JPH06238478A - Laser beam welding method for thick metal plates - Google Patents

Abstract

PURPOSE:To improve welding quality by providing a specified interval with materials to be welded to set up a gas interrupting plate and passing a specified a specified quantity of inert gas between the both. CONSTITUTION:A laser beam 2 generated by a laser beam generator 1 is condensed by a condenser 3, the materials 7 to be welded are irradiated through the gas interrupting plate 5 from a nozzle 4A with the laser beam and laser beam welding of the metal plates to exceed 8mm of the depth of penetration of one pass is performed. The interval of 1mm to 10mm is provided with the materials 7 to be welded to set up the gas interrupting plate 5 along the laser beam 2 irradiation side surface of the materials 7 to be welded. The inert gas of 10L/min to 50L/min is passed between the gas interrupting plate 5 and the materials 7 to be welded by using a nozzle 6 and the laser beam 2 is passed through the gas interrupting plate 5 to perform welding. Consequently, the appliable range of laser beam welding is extended and the quality of its structure can be improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to laser welding of thick metal plates of metals, especially iron and iron alloys.

[0002]

2. Description of the Related Art In recent years, various laser generators have been developed and improved, and are being widely used for welding and cutting metals.
Since laser welding uses a concentrated high energy density laser beam as a heat source, welding with high dimensional accuracy can be performed at high speed. Unlike electron beams, laser beams also have the property of not being attenuated in the atmosphere, which is a technology that will continue to expand and grow. In the case of carbon dioxide gas lasers, those with an output of over 20 kW are beginning to be marketed.

In the laser welding method, the material to be welded is irradiated with a laser beam focused by a convex lens or a concave mirror, and after melting the material, the heat source is moved or stopped to solidify again and welding is performed. With a 10 kW output carbon dioxide laser, a 10 mm thick steel plate can be penetrate-welded, and with a 20 kW output, a steel plate exceeding 20 mm can be penetrate-welded (welding technology January 1988 page 106).

However, when the material to be welded is irradiated with the laser beam, plasma vapor is generated around it. This plasma vapor absorbs the laser beam. For this reason, when performing laser welding, a method is used in which an atmosphere in which plasma vapor is unlikely to be generated is created, the generated plasma vapor is blown off, or a laser beam is intermittently irradiated. Among them, a method is generally used in which a shield gas is used to create an atmosphere in which plasma vapor is unlikely to be generated, the generated plasma vapor is blown off, and the molten metal is prevented from being oxidized.

This shield gas is usually injected from the center of the torch nozzle and a method of injecting it obliquely from the center of the torch nozzle. The injection from the center is for welding fumes, heat, etc. into the nozzle. It prevents entry, protects the condenser lens in the nozzle, and prevents the oxidation of the weld.
On the other hand, the injection from the oblique direction is mainly used to further enhance the effects such as removal of plasma vapor. Needless to say, welding can be performed only by injection from the center or injection from an angle.

Further, various measures have been taken in order to improve these efficiencies. For example, Japanese Patent Laid-Open No. 58-50191 discloses a method in which a sealed space is formed on the surface to be welded and a shield gas is introduced into this space to prevent oxidation of the welded portion, or Japanese Patent Laid-Open No. 63-76785 discloses a nozzle periphery. Various methods have been proposed for reducing the entrainment of air by constructing a shield gas curtain in. Regarding the composition of the shield gas, in addition to helium, argon, nitrogen, etc., for example, JP-A-58-173094 uses a method of blowing a small amount of oxygen, and JP-A-59-189095 uses carbon dioxide gas. Methods have also been proposed.

[0007]

When carbon dioxide gas laser welding using this shielding gas was performed on a thick steel plate,
Many pores were generated in the weld metal. This phenomenon does not occur when the plate thickness of the material to be welded is small, but it becomes remarkable as the plate thickness increases, and frequently occurs when the plate thickness exceeds 8 mm.
The present invention aims to solve the above problems.

[0008]

Means for Solving the Problems The present invention is to solve the above problems, and in laser welding of a metal plate having a penetration depth of more than 8 mm in one pass, the distance between the material to be welded and 1 mm or more and 10 mm or less. And installing a gas blocking plate along the surface of the material to be welded on the laser beam irradiation side, and flowing an inert gas between 10 liters / minute and 150 liters / minute between the gas blocking plate and the material to be welded, Further, there is provided a laser welding method for a thick metal plate, which is characterized in that the laser beam penetrates through the gas blocking plate and is welded.

