Welding method, can body manufacturing method, and welding device

Abstract

Provided are a welding method and a welding device which use a consumable electrode and can achieve both an increase in welding speed and an enlargement of the dimensional margin for a weld gap. This welding method comprises a preparation step and a welding step. This welding method comprises a preparation step and a welding step. In the welding step, in a state in which a first object (5a) to be welded and a second object (5b) to be welded are disposed such that a portion where a first end (5aa) and a second end (5ba) abut each other is formed, an arc (A) generated by a non-consumable electrode (4) having a center axis (4a) is used to weld said portion. The center axis (4a) of the non-consumable electrode (4) is inclined relative to a normal line (5c) to said portion relating to the surfaces of the first object (5a) to be welded and the second object (5b) to be welded. The center axis (4a) is inclined relative to the normal line (5c) toward the opposite direction of a movement direction of the non-consumable electrode (4) relative to said portion. The inclination angle θ of the center axis (4a) relative to the normal line (5c) is at least 40° but less than 80°.

Description

Welding method, can body manufacturing method and welding device

[0001] The present disclosure relates to a welding method, a method for manufacturing a can body, and a welding apparatus.

[0002] Conventionally, welding methods using non-consumable electrodes have been known. For example, TIG (Tungsten Inert Gas) welding, which generates an arc between a non-consumable tungsten electrode and workpieces in an inert gas atmosphere, is widely used in welding components constituting can bodies or thin plate members, etc., because it produces low-quality welds with little spatter. However, welding methods using non-consumable electrodes such as TIG welding have problems such as a slower welding speed and a smaller dimensional margin for the gap (weld gap) between workpieces compared to MAG (Metal Active Gas) welding and MIG (Metal Inert Gas) welding, which use consumable electrodes.

[0003] For this reason, for example, in Japanese Patent Application Laid-Open No. 2012-139704, a double shielding gas is flowed from the nozzle of a welding torch equipped with a tungsten electrode, thereby increasing the energy density and directionality of the arc and thereby increasing the welding speed.

[0004] JP 2012-139704 A

[0005] The welding method disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 2012-139704 can increase the welding speed, but the problem of a small dimensional margin for the weld gap remains. As described above, with conventional welding methods using non-consumable electrodes, it has been difficult to achieve both an increase in the welding speed and an increase in the dimensional margin for the weld gap.

[0006] Therefore, an object of the present disclosure is to provide a welding method and welding apparatus using a consumable electrode that can achieve both an increase in welding speed and an increase in the dimensional margin for the welding gap, as well as a method for manufacturing a can body using these.

[0007] A welding method according to the present disclosure includes a preparing step and a welding step. In the preparing step, a first workpiece having a first end and a second workpiece having a second end are prepared. In the welding step, the first workpiece and the second workpiece are arranged so that a portion where the first end and the second end are butted together is formed, and the portions are welded using an arc generated by a non-consumable electrode having a central axis. In the welding step, the portions are welded while the non-consumable electrode is moved relative to the portions. The central axis of the non-consumable electrode is inclined with respect to a normal at the portions that is related to the surfaces of the first workpiece and the second workpiece. The central axis is inclined with respect to the normal in a direction opposite to the movement direction of the non-consumable electrode with respect to the portions. The inclination angle of the central axis with respect to the normal is 40° or more and less than 80°.

[0008] A method for manufacturing a can body according to the present disclosure is a method for manufacturing a can body using the above welding method. In the preparing step, a cylindrical body portion constituting the can body is prepared as the first workpiece. In the preparing step, a head portion of the can body is prepared as the second workpiece. The first end is an annular end in the extension direction of the body portion. The second end is the outer periphery of the head portion. In the welding step, the body portion and the head portion are arranged so that a portion where the end of the body portion and the outer periphery of the head portion are butted together is formed. While the non-consumable electrode is fixed, the body portion and the head portion are rotated around a rotation axis extending along the extension direction of the body portion, and the above portion is welded. The normal line is a straight line perpendicular to the rotation axis and connecting the rotation axis and the tip of the non-consumable electrode.

[0009] A welding device according to the present disclosure includes a non-consumable electrode, a power source, and a controller. The non-consumable electrode has a central axis. The power source supplies power to the non-consumable electrode. The controller controls the attitude of the central axis of the non-consumable electrode relative to a workpiece.

[0010] According to the above, a welding method and welding apparatus using a consumable electrode, which can achieve both an increase in welding speed and an increase in the dimensional margin for the welding gap, and a can body manufacturing method using the same, can be obtained.

[0011] 5A and 5B are schematic diagrams showing the configuration of a welding apparatus according to a first embodiment; a schematic diagram for explaining a welding method according to the first embodiment; a flowchart of the welding method shown in FIG. 2; a schematic diagram for explaining a welding method according to a second embodiment; a schematic diagram as viewed from the direction indicated by the arrow in FIG. 4; a schematic diagram for explaining a modification of the welding method shown in FIGS. 4 and 5; a schematic diagram showing the configuration of a welding apparatus according to a third embodiment; a schematic diagram for explaining a welding method according to the third embodiment; a flowchart of a method for manufacturing a can body according to a fourth embodiment; a schematic diagram for explaining a method for manufacturing the can body shown in FIG. 9; a schematic diagram for explaining a method for manufacturing the can body shown in FIG. 9; a schematic diagram for explaining a method for manufacturing the can body shown in FIG. 9; a schematic diagram for explaining a method for manufacturing the can body shown in FIG. 9; a schematic diagram showing the configuration of a welding apparatus according to a fifth embodiment; a schematic diagram for explaining a welding apparatus according to a sixth embodiment; a schematic diagram for explaining a welding apparatus according to a sixth embodiment; a schematic diagram for explaining a welding apparatus according to a seventh embodiment; a graph showing the relationship between the inclination angle of the central axis of a non-consumable electrode and maximum arc pressure; a graph showing the relationship between arc length and maximum arc pressure. 10 is a graph showing the temperature distribution at each tilt angle when the arc is extinguished from the tip of the pool.

[0012] Hereinafter, embodiments of the present disclosure will be described. Note that the same reference numerals are used to designate the same components, and the description thereof will not be repeated.

[0013] Embodiment 1. <Configuration of the Welding Apparatus> As shown in FIG. 1 , the welding apparatus 1 according to this embodiment is a welding apparatus for performing the so-called TIG welding method and mainly comprises a welding torch 2, a power source 6, a control unit 7, and a drive unit 8. The welding torch 2 includes a non-consumable electrode 4 and a nozzle 3. The non-consumable electrode 4 is, for example, a tungsten electrode. The non-consumable electrode 4 can be made of pure tungsten or a tungsten alloy. Examples of tungsten alloys include tungsten containing a few percent of alloying elements such as lanthanum, cerium, and thorium. As shown in FIG. 2 , the non-consumable electrode 4 has a central axis 4 a. The non-consumable electrode 4 is disposed within the nozzle 3. When the non-consumable electrode 4 is rod-shaped, the central axis 4 a of the rod-shaped non-consumable electrode 4 is a virtual axis that extends along the extension direction of the rod-shaped non-consumable electrode 4 and passes through the center of the non-consumable electrode 4 in a cross section perpendicular to the extension direction.

[0014] The nozzle 3 supplies a shielding gas around the non-consumable electrode 4. The nozzle 3 is connected to a shielding gas supply source (not shown). Shielding gas is stored in the shielding gas supply source. The shielding gas supplied from the nozzle 3 around the non-consumable electrode 4 is sprayed from around the non-consumable electrode 4 toward the workpiece 5. Any inert gas used in TIG welding can be used as the shielding gas. For example, argon gas, helium gas, or a mixture of these can be used as the shielding gas. Alternatively, a mixed gas obtained by mixing a few percent of an active gas with the above-mentioned inert gas can be used as the shielding gas. The active gas constituting the mixed gas can be, for example, oxygen gas, nitrogen gas, or hydrogen gas.

[0015] The power source 6 supplies power to the non-consumable electrode 4 of the welding torch 2. The negative terminal of the power source 6 is connected to the non-consumable electrode 4 of the welding torch 2. The positive terminal of the power source 6 is connected to the workpiece 5. As a result, as shown in FIG. 2 , an arc A, which is a TIG arc, is generated between the non-consumable electrode 4 and the workpiece 5.

