One-side spot welding method and control device

Abstract

To provide a pressure-energized pattern capable of joining a plurality of joint planned parts having different plate gaps when one-sided spot welding is performed.SOLUTION: In a one-sided spot welding method, a first step S1, a second step S2, and a third step S3 are continuously performed. The first step S1 is of energizing an overlapped part 3 of an upper plate 1 and a lower plate 2 while pressurizing the overlapped part 3 by a first pressurizing force F1. The second step S2 is of energizing the overlapped part 3 while increasing the pressurizing force with respect to the overlapped part 3 from a first pressurizing force F1 to a second pressurizing force F2. The third step S3 is of energizing the overlapped part 3 while pressurizing the overlapped part 3 by a second pressurizing force F2. A current value in the first step S1, the second step S2, and the third step S3 is set to a constant value C1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and control device for single-sided spot welding. [Background technology]

[0002] Direct spot welding, in which a pair of electrodes sandwiches the overlapping portions of multiple metal plates and current is passed through them, is commonly used. However, depending on the shape of the parts, it may not be possible to sandwich the intended joining portions between the pair of electrodes, making direct spot welding unsuitable. In such cases, "one-sided spot welding" may be used, in which an electrode is pressed against the intended joining portions from only one side in the thickness direction, and the intended joining portions are welded without being supported from the other side in the thickness direction.

[0003] Before spot welding, there may be a small gap (gap) between the metal sheets at the welding point (the area to be joined).With direct spot welding, even if there is a gap in the area to be joined, the metal sheets can be securely contacted by being sandwiched between a pair of electrodes, so the presence or absence of a gap has almost no effect on the quality of the weld.

[0004] On the other hand, in single-side spot welding, the electrode applies pressure to the to-be-joined portion from only one side in the thickness direction, which makes the sheet assembly prone to deformation. Therefore, the electrode pressure in single-side spot welding must be smaller than the pressure in direct spot welding. Because the electrode pressure is small in single-side spot welding, if a gap exists in the to-be-joined portion, the electrode pressure may not be enough to close the gap, preventing sufficient contact between the metal sheets. Therefore, in single-side spot welding, the presence or size of a gap can easily affect the quality of the weld.

[0005] For example, the single-side spot welding method disclosed in Patent Document 1 below includes, as shown in Figure 8, step S1' of applying current while applying pressure at F1, step S2' (an intermediate step) of increasing the pressure from F1' to F2', and step S3' of applying current while applying pressure at F2'. It is said that performing single-side spot welding with the above-described pressure-current pattern can form a good nugget regardless of whether or not there is a gap. Note that the reference numerals in Figure 8 are different from those in Patent Document 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-139742 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors' investigations have revealed that the one-side spot welding method of Patent Document 1 is prone to poor welding when welding a portion to be welded where the gap between plates is relatively small.

[0008] For example, when welding a to-be-joined portion with almost no gap (e.g., less than 1 mm) using the pressure and current pattern shown in FIG. 8, a molten zone N' is formed in step S1' as shown in FIG. 9. In the subsequent step S2', the current value is reduced to cool and solidify the molten zone N', forming a nugget N. At this time, the upper plate 1' is at a high temperature and softened, so the electrode 11' continues to bite into it as the pressure force increases. In the subsequent step S3', the current value is increased to form a new molten zone N'. As a result of the above, a sufficiently large nugget is formed.

[0009] On the other hand, when welding a to-be-joined part with a large gap (for example, a gap of more than 1.5 mm) using the pressure-current pattern shown in Fig. 8, the gap is not completely closed in steps S1' and S2', so the upper sheet 1' and the lower sheet 2' do not come into contact, but in step S3' the upper sheet 1' and the lower sheet 2' come into contact and form a molten zone N', as shown in Fig. 11. At this time, a high current flows when the contact area between the upper sheet 1' and the lower sheet 2' is small, so the current density at the contact point increases and a sufficiently large nugget is formed.

