Welding quality determination system

Abstract

A welding quality determination system 100 comprises: a strain sensor (index value acquiring unit) 17 that acquires an amount of deformation of a workpiece along an arrangement direction of a first electrode 111 and a second electrode 112; a position sensor (position acquiring unit) 16 that acquires the positions of the first electrode 111 and the second electrode 112; a position control unit 43 that, on the basis of the positions acquired by the position sensor 16, controls a drive motor 14 such that the first electrode 111 and the second electrode 112 are held at predetermined welding positions during welding of the workpiece; and a quality determining unit 44 that determines that the diameter of a nugget is good if the amount of deformation (degree of deformation) during welding of the workpiece is within a predetermined allowable range, and determines that the diameter of the nugget is defective if the amount of deformation is not within the allowable range.

Description

Welding quality determination system

[0001] This specification discloses a welding quality determination system.

[0002] Conventionally, regarding a welding apparatus that welds a workpiece by energizing between a pair of electrodes that hold the workpiece, techniques for determining the welding state are known. For example, in Patent Document 1, a resistance waveform is calculated from the current value and voltage value between a pair of electrodes, a dilation amount waveform is calculated from the stroke and pressing force between the pair of electrodes, and a method for calculating the diameter of the nugget generated in the workpiece from the resistance waveform and the dilation amount waveform is described. In this method, it is determined whether the welded product is a good product by comparing the calculated diameter of the nugget with a predetermined value.

[0003] Japanese Unexamined Patent Application Publication No. 2024-034715

[0004] During welding, the workpiece expands due to the growth of the nugget generated in the workpiece, and accordingly, the positions of the pair of electrodes may fluctuate. Therefore, for example, like the method described in Patent Document 1, it is necessary to calculate the dilation amount waveform using not only the pressing force on the workpiece but also the value of the stroke between the pair of electrodes, and it is required to align the detection times of the pressing force and the stroke as accurately as possible. However, since the welding process is performed in a short time, it may be difficult to accurately align the detection times of a plurality of detection values, and there is a probability that the quality of the welding cannot be accurately determined.

[0005] This disclosure has been made in view of such problems, and an object thereof is to provide a welding quality determination system capable of further improving the accuracy of welding quality determination.

[0006] To achieve the above objective, the welding quality determination system of the present disclosure is applied to a welding apparatus that performs welding of a workpiece by passing current between the first electrode and the second electrode while the workpiece is held between the first electrode and the second electrode, which are capable of approaching and separating from each other on the same axis by a driving force from a drive motor, and determines the quality of the diameter of the nugget generated on the workpiece as the quality of the welding state, and includes an index value acquisition unit that acquires the amount of deformation of the workpiece or the resistance value of the workpiece along the alignment direction of the first electrode and the second electrode, and the position of the first electrode and the second electrode The system includes a position acquisition unit that acquires a position, a position control unit that controls the drive motor based on the position acquired by the position acquisition unit so that the first electrode and the second electrode are held in predetermined welding positions during welding of the workpiece, and a quality determination unit that determines that the diameter of the nugget is good if the degree of deformation of the workpiece or the amount of change in the resistance value based on the acquisition result of the index value acquisition unit during welding of the workpiece is within a predetermined allowable range, and determines that the diameter of the nugget is poor if the degree of deformation or the amount of change in the resistance value is not within the allowable range.

[0007] The welding quality judgment system of this disclosure makes it possible to further improve the accuracy of welding quality judgment.

[0008] This is a block diagram showing the electrical connection relationships of a spot welding apparatus to which the welding quality determination system according to the embodiment is applied. This is a schematic configuration diagram showing the welding gun and robot equipped in the spot welding apparatus. This is an explanatory diagram showing the flow of the welding process. This is an explanatory diagram showing an example of the change in electrode position over time. This is a flowchart showing an example of the quality determination process of the embodiment. This is an explanatory diagram showing an example of the tolerance range. This is an explanatory diagram showing an example of the pass / fail criteria for each workpiece. This is an explanatory diagram showing another example of the tolerance range. This is an explanatory diagram showing an example of the tolerance range for deformation speed. This is an explanatory diagram showing an example of the tolerance range for the maximum value of deformation.

[0009] An embodiment of this disclosure will be described below with reference to the drawings.

[0010] (Welding Apparatus) Figure 1 is a block diagram showing the electrical connection relationships of a welding apparatus 1 to which the welding quality determination system 100 according to the embodiment is applied. Figure 2 is a schematic configuration diagram showing the welding gun 10 and robot 20 provided in the welding apparatus 1. As shown in the figure, the welding apparatus 1 comprises a welding gun 10, a robot 20, a power supply control device 30, and a control device 40. The welding apparatus 1 is placed in a production line for products such as automobile bodies, and is used to join two workpieces W (Figure 3), such as sheet metal used in the automobile body, by spot welding. In the following description, the two workpieces W will be referred to simply as "workpieces W".

