Contact resistance measuring apparatus and contact resistance measuring method

Abstract

To provide a contact resistance measuring apparatus and a contact resistance measuring method that can selectively measure a contact resistance during a specific period while correctly simulating actual resistance spot welding conditions.SOLUTION: A contact resistance measuring apparatus 100 comprises: a pair of electrodes 29A, 29B which sandwich metal plates 23, 25; a pressurizing mechanism 31 for pressurizing between the pair of electrodes 29A, 29B; a resistance measurement part 55 which measures a contact resistance against measurement current flowing through the metal plates 23, 25; an input part 57 to which information concerning a pressurizing force based on a pressurizing pattern during resistance spot welding and information concerning a contact resistance measurement period are inputted; and a control part 53 which controls the pressurizing mechanism 31 and the resistance measurement part 55. The control part 53 drives the pressurizing mechanism 31 and applies a pressurizing force to the metal plates 23, 25 according to a pressurizing force inputted from the input part 57, and outputs information concerning the contact resistance measured by the resistance measurement part 55 during the inputted measurement period.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a contact resistance measuring device and a contact resistance measuring method. [Background technology]

[0002] Resistance spot welding, which involves welding multiple overlapping metal sheets, has traditionally been widely used in the production of vehicles and other products. To improve the welding quality of resistance spot welding, various welding conditions, such as welding current, pressure, and electrode shape, must be adjusted. These conditions vary depending on the material used, sheet thickness, and electrode shape. For this reason, various inspection devices have been developed to evaluate the surface quality of metal sheets by measuring contact resistance, such as the surface resistance and inter-sheet resistance, of sheet materials. For example, Patent Document 1 discloses a contact resistance measuring device that includes a pair of electrodes that sandwich multiple sheet materials, a pressure unit that applies pressure between the pair of electrodes, a resistivity measuring device that measures the contact resistance, and a holding unit that maintains the surface contact state of the multiple sheet materials. This contact resistance measuring device enables stable measurements with low measurement variability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-3316 Summary of the Invention [Problem to be solved by the invention]

[0004] In resistance spot welding, the main welding conditions are the pressure, current, and welding time, and the setting of the pressure is particularly important when evaluating weldability. In resistance spot welding, where the pressure is changed over time, the condition of the metal sheet surface can vary depending on the pressure and pressure duration. If the contact resistance could be measured under each of these conditions, it would be possible to set the resistance spot welding conditions with greater precision, which is expected to improve weld quality.

[0005] However, most contact resistance measurement devices to date have basically performed measurement processing according to a prescribed sequence, and have not been designed to selectively measure contact resistance over a specific period. For example, the initial pressure application period has the effect of concentrating the current by crushing the film on the metal plate surface, which affects the welding quality, while the pressure holding period after the current is applied has the effect of improving the welding quality by crushing minute cracks that occur after welding. At present, it is difficult to quantitatively grasp these effects, making it difficult to determine the quality of materials according to each welding condition. Furthermore, there is no technology capable of generating a large applied pressure suitable for resistance spot welding of thick materials, which has been attracting attention in recent years, and the range of evaluation targets is limited.

[0006] Therefore, an object of the present invention is to provide a contact resistance measuring device and a contact resistance measuring method that can selectively measure contact resistance over a specific period while accurately simulating the welding conditions of actual resistance spot welding, thereby contributing to improving the quality of metal sheets used in resistance spot welding. [Means for solving the problem]