[0010] In contrast, when welding a to-be-joined portion with an intermediate gap (e.g., a gap of 1 to 1.5 mm) using the current-applied pressure pattern shown in Figure 8, as shown in Figure 10, in step S1', the upper sheet 1' softens due to heat generated by the current and is forced downward, bringing the upper sheet 1' and the lower sheet 2' into contact. In the subsequent step S2', the pressure is increased, forcing the upper sheet 1' further downward. However, the current value at this time is small, and the downward force of the upper sheet 1' increases the contact area with the lower sheet 2', so the current density does not increase and a fusion zone does not form. In the subsequent step S3, even if the current value is increased while applying a high pressure F2', the current density does not increase because the contact area between the upper sheet 1' and the lower sheet 2' is already large, and therefore no fusion zone is formed, resulting in a poor weld. As described above, by reducing the current value in step S2', where the pressure is increased, depending on the size of the gap, a fusion zone may not form at the contact point between the metal sheets, making it impossible to join the metal sheets.

[0011] In one-side spot welding, the contact points between multiple metal sheets may not melt but may remain in a solid state when joined (such a joint is called a "solid-state joint"). In this case, as with the above, depending on the size of the gap between the sheets, the contact points between the metal sheets may not be heated sufficiently, making it impossible to join the metal sheets.

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a pressure and current pattern that allows joining of a plurality of intended joining portions having different plate gaps when performing one-side spot welding. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a one-side spot welding method in which overlapping portions of a plurality of metal plates are pressed with an electrode from one side in a thickness direction, and current is passed through the overlapping portions to perform welding in a state in which the overlapping portions are not supported from the other side in the thickness direction, the method includes successively: a first step of applying current to the polymerization section while applying a first pressure; a second step of applying current to the polymerization section while increasing the pressure applied to the polymerization section from the first pressure to a second pressure; and a third step of applying current to the polymerization section while applying the second pressure; The present invention provides a one-side spot welding method in which the current values ​​in the first step, the second step, and the third step are constant.

[0014] As described above, in the present invention, a first step in which the pressure is small, a second step in which the pressure is increased, and a third step in which the pressure is large are successively performed while maintaining a constant current value. When welding is performed using this pressure-current pattern, a molten zone N' is formed in the first step if there is almost no gap (see FIG. 3 ), and a molten zone N' is formed in the second step if the gap is large (see FIG. 5 ). Furthermore, if the gap is intermediate, the upper sheet softens and contacts the lower sheet in the first step. Then, in the second step, while increasing the pressure from the first to the second pressure, energy is continuously supplied to the contact area between the metal sheets without reducing the current value, thereby maintaining heat generation at the contact area, thereby forming a molten zone N' (see FIG. 4 ). Finally, in the third step, a current is continuously supplied while applying pressure at the second pressure, thereby growing the molten zone. As described above, when the metal sheets come into contact in the second step, by maintaining the current value constant without reducing it midway, it is possible to eliminate the wasteful idle period that only increases the contact area between the metal sheets and melt the contact area between the metal sheets. Furthermore, by keeping the current value constant and controlling the welding conditions only with the welding force, the number of parameters required to adjust the welding conditions is reduced, making it easier to set the welding conditions and improving robustness.

[0015] In the above-described one-side spot welding method, if the pressure is increased from the first pressure to the second pressure in one go, the surface pressure at the contact point between the metal sheets changes suddenly, which may cause the fusion zone to become unstable. Therefore, in the second step, it is preferable to increase the pressure stepwise in at least two stages. This prevents a sudden change in the surface pressure at the contact point between the metal sheets, making it easier to form a stable fusion zone and a good weld (nugget or solid-state weld).

[0016] The present invention provides a control device for controlling a pressing force and a current value of a one-side spot welding device that presses overlapping portions of a plurality of metal plates with an electrode from one side in a thickness direction and passes current through the overlapping portions to weld them in a state in which the overlapping portions are not supported from the other side in the thickness direction, the control device comprising: a first step of applying current to the polymerization section while applying a first pressure, a second step of applying current to the polymerization section while increasing the pressure applied to the polymerization section from the first pressure to a second pressure, and a third step of applying current to the polymerization section while applying the second pressure, It can also be characterized as a control device that keeps the current values ​​constant in the first step, the second step, and the third step. [Effects of the Invention]

