JP7241498B2 - Welding method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method for welding by energizing a plate assembly in which a plurality of metal plates are sandwiched between a plurality of electrodes while arranging a thin plate as the outermost layer.

Conventionally, a resistance spot welding method as disclosed in Patent Document 1 below, for example, has been provided in order to form a nugget of a required size without generating dust even in a plate combination with a large plate thickness ratio. . In order to achieve this object, in this welding method, as the thin plate side electrode that contacts the thin plate during welding, an electrode having a smaller radius of curvature than the thick plate side electrode that contacts the thick plate side is employed, and the applied pressure is controlled. I'm doing it.

JP 2006-055898 A

However, in recent years, in the field of spot welding for automobiles, it is required to ensure welding quality not only for so-called high-tensile steels and ultra-high-tensile steels, but also for welding of plate assemblies consisting of multiple metal plates of mild steel plates. there is Furthermore, the thickness of the metal plate forming the outermost layer tends to become thinner, and the plate thickness ratio (plate thickness ratio=total plate thickness/thickness of the thin plate forming the outermost layer) tends to increase. As a result, for example, by simply adopting the welding method disclosed in Patent Document 1, it is difficult to ensure penetration into the thin plate forming the outermost layer and a nugget diameter, and sufficient welding quality cannot be ensured. There is In addition, the conventional welding method disclosed in Patent Document 1 has problems in that it is necessary to control the applied pressure, and that it is still not possible to sufficiently deal with the generation of flakes on the thin plate side. rice field.

Therefore, the present invention is a welding method that can improve the penetration rate into the thin plate and the nugget diameter while suppressing the generation of dust even when a plate assembly with a large plate thickness ratio is to be welded. aimed at providing

The welding method of the present invention, which is provided to solve the above-described problems, is a method of welding by energizing a plate assembly in which a plurality of metal plates are laminated while arranging a thin plate as the outermost layer, sandwiched between a plurality of electrodes. Among the metal plates forming the plate combination, the electrodes in contact with the thin plates have a convex shape and have a central region located on the tip side and an outer peripheral region located on the outer peripheral side of the central region. and a groove provided at the boundary between the central side area and the outer peripheral side area.

In the welding method of the present invention, the electrode in contact with the thin plate has a convex shape and is divided into a central region located on the tip side through the groove and an outer peripheral region located on the outer peripheral side. By using such an electrode, it is possible to conduct electricity at a high current density when contacting the thin plate provided as the outermost layer and starting the electricity supply. Further, in the electrode used in the welding method of the present invention, after the start of energization, at the stage where the center side region is in contact with the thin plate and the current is energized, the heat insulation effect occurs in the center side region due to the heat insulation effect of the air in the groove. is assumed. Therefore, at the stage of continuing welding until the outer peripheral region contacts the thin plate after the start of energization, while the current density is large, that is, while the contact area between the electrode and the plate and the contact area between the plates are small, It is possible to promote the nugget to grow in the thickness direction (vertical direction) of the plate assembly and improve the rate of penetration into the outermost thin plate.

In addition, as described above, when welding is started in the vicinity of the center side region of the electrode that is mainly in contact with the thin plate side at the initial stage of energization, the metal plate softened in the vicinity of the center side region eventually bites into the groove. expected to come. When the softened metal plate bites into the groove in this manner, the contact area between the electrode and the metal plate increases accordingly. As a result, it is possible to suppress the generation of dust due to excessive heat generation at the contact portion with the electrode.

In the welding method of the present invention, after welding is started at the contact portion between the central region of the electrode and the thin plate as described above, the welding progresses until the outer peripheral region comes into contact with the thin plate. state. When welding progresses to this state, the contact area between the electrode and the thin plate further increases, further reducing the current density. This allows the nugget to grow in the width direction (horizontal direction) while suppressing the generation of dust. In this way, by performing welding in stages while using the electrode as described above, it is possible to obtain a high welding quality with a large penetration rate into the thin plate and a large nugget diameter.

