JP6979901B2 - Resistance welding method - Google Patents

Description

It relates to a resistance welding method for welding between materials to be welded.

When joining materials to be welded such as plate-shaped steel plates, the joining may be performed by spot welding. Spot welding is a type of resistance welding method that uses resistance heat generation to join metals. In the one-sided resistance welding (also called indirect welding or one-sided spot welding) method of spot welding, in a state where the materials to be welded are overlapped, the welding target in which a plurality of materials to be welded are overlapped is pressed by an electrode, and further. Energizing a current from an electrode to a path leading to the ground through a welding target (hereinafter referred to as a conduction path) (hereinafter, pressurizing the welding target and energizing the welding target is simply both pressurization and energization. (Referred to as), the welded portion is heated by resistance heat generation and locally melted, thereby joining the welded materials in a metallurgical manner.

In the one-side resistance welding method, the process of pressurizing and energizing can be divided into initial energization, pre-main energization, and main energization according to the progress of the process. The initial energization is a step of blending the contact surface between the material to be welded and the electrode to be welded and stabilizing the contact state between the materials to be welded. Pre-main energization is a step of enlarging the contact surface so that the contact surface where the two materials to be welded come into contact with each other in the welded portion approaches an appropriate contact area. This energization is a step in which a current is passed through a welding target to melt the welded portion between the welded materials in a state where a contact surface having an appropriate contact area is formed, and the welded portion is melt-bonded. In each energization process, the electrode is brought into contact with the welding target, the welding target is pressurized by the electrode, and a current is conducted from the electrode to the welding target. Therefore, as the pressurization / energization progresses, the electrodes are welded. It cuts into the target.

International Publication No. 2014/167772

However, in the conventional one-sided resistance welding method, welding is performed by adjusting the current value when energizing the object to be welded, but good welding may not be possible even when a certain amount of current is energized. As a result of diligent studies by the inventors, it was found that good welding may not be possible as a result of the current density in the welded portion not being constant even when a certain amount of current is applied. As a result of further studies, as will be described later, the electrodes bite into the welding target due to pressurization and energization, and the size of the conduction path in the weld differs depending on the amount of bite, resulting in a current density in the weld. It was found that there are cases where good welding cannot be performed due to insufficient welding.

Therefore, an object of the present invention is to provide a one-sided resistance welding method capable of good welding regardless of the amount of biting of the electrode.

In the conventional one-sided resistance welding method, welding depends on the current density in the welded portion, and the current density depends on the amount of biting of the electrode into the object to be welded. Therefore, if the amount of biting of the electrode is excessive, proper welding may not be possible. Hereinafter, the electrodes used in the conventional one-sided resistance welding method will be described, the relationship between the biting amount of the electrodes and the area of the welded portion will be described, and the effect of the area of the welded portion on the weld will be described.

In the electrode used in the conventional one-sided resistance welding method, the tip portion of the electrode is curved (see FIG. 3A), or the peripheral surface of the tip region of the electrode is inclined (see FIG. 3B). Also, in the tip region of the electrode, the width becomes narrower as it approaches the tip portion.

First, the amount of biting when pressurization and energization are performed using an electrode having such a shape will be described. As described above, at the time of welding, the electrode bites into the welding target from the tip portion of the electrode with pressurization and energization. Since the electrode used in the conventional one-sided resistance welding method has a shape in which the width becomes narrower as it approaches the tip portion, the larger the amount of electrode biting, the more the cross section of the portion where the electrode bites into the welding target on the surface of the welding target ( Hereinafter, it is referred to as a bite surface. The bite surface 21 in FIG. 6) becomes wider.

On the other hand, the welded portion corresponds to the vicinity of the contact surface between the materials to be welded in the conduction path in which the current is conducted when the current is applied. When energized, a current flows from the electrode of the portion that bites from the biting surface and is in contact with the welding target to the welding target, passes through the inside of the welding target from the electrode of this portion, and reaches the ground to form a conduction path. Therefore, the welded portion is formed in the vicinity of the region directly below the bite surface in the region sandwiching the contact surface between the materials to be welded.

From the above, the area of the contact surface between the welded materials of the welded portion (hereinafter, also referred to as the cross section of the welded portion) (hereinafter, simply referred to as the area of the welded portion) is the amount of biting of the electrode into the welding target. And it can be seen that it increases in proportion to the area of the bite surface. As described above, as the pressurization / energization progresses, the electrodes bite into the welding target, so that the area of the welded portion expands as the pressurization / energization progresses.

