A method for prolonging the life of electrodes during resistance spot welding of galvannealed steel sheets

Abstract

The application provides a method for prolonging the service life of an electrode during resistance spot welding of an aluminized zinc steel plate, and relates to the technical field of welding, and comprises the following steps: processing the aluminized zinc steel plate into a preset workpiece; pretreatment; welding process parameter setting; welding; welding spot quality evaluation: on the one hand, the welding spot nugget diameter is obtained, and on the other hand, the welding spot nugget diameter is compared with a preset nugget diameter index; when it is judged that the welding spot nugget diameter meets the requirements, shear force value judgment is performed, so that an evaluation result is output; electrode quality evaluation: on the one hand, the working surface diameter of the electrode is obtained, and on the other hand, the change of the working surface diameter of the electrode is compared with a preset working surface diameter change, so that the wear condition of the electrode is evaluated. Through the mode of optimizing the resistance spot welding process, the current is reduced, the instantaneous welding temperature is reduced, the generation and adhesion and cohesiveness of the Cu-Zn alloy with poor conductivity and thermal conductivity 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 present application relates to the technical field of welding, in particular, especially relates to a method for prolonging the electrode life in resistance spot welding of aluminum-zinc plated steel plate. BACKGROUND

[0002] With the development of modern industry, the industry has higher requirements for the corrosion resistance, heat resistance and processing performance of steel plate. As an important variety, the aluminum-zinc plated steel plate has more superior corrosion resistance than the traditional galvanized steel plate. 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 the automobile manufacturing and household appliance production industries.

[0003] Resistance spot welding is an indispensable connection method in its production and processing process. Compared with galvanized steel plate, aluminum-zinc plated steel plate is more sensitive to changes in welding parameters, and more precise control is needed to avoid welding defects. In addition, the electrode is an important consumable component of the spot welding equipment, and its service life directly affects the production efficiency and production cost. However, during the spot welding process of aluminum-zinc plated steel plate, due to the presence of the zinc plating layer, Cu-Zn alloy with weak conductivity and heat conductivity is easily generated and adhered to the electrode, accelerating the temperature rise of the electrode. Under the action of pressure, plastic deformation is increased, and the hardness of the aluminum-zinc plated steel plate is relatively higher, which causes greater wear on the electrode during spot welding, thereby accelerating the failure of the electrode. Therefore, prolonging the service life of the electrode during resistance spot welding of aluminum-zinc plated steel plate has become one of the key problems in mass production and fast-paced production in the 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 service life of resistance spot welding electrodes for low-melting-point coated steel workpieces and reducing the generation of surface defects of the welding spot. The method includes at least three stages of welding current pulses when performing the resistance spot welding process. The current acting time of each stage does not exceed 100 ms, and the cooling time between each stage does not exceed 12 ms. Through multiple pulse short-time heating and cooling, the over-heating of the welding spot surface can be effectively avoided, the heat generation between the welding electrode and the coated steel plate is reduced, and the electrode life is improved and the generation of surface over-heating cracks is reduced, thereby improving the welding quality.

[0005] Patent CN111673250 is a resistance spot welding method for passivated coated steel plate. The invention discloses a resistance spot welding method for passivated coated steel plate. The welding current I0 that causes the passivated coated steel plate to splash when the electrode pressure N1 and the welding time T0 are less than or equal to 2cyc is determined; after the interval time C, the welding current I ave that causes the passivated coated steel plate to splash at the Mth pulse is determined under the condition that the welding time of each pulse is Tave ; 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 according to I0; determine the welding current I2 of the second pulse to the Mth pulse according to I ave ; wherein no nugget spatter occurs during the welding process of the second pulse to the Mth pulse; this method can reduce electrode sticking and improve electrode life.

[0006] Patent CN102672332A A method for prolonging the service life of galvanized steel sheet resistance spot welding electrode, the invention discloses a method for prolonging the service life of galvanized steel sheet resistance spot welding electrode, which is inserted between the upper electrode and the upper layer of the electrode and the lower layer of the electrode. The copper-nickel alloy gasket is 0.05-0.2mm. This method can reduce the temperature of the electrode end surface, reduce the electrode wear and prolong the service life of the electrode.