[0016] The driver 8 arbitrarily changes the attitude and position of the welding torch 2 relative to the workpiece 5. The controller 7 controls the driver 8 to control the direction of the central axis 4a of the non-consumable electrode 4 relative to the workpiece 5. Specifically, as shown in FIG. 2 , the driver 8 controls the attitude of the welding torch 2 so that the central axis 4a of the non-consumable electrode 4 is inclined with respect to the normal 5c of the workpiece 5. The driver 8 can have any configuration. For example, a multi-axis robot arm or the like can be used as the driver 8.

[0017] It is only necessary to be able to change the relative position and attitude of non-consumable electrode 4 with respect to workpiece 5. For example, welding torch 2 including non-consumable electrode 4 may be fixed, while a holding member such as a stand that holds workpiece 5 may be moved relative to welding torch 2. In this case, welding apparatus 1 includes a moving unit that moves the holding member. Any configuration can be used as the moving unit, and an XY stage, for example, may be used.

[0018] There are no particular limitations on the material of the workpieces 5. Examples of the material of the workpieces 5 include steel materials such as carbon steel, stainless steel, aluminum alloys, magnesium alloys, nickel alloys, copper alloys, and titanium alloys.

[0019] <Welding Method> In a welding method using welding apparatus 1 shown in Fig. 1, a preparation step (S1) is first performed as shown in Fig. 3. In this step (S1), a first workpiece 5a to be welded having a first end 5aa and a second workpiece 5b to be welded having a second end 5ba are prepared as shown in Fig. 2.

[0020] Next, a welding step (S2) is performed. In this step (S2), first workpiece 5a and second workpiece 5b are arranged so that first end 5aa and second end 5ba are butted together, as shown in Fig. 2. In this state, the above-mentioned parts are welded using arc A generated by non-consumable electrode 4 having central axis 4a. This will be described in detail below.

[0021] In step (S2), the first workpiece 5a and the second workpiece 5b are plate materials, and the end face of the first end 5aa and the end face of the second end 5ba are butted together to form a butt joint. At this time, the butted end faces may be in contact with each other, or a gap (weld gap) may be formed between the two end faces.

[0022] With the first workpiece 5a and the second workpiece 5b positioned as described above, welding is performed. First, shielding gas is supplied from a shielding gas supply source (not shown) to the nozzle 3 of the welding torch 2. Next, the power source 6 is activated, and a welding current is applied between the non-consumable electrode 4 and the workpiece 5. As a result, an arc A is generated as shown in FIG. 2 . Next, the welding torch 2 is moved in a direction (welding direction) along the portion where the end face of the first end 5aa and the end face of the second end 5ba butt together. As a result, the non-consumable electrode 4 moves relative to the portion, and the portion is welded by the arc A. Specifically, the arc A melts the surface of the workpiece 5 (the surface where the first end 5aa and the second end 5ba butt together), forming a molten pool P. As the welding torch 2 moves, the molten pool P cools and solidifies into the weld metal M. As a result, the first workpiece 5a and the second workpiece 5b are welded together by the weld metal M.

[0023] At this time, welding may be performed by fixing welding torch 2 and moving workpiece 5 relative to welding torch 2. In the process described above, arc A is generated and then welding torch 2 or workpiece 5 as the base material is moved, but arc A may also be generated while welding torch 2 or workpiece 5 is moving.

[0024] In step (S2), as shown in FIGS. 1 and 2 , the central axis 4a of the non-consumable electrode 4 is inclined with respect to a normal 5c at the surface of the first workpiece 5a and the second workpiece 5b. Note that the normal 5c may be a normal to the surface of the first workpiece 5a (the surface facing the welding torch 2) where the first workpiece 5a and the second workpiece 5b are butted together. The inclination direction of the central axis 4a with respect to the normal 5c is opposite to the movement direction of the welding torch 2 relative to the butted portion of the first workpiece 5a and the second workpiece 5b. The inclination angle θ of the central axis 4a with respect to the normal 5c is equal to or greater than 40° and less than 80°. Therefore, as shown in FIG. 2 , the arc A is formed so as to extend in a direction inclined with respect to the surface of the workpiece 5. Furthermore, the arc A has a shape that spreads forward of the molten pool P in the direction in which welding progresses (the movement direction of the welding torch 2).

[0025] Furthermore, the electrode protrusion length L (see FIG. 2 ), which is the distance from the tip of the nozzle 3 of the welding torch 2 to the tip of the non-consumable electrode 4, is not particularly limited. The electrode protrusion length L is preferably set to 20 mm or less. This is because, as the electrode protrusion length L becomes longer, there is a concern that the gas shielding performance may decrease, making the welding unstable or making the weld more susceptible to oxidation. However, if the nozzle 3 is configured to spray a laminar flow of shielding gas over a long distance, the electrode protrusion length L may be set to 20 mm or more.

[0026] <Operation> A welding method according to the present disclosure includes a preparing step (S1) and a welding step (S2). In the preparing step (S1), a first workpiece 5a having a first end 5aa and a second workpiece 5b having a second end 5ba are prepared. In the welding step (S2), the first workpiece 5a and the second workpiece 5b are arranged so that a portion where the first end 5aa and the second end 5ba are butted together is formed. Then, the portion is welded using an arc A generated by a non-consumable electrode 4 having a central axis 4a. In the welding step (S2), the portion is welded while the non-consumable electrode 4 is moved relative to the portion. The central axis 4a of the non-consumable electrode 4 is inclined with respect to a normal 5c at the portion that relates to the surfaces of the first workpiece 5a and the second workpiece 5b. The central axis 4a is inclined with respect to the normal 5c in a direction opposite to the direction of movement of the non-consumable electrode 4 relative to the portion. The inclination angle θ of the central axis 4a with respect to the normal line 5c is equal to or greater than 40° and less than 80°.

[0027] In this manner, as shown in Fig. 2, arc A is formed to extend in a direction inclined relative to the surfaces of first workpiece 5a and second workpiece 5b. Arc A also spreads forward of molten metal pool P in the direction in which welding progresses (the direction in which welding torch 2 including non-consumable electrode 4 moves). This allows for increased welding current supplied to non-consumable electrode 4 and improved welding speed while suppressing the occurrence of burn-through defects. Furthermore, by preheating the area in front of molten metal pool P in the direction in which welding progresses, the dimensional margin for the weld gap can be increased. This will be described in more detail below.

[0028] In welding using the non-consumable electrode 4 and shielding gas described above, for example, TIG welding, when arc A is generated, a plasma airflow is generated by the surrounding shielding gas in a direction along the central axis 4a of the non-consumable electrode 4. This plasma airflow is blown toward the workpieces 5. The plasma airflow collides with the workpieces 5, and the direction of movement of the plasma airflow changes to a direction along the surface (face direction) of the workpieces 5. At this time, as the direction of movement of the plasma airflow is changed, a force (arc force) acts on the workpieces 5 along the initial direction of movement of the plasma airflow.

[0029] It is known that the arc force increases with an increase in the welding current supplied to the non-consumable electrode 4. To increase the welding speed, the heat input from the arc A must be increased to maintain the welding heat input per unit length applied to the workpiece 5. In other words, the welding current must be increased. In this case, the arc force also increases with an increase in the welding current. As the arc force increases, the force pushing the molten pool P downward in the thickness direction (plate thickness direction) of the workpiece 5 increases. As a result, a defect in which the molten pool P falls through downward (burn-through defect) is more likely to occur. Furthermore, such burn-through defects tend to occur more easily when the thickness (plate thickness) of the workpiece 5 is thinner.

[0030] In the welding method according to the first embodiment, welding torch 2 and non-consumable electrode 4 are tilted in the direction opposite to the direction in which welding proceeds. In addition, the tilt angle θ, which is the angle between central axis 4a of non-consumable electrode 4 and normal 5c of workpiece 5, is set to a range of 40° or more and less than 80°. This reduces the arc force that acts in a direction that presses molten pool P downward in the plate thickness direction.

