JPWO2007032176A1 - Welding method and welding apparatus - Google Patents

Abstract

A laser welding method that does not require an increase in the output of the laser oscillation source, similar to the TIG welding method, which has a deep penetration, does not use an oxide-based flux, and consumes little tungsten electrode. A pretreatment step for increasing the oxygen concentration in a contact portion with the second welding material, and a joining step for joining the first welding material and the second welding material by melting at least a part of the contact portion. Including welding method.

Description

  The present invention relates to a welding method and a welding apparatus, and in particular, in TIG welding and laser welding, as a pretreatment, a concentrated heat source is applied to a welding spot in an active gas to prepare a minute and local region in which oxygen is concentrated. The present invention relates to a welding method and a welding apparatus.

  In TIG welding, an electric arc is generated between the junction of two welding materials (materials to be welded) to be welded in an inert shielding gas such as argon and a tungsten electrode, and an arc (beam. This is a welding method in which the welding material is melted by the heat of “arc” to join the welding material.

  In the case of TIG welding, simply generating an arc does not normally concentrate the arc, so that the power density is low, the penetration of the welding material becomes shallow, and the efficiency when welding a thick welding material is lowered.

  That is, when the content of sulfur and oxygen in the weld metal is a certain value, for example, if iron, sulfur is about 50 ppm and if oxygen is about 70 ppm, it melts in the molten pool due to surface tension. If the direction of convection of the metal is reversed and the amount of sulfur or oxygen is greater than the above value, it flows in the direction of the arc (downward in the middle of the molten pool), and if the amount of sulfur or oxygen is less than the above value It flows in the direction opposite to the direction of the arc (upward in the middle of the molten pool) (FIGS. 3 and 4 of Patent Document 1). However, sulfur is removed as much as possible from the time of manufacture of the metal to be welded normally because it has an adverse effect such that the weld solidification cracking of the metal tends to occur when the content is large. In addition, oxygen is considered to have no problem as long as it is in the range of 500 pp or less from the viewpoint of corrosion resistance and low temperature toughness, but is usually as low as about 10 to 50 ppm. As a result, as it is, convection reverse to the direction of the arc occurs in the molten pool at the time of welding, and the penetration of the welding material becomes shallow.

In order to deepen the penetration of the weld material, an oxide-based flux is applied to the welded area in advance to increase the oxygen concentration in the molten metal and deepen the penetration so that convection occurs in the direction of the arc. A method of removing after welding (A-TIG welding method) has been developed and used (Patent Document 2).
In addition, a method (AA-TIG welding method) in which an appropriate amount of an active gas such as oxygen or carbon dioxide is mixed with an inert shielding gas to increase the penetration depth (AA-TIG welding method) has been developed (Patent Documents 3 and 4).
JP-A-6-277847 Japanese Patent Laid-Open No. 2002-120088 JP 2003-19561 A JP 2004-298963 A

However, since the A-TIG welding method needs to apply an oxide-based flux prior to welding and remove the flux after welding, it takes too much work.
In the AA-TIG welding method, oxygen in the inert shielding gas reacts with the tungsten electrode to generate WO ₃ , so that the tungsten electrode is heavily consumed.
For these reasons, it has been desired to develop a TIG welding method that does not use an oxide flux, consumes less tungsten electrode, and deeply penetrates.

  Also, in laser welding in which the welding material is melted with laser light and joined, the penetration is similarly shallow, so that an oxide-based flux is not used, and without increasing the output of the laser oscillation source, Moreover, development of a method with deep penetration has been desired.

  Furthermore, in laser welding, where welding materials are melted with laser light and joined, oxide penetration is not used and the output of the laser oscillation source is not increased. There was no desire to develop a method. In particular, in laser welding, when the power density is high, keyhole type welding is performed, and bubbles are generated from the tip of the keyhole, which is generated as porosity in the weld bead, so that the heat conduction type without keyhole is deep. Development of a welding method for forming a penetration weld has been desired.

