CN108857010B - Spot welding quality control method for galvanized steel sheet for automobile - Google Patents

Abstract

The invention relates to a spot welding quality control method for a galvanized steel sheet for an automobile, which comprises the following steps: step S1: analyzing the influence of welding selection process parameters on welding quality, and optimizing the process parameters; step S2: analyzing the influence of the welding selection material on the welding quality; step S3: analyzing the influence of the selected electrode cap on the welding quality; step S4: and optimizing the welding quality by adopting a current gain compensation method. According to the invention, the influences of welding process parameters, welding base metal, spot welding electrodes and the like on welding quality are researched, and the spot welding quality is controlled by adopting a proper method, so that the purposes of reducing welding spatters and burrs, preventing welding spots from being over-burnt and electrodes from being adhered, improving the strength of the welding spots of weldments and the appearance surface quality and improving the quality of the whole vehicle are achieved; meanwhile, the workshop production environment is improved, the labor intensity of workers is reduced, the production period is shortened, the production cost is reduced, resources are saved, and the enterprise market competitiveness is improved.

Description

Spot welding quality control method for galvanized steel sheet for automobile

Technical Field

The invention relates to the field of automobile part processing, in particular to a spot welding quality control method for a galvanized steel plate for an automobile.

Background

Along with the great improvement of the living standard of people, the rigidity requirement of the automobile is more and more increased. In 2010, the automobile sales volume in China breaks through 1850 thousands of automobiles, the year-by-year increase exceeds 36%, and after the year-by-year increase exceeds the first of United states by 1364 thousands of sales volume and the year-by-year increase of more than 46%, the market of the first automobile production country and the largest new automobile sales market in China are cicada again. People are increasingly conscious about resource conservation, environmental protection, driving safety and the like, and the requirements on the use performance of automobiles are increasingly strict, wherein the strengthening of the corrosion resistance of the automobiles is a field of important research. In recent years, in order to improve the corrosion resistance of automobiles, high-performance series of plated steel sheets such as an alloyed hot-dip plated layer, electrogalvanizing alloy, organic composite plated layer, hot-dip aluminum and the like having high corrosion resistance for automobiles have been rapidly developed in various countries in the world. The amount of galvanized steel sheets is the largest, and the majority of all automobile body outer plates of many brands are galvanized steel sheets.

Resistance spot welding is a welding method in which a welding piece of an overlap joint is pressed between two electrified electrodes, the welded piece is melted by heat generated by resistance, and a welding spot is formed by cooling, so that the resistance spot welding belongs to pressure welding and has the characteristic of fusion welding, also called spot welding for short. The resistance spot welding has the characteristics of high efficiency, economy, simple operation and the like, and is suitable for welding the stamped and rolled thin plate with the thickness of less than 6 mm. Therefore, spot welding plays a role in lifting weight in the field of automobile manufacturing, particularly 3500-6000 welding spots are needed by each automobile in the welding process of a white automobile body, and the application of spot welding is more than 70% of that of the whole automobile.

The knowledge and research of the resistance spot welding of the galvanized steel sheet by foreign experts and scholars has been nearly half a century, and has obtained a lot of important achievements, and has been applied to the actual production in various fields such as the automobile industry, aerospace and the like, but because the resistance spot welding is a complex welding technology integrating a plurality of disciplines such as mechanics, thermal science, electromagnetism and metallurgy and the like, people still do not completely and thoroughly recognize the technical problems in the related aspects, and a lot of problems to be solved are left at present. The resistance spot welding of galvanized steel sheets has been studied in China for more than 30 years and has achieved remarkable results, but because the research and development of galvanized steel sheets in China and the development of the automobile industry are slow, certain gap exists between the research aspect of the resistance spot welding of galvanized steel sheets and abroad. Therefore, the method still has important theoretical significance and practical application value for the research of the method.