[0009]

When the laser welding using the shielding gas which is generally performed as described above is also applied to the thick plate, many pores are generated. The inventors of the present invention have conducted research such as investigation and analysis of gas components in the pores and found that the pores are caused by the shield gas. Welding thick plates requires high laser power, which promotes the generation of plasma vapors. The shield gas flow is made faster to reduce the effect of the plasma vapor. In addition, when the plate becomes thick, the amount of molten metal also increases, and an irregular flow of molten metal occurs. In addition to this, the influence of the shield gas, which has been accelerated, adds to the turbulence of the molten metal. The generation of pores is due to irregular solidification accompanying the disturbance of the flow of the molten metal. Therefore, the effect of the shield gas is made more efficient, the influence of plasma vapor is reduced, and the method of preventing the generation of pores is provided.

First, FIG. 1 shows a conceptual diagram of the present invention. The laser beam 2 generated by the laser generator 1 is condensed by the condenser lens 3, and is irradiated from the nozzle 4A to the welding material 7 through the gas blocking plate 5 installed on the front surface of the welding material. At that time, a shield gas is injected from the nozzle 6 between the gas blocking plate and the material to be welded for the purpose of preventing oxidation and removing plasma vapor (this is referred to as an inner shield). Further, in order to further ensure the removal of plasma vapor or to protect the condenser lens, a shielding gas is ejected from the nozzle 4A and, in some cases, the nozzle 4B (this is referred to as an outer shield). Furthermore, in the case of penetration welding, the nozzle 8 is
A shield gas may be sprayed.

Even in the conventional welding method, if the penetration depth of one pass is less than 8 mm, the problem of pore formation is particularly small, 8 m.
The effect of the present invention is remarkable when m or more, and the penetration depth of one pass is set to 8 mm or more. The penetration depth is shown in FIG. In the figure, 9 is the weld metal, and 10 is the penetration depth.

As the material of the gas blocking plate 3, a metal, glass, or ceramics heat-resistant thin plate is used. Materials that are deformed or deteriorated by heat during welding are not preferable. The thickness is preferably 0.2 mm or more if it is a metallic material. If it is too thin, it will be greatly deformed by welding heat, which is not preferable. In the case of glass or the like, it is better to be thicker than a metal plate due to the strength and the like.

Further, the shape of the blocking plate may be the flat plate shown in FIG. 1, but it is preferable that the blocking plate be provided on both sides as shown in FIG. 3 so as to further enhance the shielding effect. Moreover, you may attach a sag in the front-back direction. Furthermore, the longer the length toward the rear is, the higher the effect of preventing the oxidation of the welded portion after welding is, which is preferable. If the distance between the shield plate and the material to be welded is less than 1 mm, the deformation is large due to the influence of welding heat, and it is unfavorable because it may come into contact with a surplus formed during welding. Again 1
If the distance exceeds 0 mm, the blocking effect is small,
It was set to 10 mm or less.

Further, the blocking plate may be provided with a minimum hole or groove necessary for the laser beam to pass therethrough, but if it is a thin plate, it can be easily drilled by irradiating the laser beam, and especially a hole for passing the beam. Alternatively, it may have no groove. When a beam passage hole is previously formed in the blocking plate, a slight convex portion may be provided around the hole. Providing the convex portion reduces the invasion of the external shield gas into the hole and enables the use of a larger amount of the external shield gas.

When the flow rate of the shield gas between the material to be welded and the shield plate is less than 10 liters / minute, the plasma vapor is not sufficiently removed and the penetration is shallow. If the amount exceeds 150 liters / minute, the generation of pores tends to increase, and the weld bead shape becomes poor. From these, the flow rate of the shield gas between the material to be welded and the shield plate was set to 10 liter / min or more and 150 liter / min or less. The nozzle 6 for injecting the shield gas may have a circular cross section, a quadrangle, or the like, but the nozzle 6 is ejected along the welded material so as to create a flow of the shield gas between the blocking plate and the welded material. preferable. Therefore, it is also preferable to make a flat quadrangle when the gap between the blocking plate and the material to be welded is narrow.

[0016]

The present invention will be described in detail with reference to the following examples. The outline of the examples is summarized in Table 1. 1 laser generator
A 5 kW carbon dioxide laser oscillator was used, and the output was 13 kW. The material to be welded uses a 20 mm thick mild steel plate,
Downward, bead-on welding was performed by the method of moving the material to be welded. The moving speed of the material to be welded was 1 m / min, and some of them were performed at 1.5 and 2 m / min. The number of porosity was 10 or less per 1 m of the welding length when the sample after welding was observed by X-ray fluoroscopy. Also, the penetration depth cuts the bead,
The cross section was observed.