[0017] As described above, the one-side spot welding method and control device of the present invention make it possible to set a pressure and current pattern that can join a plurality of portions to be joined that have different plate gaps. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram of a welding facility including an indirect spot welding device. [Figure 2] 1 is a graph showing a pressure and current pattern of an indirect spot welding method according to one embodiment of the present invention. [Figure 3] 10 is a cross-sectional view showing a state in which welding is performed on a to-be-joined portion with almost no gap therebetween using the above-described pressurizing and current application pattern. FIG. [Figure 4]10 is a cross-sectional view showing a state in which welding is performed on a portion to be joined with a small gap using the above-described pressure and current pattern. FIG. [Figure 5] 10 is a cross-sectional view showing a state in which welding is performed on a portion to be joined with a large gap using the above-described pressure current pattern. FIG. [Figure 6] 10 is a graph showing a pressure and current application pattern for an indirect spot welding method according to another embodiment of the present invention. [Figure 7] FIG. 1 is a block diagram of a welding facility including a series spot welding device. [Figure 8] 1 is a graph showing a pressure and current pattern of a conventional indirect spot welding method. [Figure 9] 9 is a cross-sectional view showing a state in which welding is performed on a portion to be joined with almost no gap therebetween using the pressure and current pattern of FIG. 8. FIG. [Figure 10] 9 is a cross-sectional view showing a state in which welding is performed on a portion to be joined with a small gap using the pressure and current pattern of FIG. 8. FIG. [Figure 11] 9 is a cross-sectional view showing a state in which welding is performed on a portion to be joined with a large gap using the pressure and current pattern of FIG. 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] In this embodiment, as shown in FIG. 1 , an overlapping portion 3 of an upper sheet 1 and a lower sheet 2 is joined by indirect spot welding, which is one-side spot welding according to one embodiment of the present invention. Both the upper sheet 1 and the lower sheet 2 are metal sheets, such as steel sheets. In this embodiment, the upper sheet 1 and the lower sheet 2 are mild steel sheets (steel sheets with a tensile strength of 340 MPa or less), specifically, zinc-plated mild steel sheets. Alternatively, one or both of the upper sheet 1 and the lower sheet 2 may be high-tensile steel sheets (steel sheets with a tensile strength of 490 MPa or more) or ultra-high-tensile steel sheets (steel sheets with a tensile strength of 980 MPa or more). In the illustrated example, the thickness t1 of the upper sheet 1 is thicker than the thickness t2 of the lower sheet 2. The thickness ratio t1 / t2 of the sheets 1 and 2 may be 1.2 or greater, or even 1.4 or greater. Furthermore, the thickness of the upper sheet 1 may be the same as or thinner than the thickness t2 of the lower sheet 2.

[0021] The indirect spot welding method of this embodiment is performed using welding equipment including an indirect spot welding apparatus 10 and a controller 20 connected thereto.

[0022] The indirect spot welding apparatus includes a welding electrode 11, a ground electrode 12, a power source 13 for applying current between the electrodes 11, 12, and a drive means 14 (e.g., an air cylinder) for applying pressure to the welding electrode 11 in the axial direction. The welding electrode 11 is positioned so that it can apply pressure to the portion P to be joined from one side in the thickness direction (upper side in the figure). The ground electrode 12 is brought into contact with an area of ​​the workpiece to be welded other than the portion P to be joined. In the illustrated example, the ground electrode 12 is brought into contact with an already formed weld point Q from the other side in the thickness direction (lower side in the figure).

[0023] Control device 20 controls power supply 13 and drive means 14 according to an installed control program. Specifically, by controlling drive means 14, it controls the pressure applied by welding electrode 11 to overlapping portion 3. In addition, by controlling power supply 13, it controls the value of the current flowing between welding electrode 11 and earth electrode 12 (for example, the voltage between both electrodes 11, 12).

[0024] 2 is a pressure-current pattern showing the change over time in the pressure of electrode 11 and the current value between electrodes 11 and 12 according to this embodiment. In the welding method of this embodiment, an upslope step S0, a first step S1, a second step S2, and a third step S3 are performed consecutively.

