JP2011240365A - Laser welding device and laser welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high quality welding, which prevents metal vapor from adhering to a laser beam-transmitting window, ensures the adequate weld penetration depth and suppresses occurrence of porosities, effectively for a long period of time.SOLUTION: A laser welding device is for welding by means of a laser beam in a low vacuum atmosphere, and includes: a shielding gas cylinder that is disposed along the optical axis of the laser beam at a prescribed interval from the welding site, and has a transmitting window installed on the top, while the bottom is opened in an atmosphere controlled region; and a shielding gas supply means for introducing shielding gas to the interior of the shielding cylinder from the transmitting window side of the shielding gas cylinder. Also provided is a laser welding method that employs the laser welding device.

Description

  The present invention relates to a laser welding apparatus and a laser welding method, and more particularly, to a laser welding apparatus capable of stably performing high-quality welding by suppressing adhesion of metal vapor to a laser light transmission window, and The present invention relates to a laser welding method.

  Laser welding is a welding method in which laser light, which is a heat source, is mainly focused on a metal and irradiated to locally melt and solidify the metal. Compared to conventional welding methods, laser welding is a heat source. The high energy density of this material enables high-speed deep penetration welding, and has features such as less adverse effects and deformation due to heat input to the weld metal (material to be welded).

  For this reason, it is widely adopted in the key industries such as the automobile industry and the electronics industry. In particular, the number of processes that can only be performed by laser welding, such as batteries for hybrid vehicles, has increased in recent years, and the importance of the technology has been increasing. I am doing.

  However, such laser welding equipment requires capital investment of about 10 million yen per 1 kW of output, and the demand for welding quality for welding of several tens of thousands to hundreds of millions of places per year has become increasingly severe in recent years. .

  Such laser welding has been conventionally performed in an atmospheric pressure atmosphere, and a technique capable of ensuring a sufficient penetration depth by performing laser welding at a low speed has been developed. A penetration depth of about 15 mm can be obtained at an output of 6 kW and a welding speed of about 0.1 m / min (1.7 mm / s).

  However, since this technique is welding performed in an atmospheric pressure atmosphere, in the above-described low-speed welding, porosity (porosity or voids in the weld metal) that is a weld defect occurs in the deep penetration weld. There was a problem of reducing the welding quality.

  For this reason, a technique has been developed in which the atmosphere is changed from an atmospheric pressure atmosphere to a low pressure atmosphere, and welding is performed using a low-power laser (Non-Patent Documents 1 to 4). It is now possible to obtain welds that suppress the occurrence of cracks.

  However, in the case of welding in a low-pressure atmosphere, the metal vapor (plume) generated by the laser light irradiation is ejected at a very high speed of 100 m / s (360 km / h), so that the metal vapor enters the laser light transmission window. It was difficult to prevent the adhesion to reach the maximum.

  The metal vapor that flies from the welding spot and adheres to the transmission window blocks the laser beam and makes the welding unstable, making it difficult to perform welding with a stable and sufficient penetration depth, This causes variations in welding quality. When the metal vapor further adheres, the transmission window is damaged or welding itself becomes impossible.

  For this reason, according to laser welding in a low-pressure atmosphere, while it is theoretically known that it is possible to perform welding with ensuring a sufficient penetration depth and suppressing the generation of porosity, Was not reached.

  Under such circumstances, in some fields, techniques for dealing with the above problems have been studied (Non-Patent Documents 2 and 3).

Ishide et al., “Fundamental study on high-power CO2 laser welding technology”. Mitsubishi Heavy Industries Technical Report Vol. 32 No. 2 (published March 1995), pages 109-112. Yoshikazu Suita and 7 other authors "Space LD Welding Experiments with ISS Orbital Pressure". 10th and 11th pages of the 72nd Annual Meeting of the Japan Welding Society (2003-4). Kenji Tanaka, Mineo Suzuki and 6 other authors "Technology to control deposition on optical components in space laser welding". 100-103 pages of Space Utiz Res, 22 (2006), issued by ISAS / JAXA. Yohei Abe et al., “High Power Fiber Laser Weldability in Low Vacuum”, National Conference of the Japan Welding Society, 85th (2009-9), pages 142, 143.

