JPS5827036B2 - Laser welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser welding method suitable for butt welding of members of different thickness.

As is known, the energy density of a laser beam is extremely high, and can easily be 100,000 times or more higher than that of arc welding.

To give a numerical example, the energy density of an oxyacetylene flame W/
- is about 103, and that of argon arc (200A) is about 1.5X10', while that of electron beam is 109, that of continuous laser beam is 109, and that of pulsed laser is 1013.

By using such a high energy density beam, processing such as surface hardening, welding, drilling and cutting of steel materials can be easily performed.

These quenching, welding, drilling, etc. correspond to the energy density input to the steel material, which is 1.8 x 101 J/a.
Surface hardening, 1.9X103J/Cr? If it is about 4.9X 10'J/Cn, it is evaporation (drilling, cutting).

In other words, if the amount of input energy within a given time is small, no melting will occur, and surface hardening will occur due to the rapid heating and cooling effect on the surface of the steel material, but as the amount of input energy increases, melting will occur.
It becomes evaporation.

FIG. 1 shows changes over time in the workpiece surface temperature T8 and subsurface temperature T'ss due to laser irradiation.

When the power density is 106 W or higher, the surface temperature TS reaches the evaporation temperature TV in about 1 μs, and the surface layer of the workpiece evaporates.

Within such a short period of time, the absorbed heat hardly rises.

Of course, when the surface layer evaporates, the underlying layer becomes the surface layer, so the layer evaporates, and thus drilling, cutting, etc. can be performed.

When the power density is 105 W/- or less, it takes several m5 ec for the surface temperature T8 to reach the evaporation temperature, so during this time the subsurface temperature T88 also rises as shown in the figure, and the melting temperature T
Reach M.

Note that T8 is room temperature. In this case, by adjusting the laser irradiation time appropriately, welding can be performed by stopping the laser irradiation and moving the position while the lower surface layer is melted and the surface layer has not yet evaporated.

Figure 2 shows an overview of laser welding.

10.12 is the base material to be butt welded, and 14 is its butt surface.

The laser beam 16 is projected onto the abutting surface 14 from directly above the abutting surface 14 by a CO2 laser light source 20.

In welding using an energy beam such as a laser or an electron beam, a welding groove is not particularly created, and the welded portion is the butt surface 14 itself, and the beam is focused and projected toward this portion (16a is the focal point).

A deep hole with a small diameter is created in the part of the base material that is irradiated with the laser.
This is called a keyhole.

As the laser beam or the base material moves, the keyhole moves, and the area around it becomes a molten layer.As the keyhole moves, the molten layer also moves, and the previously melted portion solidifies.

Welding is performed by allowing the phenomenon of S to progress on the abutting surfaces 14.

In the figure, 18 is molten metal, 22 is a keyhole, and 24 is solidified molten metal (bead).

F indicates the welding direction; when the beam 16 is moved and welded, the arrow F indicates the moving direction of the beam 16; when the base material is moved and welded, the base material moves in the opposite direction to the arrow F.

Factors that affect laser welding include ■ Laser power ■ Energy density, ■ Laser energy absorption of the base metal, ■ Thermal conductivity and thermal diffusivity of the base metal, ■ Specific heat, density, heat capacity, melting temperature, and melting of the base metal. There are heat, etc., but the above item (2) is particularly problematic.

If the surface of the base material has a low reflectance to the laser beam, the projected laser beam will be reflected and will not contribute to welding.

The reflectance on the base material surface is 50% for many metals.
Therefore, it is necessary to reduce this reflectance and improve the laser energy absorption rate of the base material.

The following methods can be considered to improve this absorption rate.

■Use of multiple reflection by increasing surface roughness, ■Improve wavelength absorption by thin oxide film, etc., ■Use of laser plasma.

As shown in Figure 3, 16 laser beams are coaxially connected with argon (A
gas 32 such as r), helium (He), nitrogen (N2), etc.
When the gas is ejected (numeral 30 indicates a nozzle), the gas instantly reaches a high temperature state due to the surface material of the workpiece evaporated and scattered from the surface of the workpiece 26, and becomes plasma.

This is laser plasma.

When the plasma 34 is generated, most of the energy of the laser beam is absorbed by this plasma, and less of the laser beam is directly irradiated onto the workpiece 26.

On the other hand, the plasma 34 absorbs the laser energy and becomes increasingly hot, which becomes a secondary energy source and generates the workpiece 26.
heat up.