The inventors of the present application have conducted intensive research to solve the above problems, and as a result of the pretreatment of welding, the penetration becomes deeper by increasing the oxygen concentration at the contact portion between the first welding material and the second welding material. The present invention has been found and the present invention has been completed.
The invention of each claim will be described below.

The welding method of the present invention is a welding method for welding a first welding material and a second welding material, and a pretreatment step for increasing the oxygen concentration in a contact portion between the first welding material and the second welding material; A welding method including a joining step of joining the first welding material and the second welding material by melting at least a part of the contact portion.
In the welding method of the present invention, in the pretreatment step, oxygen dissolves in the contact portion between the first welding material and the second welding material, or the contact portion reacts with oxygen to increase the oxygen concentration. For this reason, due to the influence of the surface tension, downward convection occurs in the center of the molten pool (in the cross section perpendicular to the welding direction of the molten pool), that is, convection along the direction of the arc and the direction of the laser beam occurs. As a result, the molten pool does not spread in the direction orthogonal to the welding direction, but deepens in the thickness direction of the weld material, and the penetration of the welded portion deepens.
For this reason, compared with the case of using a flux, it is not necessary to perform a labor-intensive operation of applying and removing the flux, and automation of the welding operation is further facilitated.
In the welding method of the present invention, the pretreatment step may include a step of increasing the oxygen concentration in the contact portion in a gas atmosphere containing an active gas.
In the welding method of the present invention, the pretreatment step may include a step of increasing the oxygen concentration in the contact portion by irradiating the contact portion with a heat source.
The active gas is oxygen or carbon dioxide, and the concentration of the active gas in the gas atmosphere may be 2% by volume or more.
Before creating a small, localized region enriched in oxygen by irradiating a location where the welding material is to be welded with a concentrated heat source in an active gas atmosphere or an inert shielding gas atmosphere containing an active gas. Welding that welds the portion to be welded while melting the oxygen-enriched micro-local region produced in the pretreatment step and an arc heat source or laser in an inert shielding gas atmosphere The welding method characterized by having a step is also within the scope of the present invention.

In the invention of the present application, in the pretreatment step, the portion where the welding material is welded is melted by being irradiated with a concentrated heat source in an active gas atmosphere or in an inert shield gas atmosphere containing an active gas. Oxygen dissolves or reacts with oxygen to create a micro, localized region enriched in oxygen. For this reason, when the part to be welded is melted with an arc heat source or a laser and welded, the oxygen concentration in the molten metal material in the molten pool increases, and the surface tension affects the molten pool (the welding direction of the molten pool). Downward convection occurs at the center of the cross section orthogonal to the arc, that is, along the direction of the arc and the direction of the laser beam. As a result, the molten pool does not spread in the direction orthogonal to the welding direction, but deepens in the thickness direction of the weld material, and the penetration of the welded portion deepens.
For this reason, compared with the case of using a flux, it is not necessary to perform a labor-intensive operation of applying and removing the flux, and automation of the welding operation is further facilitated.
Further, compared with the case where an appropriate amount of an active gas such as oxygen or carbon dioxide gas is mixed with the inert shielding gas to increase the penetration depth, the tungsten electrode is not severely consumed.
In arc welding, if there is an oxygen-enriched layer in the minute, local area of the part to be welded, the oxygen will melt into the molten pool during welding, so that the arc will concentrate at the center of the molten pool, Thus, it is considered that the electromagnetic convection from the concentrated molten pool top to the molten pool bottom, and the arcing effect of this arc also lead to the promotion of electromagnetic convection and contribute to the increase of the penetration depth.
In laser welding, an increase in absorption rate is thought to contribute to an increase in penetration depth.