  However, in the case of the corresponding technologies so far, it cannot be said that metal vapor is sufficiently suppressed from adhering to the laser light transmission window, and it is difficult to apply to high-power laser welding. Development of a practical technique, a low-cost and practical technique, and a technique applicable to high-power laser welding have been desired.

  As a result of intensive studies, the inventor has found that the above problems can be solved by the inventions shown in the following claims, and has completed the present invention. Hereinafter, each claim will be described.

The invention described in claim 1
A laser welding apparatus that performs welding with laser light in a low vacuum atmosphere,
A shield gas cylinder that is disposed along the optical axis of the laser beam at a predetermined interval from the weld, a transmission window is provided at the upper end, and the lower end is opened in the atmosphere control area;
A laser welding apparatus comprising: a shield gas supply means for introducing a shield gas into the shield gas cylinder from the transmission window side of the shield gas cylinder.

  In the present invention, a shield gas cylinder is provided between the transmission window and the welded portion, a shield gas is flowed from the transmission window side toward the welded portion, and an air shield is provided between the transmission window and the welded portion. It is comprised so that it may be formed.

  In this way, since an air shield is formed between the transmission window and the welded part, the flying of the metal vapor ejected toward the transmission window at a very high speed under a low vacuum is blocked, and Adhesion can be prevented, welding with a sufficient depth of penetration in a low vacuum atmosphere can be performed for a long time, and high-quality welding with reduced porosity is efficiently provided. Can do.

  In particular, in the present invention, a cylindrical body (shield gas cylinder) that is difficult for metal vapor to enter is adopted as the structure of the apparatus for forming the air shield, and further, between the shield gas cylinder and the welded portion. In addition, metal vapor can scatter around and shield gas is not sprayed directly onto the welded part, and the transmission window has a sufficient distance between the welded part at the upper end of the shield gas cylinder. Further, since the air shield is formed by the shielding gas flowing from the transmission window side toward the welded portion side, it is possible to completely prevent the metal vapor from adhering to the transmission window.

  Furthermore, the invention of this claim is laser welding performed in a low vacuum atmosphere, and since welding with a deep penetration depth can be performed stably for a long time, a low capital investment is not required. Even if it is an output laser, sufficient penetration depth can be obtained and capital investment can be suppressed.

  Specifically, according to the experiment of the present inventor, under the atmosphere of 10 kPa (1/10 of the atmospheric pressure), the same laser output 6 kW as in the case of the atmospheric pressure described above, the welding speed is about 0.1 m / min (1 7 mm / s), a penetration depth of about 30 mm, which is twice that of the atmospheric pressure atmosphere, can be obtained. This result shows that the laser output efficiency is improved by a factor of two in a low-pressure atmosphere as compared to that in an atmospheric pressure atmosphere.

  On the other hand, the invention of this claim can also be applied to welding using a high-power laser. In this case, a larger penetration depth can be obtained stably.

  In addition, since the adhesion of metal vapor to the transmission window is reliably prevented, contamination of the transmission window is suppressed, and there is no need to replace an expensive transmission window made of quartz glass in a short period of time, and the transmission window may be broken. There is nothing to do.

  The invention according to the present invention can achieve the above-described excellent effect by a very simple means of providing a shield gas cylinder having a shield gas supply means in a conventional laser welding apparatus. It is practical.

  The invention of the above-mentioned claim is completely different from the conventional assist gas system, and does not spray the shield gas onto the welded part, but blocks the gas with the metal vapor (proof) standing. .

  The invention of this claim is based on the idea that the shielding gas that works in the direction of increasing the vacuum degree is flowed in spite of the welding performed in a low vacuum atmosphere. It is a fallen thing.

  In the invention of this claim, the shield gas cylinder is made of high-strength glass from the viewpoint of confirmation of the degree of rise of the induced plume during laser welding, observation / confirmation of the fusion welding situation in the welding chamber (chamber), A cylinder made of acrylic resin or polycarbonate resin can be preferably used. The cross-sectional shape is preferably circular, but is not particularly limited, and may be square such as a quadrangle.

  The shield gas cylinder is provided with holes as supply means for introducing the shield gas, but the number is not limited to one and can be appropriately provided around the shield gas cylinder.

