JP2007253166A - Method for judging shape of nugget, spot welding method and equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spot welding method and equipment in which spot welding quality can be controlled in a spot welding process. <P>SOLUTION: In this method, at least as one of a pair of electrodes for performing spot welding, there is used an electrode which has substantially a convex electrode surface and which, at the center portion of the surface, has a recess set at a predetermined depth where a welding trace formed on the surface of a metallic body reaches a deepest part when a good nugget is formed by spot welding. Completion of spot welding is determined when a resistance value during the welding reaches a state of equilibrium. The spot welding equipment is provided with a resistance value detector for detecting a resistance value during the welding and a welding controller for completing spot welding on the basis that the resistance value reaches the state of equilibrium during the welding as detected by the resistance value detector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nugget formation determination method, a spot welding method, and a spot welding apparatus.

  It is known that spot welding evaluates the quality of spot welding quality based on the nugget diameter. Specific methods include press inspection between two spot-welded steel plates, peeling off the spot welds, measuring the joint diameter including the heat affected zone, and cutting the spot welds to nugget Individual fracture measurement such as cutting inspection that directly measures the diameter is performed.

Nondestructive measurement techniques relating to spot welding are those using ultrasonic waves (Japanese Patent Laid-Open Nos. 62-119453 and 4-265854), those using vibration (Japanese Patent Laid-Open No. 9-171007), and intermittent light. Various proposals have been made for detecting a sound wave accompanying irradiation (Japanese Patent Laid-Open No. 3-2659), detecting a reflected wave of an elastic wave emitted from a welding electrode (Japanese Patent Laid-Open No. 4-40359), and the like. Japanese Patent Laid-Open No. 2001-165911 discloses a diameter of an annular high inductance portion at the periphery of a nugget of a spot welded portion measured when a magnetic field line is passed through the spot welded portion, and the high inductance portion and the nugget central portion. Are used to express each variable as a predicted value of the nugget diameter with a discriminant and set a threshold value for discriminating whether the nugget diameter is good or bad.
JP 2001-165911 A

  In the vertical inspection, the quality of spot welding can be judged based on the size of the joint diameter including the heat affected zone, but the quality of spot welding can be directly evaluated for those not measured for fracture. Can not do it. In recent years, high-tensile (high-tensile steel) materials are often used to reduce the weight of automobile bodies, but the spot-welded part of high-tensile material is harder than the part welded with normal steel plates. It was unsuitable for performing an inspection by punching on the production line. Non-destructive inspection is disclosed in Japanese Patent Laid-Open No. 2001-165911.

  However, all of these determine the quality of spot welding after spot welding. On the other hand, none of the quality of spot welding can be judged in the spot welding process. If the quality of spot welding can be managed in the spot welding process, the management of the manufacturing process using spot welding becomes easy, and the occurrence of defects such as poor welding in spot welding can be reduced.

  Then, this invention makes it a solution subject to provide the spot welding method and spot welding apparatus which can manage the quality of spot welding in a spot welding process.

  In the spot welding method according to the present invention, at least one of the pair of welding electrodes that perform spot welding has a substantially convex curved surface, and the nugget is favorably formed by spot welding at the center of the electrode surface. When formed, spot welding is performed using a welding electrode formed with a depression set at a predetermined depth at which the welding mark formed on the surface of the metal body reaches the deepest part, and the resistance value during welding is in an equilibrium state. When this happens, the end of the spot welding is determined. Further, as the nugget formation determination method, in such spot welding, it may be determined that the nugget is properly formed in the spot welded portion based on the resistance value at the time of welding being in an equilibrium state. .

  Further, the spot welding apparatus according to the present invention can be favorably obtained by spot welding at least one of the pair of welding electrodes for spot welding, the electrode surface is a substantially convex curved surface, and the center of the electrode surface. When a nugget is formed, in a spot welding apparatus that performs spot welding using a welding electrode formed with a depression set at a predetermined depth at which a welding mark formed on the surface of the metal body reaches the deepest portion, A resistance value detection unit that detects a resistance value, and a welding control device that determines the end of the spot welding based on the resistance value at the time of welding detected by the resistance value detection unit being in an equilibrium state It is.

