JPH0454548B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method of butt welding end faces of thin steel plates together. (Prior Art) In recent years, butt welding has been widely adopted in place of flat butt welding as a method for welding thin steel plates with high efficiency and precision. In this butt welding method, as shown in Fig. 5 A and B, a thin steel plate 2, which is the material to be welded, is held between electrodes 1 and 1, which also function as a pressurizing device, and are placed facing each other, and these are pressed against each other. This is a type of pressure welding method that attempts to join the end faces of the thin steel plates 2 together in an extremely short time by passing a large current through the welding process. (Problems to be Solved by the Invention) However, when butt welding of thin steel plates, etc. is performed by the above-mentioned butt welding method, there is a problem in that uneven heat input tends to occur in the width direction of the butt surfaces. . That is, heat input tends to be insufficient at both sides of the plate end face, and conversely, heat input tends to be excessive at positions slightly inward from both sides of the plate end face. In particular, if this tendency is remarkable, melting or under-upset will occur at locations where there is excessive heat input, as shown in FIG. 3 in FIG. 6 indicates a defective joint due to excessive heat input. On the other hand, if the heat input is lowered to prevent this phenomenon, there will be insufficient heat input (cold welding) on both sides of the plate end face, resulting in poor bonding on both sides of the plate end face. The present invention aims to provide a butt welding method that can solve these problems, and was realized based on the findings based on research and experiments by the present inventors, which will be described later. (Means for Solving the Problems) First, the causes of the above-mentioned conventional problems will be explained. In other words, the inventors investigated the mechanical and electrical behavior of the causes of uneven heat input through numerical analysis using the finite element method, etc., and also conducted experiments, and found that the conventional problem is as follows. It turned out that this was due to the cause. In other words, during butt welding of thin steel plates, only the areas near the butt surfaces of the thin steel plates are rapidly heated, so the end faces of the thin steel plates 2, 2 at the initial stage of welding experience non-uniform thermal expansion as shown in Figure 4. As a result, the plate is rotated and deformed, and the two sides of the end face of the plate are not brought into sufficient contact with each other, and a non-contact portion is formed at this portion. However, if a large current continues to flow in this state, the current will concentrate in a very local part of the abutting surface adjacent to the non-contact part, resulting in a rapid concentration of heat generation (a reference diagram is attached for reference). . Moreover, on the contrary, heat generation is insufficient on both sides of the plate end surface. For this reason, the current concentration areas slightly inward from both sides of the plate end face would melt through or lack of upset, resulting in poor bonding, and on both sides of the plate end face, bonding failures would occur due to insufficient heat input. be. That is, as described above, when the current density is increased to prevent insufficient heat input on both sides of the plate end face, excessive heat input occurs at a position slightly inward from the both sides, resulting in burn-through and insufficient upset. If the current density is lowered to prevent this, on the contrary, insufficient heat input will occur on both sides of the plate end face. This is because, as shown in Figure 4, a gap is created on both sides of the plate end face, and as the welding progresses, the material softens and after a certain period of time, this gap also comes into contact and this point current will also begin to flow. However, as a result, the total energization time on both sides of the plate end surface becomes insufficient. This is the cause of insufficient heat input. Therefore, the present invention attempts to solve this shortage of total energization time by increasing the current density. That is, in the present invention, first, the current density to be applied to both sides of the end face of the thin steel plate to be welded is made equal to the current density to be applied to the center part, and after a predetermined period of time, the current density to be applied to both sides is changed. By making the current density higher than that in the central portion, the attempt is made to eliminate the bonding failure caused by the uneven heat input described above. In other words, in the present invention, as shown in FIG.
5, and a power source 6 for the electrodes 5, 5 at both ends.
are provided separately from the power supply 7 for the central electrode 4, and these power supplies 6 and 7 supply power to the respective electrodes 4 and 5 separately. At that time, the electrodes 5, 5
The current density supplied to the electrode 4 may be equal to the current density of the electrode 4 at the initial stage of welding, but after a predetermined period of time has elapsed, the current density supplied to the electrode 4 may be made higher than the current density (see FIG. 1B). In other words, at the beginning of welding, the power sources 6 and 7 supply a current that is sufficient to prevent excessive heat input, and when the gap formed on both sides of the plate end comes into contact, only the current density supplied by the electrodes 5 and 5 is applied. is made higher than the current density supplied by the electrode 4. Note that the timing at which the current density is increased can be controlled by both time and the amount of electrode movement. This eliminates the lack of heat input on both sides of the plate end face, and enables good welding on both sides of the plate end face at a current density that prevents excessive heat input at positions slightly inward from the above-mentioned both sides. be. (Example) Hereinafter, the results of implementing the method of the present invention will be explained. First, the components, dimensions, and mechanical properties of the test materials used in this example are shown in Table 1 below.

[Table] FIG. 2 also shows the positional relationship between the electrodes 5, 6 and the thin steel plate 2 when the method of the present invention is carried out. Using the test materials shown in Table 1, butt welding was performed by the method of the present invention in the positional relationship shown in FIG. 2. The results are shown in Table 2 below. Furthermore, Table 2 also shows the welding conditions. Furthermore, explanations of the symbols used in Table 2 are shown in FIG.

[Table] As is clear from Table 2 above, when the method of the present invention was applied, the cracking rate was significantly reduced compared to the conventional method. (Effects of the Invention) As explained above, in a method for butt welding the end faces of thin steel plates together, the present invention first applies the current density that should be applied to both sides of the end faces of the thin steel plates to be welded to the center part. Since current is applied at the same current density as the current density, and after a predetermined period of time, the current density on both sides is higher than the current density in the center, it eliminates the uneven heat input that conventionally occurs on both sides of the plate end face. It is possible to prevent bonding defects caused by this, and to achieve good bonding.

[Brief explanation of drawings]

Figure 1 A and B are schematic explanatory diagrams of the method of the present invention, Figure 2
The figure is an explanatory diagram of the installation position of the electrode when implementing the method of the present invention, FIG. 3 is an explanatory diagram of the welding conditions, FIGS. 4 and 6 are diagrams explaining problems in the conventional method, and FIG. 5 is an explanatory diagram of the welding conditions. It is an explanatory view of a butt welding method. 2 is a thin steel plate, 4 and 5 are electrodes, and 6 and 7 are power supplies.

Claims (1)

[Claims] 1. In the method of butt welding the end faces of thin steel plates, first, the current density to be applied to both sides of the end face of the thin steel plate to be welded is equal to the current density to be applied to the center part, and then after a predetermined period of time has elapsed. A butt welding method characterized by making the current density on both sides of the rear part higher than the current density in the center part.