[0025] The current value flowing between electrodes 11 and 12 is gradually increased to a predetermined current value C1 on an upslope S0, and then maintained at the constant current value C1 until the end of welding. By gradually increasing the current value from 0 to C1 on the upslope S0, a sudden increase in current density at the contact point between both plates 1 and 2 can be avoided, thereby preventing the occurrence of spatter.

[0026] The welding electrode 11 applies a different pressure to each of steps S1 to S3. First, in the upslope S0 and the first step S1, the welding electrode 11 applies a constant pressure F1. In the subsequent second step S2, the welding electrode 11 applies a constant pressure F1 to F2. In this embodiment, the welding electrode 11 applies a constant pressure F1 to F2. In the illustrated example, the welding electrode 11 applies a constant pressure F1 to F3, F3 to F4, and F4 to F2. In the subsequent third step S3, the welding electrode 11 applies a constant pressure F2.

[0027] Below, we will explain how to perform indirect spot welding using the above-mentioned pressure and current pattern on multiple to-be-joined parts P with different plate gaps. First, Fig. 3 shows the case where a to-be-joined part P with almost no plate gap (for example, a plate gap of less than 1 mm) is joined.

[0028] After the current value is increased to C1 on the upslope S0, in the first step S1, the current value C1 and applied pressure F1 are maintained at a constant value (see FIG. 2). At this time, since there is almost no gap at the to-be-joined portion P, the to-be-joined portion P is pressed by the welding electrode 11 in the first step S1, so that the two sheets 1 and 2 come into contact with each other, and a current path L passing through this contact area is formed (see FIG. 1). Then, resistance heating occurs at the contact area between the two sheets 1 and 2, forming a molten zone N' at this contact area (see the left diagram in FIG. 3).

[0029] In the subsequent second step S2, the current value between electrodes 11 and 12 is maintained at C1, while the pressure applied by electrode 11 is increased stepwise from F1 to F2 (see FIG. 2). At this time, the area around the contact point between upper sheet 1 and lower sheet 2 has already been softened by the current flow in first step S1. Therefore, by increasing the pressure while maintaining the current value in second step S2, upper sheet 1 is pressed downward, and the diameter of fusion zone N' expands (see the center diagram in FIG. 3). At this time, the current density at the contact point decreases as the contact area between upper sheet 1 and lower sheet 2 expands, preventing the upper sheet 1 and lower sheet 2 from excessively melting and melting away.

[0030] In the subsequent third step S3, current is continued to be applied between electrodes 11 and 12 at a current value C1 while maintaining the welding force F2 by welding electrode 11. As a result, the diameter of the already melted fusion zone N' is further enlarged by the welding force of electrode 11 (see the right diagram in FIG. 3). When the application of pressure and current is terminated, the fusion zone N' hardens, forming a nugget N of a predetermined size or larger.

[0031] Next, FIG. 4 shows a case where a portion to be joined P having a relatively small gap (for example, a gap of 1 to 1.5 mm) is joined using the above-mentioned pressurization and current application pattern.

[0032] If a gap is formed at the to-be-joined portion P, the upper sheet 1 and the lower sheet 2 do not contact each other at the beginning of the current application in the first step S1. At this time, the current between the electrodes 11 and 12 does not pass through the to-be-joined portion P, but flows along the current path of welding electrode 11 → upper sheet 1 → existing weld point Q → lower sheet 2 → earth electrode 12. When current is applied to the upper sheet 1 in this way, the upper sheet 1 softens due to resistance heating, and is pushed downward by the electrode 11 to contact the lower sheet 2 (see the left diagram in Figure 4). At this stage, the contact portion between the upper sheet 1 and the lower sheet 2 is not melted (if it were melted, the state would be the same as in Figure 3).

[0033] In the subsequent second step S2, the pressure is increased while the current value is maintained at C1 without being reduced to continue supplying energy to the to-be-joined portion P, thereby forming a molten zone N' at the contact portion between the upper sheet 1 and the lower sheet 2 (see the center diagram in FIG. 4). At this time, the to-be-joined portion P is pressed further downward by the pressure force of the electrode 11.

