RU2639200C1 - Method of double-laser welding - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method consists in directing laser beams to the place of welding and performing welding in an inert gas environment. The laser beams are focused to one optical system, and after that the laser beams are directed to the place of welding through the focal lens. A continuous laser during welding is turned on and off with a delay relative to the pulsed laser.

EFFECT: invention allows to obtain high-quality welded seam at welding of aluminium alloys and difficult-to-weld structure steels by increasing the depth of penetration for more than 2 times and weld details of a complex geometry.

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Description

The invention relates to a method for multi-beam laser welding of aluminum alloys and structural steels and can find application in various branches of engineering, in particular, when welding products in an inert gas chamber.

A known method of laser-light welding of steel (RF Patent No. 2341361, V23K 28/02, publ. 12/20/2008 Bull. No. 35), selected as an analogue.

In this method, a simultaneous exposure to a pulsed laser and continuous polychromatic radiation is performed on a local material processing zone. Polychromatic continuous radiation provides heating of the welding zone, a pulsed laser performs welding. The disadvantages of this method include the fact that polychromatic continuous and coherent pulsed radiation is supplied by each of its focal lens, which makes it difficult to weld with a complex configuration of the welded parts and welding in the chamber. In addition, continuous polychromatic radiation is difficult to focus and, due to its low absorption coefficient, is ineffective.

Closest to the claimed technical solution is the method of pulsed laser welding of thin aluminum sheets described in J.P. Bergmann and other, Effects of diode laser superposition on pulsed laser welding of aluminum. Physics Procedia 41 (2013) 180-189. In this method, two lasers are used: pulsed Nd: YAG (wavelength 1.064 μm) and continuous (wavelength 0.808 μm). The radiation from each laser comes from its focal lens. The radiation of a pulsed laser is supplied perpendicular to the surface, the radiation of a continuous laser is supplied at an angle to the surface (50 ° -80 °). This combination of lasers allows welding of aluminum alloys, allows you to adjust the position of the spots of laser beams relative to each other in a fairly wide range, which expands the capabilities of the method.

The disadvantages of this method are:

- the impossibility of welding with a complex configuration of the welded parts;

- the need to rebuild the optical system of each laser when changing the configuration of the parts to be welded;

- difficulty or inability to conduct welding in the welding chamber with a limited size of the optical window for inputting laser radiation and with a large focal distance;

- to implement the method in the welding chamber, a relatively large optical window for introducing laser radiation into the chamber is required, which entails the difficulty of protecting the window surface from contamination by welding products (metal splashes and evaporation);

- when applying continuous radiation at an angle of 50 ° - 80 ° to the surface, energy losses increase due to reflection, the heating zone has the shape of an irregular circle (becomes ovoid), which can lead to a decrease in the quality of the weld.

The objective of the proposed method is to improve the quality of the weld, expand the functionality of the method according to the configuration and material of the parts to be welded, and simplify the method.

Using the method, the following technical result is achieved:

- obtaining a high-quality weld when welding aluminum alloys and difficult to weld structural steels;

- increase in penetration depth when welding parts made of steel;

- the ability to weld parts of complex geometry;

- simplicity of tuning the optical system, ease of focusing;

- the possibility of welding in a chamber with an inert medium with limited dimensions of the optical window for inputting laser radiation;

- ease of implementation of the protection of the optical window for inputting laser radiation from contamination by welding products.

To solve this problem and achieve a technical result, a method for double-beam laser welding using pulsed Nd: YAG and continuous lasers is claimed, which consists in directing the laser beams to the welding site and conducting it in an inert gas medium, in which according to the invention the laser beams are combined into one optical system and sent to the welding zone from one optical lens. In this case, the cw laser is turned on ahead of and turned off with a delay relative to the pulsed laser.

In the invention, an optical system with one focal lens (Fig. 1) is used for two lasers. It makes it possible to reduce and focus radiation of pulsed and cw lasers into a single beam. In this case, the position of the laser beams can be both coaxial and can change relative to each other with a shift. Due to the fact that the laser radiation of both lasers enters the welding zone from one focal lens, it is possible to weld parts of complex geometry (Fig. 2), focusing of laser beams is facilitated. An inert atmosphere during welding can be used when welding in an inert gas stream or when welding in a sealed chamber in an inert gas environment.

