JP2001252780A - Method of joining by laser beam for cylinders of different kinds of metals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method by laser beam for cylindrical bodies made of different kinds of metallic materials which are strongly and surely fitted (overlapped) and joined without giving a substantial influence on the joining strength regardless of whether an intermetallic compound is substantially formed or not. SOLUTION: The method comprises a process where an inner cylinder 1 made of a metal having different components is inserted into an outer cylinder 2 and both cylinders are engaged and a process where the inner surface 5 of the inner cylinder 1 is irradiated with a laser beam in a manner that the focus 15 of the laser beam comes at a point just above the inner surface 5 of the inner cylinder 1 so that the inner cylinder 1 is completely melted in the direction of the thickness by the thermal energy radiated from the side of the cylinder 1 and an alloy layer is formed mainly by a solid-liquid phase diffusion at the boundary face 8 between the molten metal and the outer cylinder 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an airtight container by fitting inner and outer cylindrical bodies made of different kinds of metals, and more particularly to a method of manufacturing a vacuum container such as a metal thermos or an electric water heater. .

[0002]

2. Description of the Related Art Recently, the demand for high-value-added products for vacuum containers such as thermos bottles and cooking utensils has increased, and materials such as SUS304 have been used.
Is changing from austenitic stainless steel to pure titanium. The reason for using titanium is that the specific gravity is about 60% that of stainless steel, which is lighter, so that the product is lighter and has many excellent properties such as high corrosion resistance and antibacterial properties. .

[0003] However, titanium is a material having disadvantages such as being expensive and having poor workability as compared with stainless steel. Therefore, there is a demand from customers for a heterogeneous metal combination structure using titanium for the inner bottle and stainless steel for the outer bottle according to the purpose of the product.

[0004] A metal thermos is constituted by a container in which the space between two bottles is evacuated. As a manufacturing method, the inner jar is inserted into the outer jar, and then the edge of the base is TIG.
(Tungsten inert gas arc) It is manufactured by welding and the other side is evacuated from the hole drilled in the bottom of the outer bottle and then plugged.

[0005]

However, the TIG welding method has a relatively large heat input and it is difficult to finely control the heat source. Therefore, when TIG welding of different metals, the molten metal is excessively diluted and mixed. In addition, the weld metal forms a brittle intermetallic compound, and cracks occur in the weld metal due to thermal stress during solidification and cooling, and in extreme cases, the weld metal breaks. Further, even if the fracture does not occur, a crack is generated at the joint interface, which causes a vacuum leak. For this reason, the inner bottle and the outer bottle are designed and manufactured to use the same material, and it is virtually impossible to manufacture a metal thermos made of a combination of different metals.

[0006] As a joining technique for dissimilar metals, a non-fusion joining method such as a brazing method or a diffusion joining method that does not substantially melt the base material is generally known. However, these non-melt joining methods have insufficient joining strength, and have additional equipment such as vacuum pressurization equipment, which makes the equipment larger and larger.
Due to complexity, brazing and diffusion bonding have not been employed in the production of metal thermos.

[0007] From such a technical background, there is a strong demand for establishing a technique capable of firmly joining a base portion of a metal thermos without generating a brittle intermetallic compound.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and does not substantially produce an intermetallic compound or, even if it produces, an intermetallic compound without substantially affecting bonding strength. An object of the present invention is to provide a laser joining method for dissimilar metal cylinders, which can firmly and surely fit (overlap) the cylinders.

[0009]

In general, TIG welding and the like have been used for welding products such as clad metal thermos bottles. However, in dissimilar material welding, delicate control of the interface is important, but in TIG welding, it is difficult to control heat input to the interface. Therefore, in the present invention, the amount of heat input to the interface is controlled with high precision by using a laser welding method capable of finely controlling the amount of heat input, and excessive dilution of the backing material by the melt of the surface material is suppressed.

When joining dissimilar metals using the fusion joining method, it is important to suppress the formation of intermetallic compounds as much as possible and to form a weld metal that does not crack. The inventors of the present invention have made intensive studies and efforts over many months on the application of the laser welding method, and as a result, have produced substantially no intermetallic compound or even if produced, without substantially affecting the bonding strength. Thus, the present invention has been completed in which different kinds of metals can be bonded firmly and reliably.

