Method for prolonging service life of electrode during resistance spot welding of aluminum-zinc plated steel plate

Abstract

The invention provides a method for prolonging the service life of an electrode during resistance spot welding of an aluminum-zinc plated steel plate, which relates to the technical field of welding and comprises the following steps: machining the aluminum-zinc plated steel plate into a preset workpiece; performing pretreatment; setting welding process parameters; welding; the welding spot quality evaluation is used for obtaining the nugget diameter of the welding spot on one hand and comparing the nugget diameter of the welding spot with a preset nugget diameter index on the other hand, and when it is judged that the nugget diameter of the welding spot meets the requirement, shearing force value judgment is executed, and therefore an evaluation result is output; and electrode quality evaluation: on one hand, acquiring the working surface diameter of the electrode, and on the other hand, comparing the working surface diameter change of the electrode with the preset working surface diameter change so as to evaluate the wear condition of the electrode. By optimizing the resistance spot welding process, the current is reduced, so that the instantaneous welding temperature is reduced, the generation of Cu-Zn alloy with poor electrical conductivity and thermal conductivity and the adhesion on the electrode are reduced, the temperature rise of the electrode is delayed, and the service life of the electrode is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method for prolonging the life of electrodes during resistance spot welding of galvanized steel plates. Background Art

[0002] With the development of modern industry, various industries have put forward higher requirements on the corrosion resistance, heat resistance, and processing performance of steel plates. As an important variety, aluminum-zinc-coated steel plates have more superior corrosion resistance than traditional galvanized steel plates. This is because once the zinc layer is damaged, the aluminum layer can form a dense aluminum oxide protective layer to provide additional corrosion resistance. Therefore, it is widely used in industries such as automobile manufacturing and home appliance production.

[0003] Resistance spot welding is an indispensable connection method in its production and processing process. Compared with galvanized steel plates, galvanized steel plates are more sensitive to changes in welding parameters and require more precise control to avoid welding defects. In addition, as an important consumable component of spot welding equipment, the service life of electrodes directly affects production efficiency and production costs. However, during the spot welding process of galvanized steel plates, due to the presence of the galvanized layer, Cu-Zn alloys with weak electrical conductivity and thermal conductivity are easily generated and attached to the electrodes, accelerating the increase in electrode temperature. Under the action of pressure, plastic deformation is increased, and the hardness of the galvanized steel plates is relatively higher. The wear on the electrodes is greater during spot welding, which accelerates the failure of the electrodes. Therefore, extending the service life of electrodes during resistance spot welding of galvanized steel plates has become one of the key issues in large-scale and fast-beat production in industry.

[0004] Patent CN114101883B is a resistance spot welding method for low-melting-point coated steel workpieces. The invention discloses a method for improving the life of resistance spot welding electrodes for low-melting-point coated steel workpieces and reducing the occurrence of surface defects at welds. When performing the resistance spot welding process, this method includes at least 3 stages of welding current pulses, the current action time of each stage does not exceed 100ms, and the cooling time between each stage does not exceed 12ms. Through short-term heating and cooling of multiple pulses, it can effectively avoid overheating of the weld surface, reduce the heat generated between the welding electrode and the coated steel plate, thereby improving the electrode life and reducing the occurrence of surface overheating cracks, thereby improving welding quality.

[0005] Patent CN111673250 Resistance spot welding method for passivated coated steel plate, the invention discloses a resistance spot welding method for passivated coated steel plate, under the conditions of electrode pressure N1, welding time T0≤2cyc, the welding current I0 when the passivated coated steel plate causes coating splashing is determined; after the interval time C, starting from the second pulse, the welding time of each pulse is T ave , under the condition that the interval time between each pulse is C, determine the welding current I that makes the passivated coated steel plate produce weld nugget splashing at the Mth pulseave ; Determine the pulse parameters used for resistance spot welding: there is an interval time C between each pulse; determine the welding current I1 of the first pulse based on I0; based on I ave The welding current I2 from the second pulse to the Mth pulse is determined; wherein, no weld core splashing occurs during the welding process from the second pulse to the Mth pulse; and the method can reduce electrode adhesion and increase electrode life.

