JP2006198676A - Electrode for resistance welding and series spot welding equipment or indirect spot welding equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for resistance welding where, in the case a thick metal plate and a thin metal plate are lapped, and the electrode is pressed against the thick metal plate side, so as to perform series spot welding, the generation of cracks, burrs and a plate gap can be suppressed. <P>SOLUTION: The electrode for resistance welding is provided with: a tip shape with an almost conical shape in which the tip angle (a) of the cone is 120 to 165 degrees; and a flat part 3 with the diameter (b) of 1.5 to 3 mm at the central part of the tip in the cone. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resistance welding electrode suitable for series spot welding and indirect spot welding.

  Direct spot welding is widely used for welding steel sheets. In this welding method, as shown in FIG. 11, the stacked steel plates 21 and 22 are directly pressed while being sandwiched between upper and lower electrodes 23 and 24, current is passed in the thickness direction, and resistance heating of the steel plates is used. As a result, a dotted weld 25 is obtained. That is, when an electric current is passed, a melted portion of both steel plates called a nugget is formed at a contact portion between both steel plates, and both steel plates are welded in a spot shape by this nugget. The electrodes 23 and 24 include pressurization control devices 26 and 27 and a current control device 28, respectively, so that the pressurizing force and the current value to be energized are controlled.

  On the other hand, with this direct spot welding, the series spot welding that is often used at present, as shown in FIG. 12, presses the superposed steel plates 21 and 22 from one direction with a pair of electrodes 23 and 24, and then The point-like welded portions 29 and 30 are obtained. In the direct spot welding described above, since the steel plates 21 and 22 are sandwiched between the electrodes 23 and 24, it is necessary to perform welding for each point, whereas in the case of series spot welding, a large number of electrodes 23 and 24 are used. Since the spots can be welded at the same time and the speed of welding can be increased, they are currently used for welding automobile bodies.

  With regard to series spot welding, for example, in Japanese Patent Application Laid-Open No. 11-333569, a nugget is formed where metal plates are stacked. It is described. Japanese Patent Laid-Open No. 2002-239742 discloses that a seat surface that is one step higher than other portions is formed at a position where the electrode is brought into contact, and the seat surface is pressed and contacted so that the seat surface is crushed. It is described that a good welding strength can be obtained. In series spot welding, as shown in FIG. 13, only one electrode 31 may be energized, and only the electrode 31 side to which current is applied may be welded using the other electrode 32 as a power supply terminal (ground electrode). .

Other resistance welding includes, for example, indirect spot welding as described in JP-A-2002-263848. Indirect spot welding, as shown in FIG. 14 or FIG. 15, one electrode 33 is pressed against the overlapping portion 34 where the steel plates 21 and 22 are overlapped, and the other electrode 35 is moved away from the overlapping portion 34. It attaches to the other steel plate as a power supply terminal, and forms a spot-like welded part in the overlapped part. For example, as shown in FIG. 16, such indirect spot welding is a series spot welding in which it is difficult to make the pressurization angle orthogonal to the welded portion with a pair of electrodes for a workpiece having a complicated shape. Equivalent welding can be performed. For this reason, it is practically used for, for example, welding of a hemming joint portion of a panel component formed by hemming a door outer panel and a door inner panel of an automobile.
Japanese Patent Laid-Open No. 11-333569 JP 2002-239742 A JP 2002-263848 A

  In the case of series spot welding, as shown in FIG. 17, when a thick metal plate 51 and a thin metal plate 52 are overlapped and welding is performed by applying the electrodes 50 a and 50 b to the thick metal plate 51 side, the conductivity of the superimposed metal is equal. In this case, the thicker metal plate 51 is easier to pass the current than the thin metal plate 52, so that the portion where the current density is higher is biased toward the thick metal plate 51. There is a problem that it is difficult to form a nugget in the overlapping portion 53 of the metal plates 51 and 52, and a sufficient welding strength cannot be obtained. For this reason, when a nugget is to be formed by simply increasing the current value to be energized or by increasing the energization time, spatter was generated, and sufficient welding strength could not be obtained.