[0007] The present invention comprises the following configurations. (1) A contact resistance measuring device that passes a measurement current through a metal plate to be resistance spot welded in a thickness direction and measures the contact resistance of the metal plate with respect to the measurement current, a pair of electrodes sandwiching the metal plate; a pressure mechanism for applying pressure between the pair of electrodes; a resistance measuring unit that measures a contact resistance with respect to the measurement current that is passed through the metal plate; an input unit into which information on a pressing force based on a pressing pattern during resistance spot welding and information on a measurement period for the contact resistance are input; a control unit that controls the pressure mechanism and the resistance measurement unit; Equipped with the control unit drives the pressure mechanism to apply pressure to the metal plate in accordance with the pressure input from the input unit, and outputs information about the contact resistance measured by the resistance measurement unit during the input measurement period. Contact resistance measuring device. (2) A contact resistance measurement method for measuring the contact resistance of a metal plate to be resistance spot welded by passing a measurement current through the metal plate in the thickness direction, the measurement current being: The metal plate is sandwiched between a pair of electrodes, applying pressure to the metal plate between the pair of electrodes in accordance with a pressure based on the input pressure pattern for resistance spot welding; During the input measurement period of the contact resistance, the contact resistance is measured with respect to the measurement current flowing in the thickness direction of the metal plate; outputting information about the contact resistance measured during the measurement period; Contact resistance measurement method. [Effects of the Invention]

[0008] According to the present invention, it is possible to selectively measure contact resistance for a specific period while accurately simulating welding conditions of actual resistance spot welding, thereby improving the quality of metal sheets to be subjected to resistance spot welding. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic external view of a contact resistance measuring device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the internal configuration of the frame structure. [Figure 3] FIG. 3 is a functional block diagram of the contact resistance measuring device. [Figure 4] FIG. 4 is an explanatory diagram showing an example of a pressure pattern and a current pattern for resistance spot welding, and a current application period of a measurement current for measuring contact resistance according to each pattern. [Figure 5] FIG. 5 is an explanatory diagram showing types of electrode shapes for use in resistance spot welding. [Figure 6] FIG. 6 is a schematic diagram showing a specially shaped electrode having an annular groove formed in the contact surface. [Figure 7] FIG. 7 is a schematic diagram showing an electrode holder that holds a one-piece electrode having a tapered portion. [Figure 8]FIG. 8 is a schematic diagram showing an electrode holder that holds a cap-tip type electrode. [Figure 9] FIG. 9 is a graph showing the results of measuring the contact resistance when two metal plates with oxide films were placed one on top of the other and sandwiched between electrodes. [Figure 10] FIG. 10 is a graph showing the results of measuring the contact resistance when one metal plate is sandwiched between electrodes. [Figure 11] FIG. 11 is a graph showing a schematic relationship between the thickness of the oxide film on the metal plate and the measured contact resistance. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic external view of a contact resistance measuring device 100 according to an embodiment of the present invention. The contact resistance measuring device 100 measures the contact resistance of metal plates 23, 25 to be resistance spot welded by passing a current in the plate thickness direction. The metal plates 23, 25 to be measured may be a plate assembly formed by stacking multiple plates as shown in FIG. 1, or may be a single plate. The contact resistance measuring device 100 has a base plate 13 fixed to the upper surface of a base 11, and a frame structure 15 fixed on top of the base plate 13. The frame structure 15 has a lower plate 17, an upper plate 19, and four frame legs 21 connecting the lower plate 17 and the upper plate 19.

[0011] A stage 27 that supports the combination of metal plates 23 and 25 to be measured, and an electrode holder 41 that holds a lower electrode 29A are fixed on the lower plate 17 of the frame structure 15. In addition, a pressure mechanism 31 is fixed to the upper plate 19 of the frame structure 15, and has an electrode holder 49 that holds an upper electrode 29B attached to the tip of a portion that moves up and down.

[0012] FIG. 2 is a schematic diagram showing the internal configuration of frame structure 15. Stage section 27 has an upper stage plate 33, a lower stage plate 35 fixed to lower plate 17 (see FIG. 1) of frame structure 15, and four stage legs 37 connecting upper stage plate 33 and lower stage plate 35. Upper stage plate 33 serves as a support surface for the combination of metal plates 23 and 25 shown in FIG. 1, and has an electrode opening 33a formed in the center and four openings 33b formed around the periphery corresponding to stage legs 37. Each of stage legs 37 has a small-diameter shaft 37a at its upper end, which is inserted into openings 33b in upper stage plate 33. Cushion springs 39 are provided between small-diameter shafts 37a and upper stage plate 33, thereby supporting upper stage plate 33 so that it can move up and down relative to stage legs 37.