[0011] The above-mentioned vehicles are not limited to those powered solely by internal combustion engines, but also include, for example, BEVs (Battery Electric Vehicles), HEVs (Hybrid Electric Vehicles), PHEVs / PHVs (Plug-in Hybrid Electric Vehicles / Plug-in Hybrid Vehicles), and FCEVs / FCVs (Fuel Cell Electric Vehicles / Fuel Cell Vehicles). PHEVs / PHVs are vehicles that can be charged by external charging, which involves supplying power from an external power source to an onboard energy storage device, or by external power supply, which involves supplying power from the battery to external electrical appliances.

[0012] (Welding Gun) As shown in Figure 2, the welding gun 10 comprises a pair of electrodes 11 and a holding member 12 for holding the pair of electrodes 11. The pair of electrodes 11 includes a first electrode 111 and a second electrode 112 arranged coaxially so as to be able to clamp a workpiece W. Hereinafter, the direction in which the first electrode 111 and the second electrode 112 are aligned (up and down in Figure 2) will be referred to as the "gun axis direction". The first electrode 111 and the second electrode 112 are held by the holding member 12 so as to be able to approach and separate from each other in the gun axis direction. The holding member 12 is formed by branching into two to form a U shape, and has a first holding part 121 for holding the first electrode 111 and a second holding part 122 for holding the second electrode 112. Cooling liquid can be supplied to the inside of the first electrode 111 and the second electrode 112 held by the holding member 12 in this manner.

[0013] Furthermore, as shown in Figure 1, the welding gun 10 is equipped with an electric drive motor 14 for moving a pair of electrodes 11 relative to each other. The drive motor 14 is built into the holding member 12 and moves the second electrode 112, which is a movable electrode, relative to the first electrode 111, which is a fixed electrode, via a drive mechanism (not shown). Note that the first electrode 111 may be a movable electrode and the second electrode 112 may be a fixed electrode, or both the first electrode 111 and the second electrode may be movable electrodes.

[0014] Furthermore, as shown in Figure 1, the welding gun 10 is equipped with a pressure sensor (pressure acquisition unit) 15 and a position sensor (position acquisition unit) 16. The pressure sensor 15 detects the pressure applied when pressurizing the workpiece W with a pair of electrodes 11. The position sensor 16 detects the position of the pair of electrodes 11 driven by the drive motor 14. The position of the pair of electrodes 11 is the relative position of the first electrode 111 and the second electrode 112.

[0015] Furthermore, the welding gun 10 is equipped with a pair of strain sensors (index value acquisition units) 17. The pair of strain sensors 17 includes a first strain sensor (first deformation amount acquisition unit) 171 attached to the first holding unit 121 and a second strain sensor (second deformation amount acquisition unit) 172 attached to the second holding unit 122. The first strain sensor 171 detects the strain of the first holding unit 121 along the gun axis direction, and the second strain sensor 172 detects the strain of the second holding unit 122 along the gun axis direction. The pressure sensor 15, position sensor 16, and pair of strain sensors 17 output the detection results to the control device 40. The pressure sensor 15, position sensor 16, pair of strain sensors 17, and control device 40 constitute the welding quality determination system 100 according to this embodiment.

[0016] (Robot) Robot 20 is an articulated robot having a base 21, a plurality of arms 22, 23, and a plurality of joints 24, 25, 26. Arm 22 is rotatably connected to the base 21 via joint 24. Arm 23 is rotatably connected to arm 22 via joint 25. In addition, a holding member 12 for the welding gun 10 is rotatably connected to the tip of arm 23 via joint 26. Robot 20 has a plurality of detection sensors (not shown) that detect the position and rotation angle of joints 24 to 26. The detection results from each detection sensor are output to the control device 40. In response to a control signal from the control device 40, Robot 20 rotates joints 24 to 26 using driving force from an electric drive motor to adjust the position and orientation of the welding gun 10.

[0017] (Energy supply control device) The energy supply control device 30 controls the supply of energy to the pair of electrodes 11 of the welding gun 10. Specifically, the energy supply control device 30 receives an energy supply instruction signal from the control device 40 indicating that energy should be supplied to the pair of electrodes 11, and information on the applied voltage when energy is supplied. Based on the acquired energy supply instruction signal and applied voltage information, the energy supply control device 30 supplies the applied voltage from a voltage supply circuit (not shown) to the pair of electrodes 11 for a predetermined energy supply period. The voltage supply circuit may be built into the energy supply control device 30 or may be provided separately. In order to accurately manage the applied voltage and the predetermined energy supply period, the energy supply control device 30 controls the timing of energy supply using a built-in timer. For this reason, the energy supply control device 30 is also called a welding timer.