[0031] For example, according to the experiment described below, when the welding current is 100 A and the tilt angle θ is increased from 0° to 40°, the arc force acting downward in the thickness direction is halved. Furthermore, when the welding current is increased from 100 A to 200 A with the tilt angle θ set to 0°, the arc force acting downward in the thickness direction increases by approximately 2.2 times. However, by setting the tilt angle θ to 40° or greater, the arc force acting at a welding current of 200 A can be reduced to the same or less than the arc force acting at a welding current of 100 A with the tilt angle θ set to 0°. Furthermore, when the tilt angle θ is set to 80° or greater, the arc A generated between the non-consumable electrode 4 and the workpiece 5 becomes unstable, resulting in reduced welding quality or even failure to weld. Therefore, by setting the tilt angle θ to 40° or greater but less than 80°, the arc force acting downward (downward) to push the molten pool P downward during welding can be suppressed. This allows the welding current to be increased without causing burn-through defects, thereby increasing the welding speed.

[0032] Here, if the tilt angle θ is increased, the downward arc force is reduced, but the arc A is likely to become unstable. Therefore, in consideration of the reduction in the downward arc force and the stability of the arc A, it is preferable to set the tilt angle θ to be equal to or greater than 45° and equal to or less than 75°.

[0033] Furthermore, according to the welding method of the first embodiment, when the first workpiece 5a and the second workpiece 5b are made of thin plate material having a thickness of, for example, 0.1 mm to 2 mm, it is possible to increase the dimensional margin for the gap (weld gap) that occurs when the first workpiece 5a and the second workpiece 5b are butted together.

[0034] When welding thin plate materials, if the weld gap is large, there will be insufficient material to fill the weld gap. This raises concerns that the molten metals of the first workpiece 5a and the second workpiece 5b may not be joined, or that even if the molten metals are joined and a molten pool P is formed, burn-through defects may occur due to the arc force. For this reason, for example, in butt joints made by TIG welding, which does not use a welding wire, the allowable weld gap is set to a maximum of approximately 20% of the plate thickness of the workpiece 5. Therefore, when the plate thickness of the workpiece 5 is 2 mm or less, the weld gap is expected to be 0.4 mm or less.

[0035] Furthermore, when actually manufacturing a product by welding, it is necessary to take into consideration the thermal deformation of the workpiece 5 due to welding. For this reason, it is difficult to eliminate the weld gap. Therefore, a welding method that allows a large dimensional margin for the weld gap is desired.

[0036] In the welding method according to the first embodiment, the welding torch 2 is tilted in the direction opposite to the welding direction, and the tilt angle θ is set in the range of 40° or more and less than 80°, as shown in FIG. 2 . Therefore, the generated arc A spreads outward from the molten metal pool P toward the forward region in the welding direction. This effectively preheats the forward region of the molten metal pool P. When the forward region is preheated, the temperature of the workpieces 5 in the forward region increases, causing the workpieces 5 (the first workpiece 5 a and the second workpiece 5 b) to thermally expand in a direction that reduces the weld gap. This prevents problems such as the workpieces 5 not being joined or burn-through defects from occurring. This increases the dimensional margin for the weld gap.

[0037] A welding apparatus 1 according to the present disclosure includes a non-consumable electrode 4, a power source 6, and a control unit 7. The non-consumable electrode 4 has a central axis 4a. The power source 6 supplies power to the non-consumable electrode 4. The control unit 7 controls the attitude of the central axis 4a of the non-consumable electrode 4 relative to the workpiece 5. In this case, the above-described welding method can be easily performed using the welding apparatus 1.

[0038] Here, increasing the inclination angle θ, which is the angle between the central axis 4 a of the non-consumable electrode 4 and the normal 5 c of the workpiece 5, reduces the depth of the molten metal pool P formed by the arc A. Therefore, in the welding apparatus 1 according to the first embodiment, it is preferable that the thickness of the workpiece 5 be 2 mm or less. Although it is possible to use a workpiece 5 with a thickness greater than 2 mm, the depth of the molten metal pool P becomes shallower, and it may be difficult to completely melt the workpiece 5 in the entire thickness direction of the workpiece 5.

[0039] Embodiment 2. <Welding Method> As shown in Figures 4 and 5, a welding method according to embodiment 2 basically has the same configuration and can achieve the same effects as the welding method shown in Figures 2 and 3, but the shape of the workpieces 5 differs from that of the welding method shown in Figures 2 and 3. That is, in the welding method shown in Figures 4 and 5, the ends of the first workpieces 5a and the second workpieces 5b are bent as shown in Figure 5. Note that Figure 5 shows the ends of the first workpieces 5a and the second workpieces 5b as viewed from the direction indicated by arrow 10 in Figure 4. The first end 5aa of the first workpieces 5a includes a bent portion 5aa1 and an extending portion 5aa2. The bent portion 5aa1 is bent so as to form an L-shape in a cross section perpendicular to the direction of movement of the welding torch 2. The extending portion 5aa2 extends from the bent portion 5aa1 in a direction along a normal line 5c (see Figure 4). The second end 5ba of the second workpiece 5b includes a bent portion 5ba1 and an extending portion 5ba2. The bent portion 5ba1 is bent so as to form an L-shape in the cross section. The extending portion 5ba2 extends from the bent portion 5ba1 in a direction along the normal line 5c (see FIG. 4). The bent portion 5ba1 of the second end 5ba is arranged so as to face the bent portion 5aa1 of the first end 5aa. The extending portion 5ba2 of the second end 5ba is arranged so as to face the extending portion 5aa2 of the first end 5aa. In this way, the portion where the first workpiece 5a and the second workpiece 5b are butted together forms a cross-joint shape. The above-described welding method can be performed using the welding device 1 according to the first embodiment.

[0040] 4 , when welding workpiece 5, arc A is formed toward extension 5aa2 of first end 5aa and extension 5ba2 of second end 5ba. Arc A melts extensions 5aa2 and 5ba2 and causes them to flow downward, forming part of molten pool P. As welding torch 2 moves toward extensions 5aa2 and 5ba2, extensions 5aa2 and 5ba2 melt sequentially, forming molten pool P.

[0041] As shown in Fig. 6, only one of the first end 5aa and the second end 5ba may be bent. In Fig. 6, only the first end 5aa includes a bent portion 5aa1 and an extending portion 5aa2. The second end 5ba is not bent. The bent portion 5aa1 of the bent first end 5aa is disposed so that the end face of the second end 5ba faces the bent portion 5aa1.

[0042] <Function> In the above welding method, at the portion where the first end 5aa and the second end 5ba are butted together, one of the first end 5aa and the second end 5ba (first end 5aa in FIG. 6 ) may include a bent portion 5aa1 and an extending portion 5aa2. The bent portion 5aa1 may be bent so as to form an L-shape in a cross section perpendicular to the movement direction. The extending portion 5aa2 may extend from the bent portion 5aa1 in a direction along the normal line 5c. The other of the first end 5aa and the second end 5ba (second end 5ba in FIG. 6 ) may be disposed to face the bent portion 5aa1.

[0043] In the above welding method, in the portion where the first end 5aa and the second end 5ba are butted together, the other of the first end 5aa and the second end 5ba (the second end 5ba in FIG. 5 ) may include a bent portion 5ba1 and an extending portion 5ba2. The bent portion 5ba1 may be bent so as to form an L-shape in the cross section. The extending portion 5ba2 may extend from the bent portion 5ba1 in a direction along the normal line 5c. The bent portion 5ba1 of the second end 5ba may be arranged so as to face the bent portion 5aa1 of the first end 5aa. The extending portion 5ba2 of the second end 5ba may be arranged so as to face the extending portion 5aa2 of the first end 5aa.

[0044] In this case, it is possible to obtain the same effects as the welding method according to the first embodiment, and also to further increase the dimensional margin of the welding gap. This will be explained in more detail below.

[0045] In the case of a joint (butt joint) having a first end 5aa or a second end 5ba with an L-shaped cross section, as in the second embodiment, the arc A preheats the front region of the molten pool P, causing thermal deformation of the first end 5aa or the second end 5ba with an L-shaped cross section. Specifically, the first end 5aa or the second end 5ba thermally deforms in a direction that releases residual stress that occurred when the first end 5aa or the second end 5ba was machined into an L-shape. As a result, the thermal deformation deforms the first end 5aa or the second end 5ba so that the degree of bending of the L-shape becomes gentler. In a butt joint, the deformation in the direction that gentles the degree of bending of the L-shape reduces the weld gap. Therefore, by setting the inclination angle θ, which is the angle between the central axis 4a of the non-consumable electrode 4 of the welding torch 2 and the normal 5c of the workpiece 5, in the range of 40° or more and less than 80°, and further by forming a butt joint having an L-shaped first end 5aa or second end 5ba, the dimensional margin for the weld gap can be made even larger than in the welding method of embodiment 1.

