JPH07275904A - Laser beam cutting method in continuous hot rolling - Google Patents

Abstract

PURPOSE:To shorten the time of process and to improve the accuracy of press- fixing by cutting the p of a rolled stock welded with a laser beam by laser beam cutting with oxygen and cutting the part in pressurized contact with a roll by laser beam cutting with argon or nitrogen. CONSTITUTION:The abutting part of the rolled stock is composed of laser beam welding regions W1, W3 and press-contact region W2. In the laser beam welding region W1, laser beam cutting is executed at high speed by jetting oxygen. And, by instantly switching oxygen to argon or nitrogen, the press- contact region W2 is cut by the laser beam. Consequently, the press-contact region W2 is not oxidized, so joining strength by press-contact is excellent. Next, by switching argon or nitrogen to oxygen, the laser beam welding region W3 is cut at high speed by the laser beam. After cutting, the rolled stocks are brought into press-contact and the laser beam welding regions W1, W3 are welded by the laser beam. In this way, productivity is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser cutting method in continuous hot rolling which enables hot strips to be manufactured by completely continuous rolling.

[0002]

2. Description of the Related Art In a conventional hot rolling line, slabs are extracted from a heating furnace one by one and rolled into a sheet bar having a required thickness by a group of rough rolling machines. After being rolled into a strip, it is wound into a coil by a coiler. This conventional hot rolling line is a discontinuous rolling in which rolled materials are rolled one by one, which has the drawbacks of poor efficiency and poor quality.

In order to solve these problems of the conventional hot rolling line, in recent years, in order to continuously hot roll the sheet bar, the trailing end portion of the preceding rolled material and the leading end portion of the trailing rolled material are being rolled. A method has been proposed in which butt-joining is performed by butt-joining the cut surface of the shear-cut, and the joined sheet bar is continuously rolled. However, since the cut surface remains as it is, the abutting state is poor, and there is a large gap. Therefore, it is impossible to join using a laser beam that needs to be focused (usually 1 mm or less) to increase the output density. . Therefore, in Japanese Patent Laid-Open No. 4-366384, a method of cutting a hot-rolled steel plate or the like with two laser processing heads and then laser joining is used, and in Japanese Patent Laid-Open No. 56-163088, only one of the steel plates is shaped by laser cutting. Then, laser bonding is disclosed.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Japanese Laid-Open Patent Publication No. 376384 and Japanese Patent Laid-Open No. 56-163088 are improvements in the conventional laser joining method in which the cut surface of shear cutting is used for making the hot rolled material continuous. When cutting and shaping both ends, it is necessary to increase the cutting speed. Therefore, when oxygen gas is used as the processing gas, the cutting speed increases, but the cutting portion is oxidized and scale is generated. Therefore, there is a problem that a scale layer is present in the pressure contact portion and a bonding defect occurs during pressure bonding.

[0005]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned problems, and in continuous hot rolling in which laser welding and pressure welding are combined, the portion to be laser welded is cut by laser cutting with oxygen. It is intended to provide a laser cutting method that enables pressure welding without welding defects by increasing the speed and switching to argon gas or nitrogen gas that does not generate scale at the pressure welding portion. The gist of the invention is that the trailing edge of the preceding rolled material and the leading edge of the trailing rolled material are laser-cut on the finishing entry side of the rolling mill of the hot rolling mill to form the shape of the leading edge. In the laser cutting method of increasing the contact area of the butt portion and butt-welding both ends with a laser, and then continuously rolling the rolled material joined by a roll pressure welding roll, When cutting using the laser beam for forming the tip of the line material, the assist gas is instantaneously switched on the way, the laser welding part is laser cut with oxygen, and the roll pressure contact part is argon or nitrogen. A laser cutting method in continuous hot rolling is characterized in that laser cutting is performed to suppress the generation of an oxide film on the cut surface and roll pressure welding is performed.

[0006]

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a view showing a laser cutting welding nozzle structure according to the present invention. In FIG. 1, reference numeral 1 is an adaptor capable of controlling the distance between the hot-rolled plate and the nozzle tip in accordance with the focal length of the condenser mirror. Assist gas is introduced from the gas suction port 2 and spaces 5 and 6 are provided around the central axis of the nozzle upper portion 3 and the nozzle lower portion 4 so that the gas flow rate on the circumference is constant, and from this portion on the concentric circumference. Assist gas is ejected through the 12 gas ejection holes arranged. During the cutting, six holes 7 for O ₂ and six holes 7 ′ for N ₂ are drilled in order to switch the gas at a high speed midway.

