JPS6099494A - Welding method of thin steel sheets by laser - Google Patents

Abstract

PURPOSE:To increase the effective absorption rate of a laser beam and to perform stably and efficiently welding by shielding the upper and lower parts at a butt weld point by semispherical cavities and focusing the reflected and radiated energy from the weld point by multiple reflection to the weld point. CONSTITUTION:The upper and lower parts of the butt part 2 of thin steel sheets 1, 1 are shielded by semispherical cavities 4, 4'. A laser beam 3 is irradiated through a laser beam introducing hole 5 onto the weld point 2. The spot diameter of the beam 3 on the weld surface in the part where said beam is projected is made larger than the permissible accuracy for butting. An optical system is so set that the focal position of the beam 3 comes to the turning point of the upper cavity 4 as far as possible. When the beam 3 is irradiated in such a state, the effective absorption rate on the point 2 is increased by the multiple reflection effect of the cavities 4, 4'. The energy of the beam passing through the butt spacing is also reflected by the cavity 4' and further the energy radiated from the molten part is utilized by the multiple reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to butt seam welding of ultra-thin steel plates.

[Prior art]

In continuous processing lines for thin steel plates, various welding methods are used to connect the ends of the leading and trailing strips for continuous sheet threading. At present, there is no welding method that is satisfactory in terms of butting problems and welding speed, and laser welding is being considered as an alternative.

In laser welding of thin steel plates, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 54-32154, two end faces of the welding gap are usually brought into abutment, and a laser beam is irradiated from right in the center between the end faces. If the end faces are smooth and in close contact with each other, and the butting is performed with sufficient precision, the laser energy will be absorbed by both sides of the butt end faces, melting both end faces, and welding will occur.
Sill. However, if there is a gap between both end faces due to unevenness of the end face or bending caused by IJJ cutting, etc., the light will be concentrated.
- The beam passes through gaps or is absorbed only at one end, making it impossible to complete welding.

For this reason, there is a method to improve the accuracy of end face processing and reduce the gap between both end faces, but especially for wide steel plates,
The equipment cost for this becomes extremely large.

It is also conceivable to increase the diameter of the laser beam and heat and melt both end faces to perform welding even if there is a slight gap between the end faces, but in reality stable welding is difficult for the reasons described below.

Now, if the laser beam absorption rate of the steel plate surface is changed and the energy unnecessary for melting the mating part is P M Kw, the laser power PKw required for welding is P"PM/G (... (1) Become.

Generally, the absorption rate σ is determined by the surface roughness of the steel plate, the surface temperature of the coating 2,
It changes depending on the wavelength of the laser beam, etc.

For example, in the case of the C○2 laser, which is currently most commonly used industrially, the deviation is less than 0.1 at room temperature, so the laser beam energy must be input at least 10 times the minimum energy required for welding. Welding does not start. However, once the surface is heated and melted, the absorption rate σ becomes 0.9 or more, and as a result, 10 times the energy required for melting is input into the welding area, resulting in molten material falling (melt falling).

This is repeated periodically and a humping phenomenon occurs, making it impossible to perform stable welding.

Another method is to generate plasma and bring it into a stable energy absorbing state to increase the absorption rate d, but in this case, the energy density needs to be higher than the plasma generation limit, so the output of current laser machines cannot be used to The light must be focused with a small diameter, and highly accurate alignment is also required.

As explained above, in the conventional laser welding of ultra-thin plates, the welding phenomenon is unstable, making it easy for weld to drop or hump, and extremely high precision is required for coil butt control and seam tracing control of the laser beam. There's a problem.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of these problems, an object of the present invention is to provide a method that can stably and efficiently perform seam welding with a large laser beam diameter.

[Structure of the invention]

In order to achieve the above object, the present invention shields the upper and lower parts of the welding point with hemispherical cavities, and the reflected and radiant energy from the welding point is converged on the welding point by multiple reflections on the inner surface of the cavity. Increase the effective absorption rate of laser beam.

FIG. 18 does not outline the configuration of an apparatus that implements the present invention in one embodiment. ■, 1' is the thin steel plate to be butt welded, 2 is the butt part, 3 is the laser beam, 4°4' is the upper cavity and lower cavity, respectively, 5 is the laser beam introduction hole, 6.6' is the atmospheric gas inlet , 7, 7' are cavity cooling water inlets, and 8° 8' is the same outlet. In addition, the inner surface of the cavity is plated with gold on top of a mirror finish, for example, making it highly reflective, and the inner hemisphere is sized and arranged so that the welding point 2 is at its center. .