[0046] During welding, the angle between the surface of the molten zone at the extension 5aa2, 5ba2 at the first end 5aa or second end 5ba of the L-shape and the normal line 5c shown in Figure 4 may be approximately 0° (a state in which the surface of the molten zone extends in a substantially vertical direction). On the other hand, a case in which this angle is approximately 80° is also conceivable. For example, this angle varies depending on welding conditions such as the inclination angle θ, which is the angle between the central axis 4a of the non-consumable electrode 4 and the normal line 5c of the workpiece 5, the welding current, and the welding speed. It is preferable to avoid a state in which this angle is approximately 0°.

[0047] The welding method according to the second embodiment as described above allows for a larger dimensional margin for the weld gap than when a butt joint without the L-shaped first end 5aa or second end 5ba is used. Also, the welding speed can be increased compared to when a welding rod or welding wire is used to increase the dimensional margin for the weld gap for a butt joint.

[0048] Embodiment 3. <Configuration of Welding Apparatus> As shown in Fig. 7 , welding apparatus 1 according to embodiment 3 basically has the same configuration as welding apparatus 1 shown in Fig. 1 and can obtain the same effects, but differs from welding apparatus 1 shown in Fig. 1 in that it further includes a detection unit 9. Welding apparatus 1 shown in Fig. 7 includes detection unit 9 connected to control unit 7. Detection unit 9 detects the displacement of workpiece 5.

[0049] The detector 9 may be, for example, a sensor 9a that directly measures the displacement of the workpiece 5. The sensor 9a may be, for example, a position sensor such as a laser displacement meter, or an imaging device that acquires image data to measure the displacement of the workpiece 5 based on the image data. The sensor 9a may detect the position of the top surface of the extension 5aa2, 5ba2 of the first end 5aa or the second end 5ba, as shown in FIG. 8 . In this case, the sensor 9a is preferably positioned so as not to be affected by the arc A. As shown in FIG. 8 , the arc A expands forward in the welding direction (the direction from the non-consumable electrode 4 to the extension 5aa2, 5ba2 in FIG. 8 ). Therefore, the influence of the arc A must be taken into consideration when measuring the displacement of the workpiece 5 near the weld. For example, a filter that blocks light from the arc A may be installed on the sensor 9a.

[0050] Furthermore, a voltage sensor 9b that measures an arc voltage that indicates the state of the arc A can be used as the detection unit 9. When the workpiece 5 is displaced, the distance between the workpiece 5 and the non-consumable electrode 4 changes, resulting in a change in the arc voltage. Therefore, the displacement of the workpiece 5 can be indirectly measured by the arc voltage.

[0051] Control unit 7 controls drive unit 8 in accordance with the displacement of workpiece 5 detected by detection unit 9. As a result, drive unit 8 can change the position of welding torch 2 relative to workpiece 5. This makes it possible to adjust the position of welding torch 2, i.e., the position of non-consumable electrode 4.

[0052] <Welding Method> The welding method using welding device 1 shown in Fig. 7 basically has the same configuration and can achieve the same effects as the welding method shown in Fig. 4, but differs from the welding method shown in Fig. 4 in the method of controlling the position of non-consumable electrode 4 of welding torch 2 in the welding step (S2). That is, in the welding method shown in Fig. 8, the position of welding torch 2 is controlled during welding so that distance H1 from bent portions 5aa1, 5ba1 to non-consumable electrode 4 in the direction of normal line 5c is equal to or greater than distance H2 from bent portions 5aa1, 5ba1 to the top surfaces of extension portions 5aa2, 5ba2. That is, the position of welding torch 2 is adjusted so that distance h from the top surfaces of extension portions 5aa2, 5ba2 to non-consumable electrode 4 in the direction along normal line 5c is equal to or greater than zero.

[0053] The position of welding torch 2 is controlled by drive unit 8 based on a signal from control unit 7. At this time, displacement of extensions 5aa2, 5ba2 is detected by detection unit 9. A signal indicating the displacement of extensions 5aa2, 5ba2 is sent from detection unit 9 to control unit 7. Based on the signal, control unit 7 adjusts distance H1 from bent portions 5aa1, 5ba1 to non-consumable electrode 4 so as to maintain the state of arc A appropriately.

[0054] 7, since non-consumable electrode 4 is arranged so as to be inclined with respect to normal line 5c, arc A is blown from an obliquely upward direction onto extensions 5aa2, 5ba2 of workpiece 5. The portions of extensions 5aa2, 5ba2 melted by arc A become part of molten pool P.

[0055] <Function> In the above welding method, distance H1 from bent portions 5aa1, 5ba1 to non-consumable electrode 4 in the direction of normal 5c may be equal to or greater than distance H2 from bent portions 5aa1, 5ba1 to the top surfaces of extension portions 5aa2, 5ba2. In this case, non-consumable electrode 4 is positioned sufficiently far from workpiece 5, thereby reducing the arc force that acts in a direction that presses molten pool P downward in the plate thickness direction.

[0056] In the above welding method, in the welding step (S2), the distance H1 from the bent portions 5aa1, 5ba1 to the non-consumable electrode 4 may be adjusted in accordance with the displacement of the extension portions 5aa2, 5ba2. In this case, even if the extension portions 5aa2, 5ba2 are displaced due to thermal deformation of the workpiece 5 in the welding step (S2), the distance between the non-consumable electrode 4 and the extension portions 5aa2, 5ba2 of the workpiece 5 can be maintained within an appropriate range. As a result, the welding quality in the welding step (S2) can be stabilized.

[0057] The welding device 1 may include a detection unit 9 that detects displacement of the workpieces 5. The control unit 7 may control the position of the non-consumable electrode 4 in accordance with the displacement of the workpieces 5 detected by the detection unit 9. As a result, by using the welding device 1, it is possible to stabilize the welding quality even in cases where the workpieces 5 are thermally deformed during welding.

[0058] Embodiment 4. <Method for Manufacturing Can Body> A method for manufacturing a can body according to this embodiment is described below. As shown in FIG. 9 , the method for manufacturing a can body according to this embodiment first performs a step (S10) of preparing can body components. This step (S10) corresponds to the preparation step (S1) shown in FIG. 3 . In step (S10), body portion 21 and end plate portion 22 constituting can body 20 are prepared as shown in FIG. 10 . Note that can body 20 is, for example, a metal hot water storage tank in a hot water heater. Body portion 21 has a cylindrical shape. Body portion 21 corresponds to first workpiece 5a to be welded. End plate portion 22 has a U-shaped or semicircular cup-shaped cross section. End plate portion 22 corresponds to second workpiece 5b to be welded. An annular end portion 21a in the extension direction of body portion 21 corresponds to first end portion 5aa in FIGS. 4 and 5 . The outer peripheral portion 22a of the end plate portion 22 corresponds to the second end portion 5ba in Figures 4 and 5. The end portion 21a of the body portion 21 and the outer peripheral portion 22a of the end plate portion 22 are formed with the bent portion and the extended portion shown in Figures 4 and 5.

[0059] Next, a welding step (S20) is performed. This step (S20) corresponds to the welding step (S2) shown in Fig. 3. In the step (S20), as shown in Fig. 10, the body portion 21 and the end plate portion 22 are arranged so that a portion where the end portion 21a of the body portion 21 and the outer periphery 22a of the end plate portion 22 are butted together is formed. The portion where the end portion 21a and the outer periphery 22a are butted together forms a butt joint. Note that the end portion 21a and the outer periphery 22a may not have bent portions or extended portions, and the portion may be a simple butt joint.

[0060] The body 21 and the end plate 22 are arranged so that the rotation center axis 21b of the body 21 (see FIG. 11) extends horizontally. The two end plates 22 are arranged so as to sandwich the body 21. A jig 25 is installed on the end plate 22. Stress is applied to the end plate 22 by the jig 25 in the direction shown by the arrow in FIG. 10. In this state, the welding torch 2 is arranged so as to face the portion where the end 21a of the body 21 and the outer periphery 22a of the end plate 22 are butted together.