The type of shielding gas to be introduced is not limited as long as it is a gas that is not converted into plasma by laser light, but an inert gas such as Ar, He, N ₂ is preferable, and N ₂ is particularly inexpensive and is a point of oxidation prevention. To preferred.

  Also, it is preferable to set the inner diameter of the tip opening of the shield gas cylinder to about twice the diameter of the passing laser beam because the metal vapor does not penetrate excessively (for example, 10 mm or more) into the cylinder.

  Specifically, the “predetermined interval” provided between the shield gas cylinder and the welded portion is preferably about 50 to 300 mm.

  The “low vacuum atmosphere” refers to an atmosphere having a pressure of about 0.01 to 30 kPa.

Examples of the laser used in the laser welding apparatus according to the present invention include a CO ₂ laser, a YAG laser, a fiber laser, and a disk laser, but are not particularly limited.

The invention described in claim 2
2. The laser welding apparatus according to claim 1, wherein the laser welding apparatus has a focal length of 350 mm or longer.

  In the case of a long focus laser welding apparatus, in particular, in the case of a long focus laser welding apparatus having a focal length of 350 mm or more, a condensing optical system having a deep focal depth and a long Rayleigh length can be configured. However, a weld having a small bead width and deep penetration can be provided, and a higher quality weld can be provided. In addition, since welding with a small bead width can be performed, it can be applied to welding of precision parts to provide high-quality welding.

  Thus, by applying the invention of claim 1 to the long focus laser welding apparatus excellent in welding quality, laser welding in a low vacuum atmosphere can be stably performed even with a thick member. This makes it possible to suppress the generation of porosity, provide a weld having a small bead width and a deep penetration, that is, a high-quality weld, stably and continuously.

  In addition, since the long focus laser welding apparatus can sufficiently increase the distance between the shield gas cylinder and the welded portion, adhesion of the metal vapor to the transmission window can be more reliably prevented and the gas passes through the shield gas cylinder. The shield gas is sufficiently diffused without reaching the weld and does not adversely affect the welding.

The invention according to claim 3
3. The laser welding apparatus according to claim 1, wherein an annular shielding plate surrounding the laser beam passage is provided at predetermined intervals in the longitudinal direction of the inner wall of the shield gas cylinder. It is.

  By providing an annular shielding plate that surrounds the laser beam path at every predetermined interval, the introduced shielding gas can be retained in the adjacent shielding plates for a long time, so a smaller amount of shielding gas is introduced. Intrusion of metal vapor can be efficiently prevented.

The invention according to claim 4
A laser welding method using the laser welding apparatus according to any one of claims 1 to 3,
A to-be-welded material placement step for placing the to-be-welded material in the laser welding apparatus;
An atmospheric pressure control step for making the pressure atmosphere in the laser welding apparatus a low vacuum atmosphere;
A shielding gas introduction process for introducing shielding gas into the shielding gas cylinder;
A laser irradiation step of irradiating the workpiece with a laser,
The amount of the shield gas introduced is controlled by a laser welding method characterized in that the shield gas is controlled so as not to be directly sprayed onto the welded part during welding.

  In the invention of this claim, since laser welding is performed using the laser welding apparatus according to any one of claims 1 to 3, air formed by the shield gas introduced into the shield gas cylinder is formed. The shield can reliably prevent the metal vapor from adhering to the transmission window. In addition, since the amount of shield gas introduced is controlled so as not to be sprayed directly onto the welded portion, the welding is not adversely affected. As a result, it is possible to continuously perform high-quality welding while ensuring a sufficient penetration depth and suppressing the generation of porosity for a long time.

  According to the present invention, metal vapor is prevented from adhering to the laser light transmission window, a sufficient penetration depth is ensured, and high quality welding with reduced porosity is stably performed. Can be provided efficiently for a long time.

It is a perspective view which shows the laser welding apparatus of embodiment of this invention. It is sectional drawing explaining the principle of the laser welding apparatus of embodiment of this invention. It is sectional drawing which shows the other aspect of the shield gas cylinder of the laser welding apparatus of embodiment of this invention. It is a photograph showing the metal structure of the bead surface. It is a figure which shows the relationship between the penetration depth and penetration cross-sectional area, and a pressure in bead on plate welding. It is a figure which shows the relationship between the penetration depth and pressure in bead on plate welding.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(1) Description of Entire Apparatus FIG. 1 is a perspective view showing a laser welding apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view illustrating the principle of the laser welding apparatus according to the embodiment of the present invention. is there.

