JP7394089B2 - Spot welding method and spot welding control device - Google Patents

Description

The present invention relates to a spot welding method and a spot welding control device.

For example, in the assembly process of an automobile body, spot welding is performed in which electrodes are brought into contact with a plurality of steel plates and electricity is applied to melt the contact portions of the steel plates by resistance heat generation to form a nugget.

Furthermore, in spot welding, in order to form a nugget of a desired size and shape between a plurality of steel plates, it has been proposed to conduct energization in various energization patterns. For example, in Patent Document 1, while alternating a time period in which a high current value is maintained to grow the nugget and a time period in which a low current value is maintained to the extent that the steel plate is softened without generating spatter, A direct spot welding method has been proposed in which current is applied in a current pattern that gradually increases the current value.

Furthermore, Patent Document 2 discloses that, in addition to the energization pattern, a pressing force is applied in order to stably obtain a nugget of a desired size and shape regardless of the presence or absence of a gap between steel plates (also referred to as a plate gap). An indirect spot welding method has been proposed in which current is applied while changing in a predetermined pattern. Specifically, in the first step, a first current value is applied between the welding electrode and the earth electrode while pressurizing the part to be joined by the welding electrode with a first pressure force, and in the second step Then, while reducing the pressure applied by the welding electrode from the first pressure to the second pressure, a second current value lower than the first current value is applied, and in the third step, the welding electrode A third current value higher than the first current value is applied while applying pressure to the part to be welded with a second pressing force, and in a fourth step, the part to be joined is applied to the part to be joined by a second pressing force using a welding electrode. An indirect spot welding method has been proposed in which a desired nugget is stably formed by applying current at a fourth current value higher than the third current value while applying pressure.

Japanese Patent Application Publication No. 2006-181621 JP 2019-206024 Publication

By the way, in this type of spot welding, it is well known that the tip of the electrode wears out with continued use of the electrode. In the actual mass production process, the tip of the electrode may wear (deform) into a distorted shape due to factors such as individual differences in the workpieces to be welded and individual differences in teaching. If the tip of the electrode is deformed into a distorted shape in this way, the contact between the steel plates formed by applying pressure to the electrode (especially the contact at the pressurized part) will become unstable, so if the tip of the electrode is deformed into a distorted shape, the nugget will When carrying out the main energization to promote the generation and growth of electrodes, the current density at the contact area between the steel plates becomes excessive compared to when the electrodes are new, increasing the risk of welding defects such as burn-through and spatter. In particular, in the case of a board assembly in which gaps exist, the above-mentioned problem becomes even more remarkable. The welding method described in Patent Document 2 assumes that the contact state between the electrode and the steel plate is constant, that is, the shape of the tip of the electrode is constant, as long as welding is performed under the same welding conditions. There is a need to develop a new welding method that can cope with changes in contact conditions due to wear.

In view of the above circumstances, in this specification, the technical problem to be solved is to provide a spot welding method that can stably form a nugget of a desired size and shape regardless of the wear of the electrode. do.

The above problems are achieved by a spot welding method according to the present invention. In other words, this welding method is an indirect spot welding method in which the parts to be joined, which are made of multiple metal plates, are welded by applying electricity while applying pressure to the parts to be joined by the welding electrode. A first step of applying current at a first current value C1 while pressurizing the part to be welded with a first applying force F1, and changing the applying force by the welding electrode from the first applying force F1 to a second lower value. A second step of energizing the second current value C2 lower than the first current value C1 while reducing the pressure to F2, and pressurizing the part to be joined with the second pressure F2 using the welding electrode, a third step of applying current to a third current value C3 higher than the first current value C1; and a third step of applying current to a third current value C3 higher than the third current value C3 while pressurizing the part to be welded with the welding electrode with a second pressing force F2; In the indirect spot welding method comprising a fourth step of applying current to a high fourth current value C4, after the second step and before the third step, applying pressure with a second pressurizing force F2. However, a fifth current value C5 larger than the second current value C2 is energized, and then the current value at the time of energization is lowered to a sixth current value C6 smaller than the third current value C3. It is characterized by further comprising 5 steps.