As a result, the penetration shape of the workpiece is as shown in Figure 4.
The shape is a composite of the welded part A by the plasma 34 and the welded part B (the part where the keyhole is formed and its surroundings) by the laser beam incidence.

In this way, when laser welding is performed using gas in combination, plasma is generated, and the energy of the laser beam is absorbed by the plasma, reducing the amount of laser energy that is directly incident on the workpiece, but the energy is propagated through the plasma. Therefore, the energy efficiency can be several tens of times higher than when the laser beam is directly projected onto the workpiece without using gas and most of the laser beam is reflected.

Figure 5 is a diagram explaining this relationship, where a shows no gas, the welding speed is V-2, 5 mm/S, and the beam diameter is W, b and c show plasma when gas is supplied. When the welding speed is generated, b' is ■-20 doors m/S, and c is V.
-2,5 degrees/S, beam diameter, and c are both W2 as shown in the figure.

The shaded area indicates the melted area.

As is clear from the figure, there is almost no melting in case A, whereas a large amount of melting occurs in case C where the welding speed is the same, and the welding speed is approximately 1
Deep penetration can be obtained even with b of 0 times.

Of course, even in case a, a slightly deeper penetration can be obtained by narrowing down the beam diameter and increasing the energy density, but it will not be as good as in case C.

Generating plasma in combination with gas can increase the heating energy efficiency of the workpiece, but as shown in Figure 4, the penetration shape is affected by the plasma lump, which is a characteristic of laser welding. There is a problem in that a narrow and deep penetration shape cannot be obtained.

From this point of view, the presence of plasma is rather harmful, and it is necessary to avoid or adjust its influence.

In the first place, the combined use of a laser beam and a gas flow also has the meaning of gas shielding the welded part, similar to arc welding, and for this purpose, the gas used may be a simple shielding gas.

That is, since a gas with a high ionization voltage is difficult to turn into plasma, it is effective to use a large amount of such gas (for example, He) (at a high flow rate).

Furthermore, as is clear from Figure 5, c, it is also effective to set the welding speed at a constant speed.

It is also effective to blow a high-speed jet stream from the side to split and collapse the plasma.

The present invention also relates to the treatment of this plasma, and aims to press the plasma in a desired direction into the base material and effectively utilize it for welding.

The principle of the present invention is shown in FIG. 6, and an embodiment is shown in FIG.

As shown in FIG. 6, in the present invention, a nozzle 3 is used to supply a laser beam 16 and a plasma generation and shielding gas 32.
0, a nozzle 40 is provided to supply jet gas from an oblique direction.

The jet gas 42 is emitted aiming at the surface portion of the workpiece 26 onto which the laser beam is projected, as shown, and the angle between the nozzle 40 and the center line 12 of the jet gas stream 42 with respect to the center line 11 of the laser beam 16 is As shown in Figure 6, α and θ are.

That is, if the center line l11 of the laser beam is taken as two axes and the welding line (above abutting surface 14) is taken as the X axis, the center line 12 of the jet gas flow is at an angle θ (Z axis 90°-θ), and forms an angle α with respect to the X axis in the x-y plane, and the angle α is variable between positive and negative.

In this way, the velocity vector of the jet gas flow 42 has a component of z51, that is, a component in the thickness direction of the workpiece 26, so it acts to push the plasma 34 into the workpiece, thereby achieving deep penetration. .

In addition, since the velocity vector of the jet gas flow 42 has components x and yFR, the plasma 34 is pushed toward the base metal part that will be welded by the component xlff, so that the energy of the plasma is effectively used for heating the base material. This improves welding efficiency.

Further, the plasma is strongly or weakly (depending on the value of α) pressed to the left or right side of the welding line X by the yi portion, which is extremely effective for welding members of different thickness, which will be described later.

Furthermore, by blowing a jet gas stream from an oblique direction in this way, the periphery of the plasma mass is cooled down to just heated gas, and only the central part where active energy injection is performed is in a plasma state, resulting in miniaturization. A in Figure 4
The area of the part is reduced and becomes closer to part B, resulting in narrow and deep penetration, and the effect is that the molten part can be formed in the direction facing the jet gas flow and its size can be controlled. be.

In order to fully demonstrate the function of the plasma control nozzle 40 that spouts jet gas, it is necessary to make the jet gas pressure, pressure distribution, gas jet angle, gas type, etc. appropriate.