Next, the relationship between the area of the weld and the weld quality will be described. Welding is performed by melting the welded portion by the heat generated by the resistance generated by the current flowing through the welded portion. The resistance heat generation increases as the current value increases, and since the welded portion has a certain area, it increases as the current density in the welded portion increases. When the current value is constant, the current density increases as the area of the weld is smaller. Therefore, when a current having the same current value is applied, the larger the area of the welded portion, the smaller the current density and the smaller the resistance heat generation. If the resistance heat generation is too small, the welding strength is insufficient and welding defects occur. On the contrary, when a current having the same current value is applied, the smaller the area of the welded portion, the larger the current density and the larger the resistance heat generation. When resistance heat generation in an appropriate range occurs, sufficient welding strength is ensured and good welding quality is ensured. On the other hand, if the current density becomes too large, dust is generated and the surface of the welded portion is roughened, resulting in deterioration of welding quality.

As described above, in the conventional one-sided resistance welding method, the bite amount of the electrode increases as the pressurization / energization progresses, and the area of the welded portion increases. As the area of the weld increases, the current density in the weld decreases. If the current density is insufficient, the resistance heat generation of the welded portion is insufficient, the welded portion is not sufficiently melted, the welding strength is insufficient, and the welding quality is deteriorated.

Since such a problem may occur, in the conventional one-sided resistance welding method, the current value of the current to be conducted to the welding target is sufficiently increased to avoid insufficient welding strength. However, there is a limit to energizing a current having a sufficient current value, and the scale of the device for supplying power is also large. Therefore, there is a demand for a resistance welding method for stably performing good welding while suppressing the current value of the current to be conducted to the object to be welded in the main energization.

In the resistance welding method of the present invention provided in response to such a requirement, the welded material is welded at the welded portion by energizing the welded material from the electrode while pressurizing a plurality of welded materials with the electrodes. In the resistance welding method, the electrode is continuously pressed from a shoulder portion and the shoulder portion in which the electrode is inclined toward the center side of the electrode with respect to the pressurizing direction in which the electrode is pressed against the material to be welded. It is provided with a protruding portion that protrudes in the direction, and the inclination angle of the protruding surface of the protruding portion with respect to the pressurizing direction is smaller than the inclination angle of the shoulder portion, and the initial energization that blends the contact surface between the electrode and the welded material. In this case, the projecting portion is brought into contact with the material to be welded, and in the case of pre-main energization performed before the main energization, the projecting portion is made to bite into the material to be welded, and in the case of the main energization. It is characterized in that a current having a current value higher than the current value of the pre-main energization is energized to the welded material, and at least a part of the shoulder portion is made to bite into the welded material.

As described above, in the resistance welding method of the present invention, a protrusion is provided at the tip of the electrode, and the protrusion is made to bite into the material to be welded during the initial energization and the pre-main energization. Since the shoulder portion does not bite into the material to be welded by letting the projecting portion bite into the material to be welded, the area of the welded part formed by the electrode biting during the initial energization and the pre-main energization is the cross-sectional area of the protruding part. It becomes almost the same as, and does not increase any more. Therefore, since the area of the welded portion at the stage where the shoulder portion starts to bite is smaller than the area of the welded portion at the start of the main welding in the conventional one-sided resistance welding method, the area of the welded portion during the main welding is the conventional one-sided resistance welding. It is smaller than the area of the weld formed by the method. As a result, compared to the conventional one-sided resistance welding method, it is possible to secure a sufficient current density even if the current value is lowered in the current conducted to the welded portion, and to secure a sufficient welding strength. It is possible to perform good welding.

Further, when there is a gap between the materials to be welded, the action of closing the gap is generated by pressurization / energization during the initial energization and the pre-main energization. Since the reaction force received by the electrode from the material to be welded is small in the state where there is a gap, the amount of biting into the material to be welded by the electrode is smaller than in the state where there is no gap. Therefore, in the conventional one-sided resistance welding method, the amount of bite that the electrode bites into the material to be welded during the initial energization and the pre-main energization differs depending on the presence / absence and degree of the gap, and the area of the welded portion also differs. On the other hand, in the resistance welding method of the present invention, the area of the welded portion formed by the end of the pre-main welding is about the same as the cross-sectional area of the protruding portion of the electrode, and does not depend on the presence / absence / degree of the gap. As a result, in the resistance welding method of the present invention, the area of the welded portion becomes constant regardless of the presence or absence of a gap, and stable and good welding can be performed.