[0061] As shown in Figures 10 and 11 , a welding torch 2 including a non-consumable electrode 4 is fixed. In this state, the body portion 21 and the end plate portion 22 are rotated in the direction indicated by the arrow in Figure 11 around a rotation central axis 21b extending along the extension direction of the body portion 21, while welding the above-mentioned portion (the portion to be welded where the end portion 21a and the outer periphery 22a are butted together). Consider a line 20a that is perpendicular to the rotation central axis 21b and connects the rotation central axis 21b to the tip of the non-consumable electrode 4. This line 20a corresponds to the normal line 5c shown in Figure 4 . The central axis 4a of the non-consumable electrode 4 is inclined with respect to the line 20a in the direction opposite to the movement direction of the non-consumable electrode 4 (the direction indicated by the arrow in Figure 11 ). The inclination angle θ of the central axis 4a with respect to the line 20a corresponding to the normal line 5c is 40° or more and less than 80°. In this way, it is possible to reliably weld the curved joint between the body portion 21 and the end plate portion 22 (the portion where the end portion 21 a of the body portion 21 and the outer periphery 22 a of the end plate portion 22 are butted together), thereby obtaining a can body 20 in which the body portion 21 and the end plate portion 22 are joined together.

[0062] In the above step (S20), the position of the welding torch 2 may be determined as shown in FIG. 12 . That is, when viewed from a direction along the central axis of rotation 21b of the body 21, consider a line segment 20b connecting the central axis of rotation 21b and the uppermost vertex 21c of the body 21. The non-consumable electrode 4 of the welding torch 2 is disposed on the outer periphery of the body 21 and the head plate 22 at a position overlapping with the line segment 20b, or in a region located forward of the line segment 20b in the direction of rotation of the body 21 and the head plate 22. From a different perspective, the non-consumable electrode 4 is disposed in a region forward of the uppermost vertex 21c of the body 21 in the direction of rotation of the body 21 and the head plate 22 (the direction indicated by the arrow in FIG. 12 ).

[0063] In the above step (S20), the welding method shown in the second embodiment is applied as described above, but the welding method shown in the first or third embodiment described above may also be applied.

[0064] <Operation> A method for manufacturing a can body 20 according to the present disclosure is a method for manufacturing a can body 20 using the above-described welding method. In the preparing step (S1), a cylindrical body portion 21 constituting the can body 20 is prepared as the first workpiece 5a to be welded. In the preparing step (S1), an end plate portion 22 of the can body 20 is prepared as the second workpiece 5b to be welded. The first end 5aa is the annular end 21a in the extension direction of the body portion 21. The second end 5ba is the outer periphery 22a of the end plate portion 22. In the welding step (S2), the body portion 21 and the end plate portion 22 are arranged so that a portion where the end 21a of the body portion 21 and the outer periphery 22a of the end plate portion 22 are butted together is formed. While the non-consumable electrode 4 is fixed, the body 21 and the end plate 22 are welded together while rotating them about a rotation axis 21b extending in the extension direction of the body 21. The normal line 5c is a straight line 20a that is perpendicular to the rotation axis 21b and connects the rotation axis 21b and the tip of the non-consumable electrode 4.

[0065] In this way, the connection between the body portion 21 and the end plate portion 22 can be made into a high-quality welded portion.

[0066] In the above-described can body manufacturing method, in the welding step (S2), the body portion 21 and the end plate portion 22 may be arranged so that the rotation central axis 21b extends horizontally. As viewed from the direction along the rotation central axis 21b, the non-consumable electrode 4 may be arranged in a region forward of the vertex 21c, which is located at the uppermost position of the body portion 21, in the rotation direction of the body portion 21 and the end plate portion 22.

[0067] In this case, the flow of molten metal in the molten pool P (see FIG. 4) formed by welding is stabilized, and as a result, a uniform weld bead can be obtained.

[0068] Embodiment 5. <Configuration of the Welding Apparatus> As shown in FIG. 13 , welding apparatus 1 according to embodiment 5 basically has the same configuration as welding apparatus 1 shown in FIG. 1 and can achieve the same effects. However, it differs from welding apparatus 1 shown in FIG. 1 in that drive unit 8 includes linear guide 30 and guide unit 31. FIG. 16 shows the structure near welding torch 2 in welding apparatus 1. In welding apparatus 1 shown in FIG. 13 , guide unit 31 is positioned so as to contact workpiece 5. Welding torch 2 is connected to linear guide 30. Linear guide 30 is connected to guide unit 31. Linear guide 30 moves during welding to adjust the position of welding torch 2. Specifically, as described below, guide unit 31 detects the displacement of workpiece 5, and linear guide 30 moves in response to the detected displacement. As linear guide 30 moves, welding torch 2 connected to linear guide 30 also moves. This will be described in detail below.

[0069] The linear guide 30 includes a linear guide rail 30a and a linear guide block 30b. A torch holder 32 is connected to the linear guide block 30b via, for example, a flat plate 33. The welding torch 2 is connected to the torch holder 32. The linear guide rail 30a is connected to a drive unit 8 (see FIG. 1).

[0070] The guide unit 31 includes a guide roller 31a and a bracket 31b. The bracket 31b may be an L-shaped member as shown in FIG. 13 , but any other shape may also be used. The guide unit 31 is connected to a flat plate 33 connected to the linear guide block 30b. In other words, the guide unit 31 and the welding torch 2 are connected to the linear guide block 30b via the same flat plate 33. In FIG. 13 , the bracket 31b is included in the configuration of the guide unit 31, but in some cases, the guide roller 31a may be directly connected to the flat plate 33. In this case, the guide unit 31 consists only of the guide roller 31a. For example, the guide roller 31a may be a ball roller having a rotatable ball at its tip. The guide roller 31a is positioned so as to contact the workpiece 5. Therefore, other configurations may be used, not just a ball roller, as long as they can slide between the workpiece 5 and the guide roller 31a during welding.

[0071] 13 has basically the same configuration and can achieve the same effects as the welding method shown in FIG. 4 or 8, but differs from the welding method shown in FIG. 4 or 8 in the method of controlling the position of non-consumable electrode 4 of welding torch 2 in the welding step (S2). That is, in the welding method using the welding device shown in FIG. 13, guide portion 31 is positioned so as to contact workpiece 5 during welding. Therefore, linear guide 30 is displaced in accordance with the displacement of workpiece 5, thereby controlling the position of non-consumable electrode 4 of welding torch 2. Specifically, in the direction of normal 5c (see FIG. 8), distance H1 from the bent portion of workpiece 5 to non-consumable electrode 4 (or distance h from the top surface of the extended portion of workpiece 5 to non-consumable electrode 4) is adjusted.

[0072] In the above welding method, guide unit 31 and welding torch 2 are integrally formed and connected to linear guide 30. From a different perspective, guide unit 31 and welding torch 2 are connected to linear guide 30 while the relative positional relationship between guide unit 31 and welding torch 2 is fixed. The position of non-consumable electrode 4 of welding torch 2 is controlled by guide unit 31 and linear guide 30. In the method of controlling the position of non-consumable electrode 4 of welding torch 2 using detector 9 shown in FIG. 7 , there is a concern that a significant time lag may occur between detection of displacement of workpiece 5 by detector 9 and control of the position of non-consumable electrode 4 by controller 7. Therefore, when the welding speed is increased, a problem may arise because the time lag delays adjustment of the position of non-consumable electrode 4 relative to workpiece 5 in response to the displacement of workpiece 5. On the other hand, in the welding method using welding apparatus 1 according to the fifth embodiment, guide unit 31 contacts workpiece 5, and displacement of the workpiece 5 can be directly detected by guide unit 31. Furthermore, because guide portion 31 and welding torch 2 are integrally movable by linear guide 30, the position of non-consumable electrode 4 can be directly adjusted in accordance with the displacement of workpiece 5. In other words, because non-consumable electrode 4 and guide portion 31 are mechanically connected, the effect of welding speed on the adjustment of the position of non-consumable electrode 4 can be suppressed. As a result, the welding quality in the welding step (S2) can be made more stable.