In the first step of this welding method, the area to be joined is pressurized with a relatively high first pressing force F1 to ensure the contact area between the welding electrode and the metal plate and the contact area between the metal plates. be able to. In this state, by applying a low current value C1, the current density is suppressed to prevent melting and scattering on the surface of the metal plate, while increasing the contact area between the welding electrode and the metal plate and the contact area between the metal plates. be able to.

In the second step, by suppressing the current value while reducing the welding force from F1 to F2, we secure the time until the welding force decreases to F2 and stabilizes, and also protect the welding electrode and metal plate. Adjust the heat balance (the balance between the heat generated by the metal plate due to the current-carrying resistance and the heat radiation from the welding electrode and the metal plate surface) by appropriately cooling or keeping it warm. This allows a smooth transition to the subsequent third step.

In the third step, the metal plates are softened and the contact area between the metal plates is expanded by applying current at a current value C3 lower than the current value for forming the nugget while applying pressure at a low pressure F2, thereby causing sputtering. can be prevented from occurring. In this way, a nugget can be reliably formed by increasing the current to the current value C4 in the fourth step while ensuring the contact area between the metal plates.

Further, in the welding method according to the present invention, after the second step and before the third step, while applying pressure with the second pressing force F2, a fifth current larger than the second current value C2 is applied. By applying current to a value C5, the contact between the metal plates is improved by softening or partially melting the metal plates. Therefore, the contact area between the metal plates can be expanded. Then, by lowering the current value to a predetermined value (sixth current value C6) after the above-mentioned energization, the contact state can be maintained and stabilized. Moreover, it is possible to smoothly transition to the subsequent third step. Therefore, it is possible to reliably enjoy the effects of the third and fourth steps described above.

As described above, between the first step of applying current with a low current value C1 while applying pressure with a high pressing force F1, and the fourth step of applying current with a high current value C4 while applying pressure with a low pressing force F2, By providing the above-mentioned second and third steps in which the current value is adjusted in response to the change in pressure force (transition period), it is possible to prevent burns and spatter from occurring even when there is a gap between the plates. nuggets of desired size and shape can be stably formed. In addition, by providing a step (fifth step) to temporarily increase the current value between the second and third steps as described above, the metal A stable contact state (sufficiently large contact area) can be obtained between the plates, thereby making it possible to stably form a good nugget.

Further, in the spot welding method according to the present invention, the energization time of the fifth current value in the fifth step may be set shorter than the energization time in the third step.

By limiting the current application time in this way, it is possible to avoid a situation where the contact area expands more than necessary, and to prevent burn-through as a result of excessive heating. Therefore, it is possible to stably improve the contact condition (contact area) without any problems.

Moreover, the solution to the above problem is also achieved by the spot welding control device according to the present invention. In other words, this control device is connected to a spot welding device that welds the parts to be joined by applying electricity while applying pressure to the parts to be joined, which are made of multiple metal plates, with a welding electrode. and a control device for controlling a current value during energization, comprising: a first step of applying current to a first current value C1 while pressurizing a portion to be joined with a welding electrode with a first pressing force F1; a second step of energizing a second current value C2 lower than the first current value C1 while lowering the pressing force from the first pressing force F1 to a second pressing force F2 lower than the first pressing force F1; A third step of applying current to a third current value C3 higher than the first current value C1 while pressurizing the part to be joined with a second pressing force F2 using the welding electrode; A fourth step of applying current to a fourth current value C4 higher than the third current value C3 while applying pressure at a pressure F2 of 2. In the apparatus, after the second step and before the third step, a fifth current value C5 larger than the second current value C2 is energized while applying pressure with the second pressurizing force F2; It is characterized in that the pressurizing force and current value are controlled so that a fifth step is further provided in which the current value during energization is lowered to a sixth current value C6 smaller than the third current value C3. .

As described above, in the control device according to the present invention, in the same way as the welding method described above, the first step is to apply current at a low current value C1 while applying pressure with a high pressure F1, and the first step is to apply current with a low current value C1 while applying pressure with a high pressure F1. However, by providing the above-mentioned second step and third step of adjusting the current value in response to the change in pressurizing force (transition period) between the fourth step of energizing the high current value C4, Even if there is a gap between the metal plates, a nugget of a desired size and shape can be stably formed without causing burns or spatter. In addition, by providing a step (fifth step) to temporarily increase the current value between the second and third steps as described above, the metal plate A stable contact state (sufficient contact area) can be obtained between the two, thereby making it possible to stably form a good nugget.