Further, the strength of welding depends on the nugget formed by melting and solidifying the welded portion. In particular, the depth in the press direction in which the nugget is formed beyond the boundary between the materials to be welded becomes sufficiently deep, so that the joint between the materials to be welded becomes strong. Therefore, it is important to form the nugget to a sufficient depth in the resistance welding method. The amount of electrode biting has a great effect on the depth of the nugget. In the resistance welding method of the present invention, since the electrode is provided with a protruding portion, the tip portion of the electrode is formed at a deeper position even if the area of the welded portion is the same as in the conventional one-sided resistance welding method. (See FIG. 8). As a result, in the resistance welding method of the present invention, even if the area of the welded portion is about the same, the nugget can be formed to a deeper position as compared with the conventional one-sided resistance welding method, and stronger welding becomes possible. Good welding can be performed.

In the resistance welding method of the present invention, the current of the first current value is energized in the initial energization, the current of the second current value higher than the first current value is energized in the pre-main energization, and the pre-main energization is performed. Then, it is preferable to energize a current having a third current value higher than the second current value.

By increasing the current value at the time of energization according to the process in this way, it is possible to energize at the current value suitable for blending the contact surface between the material to be welded and the electrode in the initial energization. In the energization, the current value suitable for properly biting the electrodes can be energized, and in the main energization, the current value suitable for melt-bonding between the materials to be welded can be energized.

The resistance welding device of the present invention is a resistance welding device that welds the material to be welded at a welded portion by energizing the material to be welded from the electrode while pressurizing a plurality of materials to be welded by an electrode. It has a drive device for moving an electrode, a power supply device for energizing a current from the electrode, and a control device for controlling the operation of the drive device and the power supply device. The electrode is covered by the electrode. The shoulder portion inclined toward the center side of the electrode with respect to the pressurizing direction for pressurizing the weld material and the projecting portion continuously projecting from the shoulder portion in the pressurizing direction are provided. The inclination angle with respect to the pressurizing direction is smaller than the inclination angle of the shoulder portion, and the electric control device makes the protruding portion into the welded material at the time of initial energization to fit the contact surface between the electrode and the welded material. In contact with each other, during the pre-main energization performed before the main energization, the projecting portion is made to bite into the welded material, and at the time of the main energization, the current value is higher than the current value of the pre-main energization. Is energized in the material to be welded, and is controlled so that at least a part of the shoulder portion is made to bite into the material to be welded.

Also in the resistance welding apparatus of the present invention, as in the resistance welding method of the present invention, the current value at the time of conduction to the welded portion is suppressed by suppressing the welded portion from becoming larger than necessary regardless of the biting amount of the electrode. It is possible to secure a sufficient current density in the welded portion while suppressing the above, secure a sufficient welding strength, and perform good welding.

According to the present invention, good welding can be performed regardless of the biting amount of the electrode.

It is a figure which illustrates the structure of the welding object. It is a figure which illustrates the structure of the welding apparatus used in the resistance welding method of this invention. 3A and 3B are conventional electrodes, and FIG. 3C shows an electrode according to the present invention. It is a figure explaining the resistance welding method of this invention, FIG. 4A is a figure explaining a conduction process, and FIGS. It is a figure which shows the process flow of the resistance welding method of this invention. It is a figure which compares the state which the electrode bites into the welding object with the prior art. It is a figure which compares the state which the electrode bites into the welding object when there is a gap between the materials to be welded with the prior art. It is a figure explaining the formation range of a nugget.

Hereinafter, a one-sided resistance welding method according to an embodiment of the resistance welding method of the present invention will be described in detail with reference to the drawings. Prior to the description of the one-sided resistance welding method, first, a configuration example of the welding target 2 to be welded in the one-sided resistance welding method according to the present invention will be described, and when the one-sided resistance welding method according to the present invention is carried out. After explaining the configuration example of the welding apparatus 10 used, the one-side resistance welding method (one-side spot welding method) according to the embodiment of the present invention will be described.

First, a configuration example of the welding target 2 will be described.