First, an outline of the entire apparatus will be described.
As shown in FIGS. 1 and 2, the laser welding apparatus basically adjusts the focal point of a laser oscillator 11 that generates a laser beam R, an optical fiber 12, a processing head 13, and the laser beam R. The optical system 14, a transmission window 15 having a transmission plate, a chamber 30 for performing welding in a low vacuum atmosphere, a shield gas cylinder 40, and control means (not shown) are provided. A transfer device 71 for moving the test material 61 is installed in the chamber 30.

  Further, an exhaust pipe 53 is connected to the chamber 30 as pressure reducing means for making the inside of the chamber 30 a low vacuum atmosphere, and two rotary vacuum pumps (VP) 51 and 52 are connected to the exhaust pipe 53. ing. A gas pipe 22 for supplying the shield gas of the gas cylinder 21 into the shield gas cylinder 40 is connected to the shield gas cylinder 40.

  The pressure in the chamber 30 is controlled by adjusting the inflow amount of the shield gas flowing into the chamber 30 from the shield gas cylinder 40 and the exhaust amount from the chamber 30 by the vacuum pumps 51 and 52.

(2) Explanation of shield gas cylinder

  A shield gas introduction portion 43 is provided at the upper end portion 41 of the shield gas cylinder 40. A plurality of shield gas introduction holes 44 are formed in the shield gas introduction portion 43 at appropriate intervals in the circumferential direction of the shield gas cylinder 40. The transmission window 15 is fixed to the upper end portion 41 of the shield gas cylinder 40.

  A lower end portion 42 of the shield gas cylinder 40 is connected to a hole edge portion of the introduction port 32 provided in the top plate 31 of the chamber 30 and opens into the chamber 30.

  An annular fin 46 is provided at the inlet 32 of the chamber 30 in order to suppress the intrusion of the plume into the shield gas cylinder 40. The diameter of the introduction port 32 that is reduced by the annular fin 46 is set to about twice the diameter of the laser beam that passes through the introduction port 32 so as not to adversely affect the laser beam.

  The inner diameter and length of the shield gas cylinder 40 can be appropriately changed according to the type of the shield gas, the welding material, the welding energy, the focal length of the laser beam, and the like.

  The optical axis of the laser beam R and the surface of the specimen 61 are orthogonal to each other, the spot diameter of the laser beam R at the irradiated portion is set to about 300 μm, and the focal point during welding is 0 below the surface of the specimen 61. It is controlled to -10 mm.

  The output of the laser oscillator 11 is generally 1 to 20 kW kW, the core diameter of the optical fiber 12 is 15 to 300 μm, the transmission window 15 is made of quartz glass, and the chamber 30 is made of acrylic resin. It is.

(3) Welding method using laser welding apparatus Next, a welding method using the laser welding apparatus of the present embodiment will be described.

  First, after the pressure in the chamber 30 is reduced to about 30 Pa by the vacuum pumps 51 and 52, the shield gas is caused to flow into the shield gas cylinder 40 from the shield gas introduction hole 44 of the shield gas cylinder 40.

  The shield gas flows through the shield gas cylinder 40 to the lower side of the shield gas cylinder 40, flows into the chamber 30 from the introduction port 32, and is then discharged out of the chamber 30 by the vacuum pumps 51 and 52 together with the plume generated at the welded portion. (Refer to the broken arrow indicating the flow of the shielding gas in FIG. 2). During welding, the inside of the chamber 30 is controlled to 0.1 to 20 kPa by the vacuum pumps 51 and 52.

  Then, under a low vacuum atmosphere, the plume that flies by filling the shielding gas cylinder 40 with the shielding gas is blocked, and the laser light R is transmitted through the transmission window 15 while preventing the plume from adhering to the transmission window 15. The sample material (material to be welded) 61 is irradiated. At the same time, laser welding is performed while the specimen 61 is moved horizontally at a constant speed by the transfer device 71.