[0013] An electrode holder 41 is fixed to the stage lower plate 35, and a lower electrode 29A is replaceably held by the electrode holder 41. The upper end of the lower electrode 29A is inserted into the electrode opening 33a and faces the upper electrode 29B.

[0014] 1 includes a servo motor 43, which is an electromagnetic motor, a servo cylinder 45, and a rod 47. In the pressure mechanism 31, the drive of the servo motor 43 is transmitted to a ball screw mechanism (not shown), and a rod 47, which is a ball screw shaft, can move up and down from the tip of the servo cylinder 45. An electrode holder 49 is fixed to the tip of the rod 47, and an upper electrode 29B is held in the electrode holder 49 in a replaceable manner. The servo cylinder 45 is provided with a load cell 59 (FIG. 3), which will be described later, so that the pressure applied to the metal plates 23 and 25 can be measured.

[0015] In other words, lower electrode 29A and upper electrode 29B function as a pair of electrodes that sandwich metal sheets 23, 25 in the thickness direction, and pressure mechanism 31 applies pressure between the pair of electrodes using servo motor 43 as its drive source. The power source of pressure mechanism 31 is not limited to servo motor 43, and other electromagnetic motors such as linear motors may also be used. In particular, using a servo motor or linear motor enables position, speed, and the like to be controlled with high responsiveness and high precision, making it possible to reproduce the pressure operation in actual resistance spot welding with high precision.

[0016] In resistance spot welding, for example, a welding time of 1000 ms is set with an initial pressure period, a current period, and a pressure hold period, each of which is extremely short, measured in the hundreds of milliseconds. Therefore, to achieve high-speed driving of the lower electrode 29A and the upper electrode 29B, a quick drive operation is required, and a servo motor or linear motor with high responsiveness is suitable for the pressure mechanism 31. In this case, the pressure control mechanism does not become complicated, and the device can be made smaller. Depending on the conditions, an air pressure system using an air pump or the like can also be used for the pressure mechanism 31.

[0017] Furthermore, it is preferable that the pressure mechanism 31 be capable of generating a pressure force that can reliably destroy the coating on the surface of the metal plates 23, 25. Such a pressure force is preferably 1 kN or more, more preferably 5 kN or more, and even more preferably 8 kN or more, and is preferably 14 kN or less, more preferably 12 kN or less, and even more preferably 11 kN or less. The pressure mechanism can generate any pressure between 1 kN and 14 kN, for example.

[0018] Therefore, the pressure mechanism 31 can reliably generate the large pressure required for resistance spot welding thick metal plates, for example, 3 mm to 5 mm thick, which have seen increasing demand in recent years for automotive applications. This allows contact resistance to be measured under the same pressure conditions as resistance spot welding, even for thick metal plates, expanding the range of metal plate thicknesses that can be evaluated. It also allows appropriate settings for resistance spot welding conditions for thick materials.

[0019] The contact resistance measuring device 100 has a shielding frame 51 provided on a base 11 so as to cover the outside of the frame structure 15. The contact resistance measuring device 100 also includes a control unit 53 and a resistance measuring unit 55, which will be described in detail later. An input unit (input unit 57 in FIG. 3 ), such as a keyboard, a touch panel, or a control panel including switches, is connected to or attached to the control unit 53, allowing necessary information to be input. The control unit 53 executes a preset program to control the resistance measuring unit 55, the pressure mechanism 31, etc., based on the input information. In other words, the control unit 53 is configured by a computer including a processor such as a CPU (Central Processing Unit) or MPU (Micro Processor Unit), memory and storage in which various programs are stored, input / output devices, etc.

[0020] The metal plates 23, 25 shown here are preferably metals on which a coating such as an oxide film is formed, such as aluminum material made of aluminum or an aluminum alloy, copper or a copper alloy, or iron plate (high-tensile steel plate, etc.) with a plating (nickel plating, zinc plating, tin plating, etc.) on the surface. The metal plates 23, 25 may also be metal plates with irregularities formed on the surface instead of the above-mentioned coating. In the case of aluminum material, it may be a wrought material or a cast material.