As illustrated in FIG. 1, the welding target 2 is composed of a material to be welded 4 and a material to be welded 6, and the material to be welded 4 and the material to be welded 6 are welded and joined at a welded portion 8. .. For example, the material 4 to be welded is a flat plate. The material 6 to be welded is three-dimensionally formed, and one surface of the material 12 to be welded, which is also three-dimensionally formed, is joined to the inside of the open space. Then, in the welded portion 8, the back surface of the material to be welded 6 with respect to the surface in contact with the material to be welded 4 is closed in the space formed by the material to be welded 12 and the material to be welded 6. Welding may be performed by sandwiching the welding target 2 between two electrodes (direct welding), but since the electrodes cannot be provided in the space formed by the material to be welded 12 and the material to be welded 6, the electrode to be welded cannot be provided. The material 4 and the material to be welded 6 are joined by one-side spot welding. In one-side spot welding, in the welded portion 8, the electrode 1 is arranged on the back surface side of the welded material 4 with respect to the surface in contact with the welded material 6, and the ground 14 is arranged so as to be electrically conductive with the welded material 6. Weld. Then, a predetermined current is conducted from the electrode 1 to the conduction path 16 from the electrode 1 to the ground 14 via the welded material 4 and the welded material 6. The current to be conducted in the conduction path 16 melts and joins the material 4 to be welded and the material 6 to be welded in the welded portion 8.

Next, a configuration example of the welding apparatus 10 used when carrying out the one-sided resistance welding method according to the present invention will be described.

As illustrated in FIG. 2, the welding apparatus 10 of the present invention includes an electrode 1, a ground 14 paired with the electrode 1, a robot 18 having a robot arm 20 that holds the electrode 1 and is movable, and an electrode 1. A transformer 22 for conducting a current between the and the ground 14, a timer 24 for controlling the current supplied to the transformer 22, and a control device 26 for controlling the operation of the timer 24 and the robot 18 are provided.

In the welding apparatus 10, the electrode 1 pressurizes the welding target 2 and conducts a predetermined current to the welding target 2, so that the current is conducted from the electrode 1 to the conduction path 16 from the electrode 1 to the ground 14 through the welding target 2. .. In the welding target 2, the overlapping materials 4 and 6 to be welded are joined by welding. The electrode 1 pressurizes the welding target 2 and conducts a predetermined current to the welding target 2 to heat and melt the welding target 2 on the conduction path 16 to weld the welding target 2. The current conducted from the electrode 1 can be determined according to the thickness of the welding target 2, the thickness of each of the materials 4 and 6 to be welded, the required welding strength, and the like, and is adjusted by the transformer 22.

The transformer 22 converts the current supplied via the timer 24 into a predetermined current value, and then conducts the converted current from the electrode 1 to the welding target 2. For example, a current of several A at 400 V supplied via the timer 24 is converted into a current of 15000 A at 3 to 5 V and conducted from the electrode 1. Further, the timer 24 controls the timing at which the current is conducted from the electrode 1 via the transformer 22. The transformer 22 is controlled by the control device 26, and the control device 26 can also control the transformer 22 via the timer 24. Therefore, the control device 26 controls the input timing, the current value, the energization time (cycle), and the like of the current conducted from the electrode 1 to the welding target 2.

The robot 18 is a drive device that includes an electrode 1 and a robot arm 20 and drives the electrode 1. The robot 18 has a configuration in which the electrode 1 can be moved to an arbitrary position within a predetermined range by the robot arm 20, the electrode 1 is moved to a predetermined welding position, and the welding target 2 is pressed against the electrode 1. Let me. Further, the operation of the robot 18 is controlled by the control device 26.

In this way, the control device 26 controls the operation of the robot 18 to which the electrode 1 is connected, and at the same time, controls the current conducted from the electrode 1. Therefore, the control device 26 controls pressurization and energization in the welding process.

Next, the configuration of the electrode 1 in the welding apparatus 10 will be described while comparing with the electrodes used in the conventional one-sided resistance welding method. The conventional electrode 28 shown in FIG. 3A is composed of an electrode body 30 whose peripheral surface is parallel to the pressurizing direction and a curved tip surface 32 projecting in the pressurizing direction. Further, the conventional electrode 34 shown in FIG. 3B is composed of an electrode body 36 whose peripheral surface is parallel to the pressurizing direction and a tip portion 38. The tip portion 38 is composed of a shoulder portion 40 and a tip surface 42. The tip surface 42 is a plane in a direction intersecting the pressurizing direction. The shoulder portion 40 has an outer peripheral surface 44 formed from the lower end of the peripheral surface of the electrode body 36 to the tip surface 42, and the outer peripheral surface 44 is inclined in the direction from the peripheral surface of the electrode body 36 toward the inside of the electrode 34. In such electrodes 28 and 34, the tip surface 32 and the tip 38 bite into the welding target 2 from the initial energization to the main energization, respectively. Further, since the tip surface 32 is a curved surface and the shoulder portion 40 of the tip portion 38 is inclined inward, the area of the bite surface (see FIG. 6) increases as the bite amount increases.

