Resistance welding system

Abstract

This resistance welding system allows for accurate assessment of welding quality and is suitable for in-line production and quality assurance. [Solution] A resistance welding system comprising a welding control device 20 for controlling the welding current of a resistance welding apparatus, wherein the welding control device 20 has one or more of the following characteristic values: (1) electrode area or electrode diameter obtained by an electrode state confirmation means, (2) amount of strain during pressurization and current flow obtained by a strain detector provided on the electrode support part of the resistance welding apparatus. This includes using the aforementioned characteristic value as an evaluation value or a calculated value as an evaluation value, and performing a quality determination based on the evaluation value.

Description

Technical Field

[0001] The present invention relates to a resistance welding system such as spot welding.

Background Art

[0002] Conventionally, in the field of resistance welding typified by spot welding, as a method for judging the quality of welding in real time (during welding), a method of judging the properties of a welded portion (nugget) formed on a welded member is known.

[0003] For example, in Patent Document 1, by adding the amount of movement in the electrode movement direction of the driving part of the electrode due to the expansion and contraction of the welded part (nugget) during welding and the amount of deflection of the welding gun due to the pressing force applied from the electrode to the welded member, a method for detecting the amount of movement between welding electrodes for deriving the amount of movement between welding electrodes has been proposed.

[0004] Further, in Patent Document 2, a reduction difference between the maximum resistance value during the energization period detected in a state where a welded member (steel plate) is sandwiched between upper and lower electrodes and the final resistance value at the end of energization is compared with a preset threshold value for determination. When the comparison result is lower than the threshold value, energization is continued, and when it is higher, energization is stopped. A quality determination system for spot welding is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the method described in Patent Document 1, the expansion and contraction of the nugget is estimated based on the correlation between the amount of movement between electrodes and time, but this expansion and contraction of the nugget deforms the welding apparatus and is therefore not detected as the amount of movement between electrodes.

[0007] Specifically, when welding together plates of different thicknesses, determining the quality of the nugget requires multiple data points showing the correlation between electrode movement and time. Since the current measured value is then compared and judged based on these multiple correlation data points, the judgment process takes time, which ultimately slows down the welding speed. Furthermore, given the numerous variable and irregular factors such as the material of the welded component, plate thickness, and welding conditions, and the requirement for welding speed in mass production environments, it is considered unsuitable for detecting the quality of welds in-line.

[0008] On the other hand, in the invention described in Patent Document 2, the resistance value varies depending on the material and plate thickness. Therefore, it is necessary to set a threshold value according to the plate assembly. For example, as illustrated in Figure 11, even in normal welding, the difference in the decrease between the maximum and minimum resistance values ​​is smaller when welding thin plates or thin plates together compared to welding thick plates. Furthermore, the material must also be considered, and ultimately, setting a threshold for determining quality based solely on resistance values ​​becomes difficult.

[0009] On the other hand, in spot welding of automotive steel sheets and the like, welding is performed at high speed by equipping numerous welding robots with welding equipment. It is known that the welding current and energizing time of each of these welding devices are controlled by a welding control device (also called a "welding timer") that specifically controls the welding current.

[0010] Generally, quality control in resistance welding involves a complex interplay of various factors, resulting in a large amount of information that needs to be acquired. As information (e.g., resistance value, heat quantity) fluctuates with the passage of welding time, conventionally, a separate quality assurance judgment device was installed in addition to the welding control device (welding timer) that controls the welding current. The judgment results from this quality assurance judgment device were then used to control the welding conditions of the welding equipment (current value or energizing time) in the welding control device (welding timer) to ensure quality.

[0011] Therefore, in order to make a judgment using the quality assurance judgment means, it is necessary to receive information on control elements (current value or energizing time) from the welding control device (welding timer). Furthermore, in order to control the welding conditions of the welding device based on the judgment result of the quality assurance judgment means, it is necessary to transmit the judgment result data to the welding control device (welding timer). As a result, it was found that transmission and reception take time and can also be a cause of transmission and reception errors, and consequently, it is not suitable for inline production and quality assurance.