  In addition, when a hemispherical electrode 50a ′ (50b ′) having a tip of R8 is used as shown in FIG. 18, which is commonly used as a resistance welding electrode, the current concentrates on the power feeding side and is large. Cracks 61 and burrs 62 may occur.

  Further, as shown in FIG. 19, when the substantially cylindrical electrode 50a ″ (50b ″) having a substantially flat shape with the tip of R40 is used, the thick metal plate 51 side and the thin metal plate are used. In some cases, a gap 63 was formed in the overlapped portion 52, and a nugget having sufficient welding strength was not formed.

  In this way, when the thick metal plate 51 and the thin metal plate 52 are stacked and the electrodes 50a and 50b are pressed against the thick metal plate 51 to perform series spot welding, cracks 61 and burrs 62 may occur, As a result, defects such as 63 occurred, and it was difficult to obtain sufficient welding strength. The same problem occurs when indirect spot welding is performed by stacking a thick metal plate and a thin metal plate and pressing the electrode against the thick metal plate.

  The series spot welding apparatus according to the present invention has been devised in view of the above-described problems. The electrode has a substantially conical tip shape, and a conical surface having a cone tip angle of 120 to 165 degrees. The resistance welding electrode having a flat portion with a diameter of 1.5 to 3 mm at the center of the tip of the cone is used.

  If this electrode is used in a series spot welding apparatus, the flat part formed at the center of the tip of the cone of the electrode is as small as 1.5 to 3 mm in diameter. The current density can be increased, the surface of the metal plate can be heated and softened at an early stage, and the electrode can be adapted to the surface of the metal plate. In addition, since it has a substantially conical tip shape and a conical surface with a cone tip angle of 120 to 165 degrees, even if cracks or burrs occur near the area where the electrode is pressed, The conical surface of the electrode hits the surface and can be filled immediately after cracks and burrs are generated. As a result, it is possible to prevent cracks and burrs from growing and causing large defects. In addition, since the contact area of the electrode gradually increases, it is possible to prevent the formation of a plate gap in the overlapped portion of the metal. Thus, if this electrode is used, the occurrence of cracks and burrs and the occurrence of plate gaps can be suppressed, so that a good nugget can be formed in the overlapped portion of the metal plate, which is sufficient for welding of the metal plate. High welding strength can be ensured.

  Note that this resistance welding electrode is not only used for series spot welding by stacking a thick metal plate and a thin metal plate and pressing the electrode against the thick metal plate, but also for series spot welding used in other applications. It can be used as an electrode or an electrode for resistance welding such as direct spot welding in which a superposed metal plate is sandwiched between a pair of electrodes and welded, or so-called indirect spot welding.

  Hereinafter, an electrode for resistance welding and a series spot welding apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, this resistance welding electrode 1 has a substantially conical tip shape, a conical surface 2 having a cone tip angle a of 145 degrees, and a flat b having a diameter b of 2 mm at the center of the tip of the cone. Part 3 is formed.

  In FIG. 2, the resistance welding electrode 1 is used as a pair of electrodes 1 a and 1 b of the series spot welding apparatus 4, and a thick metal plate 11 and a thin metal plate 12 are stacked, and a pair of electrodes is disposed on the thick metal plate 11 side. A state in which 1a and 1b are pressed to perform series spot welding is shown.

  In this case, since the flat portion 3 formed at the center of the tip of the electrodes 1a and 1b has a diameter of 2 mm and the area in contact with the thick metal plate 11 is small in the initial stage of energization, the metal plate 11 can be obtained with a relatively small current value. , 12 can generate a portion with a high current density, and the surface of the thick metal plate 11 with which the electrodes 1a and 1b are brought into contact can be heated and softened.

  Further, as shown in FIG. 3, even when cracks 13 and burrs 14 are generated in the vicinity of the pressed electrodes 1a and 1b at the beginning of energization, when the surface of the metal plate 11 is softened, as shown in FIG. The conical surface 2 of the electrodes 1a and 1b presses against the surface of the site where the crack 13 and the burr 14 are generated, and the crack 13 and the burr 14 are filled with the pressure to eliminate this. In addition, the conical surface 2 of the electrodes 1a and 1b gradually increases in area in contact with the metal plate 11 as the metal plate 11 is heated and the surface is softened. It is hard to produce a gap.

