JPH0424158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to butt seam welding of thin steel sheets, and particularly to a laser welding method for welding a butt portion with a laser beam.

[Prior art] Various welding methods are used in continuous processing lines for thin steel sheets to connect the ends of the leading strip and the trailing strip to perform continuous sheet threading. Currently, there is no welding method that is satisfactory in terms of plate butt accuracy and welding speed, and laser welding is attracting attention as an alternative.

Laser welding of thin steel plates is described, for example, in Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent No. 32154, two end faces to be welded are usually butted together, and a laser beam is irradiated from directly above the center between the end faces. If the end faces are smooth and in close contact with each other, and abutment is performed with sufficient precision, laser energy is absorbed by both sides of the abutting end faces, and both end faces are melted and welded. However, if there is a gap between the two end faces due to unevenness of the end face or bending caused by cutting, etc., the focused laser beam may pass through the gap or be absorbed by only one end face, resulting in complete welding. I can't do it.

For this reason, there is a method of increasing the accuracy of end face processing and reducing the gap between both end faces, but this method requires extremely high equipment costs, especially for wide steel plates.

There is also a method of using a filler wire and placing it on the welding line or feeding it, but if the center of the laser beam, the center of the welding line, and the center of the wire are not aligned, stable melting cannot be obtained. If there is a positional change between the filler wire and the steel plate, stable welding cannot be achieved unless the laser beam irradiation conditions are changed. If these things do not go well, the filler wire itself may scatter or be thermally deformed, increasing the instability of welding and even making welding impossible.

As explained above, conventional laser welding of ultra-thin plates is prone to burn-through and humping due to unstable welding phenomena, and extremely high precision is required in coil butting and laser beam seam tracing control. There is.

[Object of the Invention] An object of the present invention is to provide a laser welding method that stably and efficiently performs seam welding using a welding wire.

[Structure and operation of the invention] In order to achieve the above object, the present invention has the following features:
A filler wire is placed on the welding line, the top and bottom of the welding point are shielded by a hemispherical cavity, a laser beam is irradiated, and the reflected and radiant energy from the welding point is focused on the welding point by multiple reflections on the inside of the cavity, and the welding is completed. In addition to increasing the effective absorption rate of the laser beam on the surface and allowing good bead formation even when the butt interval is wide, the laser beam is first irradiated with low power to melt the surface of the wire and weld it to the steel plate. Then, perform the main welding.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1a shows an outline of an apparatus configuration for carrying out one embodiment of the present invention. 1 and 1' are the thin steel plates to be butt welded, 2 is the butt part, 3 is the filler wire, 4 and 4' are the upper and lower cavities, respectively, 5 is the laser beam introduction hole, and 6 and 6' are the atmospheric gas inlets. , 7 and 7' are cavity cooling water inlets, 8 and 8' are cavity cooling water outlets, and LB is a laser beam. The inner surface of the cavity is, for example, mirror-finished and plated with gold, making it extremely highly reflective.

In this state, the laser beam LB is focused by a lens and irradiated onto the welding point 2. Referring to Figure 1b, which shows the cross section of the laser beam projection part, the spot diameter d on the welding surface is set to be larger than that in consideration of the required butting accuracy, and the size of the laser beam introduction hole is set to be as large as possible. In order to reduce the beam size, the optical system is set so that the beam focal point is located as close to the pole position of the upper cavity as possible.

Welding is carried out in two stages: fusion of the steel plate 1 by skin melting of the filler wire 3, and main melting. That is, the filler wire 3 is first fixed on the weld line to prevent the wire from scattering during the main welding or from shifting from the weld line due to thermal changes.

The power of the laser beam is at a level slightly higher than the skin melting of the filler wire, but not at a level that melts the center of the filler wire. In this case, the surface of the wire may be coated with a light-absorbing substance to increase the skin melting efficiency.

For water-soluble materials, the laser power is determined by the weld bead width b (= d), plate thickness t, filler wire diameter df, and welding speed.
is set with some efficiency in mind.

When a laser beam is irradiated in this state, the effective absorption rate 〓e on the welding point becomes a value close to 1 due to the multiple reflection effect of the cavity.

〓e=〓+(1-〓)〓+(1-〓) ² 〓+……≒
1 In addition, the beam energy that passes through the butt gap in the main welding to the lower part is also reflected by the lower cavity, and furthermore, the radiant energy from the welded part is similarly multiple reflected by the cavity and used. Therefore, stable and energy-efficient welding without unstable phenomena such as humping is possible. In addition, since the effective absorption rate can be high, the skin of the filler wire can be stably melted in a low energy density state. In this way, even when the butt spacing is wide, wide bead welding can be performed stably and with sufficient margin using filler wire.