[0012] Therefore, the main objective of the present invention is to provide a resistance welding system that can accurately determine welding quality and is suitable for inline production and quality assurance. [Means for solving the problem]

[0013] The implementation method that solves the above problems is as follows: (First aspect) A resistance welding system includes a resistance welding apparatus that performs resistance welding by sandwiching a workpiece between a pair of electrodes, and a welding timer that controls the welding current of the resistance welding apparatus, The welding timer acquires one or more characteristic values ​​from (1) to (2) below. (1) The electrode area or electrode diameter obtained by the electrode condition confirmation means, (2) The amount of strain during pressurization and current flow, obtained by a strain detector installed in the electrode support section of the resistance welding apparatus. A resistance welding system characterized by including the following: [Effects of the Invention]

[0014] According to the present invention, the welding quality can be accurately determined and the welding timer is provided with a quality determination unit, so that it is easy to add a welding device, and a resistance welding system suitable for in-line production and quality assurance can be provided.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic diagram of a spot welding device. [Figure 2] It is a signal processing flow chart in a spot welding device. [Figure 3] It is a determination processing flow chart. [Figure 4] It is another determination processing flow chart. [Figure 5] It is an explanatory diagram of the resistance value. [Figure 6] It is a plan view of the electrode. [Figure 7] It is a correlation diagram between the change in the tip diameter of the electrode and the resistance value. [Figure 8] It is a correlation diagram between the change in the tip diameter of the electrode and the resistance value. [Figure 9] It is a correlation diagram between the change in the tip diameter of the electrode and the resistance value. [Figure 10] It is a graph of the change in the resistance value over time. [Figure 11] It is a graph of the change in the resistance value over time with respect to the energization time. [Figure 12] It is an exemplary change graph of the strain displacement amount during pressurization and energization.

Embodiments of the Invention

[0016] Next, embodiments of the present invention will be described in detail below while referring to the drawings.

[0017] (Overview of the Welding Device) Figures 1 and 2 show an overview of the resistance welding system, in which the welding apparatus 10, which is the main body, has a pair of first electrode support parts 11A and second electrode support parts 11B. The first electrode support part 11A and the second electrode support part 11B each hold the first electrode 12A and the second electrode 12B at their tips so that they can move closer to and further apart from each other (open and close).

[0018] This welding device 10 is installed, for example, at the tip of a welding robot 14. The welding robot 14's motion is controlled by a drive control device 22 of a control device 20 installed nearby. The control device 20 includes a welding control device (welding timer) 30 that controls the welding current and energizing time of the welding device 10.

[0019] When the first electrode 12A and the second electrode 12B are moved in a direction that brings them closer to each other, a predetermined pressing force is applied to the target workpiece to be welded (for example, overlapping automotive steel plates) 2P via the tips of the first electrode 12A and the second electrode 12B.

[0020] A welding current from the welding power source 16 flows between the first electrode 12A and the second electrode 12B. Furthermore, the first electrode support portion 11A and the second electrode support portion 11B are provided with voltage detection terminals 18, 18 that can detect whether the workpiece 2P is being welded or not.

[0021] A strain detector 15 is provided on the electrode support portion, for example, the first electrode support portion 11A, and a signal is input to a welding control device (welding timer) via an amplifier (not shown).

[0022] In this embodiment, welding quality Warranty Determination A means is provided, and an example configuration is shown in Figure 2. The welding quality determination means 40 of the embodiment includes a control unit 41, a storage unit 42, a calculation unit 43, a resistance value change recording unit 43A, a calculation unit 44, a determination unit 45, an output unit 46, an input unit 47, and a conversion unit 47A.

