Welding method

Abstract

Provided is a welding method which prevents specular reflection when a surface of a material to be welded is photographed, and inhibits formation of porosity in the material to be welded.　A welding method according to the present invention is characterized by having melting steps (a), (b) in which a joint of a material to be welded 1 is melted using an electric arc 4 while blowing an inert gas 3 onto the joint, and an oxidizing step (d) in which a portion of the melted joint 7 solidifies and, while another portion is in a melted state, a gas 6 containing oxygen is supplied to the inert gas and the joint, oxidizing the joint.

Description

[Technical field]

[0001] The present invention relates to a welding method. [Background technology]

[0002] Gas-shielded arc welding, a type of welding method, is an arc welding method in which welding is performed while shielding the welding surface of the workpiece from the air with an inert gas. In other words, the workpiece is heated and melted by the welding power source, and activated, so that oxidation by oxygen in the air does not occur, and the workpiece is joined while spraying an inert gas onto it.

[0003] An example of a conventional arc welding technique is Patent Document 1. Patent Document 1 describes a consumable electrode gas-shielded arc welding method for arc-welding two steel plates using a welding torch having a consumable electrode, characterized in that arc welding is performed while supplying a shielding gas having an oxygen potential α of 1.5% to 5% represented by a predetermined formula from the welding torch toward the consumable electrode, and an oxidation-promoting gas having an oxygen potential β of 15% to 50% represented by another predetermined formula is sprayed at a flow rate of 1 to 3 m / sec onto the weld bead and weld toe that are in a state of 700°C or higher formed by the arc welding.

[0004] In the above-mentioned Patent Document 1, a pro-oxidant gas is sprayed onto the welded surface of the material to be welded. In other words, the surfaces of the weld bead and the weld toe, which are formed by arc welding and are at a temperature of 700°C or higher, are exposed to a pro-oxidant gas with a high oxygen potential β. As a result, the surfaces of the weld bead and the weld toe can be covered with conductive iron oxide slag, so that insulating Si, Mn-based slag does not appear on the surface. Therefore, even if a structural member including a weld is electrocoated, no electrocoating defects occur in the weld, and it is said that the corrosion resistance of the structural member can be improved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 126657 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional gas-shielded arc welding, the surface of the conductor is sprayed with an inert gas, so the surface of the conductor is not oxidized, has a gloss, and reflects the light of the surrounding objects like a mirror. This makes it difficult to capture the surface and boundary information of the conductor using an optical system such as a camera. In addition, when measuring the shape using a laser line distance sensor, the reflected light from the glossy surface is not diffused, which reduces the amount of reflected light received and the measurement accuracy.

[0007] One method for controlling the external gloss of a conductor is to reduce the amount of inert gas during heating and melting and intentionally oxidize the conductor. However, this method has the problem of degrading mechanical properties due to solidification defects caused by porosity.

[0008] In the above-mentioned Patent Document 1, a pro-oxidant gas is sprayed during welding, but this method may disturb the shielding gas, causing voids to form in the material to be welded, which may result in a deterioration of mechanical properties.

[0009] In view of the above circumstances, the present invention provides a welding method which prevents specular reflection when photographing the surface of a workpiece and also suppresses the occurrence of porosity in the workpiece. [Means for solving the problem]

[0010] One embodiment of the welding method of the present invention for achieving the above-mentioned object is characterized by having a melting process in which an inert gas is sprayed onto the joint of the materials to be welded while the joint is melted by arc discharge, and an oxidation process in which an inert gas and a gas containing oxygen are supplied to the joint while a portion of the molten joint 7 is solidified and the other portion is molten, to oxidize the joint.

[0011] More specific configurations of the present invention are described in the claims. Effect of the Invention

[0012] According to the present invention, it is possible to provide a welding method which prevents specular reflection when photographing the surface of a workpiece to be welded and also suppresses the occurrence of porosity in the workpiece to be welded.

[0013] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view and a graph showing an example of a flow of a welding method according to the present invention; [Diagram 2] Cross-sectional view and graph showing an example of a flow of a conventional welding method [Diagram 3] Graph showing the results of a depth profile analysis of oxygen atom density on the surface of a welded material produced by the welding method of the present invention and a welded material produced by a conventional welding method. [Figure 4] Photographs showing the results of photographing welded materials produced by the welding method of the present invention and welded materials produced by a conventional welding method using a 2D camera and a laser measuring device. [Figure 5A] FIG. 1 is a perspective view showing a first example of an oxygen supply device used in a welding method according to the present invention. [Figure 5B] FIG. 1 is a perspective view showing a first example of an oxygen supply device used in a welding method according to the present invention. [Figure 5C] 1A and 1B are a top view and a side view showing a first example of an oxygen supply device used in the welding method of the present invention. [Figure 6] 1A and 1B are a top view and a side view showing a second example of an oxygen irradiation device used in the welding method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the welding method of the present invention will be described with reference to the drawings.

[0016] Fig. 1 is a cross-sectional view and a graph showing an example of the flow of the welding method of the present invention. Fig. 1 shows the flow (a) to (f) of the welding method of the present invention together with a cross-sectional schematic diagram of the material to be welded 1, welding torch 2, shielding gas 3, arc 4, oxygen supply device 5, oxygen-containing gas 6, and joint 7, and further includes graphs of the melting phase, shielding gas flow rate, welding current, and surface temperature in each step (a) to (f).

[0017] As shown in Fig. 1, the welding method of the present invention includes melting steps (a) and (b) in which an inert gas (shielding gas) 3 is sprayed onto the joint of materials 1 to be welded while the joint is melted by arc discharge 4, and an oxidation step (d) in which, in a state in which a part of the molten joint 7 is solidified and the other part is molten, an oxygen-containing gas 6 is supplied to the inert gas 3 and the joint 7 to oxidize the joint. As a comparison with Fig. 1, Fig. 2 shows a cross-sectional view and a graph showing an example of the flow of a conventional welding method.