[0007] Patent CN101961814A A method for spot welding of hot-dip aluminum-zinc steel sheet, the method discloses a method for spot welding of hot-dip aluminum-zinc steel sheet, which is inserted between the electrode and the plated workpiece. The foil strip is used as a composite electrode, and the foil strip is used as a consumable material to isolate the electrode and the workpiece. The foil strip moves one position for each welding point. Since the foil strip is added to the electrode and the workpiece, a secondary high temperature zone is formed at the contact between the electrode and the workpiece, and the temperature field of the joint area tends to be uniform, thereby facilitating the formation of the nugget between the workpieces.

[0008] In summary, at present, the methods related to prolonging the service life of the electrode when welding plated steel sheet by resistance spot welding or requiring pulse welding current have high requirements for equipment and are not universal. Or the method needs to add a metal sheet between the electrode and the workpiece, which is complicated, high in cost and difficult to be industrialized. And the method for aluminum-zinc plated steel sheet is relatively lacking.

[0009] The present application aims to provide a method for prolonging the service life of the electrode when resistance spot welding of aluminum-zinc plated steel sheet from the perspective of optimizing the welding process, to solve the problem of serious electrode sticking and fast wear when spot welding aluminum-zinc plated steel sheet. SUMMARY

[0010] According to the above-mentioned technical problems of serious electrode sticking and fast wear when spot welding aluminum-zinc plated steel sheet, a method for prolonging the service life of the electrode when resistance spot welding of aluminum-zinc plated steel sheet is provided. The present application mainly uses the technical means of optimizing the resistance spot welding process to prolong the service life of the electrode.

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

[0012] A method for prolonging the service life of the electrode when resistance spot welding of aluminum-zinc plated steel sheet, comprising:

[0013] Cutting the aluminum-zinc plated steel plate: machining the aluminum-zinc plated steel plate into a preset workpiece;

[0014] Preprocessing: preprocessing the welding position of the workpiece;

[0015] Welding process parameter setting: 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-welding holding time is 40 cyc;

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

[0017] Welding point quality evaluation: on the one hand, the nugget diameter of the welding point is obtained, and on the other hand, the nugget diameter of the welding point is compared with the preset nugget diameter index; when it is judged that the nugget diameter of the welding point meets the requirements, the shear force value judgment is executed, and the evaluation result is output;

[0018] Electrode quality evaluation: on the one hand, the working surface diameter of the electrode is obtained, and on the other hand, the change of the working surface diameter of the electrode is compared with the preset working surface diameter change, so as to evaluate the wear of the electrode.

[0019] Further, the thickness of the aluminum-zinc plated steel plate is 0.8 mm, and the chemical composition is as follows: 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] Further, the weight of the aluminum-zinc coating is 50-100 g / m 2 ; the initial diameter of the electrode is 6 mm.

[0021] Further, the preprocessing includes grinding the welding position of the workpiece, removing the surface oxide layer and impurities, and improving the contact resistance during welding.

[0022] Further, the welding point quality evaluation includes: evaluating the welding point quality once every 50 welding points, wherein the nugget diameter of the welding point is measured by metallographic method.

[0023] Further, the mechanical properties of the welding point are evaluated by shear tensile test to obtain the shear force value, and the shear force value is the average value of the shear force values of the adjacent two welding points of the welding point from which the nugget diameter is obtained.

[0024] Further, the preset nugget diameter index is set to ≥4√t, wherein t is the thickness of the aluminum-zinc plated steel plate.

[0025] Further, when the nugget diameter of all the welding spots satisfies ≥4√t, the shear force value of the welding spot is stable and has no obvious downward trend, and thus the welding spot is qualified.

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

[0027] Further, the preset working surface diameter change is set as 20% of the increasing ratio of the diameter of the working surface of the electrode.

