam made by the hybrid welding method is characterized by an unacceptable shape with undercuts and sagging of the weld. These defects cause a decrease in the mechanical strength of the weld due to the fact that undercuts and sagging of the weld are stress concentrators.

The technical problem solved by the invention consists in ensuring the quality of the welded joint and improving the operational characteristics of the product with a weld due to the simultaneous elimination of the main defects of the weld of the butt joint, as well as in reducing the material consumption of the method by eliminating equipment that suppresses defects in the form of pores.

The essence of the invention is as follows.

A method of hybrid laser-arc welding of thin-walled butt joints involves performing a root seam by electric arc welding with a consumable electrode in a shielding gas medium together with laser welding in a single weld pool, wherein the laser beam affects the amount of edge blunting and also uses a defocused laser beam. New in the method is the identification of defects of the apex of the root suture, lying to a depth limited by half the height of the root suture, the elimination of defects of the root suture by performing an external facing suture using the specified defocused laser beam with a focal spot diameter of 1 to 8 mm, which affects the entire depth occurrence of defects of the root suture. It is advisable to identify defects using a sample on which the root suture is performed.

When performing a weld with a defocused laser beam as the last (facing) seam:

- defects of the root seam are leveled, such as undercuts in the presence of cutting of the welded edges and an underestimation of the root seam, therefore, defects that lead to a decrease in the operational characteristics of the product with a weld are eliminated;

- typical defects such as pores are eliminated, due to the fact that the root suture is re-melted to a depth of defects occurring at a shallow depth, namely from 3 mm to 6 mm, i.e. the depth of the molten bath is less, while the width is greater than when welding the root seam, respectively, the welding process is more stable, which allows gas bubbles to freely leave the weld pool, thereby forming a high-quality seam.

Based on the foregoing, welding of thin-walled butt joints occurs with and without edge cutting. Moreover, the presence or absence of cutting edges does not affect the features of the method. So, if there is a grooving of the edges, the root seam practically fills this groove, and possible undercuts are eliminated when applying the outer facing seam with a defocused laser beam. If there is a groove, the blunting of the edges is an unbroken part of the edges of the butt joint, and in the absence of a groove, the blunting of the edges is equal to the thickness of the butt joint.

The formation of the laser beam defocused with a focal spot diameter of 1-8 mm is selected from the condition of ensuring the balance of the required penetration depth and the power of the laser beam involved. In other words, if you use a laser beam with a focal spot diameter of less than 1 mm, then even with a low laser beam power, welding will be performed with deep penetration, which with a large heat sink (described above) can lead to pores remaining, and with a diameter more than 8 mm even - with a high beam power - the penetration process is impractical due to low energy efficiency.

Thus, when performing an external facing seam with a defocused laser beam, possible defects are removed due to the root seam being applied to the entire height of the non-skewed part of the edge of the edges, while the presence or absence of grooves does not affect the quality of the weld of butt thin-walled joints.

In the proposed method of hybrid laser-arc welding of butt thin-walled joints, both with edge cutting and without cutting, the elimination of defects can be integrated by multilayer welding in several successive passes, during which they perform:

- technological (tack) seam;

- the first seam with a laser beam with a focal spot diameter of 1-8 mm;

- root seam by hybrid laser-arc welding using a laser beam for the entire amount of blunting;

- the second seam (as facing) with a laser beam with a focal spot diameter of 1-8 mm.

The process of performing the method includes the steps of identifying defects of the top of the root suture and determining the depth of the defects, limited to half the height of the root suture. Moreover, the presence of defects can be determined by various methods.

It is advisable to determine the depth of defects by experimental means during preliminary testing of welding modes on the plates to be welded in accordance with GOST R ISO 15614-12-2009 “Technical requirements and certification of welding procedures for metal materials. Checking the welding procedure. Part 12. Spot, seam and relief welding. " With this mining, defects are detected on the transverse and longitudinal sections and the occurrence depth is determined. As a rule, under the established conditions of hybrid laser-arc welding, defects occur at a depth of not less than half the height of the root suture.

The depth of the root joint defects can be determined after its implementation, for example, by the methods of non-destructive quality control of welded joints. It should be noted that in the factory, when manufacturing products, non-destructive testing is performed on batches of products at an independent production site, for example, at an ultrasonic inspection site located outside the assembly-welding mill and / or outside the hybrid laser-arc welding facility. This circumstance excludes the implementation of the method of defect-free welding of butt thin-walled joints, containing the determination of the depth of defects, as a continuous process of action on one butt joint due to the inefficiency of such a process on an industrial scale.

