JP2009255172A - Method for manufacturing t-type joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method which enables the formation of inexpensive high-quality T-type joint by using ark welding method and plasma welding method which are conventional and inexpensive for welding equipment. <P>SOLUTION: In the method for manufacturing the T-type joint, an end surface of a second plate 14 is abutted at a predetermined angle to the rear side of a first plate 12, and ark welding or plasma welding is performed from the surface side of the first plate 12. Thereby, the heat of ark welding or plasma welding penetrates through the first plate 12 and melts an end surface portion of the second plate, and a T-type welded joint is formed by depositing a molten portion. In ark or plasma welding, a deep penetration method is applied by case according to a thickness of the first plate. Also, thickness-reduction working is performed on the surface of the plate when plate thickness exceeds a penetration depth. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a T-shaped joint suitable for welding a complicated structure such as a main plate or a side plate and a blade of an impeller of a relatively small fluid machine.

  Conventionally, the impeller for a small pump has been manufactured by casting in the same manner as a large one as shown in FIG. In this case, since it is cast to a shape close to the final shape, the number of manufacturing steps per product is small and the cost is low. However, casting of such a small and complicated product has difficulty in casting such that the core is thin, so that deformation and cracking are likely to occur, and gas is difficult to escape, so that defects are likely to occur. Originally, although the dimensional accuracy and the surface roughness have a great influence on the performance of the impeller, the integral casting has a rough surface because the flow path surface becomes a casting surface. In addition, since there is a change in dimension due to solidification shrinkage, it is difficult to obtain a designed dimension. Furthermore, a core must be used to make a hollow casting, but it is difficult to achieve the desired thickness and dimensions due to the displacement of the core. Since it is difficult for the grinder to enter the internal flow path, it is difficult to finish the inner surface after casting, and the narrow flow path surface cannot be reworked or corrected, and the above-described influence on performance cannot be avoided. In particular, impellers with small blade (blade) height have problems such as difficulty in casting and high defect rate. For this reason, the disposal rate after casting became high, resulting in delays in delivery and high costs.

  Therefore, in view of the difficulty in casting such a structure having a closed space, there is a manufacturing method in which a main plate and a side plate, which are parts constituting an impeller, are individually manufactured and integrated by welding them. Possible (see FIG. 13). In this case, the main plate and the side plate are integrated by abutting the end surface of the blade 14 formed on one side against the back surface of the other main plate (or side plate) 12, but the back surface side is close to the closed space, so FIG. It is difficult to form the fillet weld 56 from the back side as shown in FIG. 2, and it can be performed only from the front side of the main plate (or side plate) 12. A conventional method employed in such a case will be described with reference to the groove shape diagrams of FIGS. Here, in the case of manufacturing an impeller having a diameter of 150 mm or less, the plate thickness of the main plate or the side plate is set to about 5 mm.

  (A) and (b) of FIG. 1 use a TIG (Tungsten Inert Gas) welding method, and form slits 50 and 52 penetrating in the plate thickness direction in the main plate or side plate (first plate material) 12, thereby In this method, build-up welding is performed on a groove formed between the blade (second plate member) 14 and the tip. In the method (a), the entire thickness of the plate is used as the groove, the welded portion 54 is deep, and the cross-sectional shape of the slit 50 is widened due to penetration of the torch. The cost of Further, since the amount of welding build-up is large, time is required for welding work, the work cost is increased, and distortion due to welding heat is large.

  On the other hand, in the method (b), the tip of the blade is made to enter the slit 52 by a predetermined length to form a groove, and since the depth of the welded portion 54 is small, the slit 52 can be laser processed. It is possible and the processing cost is low, but no back wave is formed on the back side, and the quality of welding is not good. In addition, there is a problem that it takes time to position the plate in the thickness direction, that is, to adjust the depth of entry.

  On the other hand, FIG. 6C shows what is called through welding utilizing the fact that the penetration depth is large by butting a blade against the back surface of the main plate or side plate and irradiating a laser or electron beam from the front side. . Through welding using a laser or an electron beam is often used for electronic parts having a small thickness. As shown in Patent Document 1, in this method, the cost required for the processing step for forming the slit can be omitted. However, these methods are generally more expensive than the methods using arcs and plasmas, and particularly when the plate thickness is large, a large heat input is required. Further, since the amount of heat input is small, there is little penetration and it is difficult to form a well-shaped back wave.