  Thus, if this resistance welding electrode 1 is used, the generation of cracks 13 and burrs 14 and the generation of plate gaps can be suppressed. Therefore, the thick metal plate 11 is overlapped with the thick metal plate 11 and the thin metal plate 12. Even when series spot welding is performed by pressing an electrode on the side, a nugget 15 having a sufficient welding strength can be formed in the overlapping portion of the metal plates 11 and 12.

  The resistance welding electrode and the series spot welding apparatus according to one embodiment of the present invention have been described above. However, the resistance welding electrode and the series spot welding apparatus according to the present invention are not limited to the above embodiment.

  For example, as shown in FIG. 1, the resistance welding electrode is an electrode having a substantially conical tip shape, and has a conical surface 2 having a cone tip angle a of 145 degrees, and is provided at the center of the tip of the cone. Although the thing which formed the flat part 3 whose diameter b is 2 mm was illustrated, the shape of the electrode for resistance welding which concerns on this invention is not limited to said embodiment.

  If the tip angle “a” of the cone is too small, when a crack or burr occurs in the vicinity of the portion where the electrode is pressed, the conical surface 2 does not immediately press against the surface, and the effect of eliminating the crack or burr is sufficient. I can't get it. In addition, if the tip angle of the cone is too large, the entire surface of the cone surface 2 comes into contact immediately, and as in the case where a flat electrode having a tip R40 is used, a gap is easily generated in the overlapping portion, and sufficient. A nugget with welding strength may not be obtained. If the cone tip angle a is 120 to 165 degrees, the same effect as that of the resistance welding electrode described above can be obtained. More preferably, the lower limit of the cone tip angle a is 140 degrees or more, The upper limit of the angle a is preferably 160 degrees or less.

  Further, the flat portion 3 formed at the center of the tip of the cone is exemplified as having a diameter b of 2 mm. However, if the diameter b is too small, the current density becomes too large at the initial stage of energization, and sputtering is likely to occur. . On the other hand, if the diameter b is too large, it may not be possible to obtain a current density sufficient to heat and soften the metal plate in the initial stage of energization. For this reason, the flat part 3 formed in the front-end | tip center part of a cone should just have the diameter b of 1.5 mm-3.0 mm. Moreover, the flat part 3 does not need to be completely flat, and may be a substantially flat curved surface of about R40.

  Further, the resistance welding electrode may have a structure in which the tip portion described above is an electrode tip and the tip portion can be replaced.

  As described above, this resistance welding electrode can prevent cracks, burrs, and plate gaps, so when a thick metal plate and a thin metal plate are stacked and welded from the side of the thick metal plate, Spot welding can be applied. In addition, the use of this resistance welding electrode is not limited to such a use, and can be used for other uses of series spot welding and resistance welding apparatuses in general such as direct spot welding and indirect spot welding.

  As described above, a resistance welding electrode having a substantially conical tip shape, a conical surface having a cone tip angle of 120 to 165 degrees, and a flat portion having a diameter of 1.5 to 3 mm at the center of the tip of the cone. However, as shown in FIGS. 5 (a) and 5 (b), the conical surface 2 has an inclined surface 2a on the tip side thereof and an inclined surface 2b on the outer side thereof. It may be formed by a two-step conical surface that is gentler than that.

  In this embodiment, the resistance welding electrode 1c shown in FIGS. 5 (a) and 5 (b) is a resistance welding electrode having a substantially conical tip shape and a diameter of 16 mm. A 2 mm flat portion 3 is formed, a first conical surface 2a having a cone tip angle c of 155 degrees is formed in a range 2a having a diameter of 5.5 mm on the outer side thereof, and a cone tip angle d is 135 on the outer side 2b. A conical surface 2b of a predetermined degree is formed, and a conical surface 2 having a two-stage shape in which the inclination 2a on the tip side is gentler than the inclination 2b on the outer side is formed.