As described above, according to the spot welding method and the spot welding control device according to the present invention, it is possible to stably form a nugget of a desired size and shape regardless of the wear of the electrode.

FIG. 2 is a cross-sectional view showing a state immediately before indirect spot welding is performed on a part to be joined of parts made of a plurality of metal plates. FIG. 2 is a side view of the welding electrode shown in FIG. 1 (a) at the beginning of use and (b) at the time of tip wear. It is a graph which shows the pressurization energization pattern of the spot welding method based on one Embodiment of this invention. FIG. 4 is a cross-sectional view of the area around the planned welding portion at time A in FIG. 3 when the welding electrode in the state shown in FIG. 2(a) is used. When using the welding electrode in the state shown in FIG. 2(b), in FIG. C) It is a sectional view of the vicinity of the part to be joined at time C.

EMBODIMENT OF THE INVENTION Hereinafter, the content of the spot welding method and the control device for spot welding which concern on one Embodiment of this invention is demonstrated based on drawing.

In this embodiment, the detailed form will be explained by taking indirect spot welding performed in the assembly process of an automobile body as an example. In this case, the object to be welded is, for example, a vehicle body frame component 100 as shown in FIG. This frame component 100 is a frame-shaped component extending in a direction perpendicular to the plane of the drawing in FIG. It is composed of a third metal plate 3 having a hat-shaped cross section and disposed in a hollow portion formed by a plate 1 and a second metal plate 2. As the metal plates 1 to 3, for example, a steel plate is used, specifically a mild steel plate, a high tensile strength steel plate (tensile strength of 490 MPa or more), or an ultra-high tensile strength steel plate (tensile strength of 980 MPa or more).

The flange portions 2a of the first metal plate 1 and the second metal plate 2 are joined via a previously welded point Q1 by direct spot welding. The bottom portion 2b of the second metal plate 2 and the flange portion 3a of the third metal plate 3 are welded in advance by direct spot welding and are joined via a previously welded point Q2.

The top plate portion 3b of the third metal plate 3 and the first metal plate 1 are joined by an indirect spot welding method according to an embodiment of the present invention. Specifically, the joint portion P of the first metal plate 1 and the top plate portion 3b of the third metal plate 3 is pressurized with a welding electrode 10 from one side in the thickness direction (upper side in FIG. 1). By applying current between the electrodes 10 and 20 with the ground electrode 20 in contact with a portion of the skeleton component 100 that is different from the portion P to be joined, the portion P to be joined is welded. In the illustrated example, the ground electrode 20 is brought into contact with the bottom portion 2b of the second metal plate 2 from below.

This indirect spot welding method includes an indirect spot welding device having the above-mentioned welding electrode 10 and a ground electrode 20, and an indirect spot welding device that is connected to the indirect spot welding device, and is connected to the welding electrode 10 and the current between the welding electrodes 10 and 20. This is carried out in equipment equipped with a control device 30 that controls the values. The indirect spot welding device includes a pressurizing means for driving the welding electrode 10 in the axial direction to pressurize the metal plate. As the pressurizing means, an air cylinder or an electric cylinder can be used, and in this embodiment, an air cylinder is used.

As the welding electrode 10, an electrode having a known shape can be used, and in this embodiment, as shown in FIG. An electrode having a continuous tapered surface 12 is used. Of course, the shape of the tip of the welding electrode 10 is not limited to this, and for example, a welding electrode having a partially spherical tip may be used.

In this embodiment, welding is performed according to the pressure energization pattern shown in FIG. 3 in response to a command from the control device 30. This pressure energization pattern will be explained in detail below.