As described above, in the welding method of the present invention, welding is started by energizing the thin plate while the central region is in contact with the thin plate and the outer peripheral region is not in contact with the thin plate. It is desirable to include the step of continuing welding until the side region contacts the thin plate, and the step of welding while the outer peripheral region is in contact with the thin plate.

According to this method, even when a plate assembly with a large plate thickness ratio is to be welded, the penetration rate into the thin plate and the nugget diameter are further improved while further suppressing the generation of dust. be able to.

The above-described welding method of the present invention has a time period in which a high current value is maintained to the extent that a nugget is grown on the metal plate to be welded within the energization time for welding, and a It is preferable that the electrodes are energized so as to alternately repeat time zones in which a low current value enough to soften the metal plate is maintained.

In the above-described welding method, the metal plate is softened without generating spatter during the time period in which the current value is maintained high enough to grow a nugget on the metal plate to be welded within the energization time for welding. A low current value is sandwiched between them. Therefore, according to the welding method described above, the nugget can be grown in stages while gradually widening the contact area between the electrode and the metal plate. As a result, the rapid growth of nuggets can be suppressed, and the occurrence of spatter can be suppressed.

In the above-described welding method of the present invention, in the time period in which the high current value is maintained, as the time period in which the high current value is maintained and the time period in which the low current value is maintained are alternately repeated, It is preferable that the current value to be maintained is gradually increased.

According to the present invention, even when a plate assembly with a large plate thickness ratio is to be welded, welding that can improve the penetration rate into the thin plate and the nugget diameter while suppressing the generation of dust. can provide a method.

1 is a conceptual diagram showing a welding device used in a welding method according to one embodiment of the present invention; FIG. 1(a) and 1(b) are a sectional view and a perspective view, respectively, showing an electrode used in a welding method according to an embodiment of the present invention; FIG. 4 is a graph showing an energization pattern in a welding method according to one embodiment of the present invention; FIG. 3 is an explanatory diagram schematically showing the progress of welding when the electrodes shown in FIG. 2 are used;

A welding method according to an embodiment of the present invention will be described in detail below. In the following description, before describing the welding method, the configuration of the welding device 1 used for welding will be briefly described.

As illustrated in FIG. 1, the welding device 1 includes a pair of electrodes 2, 4, a gun 6, a robot 8, a transformer 10, a timer 12, a cooling device 14, a control device 16, and the like. The welding device 1 performs welding by energizing a welding object W while holding it between electrodes 2 and 4 provided on a gun 6 and pressurizing it. The object W to be welded is a metal composed of a plurality of (four in total in this embodiment) plate assembly in which a thin plate W1 is arranged as the outermost layer and a plurality (three in this embodiment) of thick plates W2 to W4 are superimposed. consists of a board.

The electrodes 2 and 4 are each made of a conductive metal such as copper. Electrodes 2 and 4 are connected to a transformer 10 via power supply lines, respectively. Therefore, current can be supplied to the electrodes 2 and 4 via the transformer 10 . Each of the electrodes 2 and 4 has a hollow structure and can be cooled by supplying cooling water to the inside thereof by a cooling device 14 .

Further, the electrode 2 is for contacting the thin plate W1 forming the object W to be welded described above. As shown in FIG. 2, the electrode 2 has a convex shape and has a central area 2a, an outer peripheral area 2b, and grooves 2c. The central region 2 a is a region provided at the tip of the electrode 2 . The central region 2 a is located substantially at the axial center of the electrode 2 . The outer peripheral region 2b is an annular region provided closer to the outer peripheral side of the electrode 2 than the central region 2a. The outer peripheral region 2b is formed substantially concentrically with the central region 2a. The groove 2c is formed in an annular shape at the boundary between the central region 2a and the outer peripheral region 2b.

The electrode 4 forms a counter electrode to the electrode 2 described above. The electrode 4 has a convex shape like the electrode 2, but does not have a groove or the like like the groove 2c of the electrode 2. As shown in FIG. Therefore, the surface of the electrode 4 is a substantially smooth surface without being divided into regions such as the central region 2a and the outer peripheral region 2b of the electrode 2 described above.