Here, the contact portion between the first welding material and the second welding material is, for example, “a minute, local region”. The “fine, local region” may be in a range where the effect of the pretreatment is brought about, but in general, a region narrower than the weld bead width centering on a position where two plate materials are butted and welded, The width is usually about 3 mm, preferably about 1 mm, and the depth is about 3 mm or less, preferably about 0.5 mm.
In addition, since the oxygen-concentrated minute and local region where oxygen is concentrated during welding is extremely narrow and small in quantity, when welding the welding location depending on whether the region remains molten or cooled and solidified. The change in energy required for this is slightly less in the case of melting, and there is no significant difference. For this reason, the effect of the present invention is exhibited regardless of whether the region is melted or solidified.

Metals to be welded include steels including stainless steel that cause convection along the arc and laser direction in the weld pool when the active gas component elements melt, and titanium and aluminum for other non-ferrous metal materials. The metal.
The “active gas” is not limited as long as it is a gas that acts to narrow and deepen the welding depth of the metal to be welded by irradiating with a concentrated heat source, but generally if the metal to be welded is a steel-based metal , Oxygen or carbon dioxide gas that decomposes at high temperatures to generate oxygen.
The “concentrated heat source” is not limited as long as it is a concentrated heat source, but preferably includes laser irradiation, microplasma and the like. In particular, irradiation with a semiconductor laser is preferable because it is solid and inexpensive.

  In addition, it is the said welding method, Comprising: The said welding material (1st welding material and 2nd welding material) is a steel-type material, The welding method characterized by the above-mentioned is the range of the invention in this application.

  The welding material of the present invention is not limited as long as it is a material that causes a convection phenomenon that flows along the direction of the arc of the molten metal in the molten pool, but is not limited to steel materials, particularly carbon steel or stainless steel, especially austenitic stainless steel. The effects of the present invention are most exhibited in SUS304 (18-8 stainless steel) and SUS316 (18-8-2Mo stainless steel), which are steel.

  In the above welding method, the active gas in the pretreatment step is oxygen or carbon dioxide, and the inert shielding gas containing the active gas contains 2% by volume or more of oxygen or carbon dioxide. The welding method characterized by the above is also within the scope of the present invention.

As the active gas in the pretreatment step, oxygen or carbon dioxide is effective, and high purity oxygen is particularly preferable.
Further, when the inert shielding gas contains 2% by volume or more, preferably 30% by volume or more of oxygen or carbon dioxide gas, a sufficient pretreatment effect can be achieved.
In the case of carbon dioxide gas, it decomposes with high heat by irradiation of a concentrated heat source, and the generated oxygen contributes to the formation of a region where oxygen is concentrated.
Even if oxygen or the like is 30% by volume or less, depending on conditions, for example, when the moving speed of the concentrated heat source is slow or the welding material is thin, it is effective in the case of the non-ferrous material such as aluminum.

  In addition, the welding method, wherein the oxygen concentration in the molten pool in the welding step is 70 ppm or more, is also within the scope of the invention of the present application.

  In the invention of the present application, when the concentration of oxygen in the molten pool is 70 ppm or more, the convection generated in the molten pool is surely downward at the center of the cross section of the molten pool, that is, along the direction of the arc or laser beam. , The penetration of the welding material deepens.

  In addition, the welding method, wherein the welding using the arc heat source is TIG welding, is also within the scope of the invention of the present application.

  In TIG welding, electromagnetic convection along the arc is generated from the upper center of the molten pool to the lower (bottom) center, so that the effect of the present invention is further enhanced compared to laser welding.

  In addition, the welding method, wherein the concentrated heat source is a laser, is also within the scope of the invention of the present application.

  If a laser such as a carbon dioxide laser, YAG laser, semiconductor laser, fiber laser, disk laser, or semiconductor laser pumped solid-state laser is used, since no electrode is used, 100% oxygen can be used as a pretreatment. Become advantageous.

  In addition, the welding method in which the concentrated heat source has a higher power density than the arc heat source or laser used in the welding step is also within the scope of the invention of the present application.

  Because the power density (energy density) of the concentrated heat source is high, the oxygen-enriched region is easy to manufacture reliably and in a short time, even if it is a minute, local region where heat easily escapes to the surroundings. .