Thus, the claimed method in practice allows to obtain a high-quality product with a welded joint, free from defects, and to achieve a reduction in material consumption due to the fact that hybrid laser-arc welding is carried out on the installation using a single laser head, ensuring the implementation of the root weld and the facing weld. In this case, there is no need to use equipment for suppressing defects such as: an additional welding head (as in the prototype RU No. 2660791), a welding optical (laser) head, a welding torch or a heating device.

The implementation of the proposed method is illustrated by the example of welding large diameter pipes with a thickness of 12 mm

Before executing the method, the depth of defects on the samples in the form of plates is determined, which are welded in accordance with the selected welding conditions used on the welding mill for the manufacture of large diameter pipes: the diameter of the focal spot of the laser beam when welding the root weld is 0.4-1.6 mm; laser power 15-20 kW; for a welding torch as an electrode, a wire with a diameter of 1.0-2.0 mm; welding current 250-450 A; arc voltage 18-28 V; gas mixture - carbon dioxide and argon; for the first and second laser seams, the laser power is 5-10 kW; diameter of the focal spot of the laser 3-6 mm; root weld speed 1-3.5 m / min.

As indicated above, the pores lie at the top of the root suture, while it has been statistically established that the depth is limited to half the height of the root suture. Based on this circumstance, when performing multi-pass welding of a molded large diameter tubular billet, defects in the apex of the root suture, limited by half the height of the specified suture, are eliminated.

When welding plates, defects were found at the top of the root suture at a depth of 4 mm (from the surface of the root suture), which is less than half the height of the root suture equal to 12 mm.

Taking into account defects in the form of pores, it is quite possible to detect other defects at the top of the root joint of the plates (samples), for example, shells and cracks, which will be eliminated when performing the proposed method. Otherwise, when any defects are found in the root of the seam, it is advisable to change the parameters of the welding process to obtain samples with defects concentrated at the top of the seam.

So, multi-pass welding of a steel molded tubular billet with a Y-shaped cutting edges is as follows.

Using the method of semi-automatic welding in a shielding gas medium with a consumable electrode in the form of a welding wire, a tack (technological seam) is made by placing a tube billet on an assembly-welding mill.

For the further implementation of the method, the formed tube billet is placed in a cage of a hybrid laser-arc welding installation made with standard equipment in the form of a laser head and an electric arc torch with means for supplying protective gas, placed in front of the laser head with the possibility of forming a common weld pool during welding. The electric arc burner is equipped with a means for supplying a protective gas to the side of the melting electrode of the burner.

This installation performs the first laser seam using a defocused laser beam with a focal spot diameter of 4-6 mm, which completely remelts the technological seam with the removal of existing rust and scale to achieve a smooth surface.

For the application of the root seam, they exert a simultaneous effect on the welded surface of the laser beam and the arc of the consumable electrode in a shielding gas medium with the formation of a common weld pool. The first effect is the welding arc, the arc torch electrode is tilted in the direction of movement of the edges of the welded surface by an angle ϕ from 30 to 35 ° relative to the normal to the surface of the welded edges. The laser beam is focused in the region of the edges of the welded surface after the point of impact of the arc torch. The distance between the center of the focused spot of laser radiation and the point of arc contact of the electrode of the arc burner is set from 10 to 15 mm, inclusive. The laser beam is tilted in the direction opposite to the direction of movement of the edges of the welded surface at an angle θ from 20 to 25 °, inclusive, relative to the normal to the surface of the welded edges. In the process of welding, shielding gas is supplied to the laser radiation zone and to the electrode zone of the arc torch. The laser beam generator can be any suitable for the required power.

After receiving the root suture, defects of the specified suture occurring at a depth of 4 mm, as well as irregularities are performed by performing a facing seam with a laser beam with a focal spot diameter of 4-6 mm.

Thus, the process of hybrid laser-arc welding of butt joints of small thickness, carried out with the simultaneous elimination of defects in the root seam and smoothing the surface of the weld, reduces the material consumption of the welding process itself, because in the proposed method, there is no need to use other equipment than the standard equipment of the hybrid laser-arc welding installation. So, for the proposed multi-pass welding of the butt joint, the same laser head is used, reconfiguring the parameters of the optical head and the welding torch to make the root seam and the facing seam.

In the production of large diameter pipes, after the completion of the proposed method, the stage of product quality control by ultrasonic testing is performed.

Claims (2)

1. A method of hybrid laser-arc welding of thin-walled butt joints, including the implementation of the root seam by electric arc welding with a consumable electrode in a shielding gas medium together with laser welding in a single weld pool, with a laser beam affecting the edge bluntness, characterized in that it reveals defects of the top of the root suture, lying to a depth limited to half the height of the root suture, which is removed by performing an external facing suture using defocused laser beam with a focal spot diameter of 1 to 8 mm, which affects the entire depth of the root suture defects. 2. The method according to p. 1, characterized in that the defects are detected using a sample on which the root suture is performed.

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