  Therefore, as shown in FIG. 5E, it is conceivable to perform through welding from the surface side using arc or plasma welding. However, it is not always easy to penetrate the upper plate of a large plate thickness and produce a better back wave.

JP 2003-334680 A

  The present invention has been made in view of the above circumstances, and is capable of forming a low-cost and high-quality T-shaped joint by using arc welding or plasma welding, which is a general welding equipment and is inexpensive. It aims at providing the manufacturing method of a T type joint.

  In order to achieve the object, the method of manufacturing a T-shaped joint according to claim 1, the end surface of the second plate member is brought into contact with the back surface side of the first plate member at a predetermined angle, and the surface side of the first plate member Arc welding or plasma welding is performed, the first plate member is penetrated by the arc or plasma welding heat, the end surface portion of the second plate member is melted, and these are welded to form a welded joint.

  According to the first aspect of the present invention, through welding is performed in a general arc or plasma welding method, the first plate member and the second plate member are arced or plasma welded from the surface side of the first plate member, and these are welded. This eliminates complicated and costly operations such as groove formation and multilayer overlaying, and provides a low-cost, high-quality T-shaped joint.

  According to a second aspect of the present invention, there is provided a method for manufacturing a T-shaped joint. In the invention according to the first aspect, the thickness reducing groove is processed in advance in a portion where the second plate material of the first plate material abuts. Welding is performed along the line.

  According to the invention of claim 2, even when the plate thickness of the first plate material is large enough to exceed the penetration depth of arc or plasma welding, when performing through welding using a general arc or plasma welding method, With only relatively simple processing, the end surface of the second plate material is sufficiently input and melted to form a defect-free joint. This eliminates complicated operations such as groove formation and multilayer overlaying, and provides a low-cost, high-quality T-shaped joint.

  According to a third aspect of the present invention, there is provided a method for manufacturing a T-shaped joint. In the invention of the second aspect, the width of the bottom portion of the thickness reducing groove is set to be larger than the thickness of the second plate member. The melted metal forms a back bead at a location where the second plate contacts the back surface of the first plate.

  According to the invention described in claim 3, the first plate material is sufficiently melted at the upper portion of the edge portion of the end surface of the second plate material, and sufficient heat input is supplied to the edge portion of the end surface of the second plate material. Thus, a good back bead is formed at the corner where the back surface of the first plate material and the edge portion of the end surface of the second plate material intersect.

  According to a fourth aspect of the present invention, there is provided the method for manufacturing a T-shaped joint according to the third aspect, wherein the thickness reduction groove has a cross-section at a position corresponding to an edge of the end face of the second plate member. The thickness is increased from the center toward the outside.

  According to the fourth aspect of the present invention, the center side of the thickness reducing groove is easily melted at the position corresponding to the edge of the end face of the second plate member, and the outside is difficult to melt. It is held and maintains its shape by surface tension, prevents the occurrence of cracks and burn-off at the relevant part, and forms a weld with no defects.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a T-shaped joint, wherein the cross-section of the thickness reducing groove is smoothly changed at a position corresponding to an edge of an end surface of the second plate member. It is characterized by becoming. Thereby, since the shape changes smoothly, it is prevented that a tangential direction changes rapidly at the melting boundary and a large force acts on the boundary.

  According to a sixth aspect of the present invention, there is provided a method for manufacturing a T-shaped joint according to the fifth aspect of the present invention, wherein the thickness reduction groove has a circular arc cross section. Thereby, the formation of the groove having the arcuate section is easy to machine and reduces the machining cost.

  The method for manufacturing a T-shaped joint according to claim 7 is the invention according to any one of claims 1 to 6, wherein the first plate member is a main plate or a side plate of an impeller of a fluid machine. The two-plate material is a blade of an impeller of a fluid machine.

  According to the seventh aspect of the invention, the manufacturing process of the impeller of the fluid machine can be greatly simplified, and a high-quality impeller can be manufactured at low cost.

  The method for manufacturing a T-shaped joint according to claim 8 is the invention according to claim 7, wherein the main plate and the side plate are obtained by machining a near net shape material cast in a shape close to the final shape. It is characterized by.