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

[0029] The present application reduces the current by optimizing the resistance spot welding process, reduces the instantaneous welding temperature, reduces the generation and adhesion and sticking of the Cu-Zn alloy with poor conductivity and thermal conductivity on the electrode, and further delays the increase of the electrode temperature; in order to ensure smooth welding and form a good welding spot, the welding time is appropriately prolonged; in addition, the electrode pressure and the pre-pressing time are increased, so that the workpieces to be welded are fully pressed before power-on, to ensure the consistency of the contact resistance of the welding area and avoid unstable welding current; at the same time, the post-welding holding time is increased, so that the metal of the welding area is fully cooled and solidified under the action of the electrode pressure, to avoid insufficient welding spot strength caused by loose internal structure of the welding spot.

[0030] By the method of the present application, while ensuring the welding quality (nugget diameter and tensile shear force meet the requirements), the increase of the diameter of the working surface caused by electrode wear and plastic deformation can be slowed down, and the electrode life can be effectively prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0032] Figure 1 The present application is a method flowchart.

[0033] Figure 2 The present application is a schematic diagram of the electrode after welding 300 welding spots by the process of Example 1.

[0034] Figure 3 The present application is a schematic diagram of the electrode after welding 300 welding spots by the process of Example 2.

[0035] Figure 4 The present application is a schematic diagram of the electrode after welding 300 welding spots by the process of the comparative example. DETAILED DESCRIPTION

[0036] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0037] To make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not intended to limit the present application and its application or use in any way. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a reference to the presence of a feature, step, operation, device, component and / or combinations thereof.

[0039] Unless specifically stated otherwise, the relative arrangements of the components and steps illustrated in these embodiments and the numerical expressions and values set forth herein are not limiting of the scope of the present application. It should be understood that the various parts of the drawings are not necessarily drawn to scale, and that, for the purpose of convenience and clarity, not all components and steps can be shown in a given figure. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail, but are intended to be a part of the specification when appropriate. In all examples shown and discussed herein, any specific values are intended to be exemplary only, and are not to be construed as limiting. Other examples of the exemplary embodiments can have different values. It should be noted that like reference numerals and letters in the various figures indicate like elements, and thus, once an element is defined in one figure, it should not have to be discussed further in subsequent figures.

[0040] The present application provides a method for prolonging the service life of an electrode during resistance spot welding of an aluminum-zinc plated steel sheet, as shown in Figures 1-4 The technical problem to be solved by the present application is to prolong the service life of the electrode by optimizing the technical means of resistance spot welding process, which is simple in design and strong in adaptability.

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

[0042] The method comprises the following steps:

[0043] (1) cutting the aluminum-zinc plated steel plate: processing the aluminum-zinc plated steel plate into a workpiece with a desired size;

[0044] (2) pretreatment of the workpiece before welding: polishing the position to be welded of the workpiece to remove the surface oxide layer and impurities, so as to improve the contact resistance during welding;

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

[0046] (4) welding: using the optimized welding process to perform continuous spot welding, and 301 welding points are welded by the same process;

[0047] (5) evaluation of the quality of the welding points: the welding quality is evaluated once every 50 welding points, the nugget diameter of the 2nd, 50th, 100th, 150th, 200th, 250th and 300th welding points is measured by a metallographic method, the average value of the tensile shear force of the 1st and 3rd welding points is taken as the tensile shear force value of the 2nd welding point, the average value of the tensile shear force of the 49th and 51st welding points is taken as the tensile shear force value of the 50th welding point,..., and the average value of the tensile shear force of the 299th and 301st welding points is taken as the tensile shear force value of the 300th welding point;

[0048] (6) evaluation of the quality of the electrode: the working surface diameter of the electrode is measured once every 50 welding points to evaluate the wear of the electrode.

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

[0050] Table 1: setting of resistance spot welding process parameters

[0051]

[0052] Example 1

[0053] The corresponding welding process in Table 1 was used for resistance spot welding, and the weld quality was evaluated according to step (5) and the electrode quality was evaluated according to step (6) after welding, and the results are shown in Table 2. (wherein t is the thickness of the plated aluminum-zinc steel plate); the shear force value is stable and has no obvious downward trend; the upper electrode is measured, and the electrode diameter is 6.93 mm after 300 welds, an increase of 15.5%, as shown in Figure 2 .