(S1) First Step In the first step S1, the welding electrode 10 pressurizes the portion P to be joined with a relatively high first pressurizing force F1. This closes the gap between the metal plates 1 and 3 (3b) to ensure that both metal plates 1 and 3 are in contact with each other, and also reduces the contact area between the welding electrode 10 and the first metal plate 1, and the contact area between the welding electrode 10 and the first metal plate 1. A contact area between the plate 1 and the third metal plate 3 (top plate portion 3b thereof) is ensured. In this state, by passing a relatively low first current value C1 between the electrodes 10 and 20, the metal plate 1 is heated while suppressing the current density and preventing the surfaces of the metal plates 1 and 3 from melting and scattering. By softening, the contact area between the welding electrode 10 and the first metal plate 1 and the contact area between the first metal plate 1 and the third metal plate 3 can be expanded (see FIG. 4). The hatched area in FIG. 4 is the contact portion M. In this step S1, the contact portion M may be a portion where the metal plates 1 and 3 are in close contact with each other, or may be a portion where a portion of the metal plates 1 and 3 is melted. . Which event should be generated can be appropriately selected by adjusting the first current value C1 and/or the first pressing force F1 in step S1.

(S2) Second Step In the second step S2, first, a command is issued to the pressurizing means that applies a pressurizing force to the welding electrode 10 to reduce the pressurizing force (see FIG. 3). At this time, due to the structure of the pressurizing means, the actual pressurizing force does not instantly drop from F1 to F2 as soon as the command is received, but there is inevitably a transition period in which it gradually decreases from F1 to F2 at a predetermined gradient, for example. established in In particular, when an air cylinder is used as a pressurizing means for the welding electrode 10 as in this embodiment, the response to changes in pressurizing force is poorer than when using an electric cylinder, for example, and it takes time for the pressurizing force to decrease. However, the pressure value becomes unstable. If a high current value is applied in a state where the pressurizing force is unstable as described above, the current application state (current density) becomes unstable, and there is a possibility that variations in the welding state occur.

Therefore, in the second step S2, while decreasing the pressing force from F1 to F2, current is applied at a current value C2 that is even lower than the current value C1 in the first step. In this way, by suppressing the amount of heat input when the pressurizing force is unstable, the welding electrode 10 and the metal plates 1 and 3 can be appropriately cooled or kept warm, and the heat balance around the part P to be welded can be adjusted. can. At this time, it is preferable to suppress the current value (maintain the second current value C2) during the entire period when the pressurizing force is decreasing, and in the illustrated example, the current is applied during the period when the pressurizing force is decreasing and at the current value C2. The period of In this second step S2, the state around the joint portion P of the metal plates 1 and 3 hardly changes.

(S3) Third step Then, in response to the fact that the pressurizing force detecting unit (not shown) that detects the pressurizing force of the pressurizing means detects that the pressurizing force has decreased from F1 to F2, the control device 30 increases the current value. In this embodiment, after the pressurizing force has decreased to F2, the current value is increased after a predetermined time has elapsed (see FIG. 3). At this time, from the low current value C2 of the second step S2 (more precisely, the low current value C6 of the fifth step S5, which will be described later), the current value of the main energization that forms the nugget (the current value of the next fourth step S4) is changed. If the current value is suddenly increased to the current value C4), spatter may occur. Therefore, in the third step S3, the metal plates 1 and 3 are softened by first applying current at a current value C3 lower than the current value C4 of the main energization while applying pressure at a low pressing force F2. We aim to expand the contact area between the three.

(S4) Fourth step In this way, with the contact area between the metal plates 1 and 3 secured, the current value is increased from C3 to C4 in the subsequent fourth step S4 (see FIG. 3). reference). Thereby, nugget seeds (nuggets that do not reach the desired size) can be reliably formed without causing spatter. For example, in this embodiment, although not shown, in the fourth step S4, an annular nugget is formed at the joint portion P between the metal plates 1 and 3.

(S5) Fifth step In addition, after the second step S2 and before the third step S3, the contact state between the metal plates 1 and 3 is determined by energizing with a high current value C5 for a short time. We aim to improve this. To explain in detail, when indirect spot welding as in this embodiment is repeatedly performed, it is assumed that the tip of the welding electrode 10 will wear out and the shape of the tip will change into distortion. Specifically, as shown in FIG. 2(a), when the welding electrode 10, which is initially provided with the flat surface 11 perpendicular to the central axis, is repeatedly used, the welding electrode 10 shown in FIG. As shown in b), the tip of the welding electrode 10 may be deformed into a distorted shape. In this illustrated example, the area of the flat surface 11 is expanded compared to the time when use is started, and the flat surface 11 is in a state of being largely tilted with respect to the central axis.

