JP2006218497A - Laser welding method for plate material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for laser beam butt welding of metallic sheets having different thicknesses, which method can eliminate recessed portions formed on the bottom surface of a welding bead, and does not cause the loss of welding energy even if some clearances exist in butted portions, and can weld tailored blank materials having excellent formability with small electric energy consumption and high productivity. <P>SOLUTION: In the method for laser beam welding, two sheets having different thicknesses are butted in the state that one side surfaces of them are shifted from each other, and are welded by moving a laser beam relative to the sheet material while radiating the laser beam to the shifted surface side of the one side surfaces along the butted line. In the welding method, the whole of the laser beam are radiated on the thick sheet side, and the welding speed is varied during the welding operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser welding method in which two plate materials having different plate thicknesses are butted and welded by irradiating a laser beam along the butting line to form a good weld bead.

  In recent years, it has been applied to technology for forming metal plates with different thicknesses in advance by joining them together by laser welding and forming the metal plates into a desired shape by secondary processing by composition processing such as press molding. If metal plates with different thicknesses (different thickness) are being joined together and press-molded as a single metal plate (blank), partial reinforcement and weight reduction of the parts can be promoted. .

  As a method of laser butt welding of metal plates having different thicknesses, as shown in the overall view of laser butt welding of the plate material in FIG. 1, a thick metal plate 2 and a thin metal plate 3 are butted, and laser is applied from the laser torch 4 to the butt position. Welding is performed to form a weld bead 6 by irradiating a beam 5, and in order to accurately irradiate a laser beam to the butt position, the butt position before welding is detected and the amount of deviation between the weld position and the butt position is calculated. However, there is a laser welding apparatus that moves the welding head in a direction to eliminate the deviation (see, for example, Patent Document 1).

  However, when metal plates having different thicknesses are butt-welded by irradiating a laser beam, irradiation with the laser beam 1 is performed as shown in the welding cross-sectional view in the case of irradiating the butt position in FIG. When the irradiation is performed with the position being matched with the butted portion 7 of the thick metal plate 2 and the thin metal plate 3, as shown in the welding result of FIG. 1B, the weld bead 6 of the welded metal plates 2 and 3 is used. The melting amount of the metal plate on the thick plate side is smaller than the melting amount of the metal plate 3 on the thin plate side. For this reason, the sharp level | step difference 8 will be formed in the metal plate by the side of a thick plate in a welding part. When a sharp step is formed in the welded portion, the weld joint strength is lowered, and galling with the press die occurs during press molding, resulting in a problem that the formability is deteriorated.

  In order to solve such problems, the laser beam condenser lens is tilted by a predetermined amount with respect to the optical axis, and the energy density of the laser beam irradiated to the metal plate having a large thickness is changed to the metal plate having a small thickness. A butt laser welding method has been proposed in which the energy density of the laser beam is larger than the energy density of the laser beam irradiated to both metal plates so that both metal plates can be melted equally ( For example, see Patent Document 2).

  However, when this welding method is applied to butt welding of thin steel plates used in automobile bodies, etc., it is difficult to control the energy density distribution of the laser beam irradiated to the thick plate side and the thin plate side, so both metal plates The problem arises that they cannot be melted equally.

  In order to solve this problem, as a laser welding method for different thickness materials in which metal plates having different thicknesses are butted and a butted portion of the metal plate is irradiated with a laser beam to perform butt welding, the irradiation position of the laser beam is set to metal. There has been proposed a laser welding method for different plate thickness materials, characterized in that the plate is moved from the butted portion toward the thick plate according to the difference in plate thickness (see, for example, Patent Document 3).

  However, the conventional laser welding methods for metal plates having different plate thicknesses that have been proposed have not solved the problem caused by the gaps between the plate end surfaces of the butt portion. That is, the metal plate used for welding is generally cut out by a shearing process, but the cut plate has a slightly curved end surface. In such a butt welding of the plate, as shown in FIG. In addition, it is inevitable that a gap 9 between the end surfaces of the plates is generated at the butted portion before welding.

  When the butt gap exists, a recess 10 is formed on the lower surface of the weld bead 6, the joint strength is lowered, and a problem of mold galling occurs during press molding. That is, the weld bead is formed by the molten material being cooled and solidified, but if there is a gap at the butt, there is not enough molten material to fill the gap, and unless another material is supplied to fill the gap. The bottom surface of the weld bead is recessed. Furthermore, there is a problem that the laser beam penetrates in a portion where the gap is wide, and the energy efficiency of welding deteriorates due to the penetrated beam 11.