[0021] FIG. 3 is a functional block diagram of contact resistance measuring device 100. Here, the procedure for measuring contact resistance will be described with reference to FIG. 3. To measure contact resistance using resistance measuring unit 55, first, current lines LI_U and LI_D for passing measurement current Im and voltage lines LE_U and LE_D for voltage detection are connected to lower electrode 29A and upper electrode 29B. In addition, a plate assembly of metal plates 23 and 25 is sandwiched between lower electrode 29A and upper electrode 29B, and voltage lines LE_PU and LE_PD for voltage detection are connected to ends of metal plates 23 and 25, etc. The above-mentioned current lines and voltage lines may be connected in advance before measurement.

[0022] Here, the voltage between the voltage lines LE_U and LE_PU is V1, the voltage between the voltage lines LE_D and LE_PD is V2, and the voltage between the voltage lines LE_PU and LE_PD is V3. Voltage V1 corresponds to the contact resistance R1 (= V1 / Im) between the upper electrode 29B and the upper metal plate 25, voltage V2 corresponds to the contact resistance R2 (= V2 / Im) between the lower electrode 29A and the lower metal plate 23, and voltage V3 corresponds to the contact resistance R3 (= V3 / Im) between the lower metal plate 23 and the upper metal plate 25. Resistance Rt, which corresponds to the voltage Vt (= V1 + V2 + V3) between the voltage lines LE_U and LE_D, represents the total contact resistance of the surface resistance and inter-plate resistance of the metal plates 23 and 25 sandwiched between the lower electrode 29A and the upper electrode 29B. In this way, the surface resistance and inter-plate resistance between the electrodes can be measured separately, allowing for detailed evaluation of the surface conditions of the metal plates and electrodes. The above-described procedure for measuring the contact resistance is merely an example, and the contact resistance may be measured by other procedures, such as sampling and measuring voltages (V1, V2, V3, etc.) while constantly passing the measurement current Im, and extracting the contact resistance at a desired timing.

[0023] The control unit 53 includes a motor control unit 60 that drives the servo motor 43 of the pressure mechanism 31. The motor control unit 60 outputs a drive signal to the servo motor 43 so that the upper electrode 29B is pressed toward the lower electrode 29A in accordance with the pressure input from the input unit 57. The servo motor 43 extends the rod 47 in the servo cylinder 45 in accordance with the drive signal from the control unit 53, pressing the upper electrode 29B against the metal plate 25 and pressuring the metal plates 23, 25 in the plate thickness direction. The pressure applied at this time is measured by a load cell 59 provided in the servo cylinder 45. The load cell 59 outputs information on the measured pressure value to the control unit 53. The control unit 53 adjusts the drive signal so that the pressure value from the load cell 59 matches the pressure from the input unit 57. Specifically, feedback control such as PID control or feedforward control is performed using the pressure from the input unit 57 as a target value.

[0024] In this way, the control unit 53 drives the pressure mechanism 31 to apply pressure to the metal plates 23, 25 sandwiched between the lower electrode 29A and the upper electrode 29B, and also drives the resistance measurement unit 55 to output information on the measured value of the contact resistance measured by passing a measurement current Im through the metal plates 23, 25.

[0025] Next, a specific example of contact resistance measurement using the contact resistance measurement device 100 of this configuration will be described. In this configuration, the measurement period for contact resistance can be set arbitrarily. 4 is an explanatory diagram showing an example of a pressure pattern and a current pattern for resistance spot welding, and the corresponding periods for passing a measurement current for contact resistance measurement. The pressure pattern and current pattern for resistance spot welding shown here involve applying a pressure P1 between the electrodes of a resistance spot welding device from time t0 to t1, decreasing the pressure from P1 to P2 from time t1 to t2, passing a welding current during this period, and then increasing the pressure from P2 to P1 from time t2 to t3. The periods for passing measurement currents 1 to 5 correspond to the pressure pattern and current pattern described above. These periods represent the periods during which a measurement current flows between lower electrode 29A and upper electrode 29B when a resistance spot welding process is simulated using contact resistance measurement device 100, i.e., the periods during which contact resistance is measured.