  In the welding method, the irradiation of the concentrated heat source moves a heat source having an output of 10 W or more at a speed of 1000 mm / s or less, welding in the welding step is TIG welding, and a welding speed is A welding method characterized by being 100 mm / s or less is also within the scope of the present invention.

In the invention in the present application, since the pretreatment is performed under the above conditions and then welding is performed, deep penetration is obtained.
Depending on the conditions, in the case of steel materials such as stainless steel, as a pretreatment, for example, irradiation with a concentrated heat source can be performed by moving a heat source with an output of 100 W at a speed of 10 to 30 mm / s. Since the amount of oxygen supplied to the pond is neither too much nor too little and is an appropriate amount, good TIG welding is performed.
The reason why the concentrated heat source is set to 100 W is that low power is desirable as much as possible in consideration of implementation.
As the speed in the next welding, the penetration becomes deeper as the welding speed is slower, but 1 to 3 mm / s may be sufficient depending on the plate thickness.

  In the above welding method, the irradiation of the concentrated heat source moves a heat source having an output of 10 W or more at a speed of 1000 mm / s or less, welding in the welding step is TIG welding, and 5 mm / s. A welding method characterized by performing deep penetration of 5 mm or more into the welding material at the following speed is also within the scope of the present invention.

In the invention of the present application, since a high-power density laser is used, it is possible to produce a minute and localized region enriched with oxygen in a relatively short time, and oxygen is sufficiently taken into the region. Will be. For this reason, when welding a comparatively thick welding material, the deep penetration depth will be obtained by one pass.
Depending on the conditions, in the case of a steel-based material such as stainless steel, as a pretreatment, for example, irradiation with a concentrated heat source moves a heat source with an output of 100 W at a speed of 3 mm / s or less, and 2 mm / s by TIG welding. A deep penetration of 7 mm or more is obtained in the welding material at the following speed, which is preferable.
Further, the welding speed depends on the thickness of the penetration welding, but is about 0.85 mm / s when the thickness is about 11 mm, and about 1.5 mm / s when the thickness is about 8 mm. Is preferred.

The welding apparatus of the present invention is a welding apparatus for welding a first welding material and a second welding material, pretreatment means for increasing the oxygen concentration in a contact portion between the first welding material and the second welding material; Further, by melting at least a part of the contact portion, a joining means for joining the first welding material and the second welding material is provided, whereby the effect of the present invention can be obtained.
The pretreatment means may include means for increasing the oxygen concentration of the contact portion in a gas atmosphere containing an active gas.
The pretreatment means may include irradiation means for increasing the oxygen concentration in the contact portion by irradiating the contact portion with a heat source.
The irradiation unit may be a laser.
The joining unit may include a melting unit that melts at least a part of the contact portion, and the power density of the irradiation unit may be higher than the power density of the melting unit.
It should be noted that a pre-processing unit for producing a minute, local region in which oxygen is concentrated by irradiating a location where welding material is to be welded with a concentrated heat source in an active gas atmosphere or an inert shielding gas atmosphere containing an active gas. And a welded portion for welding the portion to be welded while melting an oxygen-enriched minute and local region produced in the pretreatment portion with an arc heat source or laser in an inert shielding gas atmosphere. The welding apparatus characterized by having is also the scope of the invention in this application.

  The welding apparatus, wherein the concentrated heat source irradiated in the pretreatment section has a higher power density than the arc heat source or laser used in the welding section, is also within the scope of the present invention. It is.

  In the present invention, in the pretreatment step, oxygen dissolves in the contact portion between the first welding material and the second welding material, or the contact portion reacts with oxygen to increase the oxygen concentration. Therefore, in the joining step, downward convection occurs in the center of the cross section perpendicular to the welding direction of the molten pool in the molten pool due to the influence of surface tension, that is, convection along the direction of the arc and the direction of the laser beam occurs. The weld pool does not widen and deepens, resulting in a greater depth of penetration at the weld.