[0011] The laser joining method for dissimilar metal cylinders according to the present invention comprises the steps of: inserting an inner cylinder made of a metal material having a different composition into an outer cylinder and fitting them together; Irradiating the inner surface of the inner cylinder with laser light so that the laser light comes to the front, and the inner cylinder is completely melted in the thickness direction by heat energy incident from the side of the inner cylinder. Forming an alloy layer mainly by solid-liquid diffusion at the interface between the melt and the outer cylinder.

In laser welding, a laser beam oscillated from a laser oscillator can be narrowed down to a very small beam at a focal position by an optical system, and deep penetration can be obtained by incidence of a beam beam with a high energy density. However, in the present invention, the laser beam intentionally defocused from the irradiation surface by the optical system is irradiated onto the inner surface of the inner cylinder, so that the irradiation area is enlarged and heat energy is incident on the bonding interface on average. become. As a result, the melting portion of the inner cylinder becomes wider, the penetration becomes shallower, heat energy is incident on the bonding interface on average, and an alloy layer is formed mainly at the interface between the melt and the outer cylinder by solid-liquid diffusion. You. Since this alloy layer is mainly formed by solid-liquid diffusion, a brittle intermetallic compound layer is not substantially generated, or even if an intermetallic compound layer is generated, the bonding strength is not substantially affected. For this reason, the required joining strength can be obtained without causing cracks in the weld metal portion.

It is to be noted that the metal material forming the inner cylinder may be made of a metal or an alloy which does not form a brittle compound with the second metal member either as a solid solution of the metal material forming the outer cylinder or as a solid solution. preferable. It is preferable to use pure titanium (JIS class 1) as the metal material constituting the inner cylinder, but in addition to this, pure titanium (JIS class 2 to class 4) having industrial purity,
An α-type titanium alloy, a β-type titanium alloy, an α-β type titanium alloy (for example, Ti-6Al-4V), a TiNi-based alloy (shape memory alloy), or the like can be used.

On the other hand, austenitic stainless steel (for example, JISSUS30) is used as a metal material constituting the outer cylinder.
It is preferable to use 4), but in addition, ferritic stainless steel, martensitic stainless steel, Ni-based alloy steel, CrNi-based alloy steel, CrNiCo-based alloy steel, M
o-based alloy steel, CrMo-based alloy steel, low alloy steel, carbon steel, N
i-based alloy, Cr-based alloy, Mo-based alloy, W-based alloy, Mg-based alloy, FeNi-based alloy, CrNi-based alloy, FeCrNi
Alloys, CrNiCo-based alloys, FeCrNiCo-based alloys, pure copper, Cu-based alloys, CuNi-based alloys, CuSn-based alloys, CuZn-based alloys, AlCu-based alloys, etc.
Alloys can be used.

In this case, it is desirable that the thickness of the inner cylinder is smaller than the thickness of the outer cylinder.
2.00mm range and outer cylinder thickness 0.30m
It is more desirable to be at least m. Inner cylinder thickness is 0.1
If the thickness is less than 5 mm, without the filler, the melt becomes insufficient and the surface of the outer cylinder is exposed. Therefore, the lower limit of the thickness is set to 0.15 mm. On the other hand, the thickness of the inner cylinder is 2.00 mm
When the value exceeds the limit, the out-of-focus laser light is not sufficiently incident on the interface, and the necessary bonding strength cannot be obtained or the bonding strength becomes insufficient. Therefore, the upper limit of the thickness is set to 2.00 mm.

If the thickness of the outer cylinder is less than 0.30 mm, the heat transfer in the surface direction becomes excessively large than the heat transfer in the thickness direction, so that sufficient bonding strength cannot be obtained and the heat affected zone (HAZ) Is increased, so that the lower limit of the thickness is 0.1 mm.
It was 30 mm. The upper limit of the outer cylinder is not particularly defined, because the thicker the outer cylinder, the easier the overlap joining becomes. When the thickness of the outer cylinder is small, it is desirable to cool the outer cylinder from the outer cylinder side by using an appropriate cooling means.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
In this embodiment, a case where the different-type metal thermos shown in FIG. 1 is manufactured will be described as an example.