Using the proposed method gives great advantages compared to the prototype when welding in a chamber with an inert medium: an optical system with a single focal lens allows welding with two lasers with limited dimensions of the optical window for introducing laser radiation and when using equipment and welding parts of complex geometry (Fig. 3). In addition, when using this method in combination with a small optical window for introducing laser radiation, the mechanism of protecting the optical window from welding products is greatly facilitated, which ensures its maximum protection during welding and, therefore, ensures the constant energy parameters of the laser radiation entering the zone welding, which favorably affects the quality of the weld.

Using a combination of two laser beams allows the welding of aluminum alloys (in particular, AMC) and hard-to-weld structural steels, which cannot be done using a single pulsed (Nd: YAG) laser. The continuous laser turns on ahead of time and turns off with a delay relative to the pulsed laser, which ensures the optimum temperature for the formation of the weld. A continuous laser provides preliminary heating of the local region, while decreasing the temperature gradient when exposed to a pulsed laser and increasing the absorption coefficient of laser radiation by the surface of the welded part. In this case, the efficiency of a pulsed laser increases (the absorption coefficient of laser radiation increases), and a large penetration depth is ensured. A pulsed laser provides melting of the material, after which a continuous laser provides the necessary temperature conditions for the formation of the weld, thereby avoiding the occurrence of cracks and obtaining the desired macrostructure of the weld.

The proposed method is illustrated by drawings, where:

in FIG. 1 shows an optical system of lasers; in FIG. 2 - welding of parts of complex geometry by the proposed method; in FIG. 3 - welding in a chamber with an optical window for inputting laser radiation; in FIG. 4 - microstructure of the weld of parts from an aluminum alloy obtained using two lasers; in FIG. 5 - microstructure of the weld of parts made of steel 12X18H10T obtained using a single laser; in FIG. 6 - microstructure of the weld of parts from steel 12X18H10T obtained using two lasers.

In the presented drawings (Figs. 1-3), the following are shown: 1 - emitter of a pulsed Nd: YAG laser; 2, 4 - rotary mirror; 3 - node input radiation of a continuous laser, 5 - focal lens; 6a, 6b - laser beams; 7 - welding zone; 8 - an optical window for introducing laser radiation into the welding chamber; 9 - a protective glass.

The optical system of the inventive method is constructed as follows (Fig. 1): mirror 2 directs the radiation of a pulsed laser from the emitter 1 through mirror 4 (transparent for a radiation frequency of 1.064 μm, reflects 0.808 μm) towards the focal lens 5. Mirror 4 directs the radiation of a continuous laser towards the lens 5. Turning the mirror 4 changes the relative position of the laser beams. A focal lens 5 provides focusing of two laser beams 6a and 6b in the welding zone (as shown in Fig. 2). The focusing of the rays can be not only coaxial, but also with an offset relative to each other. When welding in the chamber, the optical window 8 for introducing laser radiation is protected from the products of welding with protective glass 9.

The welding process according to the proposed method is as follows.

In the welding zone 7 for its preliminary heating from the radiation input unit of the continuous laser 3, a beam of a continuous laser 6a is fed through the focal lens 5, which turns on ahead and turns off with a delay relative to the pulsed laser. The beam of the pulsed laser 6b from the emitter 1 is fed through the mirror 2 into the focal lens 5, and then into the welding zone 7 perpendicular to the surface. A pulsed laser provides melting of the material. Mirror 4 provides adjustment of the position of the continuous laser beam relative to the pulsed. Thanks to the use of a continuous laser, the effect of a pulsed laser increases and a large penetration depth is provided. In addition, a continuous laser provides the necessary temperature conditions for the formation of a weld, thereby avoiding the formation of cracks and obtaining the desired macrostructure of the weld, which makes it possible to weld difficult-to-weld structural steels and aluminum alloys (in particular, AMTs). It is worth noting that to confirm the criterion of "industrial applicability" in the proposed method, a laser with a laser wavelength of 0.808 μm is used as a continuous laser. The absorption capacity of an aluminum surface at a wavelength of 0.808 μm is maximum and almost 3 times greater than at a wavelength of 1.064 μm, the absorption capacity of an iron surface at given wavelengths of laser radiation differs slightly. Thus, when using a continuous laser with a wavelength of 0.808 μm, the absorption efficiency of laser radiation by the surface of aluminum and its alloys is significantly increased.