  According to the invention described in claim 8, by machining a member cast into a relatively simple shape, the internal quality and surface quality of the cast material can be improved, and the processing and material costs can be reduced. Figured.

  A method for manufacturing a T-shaped joint according to claim 9 is characterized in that, in the invention according to any one of claims 1 to 8, an oxide-based welding flux is applied to the surface of the first plate member. And

  According to the ninth aspect of the invention, the oxide-based welding flux concentrates the arc and controls the amount of oxygen in the molten pool to promote deep penetration.

  A method for manufacturing a T-shaped joint according to claim 10 is the invention according to any one of claims 1 to 9, wherein a double gas shield is formed around the welding torch and oxygen is added to the outer shield gas. It is characterized by adding a source.

  According to the tenth aspect of the present invention, the double gas shield formed around the torch concentrates the arc energy and controls the oxygen amount in the molten pool to promote the deep penetration action.

  The method for manufacturing a T-shaped joint according to claim 11 is characterized in that, in the invention according to any one of claims 1 to 10, an inert gas is supplied to the back side of the first plate member during welding. To do.

  According to the eleventh aspect of the present invention, the inert gas supplied to the back surface side of the first plate member prevents, in particular, fraud of the back bead shape, oxidation, and cracking.

  The T-shaped joint according to claim 12, wherein the second plate material is brought into contact with the back surface side of the first plate material having the front surface and the back surface at a predetermined angle, and arc or plasma welding is performed from the front surface side of the first plate material, The first plate member and the second plate member are welded.

  According to the first to eleventh aspects of the invention, the manufacture of a relatively thick-walled T-shaped joint such as a main plate of a small pump and a welded portion of a blade is performed at low cost and with high quality. Can do.

  According to the invention described in claim 12, a high-quality T-shaped joint can be provided at low cost.

It is a figure explaining the (a) manufacturing process and (b) external appearance of the impeller of a small pump using the method of this invention. It is a figure explaining 1st Embodiment of the manufacturing method of the T-shaped coupling of this invention. Similarly, it is a figure explaining 2nd Embodiment of the manufacturing method of the T-shaped coupling of this invention. It is a figure explaining the thickness reduction groove | channel in the manufacturing method of the T-shaped coupling of this invention. (A) And (b) is a figure explaining a thickness reduction groove | channel in detail. (A) And (b) is a figure explaining other embodiment of a thickness reduction groove | channel. It is a figure which shows the cross-sectional structure | tissue of the T-shaped coupling of the Example of this invention. It is a figure which shows the cross-sectional structure | tissue of the T-shaped coupling of the other Example of this invention. It is a graph which shows the hardness test result in the cross section of the welding part of the Example of FIG. It is a figure which shows the cross-sectional structure | tissue of the T-shaped joint by the conventional fillet welding method. It is a graph which shows the hardness test result in the cross section of the welding part of the T-shaped coupling by the conventional method of FIG. It is a figure which shows the (a) external appearance of the impeller for pumps manufactured with the manufacturing method of the T-shaped coupling of this invention, (b) It is a figure which expands and shows the principal part. It is a figure which shows the manufacturing method of the impeller by the method of this invention. It is a figure which shows the manufacturing method of the impeller by the method of other embodiment of this invention. It is a figure which shows the manufacturing method of the impeller by casting. (A)-(d) is a figure which illustrates typically the welding method conventionally or assumed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an impeller 10 for a small pump in the case where the material is austenitic stainless steel and the effect of flux is large and the penetration is deep, and the thickness of the side plate (first plate material) 12 is about 5 mm or less. The manufacturing method of is shown. In this method, as shown in FIG. 1A, a side plate (first plate material) 12 and a main plate 16 obtained by cutting out blades (second plate material) 14 on the surface are prepared. The method for producing the side plate 12 and the main plate 16 having the blades 14 is appropriately adopted. Then, the back surface of the side plate 12 and the end surface of the blade 14 are brought into close contact with each other using a predetermined jig, and are fixed to each other as shown in FIG.

  Next, a welding torch 20 is applied from the surface side of the side plate 12 of the abutting portion along the butt line (welding line) 18 as shown in FIG. Arc or plasma welding. Thereby, a weld bead is formed along the weld line 18. The welding torch 20 has a tubular structure in which an inert gas G is supplied to the periphery of the electrode 22, and is manually or automatically welded under welding conditions for voltage, current, shield gas flow path, and the like applied to the electrode 22. Welding is performed while being moved along the abutting surface (welding line) by an apparatus (robot). In addition to supplying the inert gas G from the torch to the surface, the inert gas G is also separately supplied to the back side in order to seal the back bead portion.

