JPS63149084A - Butt welding method - Google Patents

Abstract

PURPOSE:To prevent the defective joining caused by the unevenness in heat input by making are current density to be electrified to both side parts of the end face of a thin steel plate equal to the current density to be electrified to the center part and making the current density at both side parts higher than that of the center part after the lapse of a specified time. CONSTITUTION:The electrode 4 located at the center part of a plate width and the electrodes 5, 5 located at both ends thereof are used, the power source 6 of the electrodes 5, 5 at both end parts is provided separately with the power source 7 of the electrode 4 at the center part and a power source is individually fed to the respective electrode 4, 5 by the power sources 6, 7. In this case, the current density fed to the electrodes 5, 5 is made equal to the current density of the electrode 4 at the welding initial time and after the lapse of a specified time is made higher than the current density of the electrode 4. The lack of the heat input at both side parts of the plate end face is thus eliminated and a good welding is performed even on the plate end face both side parts with the current density which can prevent the over-heat input at the position slightly approaching to the inner side from both side parts.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for welding end faces of thin steel plates together.

(Prior Art) For example, as a method for welding GI steel plates with high efficiency and high precision, butt welding has been widely adopted in place of fludge-throat welding in recent years.

This butt welding method is as shown in Figure 5 (a) and (b).
By sandwiching the thin plate 2, which is the material to be welded, between the electrodes 1 to 1 which also serve as pressurizing devices, which are arranged facing each other, and applying pressure to the thin plate 2 by butting them together, the above-mentioned 3.
This is a type of pressure welding method in which the end faces of field boards 2 are joined together.

(Problems to be Solved by the Invention) However, when butt welding of thin steel plates and the like 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.

In other words, heat input tends to be insufficient on 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 will drop or insufficient absorption will occur at the position of 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 is based on the research and research conducted by the present inventors, which will be described later.
This was established based on knowledge based on experiments.

(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. Due to the rotational deformation, 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 face.

For this reason, in the current concentration area slightly inward from both sides of the plate end face, melt drops or there is insufficient absorption, resulting in poor bonding, and on both sides of the plate end face, bonding failure occurs due to insufficient heat input. .

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 melt drop and insufficient absorption. 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 surface, and as 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. but,
As a result, the total energization time on both sides of the plate end face 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 the current density in the central portion, it is intended to eliminate the bonding failure caused by the uneven heat input described above.

In other words, in the present invention, as shown in FIG. 1(a), instead of the conventionally used electrode 1, an electrode 4 located at the center of the board width and electrodes 5 and 5 located at both ends of the electrode 4 are used. ,
Power sources 6 for the electrodes 5.5 at both ends are provided separately from a power source 7 for the electrode 4 at the center, and these power sources 6.7 supply power to each electrode 4.5 separately. At that time, the current density supplied to the electrode 5.5 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 5. (See figure (b)).

In other words, in the early stage of welding, a current sufficient to prevent excessive heat input is applied by the power source 6.7, and when the gap formed on the side of the plate end surface comes into contact, the current density supplied by the electrode 5.5 is increased. The current density 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 the sides of the plate end face, and enables good welding on both sides of the plate end face with a current density that prevents excessive heat input at positions slightly inward from both sides. It is.

(Example) The results of implementing the method of the present invention will be explained below.

First, the components, dimensions, and mechanical properties of the test materials used in this example are shown in Table 1 below.

Table 1 (unit duplex weight %) Also, electrode 5.6 and a steel plate 2 when carrying out the method of the present invention
Figure 2 shows the positional relationship between the two.

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.

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 the method of 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 three steel plates to be welded to the central 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 the drawing]

Figures 1 (A) and (B) are schematic explanatory diagrams of the method of the present invention, Figure 2 is an explanatory diagram of the installation position of the electrode when implementing the method of the present invention, Figure 3 is an explanatory diagram of the welding conditions, and Figures 4 and FIG. 6 is a diagram illustrating problems with the conventional method, and FIG. 5 is a diagram illustrating the butt welding method. 2 is a thin steel plate, 4.5 is an electrode, and 6.7 is a power source. Figure 1 (a) Figure 2 Figure 4 Figure 5 (a)

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, and then A butt welding method characterized by making the current density at both sides higher than the current density at the center after a period of time has elapsed.