A method of controlling current waveform of resistance welding spot

Abstract

The application discloses a current waveform control method of resistance welding spot, and belongs to the technical field of resistance spot welding quality control. The method first collects welding current and electrode voltage in real time in the actual production process of resistance spot welding, calculates a dynamic resistance curve, obtains the integral of the welding spot heat at each moment according to the Joule law, forms a waveform diagram of the welding spot heat according to time, fits a broken line diagram of the welding spot heat by using the least square method, calculates the cosine value x of the angle between the welding spot heat broken line and the time axis, and finally controls the welding spot quality through analysis of the value. The application takes the cosine value of the angle between the fitting straight line of the welding spot heat and the time axis as the basis for the welding process control, reflects the state of the welding spot nugget through threshold comparison, further realizes the judgment of the welding spot quality, effectively improves the efficiency of the welding spot quality control, and has obvious effects.

Description

Technical Field

[0001] The invention relates to the field of welding technology, and in particular to a method for controlling the current waveform of resistance welding joints. Background Technology

[0002] Resistance spot welding is a widely used welding method for joining metal parts, especially in the welding of thin sheet metal parts, such as in automobile manufacturing. Weld quality is the most crucial factor in determining the qualification of resistance spot welding. It is mainly determined by measuring aspects such as the size of the weld nugget, tensile and shear force, and torsional strength. However, the inspection of weld quality often requires destructive methods such as disassembly and cutting. While non-destructive testing using ultrasonic waves exists, these methods have limitations, such as damaging the integrity of the parts, rendering them unusable, requiring the application of ultrasonic coupling agents, and low efficiency. Therefore, a non-destructive, convenient, and rapid method for controlling resistance spot welding quality is needed to effectively improve weld quality and eliminate the need for frequent disassembly and other destructive operations.

[0003] Existing resistance spot welding is a complex process involving multiple coupled parameters, which presents challenges to controlling weld quality. Resistance spot welding involves applying a current to a metal workpiece using upper and lower electrodes. According to Joule's law, the heat generated by current passing through a conductor is proportional to the square of the current, the conductor's resistance, and the duration of the current flow. In resistance spot welding, the contact resistance between the workpieces accounts for a large portion of the current loop resistance; therefore, welding heat primarily occurs at the contact surface between the two workpieces. Over time, the heat gradually accumulates, eventually reaching the melting point of the workpieces, causing the contact surface to melt. Under the pressure of the upper and lower electrodes, the two workpieces eventually form a solid connection, creating the final weld. Therefore, the welding heat is related to the size of the weld nugget, which directly affects the weld's tensile and torsional strength, among other weld quality criteria, thus enabling quality control. Therefore, the formation of a weld is closely related to the heat applied to it, and similarly, the quality of the weld is also related to the heat applied to it.

[0004] In summary, how to design a current waveform control method suitable for resistance welding joints, and combine the above factors to achieve optimal quality control of the welding joints, has become a technical problem that urgently needs to be solved by those in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a current waveform control method for resistance welding joints. This method uses the cosine value of the angle between the weld joint heat fitting line and the time axis as the basis for welding process control, and reflects the state of the weld joint nucleus through threshold comparison, thereby further enabling the judgment of weld joint quality.

[0006] A method for controlling the current waveform of a resistance welding joint includes the following steps:

[0007] Step 1: First, collect the welding current and inter-electrode voltage during the actual resistance spot welding production process;

[0008] Step 2: According to Ohm's law, divide the voltage and current to calculate the dynamic resistance r in real time;

[0009] Step 3: Obtain a standard dynamic resistance curve from the production process;

[0010] Step 4: According to Joule's law, calculate the heat q on the solder joint based on the standard resistance curve, that is, calculate the integral of the heat over time t, expressed as follows: ;

[0011] Step 5: Plot a curve of heat versus time with time as the horizontal axis and q as the vertical axis.

[0012] Step 6: Fit a straight line to the curve of heat q using the least squares method;

[0013] Step 7: Calculate the angle between the fitted line and the horizontal axis. ;

[0014] Step 8: Weld the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot the fitted straight line using the least squares method to calculate the angle with the horizontal axis. 1. As a basis for the magnitude of the output current of the control system;

[0015] Step 9: Perform welding on the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot a fitted straight line using the least squares method to calculate the angle between the line and the horizontal axis. 1. As a basis for the output current timing of the control system;

[0016] Step 10, after welding is completed, according to the final... 1 and The upper and lower limits of the threshold are compared to determine the quality.