[0073] <Operation> Welding device 1 according to the present disclosure includes guide portion 31 and linear guide 30 as an adjustment portion. Guide portion 31 contacts workpiece 5. Linear guide 30 as an adjustment portion is connected to guide portion 31 and non-consumable electrode 4. Linear guide 30 as an adjustment portion adjusts the position of non-consumable electrode 4 in accordance with the displacement of workpiece 5 detected via guide portion 31. In this case, it is possible to stabilize the welding quality.

[0074] Sixth Embodiment <Configuration of Welding Apparatus> As shown in Fig. 14 , welding apparatus 1 according to a sixth embodiment has a configuration similar to that of welding apparatus 1 shown in Fig. 13 and can achieve similar effects. However, it differs from welding apparatus 1 shown in Fig. 13 in that drive unit 8 further includes a moving stage 34. Moving stage 34 is connected between linear guide 30 and welding torch 2. Specifically, moving stage 34 is arranged to connect plate 33, which is connected to linear guide 30, with plate 35. Moving stage 34 can change the position of plate 35 relative to plate 33. Torch holder 32 is fixed to plate 35. Welding torch 2 is connected to torch holder 32. Moving stage 34 adjusts the distance between the tip of guide roller 31 a and the tip of non-consumable electrode 4 of welding torch 2. That is, the distance h between the workpiece 5 and the non-consumable electrode 4 (or the distance H1 from the bent portions 5aa1, 5ba1 of the workpiece 5 to the non-consumable electrode 4) can be adjusted by the movable stage 34. From a different perspective, the movable stage 34 can change the contact position between the guide unit 31 and the workpiece 5 and the relative position of the non-consumable electrode 4. In FIG. 14 , the movable stage 34 is provided between the linear guide 30 and the welding torch 2, but the movable stage 34 may be disposed in another position as long as the distance h between the workpiece 5 and the non-consumable electrode 4 can be adjusted. For example, the movable stage 34 may be disposed so as to connect the linear guide 30 and the guide unit 31, and the relative position of the guide unit 31 with respect to the linear guide 30 may be adjusted by the movable stage 34.

[0075] Fig. 15 is a schematic diagram showing the configuration of a modified example of welding device 1 according to embodiment 6. As shown in Fig. 15, the modified example of welding device 1 according to embodiment 6 basically has the same configuration as welding device 1 shown in Fig. 13 and can obtain the same effects as welding device 1 shown in Fig. 13, but differs from welding device 1 shown in Fig. 13 in that drive unit 8 further includes air cylinder 36.

[0076] The air cylinder 36 is disposed to connect the linear guide 30 and the guide portion 31. Specifically, the air cylinder 36 connects the plate 33 connected to the linear guide 30 to the guide roller 31a of the guide portion 31. The air cylinder 36 adjusts the length X of the guide roller 31a protruding from the lower end of the plate 33. That is, the distance h between the workpiece 5 and the non-consumable electrode 4 can be adjusted by the air cylinder 36. From a different perspective, the air cylinder 36 can change the contact position between the guide portion 31 and the workpiece 5 and the relative position of the non-consumable electrode 4. In FIG. 15 , the air cylinder 36 is disposed between the linear guide 30 and the guide portion 31, but the air cylinder 36 may be disposed at another position as long as the distance h between the workpiece 5 and the non-consumable electrode 4 can be adjusted. For example, the air cylinder 36 may be disposed between the linear guide 30 and the welding torch 2, and the relative position of the welding torch 2 with respect to the linear guide 30 can be adjusted by the air cylinder 36.

[0077] 14 and 15, the movable stage 34 and the air cylinder 36 are connected to the control unit 7 (see FIG. 1). The control unit 7 controls the movable stage 34 and the air cylinder 36. Therefore, the movable stage 34 and the air cylinder 36 controlled by the control unit 7 can change the position of the welding torch 2 relative to the workpiece 5. As a result, the position of the welding torch 2, i.e., the position of the non-consumable electrode 4, can be adjusted.

[0078] 14 and 15 has a configuration similar to that of the welding method using the welding apparatus 1 shown in FIG. 13 and can achieve similar effects, but differs from the welding method shown in FIG. 13 in that the distance h between the workpiece 5 and the non-consumable electrode 4 can be changed during welding in the welding step (S2). In the welding method using the welding apparatus 1 shown in FIG. 13, the distance h between the workpiece 5 and the non-consumable electrode 4, which is adjusted in the step (S1) of preparing materials to be welded, is maintained constant in the welding step (S2) in accordance with the displacement of the workpiece 5. In the welding method shown in FIG. 14 and 15, the distance h between the workpiece 5 and the non-consumable electrode 4 can be adjusted during welding in the welding step (S2) as well, by the control unit 7 controlling the moving stage 34 or the air cylinder 36.

[0079] In this case, even if the optimum value of the distance h between the workpieces 5 and the non-consumable electrode 4 changes during welding due to, for example, constraints on the workpieces 5, the control unit 7 can adjust the distance h between the workpieces 5 and the non-consumable electrode 4 for each welding point by controlling the moving stage 34 or the air cylinder 36. As a result, the welding quality in the welding step (S2) can be made more stable.

[0080] An example of a case in which the appropriate value of the distance h between the workpiece 5 and the non-consumable electrode 4 changes during welding will be described. For example, in welding a can body 20 by welding a head plate 22 and a body 21 as shown in FIG. 10 , the ends of the head plate 22 and the body 21 are formed by bent portions 5aa1, 5ba1 and extended portions 5aa2, 5ba2, respectively, as shown in FIGS. 4 and 5 . In this welding, the ends formed by the bent portions 5aa1, 5ba1 and the extended portions 5aa2, 5ba2 are welded together. In this case, assuming that the entire circumference of the ends is welded, the start and end positions of the welding are the same. Alternatively, the end position is a position where the weld is overlapped beyond the start position to a specified position. In such a case, the appropriate value of the distance h between the workpiece 5 and the non-consumable electrode 4 changes at the start position, steady portion, and end position of the welding. Here, the steady portion refers to a position between the start position and the end position of the welding. For example, at the start position of welding, the shape of the weld, i.e., the width and height of the weld, changes depending on the distance h. At the end position of welding, the bent portions 5aa1 and 5ba1 and the extended portions 5aa2 and 5ba2 shown in Figures 4 and 5 have already been welded at the start position, so the shape of the weld changes. In welding a can body by welding the end plate portion 22 and the body portion 21, as described above, the start and end positions of welding are either the same or the end position is a position where the weld overlaps beyond the start position. Therefore, it is undesirable for the shape of the weld at the start position of welding to be significantly different from the shape of the weld at the end position, as this would result in an uneven shape of the weld. Therefore, it is preferable to appropriately adjust the distance h between the workpiece 5 and the non-consumable electrode 4 at each position. Furthermore, the appropriate value of the distance h between the workpiece 5 and the non-consumable electrode 4 may not be uniquely determined because it may vary depending on the performance required of the weld. In such a case, the welding method using the welding device 1 shown in FIGS. 14 and 15 is effective.

[0081] The following method can be used to change the distance h at the start position, steady-state portion, and end position of welding, for example. In the above-described welding of a can body, distance h is set at an angle corresponding to the start position of welding, an angle corresponding to the steady-state portion, and an angle corresponding to the end position of welding, relative to the angle as viewed from the center of the can body when full-circumference welding is performed. Distance h may be adjusted by controlling the movable stage 34 or the air cylinder 36 with the control unit 7 when the weld reaches a predetermined angle. Alternatively, the time required for full-circumference welding may be calculated in advance, and distance h may be set at each of the times corresponding to the start position of welding, the steady-state portion, and the end position of welding. Distance h may be adjusted by controlling the movable stage 34 or the air cylinder 36 with the control unit 7 when the predetermined time is reached during welding. Here, angle and time have been used as examples of criteria for adjusting distance h, but this is not limited thereto. For example, distance h may be set based on the length of welding. Furthermore, while an example has been shown in which distance h is set at three points, namely, the start position of welding, the steady-state portion, and the end position of welding, this is not limiting. The distance h may be increased or decreased depending on the workpieces 5 to be welded.