  According to this spot welding method and spot welding apparatus, the quality of spot welding can be managed, the manufacturing process using spot welding can be easily managed, and the occurrence of defects such as welding defects in spot welding can be reduced. .

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

  As shown in FIG. 1, when spot welding is performed using one of the electrodes 1 and 2 to be spot welded and one electrode 2 having a depression 3 formed on the electrode surface, FIG. 1 and FIG. As shown, convex welding marks 6 are formed on the surfaces of the steel plates 4 and 5 (metal bodies) corresponding to the depressions 3 formed on the electrode surface of the electrode 1. The present inventors pay attention to the convex welding trace 6 and examine the correlation between the height of the convex welding trace 6, the diameter of the nugget 7 (nugget diameter), and the tensile shear strength (TSS). It was.

  FIG. 3 shows an example of data showing the correlation between the height of the convex portion and the nugget diameter, FIG. 4 shows an example of data showing the correlation between the height of the convex portion and the tensile shear strength (TSS), and FIG. One example of data indicating the correlation between the nugget diameter and the tensile shear strength (TSS) is shown.

  Here, as shown in FIG. 1, of the pair of upper and lower electrodes 1 and 2, an electrode in which a depression is formed on the surface of the upper electrode 1 is used, and the electrode in which the depression is formed is a 3 mm cylinder. Two types of electrodes are used, one having a shape-like depression and one having a 5 mm cylindrical depression. The correlation diagrams of FIGS. 3 to 5 were obtained when two types of electrodes were used with a cylindrical depression 3 formed on the surface of the electrode 1 having a diameter of 3 mm and a diameter of 5 mm. . Each of the applied pressure is 250 kgf (about 2.45 kN) and 150 kgf (about 1.47 kN), the current value is changed between 5 kA and 13 kA, the energization time is changed between 4 cycles and 10 cycles, and the energy of spot welding Samples with different heights, nugget diameters, and tensile shear strength (TSS) were prepared. A plurality of samples were prepared for each different condition. In this embodiment, spot welding is performed with an AC power source having a frequency of 60 Hz, cycle is a unit for setting the energization time, and 1 cycle is 1/60 (second).

  As a result, as shown in FIGS. 3 to 5, there is a correlation between them, and the knowledge that the nugget diameter and the tensile shear strength (TSS) can be estimated from the height of the convex welding mark 6 was obtained. . Based on such knowledge, the present inventors, as shown in FIG. 6A, have at least one welding electrode 10 out of a pair of welding electrodes 10 and 20 that perform spot welding, and the electrode surface is a substantially convex curved surface. In addition, when the nugget 13 is satisfactorily formed by spot welding at the center of the electrode surface, the depression 12 is set to a predetermined depth at which the welding mark 15 formed on the surface of the metal body reaches the deepest portion 16. It has been considered to perform spot welding using the formed welding electrode (hereinafter referred to as “mark electrode”).

  As the mark electrode 10, as shown in FIGS. 7A and 7B, a welding electrode 10 in which the electrode surface 11 is a substantially convex curved surface and a recess 12 is formed at the center of the electrode surface 11 is used. The depression 12 formed on the electrode surface 11 of the mark electrode 10 is welded to be formed on the surface of the steel plate 14 as a metal body when the nugget 13 is formed favorably by spot welding, for example, by performing a test in advance. It may be set to a predetermined depth at which the mark 15 reaches the deepest portion 16. In this embodiment, a flat surface 17 is formed at the deepest portion 16, and a flat surface 18 is formed at the top of the weld mark 15 as shown in FIG. 6A. . Such a flat surface 18 can be used as a mark for visually confirming that the welding mark 15 has reached the deepest portion 16 of the recess 12 of the mark electrode 10. Note that the deepest portion 16 of the depression 12 of the mark electrode 10 may be provided with a predetermined uneven shape serving as a marker instead of the flat portion 17. However, in the spot welding method and spot welding apparatus according to the present invention, such a marker is not necessarily required.

