JP4753411B2 - Energization control method for spot resistance welding - Google Patents

Description

The present invention relates to an energization control method for spot resistance welding.

  In spot resistance welding, when a current is applied, a melted portion of both steel plates called a nugget is formed at a contact location of the stacked steel plates, and both steel plates are welded in a spot shape by this nugget. Direct spot welding, series spot welding, and indirect spot welding are known as spot resistance welding of steel plates.

  In direct spot welding, as shown in FIG. 1, the stacked steel plates 1 and 2 are directly pressed between the upper and lower electrodes 3 and 4 to apply a current in the thickness direction, and the resistance heating of the steel plates 1 and 2. Is used to form the spot-like welded portion 5. The electrodes 3 and 4 are respectively provided with pressurization control devices 6 and 7 and a current control device 8 so that the pressurizing force and the current value to be energized are controlled.

In addition, as shown in FIG. 2, in the series spot welding, a pair of electrodes 3 and 4 are pressed against a position separated from one side of the steel plate 1 among the superposed steel plates 1 and 2, and a current flows to form a spot shape. The welds 9 and 10 are formed. This series spot welding can be welded at multiple points with a large number of electrodes at the same time, and the speed of welding can be increased. Moreover, in series spot welding, as shown in FIG. 3, only one electrode 11 may be energized, and only the electrode 11 side through which current is energized may be welded using the other electrode 12 as a power supply terminal (ground electrode). .

  Indirect spot welding, as shown in FIG. 4 or 5, one electrode 13 is pressed against the overlapping portion 14 where the steel plates 1 and 2 are overlapped, and the other electrode is separated from the overlapping portion 14. 15 is attached to the other steel plate as a power feeding terminal, and a spot-like welded portion is formed in the overlapped portion. Such indirect spot welding is, for example, as shown in FIG. 6, when it is difficult to make the pressurization angle orthogonal to the welded part 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.

  A general energization pattern in these spot resistance welding is known, for example, in which the current value is gradually increased at the beginning of energization, and then the current value control is performed to maintain the constant current value for a predetermined time. ing. In addition, a relatively low current value is maintained for a certain period of time, then a relatively high current value is maintained for a certain period of time, a relatively high current value is maintained for a certain period of time, and then a relatively low current is maintained. A device that performs current value control that maintains a constant value for a certain time is known.

Japanese Patent Application Laid-Open No. 11-333569 describes that a steady current is applied after a nugget is formed by applying a large current in the initial stage of energization.
Japanese Patent Laid-Open No. 11-333569

  The weld strength of the welded portion is evaluated by the tensile shear strength. When the tensile shear test is performed, a case where the base material breaks without the welded part being peeled off is referred to as base material breakage. On the other hand, the case where the welded part is removed when the tensile shear test is performed is called interface fracture. When the welded part breaks the base material, it means that the tensile shear strength of the welded part is stronger than that of the base material, and the interfacial break means that the strength of the welded part is inferior to the base material. In order to improve the collision performance of a vehicle, it is required that the welded portion has a strength sufficient to break the base material.

  When spatter is generated during welding at the welded part, cracks are likely to develop in the joint with the spattered part being the starting point, and the welded part does not break the base material and the frequency of interface fracture increases.

  In particular, when spot resistance welding is performed on a super-high tensile material of 780 MPa class or higher, the super high-tensile material has a high base material strength, and therefore the conditions for causing the base material breakage at the welded part become severe and cause the base material breakage. The nugget diameter required for this is also large. Further, when the steel plates are overlapped, a minute gap is formed in the steel plate. If it is a mild steel plate, a clearance can be eliminated by the applied pressure when the electrodes are pressed against each other, and a sufficient contact area can be secured between the steel plates. However, since the surface of the base metal is hard in the super high tensile material, a gap remains between the steel plates, and the contact area between the base material and the electrode tends to be small at the initial stage of spot welding energization. Further, in the case of ultra-high tensile material, when dust is caught between the base materials, a gap is similarly generated between the base materials, and the contact area tends to be small. In this way, in the ultra high tensile material, the contact area between the steel plates is reduced, the current density is likely to be increased, and sputtering is likely to occur. For this reason, it is difficult to obtain a stable quality of a required nugget diameter without generating spatter when spot resistance welding is performed on an ultra-high tensile material.

  In addition, the occurrence of spatter has the detrimental effect of making quality control difficult because the spatter adheres to the outer plate and the coating quality deteriorates and the variation in nugget diameter increases. There are many adverse effects on manufacturing operations, such as increasing man-hours and generating dust to remove burrs and burrs.

The energization control method for spot resistance welding according to the present invention has a predetermined high current value at which a nugget is grown on a steel plate made of an ultra-high tensile material of 780 MPa class or higher to be welded within the energization time of resistance welding. and times to maintain shorter than the time comes to generate a predetermined time, and a time zone for maintaining a predetermined time a predetermined low current value of the degree of softening of the steel sheet without causing sputtering to maintain the high current value The electrode is energized so as to alternately repeat from the first time zone to the last time zone maintaining the high current value .