The gun 6 has two tips 6a, 6b that are spaced apart and face each other. The electrode 2 described above is attached to the distal end portion 6a, and the electrode 4 is attached to the distal end portion 6b. The gun 6 is capable of protruding and retracting the electrodes 2 and 4, respectively, while driving the electrodes 2 and 4 to approach and separate from each other. Therefore, by operating the gun 6, the object W to be welded arranged between the electrodes 2 and 4 can be pressed while being sandwiched. Gun 6 is connected to arm 20 of robot 8 . Therefore, by operating the arm 20 under the control of the robot 8, the gun 6 and the electrodes 2, 4 attached thereto can be moved to desired positions.

The transformer 10 can convert the current applied via the timer 12 into a predetermined current value. Also, the timer 12 is for controlling the timing of applying current to the electrodes 2 and 4 via the transformer 10 . As described above, the transformer 10 is connected to the electrodes 2 and 4 via power lines. Therefore, the welding apparatus 1 can supply the current having the current value adjusted by the transformer 10 through the electrodes 2 and 4 to energize the object W to be welded while adjusting the timing of the current supply by the timer 12 .

A cooling device 14 is a device for cooling the electrodes 2 and 4 . The cooling device 14 may be of any type as long as it can cool the electrodes 2 and 4. For example, the cooling device 14 cools the electrodes 2 and 4 by circulating cooling water inside the electrodes 2 and 4. can be

The control device 16 is for controlling the operation of the welding device 1 by controlling the operation of each part of the welding device 1 such as the robot 8, the timer 12, the cooling device 14, and the like. The control device 16 is configured to perform control for operating each part of the welding device 1 so as to weld the object W to be welded by a welding method described in detail below.

Next, a method for welding the object W to be welded by the welding device 1 will be described in detail with reference to the drawings. In the following description, while referring in detail to the characteristic parts of the welding method of the present embodiment, description of, for example, a method related to cooling, etc., will be omitted.

As shown in FIG. 3, the welding apparatus 1 applies a current between the electrodes 2 and 4 in accordance with an energization pattern in which the current value is varied in multiple stages (seven stages in the illustrated example), so that the object W to be welded is welded. Welding can be performed. Welding according to the energization pattern shown in FIG. 3 alternately repeats time zones Ha to Hd in which a high current value is maintained and time zones La to Lc in which a low current value is maintained within the entire energization time required for welding. It is realized by performing energization control so as to form a pattern.

The time period Ha to Hd in which a high current value is maintained is provided mainly for the purpose of growing the nugget N on the steel plate forming the object W to be welded. In other words, during the time period Ha to Hd, the current is applied at a value that generates enough heat to grow the nugget N formed inside the steel plates to be welded. However, if such a current value is maintained for too long, the nugget N may grow rapidly and spatter may occur. For this reason, in the energization control method for spot resistance welding exemplified in the present embodiment, the current is increased before spatter is generated without maintaining a high current value that causes the nugget N to grow on the steel plate to be welded. lowering the value.

The time period La to Lc in which the low current value is maintained is mainly provided for the purpose of mitigating the risk of spatter generation and softening the surface of the metal plate so that the electrode pressed against the steel plate is familiar with the steel plate. . During this time period La to Lc, the current value is adjusted to a level necessary to generate enough heat to soften the surface of the metal plate without causing spatter. As a result, the rapid growth of the nugget N formed inside the object W to be welded is suppressed, and the generation of spatter is suppressed. Further, in the time period La to Lc, the metal plate is softened, so the electrodes 2 and 4 become familiar with the metal plate due to the pressure applied to the object W to be welded by the electrodes 2 and 4, and the metal plate gradually softens. and the contact area between the electrodes 2 and 4 increases. This reduces the risk of spatter generation during the time period La to Lc in which the low current value is maintained.