FIG. 2 is an explanatory diagram that defines the gas injection conditions of the nozzle. D is the distance from the laser optical axis to the center of the nozzle hole
/ 2, when the distance h from the nozzle tip to the upper surface of the cutting and joining member, the angle θ between the laser optical axis and the gas injection hole central axis, the gas injection hole diameter d, and the distance x from the gas injection hole central axis, Each h, d, θ, D / 2 is controlled and set to the optimum value,
Generates an assist gas flow required for laser cutting, which is straight with respect to the laser optical axis.

FIG. 3 is a diagram showing a combined value of gas pressure distribution when gas is ejected from the laser cutting welding nozzle according to the present invention. The gas injection conditions are set so that the synthesis of gas pressure distributions from the six holes is small in the radial direction as shown by 8, and a pressure distribution having a maximum pressure value as high as possible is obtained. FIG. 4 is a view showing the tip shape of the lower portion of the laser cutting welding nozzle according to the present invention. Oxygen and nitrogen are used by switching at high speed so as not to generate an oxidized region in a portion to be pressed during laser cutting. At this time, a total of 12 gas ejection holes are provided so that two kinds of gas pressure distributions can be obtained independently and can be switched easily and instantaneously. In the figure, a _{1 to} a ₆ are oxygen ejection holes for O ₂ , and b _{1 to} b ₆ are nitrogen ejection holes for N ₂ .

FIG. 5 is a drawing showing a butted portion of a rolled material. W ₁ and W ₃ are laser welding areas and W ₂ is a pressure welding area, but argon or nitrogen N ₂ is blown as an assist gas at this portion so that the portion of W ₂ is not oxidized during laser cutting. When oxygen gas is used as the assist gas for all of W ₁ to W ₃ , laser cutting is performed at 10 m / min, and a scale having a scale film thickness of about 20 μm adheres to the cross section of the hot rolled material. As it is, W ₁ and W ₃ are respectively laser welded from the top surface of the rolled material to 180 mm from the material end (condition of cutting area on one side is 3% of the total sectional area of the rolling) and rolled by a finishing rolling machine at a rolling reduction of 40%. The non-welded part is not joined by pressure welding, and further there is a risk of fracture during rolling due to reduction by subsequent finish rolling.

Therefore, in the W ₁ part, oxygen is jetted from a _{1 to} a ₆ to cut it, in the W ₂ part oxygen is stopped and argon or nitrogen is jetted from b _{1 to} b ₆ to cut it, and in the W ₃ part, argon is again cut. or nitrogen cut by ejecting oxygen from a ₁ ~a ₆ stop, exit full cutting process. After that, W ₁ and W ₃ were laser welded from the top surface of the rolled material to 180 mm from the material edge (condition for cutting area ratio on one side is 3% of the total cross-sectional area of the rolling) and rolled by a finishing mill at a reduction rate of 40%. The joining strength of the joined portion by the pressure welding is 5 kgf / mm ² , and the joining cross-section ratio is 75% in total with the joined portion by the laser welding, which enables good rolling without breakage.

[0011]

【Example】

Example 1 A plate thickness after rolling a slab heated in a heating furnace by a rough rolling mill, a width of 1980 mm, a temperature of 1000 ° C.,
The trailing edge of the preceding rolled material running at 100 mpm and the leading edge of the trailing rolled material under the same conditions are cut with a pendulum shear to adjust the shape of the edge and butt the laser output 25k.
w, the laser beam is focused by a focusing mirror having a focal length of 500 mm, and the entire width is laser-cut by using two laser devices under the conditions of a cutting speed of 60 mm / sec and a welding speed of 30 mm / sec. Bonding was performed at 180 mm from each end (one-sided bonding cross-sectional area ratio was 3% of the total rolling cross-sectional area).
Then, rolling with a reduction ratio of 40% was carried out with a finishing rolling mill. When the result was investigated, the non-laser joining surface was pressure-welded by the rolling mill, and the joining cross-section reached 75% or more when combined with the laser joining portion. Continuous hot rolling was performed under the conditions using the subsequent finishing rolling mill to finish the product with a plate thickness of 6 mm, and good rolling was performed without breakage. The processing gas conditions at the time of cutting at this time are as follows.

When the processing gas was oxygen, the peak pressure of the gas pressure distribution 8 shown in FIG. 2 was 2 kgf / cm ² , and the pressure spread radius at which the pressure became ½ of the peak pressure was 3 mm. The cutting speed was 60 mm / sec, no dross was attached to the cut surface, the cutting roughness was 0.1 mm or less, and the excellent cutting with the difference between the upper kerf width and the lower kerf width within 10% could be performed. When the processing gas is nitrogen, the gas pressure distribution 8 shown in FIG.
Had a peak pressure of 2 kgf / cm ² and a pressure spread radius at which the pressure became ½ of the peak pressure was 3 mm. The cutting speed was 20 mm / sec, no dross was attached to the cut surface, the cutting roughness was 0.1 mm or less, and the excellent cutting with the difference between the upper kerf width and the lower kerf width within 10% could be performed. In the above embodiment, θ = 25 ° and d = 1.5 mm shown in FIG.
φ, D / 2 = 5 mm, oxygen supply condition is supply pressure 5
kgf / cm ² , oxygen flow rate 300 l / min, nitrogen supply conditions are as follows: supply pressure 5 kgf / cm ² , nitrogen flow rate 30
It was 0 l / min.