[0006] Patent CN102672332A is a method for extending the service life of galvanized thin steel plate resistance spot welding electrodes. The invention discloses a method for extending the service life of galvanized thin steel plate resistance spot welding electrodes. When the galvanized thin steel plates are connected by resistance spot welding, 0.05-0.2mm copper-nickel alloy gaskets are inserted between the upper electrode and the upper plate to be welded, and between the lower electrode and the lower plate to be welded. The method can reduce the electrode end surface temperature, reduce electrode wear, and extend the electrode service life.

[0007] Patent CN101961814A discloses a method for spot welding of hot-dip aluminum-zinc steel sheets. The method discloses a method for spot welding of hot-dip aluminum-zinc steel sheets. An auxiliary metal foil is inserted between the electrode and the coated workpiece to prevent the electrode from being directly adhered to the coating. The combination of the foil and the original electrode can be regarded as a composite electrode. The foil acts as a consumable to isolate the electrode from the workpiece. The foil moves one position for each weld. Due to the addition of the foil, a sub-high temperature zone is formed at the contact between the electrode and the workpiece, and the temperature field in the joint area tends to be uniform, which is conducive to the formation of a molten core between the workpieces.

[0008] In summary, the current methods for extending the service life of electrodes when welding coated steel plates by resistance spot welding either require pulsed welding current, which has high requirements on equipment and is not universal; or require adding metal sheets between the electrode and the workpiece, which is relatively cumbersome, costly, and difficult to apply industrially; and methods for aluminum-zinc coated steel plates are relatively lacking.

[0009] The present invention aims to provide a method for extending the life of electrodes during resistance spot welding of galvanized steel plates from the perspective of optimizing the welding process, thereby solving the problems of severe electrode adhesion and rapid loss during spot welding of galvanized steel plates. Summary of the invention

[0010] According to the above technical problems of serious electrode adhesion and rapid loss in the existing spot welding of galvanized steel plates, a method for extending the life of electrodes in resistance spot welding of galvanized steel plates is provided. The present invention mainly uses technical means to optimize the resistance spot welding process to extend the service life of electrodes.

[0011] The technical means adopted by the present invention are as follows:

[0012] A method for extending the life of electrodes during resistance spot welding of galvanized steel sheets, comprising:

[0013] Galvanized steel plate cutting: processing galvanized steel plate into preset workpieces;

[0014] Pretreatment: pretreatment of the workpiece where welding is to be carried out;

[0015] Welding process parameter settings: pre-pressing time is 40 cyc, electrode pressure is 3.2-3.6 kN, welding current is 7.6-8.0 kA, welding time is 15-18 cyc, and post-weld holding time is 40 cyc;

[0016] Welding: Continuous spot welding is performed using the set welding process;

[0017] Welding spot quality evaluation: on the one hand, it is used to obtain the nugget diameter of the welding spot, and on the other hand, it is used to compare the nugget diameter of the welding spot with the preset nugget diameter index; when it is judged that the nugget diameter of the welding spot meets the requirements, the shear force value judgment is performed to output the evaluation result;

[0018] Electrode quality evaluation: On the one hand, it is used to obtain the working surface diameter of the electrode; on the other hand, it is used to compare the change in the working surface diameter of the electrode with the preset working surface diameter change, so as to evaluate the wear of the electrode.

[0019] Furthermore, the thickness of the galvanized steel sheet is 0.8 mm, and its chemical composition by weight is: C≤0.12%, Si≤0.50%, Mn≤0.60%, P≤0.10%, S≤0.045%, Ti≤0.30%, and the rest is Fe and unavoidable impurities.

[0020] Furthermore, the weight of the aluminum-zinc coating is 50-100 g / m 2 ; The initial diameter of the electrode is 6 mm.

[0021] Furthermore, the pretreatment includes grinding the position of the workpiece to be welded to remove the oxide layer and impurities on the surface and improve the contact resistance during welding.

[0022] Further, the solder joint quality evaluation includes: evaluating the solder joint quality once for every 50 solder joints, wherein the nugget diameter of the solder joint is measured by metallographic method.

[0023] Furthermore, the mechanical properties of the weld are evaluated by obtaining a shear force value through a shear tensile test, wherein the shear force value is an average value of the shear force values ​​of two adjacent welds of the weld for obtaining the nugget diameter.

[0024] Furthermore, the preset nugget diameter index is set to ≥4√t, where t is the thickness of the galvanized steel sheet.