When the galvanized steel sheet is spot-welded, the abrasion rate of the electrode is accelerated, and the failure process of the electrode is accelerated. With the same spot welding electrode, the total number of welding spots can reach more than 2 ten thousand when the non-galvanized steel plate is spot-welded, and the total number of welding spots when the galvanized steel plate is spot-welded is sharply reduced to 2000-3000. The unit price of each commonly used electrode cap is 7-10 yuan, each vehicle consumes 3, and an automobile manufacturer with annual output of 90000 vehicles needs to spend about 250 ten thousand yuan of RMB in the aspect of electrode consumption every year. In addition, the working hours spent on frequent electrode grinding or replacement treatment seriously affect the beat on the production line and the productivity of enterprises, further have certain influence on the economic benefit of the enterprises, and are equivalent to the increase of the production cost. Therefore, the problem of an increase in production cost caused by the electrode cap is not negligible.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for controlling the spot welding quality of the galvanized steel plate for the automobile, which solves the problems that the abrasion rate of an electrode is accelerated, the failure process of the electrode is accelerated and the total amount of an electric welding electrode is greatly reduced when the galvanized steel plate is spot-welded.

The technical scheme for solving the technical problems is as follows: the spot welding quality control method for the galvanized steel sheet for the automobile comprises the following steps of:

step S1: analyzing the influence of welding selection process parameters on welding quality, and optimizing the process parameters;

step S2: analyzing the influence of the welding selection material on the welding quality;

step S3: analyzing the influence of the selected electrode cap on the welding quality;

step S4: and controlling the welding quality by adopting a current gain compensation method.

Further: the specific implementation process of the step S1 is as follows:

step S11: selecting a galvanized steel sheet with a certain thickness;

step S12: acquiring the optimal welding process parameters when two layers of galvanized steel plates are assembled by adopting a welding joint form of an overlap joint;

step S13: and acquiring the optimal welding process parameters during the assembly of the three-layer galvanized steel plate by adopting a welding joint form of the lap joint.

Further: the specific implementation process of the step S2 is as follows:

step S21: selecting three groups of galvanized steel plates A1, A2 and A3 with different thicknesses, and respectively obtaining current values B1, B2 and B3 of the three groups of galvanized steel plates A1, A2 and A3 when qualified welding spots are formed and maximum current values C1, C2 and C3 of the three groups of galvanized steel plates A1, A2 and A3 when splashing is not generated; wherein the welding current windows of the three groups of galvanized steel sheets a1, a2 and A3 are the regions between the respective current values B1, B2 and B3 and the respective maximum current values C1, C2 and C3;

step S22: judging the specific position of the existing welding current value D in the welding current window according to the welding current window;

step S23: obtaining the optimal welding currents E1, E2 and E3 when the coverage rates of the zinc coating on the surface of the galvanized steel sheet are respectively 0%, 50% and 100% when the two galvanized steel sheets are assembled;

step S24: when the three-layer galvanized steel sheet is assembled, the optimal welding currents F1 and F2 are obtained when the coverage rate of the galvanized layer on the surface of the galvanized steel sheet is 0% and 100%, respectively.

Further: the specific implementation process of the step S3 is as follows:

step S31: selecting an electrode cap made of a proper material according to the plastic deformability, the wear resistance, the mechanical property of a welding spot and the diameter of a nugget;

step S32: the deformation degree, the mechanical property, the nugget diameter and the service life of two electrode caps which are made of the same material and have different shapes and have the same welding points are compared.

Further: the specific implementation manner of step S4 is as follows:

step S41: analyzing the welding quality of the chromium-zirconium-copper electrode adopting X groups of welding process parameters and the aluminum oxide-copper electrode adopting the optimal current step when two layers of plates are welded;

step S42: and analyzing the welding quality of the aluminum oxide copper electrode adopting the Y-group welding process parameters and the chromium zirconium copper electrode adopting the optimal current step when the two layers of plates are welded.

The invention has the beneficial effects that: the influence of welding process parameters, welding base metal, spot welding electrodes and the like on welding quality is researched, and the spot welding quality is controlled by adopting a proper method, so that the aims of reducing welding spatters and burrs, preventing over-burning of welding spots and electrode adhesion, improving the strength of the welding spots of welding parts and the appearance surface quality and improving the quality of a finished automobile are fulfilled; meanwhile, the production environment of a workshop is improved, the labor intensity of workers is reduced, the production period is shortened, the production cost is reduced, resources are saved, and the market competitiveness of enterprises is improved.