[0018] (Control device) The control device 40 is composed of input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc. The control device 40 includes, as functional units, a robot control unit 41, a power supply control unit 42, a position control unit 43, and a quality determination unit 44. The control device 40 acquires information necessary for the overall control of the welding apparatus 1, such as information about the workpiece W, from a control device that manages the production line, for example, and executes processing by each functional unit based on the acquired information.

[0019] The robot control unit 41 acquires the position and rotation angle of the joints 24-26 from multiple detection sensors of the robot 20, and controls the drive motor of the robot 20 based on the acquired information, thereby controlling the position and orientation of the welding gun 10 by the robot 20. The power supply control unit 42 outputs the power supply instruction signal and applied voltage information to the power supply control device 30.

[0020] The position control unit 43 controls the position of the pair of electrodes 11 by driving and controlling the drive motor 14. Specifically, the position control unit 43 performs pressure control by feedback controlling the drive motor 14 so that the pressure applied to the workpiece W from the pair of electrodes 11 becomes the target pressure, based on the pressure detected by the pressure sensor 15. The position control unit 43 also performs position control by feedback controlling the drive motor 14 so that the pair of electrodes 11 are in the target position, based on the position of the pair of electrodes 11 detected by the position sensor 16.

[0021] The quality determination unit 44 determines whether the welding condition applied to each welding point WP of the workpiece W is good or not, based on the detection results of the pair of strain sensors 17. The quality determination unit 44 also determines whether the overall welding condition of the workpiece W meets or fails a predetermined standard, based on the proportion of welding points WP that are determined to have a good welding condition.

[0022] (Welding Process) Next, the welding process using the welding apparatus 1 will be described. Figure 3 is an explanatory diagram showing the flow of the welding process. As shown in the figure, the control device 40 controls the robot 20 to adjust the position and orientation of the welding gun 10 so that the workpiece W is positioned between the pair of electrodes 11 (step ST1). The pair of electrodes 11 are held at positions separated from each other by the position control of the drive motor 14. Figure 3 illustrates the state in which the workpiece W is in contact with the first electrode 111, which is a fixed electrode.

[0023] Next, the control device 40 controls the drive motor 14 by position control so that the second electrode 112 moves to a position where it contacts the workpiece W (step ST2). Whether or not the second electrode 112 has contacted the workpiece W, that is, whether or not the workpiece W has been gripped by the pair of electrodes 11, can be determined by whether or not the pressure sensor 15 detects pressure.

[0024] Next, the control device 40 controls the drive motor 14 by pressurization control to apply pressure to the workpiece W from the pair of electrodes 11 (step ST3). At this time, the control device 40 sets the target pressure to be applied to the workpiece W to a predetermined first predetermined pressure (predetermined pressure). The first predetermined pressure is set so that there is no excess or deficiency in the pressure applied to the workpiece W, taking into consideration that the workpiece W expands during welding. In Figure 3, the process of applying pressure to the workpiece W is shown by solid arrows.

[0025] When the pressure detected by the pressure sensor 15 reaches a first predetermined pressure, the control device 40 switches the drive motor 14 to position control (step ST4). Specifically, the control device 40 sets the position of the pair of electrodes 11 at the time the pressure reaches the first predetermined pressure to a predetermined welding position, and controls the drive motor 14 by position control so that the pair of electrodes 11 are held at the predetermined welding position. At this time, the pair of electrodes 11 only needs to be maintained within a predetermined distance range relative to the predetermined welding position. Note that in steps ST4 to ST7 of Figure 3, the solid arrows indicating the pressure have been omitted to show that the control has switched from pressure control to position control.

[0026] Then, the control device 40 outputs an energization instruction signal and applied voltage information from the energization control unit 42 to the energization control device 30, initiating the energization of the pair of electrodes 11 (step ST5). The energization is performed so that a predetermined target voltage is applied between the pair of electrodes 11 for a predetermined energization period. As a result, as shown in steps ST5 to ST7, a nugget N is formed at the welding point WP of the workpiece W, which changes from a solid to a liquid state, and the nugget N expands over time. In addition, during the energization period, a coolant is supplied to the inside of the pair of electrodes 11 to suppress excessive temperature rise. In the figure, the flow of the coolant inside the second electrode 112 in step ST5 is schematically shown by a dashed arrow.

[0027] When the predetermined energizing period has elapsed, the control device 40 terminates the energizing, switches the drive motor 14 to pressurized control, and supplies coolant for a predetermined cooling period (step ST8).