[0023] The input unit 47 of the welding quality determination means 40 receives current values ​​and voltage values ​​from the current value detection means 10A and voltage value detection means 10B provided in the welding apparatus 10.

[0024] On the other hand, the welding apparatus 10 is provided with an electrode state confirmation means 50 for the electrodes 12 (first electrode 12A, second electrode 12B). The electrode state confirmation means 50 is, for example, an imaging device such as a camera, which confirms the state of the electrode tip (for example, measuring the electrode tip diameter φ shown in Figure 6) before the start of welding or after the completion of welding (for a particular product). Specifically, the "Network-type electrode tip monitoring camera TMN-01" commercially available from Kyokuto Co., Ltd. can be given as an example. Note that arranging a line sensor camera near the tip dresser to measure the electrode tip diameter is disclosed in Japanese Patent Application Publication No. 07-148581.

[0025] As described above, the input unit 47 of the welding quality determination means 40 receives the current value and voltage value, and the calculation unit 43 calculates the resistance value between electrodes based on the voltage value and current value. In addition to being stored in the storage unit 42, control commands such as energizing time and current value are sent to the welding apparatus 10 via the control unit 41. On the other hand, electrode tip state information from electrode state confirmation means 50 is also taken into input unit 47, and the electrode area is input to calculation unit 43 via conversion unit 47A which calculates the electrode area from the electrode tip diameter, and the evaluation value is calculated by calculation unit 44 which calculates an evaluation value using the calculated resistance value and electrode area, and the quality determination unit 45 determines whether the welding quality is good or bad. The result of the welding quality assessment is displayed on a display device D1 near the welding apparatus 10 via the output unit 46, as well as on a display device D2 installed in the area where quality control is being performed.

[0026] The control unit 41 controls the current value to reach the target heat generation amount based on the resistance value calculated by the calculation unit 43. Even as electrode wear progresses, the current value is constantly adjusted to maintain the optimal heat output, preventing welding defects.

[0027] Before going into detail, the "resistance between electrodes" as used in this invention includes various "resistance values," such as those shown in Table 1 and Figure 5. In other words, the "resistance value with product" shown in (a) is the resistance value when the workpiece to be welded is sandwiched between the pair of electrodes. The "dry firing resistance value" (resistance value without product) shown in (b) is the resistance value between a pair of electrodes when there is no member to be welded (plate assembly product) present. The "product resistance value" shown in (c) is the resistance value that occurs only between the welded components (plate assembly products) when they are sandwiched between a pair of electrodes. In other words, "resistance with product (a)" = "resistance without product (b)" + "resistance with product (c)".

[0028] [Table 1]

[0029] [Table 2]

[0030] [Table 3]

[0031] The "contact resistance value" shown in Table 2, along with the measured values, represents how much the voltage drops (energy loss) when current passes through the contact surface between the electrode and the workpiece. It is an indicator of how easily electricity flows through the contact surface and is calculated by multiplying the "dry firing resistance value" (resistance value without product) by the "electrode area". In other words, "contact resistance value" = "dry firing resistance value (b)" (resistance value without product) × "electrode area" Furthermore, the "resistance per electrode area" shown in Table 3 along with the measured values ​​is calculated for the 1mm of the electrode tip. 2This represents the electrical resistance of the welded component per unit area, and is calculated by dividing the "product resistance value" by the "electrode area." In other words, "resistance value per electrode area" = "product resistance value (c)" ÷ "electrode area" All of these factors involve the "electrode area." The "contact resistance value" and the "resistance value per electrode area" are used as evaluation values ​​or thresholds for determining welding quality.

[0032] In this embodiment of the present invention, the welding quality determination means 40 includes an information acquisition unit (corresponding to the input unit 47 in the example shown in Figure 2) that acquires the resistance value between electrodes and the electrode area, and a determination unit 45 that determines the welding quality based on an evaluation value including the relationship between the electrode area and the resistance value, and a set threshold.