In FIG. 2 shows welding of parts of complex geometry. When welding parts with bulges and depressions relative to the welding zone 7, the use of an optical system with one focal lens 5 allows you to provide a given focal length, which gives a constant power density of the laser radiation of both lasers and favorably affects the quality of the weld.

In FIG. 3 shows welding in a chamber with an inert medium with the limited dimensions of the optical window 8 for introducing laser radiation 6a and 6b. The protective glass 9 prevents contamination of the optical window 8 with welding products.

Examples of specific performance

For an example of execution, a cylindrical specimen was welded from aluminum alloy AMts (example 1), as well as 2 cylindrical specimens from steel 12Kh18N10T (examples 2 and 3). As the lasers, a pulsed Nd: YAG laser (wavelength 1.064 μm) and a cw diode laser with a wavelength of 0.808 μm were used. A laser with such a wavelength was chosen specifically to improve the efficiency of absorption of laser radiation by aluminum. The present invention is not limited to the examples given.

Example 1 - welding of a sample from AMC.

Before welding, the surface of the parts was prepared: degreased, etched in a NaOH solution, followed by clarification in a 30% HNO ₃ solution, an oxide film was removed in the welding zone. Then the parts were washed with water. To prevent the formation of an oxide film, the parts were stored in argon medium prior to welding. Welding was carried out in air in a stream of argon. Welding parameters are shown in table 1 (pos. No. 1).

The diameter of the focused beam of a pulsed laser is 0.6 mm, the diameter of the focused beam of a continuous laser is 2 mm.

First, a cw laser was supplied to the welding zone 7 (the diameter of the laser beam spot was 2 mm). In this case, local heating of the surface took place. After 2 seconds, a pulsed laser radiation was supplied to the welding zone 7, providing melting of the material. The laser beams were directed coaxially. After completion of the weld, the action of a pulsed laser ceased, then continuous (after 1 sec). The microstructure of the weld obtained in this way is shown in FIG. 4. As you can see, there are no defects in the weld and using this method it is possible to weld parts from aluminum alloys.

Examples 2 and 3 - welding of 2 samples of steel 12X18H10T

Before welding samples of steel 12X18H10T, the surface was degreased. Welding was carried out in air in a stream of argon. Welding parameters are shown in table 1 (pos. No. 2, 3). The first sample (table 1, pos. No. 2) was welded using one pulsed laser, the second sample (table 1, pos. No. 3) using two lasers. In both cases, the parameters of the pulsed laser were the same. The welding process is similar to example 1. The microstructure of the obtained welds using one pulsed and two lasers is shown in FIG. 5 and FIG. 6 respectively. As you can see, the penetration depth when using two lasers according to the claimed method has more than doubled.

Thus, from the above examples it follows that the inventive method allows to obtain high-quality welds when welding parts from aluminum and its alloys and from structural steels. Moreover, the inventive method allows welding of parts of complex configuration by simplifying the setup and focusing of the optical system.

Claims (1)

A method of double-beam laser welding of aluminum alloys and hard-to-weld structural steels, including the use of pulsed Nd: YAG and cw lasers, the laser beams being brought together into one optical system and directed to the welding site, which is performed in an inert gas medium, the cw laser being turned on ahead of relative to a pulsed laser, characterized in that the continuous laser is turned off with a delay relative to the pulsed laser, while ensuring the coaxial position of the laser beams in one beam or change the position of the laser beams relative to each other with an offset.

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