JPS6025230B2 - Flash welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to flash welding methods, and more particularly to improving the quality of flash weld joints.

In the flash welding method, a voltage is applied between opposing welding materials, and the end surfaces are heated by resistance heat generation, arc discharge, etc. generated by contact between the end surfaces of the welding materials, and the melting temperature of the welding materials is reached. This welding method then applies pressure between the materials to be welded to form a joint.

Currently, the flash welding method is employed in a wide range of fields, but in recent years, the issue of axiality of flash welds has become important as the cross-sections of materials to be welded have become larger or the strength has increased.

For example, fittings for large-diameter pipes in petroleum pipelines are required to have high rutting resistance at low temperatures due to the environment in which they are used, and this is a major issue to be resolved when applying the flash welding method.

In addition, this flash welding method has been adopted for manufacturing chains for ships, etc., but as the strength and diameter of the chain increases, the stiffness of the welded part tends to increase, especially in the welded part. A major problem has emerged: the deterioration of hostilities. The reasons for this deterioration in joint strength due to flash welding are as follows.

The first reason is that in joints made by flash welding, the end faces are heated in the process described above and the materials to be welded are melted and pressurized to join the two end faces. In the flash welding method, TIG, MIG
This is because, unlike arc welding such as hot arc welding, no welding material is used. That is, in flash welded joints, no alloying elements are added from the outside, and therefore the grade of the joint is influenced by the components of the materials to be welded. On the other hand, the IG of the material used as the material to be welded
The chemical composition is not determined with flash weldability taken into account, but simply based on the intended use. The strength and toughness of such materials to be welded are obtained through rolling, heat treatment, etc., and therefore, once heated and melted, such as in the joints of flash welded joints, these properties are lost. This is the cause of deterioration in gourd quality. The second cause of quality deterioration is welding defects.

In order to eliminate defects in flash welded joints, it is necessary to generate a uniform flash during flashing, which is the heating process, and to make sure that the end face temperature of the welded material reaches the melting temperature just before pressurization (upset), which is the final welding process. It is necessary that the end face is kept clean without causing oxidation, or that the end face has few irregularities. However, when flash welding materials with a large cross-sectional area, such as thin wide medium materials, large-diameter pipes, and large-diameter round pieces, it is difficult to generate flash uniformly over the entire end surface, and the end surface has large irregularities. Welding defects often occur due to these factors.

This is because flash occurs locally, resulting in the formation of concave depressions (craters) in concentrated areas, which remain as defects after welding and cause deterioration of graininess of the welded joint. In the past, various measures have been taken to solve the above problems, such as lowering the flash voltage, lowering the impedance of the welding machine, examining control methods, and examining the upset pressure force, thereby improving rice grain properties and quality. I've been trying. However, although such a method has the effect of suppressing the occurrence of defects to some extent, it cannot prevent the deterioration of taste due to the first reason, and there is a limit to the improvement of toughness. In view of the above-mentioned points, it is an object of the present invention to improve the quality of a welded joint by externally adding alloying elements to the joint portion of the flash welded joint.

That is, the present invention is a flash welding method characterized in that an auxiliary material is provided on the welding transformer side surface adjacent to the abutting ends of the materials to be welded, and these materials are flashed simultaneously.

A detailed explanation will be given below according to the drawings.

As shown in Figure 1, in the flash welding method, a voltage (flash voltage) is applied between the workpieces 1 fixed to an electrode 2, and the ends of the workpieces are brought into light contact with each other (this process is called flashing). ) Both end faces are heated, and when the end faces reach a sufficient melting temperature, pressure is rapidly applied between both end faces (this process is called upset) to complete welding. During flushing, both end faces partially come into contact, but at this time, a large short-circuit current flows through the contact portion, and the contact portion reaches a melting temperature in a short time and is instantly burned out. The present inventors observed the phenomenon of this contact area in detail, and as shown in FIG. , or scattered.

This phenomenon is explained as follows.