  In the example shown in FIG. 6A, spot welding uses the mark electrode 10 for one electrode and the normal spot welding electrode 20 for the other, but a pair of welding electrodes for spot welding is used. Mark electrodes may be used for both 10 and 20.

  When spot welding is performed using such a mark electrode 10, a convex welding mark 15 corresponding to the mark electrode 10 is formed on the surface of the steel plate 14 as shown in FIG. The depression 12 formed on the electrode surface 11 of the mark electrode 10 has a predetermined depth at which the welding mark 15 formed on the surface of the steel plate 14 reaches the deepest portion 16 when the nugget 13 is formed favorably by spot welding. It is set. For this reason, when the nugget 13 formed by spot welding is insufficient, the welding mark 15 formed on the surface of the steel plate 14 does not reach the deepest portion 16 as shown in FIG. On the other hand, when the nugget 13 is formed satisfactorily by spot welding, the welding mark 15 formed on the surface of the steel plate 14 reaches the deepest portion 16 as shown in FIG. The depth of the recess 12 may be set by finding a suitable depth for performing such a function by conducting a basic experiment in advance.

  When spot welding is performed using such a mark electrode 10, as shown in FIG. 6A, is a predetermined convex welding mark 15 corresponding to the mark electrode 10 formed on the surface of the steel plate 14? The quality of spot welding quality can be determined based on the result. That is, if a predetermined convex welding mark 15 corresponding to the mark electrode 10 is formed on the surface of the steel plate 14, a good nugget 13 is formed inside the welded steel plate 14. If a predetermined convex welding mark 15 corresponding to the mark electrode 10 is not formed on the surface of the steel sheet, it is determined that there is a possibility that a good nugget 13 may not be formed in the welded steel plate 14. Can do.

  Furthermore, when spot welding is performed using the mark electrode 10, the inventors observe a resistance value in a process in which a predetermined convex welding mark 15 corresponding to the depression 12 of the mark electrode 10 is formed. The sample was taken at every timing of the energization time, and the nugget formation status was examined. As a result, when spot welding is performed using the mark electrode 10, the inventors show in FIG. 8 a process in which a predetermined convex welding mark 15 corresponding to the depression 12 of the mark electrode 10 is formed. Thus, the resistance value A at the time of welding gradually decreases as the energization time elapses, and when the convex welding mark 15 is formed, the resistance value tends to be in an equilibrium state thereafter. did. When the resistance value A during welding is in an equilibrium state, in other words, a state in which the resistance value during welding hardly changes for a certain period of time. Such a tendency was able to be observed even when the test was conducted with various changes in the energization pattern, as shown in FIG. 9, regardless of the type and thickness of the steel plate to be welded. 8 and 9, A indicates a resistance value at the time of welding, and B indicates a current value for energizing the pair of electrodes at the time of welding. Incidentally, FIG. 8 controls the current value and the energization time so that the current value during the energization time becomes a constant value, and FIG. 9 shows the current value and the current value so that the current value during the energization time changes in seven stages. The energization time is controlled.

  This trend is observed as an event for the following reasons. That is, the predetermined convex welding mark 15 corresponding to the depression 12 of the mark electrode 10 is gradually softened due to Joule heat on the surface of the steel plate 14 during welding, and the steel plate 14 is adapted to the depression 12 of the mark electrode 10. Is formed. At this time, it is considered that the resistance value A during welding gradually decreases as the contact area between the mark electrode 10 and the steel plate 14 increases in the process in which the steel plate 14 gradually adapts to the recess 12 of the mark electrode 10. It is done. And it is thought that the resistance value A at the time of welding will be in an equilibrium state in the stage where the predetermined convex welding trace 15 corresponding to the hollow 12 of the mark electrode 10 was formed.

  The inventors of the present invention have properly formed the convex welding mark 15 for the resistance value A at the time of welding in an equilibrium state, formed a good nugget 13, and performed spot welding well. I confirmed that. Moreover, about the thing before resistance value A at the time of welding will be in an equilibrium state, it has also confirmed that the convex-shaped welding trace 15 was not formed appropriately and the formation of the nugget 13 might be inadequate. From such a test, when the resistance value A during welding is in an equilibrium state, it can be determined that a predetermined convex welding mark 15 corresponding to the depression 12 of the mark electrode 10 has been formed. If energization is continued after the equilibrium state continues, dust may be generated due to excessive energization.