[0026] The initial pressure application between times t0 and t1 before the welding current is applied is intended to apply pressure locally to the surfaces of the metal sheets 23 and 25 to crush any coatings, such as oxide films, that may have formed on the surfaces, concentrating the current path during current application. Therefore, the contact resistance measurement device 100 is used to simulate the initial pressure application described above for resistance spot welding. The metal sheets 23 and 25 are sandwiched between a pair of electrodes, and pressure is applied between the electrodes according to the pressure application pattern. Then, during the period DP1 between times t0 and t1, indicated by measurement current 1, the resistance measurement unit 55 applies a measurement current Im between the electrodes. In this way, the contact resistance is measured only during the period DP1. By measuring the contact resistance during this period DP1, the contact resistance value during the initial pressure application can be selectively obtained without being affected by changes in the state of the metal sheets 23 and 25 or the electrode surfaces that may occur during other periods.

[0027] Furthermore, as shown by measurement current 2, during the pressure holding period after the welding current is applied, i.e., during the period DP2 between times t2 and t3, resistance measurement unit 55 applies measurement current Im between the electrodes. In this way, the contact resistance value during the period DP2 corresponding to the pressure holding period after the welding current is applied can be selectively obtained. This pressure holding period is a period for crushing defects such as minute cracks that occur after the welding current is applied by the welding force, thereby improving the joint quality. By measuring the contact resistance during the period DP2 corresponding to this pressure holding period, the contact resistance value for only the pressure holding period can be selectively obtained.

[0028] Furthermore, contact resistance values ​​can be similarly measured for each period, such as period DP3 from time t1 to t2, which is the welding current flow period shown in measurement current 3, period DP4 from time t0 to t2 from the initial pressure application to the end of welding current flow shown in measurement current 4, and period DP5 from time t1 to t3 from the start of welding current flow to the end of the pressure holding period shown in measurement current 5. That is, by applying pressure between the electrodes according to the pressure pattern using contact resistance measuring device 100 in the same manner as described above and flowing a measurement current between the electrodes during each of periods DP3, DP4, and DP5, it is possible to selectively obtain the contact resistance values ​​for each of periods DP3, DP4, and DP5.

[0029] The measurement of the contact resistance during the period DPn (n: 1 to 5) for measuring the contact resistance can be performed by the control unit 53 generating a program that specifies the timing for flowing the measurement current, and by the control unit 53 executing the program.

[0030] In this way, by setting the contact resistance measurement period by program, it is possible to accurately measure the contact resistance for any period, and the surface condition of metal plates 23, 25, lower electrode 29A, and upper electrode 29B can be accurately evaluated for each period. As a result, the quality of the materials used can be determined from the obtained evaluation results, and the welding quality can be improved when welding is performed under the set conditions. Note that the contact resistance value measured during the measurement period may be the average value of the measurements during the period, or may be a representative measurement value at a specific timing.

[0031] The above-described measurement of contact resistance can also be useful for selecting and evaluating the shape of an electrode used in resistance spot welding. 5 is an explanatory diagram showing various electrode shapes for use in resistance spot welding. Electrodes used in resistance spot welding come in a variety of shapes, including a flat (F) shape with a flat contact surface, a radius (R) shape with a gently sloping entire tip, a dome (D) shape with a curved surface that is more obtuse than a radius, a dome radius (DR) shape with a dome-shaped tip with a radius contact surface, a cone flat (CF) shape with a cone-shaped tip with a flat contact surface, a cone radius (CR) shape with a cone-shaped tip with a radius contact surface, and an offset (E) shape with a contact surface formed at a position offset from the central axis.

[0032] By measuring the contact resistance using these various types of welding electrodes or electrodes simulating them as lower electrode 29A and upper electrode 29B of contact resistance measurement device 100, the contact resistance at each electrode can be easily determined. This allows for the design of materials (surfaces) suitable for each welding condition.