[0017] Preferably, step 3 further includes the following sub-steps:

[0018] Step 3.1: Obtain a set of dynamic resistance curves for qualified solder joints, typically 20-50 in total;

[0019] Step 3.2: Select a subset of curves with good consistency as the fitting curves, generally controlling it to be within 80% of the total.

[0020] Step 3.3: Calculate the mean value of each point of a set of fitted curves to obtain the standard resistance array, and plot the standard resistance curve;

[0021] Step 3.4: At the end of the standard resistance curve, there should be a period where the resistance value remains basically unchanged.

[0022] Preferably, step 4 further includes the following sub-steps:

[0023] Step 4.1: In the initial stage of current output, the resistance heat mainly acts on the electrode and the workpiece surface. At this time, the resistance is relatively large, so the heat generation in this section is not calculated.

[0024] Step 4.2: In the latter part of the curve, there should be a section where the resistance value remains basically unchanged. This indicates that the main role of welding heat is no longer to form a weld nugget, but to be lost through water cooling, heat dissipation, etc., forming a balance between heat generation and heat dissipation. Therefore, when calculating the heat q, the heat generation in this section is not calculated.

[0025] Step 4.3: Based on a typical dynamic resistance curve, consider the two cases mentioned above during the calculation, and only calculate the heat generated within 10-280ms.

[0026] Preferably, step 8 includes the following two cases:

[0027] (1) If q1 is less than q, then increase the current output of the system;

[0028] (2) If q1 is greater than q, then reduce the current output of the system.

[0029] Preferably, step 9 includes three cases:

[0030] (1) If the preset welding time is reached, 1 is still less than And less than the lower limit of the included angle If min, then the final output current magnitude is maintained and the current output time is extended until q1 is equal to q;

[0031] (2) If the preset welding time is reached, 1 greater than And greater than the upper limit of the included angle If the current is maxed out, then stop the current output for this time;

[0032] (3) If the preset welding time is reached, 1 at the upper limit of the included angle max and lower limit If the current output is within a certain timeframe (min), then stop the current output.

[0033] In the above three situations, min and max is a preset value related to The thresholds are the lower limit and the upper limit, respectively; the maximum current extension time is twice the original welding time.

[0034] Preferably, step 10 includes the following two cases:

[0035] (1) If 1 less than min indicates a cold solder joint;

[0036] (2) If 1 greater than The value is max, indicating over-soldering.

[0037] The advantages and technical effects of this invention are as follows:

[0038] The present invention discloses a current waveform control method for resistance welding joints. First, during the actual production process of resistance spot welding, the welding current and inter-electrode voltage are collected in real time to calculate the dynamic resistance curve. Then, the integral of the heat of the weld joint at each moment is calculated according to Joule's law. The heat of the weld joint is then plotted as a time-time waveform. The least squares method is used to fit a line graph of the heat of the weld joint. The cosine value x of the angle between the heat of the weld joint line and the time axis is calculated. By analyzing this value, the quality of the weld joint can be controlled.

[0039] This invention provides a current waveform control method for resistance welding joints, solving the problems existing in current resistance spot welding quality control. It calculates the cosine of the angle between the weld joint heat fitting line and the time axis, using this as the basis for welding process control. Furthermore, it reflects the state of the weld nugget through threshold comparison, further enabling the judgment of weld joint quality. In addition, this invention can achieve online control of weld joint quality, better suited to actual working conditions, with greater applicability, improved efficiency in weld joint quality control, and significant effects. Attached Figure Description

[0040] Figure 1 This is a physical image of the actual weld nugget cross-section after applying the method of this invention;

[0041] Figure 2 A physical image of the weld nugget cross-section without applying the method of this invention. Figure 1 (Comparison diagram)

[0042] Figure 3 This is a schematic diagram of a typical dynamic resistance curve in step 4 of the present invention;

[0043] Figure 4 This is a schematic diagram of the heat versus time curve in step 5 of the present invention;

[0044] Figure 5 This is a schematic diagram of the linear fitting of the heat q curve in step 6 of the present invention;

[0045] Figure 6This is a schematic diagram of the actual current and resistance change curves during a single welding process in an embodiment of the present invention;

[0046] Figure 7 This is a schematic diagram of the actual welding heat change curve during a single welding process in an embodiment of the invention. Detailed Implementation

[0047] Embodiments of the invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the invention, and should not be construed as limiting the invention.