[0033] The electrode diameter gradually increases during the welding process (in the example shown in Table 1, φ6 → φ7 → φ8.5), and when a certain electrode (tip) diameter is reached (for example, φ8.5), the welding quality deteriorates. Therefore, it might be considered to use only the electrode diameter as the evaluation value, but this would not be possible if there are impurities such as plating. If there are impurities such as plating, the resistance in that area increases and heat is generated, while the resistance between the plates decreases and less heat is generated, which can lead to poor welding. Furthermore, as in Patent Document 2, it is conceivable to set only the resistance value detected with the welded material (steel plate) sandwiched between the upper and lower electrodes as the evaluation value for judgment. However, if the range between good and defective products in the evaluation value is narrow, setting a threshold becomes difficult. For example, as can be seen in Table 1 and Figure 7, the change in the resistance value with the product is small.

[0034] However, instead of judging solely by resistance value, if the evaluation value includes the relationship between electrode area (chip area) and resistance value, as in the embodiment of the present invention, the range between good and defective products in the evaluation value is widened because area is related to the square of the radius, and setting the threshold becomes easier (the stability and reliability of distinguishing between good and defective products are increased by setting the threshold).

[0035] The first example of the "evaluation value including the relationship between resistance value and electrode area" according to the present invention is, as shown in Table 2, an evaluation value of "contact resistance value" obtained by multiplying "dry firing resistance value" by "electrode area" (tip area). As illustrated in Figure 8, the electrode condition can be determined by setting the evaluation value based on "contact resistance value", in which the range between good and defective products in the evaluation value is widened, as a threshold.

[0036] A second example of the "evaluation value including the relationship between resistance value and electrode area" according to the present invention, as shown in Table 3, uses the "resistance value per electrode area," which is obtained by dividing the "product resistance value" (resistance value of the member to be welded) by the "electrode area" (tip area), as the evaluation value. As illustrated in Figure 9, the welding state can be determined by setting the evaluation value based on the "resistance value per electrode area," which widens the range between good and defective products in the evaluation value, as the threshold.

[0037] If the evaluation value is defined as the resistance value per electrode area, the welding state can be determined. In other words, it is possible to determine whether the welding state deteriorates during the current application process for each welding point, potentially resulting in a defective product. In this case, it is preferable to use the "product resistance value," which is obtained by subtracting the "dry firing resistance value" (when the welding material is not sandwiched between the electrodes) from the "product resistance value" (when the welding material is sandwiched between the pair of electrodes) when the welding material is sandwiched between the electrodes. In other words, since "product resistance value" = "resistance value with product" - "resistance value without product" the evaluation value is calculated as "resistance value per electrode area" = {"resistance value with product" - "resistance value without product"} ÷ "electrode area". By using the "product resistance value," the resistance value generated in the molten part (nugget) is detected, thus reducing the load on the calculation unit 43 and the calculation unit 44.

[0038] By incorporating the "electrode area" factor along with the resistance value as an evaluation value, it becomes possible to determine whether or not the welding condition deteriorates during the current flow process for each dotting point, potentially resulting in a defective product. This means that the quality of each dotting point can be evaluated and judged.

[0039] Referring to Figure 3, the "resistance value with product" is obtained during the workpiece welding current application stage, while the "dry firing resistance value" is obtained during the short-circuit current application stage after the electrode area calculation.

[0040] On the other hand, the resistance value can be defined as the "dry firing resistance value" when no workpiece is placed between the pair of electrodes, and the "contact resistance value," which is the "dry firing resistance value" multiplied by the "electrode area," can also be used as the evaluation value. As shown in Figure 4, the evaluation value can be obtained by calculating the electrode area and performing a short-circuit current application (dry firing).