  According to such a tip-side slope 2a formed by a two-step conical surface 2a, 2b that is gentler than the outer slope 2b, the tip has substantially the same shape as the resistance welding electrode shown in FIG. I have. For this reason, in the initial stage of energization where the tip of the resistance welding electrode is pressed against the metal plate and energized, cracks and burrs occur in the vicinity of the area where the electrode 1c is pressed as in the resistance welding electrode shown in FIG. In addition, the conical surface 2a immediately contacts the cracks and burrs and acts to eliminate the cracks and burrs.

  Furthermore, as shown in FIG. 6, even when the metal plate 11 is elastically raised around the position 11a where the electrode 1c is pressed in the initial stage of energization, the inclination 2b on the outer side of the electrode tip is larger than the inclination 2a on the tip side. Since it has stood up, it can prevent contacting with the site | part 11a which the metal plate 11 rose. Such an event may occur, for example, when there is a plate alignment error and the metal plate 11 that presses the electrode 1c is floating with respect to the other metal plate 12 as shown in FIG. In the latter stage of the energization cycle, as the surface of the metal plate 11 is heated and the surface thereof is softened, the area where the electrode 1c is in contact with the metal plate 11 gradually increases. Even if the conical surface 2b on the outer side of the electrode tip contacts, there is no problem in welding. In addition, the tip-side slope 2a formed by the two-step conical surfaces 2a and 2b that are gentler than the outer slope 2b is formed as described above. 11 is difficult to contact, and therefore teaching errors such as the angle at which the electrode is pressed by a robot or the like can be tolerated to some extent, so that the teaching accuracy can be relaxed.

  Next, an example of a suitable energization pattern when using the resistance welding electrode 1 will be described.

  The energization pattern is controlled by, for example, a current control device configured by combining an inverter and a transistor switch.

  In this embodiment, the current control device softens the surface of the workpiece to be welded by maintaining the current value gradually increased from the start of energization at a current value that can suppress the occurrence of spatter for a predetermined time in the initial stage of energization, Thereafter, the current value of the current flowing through the electrode is controlled so that the time zone in which the current value is kept high and the time zone in which the current value is kept low are alternately repeated. Furthermore, as the time zone in which the current value is kept high and the time zone in which the current value is kept low are alternately repeated, the current value in the time zone where the current value is kept high is gradually increased. The purpose of maintaining the high current value is to grow nuggets on the steel sheet to be welded, and the purpose of maintaining the low current value is to soften the pressed steel sheet without spattering. Yes.

  For example, when spot welding is performed by pressing a pair of electrodes from the side of a 1.2 mm thick metal plate to an SPC 270, 1.2 mm thick metal plate and a SPC 270, 0.6 mm thick metal plate As shown in FIG. 8, the initial 0 to 2 cycles of the energization time gradually increase the current value, 2 to 4 cycles to 3 kA, 4 to 9 cycles to 5 kA, 9 to 11 cycles to 4.5 kA, and 11 to 16 cycles. Was set to 6 kA, 16 to 19 cycles was set to 5.5 kA, 19 to 24 cycles were set to 7 kA, 24 to 27 cycles were set to 6.5 kA, and 27 to 30 cycles were set to 8 kA. In this embodiment, spot welding is performed with an alternating current having a frequency of 60 Hz, cycle is a unit for setting the energization time, and 1 cycle is 1/60 sec. Further, welding was performed with the applied pressure applied to the electrode being 20 kgf.

  In this case, at 0 to 4 cycles of energization time, as shown in FIG. 2, the surface of the metal plate 11 against which the electrodes 1a and 1b are pressed is not sufficiently softened, so that the contact area of the electrodes 1a and 1b is small. For this reason, the electric current value is suppressed to be lower than 3 kA, and the problem that spatter is generated at the initial stage of energization is suppressed. During this time, the surface of the metal plate 11 is heated and softened, and the tips of the electrodes 1a and 1b gradually sink into the surface of the metal plate 11, thereby increasing the contact area between the metal plate 11 and the electrodes 1a and 1b. .