As for the type of gas, He, which has a higher ionization voltage, is preferable to Ar, N2, etc.

The ionization voltage of He is 24.588V, and that of Ar is 1
5.760V, that of N2 is 14.53V.

The gas 32 supplied through the noise 30 is preferably He and is preferably supplied at a low flow rate in order to generate the necessary minimum amount of plasma.

A diatomic gas in a high temperature state has energy of dissociation and energy of ionization, is in a high energy state, and is easily turned into plasma, so it is also good to use a hot gas as the gas 32.

Of the gas ejection angles, α is within a range of about ±60', and θ
is appropriately selected within the range of 3σ to 8σ.

Note that when θξO° is used, the plasma is simply blown off along the surface of the base material, and there is not much difference from the case where no gas is used and therefore no plasma is generated.

The effect of plasma control using jet gas will be explained with reference to FIG. 7. FIG. 7a shows the case without plasma control, and FIG. 7b shows the case with plasma control.

The welded portions shown with mesh lines are wine cup-shaped in case a, and beer barrel-shaped in case b, and it can be seen that there is a great improvement in terms of narrow width and deep penetration.

In this example, the ejection angle α of the jet gas is 0. θ=45
°.

FIG. 8 shows an embodiment of the present invention applied to welding of different thicknesses.

There are many steps in the manufacturing process in the steel industry that require welding. For example, after hot rolling, steel plates are subjected to pickling, annealing, cold rolling, etc. The coil and leader coil are butt welded, and this is the welding.

For example, when welding a product coil and a leader coil, the thickness of each coil is different, such as 6 m1rL and 3 mm, resulting in the state shown in FIG. 8.

If this were to be done by normal laser welding, the laser beam would be projected as indicated by the dotted line 16b, but this would melt the non-welded portion.

In order to avoid this, if the 16th embodiment is used, the parts other than the abutting surfaces will be melted, which is a problem.

In such a case, in the present invention, the oblique angle α is appropriately selected to press the plasma 34 toward the thick base material 10 side.

In this way, the molten metal portions will be formed on both sides of the abutting surfaces, making it possible to perform reliable welding.

Figures 9a and 9b show examples of cross sections of base metals welded with different thicknesses using the method of the present invention.

A shows a case where plasma control is insufficient, and b shows a case where sufficient plasma control is performed, and the manner in which the molten part moves due to the jet gas can be clearly observed.

Another example in which the direction of plasma pressing is changed to a desired direction by jet gas is when welding is performed along a curved welding line.

In this case, it is preferable to make the ejection angle α of the jet gas coincide with the smelting direction at the welding point of the curve so that the plasma is always pressed toward the base metal portion to be welded.

Of course, if necessary, α in the nucleus may be made larger or smaller than the angle formed by the tangent line, so that the τ plasma is pressed more toward one of the base materials to be abutted.

As explained in detail above, in the present invention, gas is supplied together with a laser beam to generate plasma, and the plasma is pressed into the base metal in any direction in front of the welding point and on both sides of the weld line by jet gas. Therefore, effects such as increasing the energy absorption rate of the base metal, adjusting the position of the base metal fusion zone, and downsizing the plasma to enable narrow and deep penetration can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between laser energy density and melting, evaporation, etc. Figure 2 is an illustration of laser welding, Figures 3 and 4 are illustrations of laser welding using gas, and Figure 5 6 is an explanatory diagram of the heating results by laser, FIGS. 6 a and b are explanatory diagrams of the method of the present invention, FIGS. 7 a and b are explanatory diagrams comparing the welding results of the present invention and the conventional method, and FIG. 8 is an explanatory diagram of the welding results of the present invention. 9A and 9B are detailed explanatory diagrams of the welding results. In the drawing, 16 is a laser beam, 32 is a gas, the x-2 plane is a vertical plane including the welding line, the x-y plane is a horizontal plane including the welding line, 3
4 indicates plasma, and F indicates the welding direction.

Claims (1)

[Claims] 1. In a laser welding method in which gas is supplied together with a laser beam to generate plasma on a base material, inclination angles θ and α with respect to the weld line in a vertical plane including the weld line and in a horizontal plane, respectively. The method is characterized in that jet gas is injected toward the welding point with a jet gas, and welding is performed while pressing the plasma into the base metal in a desired direction including the base metal part to be welded and both sides of the weld line. Laser welding method. 2. The laser welding method according to claim 1, wherein the inclination angle α in the horizontal plane including the weld line is variable.