Drawings

FIG. 1 is a flow chart of a spot welding quality control method for a galvanized steel sheet for an automobile.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

As shown in fig. 1, a spot welding quality control method for a galvanized steel sheet for an automobile includes the following steps:

step S1: analyzing the influence of welding selection process parameters on welding quality, and optimizing the process parameters;

step S2: analyzing the influence of the welding selection material on the welding quality;

step S3: analyzing the influence of the selected electrode cap on the welding quality;

step S4: and controlling the welding quality by adopting a current gain compensation method.

Preferably: the process parameters in the step S1 include welding time, welding pressure, welding current and current density.

Preferably: the specific implementation process of the step S1 is as follows:

step S11: selecting a galvanized steel sheet with a certain thickness;

step S12: acquiring the optimal welding process parameters when two layers of galvanized steel plates are assembled by adopting a welding joint form of an overlap joint;

step S13: and acquiring the optimal welding process parameters during the assembly of the three-layer galvanized steel plate by adopting a welding joint form of the lap joint.

The specific experimental contents of step S1 are as follows:

(1) the method selects the test parent metal as the galvanized steel plate with more thickness of 0.7mm used on the vehicle body, adopts two assembling forms of B-type steel plate 0.7mm +0.7mm and 0.7mm +0.7mm +0.7mm, and the welding joint form of the test design is lap joint, and the model of the electrode cap is as follows: a P911310400 type Cr-Zr-Cu material;

(2) when the two-layer plates are assembled, the optimized intervals of welding time, welding pressure and welding current are respectively 10-14 cycles, 1.9-2.3 kN and 10-12 kA; under the condition of three-layer plate assembly, the optimized intervals of welding time, welding pressure and welding current are 10-14 Cycles, 1.9-2.3 kN and 11-13 kA in sequence;

(3) under the precondition that the formation of a nugget in a welding joint area is guaranteed, when two layers of plates are assembled, the welding time is the most main influence factor, the welding current is the secondary influence factor, and the welding pressure has the smallest influence on the welding quality and is the weakest influence factor; however, in the three-layer plate assembly, the primary influence factor is the welding current, the secondary influence factor is the welding time, and the most important influence factor is the welding pressure. Therefore, if the welding quality problems of different assembly layers caused by welding process parameters in workshop production are caused, the field problems are pertinently and quickly solved according to the size of the influence factors, and the production is quickly recovered;

(4) when the two-layer plate is assembled, the welding time t is 12Cycles, the welding pressure P is 2.1kN and the welding current I is 11kA are the optimal welding process parameters; when the three-layer plate is assembled, the welding time t is 12Cycles, the welding pressure P is 2.3kN and the welding current I is 12kA are the optimal welding process parameters.

Preferably: the specific implementation process of the step S2 is as follows:

step S21: selecting three groups of galvanized steel plates A1, A2 and A3 with different thicknesses, and respectively obtaining current values B1, B2 and B3 of the three groups of galvanized steel plates A1, A2 and A3 when qualified welding spots are formed and maximum current values C1, C2 and C3 of the three groups of galvanized steel plates A1, A2 and A3 when splashing is not generated; wherein the welding current windows of the three groups of galvanized steel sheets a1, a2 and A3 are the regions between the respective current values B1, B2 and B3 and the respective maximum current values C1, C2 and C3;

step S22: judging the specific position of the existing welding current value D in the welding current window according to the welding current window;

step S23: obtaining the optimal welding currents E1, E2 and E3 when the coverage rates of the zinc coating on the surface of the galvanized steel sheet are respectively 0%, 50% and 100% when the two galvanized steel sheets are assembled;

step S24: when the three-layer galvanized steel sheet is assembled, the optimal welding currents F1 and F2 are obtained when the coverage rate of the galvanized layer on the surface of the galvanized steel sheet is 0% and 100%, respectively.

The specific experimental contents of step S2 are as follows: through tests and analysis, the effectiveness of current during welding is the basis for effectively controlling the welding quality under the condition of obtaining proper welding time and welding pressure and fixing.