That is, when the contact 4 occurs between the end faces, the secondary side of the welding transformer 3 becomes an open circuit, and a current of approximately several thousand to several tens of thousands of amperes flows through the secondary circuit. At this time, a magnetic flux 5 due to this large current is formed in the space around the secondary circuit, as shown in Figure 3. As can be seen from the figure, the magnetic flux distribution around this secondary circuit is dense on the inside of the secondary circuit and sparse on the outside. As a result, a driving force from the inside of the secondary circuit to the outside is generated in the arc formed between the energized molten metal of the contact part 4 or the welded material due to the interaction between the current from the eye and its magnetic field. , welding the molten metal at the contact part to the outside, i.e. welding transformer 3
Move or scatter to the opposite side. The present invention is utilized in such a situation during flash welding, and an example thereof is shown in FIG. 4. When the auxiliary material 6 is placed adjacent to the side face of the welding transformer side 3 adjacent to the butt ends of both materials 1 to be welded, and these materials are simultaneously flash welded, the end surfaces of the materials 1 and 6 will be damaged during flashing. A flash occurs equally in both, and both are heated and melted. At this time, the molten metal formed by the contact between the six auxiliary materials adjacent to the welded material 1 moves between the end faces of the welded material in the direction opposite to the welding transformer 3 due to the phenomenon described above. Or scatter. As a result of this movement, the molten metal reaches the opposite side of the welding transformer 3 of the workpiece 1 and ends up being scattered. In this way, the molten metal of the auxiliary material moves in the opposite direction of the welding transformer and scatters, leaving a portion of the molten metal of the auxiliary material on the end face of the welded material. A layer of molten metal of the auxiliary material 6 is formed on the entire end surface of the material, and as a result, combined with the molten metal of the material to be welded 1, the end surface of the metal to be welded has a composition different from that of the material to be welded. A molten metal alloy layer is formed. By forming such a molten metal layer having a composition different from that of the material to be welded, it is possible to obtain a welded joint whose quality is different from that of a joint obtained by the secondary flash welding method. Here, the material used as the auxiliary material 6 is a single element material consisting of elements that are effective in improving the graininess of the joint of the welded material;
Alternatively, by using an alloying element consisting of two types of elements, an element for improving toughness can be added to the end face of the welded material.

As a result, it is possible to obtain a flash welded joint with significantly superior rutting resistance compared to conventional joints. Further, according to the present invention, it is possible to control the flash welding phenomenon by using the auxiliary material 6, and as a result, it is possible to reduce defects in the joint. In other words, in the flash welding phenomenon, it is generally known that the composition of the molten metal formed on the end face of the welded material changes greatly depending on the temperature, but by adding alloying elements using the auxiliary materials mentioned above, The composition of the molten metal or its physical properties such as melting point and viscosity can be changed. If the composition or amount of the added element is selected according to the material to be welded, it becomes possible to generate a uniform and fine flash, resulting in a smooth end surface of the material to be welded, and as a result, a flash welded joint without defects. can be obtained. Furthermore, many inclusions made of oxides such as Si and Mn are generally formed on the welded joint surface, and these are harmful to the rutting property of the joint.

The reason why such inclusions are likely to be formed is that air is likely to be trapped between the end faces of the welded material during flushing. According to the method of the present invention, the generation of such inclusions can also be prevented by T
This can be suppressed by adding deoxidizing elements such as i, Nb, and N, and rice grain quality can be improved. According to the above description of the present invention, the auxiliary material must be placed adjacent to the material to be welded and on the side where the welding transformer is located. When the auxiliary material is placed on the side opposite to the side where the welding transformer is located, it is difficult to make the alloying elements uniform over the entire end face of the welded material. According to the studies conducted by the present inventors so far, the size of the auxiliary material used in the present invention is as shown in FIG.
It is sufficient that the length 1 is the same as that of the inside, and the inside a is equal to or longer than the flashing distance on one side of the workpiece 1 to be welded.

The thickness b of the auxiliary material may be selected depending on the thickness of the material to be welded, and when the material to be welded is thick, better results can be obtained by making the auxiliary material thicker as well. In addition, the shape of the auxiliary material used is
It is necessary to select according to the shape of the material to be welded. In other words, Fig. 4 shows the case where the material to be welded is a flat plate, but if the material to be welded is a round bar or pipe, the shape or arrangement of the auxiliary materials should be as shown in Figs. 5 and 6. There is a need.
Furthermore, when the material to be welded 1 is a pipe material, Figs. 7 and 8
As shown in the figure, an annular welding transformer 9 may be placed outside or inside the pipe material and flash welded.
In such a case, as shown in FIGS. 7 and 8, the auxiliary material 6 may be placed on the outer or inner surface of the material to be welded 1 depending on the arrangement of the welding transformer 9. The embodiment shown in FIG. 7 is also applicable to the case of bamboo wood. In addition, in the present invention, it goes without saying that the auxiliary material is not limited to one type,
Depending on the purpose, several types of auxiliary materials can be used in appropriate combinations at the same time.