The main body of the dissimilar metal thermos 3 comprises an inner bottle 1, an outer bottle 2 and an outer lid 22. Inner bottle 1 and outer bottle 2
The outer lid 22 is formed by deep drawing the outer bottle 2 or welding another member of the same material as the outer bottle 2 to the open end of the outer bottle 2. . After fitting the inner bottle 1 into the outer bottle 2, the edge of the base is laser-welded, and the other side is evacuated through a stopper port 23 opened at the bottom of the outer lid 22, and then stoppered. Make the inside airtight.

Table 1 shows the compositions of pure titanium (JIS Class 1) used as the inner bottle 1 and stainless steel (JISSUS304) used as the outer bottle 2. The titanium-based material is not limited to the above composition, and may be, for example, Ti-6Al-4V or Ti-4.5V-3
Examples thereof include Al-2Mo-2Fe and Ti-Ni shape memory alloy.

The laser welding machine 10 includes a laser oscillator and an output controller (not shown). An optical fiber 12 and two optical lenses 13a and 13b are housed in a welding torch 11 of the laser welding machine 10. Welding toe
The tube 11 communicates with an inert gas supply source (not shown) so that an appropriate amount of argon gas is supplied to the laser irradiation surface 5 through the inside of the welding torch 11.

The optical fiber 12 is optically connected to a light source of a laser oscillator (not shown). The first and second optical lenses 13a and 13b are movably supported by actuators (not shown) so that the position of the focal point 15 can be changed and the beam diameter can be reduced or enlarged.

An output controller (not shown) adjusts the amount of power supplied from the power supply to the laser oscillator, and controls ON / OFF of the power supply for pulse oscillation of the laser. One pulse time is preferably in the range of 5 to 20 microseconds. The laser light used in this embodiment is a pulse YAG laser, but may be a continuous wave YAG laser or a continuous wave CO ₂ laser, and is not limited to this.

Here, the irradiation diameter of the laser beam is 1 mm.
Is defocused so as to be about 1.2 mm from the center. This is because if the irradiation diameter is small, the melting region advances to the lower plate 2 and it is difficult to control the generated intermetallic compound. On the other hand, if it is larger than this, a sufficient melting region cannot be obtained, and no bonding layer is formed at the interface.

When a pulse laser is used,
Preferably, the energy per pulse is between 5 J and 10 J. In the case of 5 J / pulse or less, the heat input for forming the diffusion layer 6 at the interface 8 stably is not obtained,
This is because if the beam diameter is J / pulse or more, the lower plate is excessively melted even if the beam diameter is increased, and a brittle intermetallic compound is formed.

Here, it is important not to form an intermetallic compound at the interface 8. For this purpose, for example, the metal component (titanium) constituting the inner cylinder is composed of the outer cylinder as in the case of titanium and iron. It is preferable that a large amount of the metal component (iron) can be dissolved in a solid solution, so that an intermetallic compound is hardly formed. This is because, in the case of the combination, even if the metal component of the outer cylinder is melted in the region melted by the laser irradiation, a brittle intermetallic compound is not formed if the metal component is dissolved.

As shown in FIG. 2, in the present invention, the focal point 15 is positioned before the irradiation surface 5 of the inner cylinder 1 by variably adjusting the positions of the two optical lenses 13a and 13b, and the wide laser light 14 Is irradiated. At this time, the heat input density Q supplied to the first metal member 1 is obtained by the following equation (1). Here, W1 is the core diameter of the optical fiber, and θ1 is the divergence angle (here, air) obtained from the numerical aperture NA of the optical fiber (the product of the sine of the divergence angle of the light diverging from the fiber opening and the absolute refractive index in the object space). Has a refractive index n0 of about 1
F1 is the focal length of the first lens 13a, f2 is the focal length of the second lens 13b, L1 is the distance from the focal point to the irradiation surface, θ2 is the inclination angle of the laser optical axis with respect to the vertical line, and P is the laser oscillator And η1 respectively represent the absorptance of the first metal member. The numerical aperture NA is
The product n sin of the sine of the angle u at which the radius of the entrance pupil (aperture) extends at the object point and the absolute refractive index n of the object space in the optical instrument
u.