  According to the energization control method of this spot resistance welding, spatter does not occur during a time period in which a current value high enough to grow a nugget on the steel plate to be welded is maintained within the energization time of resistance welding. Since a current value that is low enough to soften the steel plate is sandwiched, the nugget can be grown in stages while gradually increasing the contact area. As a result, it is possible to suppress the rapid growth of the nugget and suppress the occurrence of spatter. Therefore, even when spot resistance welding is performed on a super-high tensile material of 780 MPa class or higher, the quality of the welded part is ensured and efficient. Spot resistance welding can be performed.

  Hereinafter, an energization control method for spot resistance welding according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 7, the spot resistance welding energization control method includes time zones 31a to 31d for maintaining a high current value and time zones 32a to 32c for maintaining a low current value within the energization time of resistance welding. The electrodes are energized by alternately energizing patterns 30. Such energization pattern control may be performed by, for example, a current control device provided in the welding machine.

  The time zones 31a to 31d for maintaining a high current value are mainly intended for growing nuggets on the steel plates to be welded. That is, in these time zones 31a to 31d, energization is performed at a current value that generates heat to such an extent that the nugget formed in the steel sheet to be welded is grown. However, if such a current value is kept too long, the nugget may grow rapidly and spatter may occur. For this reason, this current control method for spot resistance welding keeps the current value lower than before spatter occurs without continuing to maintain a high current value for growing nuggets on the steel sheet to be welded. .

  In the time zones 32a to 32c in which the low current value is maintained, the purpose is mainly to alleviate the risk of spattering and to soften the surface of the steel plate so that the pressed electrode fits the steel plate. In these time zones 32a to 32c, energization is performed at a current value that generates heat to the extent that the steel sheet surface is softened without generating spatter, and the rapid growth of nuggets formed inside the steel sheet is suppressed. Sputtering is suppressed. In addition, since the steel plate is softened during this time, the electrode is adapted to the steel plate by the pressure applied to the electrode, and the contact area between the steel plate and the electrode gradually increases. Thereby, in the time slot | zones 32a-32c which maintain a low electric current value, the danger that a sputter | spatter will generate | occur | produce is eased.

  In this time zone 32a to 32c, the situation in which spattering occurs may be relaxed. Therefore, if the situation in which sputtering occurs is mitigated, the nugget is efficiently formed. It should be high.

  As described above, according to the energization control method of spot resistance welding, the time zone 32a to maintain the low current value during the time zone 31a to 31d to maintain the high current value without continuing to maintain the high current value. Since 32c is sandwiched, the nugget does not grow rapidly and spatter does not occur. In addition, the contact area between the steel plate and the electrode is widened in the time zones 32a to 32c for maintaining a low current value, and the situation where spatter is generated inside the steel plate on which the nugget is formed is alleviated. Spatter does not occur immediately even if the value is increased.

Further, since the contact area between the steel plate and the electrode is increased in the time zones 32a to 32c for maintaining the low current value, when the current value is increased to such an extent that the nugget is grown again after that, the current value is decreased. However, spatter does not occur even when the current value is increased. Therefore, in the energization pattern shown in FIG. 7, in the time zones 31a to 31d for maintaining a high current value, the time zones 31a to 31d for maintaining a high current value and the time zones 32a to 32c for maintaining a low current value are alternated. as repeated, time zone 31a~31d to maintain a high current value is gradually increased current value to maintain the respective time slot 31 a to 31 c. In addition, since the contact area between the steel plate and the electrode gradually increases and the condition of the current value at which sputtering occurs increases, the time zones 32a to 32c for maintaining a low current value are also maintained for each time zone 32a to 32c. The current value is gradually increased.

  In addition, in each time zone of the energization pattern 30, as the current value is increased to such an extent that spatter does not occur, the electrical energy input to the steel sheet increases, so that the nugget can be formed efficiently and welding is performed. The required time can be shortened.

  As described above, according to the energization control method of this spot resistance welding, the generation of spatter can be suppressed and the nugget can be formed efficiently, so that the spot resistance welding with high quality can be stably performed. Quality control becomes easy. Moreover, since spatter adheres to the outer plate and the generation of dust is suppressed, workability and work environment can be improved.

  Hereinafter, an embodiment of an energization pattern using the energization control method of spot resistance welding will be described.

  In this example, welding of a superposed portion in which two SPC780 and 1.2 mm-thick steel plates were stacked was performed by direct spot welding shown in FIG. In this example, electrodes 3 and 4 having an R15 curved surface were used, and welding was performed by applying a pressure of 340 kgf to the electrodes. Moreover, the current control was performed using a single-phase AC current control device.

