Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K11/00—Resistance welding; Severing by resistance heating
  • B23K11/10—Spot welding; Stitch welding
  • B23K11/11—Spot welding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K11/00—Resistance welding; Severing by resistance heating
  • B23K11/24—Electric supply or control circuits therefor

Definitions

• the present invention relates to a method for manufacturing resistance spot welded joints.
• the diameter of the nugget will also be referred to as the nugget diameter.
• the nugget diameter is determined by the welding conditions, such as the pressure, welding current, and welding time. Therefore, to obtain a nugget diameter within the appropriate range, the above welding conditions must be set appropriately according to the conditions of the workpiece, such as the material, plate thickness, and number of overlapping sheets.
• a resistance spot welding method in which a workpiece made of overlapping metal plates is sandwiched between a pair of electrodes and joined by applying current while applying pressure, A main welding and a test welding prior to the main welding are performed, and the test welding is performed under two or more welding conditions,
• a pre-energization is performed by constant current control using the same energization pattern, and the electrical characteristics between the electrodes at the time of the pre-energization are stored;
• current is applied under constant current control, and a time change curve of the instantaneous heat generation amount per unit volume and a cumulative heat generation amount per unit volume calculated from the electrical characteristics between the electrodes when an appropriate nugget is formed are stored;
• a preliminary current is applied by constant current control using the same current pattern as the test welding, and the electrical characteristics between the electrodes in the preliminary current are compared with the electrical characteristics between the electrodes stored in the preliminary current
• the time change curve of the instantaneous heat generation per unit volume and the cumulative heat generation per unit volume in the main current for the test welding stored under the welding conditions with the smallest difference are set as target values for the main current for the main welding.
• adaptive control welding is performed in which the current supply amount is controlled in accordance with the target value. Resistance spot welding method. and disclosed it in Patent Document 1.
• Patent Document 1 makes it possible to obtain a nugget diameter within an appropriate range without expulsion, even when disturbances are present.
• a difference may occur between the nugget diameter of the resistance spot welded joint actually obtained by the actual welding and the target diameter (hereinafter also referred to as nugget diameter deviation). Improvements in this area are currently desired from the perspective of further improving product precision.
• the difference between the inter-electrode electrical characteristics of the pre-current in the actual welding and the inter-electrode electrical characteristics of the pre-current in each test welding was compared, and the test welding pattern that minimized the difference was selected (hereinafter also referred to as comparing the inter-electrode electrical characteristics of the pre-current).
• the time change curve for the main current stored in the selected test welding is set as the target value, and the main current for the main welding is performed using adaptive control welding. The inventors believe that this may reduce deviations in nugget diameter.
• the inventors then conducted further experiments and studies. As a result, they discovered that by reducing the pressure applied during the pre-current application of test welding, particularly to less than 2.5 kN, it is possible to consistently reduce deviations in nugget diameter.
• the intensity of the disturbance is reflected in the electrical characteristics between the electrodes during pre-current, preferably the integrated value of the inter-electrode resistance.
• This improves the accuracy of selecting the optimal time change curve, etc. of test welding, as the target value for the actual current in actual welding.
• the time change curve, etc. obtained under conditions similar to the disturbance condition in actual welding hereinafter also referred to as target value selection accuracy in actual welding.
• target value selection accuracy in actual welding As a result, deviations in nugget diameter are consistently reduced, making it possible to consistently obtain nuggets of the target diameter.
• the present invention was completed based on the above findings and further investigation. Specifically, the gist of the present invention is as follows:
• a method for manufacturing a resistance spot welded joint in which a workpiece made of overlapping metal plates is sandwiched between a pair of electrodes and joined by applying pressure and passing current through the workpiece, thereby obtaining a resistance spot welded joint, Main welding and test welding prior to the main welding are performed, and the test welding is performed in two or more patterns, In the test welding, for each of the patterns, Pre-energization is performed under constant current control under the same energization conditions and with a pressure of less than 2.5 kN, and the electrical characteristics between the electrodes during pre-energization are stored.