[0028] When a predetermined cooling period has elapsed, the control device 40 releases the pressurization control and reduces the pressurization force to a value of 0 (step ST9). Furthermore, the control device 40 switches the drive motor 14 to position control and separates the pair of electrodes 11 from each other (step ST10). This completes the welding process for the welding location WP. After that, the control device 40 controls the robot 20 to move the welding gun 10 to the next welding location WP and executes the process again from step ST1.

[0029] The positional changes of the pair of electrodes 11 in the welding process described above will be explained with reference to Figure 4. Figure 4 is an explanatory diagram showing an example of the change in electrode position over time. The solid line in the figure shows the position (relative position) ΔPA of the pair of electrodes 11 detected by the position sensor 16 in the welding process of the embodiment. The dashed line shows the position (relative position) ΔPB of the pair of electrodes 11 detected by the position sensor 16 in the welding process of the comparative example. The positions ΔPA and ΔPB decrease when the pair of electrodes 11 are close to each other and increase when they are far apart. The dashed line in the figure will be explained later.

[0030] In the welding process of this embodiment, position control brings the pair of electrodes 11 closer together until they clamp the workpiece W (until time t1: steps ST1 to ST2 in Figure 3). Then, pressurization control is performed (times t1 to t2: step ST3), and the positions of the pair of electrodes 11 are maintained by position control, and current is applied (times t2 to t3: steps ST4 to ST7). A cooling period accompanied by pressurization control is also provided (times t3 to t4: step ST8). The position ΔPA of the pair of electrodes 11 does not change during the period (times t1 to t4) in which the pair of electrodes 11 clamp the workpiece W, including the current application period (times t2 to t3) (see the solid line in the figure). After that, the pressurization control is released, and the pair of electrodes 11 move apart from each other by position control (times t4 onwards: steps ST9, ST10).

[0031] On the other hand, in the welding process of the comparative example, pressure control is performed to apply a first predetermined pressure force from time t1 to time t4 in the figure (from step ST3 to step ST8 in Figure 3). As a result, the thickness of the workpiece W decreases as the workpiece W melts. Consequently, the pair of electrodes 11 move closer to each other during energization (times t2 to t3) as the thickness of the workpiece W decreases, as shown by the dashed line in the figure. Therefore, the position ΔPB changes.

[0032] (Welding Quality Determination Process) Next, the welding quality determination process for the workpiece W, which is performed by the quality determination unit 44, will be described. Figure 5 is a flowchart showing an example of the quality determination process in this embodiment. The process shown in Figure 5 is performed by the quality determination unit 44 until the welding process is completed for all welding locations on the workpiece W.

[0033] The quality determination unit 44 acquires the detection result of the strain sensor 17 for the current welding location WP (step ST20). Next, the quality determination unit 44 calculates the amount of deformation in the gun axis direction generated in the workpiece W due to welding based on the detection result of the strain sensor 17 (step ST21). During welding, a nugget N is formed in the workpiece W as described above. This causes strain in the first holding part 121 and the second holding part 122 that hold the pair of electrodes 11 due to the formation of the nugget N. Each strain sensor 17 detects the strain generated in the first holding part 121 and the second holding part 122, respectively. The quality determination unit 44 calculates the amount of deformation in the gun axis direction of the workpiece W based on the detected strain of the first holding part 121 and the second holding part 122. Here, the value calculated based on the strain of the first holding part 121 detected by the first strain sensor 171 (based on the amount of deformation) is called "deformation amount ΔC1", and the value calculated from the strain detected by the second strain sensor 172 is called "deformation amount ΔC2". The dashed line in Figure 4 shows an example of how the deformation amounts ΔC1 and ΔC2 change over time.

[0034] As described above, in the comparative example's welding process, the position ΔPB of the pair of electrodes 11 changes during energization. Therefore, in order to calculate the amount of deformation of the workpiece W in the gun axis direction, the change in position ΔPB must be considered in addition to the amount of deformation of the first holding part 121 and the second holding part 122 in the gun axis direction detected by each strain sensor 17. In this case, it is required to perform the calculation by matching the detection time of the position ΔPB detected by the position sensor 16 and the strain detected by each strain sensor 17 as accurately as possible. However, the welding process is performed in a very short time. Furthermore, the state of the weld changes in an even shorter time. Therefore, it may be difficult to accurately match an arbitrary detection time, and there is a high probability that the deformation amounts ΔC1 and ΔC2 of the workpiece W cannot be calculated accurately in the comparative example's welding process.