[0041] The primary cause of welding defects in spot welding is the condition of the electrode tip. Therefore, if the electrode tip is in poor condition after welding, the welded component can also be judged as having a welding defect. By taking the electrode area into consideration when judging the condition of the electrodes, the difference between good and defective products becomes clearer, making it easier to determine whether a product is good or bad against the threshold. If the "contact resistance value," or "dry firing resistance value," is excessively high, it means that the heat that should be generated in the molten area (nugget) is being generated at the electrodes. It is easy to predict that when the actual welding current is applied, the amount of heat generated in the molten area (nugget) will be reduced, leading to poor welding.

[0042] The calculation unit 43 has a resistance value change recording unit 43A that records the change in the calculated resistance value between electrodes over time. When the contact resistance value is below a threshold, the process proceeds to the welding stage. Preferably, the judgment unit 45 makes a judgment on the quality of each welding point based on the average value of the change in resistance value over time or the magnitude of the change over time, as shown in Figure 10(a) for thick plate-to-thick plate welding or (b) for thin plate-to-thin plate welding.

[0043] If the contact resistance value is below a threshold, i.e., the electrode condition is judged to be good, and then the change in resistance value over time during the welding stage is judged; in other words, the judgment is made in two stages, and by monitoring all welding points, the reliability of quality assurance is enhanced.

[0044] The information, including electrode area information from the input unit 47 and resistance value information output from the calculation unit 43, can be input to a welding timer 30, which includes a calculation unit that controls the welding apparatus 10, and calculated by the calculation unit. The parameters in this embodiment are current, voltage, and electrode area. Since the current value is controlled and recorded by the welding timer 30, the overall processing speed of the control system is increased by consolidating the other parameters into the welding timer 30 as well. If necessary, information may be incorporated into the welding timer via a conversion device (interface).

[0045] If the welding quality determination result from the determination unit 45 is negative, the output unit 46 can selectively display the product identification number and the dot identification number on the display device D1 and / or the display device D2. If a welding anomaly occurs, the welding robot can be stopped by notifying the producer, preventing the continuous production of defective products. Furthermore, it allows for the use of both quality judgment per workpiece and quality judgment per welding point.

[0046] The welding control device 20 in this embodiment is a resistance welding system equipped with the following timer, The welding timer includes a quality determination unit 45 that acquires one or more characteristic values ​​from (1) to (2) below, uses a value selected from the characteristic values ​​or a calculated value as an evaluation value, and performs a quality determination based on this evaluation value. (1) The electrode area or electrode diameter obtained by the electrode condition confirmation means, (2) Amount of strain during pressurization and current flow, obtained by a strain detector installed in the electrode support section of the resistance welding apparatus.

[0047] Furthermore, the welding timer is (3) The resistance value obtained between a pair of electrodes based on the current from the current detection means and the voltage from the voltage detection means is obtained as a characteristic value, and a value selected from these characteristic values ​​or a calculated value is used as an evaluation value, and quality judgment can be made based on this evaluation value.

[0048] Furthermore, the quality determination unit 45 has a logic switching unit that selectively switches between the following determination logic (A) and determination logic (B). (A) A determination logic based on resistance value and electrode area or electrode diameter. (B) A judgment logic based on the amount of distortion.

[0049] According to the judgment logic (A), it is not affected by the thickness of the plate being welded, making it suitable for resistance welding when overlapping thin plates. According to the judgment logic (B), when resistance welding is performed by overlapping two thick plates, the growth of the welded area (nugget) can be accurately determined. Therefore, to avoid being affected by plate thickness, appropriate quality evaluation can be performed by selectively switching between judgment logic (A) and judgment logic (B) depending on the plate assembly.

[0050] The evaluation value based on the aforementioned resistance value is preferably determined by calculating the magnitude of the difference between the maximum resistance value and the minimum resistance value during the period from the start to the end of resistance value acquisition, and only if the AND condition of a large difference and a small electrode area or electrode diameter is met is considered good.