[0048] In the description of the invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] A method for controlling the current waveform of a resistance welding joint includes the following steps:

[0050] Step 1: First, collect the welding current and inter-electrode voltage during the actual resistance spot welding production process;

[0051] Step 2: According to Ohm's law, divide the voltage and current to calculate the dynamic resistance r in real time;

[0052] Step 3: Obtain a standard dynamic resistance curve from the production process;

[0053] Step 4: According to Joule's law, calculate the heat q on the solder joint based on the standard resistance curve, that is, calculate the integral of the heat over time t, expressed as follows: ;

[0054] Step 5: Plot a curve of heat versus time with time as the horizontal axis and q as the vertical axis.

[0055] Step 6: Fit a straight line to the curve of heat q using the least squares method;

[0056] Step 7: Calculate the angle between the fitted line and the horizontal axis. ;

[0057] Step 8: Weld the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot the fitted straight line using the least squares method to calculate the angle with the horizontal axis. 1. As a basis for the magnitude of the output current of the control system;

[0058] Step 9: Perform welding on the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot a fitted straight line using the least squares method to calculate the angle between the line and the horizontal axis. 1. As a basis for the output current timing of the control system;

[0059] Step 10, after welding is completed, according to the final... 1 and The upper and lower limits of the threshold are compared to determine the quality.

[0060] Preferably, step 3 further includes the following sub-steps:

[0061] Step 3.1: Obtain a set of dynamic resistance curves for qualified solder joints, typically 20-50 in total;

[0062] Step 3.2: Select a subset of curves with good consistency as the fitting curves, generally controlling it to be within 80% of the total.

[0063] Step 3.3: Calculate the mean value of each point of a set of fitted curves to obtain the standard resistance array, and plot the standard resistance curve;

[0064] Step 3.4: At the end of the standard resistance curve, there should be a period where the resistance value remains basically unchanged.

[0065] Preferably, step 4 further includes the following sub-steps:

[0066] Step 4.1: In the initial stage of current output, the resistance heat mainly acts on the electrode and the workpiece surface. At this time, the resistance is relatively large, so the heat generation in this section is not calculated.

[0067] Step 4.2: In the latter part of the curve, there should be a section where the resistance value remains basically unchanged. This indicates that the main role of welding heat is no longer to form a weld nugget, but to be lost through water cooling, heat dissipation, etc., forming a balance between heat generation and heat dissipation. Therefore, when calculating the heat q, the heat generation in this section is not calculated.

[0068] Step 4.3: Based on a typical dynamic resistance curve, consider the two cases mentioned above during the calculation, and only calculate the heat generated within 10-280ms.

[0069] Preferably, step 8 includes the following two cases:

[0070] (1) If q1 is less than q, then increase the current output of the system;

[0071] (2) If q1 is greater than q, then reduce the current output of the system.

[0072] Preferably, step 9 includes three cases:

[0073] (1) If the preset welding time is reached, 1 is still less than And less than the lower limit of the included angle If min, then the final output current magnitude is maintained and the current output time is extended until q1 is equal to q;

[0074] (2) If the preset welding time is reached, 1 greater than And greater than the upper limit of the included angle If the current is maxed out, then stop the current output for this time;

[0075] (3) If the preset welding time is reached, 1 at the upper limit of the included angle max and lower limit If the current output is within a certain timeframe (min), then stop the current output.

[0076] In the above three situations, min and max is a preset value related to The thresholds are the lower limit and the upper limit, respectively; the maximum current extension time is twice the original welding time.

[0077] Preferably, step 10 includes the following two cases:

[0078] (1) If 1 less than min indicates a cold solder joint;

[0079] (2) If 1 greater than The value is max, indicating over-soldering.

[0080] To more clearly illustrate the specific embodiments of the present invention, an example is provided below:

[0081] The present invention provides a current waveform control method for resistance welding joints, such as... Figure 6 and Figure 7 As shown, the two welding materials are CR590T (1.5mm thick) and CR1180T (1.9mm thick).

[0082] (1) Angle q1 at 100ms Angle 1 greater than q But smaller than At max, reduce the current output at this point, and then... 1 Gradually towards near;

[0083] (2) Φ1 at 275ms and All sizes;

[0084] (3) Φ1 is less than after 275ms But greater than At min, the output current should be increased appropriately.

[0085] (4) The preset welding time was reached at 400ms, but 1 less than Greater than min, at this time maintain the last welding current magnitude and delay for a long time until q1 equals q, and the current output ends at 450ms.