[0035] In contrast, in the welding process of this embodiment, the position ΔPA of the pair of electrodes 11 does not change during energization. Therefore, there is no need to consider the position ΔPA when calculating the deformation amounts ΔC1 and ΔC2 of the workpiece W, and the deformation amounts ΔC1 and ΔC2 of the workpiece W can be calculated accurately using the detection results of each strain sensor 17. The deformation amounts ΔC1 and ΔC2 should be values ​​at appropriate points in time for determining the quality of the diameter of the nugget N during the period when the nugget N is formed on the workpiece W, that is, during the period when the nugget N expands and contracts (times t2 to t4). For example, the deformation amounts ΔC1 and ΔC2 are values ​​at the end of energization (time t3 in Figure 4) or at the end of the cooling period (time t4). Furthermore, the deformation amounts ΔC1 and ΔC2 may be deformation waveforms for the entire period or a part of the period during which the nugget N is formed, and the allowable range ΔCref, which will be described later, may also be set relative to the deformation waveform.

[0036] Next, the quality determination unit 44 uses the calculated deformation amounts ΔC1 and ΔC2 as the degree of deformation of the workpiece W and determines whether the deformation amounts ΔC1 and ΔC2 are within a predetermined tolerance range ΔCref (step ST22). Figure 6 is an explanatory diagram showing an example of the tolerance range ΔCref. In the example shown in Figure 6, tolerance ranges ΔCref 11, ΔCref 12, and ΔCref 13 are set corresponding to the welding locations WP11, W12, and W13 set on the workpiece W1. Also, tolerance ranges ΔCref 21, ΔCref 22, and ΔCref 23 are set corresponding to the welding locations WP21, WP22, and W23 set on workpiece W2, which is of a different type from workpiece W1. In this way, the tolerance range ΔCref should be predetermined by experimentation or analysis to a value that indicates a good state in which the diameter of the nugget N has grown without excess or deficiency, according to the type of workpiece W and the welding location WP. The type of workpiece W can be classified according to various conditions, such as the material of the workpiece W, or it can be classified according to the combination of workpieces W to be joined. Furthermore, the welding location WP can be classified according to various conditions, such as plate thickness and shape.

[0037] If the quality determination unit 44 determines that both deformation amounts ΔC1 and ΔC2 are within the allowable range ΔCref (Yes in step ST22), it determines that the nugget diameter of the workpiece W at the current welding location WP is good (the welding condition is good) (step ST23). On the other hand, if the quality determination unit 44 determines that either deformation amount ΔC1 or ΔC2 is not within the allowable range ΔCref (No in step ST22), it determines that the nugget diameter of the workpiece W at the current welding location WP is poor (the welding condition is poor) (step ST24).

[0038] Next, the quality determination unit 44 determines whether the quality determination has been completed for all welding locations WP set on the workpiece W (step ST25). If the quality determination unit 44 determines that the quality determination has not been completed for all welding locations WP (No in step ST25), it repeats the process from step ST20 onwards for the next welding location WP. In this way, the quality determination described above is repeatedly performed until the quality determination is completed for all welding locations WP.

[0039] On the other hand, if the quality determination unit 44 determines that quality determination has been completed for all welding locations WP (Yes in step ST25), it determines whether the proportion of good locations, where the diameter of the nugget N is determined to be good, is above a predetermined proportion for all welding locations WP (step ST26). If the quality determination unit 44 determines that the proportion of good locations is above a predetermined proportion (Yes in step ST26), it determines the welding condition of the entire workpiece W as "pass" (step ST27). On the other hand, if the quality determination unit 44 determines that the proportion of good locations is below a predetermined proportion (No in step ST26), it determines the welding condition of the entire workpiece W as "fail" (step ST28).

[0040] Figure 7 is an explanatory diagram showing an example of the pass / fail criteria for each workpiece W. For example, suppose that for a certain workpiece W1, the predetermined ratio is set at 0.98 ("98 (%)" in the figure), and for workpieces W2 and W3, which are different from workpiece W1, the predetermined ratio is set at 0.99 ("99 (%)" in the figure). In this case, workpiece W1 has a ratio of good areas equal to or greater than the predetermined ratio of 0.99 ("99 (%)" in the figure), and workpiece W2 has a ratio of good areas equal to or greater than the predetermined ratio of 0.995 ("99.5 (%)" in the figure), so the welding condition is considered acceptable. On the other hand, in workpiece W3, the ratio of good areas is less than the predetermined ratio of 0.98 ("98 (%)" in the figure), so the welding condition is considered unacceptable. The predetermined ratio should be set to meet the welding quality standards determined according to the type of workpiece W. The predetermined ratio may be set to the same value for all workpieces W. Alternatively, the predetermined ratio may be set to a ratio of 1 (value 100 (%)). Once the determination of the welding condition of the entire workpiece W is complete, the quality determination unit 44 terminates the routine shown in Figure 5.