(1) When the plate thickness of the galvanized steel sheet is 0.6mm, 0.7mm and 1.5mm, the current values of the formed qualified welding points are 8.75kA, 9kA and 10kA respectively, the maximum current without splashing is 11.5kA, 11.75kA and 13.5kA, and the area between the two groups of corresponding data is a welding current window of the corresponding reference plate thickness;

(2) the specific position of the existing welding current in the welding window and the effectiveness of the fluctuation range of the welding current can be judged according to the welding window, and when the welding current of different reference plate thicknesses is unknown, the welding current can be adjusted according to the window;

(3) when the two-layer plates are assembled, when the coverage rate of the zinc coating on the surface of the steel plate is 0%, 50% and 100%, the optimal welding current is 8.5kA, 10kA and 11kA in sequence; when the three-layer plates are assembled, the optimal welding current is respectively 9kA and 12kA when the coverage rate of the zinc coating on the surface of the steel plate is 0 percent and 100 percent. Meanwhile, the welding current of the galvanized layer on the surface of the steel plate is increased by 15-20% when the coverage rate of the galvanized layer on the surface of the steel plate is increased by 50%.

Preferably: the specific implementation process of the step S3 is as follows:

step S31: selecting an electrode cap made of a proper material according to the plastic deformability, the wear resistance, the mechanical property of a welding spot and the diameter of a nugget;

step S32: the deformation degree, the mechanical property, the nugget diameter and the service life of two electrode caps which are made of the same material and have different shapes and have the same welding points are compared. (two electrode caps of chromium zirconium copper electrode of the truncated cone type P911310112 and of the truncated cone type P911310400.)

The specific experimental contents of step S3 are as follows: through tests and analysis, the welding quality is ensured, and meanwhile, various influences of electrodes made of different materials and electrodes in different shapes on resistance spot welding are obtained under specific technological parameters, so that the materials and the shapes of the spot welding electrodes are selected.

(1) Because the welding of welding robot is extremely sensitive to the adhesion of electrode, guarantee the beat on the production line, should select the electrode of chromium zirconium copper material for use. The electrode made of the chromium-zirconium-copper material has small plastic deformation and abrasion degree, the mechanical property and the nugget diameter of a welding spot are good, the unit price of the chromium-zirconium-copper electrode is cheaper than that of aluminum copper, and the electrode made of the chromium-zirconium-copper material is relatively good when the chromium-zirconium-copper electrode is used in manual spot welding. The electrode of chromium zirconium copper material is the best choice under the condition of the process parameters from the viewpoint of the service life of the electrode.

(2) Analysis shows that under the condition of the existing process parameters, the chromium zirconium copper electrodes with the cone frustum type of P911310112 and the cone frustum type of P911310400 have smaller deformation degree of the end surface shape of the former electrode, the reduction of the axial length of the electrode is far smaller than that of the latter electrode, and the mechanical property, the nugget diameter and the service life of the electrode of the former electrode are superior to those of the latter electrode when the number of the accumulated welding points is the same.

Preferably, the specific implementation manner of step S4 is:

step S41: analyzing the welding quality of the chromium-zirconium-copper electrode adopting X groups of welding process parameters and the aluminum oxide-copper electrode adopting the optimal current step when two layers of plates are welded;

step S42: and analyzing the welding quality of the aluminum oxide copper electrode adopting the Y-group welding process parameters and the chromium zirconium copper electrode adopting the optimal current step when the two layers of plates are welded.

The specific experimental contents of step S4 are as follows: after a plurality of groups of tests, three groups of samples are randomly extracted, two layers of plates welded by adopting X groups of welding process parameters and the optimal current step of the alumina copper electrode are adopted for the chromium-zirconium-copper electrode, and the two layers of plates welded by adopting Y groups of welding process parameters and the optimal current step of the chromium-zirconium-copper electrode are stripped to obtain: the diameter of a nugget of 20-40 welding spots is smaller than 4mm, the shape of the welding spot nugget is irregular, the welding spot fracture type is welding spot fracture, 10 welding spots are cold joints, the surface quality of the welding spots is poor, and the abrasion degree of an electrode cap is obviously larger than that of an electrode in an X group test. All welding points of the electrode are round and full, the nugget diameter of the electrode is larger than 4mm, the appearance molding meets the requirement, and the electrode can be normally used after being polished;

the following conclusions can be obtained through a series of researches and analyses:

(1) when the two electrode caps are used for spot welding of galvanized steel plates, the condition of assembling two layers of steel plates and three layers of steel plates can be met simultaneously by adopting each new current step, and the diameter size of all welding spot nuggets is larger than the critical value of the qualified standard.