[0086] The cross-sectional view of the weld nugget applied using this method shows that the nugget diameter L1 reached 6.58 mm, indicating good weld quality with no cracks or voids. Figure 1 As shown.

[0087] The cross-sectional view of the weld nugget without applying this method shows a nugget diameter L1 of 6.01 mm. Although the weld joint has good appearance quality, there are gaps in the middle, which will affect the quality of subsequent weld joints. Figure 2 As shown.

[0088] This further demonstrates that the method can effectively improve the quality of solder joints and can be used as a basis for judging the quality of solder joints.

[0089] Finally, any parts of the invention not fully described herein utilize existing mature products and technologies.

[0090] In the description of this specification, references to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in the embodiment or example of the invention.

[0091] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for controlling the current waveform of a resistance welding joint, characterized in that, Includes the following steps: Step 1: First, collect the welding current and inter-electrode voltage during the actual resistance spot welding production process; Step 2: According to Ohm's law, divide the voltage and current to calculate the dynamic resistance r in real time; Step 3: Obtain a standard dynamic resistance curve during the production process; Step 4: According to Joule's law, calculate the heat q on the solder joint based on the standard resistance curve, that is, calculate the integral of the heat over time t, expressed as follows: ; Step 5: Plot a curve of heat versus time with time as the horizontal axis and q as the vertical axis. Step 6: Fit a straight line to the curve of heat q using the least squares method; Step 7: Calculate the angle between the fitted line and the horizontal axis. ; Step 8: Weld the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot the fitted straight line using the least squares method to calculate the angle with the horizontal axis.

1. As a basis for the magnitude of the output current of the control system; Step 9: Perform welding on the new weld joint. Collect current and voltage data at a certain frequency, calculate the real-time heat q1 of the new weld joint, and plot a fitted straight line using the least squares method to calculate the angle between the line and the horizontal axis.

1. As a basis for the output current timing of the control system; Step 10, after welding is completed, according to the final... 1 and The upper and lower limits of the threshold are compared to determine the quality.

2. The current waveform control method for resistance welding joints according to claim 1, characterized in that: Step 3 further includes the following sub-steps: Step 3.1: Obtain a set of dynamic resistance curves for qualified solder joints, typically 20-50 in total; Step 3.2: Select a subset of curves with good consistency as the fitting curves, generally controlling it to be within 80% of the total. Step 3.3: Calculate the mean value of each point of a set of fitted curves to obtain the standard resistance array, and plot the standard resistance curve; Step 3.4: At the end of the standard resistance curve, there should be a period where the resistance value remains basically unchanged.

3. The current waveform control method for resistance welding joints according to claim 1, characterized in that: Step 4 also includes the following sub-steps: Step 4.1: In the initial stage of current output, the resistance heat mainly acts on the electrode and the workpiece surface. At this time, the resistance is relatively large, so the heat generation in this section is not calculated. Step 4.2: In the latter part of the curve, there should be a section where the resistance value remains basically unchanged. This indicates that the main role of welding heat is no longer to form a weld nugget, but to be lost through water cooling and heat dissipation, forming a balance between heat generation and heat dissipation. Therefore, when calculating the heat q, the heat generation in this section is not calculated. Step 4.3: Based on a typical dynamic resistance curve, consider the two cases mentioned above during the calculation, and only calculate the heat generated within 10-280ms.

4. The current waveform control method for resistance welding joints according to claim 1, characterized in that: Step 8 includes the following two cases: (1) If q1 is less than q, then increase the current output of the system; (2) If q1 is greater than q, then reduce the current output of the system.

5. The current waveform control method for resistance welding joints according to claim 1, characterized in that: Step 9 includes three scenarios: (1) If the preset welding time is reached, 1 is still less than And less than the lower limit of the included angle If min, then the final output current magnitude is maintained and the current output time is extended until q1 is equal to q; (2) If the preset welding time is reached, 1 greater than And greater than the upper limit of the included angle If the current is maxed out, then stop the current output for this time; (3) If the preset welding time is reached, 1 at the upper limit of the included angle max and lower limit If the current output is within a certain timeframe (min), then stop the current output. In the above three situations, min and max is a preset value related to The thresholds are the lower limit and the upper limit, respectively; The maximum current extension time is twice the original welding time.

6. The current waveform control method for resistance welding joints according to claim 1, characterized in that: Step 10 includes the following two cases: (1) If 1 less than min indicates a cold solder joint; (2) If 1 greater than The value is max, indicating over-soldering.

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