  Further, as indicated by a broken line arrow in FIG. 2, the shield gas flows into the chamber 30 and diffuses in the chamber 30. For this reason, if a sufficient distance between the introduction port 32 and the welded portion is ensured, adverse effects on the welded portion due to the shielding gas can be avoided. For example, when the focal length of the long focal length optical system 14 is 1000 mm, if the length of the shield gas cylinder 40 is 500 mm, the distance from the inlet 32 of the chamber 30 to the welded portion is about 450 mm (about on the cylinder). When a condensing lens is installed 50 mm above), it is easy to avoid the adverse effect of the shielding gas on the welded portion.

(3) Other Aspects of Shield Gas Cylinder FIG. 3 is a cross-sectional view showing another aspect of the shield gas cylinder. As shown in FIG. 3, the shield gas cylinder 40 has a plurality of inner fin-shaped inner fins 45 formed on the inner peripheral side thereof with appropriate intervals in the vertical direction.

  According to the shield gas cylinder 40, the shield gas introduced into the shield gas cylinder 40 from the shield gas introduction hole 44 is retained by the internal fin 45 in the middle of the shield gas cylinder 40. Since the gas pressure in the shield gas cylinder 40 also increases, the plume shield effect can be increased.

(1) Example A for evaluating the stability of welding
In Example A, welding was performed by measuring a bead length that can be continuously welded using an experimental apparatus having the shield gas cylinder (the laser welding apparatus described above) and an experimental apparatus having no shield gas cylinder. The stability of was evaluated.

(A) Examples and Comparative Examples In the examples, welding was performed under the welding conditions shown below using an experimental apparatus having a shield gas cylinder, and the bead length that could be continuously welded was measured.

  In the comparative example, using an experimental apparatus having no shield gas cylinder, welding was performed under the following welding conditions, and the bead length that could be continuously welded was measured. The experimental apparatus used in the comparative example has the same configuration as the laser welding apparatus described above except that there is no shield gas cylinder and a transmission window is attached to the introduction port.

The welding conditions are as follows.
Pressure in the chamber: 0.1 kPa
Length and inner diameter of shield gas cylinder: 430mm, 60mm
Supply amount of shielding gas (N ₂ ): 100 to 200 cc / min
Laser power: 8kW
Welding speed: 0.3 m / min
Focus position (defocus amount): Focus position (0 mm)
Material and thickness of test material: Stainless steel (SUS304), 50mm
Optical fiber core diameter: 100 μm
Pumping speed of two vacuum pumps:
162 liters / min, 500 liters / min

(B) Evaluation method The stability of welding was evaluated by investigating the continuous welding time.

(C) Welding result FIG. 4 is a photograph showing the metal structure of the bead surface. FIG. 4A is a photograph of the example, and FIG. 4B is a photograph of the comparative example.

  In the case of the example, since the plume did not adhere to the transmission window even after 1.2 minutes from the start of laser welding, stable welding could be performed. And when 1.2 minutes passed, welding was stopped and the bead of length 350mm was able to be drawn. On the other hand, in the case of the comparative example, since the plume adhered to the transmission window, the welding became unstable 0.27 minutes after the start of laser welding, so that only a bead with a length of 80 mm could be drawn.

(D) Evaluation In the case of an experimental apparatus with a shield gas cylinder, unlike the experimental apparatus without a shield gas cylinder, the bead length can be greatly increased, and it has been confirmed that practical use is possible.

(2) Example B for welding quality evaluation
In Example B, a welding apparatus having a shield gas cylinder was used to evaluate the welding quality due to the difference in pressure in the chamber.

(A) Examples and Comparative Examples Using an experimental apparatus having the shield gas cylinder (the above laser welding apparatus), the pressure in the chamber was changed under the following welding conditions, and the shape of the bead surface and the penetration cross section The penetration depth and penetration cross-sectional area were observed and measured.