  In 4 to 9 cycles, since the contact area between the metal plate 11 and the electrodes 1a and 1b is larger than that at the initial stage of energization, the current value is increased to such an extent that spatter does not occur at this timing. The nugget 15 is formed or grown by increasing the current density generated in the superposed portion 12.

  If the current value is continuously maintained at a value of 5 kA or higher continuously from 9 cycles during this period, sputtering is likely to occur. For this reason, the current value is lowered to 4.5 kA in the ninth to eleventh cycles. At this timing, the generation of spatter can be suppressed by once reducing the current value to the extent that spatter does not occur. In addition, in the ninth to eleventh cycles, the surface of the metal plate 11 is softened while maintaining the state of heating the metal plates 11 and 12 by reducing the current value to the extent that sputtering does not occur without completely stopping energization. be able to. As a result, as shown in FIG. 3, even when cracks 13 and burrs 14 occur in the previous 4 to 9 cycle time zone, the surface resists in the 9 to 11 cycle time zone as shown in FIG. The conical surface 2 of the welding electrodes 1a and 1b presses against the surface of the site where the crack 13 and the burr 14 are generated, so that the crack 13 and the burr 14 are filled, and the crack 13 and the burr 14 can be eliminated.

  Next, the time period in which the current value is kept high by setting 11 to 16 cycles to 6 kA, 16 to 19 cycles to 5.5 kA, 19 to 24 cycles to 7 kA, 24 to 27 cycles to 6.5 kA, and 27 to 30 cycles to 8 kA And the time slot | zone which keeps an electric current value low is provided alternately. This is because the nugget is grown in the time zone in which the current value is kept high, and in the time zone in which the current value is kept low, the electrode is made to conform to the metal plate, and the surface of the part where cracks and burrs are generated becomes the conical surface of the electrode. This is for repeatedly pressing the metal plate and filling the cracks and burrs. Thereby, a nugget with sufficient welding strength can be formed without causing spattering.

  Moreover, in this embodiment, 4-9 cycles (5.0 kA), 11-16 cycles (6.0 kA), 19-24 cycles (7.0 kA), 27-30 cycles (8.0 kA) in the time zone in which the current value was maintained high. ), The current value is gradually increased. As the energization time elapses, the contact area of the electrode gradually increases.In this way, by gradually increasing the current value during the time period in which the current value is maintained high, the current density required for nugget growth is increased. Can be secured.

  According to this energization pattern, when SPC 270, metal plate 11 having a thickness of 1.2 mm, and SPC 270, metal plate 12 having a thickness of 0.6 mm are pressed against the thick metal plate 11 from the side of the metal plate 11, series spot welding is performed. The nugget can be grown while suppressing the generation of spatters and eliminating the occurrence of cracks 13 and burrs 14. In this case, when the metal structure of the overlapping portion of the metal plates 11 and 12 is observed, the metal in the overlapping portion of the metal plates 11 and 12 is finely and partially melted and recrystallized compared to a conventional normal nugget. A large number of events are observed. In some cases, bonding is performed in a so-called diffusion bonding state, and in other cases, bonding is performed in an event different from a conventional normal nugget. Even when such diffusion bonding occurs, sufficient welding strength can be obtained.

  In this embodiment, the SPC 270, the metal plate 11 having a thickness of 1.2 mm, and the SPC 270, the metal plate 12 having a thickness of 0.6 mm are pressed against the electrode from the thick metal plate 11 side to perform series spot welding. However, if the material and thickness of the metal plate are different, the current value in each time zone, the energizing time in each time zone, the number of times the current value is repeated in the high time zone and the low time zone, etc. It is good to adjust appropriately according to the material and thickness of the board.

  In addition, in the case of single-side welding, unlike the direct spot welding, the overlapping portion of the plate is not sandwiched between the pair of electrodes for pressurization, so that the electrode pressing force is restricted as compared with direct spot welding. For this reason, in an actual production line, there may be a gap in the overlapped portion of the metal plates, and the gap may not be eliminated only by pressing the electrodes. When energized in this state, it is conceivable that the metal plate 11 against which the electrode 1 is pressed excessively generates heat, resulting in spatter and plate breakage.