[0018] In the present invention, as shown in Fig. 1, two materials to be welded (conductors) 1 are placed, and their tips are brought into contact with each other by controlling an arc (heat source) 4 to obtain a joint (molten part) 7. At this time, the joint 7 solidifies from the bottom toward the top (surface), but while the surface is still molten, i.e., before solidification of the surface is complete, an oxygen-containing gas 6 is sprayed onto the inert gas 3 and the joint 7 to oxidize the surface of the joint 7.

[0019] In this way, by spraying a gas containing oxygen onto the surface of the joint 7, the inert gas 3 remaining around the joint 7 is removed, and the surface of the joint 7 is intentionally oxidized, thereby reducing the gloss of the surface of the joint 7 and preventing specular reflection when photographing.

[0020] In addition, the present invention introduces oxygen during the solidification process of the joint 7 after welding is completed, so unlike the case where oxygen is introduced during welding, there is no risk of porosity occurring inside the workpiece 1 and no risk of a decrease in the mechanical properties of the workpiece 1.

[0021] In the present invention, since the oxygen-containing gas 6 is sprayed into the inert gas 3 to remove the inert gas 3, it is not necessary to stop the supply of the inert gas 3. Therefore, the electrodes of the welding torch 2 can be preserved.

[0022] The oxygen supply step is preferably carried out when the temperature of the surface of the joint 7 of the workpiece 1 is 400° C. or higher. If the temperature of the surface of the joint 7 of the workpiece 1 is less than 400° C., the surface of the joint 7 of the workpiece 1 cannot be efficiently oxidized.

[0023] The oxygen-containing gas 6 is not particularly limited as long as it is a gas containing oxygen, but it is convenient to use air. The oxygen supply device 5 is also not particularly limited, and may be in any form as long as it can efficiently supply the oxygen-containing gas 6 to the surface of the joint 7.

[0024] Fig. 3 is a graph showing the results of a depth profile analysis of oxygen atom density on the surface of a welded material produced by the welding method of the present invention and a welded material produced by a conventional welding method. As shown in Fig. 3, it can be seen that the oxygen concentration on the surface of the welded material is higher according to the method of the present invention shown in Fig. 1 than that of the welded material produced by the conventional method. Although the surface of the welded material is naturally oxidized to some extent, it can be seen that when the oxygen supply process is carried out as in the present invention, the oxygen concentration is significantly higher than that of natural oxidation. The concentration of oxygen atoms on the surface can be analyzed by SEM (Scanning Electron Microscope) or ESCA (Electron Spectroscopy for Chemical Analysis).

[0025] Figure 4 is a photograph showing the results of photographing a welded material produced by the welding method of the present invention and a welded material produced by a conventional welding method using a 2D camera and a laser measuring device. As shown in the 2D camera photograph in Figure 4, the surface of the welded material produced by the conventional welding method is difficult to observe due to reflections from surrounding objects, mirror reflections from the camera, and mirror reflections from the lighting. On the other hand, the surface of the welded material produced by the welding method of the present invention has no surface gloss and clear edges can be confirmed.

[0026] Also, comparing the photographs taken with the laser measuring device in Figure 4, it can be seen that the surface of the workpiece prepared by the conventional welding method has missing data (dotted line area) because the mirror-reflecting parts cannot receive light and cannot be measured, whereas the surface of the workpiece prepared by the welding method of the present invention does not have such missing data.

[0027] 5A and 5B are perspective views showing a first example of an oxygen supplying device used in the welding method of the present invention, and Fig. 5C is a top view and a side view showing the first example of the oxygen supplying device used in the welding method of the present invention. The oxygen supplying device 5 may have a form having a plurality of gas outlets, for example, as shown in Figs. 5A to 5B.

[0028] Fig. 6 is a top view and a side view showing a second example of an oxygen supply device used in the welding method of the present invention. The oxygen supply device shown in Fig. 6 has an ejection part 8 that ejects oxygen-containing gas and an intake part 9 that sucks the oxygen-containing gas. In this way, the oxygen-containing gas may be recovered. With such a configuration, the supply amount of oxygen-containing gas can be easily controlled.

[0029] As described above, according to the present invention, it has been shown that a welding method can be provided that prevents specular reflection when photographing the surface of the workpiece and also suppresses the occurrence of porosity in the workpiece. The present invention is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations described. It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0030] 1...workpiece, 2...torch, 3...shielding gas, 4...arc, 5...oxygen supply device, 6...oxygen-containing gas, 7...molten part of workpiece.

Claims

1. a melting step of melting the joint by arc discharge while spraying an inert gas onto the joint of the workpieces; and an oxidation step of supplying an inert gas and a gas containing oxygen to the molten joint while a portion of the molten joint is solidified and another portion is molten, thereby oxidizing the joint.

2. A welding torch is placed facing the surface of the joint of the workpiece, In the melting step, the inert gas is supplied in a direction from the welding torch toward the workpiece, and melting of the joint begins from the surface of the workpiece facing the welding torch, The welding method according to claim 1 , wherein the oxidation step oxidizes at least the surface of the joint that faces the welding torch.

3. 2. The welding method according to claim 1, wherein the oxidation step is carried out when the surface temperature of the workpiece is 400° C. or higher.

4. The welding method according to claim 1 , wherein the melting step melts ends of the two workpieces together.

5. The welding method according to claim 4 , wherein the oxidation step comprises removing the inert gas to oxidize the ends of the two workpieces while the ends of the workpieces are melted.

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