Example 2 Similar to Example 1, a slab heated in a heating furnace was rolled by a rough rolling mill to have a plate thickness of 40 mm and a width of 1550 m.
m, a temperature of 1050 ° C., a laser output of 25 kw for the trailing edge of the leading material and the trailing edge of the rolled material running at 50 mpm,
Focusing with a focusing mirror with a focal length of 500 mm, cutting speed 1
After laser cutting the entire width using two laser devices with cutting / welding conditions at a welding speed of 20 mm / sec and a welding speed of 60 mm / sec, 320 mm each from the material end from the top surface of the rolled material.
Bonding was carried out under the condition that the one-sided bonding cross-sectional area ratio was 8% of the total rolling cross-sectional area. The processing gas conditions at the time of cutting at this time are as follows.

When the processing gas was oxygen, the peak pressure of the gas pressure distribution 8 shown in FIG. 3 was 4 kgf / cm ² , and the pressure spread radius at which the pressure became ½ of the peak pressure was 4 mm. The cutting speed was 120 mm / sec, no dross adhered to the cut surface, the cutting roughness was 0.1 mm or less, and the excellent cutting with the difference between the upper kerf width and the lower kerf width within 10% could be performed. When the processing gas was nitrogen, the peak pressure of the gas pressure distribution 8 shown in FIG. 3 was 4 kgf / cm ² , and the pressure spread radius at which the pressure became ½ of the peak pressure was 4 mm. The cutting speed was 40 mm / sec, the cutting surface was free of dross, the cutting roughness was 0.1 mm or less, and the difference between the upper kerf width and the lower kerf width was within 10%, and good cutting could be performed. In the above embodiment, θ = 15 ° and d = 1.0 m shown in FIG.
mφ, D / 2 = 7 mm, oxygen supply condition is supply pressure 7 kgf / cm ² , oxygen flow rate 500 l / min, nitrogen supply condition is supply pressure 7 kgf / cm ² , nitrogen flow rate 5
It was 001 / min.

[0015]

As described above, when the gas switching laser cutting welding nozzle according to the present invention is used, the cutting speed is increased by first using oxygen gas, and argon gas or nitrogen gas is used in the press contact portion. The pressure welding is performed while preventing scale generation due to oxidation of the cut part.
As a result, there is an excellent effect that the productivity can be improved by the shortening of the process time and the crimping accuracy can be achieved.

[Brief description of drawings]

FIG. 1 is a view showing a laser cutting welding nozzle structure according to the present invention,

FIG. 2 is an explanatory diagram in which gas injection conditions of nozzles are determined,

FIG. 3 is a diagram showing a composite value of gas pressure distribution when gas is ejected from a laser cutting welding nozzle according to the present invention,

FIG. 4 is a view showing a tip shape of a lower portion of a laser cutting welding nozzle according to the present invention,

FIG. 5 is a drawing showing a butted portion of a rolled material.

[Explanation of symbols]

1 Adapter 2 Gas suction port 3 Nozzle upper part 4 Nozzle lower part 5, 6 Space 7, 7'Nozzle hole 8 Gas pressure distribution D / 2 Distance h from laser optical axis to nozzle hole center h, from nozzle tip to cutting member upper surface Distance θ Angle formed by gas optical axis and gas ejection hole center axis d Gas ejection hole diameter x Distance from gas ejection hole central axis a _{1 to} a ₆ Oxygen ejection holes b _{1 to} b ₆ Nitrogen ejection holes W ₁ and W ₃ Laser welding area W ₂ pressure welding area

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B23K 26/14 Z

Claims (1)

[Claims] 1. The finishing entry side of the rolling mill of the hot rolling mill,
After laser cutting the trailing end of the preceding rolled material and the trailing end of the following rolled material, shaping the shape of the tip to increase the contact area of the butted part and butt welding both ends with laser, In a laser cutting method of continuously rolling a rolled material joined by a roll pressure welding roll, when cutting is performed using a laser beam for forming a trailing end portion of the preceding material and a leading end portion of the following material, an assist gas is used. The feature is that the part to be laser-welded is laser-cut with oxygen, and the roll-pressure-bonded part is laser-cut with argon or nitrogen to suppress the generation of an oxide film on the cut surface and roll-weld while being switched instantaneously on the way. Laser cutting method in continuous hot rolling.