  Based on this discovery, the inventors perform spot welding using at least one of the pair of welding electrodes 10 and 20 that perform spot welding using the mark electrode 10 as shown in FIG. The spot welding method for determining the end of the spot welding when the resistance value A during welding is in an equilibrium state, and the spot welding when the resistance value A during welding is also in an equilibrium state. The present inventors have come up with a nugget formation determination method for determining that a nugget has been properly formed in a part.

  According to this spot welding method, as shown in FIG. 6A, spot welding is performed using at least one welding electrode among the pair of welding electrodes for spot welding using the mark electrode 10, and at the time of welding. Since the end of the spot welding is determined when the resistance value A is in an equilibrium state, a predetermined convex welding mark 15 is appropriately formed in a portion corresponding to the depression 12 of the mark electrode 10. The end of spot welding can be determined. Thus, according to this spot welding method, since the end determination of spot welding is determined by observing the resistance value A at the time of welding, for example, appropriate spot welding is performed even on steel plates having individual differences. be able to. In addition, since the end of the spot welding is determined when the resistance value A during welding reaches an equilibrium state, generation of dust due to excessive energization can also be prevented.

  When the resistance value A at the time of welding is in an equilibrium state, in other words, the resistance value A at the time of welding hardly changes for a certain time, but the resistance value A at the time of welding is, for example, spot welding. It is good to judge with the resistance value between a pair of welding electrodes 10 and 20 which perform this. The resistance value A that can be determined that the resistance value A is in an equilibrium state does not mean that the resistance value A is maintained at a strictly constant value. The resistance value A that can be determined that the resistance value A is in an equilibrium state may be determined by maintaining the resistance value A with a constant small change width. At this time, the width of the change in the resistance value A that can be determined that the resistance value A is in an equilibrium state varies depending on the type and thickness of the steel plate to be welded. For this reason, when the resistance value A changes, it is necessary to set an appropriate standard depending on the type and thickness of the steel sheet to be welded. . In addition, in order to prevent generation of dust due to excessive energization, the resistance value A during welding is in an equilibrium state when the state in which the resistance value A hardly changes during welding is maintained for how long. It is necessary to set an appropriate standard depending on the type and thickness of the steel plate to be welded. These may be tested in advance to determine an appropriate standard for determining that the resistance value A has reached an equilibrium state.

  In addition, as shown in FIG. 6A, an embodiment of a spot welding apparatus 30 that embodies such a spot welding method includes at least one welding electrode among a pair of welding electrodes 10 and 20 that perform spot welding. 10 based on the resistance value detection unit 31 that detects the resistance value A at the time of welding using the mark electrode 10 and the resistance value A at the time of welding detected by the resistance value detection unit 31 in an equilibrium state. It can be set as the structure provided with the welding control apparatus 32 which determines the completion | finish of the said spot welding. For the resistance value detection unit 31, for example, a device that can observe the resistance value between the pair of welding electrodes 10 and 20 that perform spot welding, such as a timer contactor, may be used. In addition, the welding control device 32 includes, for example, a determination unit that determines the end of spot welding on the condition that the resistance value A during welding detected by the resistance value detection unit 31 is in an equilibrium state. It can be. Furthermore, as a configuration for performing spot welding end processing based on such spot welding end determination, a control signal is sent to the energizing device 33 that energizes the pair of welding electrodes 10 and 20 that perform spot welding. A control device to which a configuration for controlling energization by the device 33 is added may be used.