  Further, in the production of a welded metal plate such as a tailored blank by butt laser welding, a reduction in production cost is required. For this reason, high-speed welding is intended. However, under a high-speed welding condition at a certain speed or higher, a welding heat source by a laser is relatively insufficient, so that a sufficient bead is not formed, resulting in an incomplete welding state.

  Therefore, there is a problem that a high-power laser is required at high-speed welding, and the power cost increases. On the other hand, when a low-power laser is used in order to save power, there is a problem that productivity cannot be increased and cost cannot be reduced. For example, the oscillation efficiency of a carbon dioxide laser is 10% of the input power, and the remaining 90% of the energy is dissipated to the atmosphere through a heat exchanger. Therefore, a 6 kW laser transmitter for a general tailored blank device is about It consumes a huge amount of power of 140 kW.

Japanese Patent Laid-Open No. 11-33760 JP-A-7-195187 JP-A-5-57467

  When two metal plates with different plate thicknesses are butted so that one surface is the same, and a laser beam is irradiated from the side where the surface has shifted, the sharp step on the upper surface of the weld bead can be solved with existing technology. However, the technique of eliminating the dent formed on the lower surface of the bead, which causes stress concentration during press molding and causes cracking, is an unsolved problem.

  In addition, even if a laser beam is irradiated on the butted part where there is a gap, the energy penetrates the gap and is wasted, so the energy efficiency of the welding deteriorates, and therefore higher laser energy is required. there were. Furthermore, it is required to reduce the manufacturing cost.

  Therefore, the present invention eliminates the dent formed on the lower surface of the weld bead when the metal plates with different plate thicknesses are butted and laser-welded, and does not cause a welding energy loss even if there is a gap in the butted portion, And it aims at providing the laser butt-welding method which can weld the tailored blank material with low power consumption, high productivity, and good shaping | molding.

  The present inventor has eagerly studied to solve the above problem, and as a result, when two metal plates having different thicknesses are laser butt welded, all the laser beams are irradiated only on the thick metal plate, And it discovered that the said problem could be solved by changing welding speed.

  The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

  (1) The surfaces of two plates having different plate thicknesses are butted against each other, and the laser beam is irradiated while irradiating the laser beam on the side where the surfaces of the other sides are displaced from each other along the abutting line. In the laser welding method of welding by moving the plate and the plate relative to each other, all the laser light is irradiated to the plate on the thick side, and the welding speed is changed during welding.

  (2) The laser irradiation position is controlled by the apparatus for detecting the butt line by image processing and the means for controlling the laser irradiation position so as to realize a preset shift amount (1) The laser welding method described in 1.

  (3) The laser welding method according to claim 1 or 2, wherein the welding speed at the welding start / end portion is lowered.

  According to the present invention, in laser butt welding of metal plates having different plate thicknesses, a smooth weld bead shape without a sharp step in the weld bead portion or a dent on the back surface of the bead is obtained with low power consumption and high productivity. As a result, it is possible to obtain a weld metal plate (blank) having good formability, which is free from a decrease in strength of the joint portion as in the prior art and galling of the mold during press molding.

  Hereinafter, the present invention will be described in detail.

  FIG. 3 is a diagram showing an example of the present invention in which only a thick metal plate is irradiated with a laser beam when metal plates having different thicknesses are butted and laser butt-welded.

  When the plate material is irradiated with a laser beam, a weld bead is formed by melting by receiving heat conduction from not only the irradiated portion but also the irradiated portion of the surrounding material.

  In general, the width of the weld bead is two to three times the width at the laser beam irradiation position.

  As shown in FIG. 3, two metal plates with different plate thicknesses are butted so that one side (the side that becomes the back side during welding) is the same, and the surface is shifted to the higher side. If the metal plate 2 with the larger thickness is irradiated with the laser beam 1 and the irradiation position is within the range where the edge portion is also melted, the thicker melted material is thinner due to gravity and surface tension. The metal plate 3 can be cross-linked and welded. At this time, since the stepped portion of the butt surface is also melted, the formed weld bead has a very smooth surface and is in a 12 state without sharp steps.

  Further, even when there is a gap in the abutting portion, there is no beam irradiated to that portion, so it is possible to put 100% laser beam energy into the metal plate to be welded.