When welding shown in FIGS. 1 and 3 is performed using the welding electrode 10 (see FIG. 2(b)) in which the flat surface 11 is greatly inclined with respect to the central axis, for example, the second At the end of step S2 (time A in FIG. 3), the first metal plate 1 and the top plate part 3b of the third metal plate 3 are in partial contact, and the contact area (of the contact part M) is The contact state is not stable, as the area (area) decreases compared to the time at the start of welding shown in FIG. 4 (see FIG. 5(a)). In this way, if the subsequent energization steps (third and fourth steps S3 and S4) are performed while the contact state remains unstable, the current density at the contact portion M will be lower than when the welding electrode 10 starts to be used. This increases the risk of welding defects such as burn-through and spatter.

In view of the above points, in the fifth step S5, a fifth current value C5 larger than the second current value C2 is applied between both electrodes 10 and 20 while applying pressure with a relatively low pressing force F2. do. As a result, the contact area M between the metal plates 1 and 3 (3b) is reheated, and the softening of the metal plates 1 and 3 (if the contact area M includes a melted part, the melted part is remelted). promoted. As a result, the contact area can be expanded (see FIG. 5(b)). After the above-mentioned energization, the current value is lowered to a predetermined value (sixth current value C6). As a result, the state of the enlarged contact portion M can be stabilized (see FIG. 5(c)), so that it is possible to smoothly proceed to the subsequent third step S3.

The fifth current value C5 in this step S5 is preferably a large current that does not cause spatter, for example, and in terms of the relationship between the current values C1 to C6 shown in FIG. It is desirable that the current value be smaller than the fourth current value C4.

In addition, in this step S5, from the viewpoint of avoiding the situation where the contact area between the metal plates 1 and 3 (area of the contact portion M) increases more than necessary or preventing burn-through due to excessive heating, the following steps are taken. It is preferable to set the energization time for the current value C5 in step S3 to be shorter than the energization time in the third step S3.

Further, in this step S5, when lowering the current value from the fifth current value C5 to the sixth current value C6, the sixth current value C6 is, for example, the same as the second current value C2 in the second step S2, or It is desirable to keep it within the range of ±10%.

(S6) Sixth step After improving the contact state between the metal plates 1 and 3 as described above and forming a nugget (seed) in the fourth step S4, in the sixth step S6 , a seventh current value C7 lower than the fourth current value C4 is applied between both electrodes 10 and 20 while applying pressure with the second pressing force F2 (see FIG. 3). In the illustrated example, the seventh current value C7 is set to be lower than the third current value C3 and further lower than the first current value C1. On the other hand, the seventh current value C7 is set to be higher than the second current value C2. By energizing in this sixth step S6, the state of the nugget is stabilized by using the preheating of the metal plates 1 and 3 heated in the fourth step S4 while suppressing the amount of heat input to the metal plates 1 and 3. can be grown while growing. As a result, for example, although not shown in the drawings, the annular nugget formed in the fourth step S4 grows inwardly, filling the hollow portion and becoming approximately disk-shaped.

From the above, the desired size and shape (particularly in the thickness direction of the third metal plate 3) are provided for the planned joining portion P between the top plate portion 3b of the first metal plate 1 and the third metal plate 3. A nugget having a melt penetration amount) is formed, and both metal plates 1 and 3 are joined via this nugget.

As described above, according to the indirect spot welding method according to the present embodiment, the first step S1 is to apply electricity at a low current value C1 while applying pressure with a high pressing force F1, and the first step S1 is to apply electricity at a low current value C1 while applying pressure with a high pressing force F1, and while applying pressure with a low pressing force F2. By providing a second step S2 and a third step S3 in which the current value is adjusted in response to a change in pressurizing force (transition period) between the fourth step S4 in which the high current value C4 is energized, Even if there is a gap between the metal plates 1 and 3, a nugget of a desired size and shape can be stably formed without causing burns or spatter. Furthermore, by providing a step (fifth step S5) of temporarily increasing the current value between the second step S2 and the third step S3 as described above, the state of wear at the tip of the welding electrode 10 can be improved. Regardless of the method, a stable contact state (contact area) can be provided between the metal plates 1 and 3, and thereby a good nugget can be stably formed.