On the other hand, the electrode 1 used in the one-sided resistance welding method according to the present invention shown in FIG. 3C is composed of an electrode body 3 whose peripheral surface is parallel to the pressurizing direction and a tip portion 5. The tip portion 5 is composed of a shoulder portion 7 and a protruding portion 9. The shoulder portion 7 is continuously formed on the electrode body 3 on the pressurizing direction side, and is inclined so that the peripheral surface 11 of the shoulder portion 7 approaches the inside of the electrode 1 as the distance from the electrode body 3 increases. The protruding portion 9 is formed so as to protrude from the tip of the shoulder portion 7 in the pressurizing direction with a protrusion amount H, and includes a protruding surface 13 and a tip surface 15 parallel to the pressurizing direction. The tip surface 15 is formed at the tip of the protruding portion 9 in the pressurizing direction, and the tip surface 15 is a curved surface or a flat surface projecting in the pressurizing direction. In the present embodiment, the tip surface 15 is illustrated and described as a curved surface.

Next, the one-sided resistance welding method according to the present invention will be described.

First, the initial energization is performed. In the initial energization, as shown in FIG. 4A, the welding target 2 is pressurized with a predetermined pressing force by the electrode 1 while the current of the current value of the electrode 1 to the I1 is conducted to the welding target 2 (FIG. Step 1 of 5). In the initial energization, first, the tip surface 15 of the protruding portion 9 of the electrode 1 comes into contact with the surface 17 of the welding target 2. After that, when the current is conducted through the welding target 2, the welding target 2 is heated in a range where the welding target 2 does not melt, and the protruding portion 9 of the electrode 1 starts to bite into the welding target 2 from the surface 17 (FIG. 4 (b)). By such pressurization and energization, the contact surface between the material 4 to be welded and the electrode 1 of the welding target 2 is made to fit in the initial energization. The pressing force and the current value in the initial energization are, for example, the pressing force is about 30 kgf to 100 kgf, and the I1 is about 2 kA to 3 kA.

Next, pre-main energization is performed. In the pre-main energization, as shown in FIG. 4A, the welding target 2 is pressurized with the same predetermined pressing force as the initial energization by the electrode 1, and the current of the current value of I2, which is higher than the current value of I1, is applied. Conduction is performed from the electrode 1 to the welding target 2 (step 2 in FIG. 5). In the pre-main energization, since the current of the current value of I2 higher than the initial energization is conducted, the welding target 2 is heated to a temperature higher than that at the time of the initial energization, and the electrode 1 is promoted to bite into the welding target 2. It should be noted that I2 is about 4 kA to 6 kA, and the current value is such that the welding target 2 does not melt, and the melt-bonding between the materials to be welded 4 and 6 is not performed. Further, in the pre-main energization, the protrusion amount H in the pressurizing direction of the projecting portion 9 and the pressing force and the current value in the pressurizing / energizing are adjusted so that the shoulder portion 7 of the electrode 1 does not bite into the projecting portion 9. Only bites into the welding target 2. The biting surface 21 which is a cross section of the surface 17 of the welding target 2 at the portion where the electrode 1 bites into the welding target 2 substantially coincides with the cross section of the protruding portion 9 on the surface parallel to the surface 17. Further, since only the protruding portion 9 bites into the welding target 2 in the initial energization and the pre-main energization, the biting surface 21 becomes substantially constant from the initial energization to the pre-main energization (FIG. 4 (c)).

Finally, the main energization is performed. In the main energization, as shown in FIG. 4A, the current value of I3, which is higher than the current value of I2, is increased while the electrode 1 pressurizes the welding target 2 with the same predetermined pressing force as the initial energization and the pre-main energization. Is conducted from the electrode 1 to the welding target 2 (step 3 in FIG. 5). In the main energization, the current of the current value of I3, which is higher than that of the pre-main energization, is conducted, so that the welding target 2 is heated to a higher temperature than the pre-main energization, and the electrode 1 is promoted to bite into the welding target 2, and the shoulder. The portion 7 bites into the welding target 2. Therefore, the biting surface 21 coincides with the cross section of the biting shoulder portion 7, and is larger than the biting surface 21 in the pre-main energization. The I3 is about 6 kA to 10 kA, the welding target 2 can be sufficiently melted, and the welded materials 4 and 6 are melt-bonded.