[0054] Example 2

[0055] The corresponding welding process in Table 1 was used for resistance spot welding, and the weld quality was evaluated according to step (5) and the electrode quality was evaluated according to step (6) after welding, and the results are shown in Table 2. (wherein t is the thickness of the plated aluminum-zinc steel plate); the shear force value is stable and has no obvious downward trend; the upper electrode is measured, and the electrode diameter is 7.00 mm after 300 welds, an increase of 16.7%, as shown in Figure 3 .

[0056] Comparative Example

[0057] The corresponding welding process in Table 1 was used for resistance spot welding, and the weld quality was evaluated according to step (5) and the electrode quality was evaluated according to step (6) after welding, and the results are shown in Table 2. The nugget diameter of the 300th weld has a significant decreasing trend, which is due to the decrease in current density caused by the increase in the size of the working surface of the electrode, and the adhesion of Cu-Zn alloy on the electrode causes unstable current; correspondingly, the shear force value of the 300th weld is significantly reduced; the upper electrode is measured, and the electrode diameter is 7.42 mm after 300 welds, an increase of 23.7%, as shown in Figure 4 , and there are more bright white alloy adhesions on the surface of the electrode.

[0058] Table 2 Evaluation results of weld quality

[0059]

[0060]

[0061] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets, characterized in that, include: Cutting of aluminized zinc-coated steel sheet: Processing aluminized zinc-coated steel sheet with a thickness of 0.8mm into a pre-set workpiece; Pre-treatment: Pre-treat the areas of the workpiece to be welded; Welding process parameter settings: pre-pressure time is 40 cyc, electrode pressure is 3.5-3.6 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 parameters; Solder joint quality evaluation: On the one hand, it is used to obtain the weld nugget diameter of the solder joint; on the other hand, it is used to compare the weld nugget diameter with the preset weld nugget diameter index. When it is determined that the weld nugget diameter meets the requirements, the shear force value is judged, and the evaluation result is output. The preset melting nucleus diameter index is set to 4. , where t is the thickness of the aluminized zinc-coated steel sheet; When the weld nugget diameter of the weld joint is ≥4 If the shear force value of the weld joint is stable and shows no obvious downward trend, then the weld joint is qualified. Electrode quality evaluation: On the one hand, it is used to obtain the working surface diameter of the electrode, and on the other hand, it is used to compare the change in the working surface diameter of the electrode with the preset change in the working surface diameter, so as to evaluate the wear of the electrode. Electrode quality evaluation includes: evaluating electrode quality once every 50 weld points, and judging the wear condition of the electrode by the change in the diameter of the working surface of the electrode; The preset change in the working surface diameter is set to 20% of the original diameter of the electrode working surface.

2. The method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets according to claim 1, characterized in that, The chemical composition of the aluminized zinc steel sheet by weight is as follows: C≤0.12%, Si≤0.50%, Mn≤0.60%, P≤0.10%, S≤0.045%, Ti≤0.30%, with the remainder being Fe and unavoidable impurities.

3. The method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets according to claim 2, characterized in that, The aluminum-zinc coating of the aluminized steel sheet has a weight of 50-100 g / m². 2 The initial diameter of the electrode is 6 mm.

4. The method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets according to claim 1, characterized in that, The pretreatment includes grinding the workpiece at the welding location to remove the oxide layer and impurities on the surface and improve the contact resistance during welding.

5. The method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets according to claim 1, characterized in that, The quality evaluation of solder joints includes evaluating the quality of every 50 solder joints, including measuring the diameter of the weld nugget using metallographic methods.

6. The method for extending electrode life during resistance spot welding of aluminized zinc-coated steel sheets according to claim 5, characterized in that, The mechanical properties of the weld joint are evaluated by obtaining the shear force value through shear tensile testing. The shear force value is the average of the shear force values ​​of two adjacent weld joints of the weld joint with the obtained weld nugget diameter.

Images