[0041] (Effects of the Embodiment) As described above, in the welding quality determination system 100 of the embodiment, it is not necessary to consider the change in the position ΔPA of the pair of electrodes 11 when calculating the deformation amounts ΔC1 and ΔC2 of the workpiece W, and the deformation amounts ΔC1 and ΔC2 can be calculated with high accuracy from the detection results of each strain sensor 17. Therefore, the welding quality determination system 100 can accurately determine the quality of the diameter of the nugget N, and the accuracy of welding quality determination can be further improved. In addition, the welding quality determination system 100 can easily perform quality determination as a 100% inspection for each welding location WP. Therefore, it is not necessary to perform sampling inspections such as chisel inspections to check the welding condition, and the manufacturing man-hours for the product can be reduced.

[0042] Further, when the pressing force reaches the first predetermined pressing force (predetermined pressing force), the position control unit 43 sets the positions of the first electrode 111 and the second electrode 112 as a predetermined welding position, and controls the drive motor 14 so that the first electrode 111 and the second electrode 112 are held at the predetermined welding position during the welding of the work W. With this configuration, the welding quality determination system 100 can apply an appropriate pressing force to the work W and ensure the welding quality.

[0043] Furthermore, the degree of deformation of the work W is the deformation amounts ΔC1 and ΔC2 of the work W included in any period during which the nugget N occurs in the work W. With this configuration, the welding quality determination system 100 can determine the quality of the diameter of the nugget N using the deformation amounts ΔC1 and ΔC2, thereby suppressing the complication of the process.

[0044] Then, when both of the deformation amounts ΔC1 and ΔC2 are within the allowable range ΔCref, the pass / fail determination unit 44 determines that the diameter of the nugget N is good, and when either one of the deformation amounts ΔC1 and ΔC2 is not within the allowable range ΔCref, the pass / fail determination unit 44 determines that the diameter of the nugget N is bad. With this configuration, the welding quality determination system 100 can more accurately determine the quality of the diameter of the nugget N.

[0045] In addition, when the proportion of good locations is equal to or greater than a predetermined proportion with respect to all the welding locations WP set on the work W, the pass / fail determination unit 44 determines that the welding state of the entire work W is acceptable, and when the proportion of good locations is less than the predetermined proportion with respect to all the welding locations WP, the pass / fail determination unit 44 determines that the welding state of the work is unacceptable. With this configuration, the welding quality determination system 100 can easily determine whether the welding quality of the entire work W satisfies a sufficient quality. Therefore, it is not necessary to perform sampling inspection as described above.

[0046] Furthermore, the tolerance range ΔCref is predetermined according to the type of workpiece W (Figure 6). With this configuration, the welding quality determination system 100 can set an appropriate tolerance range ΔCref corresponding to the characteristics of the type of workpiece W, such as the material. Furthermore, the tolerance range ΔCref is predetermined according to the welding location WP set on the workpiece W. With this configuration, the welding quality determination system 100 can set an appropriate tolerance range ΔCref corresponding to the characteristics of the welding location WP, such as the plate thickness and shape.

[0047] Figure 8 is an explanatory diagram showing another example of the tolerance range ΔCref. The tolerance range ΔCref may be predetermined according to the welding order of the welding points WP set on the workpiece W. In Figure 8, as an example, the welding order is set so that welding point WP31 is welded first, welding point WP32 is welded second, and welding point WP33 is welded third, and tolerance ranges ΔCref31, ΔCref32, and ΔCref33 are set corresponding to each welding order. This makes it possible to set an appropriate tolerance range ΔCref for each welding order.

[0048] Further, the degree of deformation of the workpiece W may be the changing tendency of the deformation amounts ΔC1 and ΔC2 included in the period (time t2 to t4) during which the nugget N is formed on the workpiece W. More specifically, the changing tendency may be, for example, the deformation speed as the time differential value of the deformation amounts ΔC1 and ΔC2. The pass / fail determination unit 44 can, for example, determine that the welding state is poor because the nugget N has not grown sufficiently when the deformation speed is too slow, or determine that the welding state is poor because spatter may occur during welding when the deformation speed is too fast. When the deformation speed is used as an index value of the degree of deformation in this way, the allowable range is set as the allowable range ΔVref (mm / s) of the deformation speed as shown in FIG. 9. In this example, allowable ranges ΔVref11, ΔVref12, and ΔVref13 are set corresponding to the welding locations WP11, WP12, and WP13. Thereby, the welding pass / fail determination system 100 can monitor the growth tendency of the nugget N based on the above-described change speed and perform a pass / fail determination of the diameter of the nugget N. Further, since the welding pass / fail determination system 100 only needs to calculate the deformation speed from the deformation amounts ΔC1 and ΔC2, it can suppress the complication of the processing. Note that the changing tendency may be an integral value within a predetermined period of the deformation amounts ΔC1 and ΔC2 or the like.