[0033] Furthermore, the electrodes used for resistance spot welding may be of a type other than the typical type shown in FIG. 5, for example, one having a recessed groove formed on the contact surface. 6 is a schematic diagram showing a specially shaped electrode 61 having an annular groove formed in the contact surface. This electrode 61 has a dome radius DR shape and a concentric groove 61a centered on the electrode central axis Lc. Even with such a specially shaped electrode 61, by measuring contact resistance using the electrode 61 as the lower electrode 29A and the upper electrode 29B in the contact resistance measuring device 100, it is possible to predict the weld quality when resistance spot welding is performed using the actual electrode 61.

[0034] In contact resistance measuring device 100, electrode holders 41 and 49 are preferably configured in the same manner as in a resistance spot welding device so that electrodes of various shapes for the above-mentioned existing resistance spot welding can be used.

[0035] FIG. 7 is a schematic diagram showing an electrode holder 41, 49 holding an integrated electrode 63 having a tapered portion 63a. FIG. 8 is a schematic diagram showing an electrode holder 41, 49 holding a cap-tip type electrode 65. The integrated electrode 63 can be fixed to the electrode holder 41, 49 by fitting the tapered portion 63a at its base end into the tapered hole 67 of the electrode holder 41, 49. The cap-tip type electrode 65 has an electrode tip portion 65A and a shank portion 65B. The tapered portion 71 formed on one end of the shank portion 65B is fitted into the tapered hole 69 of the electrode tip portion 65A, thereby forming an integrated electrode. The shank portion 65B can be fixed to the electrode holder 41, 49 by fitting the tapered portion 73 formed on the other end of the shank portion 65B into the tapered hole 67 of the electrode holder 41, 49.

[0036] The use of electrode holders 41 and 49 described above allows the use of various types of electrodes commonly used for resistance spot welding, making it possible to easily measure contact resistance under the same conditions as actual resistance spot welding. Electrode holders 41 and 49 may be electrode holders for other types, such as two-point welding, in addition to the single-point type.

[0037] Figure 9 is a graph showing the results of measuring the contact resistance when two metal plates with oxide films are sandwiched between electrodes. Here, electrode A is an R-shaped electrode with a curvature radius of 100 mm, and electrode B is the specially shaped electrode 61 shown in Figure 6. In this case, the total contact resistance measured is the contact resistance between the electrode and the metal plate and the contact resistance between the metal plates. The contact resistance measured with electrode B is lower than that measured with electrode A, regardless of the thickness of the oxide film.

[0038] Figure 10 is a graph showing the results of measuring the contact resistance when a metal plate is sandwiched between electrodes. In this case, the contact resistance between the electrode and the metal plate is measured, and it can be seen that the contact resistance of electrode B is significantly lower than that of electrode A.

[0039] 9 and 10, it is clear that the contact resistance between the electrode and the metal plate varies depending on the electrode shape, and the contact resistance when two metal plates are sandwiched between a pair of electrodes increases or decreases depending on the electrode shape. Therefore, by measuring the contact resistance, it is possible to evaluate the difference in heat generation behavior depending on the electrode during resistance spot welding.

[0040] Figure 11 is a graph showing the relationship between the thickness of the oxide film on the metal plate and the measured contact resistance. As shown in Figure 11, although the measured contact resistance varies, it tends to increase as the oxide film thickness increases. In other words, by measuring the contact resistance, it is possible to evaluate the surface condition of the metal plate or electrode.

[0041] By measuring contact resistance as described above, it is possible to evaluate the heat generation behavior and the surface condition of the metal sheet during resistance spot welding, and to predict the welding condition during actual resistance spot welding, for example, determining whether the welding condition is within an acceptable range. Therefore, when welding under set welding conditions, the measured contact resistance can be used to easily evaluate whether the surface quality of the metal sheet used is appropriate. Furthermore, based on the evaluation results, improvement guidelines for the surface quality of the metal sheet can be formulated, further improving welding quality. For example, if the measured contact resistance is too high, this may be due to an oxide film that is too thick. Therefore, guidelines for improving the surface condition include improving the cleaning conditions, such as increasing the concentration or temperature of the cleaning solution or lengthening the cleaning time to enhance the oxide film removal cleaning power. Conversely, if the resistance is too low, this may be due to an oxide film that is too thin. Therefore, guidelines for improving the cleaning conditions include reducing the concentration or temperature of the cleaning solution or shortening the cleaning time to weaken the oxide film removal cleaning power.

