JPS6096382A - Welding method of ultra thin steel sheet by laser - Google Patents

Abstract

PURPOSE:To perform stable welding with high energy efficiency by controlling the surface condition of steel sheets as well as the wavelength, energy density and welding speed of a laser. CONSTITUTION:The ratio in absorptivity between the time when steel sheets are not melted and the time when the sheets are melted is decreased by using a YAG laser. The surface condition of the steel sheets such as roughness, temp., film, etc. as well as the wavelength, beam diameter, energy density such as output of the laser and welding speed are controlled. The surface of the steel sheet is controlled to the energy absorption state in which substantial penetration melting is attained when the steel sheets are not melted and to such condition in which the melting width is made >=2-fold the thickness of the steel sheets without melt-down (hamping) when the steel sheets are melted.

Description

[Detailed description of the invention] [Industrial application field] The present invention is suitable for butt welding of ultra-thin steel plates. Relating to a laser welding method.

[Prior art]

FIG. 1 schematically shows laser welding of steel plates in abutted state, as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-32154. That is, the end surfaces CL and CR of the steel plates ML and MR to be welded are brought together and the laser beam LB is irradiated to the center between the end surfaces. When the end faces are smooth and in close contact, the focused laser beam LB is distributed over both the abutting end faces c, , CR, and both end faces are welded.

However, as shown in Fig. 2, the end face is uneven or
There is a gap g between the end faces due to bending of the end faces caused by cutting.
If a laser beam LB or LB' focused in this abutting state is irradiated, the laser beam will pass between the end faces, or it will be irradiated only on one end face, and both end faces or which one end face will be irradiated. It will not melt and the weld will be incomplete.

In order to solve these problems, conventional methods have been to improve the precision of end face machining and reduce the distance between the two end faces, but as the thickness of the steel plate becomes thinner, The longer the length, the higher the accuracy required for end face processing, which inevitably limits the required distance, making it impossible to obtain the necessary spacing for welding, and making the process extremely time-consuming. 1 It was a hassle.

[Purpose of the invention]

It is an object of the present invention to solve these problems of the prior art and to make it possible to reliably perform laser welding even when there is a gap between the abutting portions of ultra-thin steel plates.

[Structure 9 of the Invention] In order to achieve the above object, in the present invention, for example, in welding ultra-thin steel plates of 0.5 mm or less, the ratio of the energy absorption rate of the laser beam when the steel plate surface is not melted and when it is melted is determined. It is an energy-absorbing state that reduces the melting point and achieves sufficient penetration melting when not melting, and also reduces melting when melting (
Humping) is within the range of energy absorption that does not occur, and the melting width is at least twice the thickness of the steel plate.
Table 3 of Steel Plate - This relates to a method for welding ultra-thin steel plates using a laser, which is characterized by controlling the surface condition, wavelength, energy density, and welding speed of the laser beam.

The present invention will be explained in detail below with reference to the drawings.

Figure 3 shows steel plates M and L with their ends butted together for welding.

This shows a case where there is an interval between MRs.

At this time, the thickness of the steel plates ML and MR is tmm, and the interval is gmm.
In this case, the beam diameter S is set to several times the distance g so that the laser beam LB covers the distance g, and the laser beams ① and B are irradiated. In this way, the laser beam L8 hits the end faces CLI CR of both steel plates M L and M R.
Welding is performed by heating and melting the ends of the However, in this case, as mentioned above, if the diameter of the laser beam is greater than or equal to the distance g between the steel plates, and the energy density is low, most of the laser beam irradiated onto the steel plate surface will be reflected, and the laser beam will be absorbed into the steel plate. The amount absorbed becomes small, making it impossible to obtain good heating and melting phenomena.

Therefore, in the present invention, the absorption characteristics of the laser beam on the surface of the steel sheet are changed respectively when the steel sheet is not melted and when it is melted, and the output energy of the laser is
By controlling the beam diameter, welding speed, etc., it was possible to prevent the phenomenon of under-melting or dripping due to over-melting during welding, making stable welding possible.

4 and 5 are explanatory diagrams showing the absorption rate d of the laser beam L8 on the steel plate surface Ms. The absorption rate d is expressed by the input energy Eo and the absorbed energy E1 as follows.

d=E1/Eo...(1) Also, the energy E2 of the reflected laser beam is E2
=Eo-El (2) It is expressed as follows.

On the other hand, the change in the absorption rate of the laser beam when the steel sheet surface is in a non-melting state (FIG. 5a) and when it is melting (FIG. 5b) is as follows.