[0049] Furthermore, the degree of deformation of the workpiece W may be the maximum values ​​of the deformation amounts ΔC1 and ΔC2 during the period (times t2 to t4) when the nugget N is formed on the workpiece W. The quality determination unit 44 can, for example, determine that the nugget N has not grown sufficiently and the welding condition is poor if the maximum values ​​of the deformation amounts ΔC1 and ΔC2 are small compared to the allowable range ΔCmref, and determine that the welding condition is poor if the maximum values ​​of the deformation amounts ΔC1 and ΔC2 are large compared to the allowable range ΔCmref, as there is a risk that the workpiece W has been damaged due to excessive heat input. When the maximum values ​​of the deformation amounts ΔC1 and ΔC2 are used as indicator values ​​for the degree of deformation in this way, the allowable range is set as the allowable range ΔCmref (mm) of the maximum values ​​of the deformation amounts ΔC1 and ΔC2, as shown in Figure 10. In this example, the allowable ranges ΔCmref11, ΔCmref12, and ΔCmref13 are set corresponding to the welding locations WP11, WP12, and WP13. As a result, the welding quality determination system 100 can determine the quality of the nugget N diameter based on the amount of deformation of the workpiece W at the peak of nugget N growth. Furthermore, since the welding quality determination system 100 only needs to extract the maximum value from the deformation amounts ΔC1 and ΔC2 during the period in which the nugget N is formed and compare it with the above-mentioned allowable range ΔCmref, the complexity of the processing can be suppressed compared to when the entire deformation waveform is analyzed.

[0050] Furthermore, the welding quality determination system 100 may determine the quality of the diameter of the nugget N by combining the deformation amounts ΔC1, ΔC2, the maximum values ​​of the deformation amounts ΔC1, ΔC2, and the trend of change of the deformation amounts ΔC1, ΔC2 during the period (times t2 to t4) in which the nugget N is formed on the workpiece W as index values. The welding quality determination system 100 may, for example, determine that the welding condition of the workpiece W is good if all three index values ​​are within the corresponding allowable range described above, and determine that the welding condition of the workpiece W is poor if any one of them is outside the corresponding allowable range. Alternatively, the welding quality determination system 100 may, for example, determine that the welding condition of the workpiece W is good if one or more of the three index values ​​are within the corresponding allowable range, and determine that the welding condition of the workpiece W is poor if all three index values ​​are outside the corresponding allowable range. As described above, the welding quality determination system 100 may use at least one of the deformation amounts ΔC1, ΔC2, the maximum values ​​of the deformation amounts ΔC1, ΔC2, and the trend of change of the deformation amounts ΔC1, ΔC2 as the degree of deformation (index value).

[0051] This concludes the description of the embodiments, but the embodiments of this disclosure are not limited to these embodiments. For example, in this embodiment, the deformation amounts ΔC1 and ΔC2 are calculated from the detection results of the first strain sensor 171 and the second strain sensor 172 to determine whether the diameter of the nugget N is good or bad. However, as long as the reliability of the good or bad determination can be ensured, either the first strain sensor 171 or the second strain sensor 172 may be omitted, and the good or bad determination may be made based on the detection result of the other.

[0052] Furthermore, in this embodiment, the welding quality determination system 100 determines the quality of the diameter of the nugget N using the degree of deformation based on the deformation amounts ΔC1 and ΔC2 of the workpiece W in the gun axis direction. However, the welding quality determination system 100 may also obtain the strain in the gun axis direction of the workpiece W from the strain detected by the strain sensor 17, set the above-mentioned tolerance range values ​​for the strain of the workpiece W itself and the trend of changes such as strain rate, and then determine the quality of the diameter of the nugget N.

[0053] Furthermore, the welding quality determination system 100 may calculate the sum of the deformation amounts ΔC1 and ΔC2 within a predetermined period included in time t2 to t4, and use the calculated sum as the degree of deformation (index value). The same applies to deformation speed, strain, and strain speed.

[0054] Furthermore, the welding quality determination system 100 may include a resistance value measuring device (index value acquisition unit) for measuring the resistance value of the workpiece W while current is being supplied to the pair of electrodes 11. The resistance value measuring device may be of a well-known configuration. During welding, for example, the contact resistance between the pair of electrodes 11 and the workpiece W, and the contact resistance between the workpieces W themselves, changes depending on the pressure applied to the workpiece W. That is, if the pressure changes due to the generation of nuggets N, the above-mentioned contact resistance may also change.

[0055] Therefore, the quality determination unit 44 may use the change in resistance value as an index value that can be used as the degree of deformation, based on the resistance value of the workpiece W detected by the resistance value measuring device. In other words, the above-mentioned tolerance range may be set in advance for the change in the resistance value of the workpiece W. The quality determination unit 44 may then determine that the diameter of the nugget N is good if the change in the resistance value of the workpiece W is within a predetermined tolerance range, and determine that the diameter of the nugget N is poor if the change in the resistance value of the workpiece W is not within a predetermined tolerance range.