[0034] In the subsequent third step S3, while maintaining the current value at C1, the electrode 11 continues to press the to-be-joined portion P downward with a pressure force F2, which causes the to-be-joined portion P to be pressed further downward and expands the diameter of the fusion zone N' (see the right diagram in FIG. 4). When the current supply is terminated, the fusion zone N' hardens, forming a nugget N of a predetermined size or larger.

[0035] Next, FIG. 5 shows a case where a portion to be joined P having a relatively large gap (for example, a gap of 1.5 mm or more) is joined using the above-mentioned pressurizing and current application pattern.

[0036] In the first step S1, there is a relatively large gap between the upper plate 1 and the lower plate 2, so the first pressure F1 prevents the two plates 1 and 2 from coming into contact (see the left diagram in FIG. 5). In particular, in this embodiment, the upper plate 1 is thicker than the lower plate 2, so the upper plate 1 is less likely to deform, and the upper plate 1 and the lower plate 2 do not come into contact even when pressure is applied at a low pressure F1.

[0037] In the subsequent second step S2, by continuing to apply current value C1 (see FIG. 2), the upper sheet 1 softens due to resistance heating and is pressed downward by electrode 11, thereby closing the gap between the upper sheet 1 and the lower sheet 2 (see the center diagram in FIG. 5). In this way, after the first step S1, by maintaining the current value at C1 without reducing it and continuing to supply energy to the to-be-joined portion P, while increasing the pressure, even if a large gap exceeding 2 mm is formed between the upper sheet 1 and the lower sheet 2, this gap can be closed and the upper sheet 1 and the lower sheet 2 can be brought into contact with each other.

[0038] In the subsequent third step S3, the pressure F2 and the current value C1 are maintained and energy is continuously supplied to the to-be-joined portion P, whereby a molten zone N' is formed around the to-be-joined portion P, and the diameter of the molten zone N' is expanded by the pressure F2 of the electrode 11 (see the right diagram in FIG. 5). When the current supply is terminated, the molten zone N' hardens, forming a nugget N of a predetermined size or larger.

[0039] In the conventional pressure and current pattern of one-side spot welding (see Figure 8), the timing of melting the contact area between the sheets was intentionally varied, making it possible to join areas to be joined with various sheet gaps using the same pressure and current pattern. However, in this pressure and current pattern, the current value was lowered in step S2', which increases the pressure. Therefore, when the upper and lower sheets come into contact in step S2' (when the sheet gap is an intermediate value), the contact area between the two sheets simply increases, without increasing the current density in the contact area, and therefore a molten zone could not be formed even if the current value was increased in the subsequent step S3' (see Figure 10).

[0040] In this embodiment, as described above, in the second step S2 in which the applied pressure is increased, the current value is maintained at C1 rather than reduced, and energy is continuously supplied to the to-be-joined portion P. As a result, when the upper and lower sheets come into contact in the second step S2, the continuous supply of energy to the contact portion eliminates the wasteful idle period that simply increases the contact area between the metal sheets, and the contact portion can be melted (see the center diagram in FIG. 4). On the other hand, when there is almost no gap between the sheets (see FIG. 3), even if the current value is maintained at C1 and energy is continuously supplied in the second step S2, the contact area between the upper sheet 1 and the lower sheet 2 increases, and no burn-through occurs. Furthermore, when the gap is large (see FIG. 5), the current value is maintained at C1 and energy is continuously supplied in the second step S2, thereby closing the gap and bringing the upper and lower sheets into contact.

[0041] According to the above-described pressure and current pattern, even if there is a large variation in the gaps between the multiple to-be-joined portions P (for example, gaps of about 0 to 3 mm), it is possible to melt the contact area between the plates in any of steps S1 to S3 and form a good nugget. In other words, according to the above-described pressure and current pattern, it is possible to set the welding conditions so that the contact area between the plates will melt in any of steps S1 to S3, regardless of the size of the gap between the to-be-joined portions P.

[0042] In this embodiment, the welding conditions are controlled by keeping the current constant (C1) and varying only the pressure in steps S1 to S3. This reduces the number of parameters to be changed to adjust the welding conditions compared to when both the current and pressure are varied, making it easier to set the welding conditions and improving robustness.