In this state, the laser beam 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 butt tolerance δ, and the size of the laser beam introduction hole is made as small as possible. In order to do this, the optical system is set so that the beam focal position is as close to the pole position of the upper cavity as possible. The laser beam power is set in consideration of the welding part melting energy PM determined from the welding bead width b (:d), the plate thickness t, and the welding speed V, and some efficiency η.

When the laser beam 11 is irradiated in this state, the effective absorption coefficients d and e on the welding point become values close to 1 due to the multiple reflection effect of the cavity.

ae=c(+(L -a)+(] +c02(i+--
−−1・・・・・・(2) In addition, the beam energy that passed through the gap between the butts to the bottom is also reflected by the lower cavity, and the radiant energy from the molten part is similarly reflected multiple times in the cavity and used. Ru. Therefore, stable and energy-efficient welding without unstable phenomena such as humping is possible.

Furthermore, since the effective absorption rate can be high, welding can be performed with the beam focus removed from the steel plate surface, so wide bead welding can be performed with ample margin for the butt gap.

FIG. 2 shows a drawing for explaining the invention in detail.

In the figure, 9 is a calibration laser (for example, He-Ne), and IO is a gap sensor placed opposite the upper cavity l.

Normally, the calibration laser 9 is installed coaxially with the welding power laser 11 and is used for adjusting the optical path of the power laser. By running it, the gap δ between the abutting surfaces and the weld line shape are optically detected and stored in the control device 12. Next, the diameter d of the power laser beam on the steel plate is set, taking into consideration the maximum value δn1aX of the detected gap δ, and then the width of the molten bead is determined.

Laser power P required for welding is set from welding conditions such as plate thickness tyWj and contact speed V, and welding is started.

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

As described above, by welding using a cavity with an effective absorption rate close to 1, it is possible to perform stable and highly energy-efficient welding, and it is also possible to perform welding with the necessary wide beat width, so that the butt end face can be The precision required for laser welding has been relaxed, and the hook temporary cutting device, flit,
Additional theories such as 5i presser mechanism (i#) Costs are reduced, laser beam tracing control becomes easier, and automation becomes possible.

In the method of the present invention, atmospheric gas can be introduced into the cavity from the upper surface of the cavity, as shown in FIG. 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, and therefore spatter is extremely small. If there is a possibility that the gas may adhere to the inner surface of the cavity, this gas serves to suppress this. Figure 3a shows the cross-sectional shape of the weld, which is often seen as a curve when wide bead welding is performed, and is bent downward due to the gravity of the molten part. By increasing the height, it is possible to obtain a flat cross-sectional shape as shown in FIG. 3b.

〔Example〕

Using a YAG laser with an output of 200W, a radius of 1.0 m
When welding a thin steel plate with a thickness of 0.2 mm using a +n gold-plated copper, water-cooled cabinet with a beam boss h1 mm on the steel plate, an extremely stable seam was obtained even though the butt gap was 0.05 mm. welding is done,
The welding speed was 10 m/min.

This is twice the welding speed when using a YAG laser of the same output, and humping occurs when welding using a CO2 laser, making stable welding impossible.

〔Effect of the invention〕

As explained above, in the present invention, efficient and stable beam welding can be performed with a large laser beam diameter, so the processing accuracy of the butt surface of the steel plate is relaxed, and therefore the steel plate cutting device is improved.

The cost of ancillary equipment such as a steel plate holding mechanism can be reduced, and the laser beam tracing control is also facilitated, making automation easy.

[Brief explanation of the drawing]

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. 2 is a block diagram showing the configuration of a butt gap and weld line measuring device in one embodiment of the present invention. FIG. 3a is an explanatory diagram showing a cross-sectional shape of a welded part by a conventional welding method, and FIG. 3b is an explanatory diagram showing a cross-sectional shape of a welded part according to an embodiment of the present invention. ], 1': Thin steel plate 2: Butt part 3: Laser beam 4: Upper cavity 4+ = lower cavity 5: Laser beam inlet 6.6': Atmospheric gas inlet A, 7': Cavity cooling water inlet 8.8' : Cavity cooling water outlet d: Power laser beam diameter 9: Laser for calibration 1O: Gap sensor 11: Power laser for welding 12: Control device patent applicant Nippon Steel Corporation No. 1a, 6', Fig. 2, Fig. 3a Figure 3b

Claims (1)

[Claims] The upper and lower parts of the welding point are shielded by hemispherical cavities. A method for welding thin steel plates using a laser, characterized in that reflected and radiant energy from the welding point is focused on the welding point by multiple reflections on the inner surface of the cavity, thereby increasing the effective absorption rate of the laser beam at the welding surface.