[0056] The "change in resistance" may be, for example, the value at any point in time t2 to t4, based on the resistance of the workpiece W before the start of the welding process, or it may be the sum of the changes in resistance within a predetermined period included in time t2 to t4.

[0057] 1 Welding apparatus 10 Welding gun 11 Pair of electrodes 111 First electrode 112 Second electrode 12 Holding member 121 First holding part 122 Second holding part 14 Drive motor 15 Pressure sensor (Pressure acquisition unit) 16 Position sensor (Position acquisition unit) 17 Strain sensor (Index value acquisition unit) 171 First strain sensor (First deformation amount acquisition unit) 172 Second strain sensor (Second deformation amount acquisition unit) 20 Robot 30 Power supply control device 40 Control device 41 Robot control unit 42 Power supply control unit 43 Position control unit 44 Quality judgment unit 100 Weld quality judgment system N Nugget W, W1 to W3 Workpiece WP, WP11 to WP33 Welding location ΔC1, ΔC2 Deformation amount ΔCref, ΔCref11 to ΔCref33 Allowable range of deformation ΔVref, ΔVref11 to ΔVref33 Allowable range of deformation speed

Claims

1. A welding quality determination system applied to a welding apparatus that performs welding of a workpiece by clamping the workpiece between a first electrode and a second electrode that can move coaxially closer to and further apart from each other by a driving force from a drive motor, and by passing current between the first electrode and the second electrode, the system determines the quality of the weld by determining the quality of the diameter of the nugget generated on the workpiece, comprising: an index value acquisition unit that acquires the amount of deformation of the workpiece or the resistance value of the workpiece along the direction in which the first electrode and the second electrode are aligned; a position acquisition unit that acquires the positions of the first electrode and the second electrode; a position control unit that controls the drive motor so that the first electrode and the second electrode are held in predetermined welding positions during welding of the workpiece based on the positions acquired by the position acquisition unit; and a quality determination unit that determines that the diameter of the nugget is good if the degree of deformation of the workpiece or the amount of change in the resistance value based on the acquisition results of the index value acquisition unit during welding of the workpiece is within a predetermined allowable range, and determines that the diameter of the nugget is poor if the degree of deformation or the amount of change in the resistance value is not within the allowable range. A welding quality determination system equipped with the following features.

2. A welding quality determination system according to claim 1, further comprising: a pressure acquisition unit that acquires the pressure applied to the workpiece from the first electrode and the second electrode; and a current control unit that energizes the first electrode and the second electrode when the pressure acquired by the pressure acquisition unit reaches a predetermined pressure, wherein the position control unit controls the drive motor so that the first electrode and the second electrode are held at the predetermined welding position during welding of the workpiece, with the positions of the first electrode and the second electrode when the pressure reaches the predetermined pressure being the predetermined welding position.

3. The welding quality determination system according to claim 1 or 2, wherein the degree of deformation of the workpiece is at least one of the amount of deformation of the workpiece, the maximum value of the amount of deformation, and the trend of change of the amount of deformation, which are included in any of the periods during which the nugget is formed on the workpiece.

4. The welding quality determination system according to claim 1 or 2, wherein the index value acquisition unit includes a first deformation amount acquisition unit that acquires the deformation amount of the workpiece based on the deformation amount of a first holding part that holds the first electrode, and a second deformation amount acquisition unit that acquires the deformation amount of the workpiece based on the deformation amount of a second holding part that holds the second electrode, and the quality determination unit determines that the diameter of the nugget is good when both the degree of deformation based on the acquisition results of the first deformation amount acquisition unit and the second deformation amount acquisition unit are within the allowable range, and determines that the diameter of the nugget is poor when either the degree of deformation based on the acquisition results of the first deformation amount acquisition unit and the second deformation amount acquisition unit is outside the allowable range.

5. The welding quality determination system according to claim 1 or 2, wherein the tolerance range is predetermined according to the type of workpiece.

6. The welding quality determination system according to claim 1 or 2, wherein the tolerance range is predetermined according to the welding location set on the workpiece.

7. The welding quality determination system according to claim 1 or 2, wherein the tolerance range is predetermined according to the welding order of the welding locations set on the workpiece.

8. The welding quality determination system according to claim 1 or 2, wherein the quality determination unit determines that the welding condition of the entire workpiece is acceptable if the number of good locations, which are welding locations where the diameter of the nugget is determined to be good, is equal to or greater than a predetermined proportion of all the welding locations set on the workpiece, and determines that the welding condition of the entire workpiece is unacceptable if the number of good locations is less than the predetermined proportion of all the welding locations.

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