  In the energization pattern used in this example, as shown in FIG. 8, the current value is gradually increased in the initial 0 to 1 cycle of the energization time, 1 to 3 cycles is set to 6.5 kA, and 3 to 5 cycles is set to 6.3 kA. 5-7 cycles are set to 7.6 kA, 7-9 cycles are set to 7.3 kA, 9-11 cycles are set to 8.0 kA, 11-13 cycles are set to 7.8 kA, and 13-15 cycles are set to 8.6 kA. It was. 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.

In this embodiment, the time zones of 1 to 3 cycles, 5 to 7 cycles, 9 to 11 cycles, and 13 to 15 cycles are the time zones 31a to 31d maintained at a high current value that allows the nugget to grow on the steel plate to be welded. , 3~5cycle, 7~9cycle, time zone 11~13cycle is a time zone 32a~32c maintained to the extent of low current value to soften the steel sheet without causing sputtering.

  In this embodiment, the time zones 31a to 31d of 1 to 3 cycles, 5 to 7 cycles, 9 to 11 cycles, and 13 to 15 cycles that are maintained at high current values are the time zones 32a to 32c that are maintained at low current values in between. By sandwiching, the situation where spatter is generated is alleviated, so that the current value maintained for each time zone is gradually increased. Thereby, electrical energy can be input appropriately to the steel sheet, and the nugget can be grown efficiently.

  With this energization pattern, it is possible to stably form a nugget diameter of 5.8 mm or more, in which the occurrence of spatter is suppressed in the welding of such steel sheets, and the base material breaks, and the energization time is 15 cycles from the start. It is possible to perform welding efficiently.

  As mentioned above, although the Example which applied the energization control method of spot resistance welding concerning the present invention to welding of super high-tensile material was described, the energization control method of spot resistance welding concerning the present invention is limited to the above-mentioned example. It is not something.

In the above-described embodiment, the welding of the overlapped portion where two steel plates are stacked is illustrated. However, the present invention is not limited to this, and spattering can be suppressed and nuggets can be appropriately formed, so that three or more steel plates are stacked. It can also be applied to welding at the polymerization site. Moreover, although the Example applied to direct spot resistance welding was illustrated, it is not limited to direct spot resistance welding, It can apply to various spot resistance welding, such as series spot resistance welding and indirect spot resistance welding.

  Moreover, in the energization pattern illustrated in the above embodiment, the time zone for maintaining a high current value is provided four times, and the time zone for maintaining a low current value is provided three times, but the time zone for maintaining a high current value is provided. The number of times of repeating the time zone for maintaining a low current value is not limited to the above embodiment. The energization pattern may be set so that the time zone for maintaining a high current value and the time zone for maintaining a low current value are repeated twice or more each time.

  In addition, the energization pattern depends on the welding conditions such as the material of the steel plate to be welded, the plate thickness, the number of steel plates to be stacked, the spot resistance welding method to be used, the electrode to be used, etc. The energization time and the like may be appropriately changed as appropriate.

  Further, in the initial stage of energization, there may be a small gap between the steel plates, or dust may be sandwiched between the steel plates, so that the contact area between the steel plates may be small. For example, as shown in FIG. Before the energization pattern, a time zone 33 for keeping the current value low at the initial stage of the energization time may be provided. This time zone 33 sets a current value and energizing time that do not generate spatter and generate heat in the steel plate that softens the steel plate. As a result, a minute gap generated between the steel plates can be filled and the contact area in the second half can be sufficiently increased, so that the occurrence of spatter can be more reliably suppressed.

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 electricity supply pattern of the electricity supply control method of the spot resistance welding which concerns on one Embodiment of this invention. The figure which shows the specific example of the electricity supply pattern of the electricity supply control method of the spot resistance welding which concerns on this invention. The figure which shows the electricity supply pattern of the electricity supply control method of the spot resistance welding which concerns on other embodiment of this invention.

Explanation of symbols

30 Energizing patterns 31a to 31d Time zone for maintaining a high current value 32a to 32c Time zone for maintaining a low current value

Claims (2)

A time period for maintaining a predetermined high current value for growing nuggets on a steel plate made of super high-tensile material of 780 MPa class or higher to be welded for a predetermined time shorter than the time until spattering occurs within the energization time of resistance welding. When, finally maintaining the high current value a predetermined low current value of the degree of softening of the steel sheet without causing sputtering and times to maintain a predetermined time from the first time period for maintaining the high current value An energization control method for spot resistance welding, wherein the electrode is energized so as to be alternately repeated over a period of time .   In the time zone for maintaining the high current value, the current value to be maintained for each time zone is gradually increased as the time zone for maintaining the high current value and the time zone for maintaining the low current value are alternately repeated. The energization control method of spot resistance welding according to claim 1.