[0082] As described above, the welding apparatus 1 may include a moving stage 34 between the linear guide 30 and the welding torch 2. The control unit 7 may also include an air cylinder 36 between the linear guide 30 and the guide unit 31. The control unit 7 may control the moving stage 34 and the air cylinder 36 to control the distance h between the workpiece 5 and the non-consumable electrode 4. Alternatively, the welding apparatus 1 may be configured so that the protruding length X of the guide roller 31a of the guide unit 31 can be adjusted using a screw. Furthermore, the welding apparatus 1 may include a screw driver that can automatically adjust the length X. The control unit 7 may control the driver to adjust the protruding length X of the guide roller 31a. The welding apparatus 1 may also include multiple guide rollers 31a, and the protruding length X of each guide roller 31a may be adjusted in advance, and the control unit 7 may switch between the multiple guide rollers 31a to adjust the length X of the guide rollers 31a. As a result, by using the welding apparatus 1, welding quality can be stabilized even when the appropriate distance h varies for each welding point on the workpiece 5.

[0083] <Function> In the welding method according to the present disclosure, in the welding step (S2), the distance H1 from bent portions 5aa1, 5ba1 to non-consumable electrode 4 (i.e., the distance h between workpieces 5 and non-consumable electrode 4) can be changed for each different position in the portion where the first end of first workpiece 5a and the second end of second workpiece 5b are butted together. In this case, the welding quality can be stabilized.

[0084] The welding device according to the present disclosure includes a movable stage 34 or an air cylinder 36 as a position adjustment mechanism. The position adjustment mechanism (movable stage 34 or air cylinder 36) can change the relative position of the contact position between the guide portion 31 and the workpiece 5 and the non-consumable electrode 4. The control unit 7 controls the position adjustment mechanism (movable stage 34 or air cylinder 36) to change the relative position of the contact position and the non-consumable electrode 4. In this case, even if the optimal distance H1 (or distance h) differs for each part to be welded, it is possible to stabilize the welding quality.

[0085] 2 and 3 , but differs in the operation of control unit 7 in the welding step (S2). That is, in the welding method according to the seventh embodiment, while arc A (see FIG. 2 ) is generated, control unit 7 (see FIG. 1 ) controls drive unit 8 (see FIG. 1 ) in accordance with the welding location of workpiece 5 (see FIG. 1 ) to control the attitude of center axis 4 a (see FIG. 16 ) of non-consumable electrode 4 (see FIG. 16 ) relative to workpiece 5. Specifically, control unit 7 controls drive unit 8 to adjust, while arc A is generated, the tilt angle θ of center axis 4 a with respect to normal 5 c within a range of 40° or more and less than 80°, as shown in FIG. 16 . At this time, the attitude of the central axis 4a of the non-consumable electrode 4 relative to the workpiece 5 may be controlled so that the tip position of the non-consumable electrode 4 changes, but it is preferable to control the attitude of the central axis 4a of the non-consumable electrode 4 so that the tip position of the non-consumable electrode 4 does not change.

[0086] The drive unit 8 for controlling the attitude of the non-consumable electrode 4 as described above can be configured, for example, by a robot arm or a rotary stage. Alternatively, as shown in FIG. 16 , a torch holder 32 for holding the welding torch 2 can be moved along an arc-shaped trajectory. Specifically, a plate has a groove formed therein for fitting the torch holder 32, and the torch holder 32 is fitted into the groove. The torch holder 32 is then moved along the groove. Any method can be used to move the torch holder 32. For example, a telescopic cylinder can be connected to the torch holder 32, and the torch holder 32 can be moved along the groove by extending or retracting the telescopic cylinder.

[0087] In the above welding method, while arc A is being generated in the welding step (S2), control unit 7 controls drive unit 8 to control the attitude of center axis 4 a of non-consumable electrode 4 relative to workpiece 5. In this case, for example, in a case where the attitude of center axis 4 a of non-consumable electrode 4 relative to workpiece 5, i.e., the inclination angle θ of center axis 4 a relative to normal 5 c, needs to be changed depending on the welding location, it becomes possible to set an appropriate inclination angle θ for each welding location. As a result, the welding quality in the welding step (S2) can be made more stable.

[0088] In the welding method according to the present disclosure, in the welding step (S2), the inclination angle θ can be changed within a range of 40° or more and less than 80° for each different position in the butted portion of the first end of the first workpiece 5 a and the second end of the second workpiece 5 b, thereby stabilizing the welding quality.

[0089] The following experiment was carried out to verify the effects of the above-described welding device and welding method.

[0090] (Experimental Example 1) <Sample> The material constituting the sample was SUS436L as specified in the JIS standard. The sample was in the form of a plate. The thickness of the sample was 0.6 mm. The end portions to be welded were bent into an L-shape. The bent portions were butted together to form a weld.

[0091] <Test Method> The above welds were welded using a TIG welding device having the configuration shown in Figure 1. To define the weld gap (the distance between the workpieces) at the weld, a shim plate was placed between the opposing workpieces at the weld. The inclination angle θ, which is the angle between the normal to the weld of the workpieces and the central axis 4a (see Figure 2) of the tungsten electrode, which is the non-consumable electrode 4 of the welding torch 2, was changed to 25°, 45°, 50°, and 60°. The condition of the weld was then visually inspected. The welding conditions are shown in Table 1.

[0092]

[0093] <Results> The test results are shown in Table 2. In Table 2, in the welding result column, A indicates a good condition of the welded part after welding, and B indicates a defect such as an improperly formed welded part.

[0094]

[0095] As shown in Table 2, when the tilt angle is 25°, a good weld can be obtained with a welding gap of 0.1 mm, but a welding gap of 0.15 mm results in a defective weld. On the other hand, when the tilt angle is 45° or 50°, a welding gap of 0.2 mm or less results in a good weld. Also, when the tilt angle is 60°, a welding gap of 0.3 mm or less results in a good weld.

[0096] Thus, it was shown that when the inclination angle is 45° or more, the weld gap value at which good weld quality can be obtained is two to three times larger than when the inclination angle is 25°.

[0097] When the inclination angle was set to 80°, the arc A (see FIG. 4) became unstable, and defects occurred in the weld regardless of the welding gap. Therefore, it was shown that good welding quality can be obtained by setting the inclination angle to less than 80°.

[0098] (Experimental Example 2) <Test Method> The vertically downward pressure component of the arc pressure was measured by varying the inclination angle (also called the torch angle) of the central axis of a tungsten electrode serving as a non-consumable electrode and the welding current. The vertically downward pressure component of the arc pressure was also measured by varying the height (also called the arc length) from the surface of the workpiece to the tip of the tungsten electrode and the welding current. To measure the vertically downward pressure component of the arc pressure, a water-cooled copper base plate with a through-hole formed therein was prepared as the workpiece. A differential pressure gauge was connected to the through-hole from the back side of the water-cooled copper base plate. In this measurement system, an arc was generated from the surface side of the water-cooled copper base plate to the portion with the through-hole formed, and the pressure component was measured. The measurement conditions are shown in Table 3.

[0099]

[0100] <Results> Figure 17 shows the relationship between the tilt angle and the vertically downward pressure component of the arc pressure. In Figure 17, the horizontal axis represents the tilt angle, and the vertical axis represents the vertically downward pressure component of the arc pressure. Here, the maximum value during measurement (also referred to as maximum arc pressure) was used as the pressure component. Figure 17 also shows relative values, with the pressure component being 1 when the tilt angle was 0°, the welding current was 100 A, and the arc length was 3 mm. Measurements were performed under conditions of a welding current of 100 A or 200 A and a tilt angle of 0°, 25°, and 50°.

[0101] As can be seen from FIG. 17, the degree of decrease in maximum arc pressure when the tilt angle is 50° compared to when the tilt angle is 25° is relatively greater than the degree of decrease in maximum arc pressure when the tilt angle is 25° compared to when the tilt angle is 0°.

[0102] Furthermore, as can be seen from Figure 17, when the welding current is 100 A, by setting the tilt angle to 40° or more, the maximum arc pressure is halved compared to when the tilt angle is 0°. Furthermore, when the tilt angle is 0°, by increasing the welding current from 100 A to 200 A, the maximum arc pressure is approximately 2.2 times higher. On the other hand, when the welding current is 200 A and the tilt angle is 50°, the maximum arc pressure is equal to or less than the maximum arc pressure when the welding current is 100 A and the tilt angle is 0°. This tendency can be confirmed when the tilt angle is 40° or more. This shows that the increase in arc pressure due to an increase in welding current can be suppressed by increasing the tilt angle.