Q = η1 × P / [{(W1 × f2 / f1) + (L1 × θ1 × f1 / f2)} / cos θ2] (1) Such a heat input density Q from the irradiation surface 5 to the inner cylinder When the light is incident on the metal layer 1, the metal under the irradiation surface is melted in the thickness direction and the surface direction, and the diffusion layer 6 is formed. Of these, the molten region in the thickness direction does not progress further when reaching the interface 8, but
The melt in the inner cylinder comes into contact with the outer cylinder, causing mutual diffusion at the interface 8. Due to the substantial solid-phase diffusion at the solid-liquid interface 8, the inner cylinder 1
And a joining layer 7 for joining the outer cylinder 2 to the outer cylinder 2. At this time, the output power P of the laser oscillator is controlled to make the penetration depth d substantially equal to the thickness t1 of the inner cylinder.

Next, various embodiments of the present invention will be described.

(Example 1) Using a pulse YAG laser, dissimilar metal laser welding was performed between an inner bottle of pure titanium having a thickness of 0.3 mm and an outer bottle of austenitic stainless steel (SUS304) having a thickness of 0.4 mm. Where the diameter of the inner bottle (inner diameter)
Is 46 mm. The laser irradiation position was from the side of the inner bottle, and the irradiation angle was inclined at about 45 ° from vertical. This inclination angle is 30
It can be freely changed within the range of ° to 60 °. Laser welding was performed under the conditions that the pulse width was 10 microseconds, the defocus was 1 mm (beam diameter 1.2 mm), the repetition was 30 Hz, and the welding speed was 10 mm / second, and a leak test was performed on the completed cylinder.

The leak test was performed using a helium leak detector. The subject is attached to a helium leak detector, the outer bottom is brought into close contact with a rubber packing, and the inside of the double container is evacuated until the internal pressure becomes 1.0 × 10 ⁻³ Torr or less. If there is a large leak, it will be rejected at this evacuation stage. Exhaust time is about 45 seconds (same as mass production)
It is.

After exhausting, the entire box-shaped cover is lowered from above, He gas is released from the thin hose-shaped thing to the inside of the inner cylinder for a certain time, and the flow rate of the He gas is measured for a certain time by the detector on the exhaust side. Measure. Those exceeding a certain flow rate are rejected. In this case, the He gas ejection time is about 4 hours.
Seconds (same as in mass production), and the measurement time was about 10 seconds (same in mass production). Those with a leak rate of 3.0 × 10 ⁻⁹ Pa · m ³ / sec or less when flowing He gas for 4 seconds were judged as acceptable, and those with a leak rate exceeding this were judged as unacceptable. Table 2
Shows the results of the helium leak test. FIG. 4 shows the relationship between the irradiation energy and the shear strength of the flat plate test piece manufactured under the same conditions for reference. In the figure, a curve A connecting white triangles indicates a shear load / laser irradiation energy correlation characteristic line, and a curve B connecting black triangles indicates a shear stress / laser irradiation energy correlation characteristic line. As is clear from Table 2 and FIG. 4, those with a laser irradiation energy of 5 J / pulse or more passed the helium leak test, and those with a laser irradiation energy of 4 J / pulse or less failed the helium leak test. It was also found that the rejected products had a low breaking strength of 1 kN / 20 mm or less. This is considered to be due to the fact that the unheated portion was generated due to the low heating energy due to the shortage of irradiation energy, which led to the leakage. On the other hand, when the irradiation energy was 8 J / pulse or more, the bonding strength was slightly lowered, but the result of the leak test passed. This is because it is important that the entire vessel be joined with high heat even if the strength of the vacuum vessel is somewhat low. However, when the irradiation energy was 12 J / pulse or more, a large amount of intermetallic compound was generated in the weld metal due to excessive dilution of the outer cylinder (stainless steel), and cracks were generated in the joint. It has been found that even when the irradiation energy becomes excessive, the vacuum of the container cannot be maintained. Therefore, it is preferable that the laser irradiation energy be in the range of 5 to 10 J / pulse under the conditions of the present embodiment, and 6 to 10 J / pulse.
It can be said that the range of 8 J / pulse is more preferable.

Example 2 Using a pulsed YAG laser, an inner bottle of pure titanium having a thickness of 0.3 mm and an outer bottle of austenitic stainless steel (SUS304) having a thickness of 0.4 mm were laser-welded. Here, the diameter is 46 mm. The laser irradiation position was from the inner bottle, and the irradiation angle was inclined at an angle of 60 degrees from the vertical. Pulse width 20 microseconds, irradiation energy 4 J / pulse, defocus 1 mm (beam diameter 1.
2 mm), the repetition rate is 25 Hz, and the welding speed is 2.5
mm / sec (1 rpm), no leakage occurred,
It was found that the vacuum was kept. It is considered that the reason why the energy can be lower than that in the case of 10 microseconds is that since the pulse width is long and the speed is low, the melting and mixing are shallow and the interface easily forms a diffusion junction.