(2) The use of the current gain compensation control method of the new current step enables the abrasion loss of the diameters of the two electrode caps to be controlled within 1.5mm and 1.8mm respectively, the current density to be larger than 275A/mm, and the electrode caps can be used continuously after being polished while qualified welding points are obtained.

(3) When the new current step is used for actual production, the welding spot strength of the new current step and the welding spot strength of the new current step are high, the welding quality is stable and reliable, the beat of batch production can be ensured, and the new current step is superior to the original current step. And the qualified points of each pair of electrode caps of the chromium-zirconium-copper material are increased by 120-180 in comparison with the original points, so that the production cost of an enterprise is reduced.

By adopting the spot welding quality control method of the galvanized steel sheet for the automobile, the optimal welding process parameters of the two-layer plate and the three-layer plate during assembly are obtained, and the technical indexes are as follows:

welding time: 12 cyc;

welding pressure: 2.1kN and 2.3 kN;

welding current: 11kA and 12 kA;

current density: 275A/mm.

The invention has the beneficial effects that: the influence of welding process parameters, welding base metal, spot welding electrodes and the like on welding quality is researched, and the spot welding quality is controlled by adopting a proper method, so that the aims of reducing welding spatters and burrs, preventing over-burning of welding spots and electrode adhesion, improving the strength of the welding spots of welding parts and the appearance surface quality and improving the quality of a finished automobile are fulfilled; meanwhile, the production environment of a workshop is improved, the labor intensity of workers is reduced, the production period is shortened, the production cost is reduced, resources are saved, and the market competitiveness of enterprises is improved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (1)

1. A spot welding quality control method for galvanized steel sheets for automobiles is characterized by comprising the following steps: the method comprises the following steps:

step S1: analyzing the influence of welding selection process parameters on welding quality, and optimizing the process parameters;

the specific implementation process of step S1 is as follows:

step S11: selecting a galvanized steel sheet with a certain thickness;

step S12: acquiring the optimal welding process parameters when two layers of galvanized steel plates are assembled by adopting a welding joint form of an overlap joint;

step S13: acquiring the optimal welding process parameters when the three-layer galvanized steel plate is assembled by adopting a welding joint form of an overlap joint;

step S2: analyzing the influence of the welding selection material on the welding quality;

the specific implementation process of step S2 is as follows:

step S21: selecting three groups of galvanized steel plates A1, A2 and A3 with different thicknesses, and respectively obtaining current values B1, B2 and B3 of the three groups of galvanized steel plates A1, A2 and A3 when qualified welding spots are formed and maximum current values C1, C2 and C3 of the three groups of galvanized steel plates A1, A2 and A3 when splashing is not generated; wherein the welding current windows of the three groups of galvanized steel sheets a1, a2 and A3 are the regions between the respective current values B1, B2 and B3 and the respective maximum current values C1, C2 and C3;

step S22: judging the specific position of the existing welding current value D in the welding current window according to the welding current window;

step S23: obtaining the optimal welding currents E1, E2 and E3 when the coverage rates of the zinc coating on the surface of the galvanized steel sheet are respectively 0%, 50% and 100% when the two galvanized steel sheets are assembled;

step S24: obtaining optimal welding currents F1 and F2 when the coverage rates of the zinc coating on the surface of the galvanized steel sheet are 0% and 100% respectively when the three-layer galvanized steel sheet is assembled;

step S3: analyzing the influence of the selected electrode cap on the welding quality;

the specific implementation process of step S3 is as follows:

step S31: selecting an electrode cap made of a proper material according to the plastic deformability, the wear resistance, the mechanical property of a welding spot and the diameter of a nugget;

step S32: comparing the deformation degree, the mechanical property, the nugget diameter and the service life of two electrode caps which are made of the same material and have different shapes and have the same welding point number;

step S4: controlling the welding quality by adopting a current gain compensation method;

the specific implementation manner of step S4 is:

step S41: analyzing the welding quality of the chromium-zirconium-copper electrode adopting X groups of welding process parameters and the aluminum oxide-copper electrode adopting the optimal current step when two layers of plates are welded;

step S42: and analyzing the welding quality of the aluminum oxide copper electrode adopting the Y-group welding process parameters and the chromium zirconium copper electrode adopting the optimal current step when the two layers of plates are welded.

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