  Therefore, as described above, the current value is kept low as shown in FIG. 9 in order to secure the certainty of welding and enhance the versatility with the energization pattern that repeats the time zone in which the current value is high and the time zone in which the current value is low. The current values in the time zones 32a to 32c may be set to a current value A1 that does not cause sputtering or cutting even when the metal plate 11 that presses the electrode is a single plate. That is, even when the metal plate 11 against which the electrode is pressed is a single plate, a safe current value that does not cause spattering or plate breakage is obtained at the laboratory level. With the current value obtained here as the base current A1, in the energization pattern 30 in which the current values shown in FIG. 9 repeat the high time zones 31a to 31d and the low time zones 32a to 32c, the time zones 32a to 32c for keeping the current values low. It is good to adopt for the current value.

  For example, in the laboratory, as shown in FIGS. 10A and 10B, a spacer 33 is provided between the metal plate 11 that presses the electrode 1 a and the metal plate 12 at a location where the electrode 1 a is pressed. The plate gap is intentionally formed so as not to be eliminated even if the electrode 1a is pressed against the metal plate 11 between the metal plates 11. In this state, a predetermined energization time longer than the total energization time of the energization patterns employed in actual welding is set, and the plate 1 is pressed against the metal plate 11 that presses the electrode 1a even if energization is continuously performed in such energization time. Find the current value at which no break occurs. Specifically, when the total energization time of the energization patterns employed in actual welding is 28 cycles, an energization time of about 31 cycles longer than that is set. And even if it supplies continuously for the set electricity supply time, it is good to calculate the electric current value of the boundary which does not produce a sputter | spatter and plate | board breakage to the metal plate 11, and sets the base current A1 considering the safety factor to this.

  For example, in the set energization cycle, the experiment is repeated while changing the current value intermittently, and among the current values that do not cause the metal plate 11 to be sputtered or cut, the highest current value is 3 kA. Taking this into consideration, a current value of about 2 kA may be set as the base current. When the base current A1 is set, if the base current A1 is too low, the surface of the metal plate 11 cannot be maintained in a molten state in a time period for keeping the current value low, and cracks and burrs are buried, The effect of setting the time zones 32a to 32c for eliminating the burr and maintaining the current value low cannot be obtained. For this reason, at the laboratory level, the function of the time periods 32a to 32c for keeping the current value low is not impaired, and even when there is a gap, the metal plate 11 is not spattered or broken. It is preferable to find an appropriate base current A1.

  The base current A1 is obtained as described above, and as shown in FIG. 9, the time periods 31a to 31d for keeping the current value high and the time for keeping the current value low within the energization time of series spot welding or indirect spot welding. In the control of alternately repeating the bands 32a to 32c, the base current obtained above is adopted as the current values of the time periods 32a to 32c for keeping the current value low. As a result, even if there is a gap between the metal plate 11 that presses the electrode 1 and the metal plate 12, and this does not disappear by simply pressing the electrode 1, spatter or cutting of the metal plate 11 occurs. Can be reliably prevented. Thus, by adopting the base current A1 as the current value in the time zones 32a to 32c for keeping the current value low, it is possible to reliably prevent the metal plate 11 from being sputtered or broken. Setting of the current value in the energization cycle becomes easy.

  In the energization cycle shown in FIG. 9, the energization cycle is divided into seven time zones, and the time zones 31a to 31d for keeping the current value high and the time zones 32a to 32c for keeping the current value low are alternately repeated. In the energization pattern 30, the base current described above is employed in the time zones 32a to 32c for keeping the current value low. In this case, in the time zones 31a to 31d in which the current value of the first stage is kept high, it is preferable to set the current value to such a degree that the metal plates 11 and 12 are lightly welded, and the third stage, the fifth stage, and the seventh stage. The respective current values may be set so that the welding diameter gradually increases as the electrodes become familiar. In the energization pattern 30 in which the base current A1 is set as described above, the current value and energization time in each time zone, the number of times the current value is repeated in the high time zone and the low time zone, and the like are determined depending on the material and thickness of the metal plate. It is good to adjust appropriately according to the above.