Hereinafter, the effect of the one-sided resistance welding method according to the present invention will be described while comparing with the conventional one-sided resistance welding method. Regarding the effects, the effect that the welded portion 23 does not expand too much, the effect that the change in the welding strength is small depending on the presence or absence of the gap between the materials to be welded 4 and 6, and the effect that the depth of the nugget 25 can be secured. Each of them will be explained.

First, according to the one-sided resistance welding method according to the present invention, the welded portion 23 does not expand more than necessary during the main energization, and the current density in the welded portion 23 is sufficiently secured while suppressing the current value at the time of energization. It is possible to perform good welding. This will be described in detail with reference to FIG. FIG. 6 shows how the electrodes 1 and 34 bite into the welding target 2 in each energization process, and a cross section of the welded portion 23 in each energization process.

Here, as described above, the welding quality such as the welding strength in resistance welding is affected by the area of the welded portion 23 in the current conduction path 16 and the current density in the welded portion 23 determined by the conducting current value. Weld. Further, the area of the welded portion 23 substantially coincides with the area of the biting surface when the electrodes (1, 28, 34) bite into the welding target 2.

In the conventional one-sided resistance welding method using the electrode 34, the electrode 34 comes into contact with the welding target 2 at the time of initial energization, and the electrode 34 starts to bite into the welding target 2 with the pressurization / energization. The biting surface 21 in a state where the electrode 34 is in contact with the welding target 2 coincides with the tip surface 42, and the area of the cross section s1 in the conduction path 16 of the welded portion 23 also coincides with the area of the tip surface 42. After that, the electrode 34 bites into the welding target 2 from the initial energization to the pre-main energization. As the electrode 34 bites into the welding target 2, the shoulder portion 40 of the electrode 34 bites into the welding target 2, and the cross section s2 of the biting surface 21 and the welded portion 23 expands according to the biting amount (FIG. 6 (a). ), (B)). Similarly, even in the main energization, the cross section s3 of the biting surface 21 and the welded portion 23 further expands with the pressurization and energization. Since welding is performed in the main energization, a current having a size that can secure an appropriate current density is conducted in the widened welded portion 23 (FIG. 6 (c)).

In the one-sided resistance welding method using the electrode 1 according to the present invention, the protruding portion 9 of the electrode 1 comes into contact with the welding target 2 at the time of initial energization, and the protruding portion 9 of the electrode 1 is brought into contact with the welding target 2 due to pressurization and energization. Start to bite into. The biting surface 21 in a state where the protruding portion 9 of the electrode 1 bites into the welding target 2 coincides with the cross section of the protruding portion 9 that bites into the surface 17 of the material 4 to be welded, and the cross section S1 in the conduction path 16 of the welded portion 23. The area of is also the same as the area of the cross section of the protrusion 9 (FIG. 6 (d)). After that, the electrode 1 bites into the welding target 2 from the initial energization to the pre-main energization. As described with reference to FIG. 4, in the initial energization and the pre-main energization, only the protruding portion 9 of the electrode 1 bites into the welding target 2. Therefore, in the initial energization and the pre-main energization, the cross section S2 of the bite surface 21 and the welded portion 23 is substantially constant regardless of the bite amount (FIG. 6 (e)). During the main energization, the shoulder portion 7 of the electrode 1 begins to bite into the welding target 2 with the pressurization and energization, and the cross section S3 of the biting surface 21 and the welded portion 23 expands accordingly, which is sufficiently wide. It becomes the welded portion 23. Since welding is performed in the main energization, a current having a size that can secure an appropriate current density is conducted in the widened welded portion 23 (FIG. 6 (f)).