  This welding does not build up the notched groove as shown in FIGS. 16 (a) and 16 (b), but penetrates the respective base materials of the side plate 12 and the blade 14 to be fused together. It is welding. That is, the arc heat melts the first plate 12, penetrates the first plate 12, and further melts the end of the second plate 14. Thereby, the molten pool 24 including the edge part of the 1st board | plate material 12 and a 2nd board | plate material which is shown with the hatching of hatching in Fig.2 (a) is formed. When this is cooled, as shown in FIG. 2B, a weld bead 26 in which the surface side of the side plate 12 is slightly depressed by gravity is formed, and the weld metal 24 has an appropriate curvature at the corner where the plate material on the back side is joined. A back wave 28 having a convex shape is formed.

  Here, in the conventional TIG welding, when the plate thickness is less than 2 mm, the plate is too thin to ensure the fillet by the back bead. In addition, when the plate thickness is 2 to 4 mm, since the penetration is shallow in normal welding, a uniform back surface cannot be secured. Even if the current is increased in order to increase the penetration, the penetration only spreads laterally and does not deepen. As a result, the melted portion melts down. For this reason, it is necessary to use a so-called deep penetration method in which the arc is concentrated in a narrower range than in the case of normal welding to increase the penetration depth. Hereinafter, a method for carrying out the deep penetration method in the commonly used TIG welding method will be described in detail.

(1) A-TIG (Active Flux TIG)
As shown in Fig. 2, by applying flux 30 containing metal oxide as the main component to the surface of the material to be welded and performing arc welding, the generation of arc and heat divergence are controlled to achieve deep penetration. It is a method to do. Although this method has been developed as a method for compensating for the disadvantages of arc welding, it can be applied to the penetration welding of the present invention. As a component of the flux 30, TiO ₂ , Cr ₂ O ₃ , SiO ₂ or the like is preferable. The reason why such a flux 30 is effective is that the flux 30 covers the surface at the time of welding to concentrate arc generation, and increases the amount of oxygen in the molten pool to reverse the convection in the molten pool. It is said that.

(2) AA-TIG (Advanced A-TIG)
In view of the fact that the A-TIG method requires the material cost of the flux, the application work cost, etc., as a simpler method, an oxidizing component (O ₂ or CO ₂₎ is added to the shielding gas G injected from the periphery of the electrode toward the solvent or the like. ) Has been proposed. For example, Ar + 0.3 to 0.5% O ₂ or Ar + 0.3 to 0.5% CO ₂ is effective. Since this method can be manufactured without using a flux, the cost can be reduced.

(3) Double shield TIG
AA-TIG was developed because it causes consumption due to oxidation of electrodes. This is because, as shown in FIG. 3, the conventional shielding gas G from the inside of the welding torch 32 of the double pipe structure, supplying a shield gas G ₂ containing an oxidizing component from the outside. Thereby, while ensuring the oxygen supply to the molten pool 24, the deep penetration by the further concentration of energy can be achieved. In the present invention, in addition to the method described above, an appropriate deep penetration method can be adopted.

Next, when the plate thickness of the side plate 12 is 5 mm or more, it is difficult to form a fillet by the back bead even if the deep penetration method is used. Therefore, as schematically shown in FIG. By processing the thickness reducing groove 60 on the surface side of the butted portion, the welded portion is locally reduced in thickness. The width w of the bottom of the thickness reducing groove 60 is set larger than the thickness t ₂ of the blade 14, so that the molten metal forms the back wave 28 during welding. The thickness reduction groove 60 is buried by overlay welding after penetration welding.