  For this reason, the bead surface is formed in a smooth linear shape from the surface of the thick metal plate 2 to the surface of the thin metal plate 3 within the range of the width of the weld bead 6. In other words, the sharp stepped portion of the butted portion melts and becomes a smooth straight line, and the molten metal that has flowed out fills the gap in the butted portion. In this case, by injecting the welding beam irradiation into the thicker material, the bead surface has a more gentle inclination, and a material that fills many voids is provided. It becomes. Although the focal point of the laser beam varies depending on the output of the laser beam, it usually has a condensing diameter of about 0.2 to 0.3 mm in diameter, so the laser beam is irradiated only to the thicker metal plate. The center position of the focal point of laser beam irradiation needs to be a position at a distance of 0.1 mm or more from the abutting position (edge) of the thick metal plate.

  Also, if the beam irradiation position is too far from the butting position on the thick plate, the end face will eventually not melt and welding will not be possible. For this reason, it is preferable to be within 0.4 mm from the butting position.

  In addition, if the difference in plate thickness between the butt metal plates is too large, it becomes difficult to form a smooth linear weld bead surface. Therefore, the plate thickness difference is preferably 4 mm or less. More preferably, it is 2 mm or less.

  If the plate thickness of the metal plate to be welded is increased, the amount of molten metal during welding increases even if the plate thickness difference is increased, so a smooth direct weld bead surface should be formed even if the plate thickness difference is large. In addition, it is possible to obtain a weld bead having no dent on the back surface of the weld bead. However, as a metal plate applied to laser butt welding, a thin steel plate of about 0.6 to 6 mm is practically used.

  The laser welding speed depends on the laser output, but if the welding speed is high, the surface bead width becomes wide and the surface bead becomes small, so 5-8 m / min is preferable.

  By selecting the laser welding speed, good weld joint strength can be obtained, and when a weld metal plate (blank material) is press-molded into a product, cracks do not occur and the press mold has good strength. Goods can be obtained.

  In order to maintain a constant distance from the end face of the beam irradiation position and obtain a good quality bead, the butt position is detected by the optical cutting method upstream of the welding line, and the laser head is moved to a preset shift value accordingly. Control with offset.

  FIG. 4 is a diagram showing an example of a method for controlling the laser irradiation position in the present invention.

  In order to control the laser irradiation position, as shown in FIG. 4, first, a butt line is detected by a cap position detection device 14 that detects a butt line (gap position) to be welded by image processing. Next, a laser beam is irradiated from the laser head 15 that moves along the weld line. The irradiation position is shifted by a preset shift amount toward the thick metal plate 2 by operating the laser head driving device 16.

  That is, the detected butt line position and a preset shift amount are input to the arithmetic device, the laser head driving device is operated by the output from the arithmetic device, the laser head is shifted by a predetermined amount, and the laser irradiation position is controlled. is there.

  Moreover, in order to reduce the manufacturing cost of a welded metal plate (tailored blank), it is necessary to increase the welding speed to improve productivity and to perform welding with the lowest possible laser power consumption.

  Since welded metal plates such as tailored blanks are subjected to press forming after welding, formability is required. In particular, in the vicinity of the welded portion, strain concentrates on the low-strength material with a small plate thickness, so that it easily breaks, and this portion often becomes a formability neck.

  That is, cracks are likely to occur from the welding start / end portion during press working. This is because the plastic working strain limit is small at the welding start / end portion because the strain becomes short-axis tensile during press working.

  On the other hand, when observed along the weld bead portion, in some cases, workability is not required as much as the welding start / end portion, and there are places where it is better to adopt a manufacturing method that emphasizes economics. In other words, in the weld line, an attempt is made to balance the formability and the economy by optimally controlling the welding parameters by dividing the area into which the formability is important and the area where the economy is important.

  However, since the relationship between welding parameters and formability is not clear, the relationship between welding speed and formability was first investigated. Mild steel sheets having thicknesses of 1.4 mm and 0.7 mm were butt welded using a 6 kW carbon dioxide laser. The target position of the beam was set within a range of ± 0.15 mm from the butt line. Formability was determined by the Eriksen test. FIG. 6 shows the welding speed and formability results. From this result, it was found that formability was improved by lowering the welding speed. That is, among the weld lines, in the formability priority area, the welding speed is lowered to ensure the formability while sacrificing the economy, while in the economical priority area where high formability is unnecessary, the welding speed is increased and welding is performed. By doing so, both moldability and economy can be achieved. The mechanism by which the formability improves when the welding speed is lowered is thought to be because the cross-sectional area of the weld bead is increased by lowering the welding speed. Since the weld bead is hardened by welding heat, its hardness is significantly higher than that of the base metal, making it difficult to deform. If this part is large, deformation of the low-strength side material near the weld is constrained. It is considered that the degree is increased, and as a result, breakage of the low-strength side material is difficult to place and the moldability is improved.