When not melted: Absorption rate is dc, amount of absorbed energy Ec1
=Eo It is something to do.

In this case, the absorption rate d is the roughness and temperature of the steel plate surface.

Although it can be changed depending on the coating, the wavelength of the laser beam, etc., the improvement of the absorption rate depending on the wavelength of the laser beam will be explained here.

Representative industrial lasers that are commonly used include C02 laser and YAG laser. The wavelength of the CO2 laser is 10.6 μm, and the wavelength of the YAG laser is 1.06 μm.

Further, the absorption coefficient d of each wavelength λ on the surface of the cold-rolled steel sheet and the electromagnetic steel sheet is as shown in FIG. So, to explain the case of electromagnetic steel sheet, the absorption rate dc of Co2 laser is
o2 is less than 0.08, but the absorption rate c of YAG laser
(y a g is 0.4 or more. In other words, if a certain amount of energy is to be absorbed by the surface of the steel sheet when it is not melted, the Co2 laser requires an output power that is five times or more that of the YAG laser.

6- However, when the surface of the steel plate becomes molten, the absorption rate becomes 0.9 or more in all cases. Therefore, the ratio of the absorption rate when not melted and when it is melted is Ry>2.5 in the case of YAG laser. In the case of C○2 laser, RCO2>11.

Therefore, in the present invention, by using a YAG laser, the ratio of absorption rate when the steel plate is not melted and when it is melted is reduced.

Furthermore, by controlling the steel plate surface conditions such as roughness, temperature, and film, and the energy density and welding speed such as laser wavelength, beam diameter, and output, we can create an energy absorption state that allows sufficient penetration melting when the steel plate surface is not melted. Also, during melting, the melt should not drip (humping), and the melt width should be at least twice the thickness of the steel plate.

FIG. 7 is an explanatory diagram showing the shape of the fusion zone.

Assuming that the thickness of the steel plate is t, the melting width is W, and the melting speed is V,
The minimum energy (c(P)+) required for penetrating melting is (dP)M=t°W°v°ρ° (ΔT1'CP1+λ
)10.24・71...(3) 7- ρ: Heavy density T, :T, -T.

CPI: Specific heat λ: latent heat η: Energy use efficiency It is.

Among these, the energy utilization efficiency η is determined by factors other than the absorption rate of the laser beam, and is largely due to thermal diffusion of the steel plate, and its value is generally 0.3 to 0.8.

In addition, the energy (cf
P)H is (cfP) +=t °w−v 1p 0(ΔT+1C
pl+λ+ΔT H-CR2) 10.24・η・・・・
・(4) becomes.

Also, the temperature TH at which humping occurs is TH=TM+Δ
TH... (5), irradiation energy (cfP)
+, determined by welding speed V, fusion width W, etc.

Therefore, the second feature of the present invention is to control the energy input by the laser to an optimal condition based on the above conditions. Figure 8 shows the region of melting phenomenon depending on the input energy amount, but when the input energy is less than (c(P)M), the non-melting region (T)
Therefore, the surface temperature also becomes below TMM. Furthermore, when the input energy is between (c(P) If it exceeds +, it becomes a humping region (III).

Therefore, in the present invention, the absorption ratio (
Ry > 2.5), or by adding, for example, the roughness of the steel plate, the effect of the absorption film, etc., the absorption rate ratio is reduced, and furthermore, the distance g between the butt parts of the steel plates, the laser output P, the beam diameter a,
Each condition, such as the welding speed V, is controlled so that the input energy is always maintained in region (II) in FIG.

FIG. 9 and FIG. 10 show the humping phenomenon caused by the melt falling due to the large absorption rate ratio between the non-melting state and the melting state. FIG. 9 shows the state of humping from the side along the weld line 9-, and FIG. 10 shows the state of humping from the top. The period from the time of non-melting to the time when melting starts until melting starts to drop is defined as np, and the melting melting range is indicated by hp. The lengths and proportions of np and hp are determined by the laser power p, beam diameter a, and welding speed V. Focus the laser beam to achieve an energy density of 3 to 5
When K11/mm2 or more, plasma is generated and the generation area becomes np, resulting in a similar humping phenomenon.

FIG. 11 shows the top surface of a stable weld bead in which the absorption rate ratio is reduced, the gap g is taken into consideration, and the fusion width is set to W.

Further, in the present invention, as shown in FIG. 12, a gap sensor 1 is provided to measure the distance g between the abutting portions of the steel plates M L and M R, and the control mechanism 2 is controlled based on the result to determine the laser beam diameter a, Laser output Px, welding speed vx
It is possible to determine the value of and perform stable automatically controlled laser welding.