The shape and size of the thickness reducing groove 60 will be described in more detail below. In the following example, it is assumed that the thickness (t ₁ ) of the side plate 12 is about 10 mm with respect to the thickness (t ₂ ) of the blade 14 5 mm. FIG. 5A shows a case where the cross-sectional shape of the thickness reducing groove 60 is substantially trapezoidal. The center of the bottom of the thickness reducing groove 60 is flat, and the corner between the bottom and the side is smoothly connected by an arcuate portion. The width (w) of the bottom part that melts during welding is set to be larger than the thickness (t ₂ ) of the blade 14. Further, the thickness (t ₀ ) of the flat bottom is set to such an extent that the bottom including the bottom of the first member and the top of the second member are sufficiently melted during welding (2 mm in this example). At the top of the edge 62 of the end face of the blade 14, the bottom of the first member is an arc-shaped portion, and the thickness of the bottom increases from the center of the thickness reducing groove 60 toward the outside. The amount of unit heat input gradually decreases from the center toward the outside, and unmelted portions are likely to be formed on both sides of the central molten portion.

  With such a configuration, the melted portion is stably supported by the unmelted portion, and the melted portion is solidified after being slightly lowered by gravity to form a molten metal having no defects including a back wave. In addition, the formation of an unmelted portion whose thickness increases from the center toward the outside hardly causes the molten metal to be separated from the unmelted portion (melted down). In FIG. 5B, the thickness reduction groove 60 having substantially the same shape as that in FIG. 5A is formed, but the cross section is formed by a discontinuous straight line. Although this example also has the effects of the above-described example, it seems that the action of stably holding the melted portion is somewhat impaired.

FIG. 6A shows a case where the thickness reduction groove 60 has a semicircular cross-sectional shape. As shown in FIG. 6B, the width (w) of the bottom part that melts during welding is set to be larger than the thickness (t ₂ ) of the blade 14. The minimum thickness (t ₀ ) of the bottom is set to such an extent that the bottom of the first member and the top including the end face of the second member are sufficiently melted during welding. This example also has the same effects as the example of FIG. 5A, such as the formation of the back wave 28 having a good shape. Moreover, in this example, since the cross section of the thickness reducing groove 60 is circular, it can be formed only by a rotary tool, and there is an advantage that the processing of the groove is greatly facilitated. Of course, it does not have to be semicircular, but may be a partial arc-shaped groove, and the depth and width can be set appropriately.

Example 1
(1) For the austenitic stainless steel (18Cr-8Ni) and martensitic stainless steel (13Cr-4Ni) using the A-TIG method, the test pieces of the first plate and the second plate with a thickness of 5 mm are orthogonal to each other. The made T-shaped joint was made by through welding. Further, when the material is martensitic stainless steel (13Cr-4Ni) and the thickness of the first plate is 10 mm, the groove thickness shown in FIG. Through-welding was carried out with the thickness t ₀ ) reduced to 2 mm.

For the flux, Speedig F (trade name: manufactured by Taseto Co., Ltd.), which is a deep penetration agent for TIG based on TiO ₂ , Cr ₂ O ₃ and SiO ₂ , was used. Table 1 shows the welding conditions, and Table 2 shows the components of the flux.

  The cross-sectional structure of the 5 mm thick austenitic stainless steel was sound as shown in FIG. 7 (a), and the formation of back waves was similar to fillet welding. As for the martensitic stainless steel (13Cr-4Ni) having a thickness of 5 mm, a magnetic blowing phenomenon was observed in which the arc was deflected by the influence of a magnetic field, as shown in FIG. 7B.

  For martensitic stainless steel (13Cr-4Ni) with a thickness reduction groove 60 having a thickness of 10 mm, a sound welded structure was obtained as shown in FIG. About this joint, the hardness test in a cross section was done. The results are shown in FIG. As a comparative example, FIGS. 10 and 11 show a cross-sectional structure and a hardness test result when fillet welding is performed. All the hardness of this Example has shown the hardness of molten metal, and even if it compares with fillet welding, it is thought that there is no problem.

(Example 2)
Cast a main plate with blades made of martensite stainless steel (13Cr-4Ni), and use the side plate with the rolled material as the first plate to perform through welding in the same way as in Fig. 1. A car was manufactured. As the deep penetration method, the same A-TIG method as in Example 1 was used. Table 3 shows the welding conditions. The flux is the same as in Example 1. Welding was performed by teaching a welding robot.

  FIG. 12 (a) shows the appearance of the weld bead on the side plate in a state where finishing is performed after welding, and FIG. 12 (b) shows a cross section of the blade and side plate at the impeller end surface. A good bead with no defects was obtained.