  As described above, the resistance welding electrode and the series spot welding apparatus or the indirect spot welding apparatus according to one embodiment of the present invention have been described. However, the present invention is not limited to the above embodiment, and various modifications can be made. Is possible. Further, the method for detecting the base current is not limited to the method described in the above embodiment.

The front view which shows the electrode for resistance welding which concerns on one Embodiment of this invention. Sectional drawing which shows the use condition of the series spot welding apparatus provided with the electrode for resistance welding which concerns on one Embodiment of this invention. Sectional drawing which shows the state at the time of the energization initial stage of the resistance welding electrode which concerns on one Embodiment of this invention. Sectional drawing which shows the effect | action which eliminates a crack and a burr | flash in the electrode for resistance welding which concerns on one Embodiment of this invention. (A) is a front view which shows the electrode for resistance welding which concerns on other embodiment of this invention, (b) is an end elevation of the front-end | tip. The figure which shows the use condition of the electrode for resistance welding which concerns on other embodiment of this invention. The figure which shows the use condition of the electrode for resistance welding which concerns on other embodiment of this invention. The figure which shows the electricity supply pattern of the series spot welding apparatus using the electrode for resistance welding which concerns on one Embodiment of this invention. The figure which shows the electricity supply pattern of the series spot welding apparatus which concerns on other embodiment of this invention. (A) The top view which shows an example of the detection method of a base current, (b) is the side view. The figure which shows the welding method of direct spot resistance welding. The figure which shows the welding method of series spot resistance welding. The figure which shows the welding method of series spot resistance welding. The figure which shows the welding method of indirect spot resistance welding. The figure which shows the welding method of indirect spot resistance welding. The figure which shows the welding method of indirect spot resistance welding. The figure which shows the conventional series spot welding. The figure which shows the problem in the conventional series spot welding. The figure which shows the problem in the conventional series spot welding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resistance welding electrode 2, 2a, 2b Conical surface 3 Flat part 4 Series spot welding apparatus A1 Base current

Claims (7)

  An electrode for resistance welding having a substantially conical tip shape, a cone surface having a cone tip angle of 120 to 165 degrees, and a flat portion having a diameter of 1.5 to 3 mm at the center of the tip of the cone.   2. The resistance welding electrode according to claim 1, wherein the conical surface is formed of a two-step conical surface whose inclination on the tip side is gentler than that on the outer side. In a series spot welding apparatus or an indirect spot welding apparatus that performs welding by pressing a pair of electrodes against a distant position of at least two superimposed metal plates,
The electrode is a resistance welding electrode having a substantially conical tip shape, and a conical surface having a cone tip angle of 120 to 165 degrees, and a diameter of 1.5 to 1.5 at a center portion of the tip of the cone. A series spot welding apparatus or indirect spot welding apparatus comprising an electrode having a 3 mm flat portion.   4. The series spot welding apparatus or indirect spot welding apparatus according to claim 3, wherein the conical surface of the electrode is formed of a two-step conical surface whose inclination on the tip side is gentler than the inclination on the outer side. .   Current that controls the current value of the current that flows through the electrode so that the time zone in which the current value is kept high and the time zone in which the current value is kept low are alternately repeated within the energization time of series spot welding or indirect spot welding. The series spot welding apparatus or indirect spot welding apparatus according to claim 3, further comprising a control device.   The current control device is characterized by gradually increasing a current value in a time zone for maintaining a high current value as the time zone for maintaining a high current value and a time zone for maintaining a low current value are alternately repeated. The series spot welding apparatus or indirect spot welding apparatus according to claim 3.   The current control device is characterized in that it is set to a current value in a time zone in which the current value is kept low, and a current value that does not cause spattering or plate breakage even when a metal plate that presses the electrode is energized for a predetermined time. The series spot welding apparatus or indirect spot welding apparatus according to claim 5.

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