The welding conditions are as follows.
Chamber pressure: 0.1 kPa (Example 1)
1 kPa (Example 2)
10 kPa (Example 3)
101.3kPa (comparative example) (atmospheric pressure)
Length and inner diameter of shield gas cylinder: 430mm, 60mm
Supply amount of shielding gas (N ₂ ): 100 to 200 cc / min (Example 1)
200 to 300 cc / min (Example 2)
500 cc / min (Example 3)
40000cc / min (atmospheric pressure)
Laser power: 10kW
Welding speed: 0.1 m / min
Focus position (defocus amount): Focus position (0 mm)
Material and thickness of test material: Stainless steel (SUS304), 50mm
Optical fiber core diameter: 100 μm
Pumping speed of two vacuum pumps: 162 l / min,
500 liters / min

(B) Evaluation method Weld quality was evaluated based on the surface state of the bead, the shape of the penetration cross section, the penetration depth, and the penetration cross sectional area.

(C) Welding results FIGS. 5 and 6 show the welding results. FIG. 5 is a diagram showing the bead surface and cross-sectional shape, penetration depth, and penetration cross-sectional area of bead-on-plate welding under each pressure, and (a) shows a welding speed of 0.1 m / min. It is a result and (b) is a result whose welding speed is 0.3 m / min. FIG. 6 is a diagram showing the relationship between pressure and penetration depth based on the results of FIG.

(D) Evaluation (b) Surface condition of beads In Examples 1 to 3, the width of the beads is thin and clean, and in the comparative example, the width of the beads is large and not clean.

(B) Penetration depth In Examples 1 to 3, the penetration depth is deep and the penetration depth exceeds 30 mm for both welding speeds of 0.1 m / min and 0.3 m / min. On the other hand, the comparative example has confirmed that the penetration depth was shallower than those of Examples 1-3.

(C) Shape of penetration cross section In the case of the example, it was confirmed that the bead width was small and deep penetration was obtained. In the case of the comparative example, it was confirmed that the bead width was large and the penetration was shallow. Furthermore, in Examples 1 to 3, the presence of porosity was not recognized in the welded portion, and it was confirmed that the welding was of high quality.

(D) Penetration sectional area About penetration sectional area, when welding speed was 0.1 m / min, the direction of Examples 1-3 became large. On the other hand, when the welding speed was 0.3 m / min, since the weld bead width was narrow, Examples 1 to 3 were smaller.

  From the above, it has been confirmed that high quality welding can be performed stably by performing laser welding in a low vacuum atmosphere using a shield gas cylinder.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above embodiment. Various modifications can be made to the above embodiments within the same and equivalent scope as the present invention.

DESCRIPTION OF SYMBOLS 11 Laser oscillator 12 Optical fiber 13 Processing head 14 Optical system 15 Transmission window 21 Gas cylinder 22 Gas piping 30 Chamber 31 Chamber top plate 32 Inlet 40 Shield gas cylinder 41 Upper end of shield gas cylinder 42 Lower end of shield gas cylinder 43 Shield gas introduction Portion 44 Shield gas introduction hole 45 Inner fin 46 Annular fins 51, 52 Vacuum pump 53 Exhaust pipe 61 Test material (material to be welded)
71 Transfer device R Laser light

Claims (4)

A laser welding apparatus that performs welding with laser light in a low vacuum atmosphere,
A shield gas cylinder that is disposed along the optical axis of the laser beam at a predetermined interval from the weld, a transmission window is provided at the upper end, and the lower end is opened in the atmosphere control area;
A laser welding apparatus, comprising: a shield gas supply means for introducing a shield gas into the shield gas cylinder from the transmission window side of the shield gas cylinder.   The laser welding apparatus according to claim 1, wherein the laser welding apparatus is a long-focus laser welding apparatus having a focal length of 350 mm or more.   3. The laser welding apparatus according to claim 1, wherein an annular shielding plate surrounding the laser beam passage is provided at predetermined intervals in the longitudinal direction of the inner wall of the shield gas cylinder. . A laser welding method using the laser welding apparatus according to any one of claims 1 to 3,
A to-be-welded material placement step for placing the to-be-welded material in the laser welding apparatus;
An atmospheric pressure control step for making the pressure atmosphere in the laser welding apparatus a low vacuum atmosphere;
A shielding gas introduction process for introducing shielding gas into the shielding gas cylinder;
A laser irradiation step of irradiating the workpiece with a laser,
The laser welding method according to claim 1, wherein the introduction amount of the shielding gas is controlled so that the shielding gas is not sprayed directly on the welded part during welding.