  As described above, the manufacturing method of the T-shaped joint of the present invention makes it possible to manufacture a T-shaped joint of a relatively thick plate material such as a main plate of a small pump and a welded portion of a blade with low cost and high quality. It became possible to carry out. Below, the method of manufacturing fluid machines, such as a small pump, using the manufacturing method of this T type joint is explained.

  In FIG. 13, the forged steel material is cut into the shapes of the main plate 16 and the side plate 12, and the blade (blade) is cut out on one of them (main plate in the figure). And after joining and integrating a main board and a side board by welding, it finishes and makes it a product. In this manufacturing method, there are almost no defects in the material, and the blade shape is processed by machining, so the dimensions and shape as designed can be achieved. Since the machined surface is also smooth, an impeller with high performance can be manufactured. On the other hand, since the forging material is expensive and the amount of machining is large, both the processing cost and the material cost increase, so the manufacturing cost is relatively high.

  FIG. 14 uses a material cast into a shape (near net shape) having a shape close to the shapes of the main plate 16 and the side plate 12 and provided with machining margins on all necessary surfaces, instead of the forged steel material. As in the previous case, these materials are cut into the shapes of the main plate 16 and the side plate 12, and the blades (blades) are cut out on one of them (the main plate in the figure). And after joining and integrating a main board and a side board by welding, it finishes and makes it a product.

  In this manufacturing method, since the entire surface is machined, the surface is smooth and has less variation, and a shape as designed can be obtained. In addition, even if the material is cast, the main plate and the side plate are cast separately, so that casting is easy and there are almost no inherent defects. And since the material of the main plate and the side plate is made in a shape close to the final shape, the amount of machining is small, and both the material cost and the processing cost can be greatly reduced compared to using forging.

12 Main plate (first plate)
14 blades (second plate)
16 Side plate 18 Welding line 20 Welding torch 22 Electrode 24 Weld pool 26 Weld bead 28 Back wave 30 Flux 32 Double pipe welding torch 60 Thickening groove 62 Edge G, G2 Shielding gas

Claims (12)

Abutting the end surface of the second plate material at a predetermined angle on the back surface side of the first plate material;
Arc welding or plasma welding is performed from the surface side of the first plate material, the first plate material is penetrated by the arc or plasma welding heat, the end surface portion of the second plate material is melted, and these are welded to form a welded joint. A method for producing a T-shaped joint.   2. The method of manufacturing a T-shaped joint according to claim 1, wherein a thickness reduction groove is processed in advance in a portion of the first plate material that contacts the second plate material, and welding is performed along the thickness reduction groove. .   The width of the bottom portion of the thickness reducing groove is set to be larger than the thickness of the second plate member, so that the metal melted at the place where the second plate member is in contact with the back surface of the first plate member during welding The manufacturing method according to claim 2, wherein:   The thickness of the cross section of the thickness-reducing groove increases at the position corresponding to the edge of the end face of the second plate member from the center of the thickness-reducing groove toward the outside. Item 4. The manufacturing method according to Item 3.   5. The manufacturing method according to claim 4, wherein a cross section of the thickness reduction groove is smoothly changed at a position corresponding to an edge of an end face of the second plate member.   The manufacturing method according to claim 5, wherein a cross section of the thickness reducing groove is arcuate.   The first plate member is a main plate or a side plate of an impeller of a fluid machine, and the second plate member is a blade of an impeller of the fluid machine. Of manufacturing a T-shaped joint.   8. The method of manufacturing a T-shaped joint according to claim 7, wherein the main plate and the side plate are obtained by machining a near net shape material cast in a shape close to a final shape.   9. The method for manufacturing a T-shaped joint according to claim 1, wherein an oxide-based welding flux is applied to the surface of the first plate member.   The method for manufacturing a T-shaped joint according to any one of claims 1 to 9, wherein a double gas shield is formed around the welding torch, and an oxygen source is added to the outer shield gas.   The method for manufacturing a T-shaped joint according to any one of claims 1 to 10, wherein an inert gas is supplied to a back surface side of the first plate member during welding.   A second plate material is brought into contact with the back surface side of the first plate material having a front surface and a back surface at a predetermined angle, arc or plasma welding is performed from the front surface side of the first plate material, and the first plate material and the second plate material are welded. A T-shaped joint characterized by having been made.

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