[0043] In addition, in the second step S2, by gradually increasing the pressure in two or more stages, sudden changes in the surface pressure at the contact point between the upper plate 1 and the lower plate 2 are suppressed, making it easier to form a stable molten zone N' and a good nugget.

[0044] Furthermore, in one-side spot welding, if the timing of changing the pressure and the timing of changing the current value overlap, the state of the fusion zone N' becomes unstable, making welding defects more likely to occur. In the above pressure-current pattern, when the pressure is changed, specifically when the pressure is increased from F1 to F3, F3 to F4, and F4 to F2, the current value is constant, so the state of the fusion zone N' is prevented from becoming unstable, making welding defects less likely to occur.

[0045] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to those of the above-described embodiment will be omitted.

[0046] In one-side spot welding, the contact area (part to be joined P) between multiple metal plates (upper plate 1 and lower plate 2) may be joined in a solid state without melting. In this case, by applying the present invention, the same effect as in the above embodiment can be obtained. That is, when metal plates are joined in a solid state, in the description of the welding method of the above embodiment (see FIGS. 3 to 5), the molten zone N' can be read as "a part of the periphery of the contact area between the metal plates that is sufficiently heated in a solid state," and the nugget N can be read as "solid-state welded part."

[0047] The pressure and current application pattern is not limited to the above embodiment. For example, in the second step S2, the pressure may be increased in two stages or four or more stages. The increase in pressure may be varied in each stage. In the second step S2, the pressure may be gradually increased from F1 to F2. In addition to steps S1 to S3, in which the current value is constant, steps in which the current value is different from these may be provided. For example, as shown in FIG. 6, after the third step S3, a fourth step S4 may be provided in which the pressure is maintained at F2 and a current value C2 higher than C1 is applied.

[0048] The present invention is not limited to indirect spot welding, and can also be applied to series spot welding as shown in Fig. 7. This series spot welding device has welding electrodes 11a, 11b, power source 13 for passing current between electrodes 11a, 11b, and drive means 14a, 14b for applying pressure to welding electrodes 11a, 11b in the axial direction. Welding electrodes 11a, 11b press joint portions P1, P2 of upper sheet 1 and lower sheet 2 from one side in the thickness direction (upper side in the figure), and in this state, welding is performed using the same pressure and current pattern as in the above embodiment, thereby joining joint portions P1, P2. [Explanation of symbols]

[0049] 1 Upper plate (metal plate) 2 Lower plate (metal plate) 3 Polymerization section 10 Indirect spot welding equipment 11 Welding electrodes 12 Earth electrode 13 Power supply 14 Driving means 20 Control device C1 current value F1 First pressure force F2 Second pressure force L Current path N Nugget N' fusion zone P Joint area Q Existing weld points S0 Upslope S1 First Step S2 Second step S3 Third step

Claims

1. A one-side spot welding method for welding overlapping portions of a plurality of metal plates by pressing the overlapping portions with an electrode from one side in a thickness direction and passing current through the overlapping portions while not supporting the overlapping portions from the other side in the thickness direction, the method includes successively: a first step of applying current to the polymerization section while applying a first pressure; a second step of applying current to the polymerization section while increasing the pressure applied to the polymerization section from the first pressure to a second pressure; and a third step of applying current to the polymerization section while applying the second pressure; A one-side spot welding method, wherein the current values ​​in the first step, the second step, and the third step are constant.

2. 2. The one-side spot welding method according to claim 1, wherein in the second step, the applied pressure is increased in at least two stages.

3. A control device for controlling a pressing force and a current value of a one-side spot welding device that presses overlapping portions of a plurality of metal plates with an electrode from one side in a thickness direction and passes current through the overlapping portions to weld them in a state in which the overlapping portions are not supported from the other side in the thickness direction, a first step of energizing the polymerization section while applying a first pressure to the polymerization section, a second step of energizing the polymerization section while increasing the pressure applied to the polymerization section from the first pressure to a second pressure, and a third step of energizing the polymerization section while applying the second pressure to the polymerization section, A control device that keeps the current values ​​constant in the first step, the second step, and the third step.

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