Although one embodiment of the present invention has been described above, the method for determining the quality of spot welding according to the present invention may have a configuration other than the above without departing from the spirit thereof.

For example, in the above embodiment, steps S3 and S4 related to the formation and growth of the nugget include a step of energizing at a higher current value than the current values C2 and C6 in the immediately preceding step S2 (S3), respectively. Although the case is shown as an example, it is of course not limited to this. For example, although not shown, after the fourth step S4, there may be further provided a step of supplying current at a current value one step higher than the current value C4 at the fourth step S4.

Further, in the above embodiment, after the fourth step S4, the current value is lowered than the current value at the time of the fourth step S4 (fourth current value C4), and the current value is lowered than the current value at the fourth step S4. Although a case has been illustrated in which a sixth step S6 for performing energization for a certain period of time is provided, the sixth step S6 is not essential. For example, if the energization time in the fourth step S4 is made longer than the time illustrated in FIG. 3 etc., and a nugget of the desired size and shape is formed during the step S4, the sixth step S6 is omitted. You may.

Further, in the above embodiment, the case where the present invention is applied to indirect spot welding is illustrated, but it goes without saying that the present invention can also be applied to direct spot welding without any problem. In other words, even when the present invention is applied to direct spot welding, it is possible to stably form a good nugget regardless of electrode wear. It becomes possible to apply the pressurized energization pattern (control device 30) according to the invention.

1 First metal plate 2 Second metal plate 2a Flange portion 2b Bottom portion 3 Third metal plate 3a Flange portion 3b Top plate portion 10 Welding electrode 11 Flat surface 12 Tapered surface 20 Earth electrode 30 Control device 100 Skeleton component C1, C2, C3, C4, C5, C6, C7 Current value F1, F2 Pressure force M Contact part P Planned joining part Q1, Q2 Already welded point

Claims (3)

A spot welding method for welding a part to be joined by applying electricity while applying pressure to the part to be joined by a welding electrode of a part made of a plurality of metal plates, the method comprising:
A first step of applying current to a first current value C1 while pressurizing the portion to be welded with a first pressing force F1 using the welding electrode;
A second current value C2 that is lower than the first current value C1 is applied while lowering the applied force by the welding electrode from the first applied force F1 to a second applied force F2 lower than the first applied force F1. step and
A third step of applying a third current value C3 higher than the first current value C1 while pressurizing the welding portion with a second pressing force F2 using the welding electrode;
an indirect spot comprising at least a fourth step of applying current to a fourth current value C4 higher than the third current value C3 while pressurizing the planned welding portion with a second pressurizing force F2 using the welding electrode; In the welding method,
After the second step and before the third step, while pressurizing with the second pressurizing force F2, a fifth current value C5 larger than the second current value C2 is applied, and then, The spot welding method further comprises a fifth step of lowering the current value during energization to a sixth current value C6 smaller than the third current value C3. The spot welding method according to claim 1, wherein the energization time of the fifth current value in the fifth step is set shorter than the energization time in the third step. By energizing the parts to be welded with a welding electrode while applying pressure to the parts to be joined, which are made of a plurality of metal plates, the parts are connected to a spot welding device that welds the parts to be joined, and the pressure of the welding electrodes and the current when energized are connected to the spot welding device. A control device that controls a value,
A first step of applying current to a first current value C1 while pressurizing the portion to be welded with a first pressing force F1 using the welding electrode;
A second current value C2 that is lower than the first current value C1 is applied while reducing the pressing force by the welding electrode from the first pressing force F1 to a second pressing force F2 lower than the first pressing force F1. step and
A third step of applying a third current value C3 higher than the first current value C1 while pressurizing the welding portion with a second pressing force F2 using the welding electrode;
a fourth step of applying current to a fourth current value C4 higher than the third current value C3 while applying pressure to the welding portion to be welded with a second pressing force F2; and an indirect spot welding control device that controls the current value,
After the second step and before the third step, while pressurizing with the second pressurizing force F2, a fifth current value C5 larger than the second current value C2 is applied, and then, For spot welding, the pressurizing force and current value are controlled so as to further include a fifth step of lowering the current value during energization to a sixth current value C6 smaller than the third current value C3. Control device.

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