• the main current application current is applied under constant current control, and the time change curve of the instantaneous heat generation amount per unit volume and the cumulative heat generation amount per unit volume at which a nugget having a target diameter is formed are stored; Furthermore, in the main welding, A preliminary current is applied under constant current control under the same current conditions as the preliminary current for the test welding, and the electrical characteristics between the electrodes in the preliminary current are compared with the electrical characteristics between the electrodes stored in the preliminary current for the test welding for each pattern. The time change curve of the instantaneous heat generation per unit volume and the cumulative heat generation per unit volume in the main current for the test welding, which are stored in the pattern with the smallest difference, are set as target values for the main current for the main welding. Next, as the main current supply, adaptive control welding is performed in which the current supply amount is controlled in accordance with the target value. Method for manufacturing resistance spot welded joints.
• test welding is performed by simulating the same type of disturbance using two or more patterns.
• the present invention makes it possible to minimize deviations in nugget diameter and consistently obtain nuggets of the target diameter, regardless of the type or degree of disturbance.
• the present invention makes it possible to effectively respond to fluctuations in the state of disturbance and obtain nuggets of the target diameter, which is extremely advantageous in terms of improving product precision.
• a welding device that can be used in a manufacturing method for a resistance spot welded joint according to one embodiment of the present invention may be equipped with a pair of upper and lower electrodes, and be capable of freely controlling the pressure and welding current during welding.
• the pressure mechanism air cylinder, servo motor, etc.
• type stationary, robot gun, etc.
• electrode shape etc.
• the device may also be equipped with a memory device that stores time-varying curves, etc.
• the term "gap” refers to the gap (distance between the mating surfaces) between the metal plates that will be welded together (before pressure is applied by the electrodes).
• the gap variation for each test welding pattern may or may not be constant.
• the test welding should simulate gaps between the metal plates where gaps are expected to occur during actual welding (actual welding). In this case, for example, the gap should be simulated between the outermost plate (the metal plate positioned farthest out in the material to be welded) and the metal plate adjacent to that outermost plate.
• Clearance is the gap between the electrode and the metal plate (the distance between the opposite electrode and the metal plate when one electrode first comes into contact with the metal plate during welding).
• the impact angle is the inclination of the electrode relative to the direction perpendicular to the surface of the metal plate. In this case, it is preferable to perform test welding in multiple patterns in which the impact angle is varied between 0 degrees (no impact angle) and 10 degrees, for example, no impact angle, impact angle: 1 degree, impact angle: 5 degrees, and impact angle: 10 degrees (disturbance strength).
• Misalignment is the distance between contact points 1 and 2 on the same plane (a plane parallel to the surface of the metal plate) when viewed from a direction perpendicular to the surface of the metal plate.
• contact point 1 is the point of contact between one electrode and the surface of the metal plate.
• Contact point 2 is the point of contact between the other electrode and the surface of the metal plate.
• preliminary current and main current are applied for each pattern as follows:
• test welding pre-current is controlled by constant current control, and the electrical characteristics between the electrodes during the pre-current are stored.
• applied pressure preset applied pressure
• the current value I1 during pre-current test welding is preferably in the range of 1 to 2 kA.
• the current duration T1 during pre-current test welding is preferably in the range of 20 to 100 ms.
• Test welding actual current In test welding, a pre-current is applied for each pattern, followed by a main current. In the main current application for test welding, current is applied under constant current control to form a nugget of the target diameter, and the time change curve of the instantaneous heat generation per unit volume and the cumulative heat generation per unit volume are stored.
• Test welding patterns other than those described above are not particularly limited. Test welding patterns can be set, for example, by conducting preliminary welding tests in advance (specifically, using welded materials of the same steel type and thickness as those actually used, and conducting welding under various conditions with constant current control, either in a state simulating the above-mentioned disturbances or in a state without any disturbances).