As shown in FIGS. 6A and 6B, in the conventional one-sided resistance welding method, the cross sections s1 and s2 of the welded portion 23 expand with pressurization and energization in the initial energization and the pre-main energization. In the one-sided resistance welding method according to the present invention, as shown in FIGS. 6 (d) and 6 (e), the cross sections S1 and S2 of the welded portion 23 do not extend beyond the cross section of the protruding portion 9. Therefore, as can be seen by comparing s2 in FIG. 6 (b) with S2 in FIG. 6 (e), in the initial energization and the pre-main energization, the cross section S2 of the welded portion 23 in the one-side resistance welding method according to the present invention is It is narrower than the cross section s2 of the welded portion 23 in the conventional one-sided resistance welding method. In the main energization, the cross sections s3 and S3 of the welded portion 23 gradually widen, but in the present invention, since the cross section S2 of the welded portion 23 at the start of the main energization is narrower than the conventional cross section s2, welding in the main energization The cross section S3 of the portion 23 is narrower than the conventional cross section s3. As a result, in the one-sided resistance welding method according to the present invention, the current density in the welded portion 23 is sufficiently secured even if the current value conducted to the welded portion 23 is lowered as compared with the conventional one-sided resistance welding method. This makes it possible to secure sufficient welding strength and perform good welding.

Next, the effect of reducing the change in welding strength depending on the presence or absence of the gap t between the materials to be welded 4 and 6 will be described with reference to FIGS. 6 and 7. FIG. 7 also shows how the electrodes 1 and 34 bite into the welding target 2 in each energization process, and a cross section of the welded portion 23 in each energization process.

When there is a gap t between the materials 4 and 6 to be welded, it is necessary to close the gap t between the materials 4 and 6 to be welded in the initial energization, so the biting amount of the electrode 34 is smaller than when there is no gap. .. Therefore, in the conventional one-sided resistance welding method, the cross sections s4 and s5 of the welded portion 23 in the initial energization and the pre-main energization are smaller than the cross sections s1 and s2 when there is no gap (FIGS. 7A and 7B). ). Along with this, the cross section s6 of the welded portion 23 in the main energization is also smaller than the cross section s3 when there is no gap (FIG. 7 (c)). As described above, in the conventional one-sided resistance welding method, the cross-sectional area of the welded portion 23 in the main current is different depending on the presence or absence of the gap t between the materials to be welded 4 and 6, and the currents having the same current value are present. When the current is conducted, the current density is different and the welding quality is different. For example, when a current having an optimum current value when there is no gap t is conducted in the main energization regardless of the presence or absence of the gap t, the cross section s6 of the welded portion 23 is smaller than the cross section s3 when the gap t is present. Therefore, the current density becomes excessive, and dust and surface roughness may occur. On the contrary, regardless of the presence or absence of the gap t, when the current of the optimum current value when the gap t is present is conducted in the main energization, when there is no gap t, the cross section s3 of the welded portion 23 is more than the cross section s6. Due to its large size, the current density may be insufficient and the welding strength may be insufficient.

On the other hand, in the one-sided resistance welding method according to the present invention, although it is necessary to close the gap t between the materials to be welded 4 and 6, only the protruding portion 9 of the electrode 1 becomes the welding target 2 in the initial energization and the pre-main energization. In order to bite into the welded portion 23, the cross sections S4 and S5 of the welded portion 23 substantially coincide with the cross section of the protruding portion 9, and the cross sections S4 and S5 of the welded portion 23 coincide with the cross sections S1 and S2 regardless of the presence or absence of the gap t (FIG. 7 (FIG. 7). d), (e)). Since the gap t between the materials to be welded 4 and 6 is already closed during the main energization, the amount of bite of the electrode 1 in the main energization has nothing to do with the presence or absence of the gap t in the initial energization. The cross section S6 of the welded portion 23 coincides with the cross section S3 (FIG. 7 (f)). As a result, in the one-sided resistance welding method according to the present invention, the cross sections S3 and S6 of the welded portion 23 at the time of main energization are about the same regardless of the presence or absence of the gap t between the materials to be welded 4 and 6, and the same current is obtained. Even if a value current is conducted, the current density becomes the same, the welding quality such as welding strength becomes constant, and stable and good welding can be performed.

Further, according to the one-sided resistance welding method according to the present invention, the depth of the nugget 25 can be secured without enlarging the cross section of the welded portion 23, and good welding can be performed. Such an effect will be described in detail after explaining the relationship between the depth of the nugget 25 and the welding strength.

The nugget 25 is a portion where the materials 4 and 6 to be welded are melted and solidified in the welded portion 23. Further, the nugget 25 grows from the electrode 1 along the conduction path 16. In order to satisfactorily weld between the materials 4 and 6 to be welded, it is necessary to grow the nugget 25 from the material 4 to be welded to a sufficiently deep region of the material 6 to be welded.