[0103] The relationship between arc length and the vertically downward pressure component of the arc pressure is shown in Figure 18. In Figure 18, the horizontal axis represents arc length, and the vertical axis represents the vertically downward pressure component of the arc pressure. As in Figure 17, the maximum value during measurement (also referred to as maximum arc pressure) was used as the pressure component. Figure 18 also shows relative values, with the pressure component being set to 1 when the tilt angle was 0°, the welding current was 100 A, and the arc length was 1 mm. Measurements were performed under conditions of welding currents of 100 A or 200 A, and arc lengths of 1 mm, 3 mm, and 5 mm. The tilt angle under each condition was set to 0°.

[0104] As can be seen from Figure 18, the maximum arc pressure also changes depending on the arc length. The arc pressure can be reduced by increasing the arc length, i.e., by increasing the height from the workpiece to the tip of the tungsten electrode.

[0105] (Experimental Example 3) <Sample> The same sample as that used in Experimental Example 1 was used.

[0106] <Test method> The inclination angle (torch angle) of the central axis of a tungsten electrode (non-consumable electrode) was changed to measure the temperature distribution in the front region of the molten pool at the end of welding. A K-type thermocouple was used as the temperature measuring device. The measurement conditions are shown in Table 4.

[0107]

[0108] <Results> The results are shown in Figure 19. In Figure 19, the horizontal axis represents the distance from the tip of the molten pool. The vertical axis represents the temperature at each position on the workpiece at the end of welding (i.e., when the arc is extinguished). Figure 19 shows the results when the tilt angles were 25° and 60°.

[0109] As can be seen from Figure 19, the temperature in the front region of the molten pool was higher when the tilt angle was 60° than when the tilt angle was 25°. In other words, it was shown that increasing the tilt angle can increase the preheating effect in the front region of the molten pool.

[0110] In the above-described experimental example, the experiment was conducted using flat plates as the workpieces, but similar results can be obtained even if the surfaces of the workpieces are curved (i.e., if the body and end plate portions constituting the can body in embodiment 4 are used as the workpieces).

[0111] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. Unless there is a contradiction, at least two of the embodiments disclosed herein may be combined. The basic scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0112] 1 Welding device, 2 Welding torch, 3 Nozzle, 4 Non-consumable electrode, 4a Central axis, 5 Workpiece, 5a First workpiece, 5aa1, 5ba1 Bent portion, 5aa2, 5ba2 Extension portion, 5aa First end, 5b Second workpiece, 5ba Second end, 5c Normal, 6 Power source, 7 Control unit, 8 Drive unit, 9 Detection unit, 9a Sensor, 9b Voltage sensor, 10 Arrow, 20 Can body, 20a Straight line, 20b Line segment, 21 Body portion, 21a End, 21b Rotation central axis, 21c Vertex, 22 End plate portion, 22a Outer periphery, 25 Jig, 30 Linear guide, 30a Linear guide rail, 30b Linear guide block, 31 Guide portion, 31a Guide roller, 31b Bracket, 32 Torch holder, 33, 35 Plate, 34 Moving stage, 36 Air cylinder, A Arc, H1, H2, h Distance, L Length, M Weld metal, P Molten pool.

Claims

1. Providing a first workpiece having a first end and a second workpiece having a second end; and welding the first workpiece and the second workpiece to be welded together using an arc generated by a non-consumable electrode having a central axis, while the first workpiece and the second workpiece are arranged so as to form a portion where the first end and the second end are butted together. In the welding step, welding the parts while moving the non-consumable electrode relative to the parts; the central axis of the non-consumable electrode is inclined in a direction opposite to a direction of movement of the non-consumable electrode relative to a normal at the portion with respect to a surface of the first workpiece and the second workpiece; A welding method, wherein an inclination angle of the central axis with respect to the normal line is equal to or greater than 45° and less than 80°.

2. A method of welding a first workpiece having a first end and a second workpiece having a second end; and welding the first workpiece and the second workpiece to be welded together using an arc generated by a non-consumable electrode having a central axis, while the first workpiece and the second workpiece are arranged so as to form a portion where the first end and the second end are butted together. In the welding step, welding the parts while moving the non-consumable electrode relative to the parts; the central axis of the non-consumable electrode is inclined in a direction opposite to a direction of movement of the non-consumable electrode relative to a normal at the portion with respect to a surface of the first workpiece and the second workpiece; The inclination angle of the central axis with respect to the normal line is equal to or greater than 40° and less than 80°, In the portion, one of the first end portion and the second end portion includes a bent portion bent so as to be L-shaped in a cross section perpendicular to the moving direction, and an extension portion extending from the bent portion in a direction along the normal line, The welding method includes arranging the first end portion and the second end portion so that the other of the first end portion and the second end portion faces the bent portion.

3. The welding method according to claim 2 , wherein a distance from the bent portion to the non-consumable electrode in the normal direction is equal to or greater than a distance from the bent portion to a top surface of the extension portion.

4. The welding method according to claim 3 , wherein in the welding step, a distance from the bent portion to the non-consumable electrode is adjusted in response to the displacement of the extension portion.

5. 5. The method of claim 4, wherein in the welding step, the distance from the bent portion to the non-consumable electrode is variable for different locations on the portion.

6. The welding method according to claim 2 , wherein in the welding step, the inclination angle is changeable for each different position of the portion within a range of 40° or more and less than 80°.

7. The welding method as described in claim 1, wherein, in the welding process, the inclination angle is changeable for different positions of the part within a range of 45° or more and less than 80°.

8. A welding method as described in any one of claims 1, 2 and 7, wherein in the welding process, only non-consumable electrodes are used as electrodes.

9. A method of welding a first workpiece having a first end and a second workpiece having a second end; and welding the first workpiece and the second workpiece to be welded together using an arc generated by a non-consumable electrode having a central axis, while the first workpiece and the second workpiece are arranged so as to form a portion where the first end and the second end are butted together. In the welding step, welding the parts while moving the non-consumable electrode relative to the parts; the central axis of the non-consumable electrode is inclined in a direction opposite to a direction of movement of the non-consumable electrode relative to a normal at the portion with respect to a surface of the first workpiece and the second workpiece; The inclination angle of the central axis with respect to the normal line is equal to or greater than 40° and less than 80°, In the preparing step, As the first workpiece, a cylindrical body portion constituting the can body is prepared; As the second object to be welded, a head plate portion of the can body is prepared; The first end portion is an annular end portion in an extension direction of the body portion, The second end portion is an outer periphery of the end plate portion, In the welding step, A method for manufacturing a can body, wherein the body portion and the end plate portion are positioned so that a portion is formed where the end portion of the body portion and the outer periphery of the end plate portion are butted together.

10. In the welding step, While the non-consumable electrode is fixed, the body portion and the end plate portion are rotated about a rotation center axis extending along the extension direction of the body portion while welding the portions; The method for manufacturing a can body according to claim 9 , wherein the normal line is a straight line that is perpendicular to the central axis of rotation and connects the central axis of rotation and the tip of the non-consumable electrode.

11. In the welding step, The body portion and the end plate portion are arranged so that the rotation central axis extends along a horizontal direction, A method for manufacturing a can body as described in claim 9 or claim 10, wherein, when viewed from a direction along the central axis of rotation, the non-consumable electrode is arranged in a forward region in the rotational direction of the body portion and the end plate portion from the uppermost vertex of the body portion.

12. A welding apparatus for use in the welding method according to claim 1 or 2, a non-consumable electrode having a central axis; a power source for supplying power to the non-consumable electrode; and a control unit that controls an attitude of the central axis of the non-consumable electrode relative to a workpiece.

13. A detection unit for detecting a displacement of the workpiece is provided, The welding device according to claim 12 , wherein the control unit controls a position of the non-consumable electrode in response to a displacement of the workpiece detected by the detection unit.

14. A guide portion that comes into contact with the workpiece; an adjustment portion connected to the guide portion and the non-consumable electrode; The welding device according to claim 12 , wherein the adjustment unit adjusts a position of the non-consumable electrode in response to a displacement of the workpiece detected via the guide unit.

15. a position adjustment mechanism that can change a relative position between the contact position of the guide portion and the workpiece and the non-consumable electrode, The welding device according to claim 14 , wherein the control unit changes the relative position between the contact position and the non-consumable electrode by controlling the position adjustment mechanism.