[0051] Based on Table 2, if the growth of the welded area (nugget) is appropriate, that is, if sufficient heat is generated, then the welding is being performed properly. Joule's Law (Q=I 2 According to (×R×t), a high resistance value R is necessary to obtain a sufficient amount of heat. However, in Table 2, the dry-firing resistance value for an electrode diameter of φ8.5 (NG product) at 500 dots is similar to the dry-firing resistance value for an electrode diameter of φ7 (OK product) at 60 dots. However, for example, an electrode diameter of φ8.5 (NG product) at 500 dots already results in an electrode area of ​​56.7 mm². 2As a result, the contact resistance value is abnormally high. This is likely because the electrodes are worn, and a plating film is interposed between the electrodes and the workpiece, preventing sufficient heat generation, yet the contact resistance value remains abnormally high. Therefore, it is desirable to calculate the magnitude of the difference between the maximum resistance value and the minimum resistance value, and to judge the device as good only if the AND condition is met that the difference is large and the electrode area or electrode diameter is small.

[0052] Based on the aforementioned resistance value, by controlling at least one of the current value and energizing time so that the target heat generation is achieved at subsequent welding points, appropriate growth of the welded portion (nugget) can be ensured.

[0053] The electrode area is calculated based on the tip diameter of the acquired electrode. When using the "Network-type electrode tip monitoring camera TMN-01" commercially available from Kyokuto Co., Ltd., a diameter of φ1 is obtained at 45°-205° and a diameter of φ2 is obtained at 135°-315°, so the area is calculated as π × φ1 × φ2 / 4.

[0054] The electrode status confirmation means outputs an imaging signal from an electrode tip monitoring camera that captures the chip-dressed electrode.

[0055] Next, we will explain the form of determination made by the determination logic (B). In this case, the form shown in Japanese Patent Publication No. 7642917, disclosed by one of the applicants, can be used as is.

[0056] In other words, the amount of strain detected by the strain detector 15 is input to the calculation unit 42 via the input unit 47, and the amount of strain displacement, which is the temporal change in the amount of strain, and its polarity are calculated. Then, the quality determination unit 45 determines the welding quality for each welding point based on the change in the polarity of the strain displacement.

[0057] To explain further, as illustrated in Figure 12, when the polarity of the strain displacement, which is the temporal change in the amount of strain during pressurization and energization detected by the strain detector 15, changes from positive to negative, it can be determined that the weld is "good" (good quality).

[0058] The welding quality determination means 40 can determine that tip dressing or tip replacement is required when the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is negative, and the negative amount of the strain displacement exceeds a predetermined threshold.

[0059] When the polarity changes from positive to negative during pressurization and energization, and the state alternates between negative and positive or zero multiple times, the weld can be determined to be good.

[0060] A weld can be determined to be good if both of the following conditions are met: the polarity changes from positive to negative during pressurization and energization, and this negative state is repeated multiple times, and the welding current remains constant.

[0061] Furthermore, if the proportion of negative values ​​during the indentation process after the polarity of the strain displacement changes from positive to negative is below a predetermined threshold, it can be determined that the welding is defective.

[0062] When the polarity changes from positive to negative during pressurization and energization, and when this negative or zero state is repeated multiple times, the weld can be determined to be good.

[0063] Even when the plate thickness of the member to be welded varies, a good weld can be determined when the value changes from positive to negative during pressurization and energization, and when this negative or zero state is repeated multiple times.

[0064] The welding quality determination means 40 can determine that the melting of the workpiece is insufficient and that it is in the expansion phase when the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is only positive.

[0065] Furthermore, the welding quality determination means 40 can determine any of the following (1) to (4). (1) When the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is only positive, it is determined that the melting of the welded member is insufficient and that it is in the expansion phase. (2) When the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is positive, and the positive amount of the strain displacement falls below a predetermined threshold, it is determined that tip dressing or tip replacement is required, or that it is an irregular weld. (3) When the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is positive, and the duration of that positive polarity is longer than a predetermined duration, it is determined that tip dressing or tip replacement is required. (4) When the polarity of the strain displacement, which is the temporal change in the amount of strain detected by the strain detector 15, is negative, and the negative amount of the strain displacement exceeds a predetermined threshold, it is determined that spatter has occurred or irregular welding has occurred.