It should be noted that during the time period La to Lc in which the low current value is maintained, the situation in which spatter occurs should be alleviated. Therefore, in order to efficiently form the nuggets N, it is preferable to increase the current value to be passed between the electrodes 2 and 4 in the time period La to Lc as long as the current value can alleviate the occurrence of spatter.

In the welding method of the present embodiment, when energizing in an energization pattern in which the current value is varied over multiple stages (seven stages in the illustrated example) as described above, the thin plate W1 side of the object W to be welded has the above-described Welding is performed using the electrode 2 of the configuration. When such an electrode 2 is used on the side of the thin plate W1, welding progresses while the contact state between each part of the electrode 2 and the thin plate W1 changes as schematically shown in FIG. A more detailed description will be given below with reference to FIG.

When welding is performed using the electrode 2 as an electrode for contacting the thin plate W1, the period from the start of energization until a while (hereinafter also referred to as the “initial energization period”) is the central region 2a as shown in FIG. is in contact with the thin plate W1, while the outer peripheral region 2b is welded in a non-contact state with the thin plate W1.

Here, in the initial energization period, only the central region 2a of the electrode 2 is in contact with the thin plate W1, so the contact area of the electrode 2 with respect to the thin plate W1 is small. Therefore, in the initial energization stage, a current flows between the electrodes 2 and 4 with a high current density. Air is contained in the groove 2c provided so as to surround the center side region 2a. Therefore, in the initial energization stage, the heat retention effect of the air in the grooves 2c can be expected, and there is a high possibility that the heat generated in the center side region 2a due to welding can be efficiently utilized for welding. Therefore, in the initial energization period, the nugget N grows in the thickness direction (longitudinal direction) of the plate assembly forming the object W to be welded, and the penetration rate into the thin plate W1 forming the outermost layer can be promoted.

Further, when welding proceeds during the initial energization period, the thin plate W1 is softened in the vicinity of the central region 2a of the electrode 2. As shown in FIG. As a result, as shown in FIG. 4(b), a portion of the thin plate W1 may bite into the groove 2c. When the softened thin plate W1 bites into the groove 2c in this manner, the contact area between the electrode 2 and the thin plate W1 increases accordingly. As a result, it is possible to avoid excessive heat generation at the contact portion between the electrode 2 and the thin plate W1, thereby suppressing the generation of dust.

When the welding progresses further from the state described above, the welding progresses until the outer peripheral region 2b comes into contact with the thin plate W1, as shown in FIG. 4(c). When welding progresses to this state, the contact area between the electrode 2 and the thin plate W1 increases by the contact area between the outer peripheral region 2b and the thin plate W1, and the current density between the electrodes 2 and 4 decreases. Thereby, the nugget N can be grown in the width direction (horizontal direction) while suppressing the generation of dust. In this way, by performing the welding through the steps described above, it is possible to improve the penetration rate into the thin plate W1 and expand the nugget N in the radial direction, thereby achieving welding with high welding quality.

As described above, in the welding method exemplified in this embodiment, the electrode 2 provided with the annular groove 2c is used as the electrode 2 used on the side of the thin plate W1. By using such an electrode 2, welding can be first performed in a state of high current density in the central region 2a inside the groove 2c, and the nugget N can grow in the thickness direction of the object W to be welded. When welding is performed using the electrode 2, the contact area between the electrode 2 and the thin plate W1 begins to increase when the thin plate W1 begins to bite into the groove 2c, and eventually the outer peripheral region 2b comes into contact with the thin plate W1. By this time, the electrode 2 and the thin plate W1 are in contact with each other over a larger contact area than at the beginning. As a result, the nugget N can be prevented from growing in the thickness direction of the object to be welded, and grown in the width direction of the object W to be welded. Using the electrode 2 in this way makes it possible to optimize the growth of the nugget N during welding, improve the rate of penetration into the thin plate W1, and increase the nugget diameter.