Therefore, it is possible to obtain an arc welding method that does not use an oxide-based flux, consumes less tungsten electrode, and deeply penetrates.
Further, a laser welding method can be obtained without using an oxide-based flux and without increasing the output of the laser oscillation source and deeply penetrating.

It is a figure which shows the mode of the welding location in TIG welding about 1st Example. It is a figure which shows the cross section of the welding location about 1st Example. It is a figure which shows the mode of the bead of a welding location about 1st Example. It is a figure which shows the cross section of the welding location in a laser welding, and the mode of a bead about 3rd Example. It is a figure which shows the welding apparatus of this invention.

Explanation of symbols

10A 1st welding material 10B 2nd welding material 11 Pre-processed part 12 Non-pre-processed part 13 Meandering 15 and 17 Places 16 and 18 where pre-processed part has been melted 19 where two plates are welded 20 Porosity 21 Unevenness 25 on the surface of the welded portion 25 Slag accumulation 30 Tip 31 of TIG welding machine Pretreatment means 32 Joining means 100 Welding device

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(Device of the present invention)
FIG. 5 shows the welding apparatus 100 of the present invention. The welding apparatus 100 is a welding apparatus that welds the first welding material 10 </ b> A and the second welding material 10 </ b> B, and includes a pretreatment unit 31 and a joining unit 32.
The pretreatment means 31 increases the oxygen concentration at the contact portion between the first welding material 10A and the second welding material 10B. The pretreatment means 31 includes means for increasing the oxygen concentration at the contact portion in a gas atmosphere containing an active gas. The pretreatment unit 31 includes an irradiation unit that irradiates the contact portion with a heat source. The irradiation means is, for example, a YAG laser.
The joining means 32 joins the first welding material 10A and the second welding material 10B by melting at least a part of the contact portion. The joining unit 32 includes a melting unit that melts at least a part of the contact portion.
In the welding apparatus 100, the pretreatment means 31 and the joining means 32 are provided separately, but the pretreatment means 31 and the joining means 32 are provided as long as the oxygen concentration at the contact portion can be increased before joining. And may be integrated.
(Test conditions)
The test conditions of various tests conducted to confirm the effect of the present invention will be described.
(1) Material Used The material used for welding is mainly austenitic stainless steel (SUS304, # 400 polished) commercial material (200 × 50 × 8 t) having a nominal value of 0.003% S (sulfur). For confirmation of the reproducibility of the phenomenon and comparative study, some experiments were also performed with 0.001% S material and 0.02% S material.
(2) Pretreatment step The pretreatment step is a step of increasing the oxygen concentration in the contact portion between the first welding material 10A and the second welding material 10B.
For example, a YAG laser was used as the irradiation means, and the portion to be butt welded was irradiated at an output of 100 W, a focal diameter of about 1 mm, and a moving speed of 0.85 mm / s to 30 mm / s.
This laser is an NEC YAG laser with a maximum output of 1.8 kW. It serves as a protection and pretreatment for the laser optical system, and oxygen (active gas) or a mixed gas of argon and oxygen (active gas) from a coaxial nozzle with a diameter of 6 mm. Gas).
When only oxygen was used as the active gas, a flow rate of 10 l / min to 20 l / min was passed.
Thus, according to the present invention, in the pretreatment step, for example, the oxygen concentration at the contact portion is increased in a gas atmosphere containing an active gas.

(3) Welding method (joining step)
The joining step is a step of joining the first welding material 10A and the second welding material 10B by melting at least a part of the contact portion.
Butt welding was performed on a copper block (250 × 200 × 30 t).
About TIG welding, a TIG welding apparatus provided with a melting means is used. Using a tungsten electrode containing Ce ₂ O ₃ with a diameter of 3.2 mm in DCEN mode (Direct Current Electrode Negative, DC rod minus), current from 75 A to 300 A, electrode height from 1 mm to 10 mm, nozzle diameter 11 mm, The nozzle height was 10 mm, and argon was flowed at 15 l / min as a shielding gas.
For laser welding, a YAG laser equipped with a melting means was used, the power was 3 kW, and argon was flowed at 30 l / min as a shielding gas.