For example, as shown in FIGS. 9 and 10, it is possible to add two or more types of alloying elements by variously combining two or more types of auxiliary materials 6, 7, and 8. In the present invention, if the thickness of the auxiliary material 6 is relatively thin compared to the material 1 to be welded, the resulting flash welded joint shape will have an upset portion 10 in the material 1 to be welded, as shown in FIG. As for the auxiliary material 6, it is deformed outward by the material to be welded 1, so that no offset portion is generated and it is separated from the material to be welded 1.

Therefore, the auxiliary material 6 can be easily removed after flash welding, and does not pose a problem when using the welded joint. The above explanation focused on the toughness of the weld, but by selecting the auxiliary material components, the tensile strength of the weld, bending,
Needless to say, various properties such as fatigue and corrosion can be improved.

As mentioned above, the present invention is based on new knowledge based on the observation of flash welding phenomena, and enables the simple addition of alloying elements to the flash weld joint surface, which has not been done in the past.

Next, the present invention will be explained in more detail with reference to Examples. Using materials having the chemical components shown in Table 1 as materials to be welded and auxiliary materials, flash welding was performed by the method of the present invention or the conventional method. Here, the conventional method refers to welding using only the materials to be welded without using any auxiliary materials. The dimensions of the material to be welded are plate thickness 6.
Legs, middle 300 ribs, length 200 sides. The dimensions of the auxiliary plate are 2 ribs thick, 30mm thick, and 15mm long. Auxiliary materials are
One type of each was arranged as shown in FIG. 1st
Table: Sample material composition (wt) The welding conditions are shown in Table 2.

Table 2 Welding Conditions Table 3 shows the Charpy impact test results of welded parts by the method of the present invention and the conventional method.

The notch position is the joint surface, and the test temperature is 000. Third
As shown in the table, according to the method of the present invention, the Charpy impact value of the welded part is improved compared to the conventional method, and the effect of the method of the present invention is clear. The other mechanical properties of the welded part obtained by the method of the present invention were also satisfactory. Table 3: Results of Schalpy impact test (2-piece V-notch, 5-willow surpise Schalpy test). This makes it possible to obtain flash welded joints with superior magnetic properties compared to conventional methods.

The method of the present invention is applicable not only to the flat plates, round bars, and pipes mentioned above, but also to
It can be applied to materials with various cross-sectional shapes. Furthermore, the method of the present invention can be applied to flash welding of nonferrous metal materials such as copper, aluminum, and alloys thereof, as well as various general steels including stainless steel as materials to be welded.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of flash welding using the secondary method, Figure 2
The figure is a Minato diagram of molten metal movement on the end face, Figure 3 is a schematic diagram showing the distribution of magnetic flux formed in the secondary circuit, and Figure 4 is a diagram showing the distribution of magnetic flux formed in the secondary circuit.
Figure 5 shows an example of the method of the present invention when the material to be welded is a round bar, and Figure 6 shows the case where the material to be welded is a pipe material in the method of the present invention. Figures 7.8 and 9.9 and 10 are diagrams illustrating examples in which an annular welded transformer is used in the method of the present invention, respectively, and Figures 9 and 10 are diagrams illustrating examples in which two or more types of auxiliary materials are used in the present invention. FIG. 11 is a diagram showing an example of a cross-sectional shape of a joint obtained by the method of the present invention. 1: material to be welded, 2: electrode, 3: welding transformer, 4: end face contact portion, 5: magnetic flux, 6, 7, 8: auxiliary material, 9: annular welding transformer, 10: abset part. Figure 1 Figure 2 Figure 6 Figure 3 Figure 4 Figure 5 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Claims] 1. A flash welding method characterized by providing auxiliary materials on the welding transformer side surface adjacent to the butt ends of the materials to be welded, and flashing these materials.