[0025] Furthermore, when the nugget diameters of all welds satisfy ≥4√t, and the shear force values ​​of the welds are stable with no obvious downward trend, the welds are qualified.

[0026] Furthermore, the electrode quality evaluation includes: evaluating the electrode quality once every 50 welding points, and judging the wear of the electrode by the change of the diameter of the working surface of the electrode.

[0027] Furthermore, the preset working surface diameter change is set to 20% of the increase ratio of the electrode working surface diameter.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The present invention reduces the current by optimizing the resistance spot welding process to lower the instantaneous welding temperature, reduce the generation of Cu-Zn alloy with poor electrical and thermal conductivity and its adhesion on the electrode, and thus delay the increase of the electrode temperature; in order to ensure smooth welding to form a good quality weld, the welding time is appropriately extended; in addition, the electrode pressure and pre-pressing time are increased to ensure that the welded workpieces are fully compressed before power is turned on to ensure the consistency of the contact resistance of the welding area and avoid unstable welding current; at the same time, the holding time after welding is increased to allow the metal in the welding area to be fully cooled and solidified under the action of the electrode pressure, so as to avoid insufficient strength of the weld due to loose internal structure of the weld.

[0030] The method of the present invention can reduce the increase in working surface diameter caused by electrode wear and plastic deformation while ensuring welding quality (the diameter of the weld core and the tensile shear force meet the requirements), thereby effectively extending the electrode life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 The figure is a flow chart of the method of the present invention.

[0033] Figure 2 This is a schematic diagram of the electrode after 300 welding points are welded according to the process of Example 1 of the present invention.

[0034] Figure 3 This is a schematic diagram of the electrode after 300 welding points are welded according to the process of Example 2 of the present invention.

[0035] Figure 4 This is a schematic diagram of the electrode after 300 welding points are welded according to the comparative example process of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, the numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0040] The present invention provides a method for extending the electrode life during resistance spot welding of galvanized steel sheets. Figure 1-4 As shown, the technical problem to be solved by the present invention is: to extend the service life of the electrode by optimizing the technical means of the resistance spot welding process, with simple design and strong adaptability.

[0041] The current thickness of the aluminum-zinc coated steel sheet is 0.8mm, and the chemical composition is: C≤0.12%, Si≤0.50%, Mn≤0.60%, P≤0.10%, S≤0.045%, Ti≤0.30%, and the rest is Fe and unavoidable impurities. The weight of the aluminum-zinc coating is 50-100g / m 2 ; Electrode initial diameter: 6mm;

[0042] The method of the present invention comprises the following steps:

[0043] (1) Cutting of galvanized steel sheets: Processing galvanized steel sheets into workpieces of required size;

[0044] (2) Pretreatment of workpiece before welding: Grind the position of the workpiece to be welded to remove the oxide layer and impurities on the surface to improve the contact resistance during welding;

[0045] (3) Welding process parameter setting: The specific process parameters are as follows: pre-pressing time: 40 cyc, electrode pressure: 3.2-3.6 kN, welding current: 7.6-8.0 kA, welding time: 15-18 cyc, post-weld holding time: 40 cyc;

[0046] (4) Welding: Continuous spot welding was performed using the optimized welding process, with 301 welds welded using the same process;

[0047] (5) Weld quality evaluation: The welding quality was evaluated once every 50 welds. The nugget diameters of the 2nd, 50th, 100th, 150th, 200th, 250th, and 300th welds were measured by metallographic method. The mechanical properties of the welds were evaluated by shear tensile test. Specifically, the average tensile shear force of the 1st and 3rd welds was taken as the tensile shear force value of the 2nd weld, the average tensile shear force of the 49th and 51st welds was taken as the tensile shear force value of the 50th weld, ..., the average tensile shear force of the 299th and 301st welds was taken as the tensile shear force value of the 300th weld.

[0048] (6) Electrode quality evaluation: The working surface diameter of the electrode is measured every 50 welds to evaluate the wear of the electrode.

[0049] Table 1 lists the parameter differences between the optimized resistance spot welding process and other processes.