• the actual welding is carried out.
• the preliminary current and the actual current are applied as follows.
• Pre-current for actual welding In the actual welding, first, a pre-current is applied under constant current control under the same current conditions as in the test welding. Then, the electrical characteristics between the electrodes in the pre-current are compared with the electrical characteristics between the electrodes stored in the pre-current for the test welding for each pattern, and the time change curve for the actual current for the test welding stored in the pattern with the smallest difference is set as the target value for the actual current for the actual welding.
• pre-current is performed using constant current control under the same current conditions as the pre-current for test welding
• pressure, current value, and current duration are set to the same values as those used for pre-current for test welding, and pre-current for actual welding is performed using constant current control.
• an error of around 5% is acceptable for the pressure, current value, and current duration.
• Adaptive control welding can be performed, for example, using a control device that directly measures or calculates changes in the current value, interelectrode voltage, interelectrode resistance, and heat generation amount during welding as electrical signals and controls input parameters such as the current value and interelectrode voltage based on these values.
• the amount of heat generated can be calculated, for example, from the electrical characteristics between the electrodes. There are no particular restrictions on the method for calculating the amount of heat generated, but the method disclosed in Japanese Patent Application Laid-Open No. 11-33743, for example, can be used.
• the calculation method for the amount of heat generated per unit volume and unit time q and the cumulative amount of heat generated per unit volume Q using this method is as follows:
• the amount of heat generated per unit volume and unit time q can be calculated from the inter-electrode voltage V, the total thickness t' of the workpieces to be welded, and the electrical resistivity r of the workpieces, and is not affected by the contact area S between the electrode and workpiece.
• equation (3) calculates the amount of heat generated from the inter-electrode voltage V
• equation (3) calculates the amount of heat generated q from the current value I, and in this case, there is no need to use the contact area S between the electrode and workpieces.
• the cumulative amount of heat generated per unit volume Q can be obtained.
• this cumulative amount of heat generated per unit volume Q can also be calculated without using the contact area S between the electrode and workpieces to be welded. Needless to say, other calculation formulas may also be used.
• the method can be used to weld steel sheets of various strengths, from mild steel to ultra-high tensile steel sheets, as well as plated steel sheets and light metal sheets such as aluminum alloys, and can also be used to weld sheet assemblies consisting of three or more stacked steel sheets. Furthermore, steel sheets with a plated layer may be placed on the surface that comes into contact with the electrode.
• test welding was performed under the conditions shown in Table 2, and actual welding was performed under the conditions shown in Table 3 to produce resistance spot welded joints.
• plating column in Table 1 no listing indicates unplated steel sheet, and GA indicates galvannealed steel sheet.
• the cycle unit of current flow time in Table 2 refers to cycles at 50 Hz. At 50 Hz, one cycle is 20 ms, so for example, 16 cycles is 320 ms.
• the same current conditions were used for each pattern, and a pre-current was applied using constant current control, with the integral value of the inter-electrode resistance during this pre-current being stored. Furthermore, for the actual current application, current was applied using constant current control, and the time change curve of the instantaneous heat generation per unit volume that results in the formation of a nugget of the target diameter, as well as the cumulative heat generation per unit volume, were stored.
• the target diameter for the nuggets was 4.0 ⁇ t for all patterns.
• a pre-current was applied using constant current control under the same current conditions as the test welding. Furthermore, the integral value of the inter-electrode resistance during the pre-current for the actual welding was compared for each pattern with the integral value of the inter-electrode resistance stored during the pre-current for the test welding. The time-varying curve of the instantaneous heat generation per unit volume and the cumulative heat generation per unit volume for the actual current stored for the pattern with the smallest difference were set as the target values for the actual current for the actual welding. Then, for the actual current for the actual welding, adaptive control welding was performed, controlling the amount of current according to these target values.

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  • 2024-12-11 JP JP2025515494A patent/JPWO2025203912A1/ja active Pending
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