(Test results)
Hereinafter, examples will be described with reference to comparative examples.
(First embodiment)
When butt welding the above-mentioned welding materials, the front half of the welded part was not pretreated for comparison, and only the rear half was pretreated. This is shown in FIG. In FIG. 1, 10A is a first welding material (a plate material to be welded), 10B is a second welding material (a plate material to be welded), 11 is a pretreated portion, and 12 is not pretreated. Reference numeral 19 denotes a butt contact portion (contact portion) of two plate members, that is, an end face of a welding portion, and 30 denotes a tip of a TIG welding machine (welding means 32). A thick line arrow indicates a welding direction.

  As the pre-processed portion 11, the upper end of the butt contact portion 19 of the two plate materials is irradiated with a YAG laser at an output of 100 W, a speed of 20 mm / s, and a flow rate of oxygen (active gas) of 10 l / min. The oxygen in the local melted part (contact part) having a depth of about 8 mm and a depth of about 0.2 mm was concentrated.

Thereafter, TIG welding was performed on the locally melted portion under the conditions of a current of 150 A, a welding speed of 2 mm / s, an argon flow rate of 15 l / min, and an electrode height of 2 mm. The penetration depth obtained was 4 mm.
When TIG welding was performed under the same conditions without pretreatment, the penetration depth was about 2 mm, and the width of the bead was wider than when pretreatment was performed.
As a result of a supplementary experiment conducted on the pre-treated portion 11 under the same conditions as described above, only the welding speed was changed to 1 mm / s, it was possible to penetrate through a plate having a thickness of 8 mm. The width ratio, D / W, was 1 or more.

  In FIG. 2, the cross section of a welding location is shown. (1) of FIG. 2 shows a cross section of a part that has been pretreated, and (2) shows a cross section of a part that has not been pretreated. In FIG. 2, 15 is a place where the penetration has been made in the pre-processed portion, and 16 is a place where the penetration has been made in the portion that has not been pre-treated. In both cases, the cross section of the welded part is symmetrical, but the pre-processed part has better objectivity, the bottom surface forms a beautiful curved surface, and the penetration depth (D) is large. It can be seen that the penetration width (W) is small and the D / W is 1 or more.

  In FIG. 3, the mode of the bead of a welding location is shown. As indicated by 14 in FIG. 3, the bead width widened at a position where the welding reached the pre-processed portion, and then a narrow bead was stably formed. Further, some meandering 13 and slag accumulation 25 were observed in the melted portion 16 in the untreated portion, but no bead meandering or obvious slag accumulation was observed in the pretreated portion 15. It was.

  From the above, it was found that the pretreatment increased the penetration depth to about twice, and nevertheless, good TIG welding was possible.

(Second embodiment)
In this example, in order to obtain deep penetration, when the welding current is large or when the welding speed is low, it is considered that a larger amount of oxygen needs to be supplied because the molten pool expands. In this case, the conditions under which penetration welding is possible were investigated.
Prior to the butt welding of the above-mentioned welding material, as pretreatment, a YAG laser is output at a welding point (contact portion between the first welding material 10A and the second welding material 10B) with an output of 100 W, a moving speed of 2 mm / s, oxygen (active gas) ) At a flow rate of 10 l / min to concentrate oxygen in the local melting part (contact part).
Thereafter, TIG welding was performed on the locally melted portion at a current of 200 A and a welding speed of 0.85 mm / s. In this case, through welding with a plate thickness of 11 mm was possible.
Further, when the welding speed was 1.5 mm / s, through welding with a plate thickness of 8 mm was possible.

For comparison, TIG welding was performed under the same conditions without performing pretreatment. In this case, the penetration depth was about 2 mm.
As a result, not only does the pretreatment deepen the penetration, but if the pretreatment speed is slowed down, the amount of oxygen concentration increases, so that it is possible to weld in one pass even if the plate thickness is large. .

(Third embodiment)
In this embodiment, laser welding is used instead of TIG welding in the first embodiment, and the pretreatment is the same as in the first embodiment.
Laser welding was performed using a YAG laser or a semiconductor laser under the conditions of an output of 3 kW, a welding speed of 10 mm / s, and an argon flow rate of 30 l / min.

  Also, as in the first example, for comparison, the front half of the welded portion was not pretreated, only the rear half was pretreated, and the difference due to the presence or absence of pretreatment was examined.

When the YAG laser when the defocusing distance is 20 mm and the semiconductor laser welding at the focal position are performed at 2 mm / s, the result similar to FIG. 2 (the cross section of the welded part is symmetrical, but the pre-processed part Is better in objectivity, has a beautiful curved bottom surface, has a large penetration depth (D), a small penetration width (W), and a D / W of 1 or more. ) Was observed, and deep penetration was obtained when pretreatment was performed in the same manner as in TIG welding. And it turned out that the welding part without a porosity is possible for heat conduction type welding.
Further, when YAG laser welding is performed so that the focal point of the laser is located on the surface of the welding material (the defocusing distance is 0 mm), the cross section of the welded portion and the state of the bead are shown in FIG. In FIG. 4, (1) shows the part which has been pre-processed, and (2) shows the part which has not been pre-processed. Further, in (1) and (2), the upper side is a cross-sectional view of a welded portion, and the lower side is a diagram showing a state of a bead. Furthermore, in FIG. 4, 20 is a porosity, 21 is the unevenness | corrugation of a welding location, and 29 shown with a dotted line is the centerline (above the butt contact part 19 of a welding material) of a welding location.
Compared to the case without pre-treatment, the pre-treatment is thin near the bead surface and the penetration depth is slightly increased, as can be seen from the narrow width of the area with surface irregularities. It was. Further, it can be seen that the porosity 20 in the melted place is reduced.
As a result, it can be seen that the pretreatment is effective for both laser welding, heat conduction type and keyhole type.

(Fourth embodiment)
As shown below, as a pretreatment, the laser irradiation speed of the irradiation unit was changed from 2 mm / s to 300 mm / s to examine how the welded portion changed. As a result, it was found that the amount of oxygen supplied to the molten pool during TIG welding can be controlled by changing the laser irradiation speed.
Furthermore, it has been found that the optimum laser irradiation speed is 10 mm / s to 30 mm / s.
The TIG welding conditions are the same as in the first example.

  The specific test results were as follows. First, at 2 mm / s and 5 mm / s, the beads were meandering as viewed from the surface, and a large amount of oxidized slag was adhered. Moreover, although the cross section was deeply penetrated, the melted part was asymmetrical in the left-right direction, or the center of the melted part was shallow. It seems that the bead was rough due to the large amount of oxygen supplied. In addition, the oxygen amount of the welding location was about 220 ppm at maximum at 2 mm / s.

  From 10 mm / s to 30 mm / s, the bead surface was clean, the melted part was symmetrical, and the bottom part was a beautiful curved surface. This is probably because the oxygen supply is appropriate. In addition, the oxygen amount of the welding location was about 135 ppm at the maximum at 20 mm / s.

  From 40 mm / s to 50 mm / s, the bead surface seems to meander again, the bead width is widening, and the penetration is becoming shallower. This is probably due to a shortage of oxygen supply.

  From 70 mm / s to 150 mm / s, the bead width was wider than that without pretreatment, and the penetration was extremely shallow. It seems to have deteriorated because of a slight supply of oxygen.

  At 200 mm / s or more, it was almost the same as the case where no pretreatment was performed. This is probably because the amount of oxygen is small, so there is no effect.

As a result, as described above, the amount of oxygen supplied to the molten pool during TIG welding can be controlled by changing the laser irradiation speed of the irradiation means, and 10 to 30 mm / s is an optimum laser irradiation speed. Not only was it known, but also the following:
When the welding material is a thick plate of 8 mm to 11 mm, the molten pool generated by welding becomes large. Therefore, if the pretreatment speed is slowed down to about 1 mm / s to increase the amount of oxygen dissolved in the minute and localized region where oxygen is concentrated, the amount of oxygen in the molten pool becomes just an appropriate concentration. Good welding can be obtained. As a result, through welding is obtained in one pass. Also, if the welding material is a plate thickness of about 4 mm, the oxygen concentration in the molten pool becomes appropriate if the pretreatment speed is about 2 mm / s, which is higher than that of a plate of 8 to 11 mm. The data that lead to the efficiency of the actual welding work, such as the ability to obtain appropriate through welding, was obtained.
The present invention has been described above.
The welding material of the present invention is not limited as long as it is a material that causes a convection phenomenon that flows along the direction of the arc of the molten metal in the molten pool. For example, steel-based materials, particularly carbon steel and stainless steel, However, the effects of the present invention are most exhibited in SUS304 (18-8 stainless steel) and SUS316 (18-8-2Mo stainless steel), which are austenitic stainless steels.
As the active gas in the pretreatment step, oxygen or carbon dioxide is effective, and high purity oxygen is particularly preferable.
Further, when the inert shielding gas contains 2% by volume or more, preferably 30% by volume or more of oxygen or carbon dioxide gas, a sufficient pretreatment effect can be achieved.
When the active gas is carbon dioxide, it is decomposed by high heat by irradiation with a concentrated heat source, and the generated oxygen contributes to the formation of a region where oxygen is concentrated.
Even if oxygen or the like is 30% by volume or less, depending on conditions, for example, when the moving speed of the concentrated heat source is slow or the welding material is thin, it is effective in the case of the non-ferrous material such as aluminum.
If lasers such as carbon dioxide laser, YAG laser, semiconductor laser, fiber laser, disk laser, semiconductor laser pumped solid laser are used as the irradiation means, since no electrode is used, 100% oxygen with a purity of 100% can be used. This is advantageous as a pretreatment.
The power density of the irradiation means is preferably higher than the power density of the melting means. When the power density (energy density) of the irradiation means is higher than the power density of the melting means, the oxygen-enriched area is reliable and short-time even if it is a minute, local area where heat easily escapes to the surroundings. This is because it becomes easy to manufacture.

Claims (9)

A welding method for welding a first welding material and a second welding material,
A pretreatment step for increasing the oxygen concentration of the contact portion between the first welding material and the second welding material;
A welding method including a joining step of joining the first welding material and the second welding material by melting at least a part of the contact portion.   The welding method according to claim 1, wherein the pretreatment step includes a step of increasing an oxygen concentration of the contact portion in a gas atmosphere containing an active gas.   The welding method according to claim 1, wherein the pretreatment step includes a step of increasing an oxygen concentration of the contact portion by irradiating the contact portion with a heat source. The active gas is oxygen or carbon dioxide,
The welding method according to claim 2, wherein the concentration of the active gas in the gas atmosphere is 2% by volume or more. A welding apparatus for welding a first welding material and a second welding material,
Pretreatment means for increasing the oxygen concentration of the contact portion between the first welding material and the second welding material;
A welding apparatus comprising: a joining unit that joins the first welding material and the second welding material by melting at least a part of the contact portion.   The welding apparatus according to claim 5, wherein the pretreatment means includes means for increasing an oxygen concentration of the contact portion in a gas atmosphere containing an active gas.   The welding apparatus according to claim 5, wherein the pretreatment unit includes an irradiation unit that irradiates the contact portion with a heat source to increase an oxygen concentration in the contact portion.   The welding apparatus according to claim 7, wherein the irradiation unit is a laser. The joining means includes a melting means for melting at least a part of the contact portion,
The welding apparatus according to claim 7, wherein a power density of the irradiation unit is higher than a power density of the melting unit.

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