[0050] Table 1 Resistance spot welding process parameter settings

[0051]

[0052] Example 1

[0053] Resistance spot welding was performed using the corresponding welding process in Table 1. After welding, the quality of the weld was evaluated according to step (5), and the quality of the electrode was evaluated according to step (6). The results are shown in Table 2. (where t is the thickness of the galvanized steel plate); the shear force value is stable and there is no obvious downward trend; the upper electrode is taken for measurement. After 300 welds, the electrode diameter is 6.93mm, which increases by 15.5%. Figure 2 shown.

[0054] Example 2

[0055] Resistance spot welding was performed using the corresponding welding process in Table 1. After welding, the quality of the weld was evaluated according to step (5), and the quality of the electrode was evaluated according to step (6). The results are shown in Table 2. (where t is the thickness of the galvanized steel plate); the shear force value is stable and there is no obvious downward trend; the upper electrode is taken for measurement. After 300 welds, the electrode diameter is 7.00 mm, which increases by 16.7%. Figure 3 shown.

[0056] Comparative Example

[0057] Resistance spot welding was performed using the corresponding welding process in Table 1. After welding, the quality of the weld was evaluated according to step (5), and the quality of the electrode was evaluated according to step (6). The results are shown in Table 2. The diameter of the nugget at the 300th weld showed a significant decreasing trend. This was because the increase in the size of the electrode working surface led to a decrease in the current density, and the adhesion of the Cu-Zn alloy on the electrode led to current instability. Correspondingly, the shear force value of the 300th weld was significantly reduced. The upper electrode was taken for measurement. After 300 welds, the electrode diameter was 7.42 mm, an increase of 23.7%. Figure 4 As shown, there is a lot of bright white alloy adhering to the electrode surface.

[0058] Table 2 Solder joint quality evaluation results

[0059]

[0060]

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extending the electrode life during resistance spot welding of galvanized steel sheets, characterized in that: include: Galvanized steel plate cutting: processing galvanized steel plate into preset workpieces; Pretreatment: pretreatment of the workpiece where welding is to be carried out; Welding process parameter settings: pre-pressing time is 40 cyc, electrode pressure is 3.2-3.6 kN, welding current is 7.6-8.0 kA, welding time is 15-18 cyc, and post-weld holding time is 40 cyc; Welding: Continuous spot welding is performed using the set welding process; Welding spot quality evaluation: on the one hand, it is used to obtain the nugget diameter of the welding spot, and on the other hand, it is used to compare the nugget diameter of the welding spot with the preset nugget diameter index; when it is judged that the nugget diameter of the welding spot meets the requirements, the shear force value judgment is performed to output the evaluation result; Electrode quality evaluation: On the one hand, it is used to obtain the working surface diameter of the electrode; on the other hand, it is used to compare the change in the working surface diameter of the electrode with the preset working surface diameter change, so as to evaluate the wear of the electrode.

2. The method for extending the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The thickness of the galvanized steel sheet is 0.8 mm, and its chemical composition by weight is: C≤0.12%, Si≤0.50%, Mn≤0.60%, P≤0.10%, S≤0.045%, Ti≤0.30%, and the rest is Fe and unavoidable impurities.

3. The method for extending the electrode life during resistance spot welding of galvanized steel sheet according to claim 2, characterized in that: The aluminum-zinc coating weight is 50-100 g / m 2 ; The initial diameter of the electrode is 6 mm.

4. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The pretreatment includes grinding the position of the workpiece to be welded, removing the oxide layer and impurities on the surface, and improving the contact resistance during welding.

5. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The solder joint quality evaluation includes: evaluating the solder joint quality once every 50 solder joints, wherein the nugget diameter of the solder joint is measured by metallographic method.

6. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 5, characterized in that: The shear force value is obtained by shear tensile test to evaluate the mechanical properties of the weld. The shear force value is the average of the shear force values ​​of two adjacent welds of the weld for obtaining the nugget diameter.

7. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The preset nugget diameter index is set to ≥4√t, where t is the thickness of the galvanized steel sheet.

8. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 7, characterized in that: When the core diameters of all welds meet ≥4√t, and the shear force values ​​of the welds are stable with no obvious downward trend, the welds are qualified.

9. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The electrode quality evaluation includes: evaluating the electrode quality every 50 welding points, and judging the electrode wear by the change of the working surface diameter of the electrode.

10. The method for prolonging the electrode life during resistance spot welding of galvanized steel sheet according to claim 1, characterized in that: The preset working surface diameter change is set to 20% of the increase ratio of the electrode working surface diameter.

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