[0066] On the other hand, as shown in Figures 1 and 2, a welding monitoring system 60 is provided outside the welding control device 20. The welding control device 20 transmits one or more characteristic values ​​for each welding point from (1) to (3) above, in correspondence with the welding conditions, to the welding monitoring system 60, and the welding monitoring system 60 can also be configured to perform quality determination based on the evaluation values.

[0067] By recording characteristic values ​​in association with welding conditions, traceability can be ensured in each welding process. Examples of welding conditions include welding current, energizing time, and power supply voltage. Characteristic values ​​can fluctuate based on welding conditions, and by managing them in association, the execution history of each welding process can be verified later. This makes it easier to understand welding quality on a product-by-product basis and to track the causes of defects.

[0068] The welding monitoring system 60 is equipped with a display device D2, and the quality determination unit 45 can be configured to transmit the quality determination result to the display device D2.

[0069] If the quality judgment result in the quality judgment unit 45 is abnormal, the welding robot 14 can be stopped, or the welding device 10 can be stopped. Since the welding control device is a welding timer, it has a judgment means for each welding device, making it easy to add welding devices and manage quality in welding lines with multiple welding devices. [Explanation of symbols]

[0070] 10... Welding equipment 11A,11B...Electrode support part 12A,12B…electrode 14... Welding robots 15... Strain detector 20... Welding control device 22… Drive control device 30... Welding timer 40...Method for determining welding quality 50...Method for checking electrode status 60... Welding monitoring system

Claims

1. A resistance welding system includes a resistance welding apparatus that performs resistance welding by sandwiching a workpiece between a pair of electrodes, and a welding timer that controls the welding current of the resistance welding apparatus, The welding timer is (1) The contact resistance value obtained by multiplying the resistance value between a pair of electrodes in the absence of the workpiece to be welded by the electrode area obtained by imaging with a camera, and The resistance value per electrode area is obtained by dividing the resistance value that occurs only between the workpieces to be welded when the workpieces are sandwiched between a pair of electrodes by the electrode area. This includes obtaining the resistance value of at least one of the following as a characteristic value: (2) This includes obtaining the amount of strain during pressurization and current flow as a characteristic value, obtained by a strain detector provided on the electrode support part of the resistance welding apparatus, Depending on whether the plate assembly is thin or thick, the evaluation based on the characteristic value of (1) and the evaluation based on the characteristic value of (2) can be selectively switched. The system includes a quality determination unit that performs a quality determination based on an evaluation value based on the characteristic value described in (1) above, or on an evaluation value based on the characteristic value described in (2) above, after selecting one of these options. A resistance welding system characterized by the following features.

2. The resistance welding system according to claim 1, wherein the amount of strain detected by the strain detector during pressurization and energization is a characteristic value, the amount of strain displacement which is the change in the characteristic value over time is an evaluation value, and the quality is determined to be good based on a threshold value of the evaluation value.

3. Furthermore, the welding timer is This includes obtaining a resistance value as a characteristic value based on the current from a current detection means and the voltage from a voltage detection means between a pair of electrodes, It includes a quality determination unit that performs quality determination based on the characteristic value of the aforementioned resistance value. The resistance welding system according to claim 1.

4. The resistance welding system includes a welding monitoring system external to the welding timer. The welding timer transmits characteristic values ​​for each welding point to the welding monitoring system, in correspondence with the welding conditions. In the welding monitoring system, quality determination is performed based on the evaluation value. The resistance welding system according to claim 1.

5. The resistance welding system according to claim 1, wherein the resistance welding system includes a monitor, and the quality determination unit transmits the result of the quality determination to the monitor.

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