In order to grow the nugget 25 to a sufficient depth, in the conventional one-sided resistance welding method, it is necessary to bite the electrode 34 deeply into the welding target 2, but if the biting amount is increased, the cross section of the welded portion 23 becomes larger. In order to form a good nugget 25, it is necessary to increase the current value to be conducted. Further, when the nugget 25 is formed deeply, the width of the nugget 25 may become larger than necessary, and when the width of the nugget 25 exceeds the range covered by the pressure applied by the electrode 34, the molten welding target 2 The material is scattered around and dust is generated.

On the other hand, in the one-sided resistance welding method according to the present invention, only the protruding portion 9 of the electrode 1 bites into the welding target 2 in the initial energization and the pre-main energization. As shown in FIG. 8, when the electrodes 34 and 1 are bitten so that the cross-sectional areas of the welded portions 23 are about the same, the depth of the electrodes 34 corresponds to d1 in the conventional one-sided resistance welding method. In the one-sided resistance welding method according to the present invention, the depth of the electrode 1 is d2, which is increased by the amount of protrusion H of the protruding portion 9. Since the depth (d2) of the electrode 1 can be increased while suppressing the excessive expansion of the width of the nugget 25 by reducing the cross section of the welded portion 23, the nugget 25 is pushed in to form a sufficiently deep region. can do. Therefore, the nugget 25 is formed over a sufficiently deep region of the material 6 to be welded, and good welding can be performed while suppressing the generation of dust. In particular, since the nugget 25 can be formed to a deep position, it is suitable for welding thick plates 4 and 6 to be welded, and for welding three or more welded materials.

The protruding surface 13 of the protruding portion 9 may be parallel to the pressurizing direction, but the peripheral surface 11 of the shoulder portion 7 is tilted at an angle smaller than the tilt angle with respect to the pressurizing direction, and the cross section of the protruding portion 9 is formed. The shape may become smaller toward the pressurizing direction. Even in this case, the cross section of the welded portion 23 in the initial energization and the pre-main energization is smaller than the cross section on the proximal end side of the protruding portion 9, and the cross section of the welded portion 23 in the initial energization and the pre-main energization is made smaller to achieve the main energization. It is possible to prevent the cross section of the welded portion 23 from becoming large at the time of. As a result, good welding can be performed even if the current value to be energized is suppressed.

Further, although the above description has been described by taking the indirect welding method (one-side spot welding method) as an example, the same can be applied to the series welding method and the direct welding method. Further, the material to be welded is not limited to two, and three or more materials to be welded can be welded.

Further, in the above description, the case where the pressurization / energization is a three-stage energization has been described as an example, but at least one of the initial energization, the pre-main energization, or the main energization is further pressurized / energized stepwise. It can also be multi-stage energized. Further, the current value to be conducted is not limited to being increased stepwise, and the current value during the process can be reduced. Further, the pressing force in at least one of the initial energization, the pre-main energization, and the main energization can be made different. As a result, the biting amount of the electrode 1, the cross section of the welded portion 23, and the current value at the time of welding can be adjusted in more detail, and better welding can be performed.

INDUSTRIAL APPLICABILITY The present invention can be suitably used in all resistance welding methods such as indirect welding and series welding in which an electrode is pressed against a welding target to perform welding.

1 Electrode 2 Welding target 4 Welded material 6 Welded material 7 Shoulder part 9 Protruding part 10 Welding device 13 Protruding surface 16 Conduction path 21 Biting surface 23 Welding part 25 Nugget

Claims (1)

It is a resistance welding method in which the welded material is welded at the welded portion by energizing the welded material from the electrode while pressurizing a plurality of the welded materials with the electrodes.
The electrode includes a shoulder portion that is inclined toward the center side of the electrode with respect to the pressurizing direction in which the electrode pressurizes the material to be welded, and a protruding portion that continuously protrudes from the shoulder portion in the pressurizing direction. The inclination angle of the protruding surface of the protruding portion with respect to the pressurizing direction is smaller than the tilt angle of the shoulder portion.
At the time of initial energization to blend the contact surface between the electrode and the material to be welded, the protrusion is brought into contact with the material to be welded.
At the time of pre-main energization performed before the main energization, the protruding portion is made to bite into the material to be welded.
At the time of the main energization, a current having a current value higher than the current value of the pre-main energization is energized to the welded material, and at least a part of the shoulder portion is made to bite into the welded material. Resistance welding method.

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