[0042] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these are included in the scope of protection sought.

[0043] As described above, the present specification discloses the following: (1) A contact resistance measuring device that passes a measurement current through a metal plate to be resistance spot welded in a thickness direction and measures the contact resistance of the metal plate with respect to the measurement current, a pair of electrodes sandwiching the metal plate; a pressure mechanism for applying pressure between the pair of electrodes; a resistance measuring unit that measures a contact resistance with respect to the measurement current that is passed through the metal plate; an input unit into which information on a pressing force based on a pressing pattern during resistance spot welding and information on a measurement period for the contact resistance are input; a control unit that controls the pressure mechanism and the resistance measurement unit; Equipped with the control unit drives the pressure mechanism to apply pressure to the metal plate in accordance with the pressure input from the input unit, and outputs information about the contact resistance measured by the resistance measurement unit during the input measurement period. Contact resistance measuring device. This contact resistance measuring device applies pressure to a metal plate sandwiched between a pair of electrodes and measures the contact resistance for a specified measurement period, allowing the surface condition of the metal plate and electrodes to be evaluated, making it easy to determine whether the metal plate is good or bad. Based on this information, it is also possible to develop guidelines for improving the surface condition of the metal plate.

[0044] (2) The contact resistance measuring device according to (1), wherein the measurement period includes at least one of an initial pressure application period, a current application period, and a pressure holding period after current application during resistance spot welding. This contact resistance measuring device allows for the measurement of contact resistance over a period of time that corresponds to the pressure pattern and current flow pattern of resistance spot welding, making it possible to predict changes in the surface condition of the metal plate and electrode for each period of time. As a result, it is possible to determine the quality of the metal plate used and improve the quality of welding when welding is performed under the set conditions.

[0045] (3) The metal plate sandwiched between the pair of electrodes is a plate assembly in which a plurality of metal plates are stacked, The contact resistance measuring device according to (1) or (2), wherein the contact resistance includes the surface resistance between the outermost metal plate of the plate set and the electrode in contact with the metal plate, and the inter-plate resistance between the plurality of metal plates arranged opposite each other. This contact resistance measuring device can measure the surface resistance and the inter-plate resistance separately, allowing for more detailed evaluation of the surface condition.

[0046] (4) The contact resistance measuring device according to any one of (1) to (3), wherein the pair of electrodes are electrodes for resistance spot welding and includes an electrode holder that holds the pair of electrodes in a replaceable manner. This contact resistance measuring device allows the use of a wide variety of electrodes commonly used for resistance spot welding, making it possible to easily measure contact resistance under conditions that are consistent with actual resistance spot welding.

[0047] (5) The contact resistance measuring device according to any one of (1) to (4), wherein the metal plate is a metal having a coating formed on its surface. This contact resistance measuring device can evaluate the influence of films such as oxide films and plating layers on welding quality.

[0048] (6) The contact resistance measuring device according to any one of (1) to (5), wherein the pressure mechanism applies pressure to the metal plate at a pressure of 1 kN or more and 14 kN or less. According to this contact resistance measuring device, the coating can be reliably destroyed by applying a high pressure to the metal plate.

[0049] (7) The contact resistance measuring device according to any one of (1) to (6), wherein the pressure mechanism is driven by an electromagnetic motor. This contact resistance measuring device allows for highly accurate control of position, speed, etc., and can reproduce with high precision the electrode operation in actual resistance spot welding.

[0050] (8) The contact resistance measuring device according to (7), wherein the electromagnetic motor is a servo motor or a linear motor. This contact resistance measuring device uses a servo motor or linear motor, which allows the device to be made smaller without complicating the pressure control mechanism, and also enables control with high responsiveness.