  Therefore, in the present invention, the welding speed is changed during welding, and as shown in FIG. 7, in the formability priority region of the welding start / end portion, the welding speed is lowered to ensure the formability, and the high-formability unnecessary economical priority is given. In the area, the welding speed was increased to achieve both formability and economy.

  The welding speed is preferably changed to 85% or less of the welding speed in the economic priority area, with the range of 70 mm or less of the welding start / end portion having an influence on the moldability as the moldability priority area.

  As described above, according to the present invention, the butt level difference is eliminated, and the dent on the back surface of the weld bead is eliminated, thereby preventing mold galling during press molding and reducing the stress concentration on the weld bead. A press-molded product can be obtained.

  Hereinafter, the present invention will be described in detail based on examples.

  In the examples of the present invention, butt joining of steel plates was performed using a carbon dioxide laser. The carbon dioxide laser torch uses two sets of reflecting mirrors, one of which condenses the laser beam with a concave mirror. This laser torch can be rotated by a servo motor to change the laser irradiation position. There is a butt edge detection device on the upstream side of the welding of this laser torch. This device irradiates the slit laser beam to the butt portion, and can automatically detect the butt position by processing the image taken by the camera. . Based on the detected edge position, the laser torch is driven and controlled from time to time so that the beam irradiation position is always applied to the thicker plate.

  In the examples, a carbon dioxide laser with a processing point output of 6 kW was used. At this time, the beam condensing diameter was 0.25 mm. Plate thicknesses of 1.4 mm and 0.7 mm were combined.

  At this time, welding was performed under the condition that the beam aiming position was moved from the butt line position to the thick plate side, and the experiment was performed with various beam shift amounts to the thick plate side.

  Also, the welding speed was 8 m / min at the welding start / end portion 50 mm, and the welding speed was 10 m / min for the other portions, and a welding experiment with a welding length of 1 m was performed.

  In this case, the welding time per sheet was 7.5 seconds, and the energy consumption during welding was 450 kJ.

  The welding results were as shown in Table 1.

  ○ mark shows a case where a smooth bead is formed without a sharp step, X mark shows a case where the weld bead is not sufficiently melted and a sharp step occurs, and Δ mark shows a part of the sharp step. Is the case. The result of the welding test is shown in FIG. 5 (ad in FIG. 5 corresponds to ad in Table 1).

  From the above results, the beam irradiation shift amount is 0.15 mm, which is the best from the viewpoints of both the smoothness of the step and the shape of the back bead, and considering the beam diameter, the laser beam irradiates the thick plate side. I understand. In addition, the energy consumption was reduced by approximately 18% by changing the welding speed.

  When a plate produced by such a method was press-molded, a good press product could be obtained without galling into the mold and without breaking the plate.

It is a figure which shows the whole laser butt welding of a board | plate material. It is sectional drawing of a laser butt welding part, (a) is a figure before welding, (b) is a figure which shows after welding. It is a figure which shows the example of this invention which irradiates a laser beam only to a thick metal plate, when a metal plate of different board thickness is butt-welded and laser butt welding is carried out. It is a figure for demonstrating control of a laser irradiation position. It is a drawing margin micrograph which shows the weld bead state of the metal plate welding part in the Example of this invention. It is a figure which shows the relationship between a welding speed and an Erichsen value. It is a figure which shows the moldability priority area | region and economical priority area | region of a weld metal plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser beam 2 Thick metal plate 3 Thin metal plate 4 Laser torch 5 Beam irradiation 6 Weld bead 7 Butting part 8 Sharp step 9 Gap 10 Depression 11 Extruded beam 12 No sharp step 13 Indentation 14 Cap position detection device 15 Laser head

Claims (3)

  The two surfaces of the two plate members having different thicknesses are butted with one surface being shifted from each other, and the laser beam and the plate material are irradiated while irradiating the laser beam on the side where the one surface is displaced from each other along the line of matching. In a laser welding method for welding by moving relatively, a laser welding method characterized by irradiating all the laser beams on a thick plate and changing a welding speed during welding.   The laser irradiation position according to claim 1, wherein the laser irradiation position is controlled by a device for detecting a butt line by image processing and a means for controlling the laser irradiation position so as to realize a preset shift amount. Welding method.   3. The laser welding method according to claim 1, wherein the welding speed at the welding start / end portion is slowed down.

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