(Comparative Example 1) A pure titanium inner bottle having a thickness of 0.3 mm and an outer bottle of austenitic stainless steel (SUS304) having a thickness of 0.4 mm were laser-welded using a pulse YAG laser. Here, the diameter is 46 mm. The laser irradiation position was from the outer bottle, and the irradiation angle was inclined at an angle of 30 degrees from the vertical. Pulse width is 10 microseconds, defocus is 2 mm (beam diameter 1.2 mm), and repetition is 30 H
z, when the welding speed is 10 mm / sec, 10 J /
Below the pulse, the latter half of the irradiation is in an unbonded state, and 12J /
Above the pulse, a hole is formed in the surface due to excessive penetration,
No vacuum vessel was formed. This is considered to be due to the difference in thermal expansion between the irradiation side (outer bottle) and the other side (inner bottle) due to the laser irradiation, whereby a gap was alive, and the difference in thermal expansion was further increased. At a high energy of 12 J / pulse or more, a joint is formed of an intermetallic compound and a crack is generated.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

According to the method of the present invention, a combination of dissimilar metals, which has conventionally been considered impossible or difficult because of the tendency to form brittle intermetallic compounds such as a combination of stainless steel and titanium, Since it can be firmly and soundly joined with almost no embrittlement, the degree of freedom in designing a product of a dissimilar metal cylinder such as a thermos bottle is greatly increased.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an outline of a metal thermos as a dissimilar metal cylinder.

FIG. 2 is a schematic view showing a laser irradiation part and its vicinity.

FIG. 3 is an enlarged schematic diagram showing a state of a bonding interface.

FIG. 4 is a characteristic diagram showing the relationship between pulse energy and shear strength.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inner bottle (inner cylinder), 2 ... Outer bottle (outer cylinder), 3 ... Thermos bottle, 4 ... Weld part, 5 ... Irradiation surface (inner surface), 6 ... Diffusion layer, 7 ... Bonding layer, 8 ... Interface Reference numeral 10: Laser welding machine, 12: Optical fiber, 13a, 13b: Lens, 14: Laser light, 15: Focus, 22: Outer lid, 23: Exhaust and stopper.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 103: 14 B23K 103: 14 (72) Inventor Jin Hiraga 2085-16 Uenoyama, Fukasawa-cho, Nagaoka City, Niigata Prefecture 16 shares F-term in the Laser Engineering Laboratory of Japan (reference) 4B002 AA01 BA22 BA31 BA44 CA32 4E068 AH02 BF00 BG02 CA03 DB01 DB04 DB05

Claims (9)

[Claims] A step of inserting an inner cylinder made of a metal material having a different composition into an outer cylinder and fitting them together; and a step of focusing the laser beam on the near side of the inner surface of the inner cylinder. By irradiating the inner surface of the cylinder with laser light, the inner cylinder is completely melted in the thickness direction by thermal energy incident from the side of the inner cylinder, and solidified mainly at the interface between the melt and the outer cylinder. Forming an alloy layer by liquid diffusion. 2. The method of claim 1, wherein said inner cylinder is made of a material having a lower coefficient of thermal expansion than said outer cylinder. 3. The method according to claim 1, wherein an irradiation area of the laser beam is 1 mm ² or more. 4. The method according to claim 1, wherein the laser light is pulsed. 5. The method according to claim 4, wherein the laser irradiation energy is in the range of 5 to 10 J. 6. The method according to claim 1, wherein the material forming the inner cylinder forms a solid solution with a large amount of the components forming the outer cylinder, or the components forming the outer cylinder. A metal or alloy that does not form a brittle compound with the alloy. 7. The method according to claim 1, wherein the inner cylinder is made of pure titanium or a titanium-based alloy, and the outer cylinder is made of an iron-based material. 8. The method according to claim 1, wherein the thickness of the inner cylinder is smaller than the thickness of the outer cylinder. 9. The method according to claim 1, wherein the thickness of the inner cylinder is in a range of 0.15 to 2.00 mm, and the thickness of the outer cylinder is 0.30 mm or more. A method comprising: