JP2021137862A - Welding method - Google Patents

Abstract

To provide a welding method in which occurrence of weld defects such as a dent of a rear side of a part to be welded after welding operation is completed can be suppressed and is handy and versatile.SOLUTION: The welding method includes a welding step in which when welding an object 10 to be welded by applying one energy A selected out of a heat energy and a light energy to a part WZ to be welded of the object to be welded, through a front side of the part WZ to be welded, the object to be welded is welded under the condition that pressure of atmosphere gas in the vicinity of the front side of the part WZ to be welded is set to be equal to barometric pressure and pressure of atmosphere gas in the vicinity of a rear side of the part WZ to be welded is set to be less than barometric pressure.SELECTED DRAWING: Figure 1

Description

The present invention relates to a welding method.

In the case of welding, it is necessary to suppress the occurrence of welding defects such as dents and oxidation in the welded portion of the object to be welded after the welding is completed.

As a method for preventing oxidation, a method of using an inert gas such as argon gas as a shield gas is widely known. For example, Patent Document 1 proposes a technique of welding the inside of a metal pipe while reducing the pressure with a vacuum pump while the chamber type torch is attached to the outer peripheral portion of a butt joint of the metal pipe. In this technique, the shield gas supplied in the closed space surrounded by the chamber type torch and the outer peripheral portion of the butt joint is sucked into the inside of the metal pipe through the gap of the butt joint portion. Then, the shield gas sucked into the metal pipe acts as a back shield gas, prevents oxidation of the back wave bead, and enables good welding.

Further, as a method for preventing the dent, for example, the technique described in Patent Document 2 and the like can be mentioned. In the technique described in Patent Document 2, a slit-shaped gas outlet formed along the root surface where the welded materials are abutted is provided on the back surface side of the groove formed by abutting the welded materials made of aluminum material. Welding is performed with the backing member placed. Therefore, since gas such as shield gas and air is discharged from the gas discharge port at the time of welding, the gas pool on the back surface side of the groove is reduced, and the root concavity (root dent) in the back bead can be suppressed.

Japanese Unexamined Patent Publication No. 2-70380 Japanese Unexamined Patent Publication No. 2016-16447

However, in the technique described in Patent Document 1, it is necessary to use a dedicated chamber type torch instead of the usual welding torch. Further, in the technique described in Patent Document 2, in order to reduce gas accumulation on the back surface side of the groove, a backing member that accurately corresponds to the dimensional shape of the material to be welded is prepared, and then the back surface side and the back surface of the groove are prepared. It is necessary to accurately align the contact member with the gas outlet. On the other hand, if the material constituting the material to be welded is a material that is difficult to oxidize, such as aluminum, oxidation during welding does not matter. However, even in this case, the possibility that a dent on the back side of the welded portion of the workpiece to be welded may occur remains.

Therefore, the conventional welding methods exemplified in Patent Documents 1 and 2 and the like can suppress the occurrence of welding defects such as dents on the back side of the welding target portion after the completion of the welding work, but tend to lack convenience and versatility. ..

The present invention has been made in view of the above circumstances, and is a welding method that can suppress the occurrence of welding defects such as dents on the back side of the welding target portion after the completion of welding work, and is more convenient and versatile. The challenge is to provide.

The above object is achieved by the following invention. That is, in the welding method of the present invention, when welding is performed by applying one of heat energy and light energy selected from thermal energy and light energy to the welding target portion from the front side of the welding target portion of the object to be welded. It is characterized by including a welding step in which welding is performed in a state where the pressure of the atmospheric gas near the front side of the welding target portion is set to atmospheric pressure and the pressure of the atmospheric gas near the back side of the welding target portion is set to less than atmospheric pressure.

In one embodiment of the welding method of the present invention, the atmospheric gas near the back side of the welding target portion is preferably an inert gas.

In another embodiment of the welding method of the present invention, it is preferable that the material constituting the object to be welded is any easily oxidizing material selected from stainless steel, titanium, nickel and zirconium.

In another embodiment of the welding method of the present invention, it is preferable that the atmospheric gas near the back side of the welding target portion is air.

In another embodiment of the welding method of the present invention, it is preferable that the material constituting the object to be welded is any non-oxidizing material selected from aluminum, iron and mild steel.

In another embodiment of the welding method of the present invention, it is preferable to perform welding while changing the angle formed by the direction of gravity and the direction of applying the energy in the welding step.

In another embodiment of the welding method of the present invention, the welding target portion is formed by abutting the groove-side end of the first work piece and the groove-side end of the second work piece. It is preferable to include a weld groove and a portion in the vicinity thereof.

In another embodiment of the welding method of the present invention, the shape of the groove formed by abutting the groove-side end of the first work piece and the groove-side end of the second work piece. Is preferably I-shaped.

In another embodiment of the welding method of the present invention, the welding target portion is formed by abutting the end portion of the second plate-shaped workpiece against one surface of the first plate-shaped workpiece. It is preferable to include a welded corner and a portion in the vicinity thereof.

According to the present invention, it is possible to provide a welding method that can suppress welding defects such as dents on the back side of the welding target portion after the completion of welding work and is more convenient and versatile.

It is a schematic diagram which shows an example of the welding method of this embodiment. Here, FIG. 1A is a diagram showing a state before applying thermal energy (arc A) to the welding target portion WZ, and FIG. 1B is a diagram showing heat with respect to the welding target portion WZ. It is also an enlarged view showing a state in which energy (arc A) is being applied and an enlarged state in the vicinity of the welding target portion WZ shown in FIG. 1 (A). It is a schematic cross-sectional view which shows an example after welding is completed by the welding method of this embodiment illustrated in FIG. It is a schematic cross-sectional view which shows an example after welding is completed by the conventional welding method. It is a schematic diagram which shows another example of the welding method of this embodiment. It is a schematic cross-sectional view which shows another example after welding is completed by the conventional welding method.

In the welding method of the present embodiment, when welding is performed by applying either heat energy or light energy selected from thermal energy and light energy to the welding target portion from the front side of the welding target portion of the object to be welded. Welding process in which the pressure of the atmospheric gas near the front side of the welding target is set to atmospheric pressure and the pressure of the atmospheric gas near the back side of the welding target is less than atmospheric pressure (hereinafter, may be referred to as the main welding process). Is).

In the welding method of the present embodiment, the relationship of "pressure of atmospheric gas near the front side of the welding target portion> pressure of atmospheric gas near the back side of the welding target portion" is always maintained during the welding work in the main welding step. .. Therefore, it is possible to prevent the back side of the welding target portion from being dented. This is because a force due to the pressure difference acts between the front side and the back side of the welding target portion in the direction from the front side to the back side, so that the back side of the welding target portion is less likely to be dented.

Further, in order to maintain the pressure of the atmospheric gas near the back side of the welding target portion below the atmospheric pressure, in addition to the vacuum pump, a simple structure is formed in which a closed space is formed near the back side of the welding target portion as needed. All you have to do is use a welding jig. In addition to this, welding is performed with the pressure of the atmospheric gas near the front side of the welding target portion set to atmospheric pressure. Therefore, as illustrated in Patent Document 1, it is not necessary to use a complicated welding device lacking versatility, such as a chamber type torch in which the pressure in the chamber is filled with a shield gas exceeding the atmospheric pressure. If the welding method can be used under atmospheric pressure, thermal energy (such as Tig welding, plasma welding, coated arc welding, mug welding, MIG welding, self-shielded arc welding, etc.), gas welding, laser welding, etc. Any of the known welding methods in which one of energy selected from arc, flame, etc.) and light energy (laser light, etc.) is applied to the welding target portion from the front side of the welding target portion can be used. In addition to this, it is not necessary to use a jig that is largely lacking in versatility, such as a backing member that accurately corresponds to the dimensional shape of the material to be welded, as exemplified in Patent Document 2.

As described above, the welding method of the present embodiment is excellent in terms of simplicity and versatility as well as being able to suppress welding defects such as dents on the back side of the welding target portion after the welding work is completed.

In this welding step, a period (pressure) in which the pressure of the atmospheric gas near the front side of the welding target portion is set to atmospheric pressure and the pressure of the atmospheric gas near the back side of the welding target portion is kept below atmospheric pressure (pressure). The control period) can be appropriately selected. However, from the viewpoint of more reliably suppressing the occurrence of welding defects such as dents, the starting point of the pressure control period is usually (1) a time point before the energy required for welding is applied to the welding target portion. The end point of the pressure control period is (2) a state in which the energy required for welding is applied to the welding target portion, and once the temperature rises, it is easily deformed and softened. It is preferable that the welded portion is cooled and completely solidified again. In particular, by setting the end point of the pressure control period to the time point shown in (2) above, the occurrence of welding defects such as dents can be suppressed more reliably.

The atmospheric gas in the vicinity of the front side and the vicinity of the back side of the weld target portion can be appropriately selected according to the material constituting the object to be welded. For example, when the material constituting the work piece is a material that is difficult to oxidize (non-oxidizing material) such as aluminum, iron, and mild steel, it is preferable to select air as the atmospheric gas.

On the other hand, when the material constituting the work piece is a material that is easily oxidized (easy-oxidizing material) such as stainless steel, titanium, nickel, and zirconium, an inert gas such as Ar gas or He gas is used as the atmospheric gas. It is preferable to select. When the material to be welded is composed of an alloy material containing a large amount of alloying elements such as iron alloy and aluminum alloy, it is a refractory material depending on the type and content of the alloying element contained in the alloying material. In some cases, it may be an easily oxidizable material.

The backside pressure during the welding work in this welding process can be appropriately selected within the range of less than atmospheric pressure, but it varies in back wave welding and fillet welding where the welding quality on the back side of the welding target portion is also required. From the viewpoint of stably suppressing the dent on the back side of the welding target part even when welding is performed under different conditions, the gauge pressure is -0.1 kPa to -2.0 kPa (approximately 760 mmHg in terms of absolute pressure). It is preferably in the range of 745 mmHg), more preferably in the range of −0.1 kPa to −1.4 kPa, and more preferably in the range of −0.2 kPa to −0.8 kPa. By setting the backside pressure within the above range, it is possible to more reliably suppress the dent on the back side of the welding target portion, and it is also easy to form a convex back wave bead having an appropriate height during back wave welding. become. Further, the backside pressure during the welding work is preferably maintained at a substantially constant pressure over time, for example, within the range of ± 0.3 kPa (± 2.25 mmHg) based on the average pressure during the welding work. It is preferably maintained, and more preferably maintained within the range of ± 0.15 kPa.

In the welding method of the present embodiment, it is desirable to weld the object to be welded by performing only the main welding step, but if necessary, the main welding step and the welding conditions different from the main welding step may be used. Welding of the object to be welded may be performed by performing the welding in combination with other welding steps. As a welding method in which the main welding process and other welding processes are combined, for example, one of the thermal energy and the light energy selected from the front side of the welding target portion of the object to be welded and the welding target portion with respect to the welding target portion. When welding is performed by applying energy, the pressure of the atmospheric gas near the front side of the welding target portion is set to atmospheric pressure, and the pressure of the atmospheric gas near the back side of the welding target portion is set to exceed the atmospheric pressure. The welding process (pre-welding process) and the second welding process (main welding) in which the pressure of the atmospheric gas near the front side of the welding target portion is set to atmospheric pressure and the pressure of the atmospheric gas near the back side of the welding target portion is set to less than atmospheric pressure. Step) and may be carried out in this order. Here, in the pre-welding step and the main welding step, the atmospheric gases in the vicinity of the front side and the vicinity of the back side of the welding target portion are all inert gases.

A welding method in which the pre-welding step and the main welding step are carried out in this order is particularly suitable when the following conditions (A) and (B) are satisfied.
(A) The material constituting the work piece is made of an easily oxidizable material.
(B) The welding target portion before the start of the welding work has a gap in which the front side and the back side of the welding target portion communicate with each other. It should be noted that such a gap is formed in, for example, a groove formed by abutting the groove-side end of the first work piece and the groove-side end of the second work piece. NS.

When the pre-welding step and the main welding step are performed in this order on the welding target portion satisfying the conditions (A) and (B), the pre-welding step provides a gap communicating the front side and the back side of the welding target portion. It is carried out for the purpose of sealing. As a result, in the main welding process, when the pressure on the back side of the welding target portion becomes negative, air leaks to the back side of the welding target portion through the gap, so that the welding target portion after the welding is completed. It is possible to more reliably prevent oxidation from occurring on the back side.

The pre-welding step is not limited to the above-mentioned welding conditions as long as it can seal the gap communicating between the front side and the back side of the welding target portion, and may be appropriately performed under other welding conditions. can. For example, it is considered that the welding method described in Patent Document 1 can be carried out as a pre-welding step. However, from the viewpoint of making the entire welding process including the main welding process simple and excellent in versatility, it is particularly preferable to carry out the pre-welding process under the above-mentioned welding conditions.

Next, a specific example of the welding method of the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic view showing an example of the welding method of the present embodiment. Specifically, the groove formed by abutting the groove side ends of two objects to be welded is welded. It is a schematic diagram explaining the case of forming a butt joint. Here, FIG. 1A is a diagram showing a state before applying thermal energy (arc A) to the welding target portion WZ, and FIG. 1B is a diagram showing heat with respect to the welding target portion WZ. It is also an enlarged view showing a state in which energy (arc A) is being applied and an enlarged state in the vicinity of the welding target portion WZ shown in FIG. 1 (A). In each of the figures shown in FIGS. 1 and 2 and thereafter, the X direction indicated by the double-headed arrow means the horizontal direction, and the Y direction orthogonal to the X direction means the vertical direction. Unless otherwise specified, the Y2 direction means a direction that coincides with the gravitational direction. In this case, the Y1 direction is referred to as "up", "upward", etc., and the Y2 direction is "down". , "Downward" and the like. Further, in each of the drawings shown in FIGS. 1 and 2 and subsequent sections, cross-sectional views are shown for the members other than the welding torch 20.

As shown in FIG. 1, first, in welding, two plate-shaped objects to be welded (first object to be welded 10A and second object to be welded 10B) are used as the object to be welded 10, and the first The upper surface 12A and the lower surface 14A of the object to be welded 10A and the upper surface 12B and the lower surface 14B of the second object to be welded 10B are flush with each other, and these four surfaces 12A, 12B, 14A and 14B are parallel to the X direction. The V-shaped groove G is formed by abutting the groove side end portion 16E of the first work piece 10A and the groove side end portion 16E of the second work piece 10B in a state of being arranged so as to form. To form. Here, the groove G and its vicinity are the portions to be the welding target portion WZ. Next, the welding torch 20 used for arc welding is arranged on the upper side of the groove G. Further, a region consisting of a bottom side or a lower side of the groove G (the back side of the welding target portion WZ) and a peripheral portion of the lower surfaces (surfaces) 14A and 14B of the objects to be welded 10A and 10B on the lower side of the groove G. (The protective region 14P1 (a portion including one region of the lower surface 14A and one region of the lower surface 14B adjacent thereto) is covered with a box-shaped sealing member 30 having an opening 32 in order to block the outside air.

In the box-shaped sealing member 30, one of the six surfaces has an opening 32 on the entire surface, and a region of the lower surfaces 14A and 14B surrounded by the opening 32 forms a protective region 14P1. Therefore, a closed space S surrounded by the closed member 30 and the protected area 14P1 located so as to block the opening 32 thereof is formed, and as a result, the protected area 14P1 is blocked from the outside air. It will be surrounded by. At this time, the sealing member 30 is placed on the lower surfaces (surfaces) 14A and 14B of the objects to be welded 10A and 10B so that there is no gap between the sealing member 30 and the lower surfaces (surfaces) 14A and 14B of the objects to be welded 10A and 10B. Adhere to the surface without any gaps. If necessary, a heat-resistant tape or the like may be used for sealing treatment so as to more reliably close the gap. Then, when carrying out this welding step, depending on the material of the object to be welded 10, the inside of the closed space S is (i) an inert gas having a pressure of less than atmospheric pressure, or (ii) a pressure of less than atmospheric pressure. It shall be filled with a gas containing oxygen (usually air). In addition, in order to realize the state shown in (i) or (ii), a vacuum pump is used to appropriately evacuate the inside of the closed space S, or an inert gas supply source such as an argon gas cylinder is sent into the closed space S. And supply an inert gas as appropriate. At this time, the vacuum exhaust and the supply of the inert gas may be carried out discontinuously or continuously. If the enclosed space S is previously filled with an inert gas having an atmospheric pressure or a pressure higher than that before the start of the main welding process, vacuum exhaust is performed in order to realize the state shown in (i). You can just do it.

A gas exhaust pipe 34, a gas supply pipe 36, and a pressure gauge (not shown in the figure) are connected to the sealing member 30. Here, one end on the side connected to the sealing member 30 of the gas exhaust pipe 34 and the other end on the opposite side are connected to a vacuum pump (not shown in the figure) such as a rotary pump. Further, a flow rate adjusting valve is appropriately provided in the middle of the gas exhaust pipe 34, and a flow rate adjusting valve and a flow meter are appropriately provided in the middle of the gas supply pipe 36. Further, the other end of the gas supply pipe 36 on the side connected to the sealing member 30 and the other end on the opposite side are connected to an inert gas supply source (not shown in the figure) such as an Ar gas cylinder, or the outside air. It is open to (atmospheric pressure air). On the other hand, the welding torch 20 and the object to be welded 10 are connected to a welding power source (not shown in the drawing), and a rod-shaped electrode 22 is provided at the tip of the welding torch 20. The welding rod used at the time of welding may also serve as the rod-shaped electrode 22, or may be prepared separately from the rod-shaped electrode 22.

Next, an example of the welding procedure when a refractory material such as aluminum is used as the material constituting the object to be welded 10 will be described.

First, by operating a vacuum pump, the air in the closed space S is exhausted to the outside of the closed member 30, and the pressure (backside pressure) in the closed space S is appropriately desired within a range of less than atmospheric pressure. Adjust to pressure. The pressure is appropriately adjusted by using, for example, a flow rate adjusting valve provided in the middle of the gas supply pipe 36 in a state where the other end is open to the outside air. Then, welding is performed in this state. At this time, since an arc A is generated between the tip of the rod-shaped electrode 22 of the welding torch 20 and the groove G of the object to be welded 10, the welding object WZ is viewed from the front side of the welding object WZ of the object 10 to be welded. Thermal energy (arc A) is applied to the heat energy (arc A).

Therefore, during the welding operation, the atmospheric gas near the front side of the welding target portion WZ is always the outside air (air at atmospheric pressure), whereas the sealing around the back side of the welding target portion WZ (that is, the protected area 14P1) is sealed. The atmospheric gas in the space S is air having a pressure lower than the atmospheric pressure. Therefore, due to the pressure difference generated between the front side and the back side of the welding target portion WZ, a force in the direction from the front side to the back side of the welding target portion WZ always acts during the welding operation. Therefore, after the welding is completed, the back wave bead B having a sufficient bulge is formed without the dent 40 on the back side of the welding joint portion C corresponding to the welding target portion WZ at the time of welding as illustrated in FIG. .. That is, the back side of the welded joint C (weld target portion WZ at the time of welding) after the completion of welding is formed with a dent 40 as illustrated in FIG. 3, and a back wave bead with insufficient swelling is formed. Welding can be suppressed more reliably.

Such effects are obtained when (1) the width of the groove G is narrow (particularly, the groove side end portion 16E of the first work piece 10A and the groove side end portion 16E of the second work piece 10B). The shape of the groove G formed by abutting the two is I-shaped), and (2) unlike the example shown in FIG. 1, the direction E for applying the energy required for welding and the direction of gravity (Y2). It is necessary for welding when the angle (direction) does not match and the angle formed by both (working angle at the time of welding) is increased (especially when the direction of gravity is 0 degrees and the direction on the opposite side is 180 degrees). Even when the direction E for applying energy (welding direction E) is around 180 degrees, it is stably exhibited.

In the case shown in (1) above, since the width of the groove G is narrow, normally, the molten or semi-molten metal M existing in the welding target portion WZ is moved from the front side to the back side of the welding target portion WZ. Flow is easily blocked. Therefore, after the welding work is completed, the back side of the welding target portion WZ is likely to be dented. However, in the welding method of the present embodiment, due to the pressure difference between the front side and the back side of the welding target portion WZ, the molten or semi-molten metal M existing in the welding target portion WZ is moved from the front side to the back side of the welding target portion WZ. Since the flow is promoted, it is easy to suppress the occurrence of dents.

Regarding the case shown in (2) above, for example, in the example shown in FIG. 1, the Y1 direction coincides with the gravity direction, in other words, the working angle at the time of welding is 180 degrees. Suppose there is. In this case, normally, the molten or semi-molten metal M existing in the welding target portion WZ is subjected to a force that always tends to flow toward the Y1 direction (gravity direction) due to the action of gravity. Will be done. However, in the welding method of the present embodiment, due to the pressure difference between the front side and the back side of the welding target portion WZ, the molten or semi-molten metal existing in the welding target portion WZ is moved from the front side to the back side of the welding target portion WZ ( That is, since a force that tends to flow acts in the Y2 direction, which is the opposite of the Y1 direction (gravity direction), it is easy to suppress the occurrence of dents.

Therefore, even when the angle formed by the gravity direction and the direction E (welding direction E) to which the energy required for welding is applied when welding to the object to be welded is different (working angle at the time of welding), the angle is different. By using the welding method of the present embodiment, the occurrence of dents can be easily suppressed at any working angle. In other words, in order to suppress the occurrence of dents, it is not necessary to rotate the object to be welded while the working angle is fixed at a substantially constant angle during welding. Therefore, in the welding method of the present embodiment, when welding is performed while changing the working angle (for example, the groove formed by abutting the ends of two pipes is 360 degrees around the entire circumference along the circumferential direction. It can also be suitably used in cases such as welding). In this case, the maximum fluctuation range of the working angle can be arbitrarily selected in the range of more than 0 degrees and 360 degrees or less depending on the shape and structure of the work piece, but the above-mentioned effect is more effectively exhibited. From 90 degrees or more and 360 degrees or less is preferable, and 180 degrees or more and 360 degrees or less is more preferable. The change in the working angle may be continuous as in the pipe welding described above, or may be discontinuous.

In the specification of the present application, the "direction E for applying energy" required for welding is parallel to the central axis of the energy applied to the welding target portion WZ and is on the front side of the welding target portion WZ. It means the direction toward. For example, in the case of performing arc welding using the welding torch 20 shown in FIG. 1, the welding target portion is parallel to the central axis of the rod-shaped electrode 22 of the welding torch 20 and is formed from the tip side of the rod-shaped electrode 22. It means the direction toward the front side of the WZ (direction E shown in FIG. 1B). Further, when gas welding is performed using a welding torch for gas welding, it means the central direction of the ejected gas (flame) ejected from the crater of the welding torch so as to spread in a conical shape. Further, when laser welding is performed, it means the direction in which the laser beam is incident on the front side of the welding target portion WZ.

Next, an example of the welding procedure when an easily oxidizing material such as stainless steel is used as the material constituting the object to be welded 10 will be described.

In this case, an inert gas such as Ar gas or He gas is used as the shield gas. As a result, during welding, the atmospheric gas in the vicinity of the front side and the vicinity of the back side of the welding target portion WZ is used as an inert gas, so that oxidation of the front side and the back side of the welding target portion WZ can also be prevented. When a refractory material such as aluminum is used as the material constituting the object to be welded 10, it is not necessary to use an inert gas.

Then, as shown in FIG. 1A, when the welding target portion WZ before the start of the welding work includes the groove G (that is, the gap communicating the front side and the back side of the welding target portion WZ), first, a name is attached. By performing the pre-welding process by welding or the like, the gap formed in the groove G is sealed. Then, the main welding process is carried out next. By carrying out the pre-welding process prior to the main welding process, it is possible to more reliably suppress the oxidation of the back surface side of the welding target portion after the welding is completed.

Here, the inert gas can be supplied to the vicinity of the front side of the welding target portion WZ via a welding torch 20 connected to an inert gas supply source (not shown in the figure) such as an Ar gas cylinder. Since the space near the front side of the welding target portion WZ is open to the outside air, even if the inert gas is supplied to the vicinity of the front side of the welding target portion WZ, the atmospheric gas near the front side of the welding target portion WZ (inert). The pressure of the gas) remains atmospheric. Further, the inert gas is supplied to the vicinity of the back side of the welding target portion WZ via a gas supply pipe 36 whose other end is connected to an inert gas supply source (not shown in the figure) such as an Ar gas cylinder. At this time, in the main welding step, the gas in the closed space S is evacuated or the inside of the closed space S is evacuated at an appropriate timing so that the pressure in the closed space S is always filled with the inert gas having a pressure lower than the atmospheric pressure. The vacuum exhaust of the gas and the supply of the inert gas into the closed space S may be performed. When the pre-welding step and the main welding step are sequentially carried out using the sealing member 30, in the state after the pre-welding step using the sealing member 30 is completed as described later, the inside of the closed space S is usually inside. , Filled with an inert gas at a pressure equal to or greater than atmospheric pressure. Therefore, when the airtightness of the closed space S with respect to the outside air is sufficiently secured, the inert gas in the closed space S is evacuated until the pressure becomes lower than the atmospheric pressure before the start of the main welding process. It may be just.

On the other hand, in the pre-welding step, the atmospheric gas at least near the back side of the welding target portion WZ is replaced with an inert gas exceeding the atmospheric pressure, and then welding is performed. The method of replacing the atmospheric gas at least near the back side of the weld target portion WZ with an inert gas exceeding atmospheric pressure is not particularly limited. For example, a) a gas exhaust pipe when the sealing member 30 shown in FIG. 1 is used. Inert gas may be supplied into the closed space S through the gas supply pipe 36 with the outlet side of 34 sealed, or b) a pair of objects to be welded 10A and 10B are made of cylindrical members. In some cases, a commercially available general-purpose welding jig (for example, purge dam, purge ring, etc.) may be used, or an inert gas may be used inside the cylindrical member with both ends sealed. May be supplied.

In the example shown in FIG. 1, plate-shaped members were used as the objects to be welded 10A and 10B, but the shapes of the objects to be welded 10A and 10B are not limited to this, and for example, a circular tubular member. There may be. Further, the welding jig used to set the pressure of the atmospheric gas near the back side of the welding target portion WZ to less than atmospheric pressure and to make the atmospheric gas an inert gas as needed is shown in the box shown in FIG. The welding jigs having various shapes and structures can be appropriately used depending on the shape and structure of the objects to be welded 10A and 10B and the welding target portion WZ, and the like. When the adhesion of the sealing member 30 to the objects to be welded 10A and 10B is low and gas leaks easily between the sealed space S and the outside air, for example, the inner chamber composed of the closed space S and the inner chamber thereof. A double-structured sealing member or the like, which is provided so as to surround the outside and is composed of an outer chamber filled with an inert gas at the time of welding in the main welding step, may be used.

Further, the welding method of the present embodiment can be used for welding various welded joints other than groove welding of butt joints (provided that back wave welding is performed) as illustrated in FIG. For example, (1) groove welding of butt joints, T joints, cross joints and square joints (however, when back wave welding is performed), (2) fillet welding of T-shaped joints, padding joints and lap joints, etc. But it can be used. Further, it is also preferable to use the welding method of the present embodiment when the plate to be welded is particularly thin (particularly when the plate thickness is 1 mm or less) in (3) welding and slot welding. This is because when a thin plate material is used for wire welding or slot welding by a conventional welding method, the influence of heat generated during welding extends to the back surface side, and oxidation and dents on the back surface side are likely to occur. FIG. 4 is a schematic view showing another example of the welding method of the present embodiment. Specifically, FIG. 4 is a T-shape by fillet welding two objects to be welded so as to form a T-shape. It is a schematic diagram explaining the case of forming a joint.

In the example shown in FIG. 4, two first plate-shaped workpieces 10C and a second plate-shaped workpiece 10D are used as the workpiece 10, and one of the first plate-shaped workpieces 10C is used. According to the welding method of the present embodiment, the corner portion CN formed by abutting the end portion 18E of the second plate-shaped workpiece 10D against the surface (upper surface 12C) and the portion in the vicinity thereof are used as the welding target portion WZ. Fillet welding of T-shaped joints is performed. In this case, the welding torch 20 is arranged at a position facing the corner CN. In the example shown in FIG. 4, only the state in which the welding torch 20 is arranged at the position facing the corner CN on one side of the two corner CNs is shown, but usually the corner on the other side is shown. The same welding is performed on the part CN. Further, the sealing member 30 is a portion of the other surface (lower surface 14C) of the first plate-shaped workpiece 10C on which the end portion 18E of the second plate-shaped workpiece 10D is arranged in the horizontal direction X. The region (protection region 14P2) including the corresponding region and its vicinity is covered with the sealing member 30 in order to block it from the outside air. Then, in this state, welding is performed by the welding method of the present embodiment in the same manner as in the case illustrated in FIG. As a result, after the welding is completed, the dent of the protective region 14P2 on the back side of the welding target portion WZ can be suppressed, and even when the first plate-shaped workpiece 10C is made of an easily oxidizable material. Oxidation of the protected region 14P2 is also suppressed. In the example shown in FIG. 4, the welding target portion WZ before the start of the welding work does not have a gap communicating the front side and the back side of the welding target portion WZ. Therefore, even when the first plate-shaped object to be welded 10C is made of an easily oxidizable material, only the main welding step needs to be performed at the time of welding.

When welding is performed with the pressure of the atmospheric gas near the back side of the welding target portion WZ as the atmospheric pressure as in the conventional welding method, the welding work is completed on the lower surface 14C as illustrated in FIG. A recess 42 is likely to be formed in the region 14D (the region substantially corresponding to the protection region 14P2 referred to in FIG. 4) corresponding to the back side of the later welding target portion WZ (welding joint portion C). This is because, at the time of welding, the vicinity of the portion J to which the end portion 18E of the second plate-shaped workpiece 10D of the first plate-shaped workpiece 10C is abutted is first heated to a high temperature by the heat of the arc A. By being heated, it becomes easy to be deformed and softened, and subsequently, volume shrinkage occurs in the process of cooling after being no longer directly exposed to the heat of arc A, which causes the formation of a dent 42 (so-called sink mark) in the region 14D. it is conceivable that. However, in the welding method of the present embodiment, the vicinity of the portion J to which the end portion 18E of the second plate-shaped welded object 10D of the first plate-shaped workpiece 10C is abutted is directly exposed to the heat of the arc A. The pressure of the atmospheric gas near the front side of the weld target WZ is set to atmospheric pressure, and the atmospheric gas near the back side of the weld target WZ is set to atmospheric pressure even before the fluidity is lost and the weld is completely solidified after the exposure is stopped. The pressure is maintained below atmospheric pressure. That is, due to the pressure difference generated between the front side and the back side of the welding target portion WZ, a force in the direction from the front side to the back side of the welding target portion WZ always acts during the welding operation. Therefore, it is possible to suppress the occurrence of a dent 42 on the back side of the welding target portion WZ (welding joint portion C) after the welding is completed.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

(Example 1)
In the embodiment shown in FIG. 1, the welding test was carried out under the conditions shown below.
<Welding conditions>
(1) Welded objects 10A, 10B: Stainless steel plate (plate thickness: 3 mm)
(2) Welding method: TIG welding (3) Welding torch 20: Commercially available welding torch (unlike the chamber type torch shown in Patent Document 1, a general welding torch in which the welding torch body is open to the outside air)
(4) Welding process: The main welding process was carried out after sealing the gap of the groove G by carrying out the pre-welding step.
(5) Pressure / atmosphere on the surfaces 12A and 12B during the pre-welding process and the main welding process:
By continuing to supply argon gas to the vicinity of the welding torch 20 and the groove G under atmospheric pressure, the vicinity of the welding torch 20 and the groove G was made into an argon gas atmosphere.
(6) Pressure / atmosphere on the back surfaces 14A and 14B during welding in the pre-welding process (however, the protected areas 14P1 and 14P2 covered with the sealing member 30) side pressure / atmosphere The outlet side of the gas exhaust pipe 34 is sealed. Argon gas was continuously supplied into the sealed space S through the gas supply pipe 36 at a substantially constant flow rate by using the sealing member 30 in the state of being welded. As a result, the inside of the closed space S was made to have an argon gas atmosphere, and the pressure (backside pressure) was maintained at + 0.1 kPa ± 0.1 kPa at the gauge pressure.
(7) Pressure / atmosphere on the back surfaces 14A and 14B (however, the protected areas 14P1 and 14P2 covered with the sealing member 30) during welding in this welding process:
By exhausting the argon gas filled in the closed space S to the outside through the gas exhaust pipe 34 in the pre-welding step, the pressure of the argon gas (backside pressure) in the closed space S is reduced by carrying out the main welding step. The gauge pressure was maintained at −0.4 kPa ± 0.1 kPa.

After the welding was completed, the appearances of the front surfaces 12A and 12B and the back surfaces 14A and 14B were visually observed. As a result, oxidation did not occur on both sides, and no dent 40 was observed in the formation on the back surface sides 14A and 14B, and a convex back wave bead B having an appropriate height was formed. .. That is, in Example 1, it was confirmed that welding was performed without any defects regarding oxidation and dents.

(Example 2)
The welding test was carried out in the same manner as in Example 1 except that the backside pressure during welding in this welding step was maintained at −0.6 kPa ± 0.1 kPa. After the welding was completed, the appearances of the front surfaces 12A and 12B and the back surfaces 14A and 14B were visually observed. As a result, no oxidation occurred on both sides, and no dent 40 was observed in the formation on the back side 14A and 14B. The height of the back wave beads B formed on the back surface sides 14A and 14B was even larger than that of the first embodiment. Therefore, in Example 2, welding was performed without any defects regarding oxidation and dents.

(Comparative Example 1)
A welding test was carried out in the same manner as in Example 1 except that the pressures and atmospheres of the back surfaces 14A and 14B during welding in this welding step were atmospheric pressure and air atmosphere. After the welding was completed, the appearances of the front surfaces 12A and 12B and the back surfaces 14A and 14B were visually observed. As a result, dents 40 and remarkable oxidation were confirmed on the back surface sides 14A and 14B. That is, in Comparative Example 1, it was confirmed that clear welding defects were generated with respect to oxidation and dents.

(Example 3)
In the embodiment shown in FIG. 1, the welding test was carried out under the conditions shown below.
<Welding conditions>
(1) Work piece 10A, 10B: Aluminum alloy plate (plate thickness: 4 mm, alloy number: A5083)
(2) Welding method: TIG welding (3) Welding torch 20: Commercially available welding torch (unlike the chamber type torch shown in Patent Document 1, a general welding torch in which the welding torch body is open to the outside air)
(4) Welding process: Only this welding process was carried out.
(5) Pressure / atmosphere on the surfaces 12A and 12B during welding:
Atmospheric pressure and air atmosphere.
(6) Pressure / atmosphere on the back surfaces 14A and 14B (however, the protected areas 14P1 and 14P2 covered with the sealing member 30) during welding:
By exhausting the air in the closed space S to the outside through the gas exhaust pipe 34, the pressure (backside pressure) of the air in the closed space S during welding can be reduced by a gauge pressure of −0.3 kPa ± 0. It was maintained at 1 kPa.

After the welding was completed, the appearances of the front surfaces 12A and 12B and the back surfaces 14A and 14B were visually observed. As a result, no dent 40 was observed in the formation on the back surface sides 14A and 14B, and a convex back wave bead B having an appropriate height was formed. That is, in Example 2, it was confirmed that welding was performed without any defects with respect to the dents. Since the objects to be welded 10A and 10B used in Example 3 are made of an aluminum alloy material (A5083) that is difficult to oxidize, oxidation that may cause a practical problem even when welded in an air atmosphere may occur. There wasn't.

(Example 4)
In the embodiment shown in FIG. 1, the welding test was carried out under the conditions shown below.
<Welding conditions>
(1) Welded objects 10A, 10B: Stainless steel pipe (outer diameter: 114.3 mm, wall thickness: 3 mm, length: 100 mm)
(2) Welding method: TIG welding (3) Welding torch 20: Commercially available welding torch (unlike the chamber type torch shown in Patent Document 1, a general welding torch in which the welding torch body is open to the outside air)
(4) Welding process: The main welding process was carried out after sealing the gap of the groove G by carrying out the pre-welding step. In the pre-welding process and the main welding process, the welding torch 20 is fixed by a robot (manipulator) along the circumferential direction of the stainless steel pipe in a state where the stainless steel pipe is arranged so that its axial direction coincides with the horizontal direction. The entire circumference of the stainless steel pipe was welded while moving at a high speed. The moving speed of the welding torch 20 in each process is as follows.
Pre-welding process: 30 cm / min
Main welding process: 14 cm / min
(5) Pressure / atmosphere on the surfaces 12A and 12B during the pre-welding process and the main welding process:
By continuing to supply argon gas to the vicinity of the welding torch 20 and the groove G under atmospheric pressure, the vicinity of the welding torch 20 and the groove G was made into an argon gas atmosphere.
(6) Pressure / atmosphere on the back surfaces 14A and 14B during welding in the pre-welding process (however, the protected areas 14P1 and 14P2 covered with the sealing member 30) side pressure / atmosphere The outlet side of the gas exhaust pipe 34 is sealed. Argon gas was continuously supplied into the sealed space S through the gas supply pipe 36 at a substantially constant flow rate by using the sealing member 30 in the state of being welded. As a result, the inside of the closed space S was made to have an argon gas atmosphere, and the pressure (backside pressure) was maintained at + 0.05 kPa ± 0.05 kPa at the gauge pressure.
(7) Pressure / atmosphere on the back surfaces 14A and 14B (however, the protected areas 14P1 and 14P2 covered with the sealing member 30) during welding in this welding process:
By exhausting the argon gas filled in the closed space S to the outside through the gas exhaust pipe 34 in the pre-welding step, the pressure of the argon gas (backside pressure) in the closed space S is reduced by carrying out the main welding step. The gauge pressure was maintained at −0.4 kPa ± 0.1 kPa.

After the welding was completed, the appearances of the front surfaces 12A and 12B and the back surfaces 14A and 14B were visually observed along the circumferential direction. As a result, oxidation did not occur on both sides, and no dent 40 was observed in the formation on the back surface sides 14A and 14B, and a convex back wave bead B having an appropriate height was formed. .. That is, in Example 4, it was confirmed that welding was performed without any defects regarding oxidation and dents.

10: Object to be welded 10A: First object to be welded 10B: Second object to be welded 10C: First plate-shaped object to be welded 10D: Second plate-shaped object to be welded 12A, 12B, 12C: Top surface (surface) )
14A, 14B, 14C: Bottom surface (back surface)
14P1, 14P2: Protected area 14D: Area 16E: Groove side end 18E: End 20: Welding torch 22: Rod-shaped electrode 30: Sealing member 32: Opening 34: Gas exhaust pipe 36: Gas supply pipe 40: Recess 42 : Dent (sink)
A: Arc B: Back wave bead C: Welded joint CN: Corner E: Welding direction (direction to apply energy required for welding)
G: Groove J: End 1 of the second plate-shaped welded object 10D of the first plate-shaped workpiece 10C
Part where 8E is abutted M: Metal in a molten or semi-molten state S: Sealed space WZ: Welded part

Claims (9)

When welding is performed by applying either heat energy or light energy selected from thermal energy and light energy to the welding target portion from the front side of the welding target portion of the object to be welded.
Welding includes a welding step in which the pressure of the atmospheric gas near the front side of the welding target portion is set to atmospheric pressure and the pressure of the atmospheric gas near the back side of the welding target portion is set to less than atmospheric pressure. Method. The welding method according to claim 1, wherein the atmospheric gas near the back side of the welding target portion is an inert gas. The welding method according to claim 2, wherein the material constituting the object to be welded is any easily oxidizing material selected from stainless steel, titanium, nickel and zirconium. The welding method according to claim 1, wherein the atmospheric gas near the back side of the welding target portion is air. The welding method according to claim 4, wherein the material constituting the object to be welded is any one of refractory materials selected from aluminum, iron and mild steel. The welding method according to any one of claims 1 to 5, wherein in the welding step, welding is performed while changing the angle formed by the direction of gravity and the direction of applying energy. The weld target portion includes a groove formed by abutting the groove side end portion of the first work piece and the groove side end portion of the second work piece, and a portion in the vicinity thereof. The welding method according to any one of claims 1 to 6, wherein the welding method is characterized. It is characterized in that the shape of the groove formed by abutting the groove-side end of the first work piece and the groove-side end of the second work piece is I-shaped. The welding method according to claim 7. The weld target portion includes a corner portion formed by abutting an end portion of the second plate-shaped workpiece against one surface of the first plate-shaped workpiece and a portion in the vicinity thereof. The welding method according to any one of claims 1 to 6, wherein the welding method is characterized.

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