[0051] (9) A contact resistance measurement method for measuring the contact resistance of a metal plate to be resistance spot welded by passing a measurement current through the metal plate in a thickness direction, the measurement current being: The metal plate is sandwiched between a pair of electrodes, applying pressure to the metal plate between the pair of electrodes in accordance with a pressure based on the input pressure pattern for resistance spot welding; During the input measurement period of the contact resistance, the contact resistance is measured with respect to the measurement current flowing in the thickness direction of the metal plate; outputting information about the contact resistance measured during the measurement period; Contact resistance measurement method. This contact resistance measurement method applies pressure to a metal plate sandwiched between a pair of electrodes and measures the contact resistance for a specified measurement period, allowing the surface conditions of the metal plate and electrodes to be evaluated, making it easy to determine whether the metal plate is good or bad. Furthermore, this information can be used to develop guidelines for improving the surface condition of the metal plate. [Explanation of symbols]

[0052] 11 Foundation 13 Base Plate 15 Frame Structure 17 Lower plate 19 Upper Plate 21 Frame legs 23,25 metal plate 27 Stage Section 29A Lower electrode (electrode) 29B Upper electrode (electrode) 31 Pressure mechanism 33 Stage Upper Plate 35 Stage bottom board 37 Stage legs 39 Cushion spring 41 Electrode holder 43 Servo motor (electromagnetic motor) 45 Servo Cylinder 47 Rod 49 Electrode holder 51 Shield Frame 53 Control Unit 55 Resistance measurement section 57 Input section 59 Load Cell 60 Motor control unit 61,63,65 electrode 61a Groove 63a, 71, 73 Tapered section 67,69 Tapered holes 100 Contact resistance measuring device

Claims

1. A contact resistance measuring device that passes a measurement current through a metal plate to be resistance spot welded in a plate thickness direction and measures the contact resistance of the metal plate with respect to the measurement current, a pair of electrodes sandwiching the metal plate; a pressure mechanism for applying pressure between the pair of electrodes; a resistance measuring unit that measures a contact resistance with respect to the measurement current that is passed through the metal plate; an input unit into which information on a pressing force based on a pressing pattern during resistance spot welding and information on a measurement period for the contact resistance are input; a control unit that controls the pressure mechanism and the resistance measurement unit; Equipped with the control unit drives the pressure mechanism to apply pressure to the metal plate in accordance with the pressure input from the input unit, and outputs information about the contact resistance measured by the resistance measurement unit during the input measurement period. Contact resistance measuring device.

2. The measurement period includes at least one of an initial pressure application period, a current application period, and a pressure holding period after current application during resistance spot welding. The contact resistance measuring device according to claim 1 .

3. The metal plate sandwiched between the pair of electrodes is a plate set in which a plurality of metal plates are stacked, The contact resistance includes a surface resistance between the outermost metal plate of the plate set and the electrode in contact with the metal plate, and an inter-plate resistance between the plurality of metal plates arranged opposite to each other.

3. The contact resistance measuring device according to claim 1 or 2.

4. The pair of electrodes are electrodes for resistance spot welding, and the electrode holder is provided to hold the pair of electrodes in a replaceable manner.

3. The contact resistance measuring device according to claim 1 or 2.

5. The metal plate is a metal having a coating formed on its surface.

3. The contact resistance measuring device according to claim 1 or 2.

6. The pressure mechanism presses the metal plate with an arbitrary pressure of 1 kN or more and 14 kN or less.

3. The contact resistance measuring device according to claim 1 or 2.

7. The pressure mechanism is driven by an electromagnetic motor.

3. The contact resistance measuring device according to claim 1 or 2.

8. The electromagnetic motor is a servo motor or a linear motor. The contact resistance measuring device according to claim 7.

9. A contact resistance measurement method for measuring contact resistance of a metal plate to be resistance spot welded by passing a measurement current through the metal plate in a thickness direction, the measurement current being: The metal plate is sandwiched between a pair of electrodes, applying pressure to the metal plate between the pair of electrodes in accordance with a pressure based on the input pressure pattern for resistance spot welding; During the input measurement period of the contact resistance, the contact resistance is measured with respect to the measurement current flowing in the thickness direction of the metal plate; outputting information about the contact resistance measured during the measurement period; Contact resistance measurement method.

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