In the electrode 2 described above, the penetration rate and the degree of growth of the nugget N in the vertical direction (thickness direction) can be adjusted as appropriate by appropriately changing the diameter of the annularly formed groove 2c. Specifically, when the diameter of the groove 2c is reduced, the heat storage effect (heat retention effect) due to the air contained in the groove 2c is enhanced during the initial energization period, and the vertical direction (thickness direction) of the nugget N is maintained while ensuring a high penetration rate. can promote growth to When different electrodes 2 with different diameters of the grooves 2c are prepared, even if welding is performed under conditions in which the same penetration rate is obtained, the nugget N with a smaller diameter of the grooves 2c has a longer vertical direction (thickness direction). By adjusting the diameter of the groove 2c based on such knowledge, the penetration rate and the degree of growth of the nugget N in the vertical direction (thickness direction) can be appropriately adjusted.

Further, in the welding method shown in this embodiment, the electrode 2 provided with grooves 2c and the like is used as the electrode arranged on the side of the thin plate W1, instead of the conventional electrode having a flat surface like the electrode 4. It can be realized by Therefore, according to the welding method described above, the existing welding apparatus 1 can be utilized for welding the object W to be welded without requiring special equipment.

Further, in the welding method exemplified in the present embodiment, the time zones La to Lc in which the low current value is maintained are sandwiched between the time zones Ha to Hd in which the high current value is maintained without continuing to maintain the high current value. Therefore, welding is performed with an energization pattern in which the current value is changed in multiple stages. Therefore, if the electrode 2 is used and welding is performed according to the energization pattern as described above, the possibility of the occurrence of spatter due to the rapid growth of the nugget N can be further reduced. In addition, if the time periods La to Lc in which the current value is maintained low as described above are provided, the contact area between the welding object W and the electrode 2 becomes large, and the inside of the welding object W where the nugget N is formed 3, the situation in which spatter occurs is alleviated, so even if the current value is increased again, it is difficult for spatter to occur immediately.

In this embodiment, an example is shown in which welding is performed with an energization pattern in which the current value is changed in seven steps between the electrodes 2 and 4, but the present invention is not limited to this. For example, the number of steps for changing the current value may be set to three steps, five steps, or the like, or the welding may be performed without changing the current value in steps.

In this embodiment, an example is shown in which welding is performed on a plate combination consisting of four metal plates, but the present invention is not limited to this, and two, three, or five or more metal plates are used. The overlapped plate assembly may be used as the object W to be welded. Further, in the present embodiment, an example in which the welding method of the present invention is applied to direct spot resistance welding has been exemplified, but the present invention is not limited to direct spot resistance welding, for example series spot resistance welding, indirect spot resistance welding. It can also be suitably applied to various spot resistance welding and the like.

It should be noted that the present invention is not limited to those exemplified in the above-described embodiments and modifications, and those skilled in the art will recognize that other embodiments are possible from the teachings and spirit of the invention without departing from the scope of the claims. easy to understand.

INDUSTRIAL APPLICABILITY The present invention can be suitably used in general welding of plate assemblies in which a plurality of metal plates are superimposed while arranging a thin plate as the outermost layer.

2: Electrode 2a: Center side area 2b: Periphery side area 2c: Groove Ha: Time zone La: Time zone W: Welding target W1: Thin plate N: Nugget

Claims (2)

A welding method for welding by sandwiching a plate assembly in which a plurality of metal plates are superimposed while arranging a thin plate as the outermost layer with a plurality of electrodes and energizing,
Among the metal plates forming the plate assembly, as electrodes in contact with the thin plates, a central region having a convex shape and located on the tip side, an outer peripheral region located on the outer peripheral side of the central region, and the A groove provided at the boundary of the center side area and the outer peripheral side area is used,
The welding method, wherein the central side area and the outer peripheral side area are curved to form the convex shape . Welding is started by energizing the outer peripheral region in a non-contact state with the thin plate while the central region is in contact with the thin plate, and welding is continued until the outer peripheral region contacts the thin plate. and
2. The welding method according to claim 1, further comprising the step of welding while the outer peripheral region is in contact with the thin plate.

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