FIG. 2a shows a drawing for explaining an embodiment of the invention. In the drawing, 9 is a calibration laser (for example, He-Ne), and 10 is a gap sensor placed opposite the upper cavity 1.
Normally, the calibration laser 9 is the welding power laser 1
1 and is used to adjust the optical path of the power laser 11. By running this laser beam along with the upper cavity 1 and the gap sensor 10 over the weld seam, the gap between the abutting surfaces can be adjusted. The weld line shape is optically detected and stored in the control device 12.

After that, as shown in Fig. 2b, the filler wire is set and fixed on the butt gap using the filler wire installation and fixing devices 20, 20', and the laser power is lowered.
Weld wire 2 to steel plate 1 using P _L. continue,
The maximum value of the detected gap 〓 Taking into account _nax ,
Set the power laser beam diameter d on the steel plate, then set the laser power P required for welding from welding conditions such as molten bead width b, plate thickness t, welding speed V,
Start welding.

During welding, the positions of upper cavity 4 and lower cavity 4' are controlled according to the previously detected weld line shape.

As described above, since the effective absorption rate can be made close to 1 using the cavity, stable and energy-efficient welding can be performed by stably welding the filler wire 2 to the steel plate 1 at the butt interval in advance. At the same time, it is possible to perform wide welding with the necessary wide bead width, which eases the required precision required for processing the butt end faces, reduces the cost of incidental equipment such as steel plate cutting equipment and steel plate holding mechanisms required for laser welding, and Laser beam scanning control becomes easier and automation becomes possible.

In the method of the present invention, as shown in FIG. 1a, atmospheric gas can be introduced into the cavity from the upper surface of the cavity. This gas acts as a sealing gas, similar to normal welding. In addition, due to the characteristics of the method of the present invention, there is no generation of plasma, and the molten part is able to perform relatively quiet welding, which is close to a heat conduction type.Therefore, spatter is extremely small, but evaporation of oil etc. on the surface of the steel plate is possible. This gas serves to prevent objects from adhering to the inside surface of the cavity.

[Example] Using a YAG laser with an output of 600 W, using a water-cooled cavity made of gold-plated copper with a radius of 15 mm, and using a beam spot on a steel plate of 1.5 mm, a thin plate with a thickness of 0.2 mm was processed using a filler wire with a diameter of 0.12 mm. For filler wire fusion, the laser power was 200W and the speed was 5.
m/min, and when this welding was performed with a laser power of 600W, extremely stable seam welding was achieved despite the butt gap of 0.10mm.
The welding speed was 10 m/min. At such welding speeds, stable welding was impossible with conventional methods due to end welding or humping.

[Effects of the Invention] As explained above, in the present invention, the filler wire can be fused to the steel plate with a large laser beam, so even when the butt gap is wide, efficient and stable seam welding can be performed. As a result, the machining accuracy of the butt surfaces of the steel plates can be relaxed, and the cost of ancillary equipment such as steel plate cutting equipment and steel plate warming mechanisms can be reduced, and laser beam tracing control can also be facilitated. Its effects are great, such as ease of automation.

[Brief explanation of drawings]

FIG. 1a is a cross-sectional view schematically showing the configuration of an apparatus for carrying out one embodiment of the present invention, and FIG. 1b is a cross-sectional view showing only a laser irradiation section. FIG. 2a is a block diagram showing the configuration of a butt gap and weld line side fixing device in one embodiment of the present invention, and FIG. 2b is an explanatory diagram of a filler wire device fixing device. 1, 1'... Thin steel plate, 2... Butt portion, 3... Filler wire, 4... Upper cavity, 4'... Lower cavity, 5... Laser beam introduction port, 6, 6'...
Atmospheric gas inlet, 7, 7'...Cavity cooling inlet,
8, 8'... Cavity cooling outlet, d... Power laser beam diameter, 9... Laser for calibration, 10... Gap sensor, 11... Power laser for welding, 12... Control device, 20, 20'... Filler wire installation fixing machine, LB ...laser beam.

Claims (1)

[Claims] 1. A welding wire is installed on the welding line, the upper and lower parts are shielded by hemispherical cavities, and the welding line is irradiated with a laser beam, and the reflected and radiant energy from the welding point is multi-reflected on the inner surface of the cavity to perform welding. Welding of thin steel plates using a laser, in which the laser beam is first irradiated with a low power to melt the surface of the wire and welded to the steel plate, and then the main welding is performed with a high power. Law. 2. The laser welding method for thin steel plates according to claim 1, wherein heat treatment is performed using low density energy after welding.