〔Example〕

Next, examples of the present invention will be shown.

10- An electromagnetic steel plate with a thickness of 0.2 mm was used as the material to be welded, and welding was performed using a YAG laser with an output of 600 W.

The results are shown in FIG. As is clear from this figure, at a welding speed of 4 to] Om/min, the melting width is 1.4 to
Welding of 0.7 mm was possible. Normally, the distance g between the steel plates is about 173 times the melting width, so in this case, the distance between the steel plates can be set to about 0.5 mm, and therefore the machining accuracy of the butt end faces can be relaxed. As a comparative example, when welding was performed using a CO2 laser with an output of 450 W, the fusion width was 0.35-0.3 mm at a welding speed of 4-6 m/min.

Therefore, in this case, complete welding cannot be achieved unless the distance between the steel plates is 0.1 mm or less.

[Effects of the Invention] As explained above, the present invention reduces the absorption ratio between the non-melting state and the melting state, and controls the surface condition of the steel plate, the laser wavelength, energy density, and welding speed, thereby achieving stable and stable welding. Since it is possible to perform welding with high energy efficiency and to perform welding with the necessary bead width, the precision required for processing the butt end faces can be relaxed, and therefore the steel plate cutting equipment, steel plate holding mechanism, etc. required for laser welding can be reduced. Both belt facilities can be simplified and costs can be reduced. In addition, the laser beam tracing control becomes easy, so automation is easy, and the effects are extremely large.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are explanatory diagrams showing the butt spacing of steel plates and laser beam absorption rate in laser welding, which is conventionally commonly performed. FIG. 6 is an explanatory diagram showing the relationship between laser wavelength and absorption rate. Figure 7 is an explanatory diagram showing the relationship between the amount of melting and the amount of input energy, Figure 8 is a graph showing the relationship between the amount of input energy and the melting phenomenon area, Figures 9 and 10
The figure is a side view and a top view showing the humping phenomenon.
The figure is an explanatory diagram showing the upper surface bead in the stable welding area obtained by the present invention, Fig. 12 is an explanatory diagram showing the case where the method of the present invention is automated, and Fig. 13 is a diagram showing an example of the embodiment of the present invention. It is. M L, M R: Steel plate cL, cFl: Butt part L
B: Laser beam g: Interval 1: Gap sensor 2: Control mechanism Patent applicant Nippon Steel Corporation 13- 1 Figure East 3 Prisoner 2 Figure B East 4 Figure 5a Figure 5b Figure 6 Figure 6 Input (μm) - East Figure 7 Figure 9 East Figure 10 ↑ Iwago 11 review Melting width Figure 12 Figure 13 Fukinama & (m/m1n) - Procedural amendment (method) February 1982 61st (, Tome Patent Office Commissioner Wakasugi Wainu 1, Incident Indication 1981 Patent Application No. 201793 2
, Title of the invention: Laser welding method for ultra-thin steel plates 3, Relationship with the amended case Patent applicant address: 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (6
65) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent 103 Phone: 03-864-6052
Address: 2-27-6-5 Higashi Nihonbashi, Chuo-ku, Tokyo; date of amendment order: January 11, 1980 (shipment date: January 31 of the same year) 6;
Subject of amendment Contents of amendment in the Detailed Description of the Invention column and Brief Description of the Drawings column 7 of the specification (1) In the 7th line of page 5 of the specification, "and Figure 5" has been replaced with "Figure 5a". and Figure 5b”. (2) "Explanatory drawings," on page 12, line 10 of the specification should be corrected to the following sentence. "Explanatory diagrams, Figures 4, 5a, and 5b are explanatory diagrams showing the absorption and reflection of a laser beam on the surface of a steel plate, as well as the absorption rate."

Claims (1)

[Claims] (]) In welding ultra-thin steel plates, the ratio of the laser beam energy absorption rate when the steel plate surface is not melted and when it is melted is made small, and the energy required to obtain sufficient penetration melting when the steel plate surface is not melted. The surface condition of the steel sheet, the wavelength of the laser beam, the energy density, and the welding must be adjusted so that the melt will be in an energy absorption state without dripping during melting, and the melt width will be at least twice the thickness of the steel sheet. A method for welding ultra-thin steel plates using a laser, which is characterized by speed control. (2) A method for welding ultra-thin steel plates using a laser according to claim (1), characterized in that the distance between the end faces of the steel plates abutted against each other is measured in advance and the diameter of the laser beam is set. .