  According to the spot welding device 30, the resistance value detection unit 31 detects the resistance value A during welding, and the welding control device 32 causes the resistance value A during welding detected by the resistance value detection unit 31 to be in an equilibrium state. Based on this, the spot welding is terminated. For this reason, for example, it can comprise so that electricity supply may be complete | finished automatically and it is also possible to make the setting of electricity supply time unnecessary. That is, according to the spot welding apparatus 30, the energization time is not set, and the spot is changed during the energization by setting an energization pattern (change in current value with time during the energization time) in advance. Appropriate spot welding can be performed even if a process of automatically ending the spot welding is performed when the end of welding is determined. Thereby, the labor concerning the setting operation | work of the welding conditions of spot welding can be reduced. Further, the spot welding is terminated based on the fact that the resistance value A at the time of welding detected by the resistance value detection unit 31 is in an equilibrium state in accordance with individual differences of the steel plates to be spot welded. Even when 14 has individual differences, appropriate spot welding can be performed, and it becomes easy to maintain a certain quality in spot welding.

  Further, when the resistance value A at the time of welding is in an equilibrium state, a predetermined convex welding mark 15 is appropriately formed in a portion corresponding to the depression 12 of the mark electrode 10. It can be determined that the nugget is properly formed in the spot weld. For this reason, as a nugget formation determination method, it may be configured to determine that the nugget is properly formed in the spot welded portion based on the fact that the resistance value A during welding has reached an equilibrium state. . According to such a nugget formation determination method, it can be determined that the nugget is properly formed during spot welding.

  Although the spot welding method and the spot welding apparatus according to one embodiment of the present invention have been described above, the spot welding method and the spot welding apparatus according to the present invention are not limited to the above embodiment.

  For example, the spot welding method and spot welding apparatus according to the present invention can be applied to various spot weldings such as direct spot welding, indirect spot welding, and series spot welding.

Schematic which shows the basic experiment which performs spot welding using the electrode which formed the hollow in the electrode surface. The longitudinal cross-sectional view of a convex welding trace. It is a figure which shows an example of the correlation with the height of the convex part formed by spot welding, and a nugget diameter. It is a figure which shows an example of the correlation of the height of the convex part formed by spot welding, and tensile shear strength (TSS). It is a figure which shows an example of correlation with a nugget diameter and tensile shear strength (TSS). (A) is a figure which shows the state in which the convex welding trace was formed in spot welding, (b) is a figure which shows the process in which a convex welding trace is formed in spot welding. (A) is a fragmentary longitudinal cross-section which shows the electrode for quality determination of the spot welding which concerns on one Embodiment of this invention. (B) is a bottom view of the electrode for quality determination of spot welding according to an embodiment of the present invention. The figure which shows the resistance value at the time of welding. The figure which shows the resistance value at the time of welding.

Explanation of symbols

10 Mark electrode (welding electrode)
11 Electrode surface 12 Dimple 13 Nugget 14 Steel plate (metal body)
15 welding mark 16 deepest part 17 deepest part flat surface (marker)
18 Flat surface (mark) of weld mark
20 Electrodes for spot welding (welding electrodes)
30 Spot Welding Device 31 Resistance Value Detection Unit 32 Welding Control Device 33 Energizing Device

Claims (3)

  The surface of the metal body when at least one of the pair of welding electrodes for spot welding has a substantially convex curved electrode surface and a good nugget is formed by spot welding at the center of the electrode surface. Spot welding is performed using a welding electrode formed with a depression set at a predetermined depth at which the welding mark formed at the deepest part reaches the deepest part, and the resistance value during welding is in an equilibrium state. A nugget formation determination method for determining that a nugget is properly formed in a weld.   The surface of the metal body when at least one of the pair of welding electrodes for spot welding has a substantially convex curved electrode surface and a good nugget is formed by spot welding at the center of the electrode surface. Spot welding is performed using a welding electrode formed with a depression set at a predetermined depth at which the welding mark formed at the deepest part reaches the deepest part, and the resistance value during welding is in an equilibrium state. Spot welding method for determining the end of welding. The surface of the metal body when at least one of the pair of welding electrodes for spot welding has a substantially convex curved electrode surface and a good nugget is formed by spot welding at the center of the electrode surface. A spot welding apparatus that performs spot welding using a welding electrode formed with a recess set at a predetermined depth at which a welding mark formed at the deepest part reaches,
A resistance value detection unit that detects a resistance value during welding, and a welding control device that determines the end of the spot welding based on the fact that the resistance value during welding detected by the resistance value detection unit is in an equilibrium state And spot welding equipment.

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