[0017]

[Table 1]

Example 1 A 0.2 mm thin iron plate was placed on the material to be welded with an interval of 2 mm, and a laser beam was irradiated from above to perform welding. Helium is flown at a rate of 15 liters / minute between the material to be welded and the shield plate, and the external shield gas on the shield plate is also 2
Run at 0 liters / minute. The bead after welding had 6 pores / m, and a good bead was obtained. The penetration is also 16 mm
However, the bead shape was also good.

Example 2 A ceramic plate having a thickness of 4 mm was placed on a laser irradiation torch and welded to a material to be welded at a distance of 5 mm. A beam passage hole having a diameter of 1.5 mm was previously provided in the ceramic material. Argon should be 50 between the material to be welded and the shield.
L / min. Flow, and the external shield gas on the shutoff plate is also 50
L / min. The bead after welding had few pores as in Example 1, sufficient penetration, and good shape.

Example 3 A 1 mm stainless steel blocking plate was placed on the material to be welded at intervals of 10 mm and welded. Side plates were provided on both sides of the barrier plate. Nitrogen was flowed between the material to be welded and the blocking plate at 150 liters / minute, and the external shielding gas on the blocking board was also flowed at 20 liters / minute. The bead after welding had few pores as in Example 1, sufficient penetration, and good shape.

Example 4 A 1 mm stainless steel blocking plate was placed on the material to be welded at intervals of 5 mm and welded. Side plates were provided on both sides of the blocking plate, and a 1.5 mm wide groove for passing the beam was provided. Flow helium at 50 liters / minute between the material to be welded and the barrier plate,
The external shield gas on the blocking plate was also flown at 20 liters / minute. As in Example 1, the welded beads had few pores, sufficient penetration, and good shape.

Comparative Example 1 Welding was performed at a welding speed of 2 m / min without installing a blocking plate. The shield gas was helium at 50 liters / minute. Porosity was small and bead shape was good, but penetration was 7
It was mm.

Comparative Example 2 As in Comparative Example 1, no blocking plate was installed and welding was performed at a welding speed of 1.5 m / min. Shield gas is helium 50
L / min. Although the penetration depth was as deep as 10 mm, pores were continuously generated.

Comparative Example 3 A 0.2 mm thick iron plate was placed on the material to be welded at intervals of 0.5 mm and welded. Helium was flown at a rate of 20 liters / minute between the material to be welded and the blocking board, and the external shield gas on the blocking board was also flowed at 50 liters / minute. During the welding, the blocking plate was greatly deformed and caught with the bead, and the bead shape was also poor.

Comparative Example 4 A 0.2 mm thin iron plate was placed on the material to be welded with an interval of 2 mm and welded. Helium was flown between the material to be welded and the blocking plate at a rate of 8 l / min, and the external shield gas on the blocking plate was also flowed at 20 l / min. The bead after welding was a good bead with few pores. However, the penetration was smaller than that of Example 1 and was not satisfactory.

Comparative Example 5 A 0.2 mm thin iron plate was placed on the material to be welded with an interval of 2 mm and welded. Helium was flowed between the material to be welded and the blocking plate at a rate of 180 liters / minute, and the external shielding gas on the blocking plate was also flowed at 50 liters / minute. The bead after welding had many pores and the bead shape was also disordered.

Comparative Example 6 A 1 mm stainless plate was placed on the material to be welded with an interval of 12 mm and welded. Helium was made to flow between the material to be welded and the shield plate at 50 liters / minute, and the external shield gas on the shield plate was also made to flow at 20 liters / minute. The bead after welding had a few large pores and had little penetration, which was not satisfactory.

[0028]

Although laser welding is being widely used, the welding of thick metal plates in the state of the art often causes porosity in the weld. By using the shielding method of the present invention, generation of pores can be easily prevented and welding quality can be remarkably improved. As a result, the applicable range of laser welding is expanded and the quality of the structure can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the concept of a laser welding method of the present invention.

FIG. 2 is a view showing a cross section of a laser welding bead.

FIG. 3 is a diagram showing an example in which a side of a blocking plate is provided with a sag.

[Explanation of symbols]

 1 Laser generator 2 Laser beam 3 Condenser lens 4A, 4B Nozzle (outside) 5 Gas blocking plate 6 Nozzle (inside) 7 Welding material 8 Nozzle (back side) 9 Welding metal 10 Penetration depth G Shield gas

Claims (1)

[Claims] 1. In laser welding of a metal plate having a penetration depth of more than 8 mm per pass, the material to be welded is 1 mm or more and 1 mm or more.
A gas blocking plate is installed along the surface of the material to be welded on the laser beam irradiation side with a space of 0 mm or less, and the inert gas is 10 liters / min or more between the gas blocking plate and the material to be welded 1
A method for laser welding a thick metal plate, which comprises flowing 50 liters / minute or less and welding the gas barrier plate with a laser beam penetrating the gas barrier plate.