CN107350613B - Resistance spot welding process for steel workpiece with coating layer - Google Patents
Resistance spot welding process for steel workpiece with coating layer Download PDFInfo
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- CN107350613B CN107350613B CN201710655949.9A CN201710655949A CN107350613B CN 107350613 B CN107350613 B CN 107350613B CN 201710655949 A CN201710655949 A CN 201710655949A CN 107350613 B CN107350613 B CN 107350613B
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- 238000003466 welding Methods 0.000 title claims abstract description 165
- 238000000034 method Methods 0.000 title claims abstract description 71
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 48
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- 239000011247 coating layer Substances 0.000 title claims abstract description 18
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- 239000011248 coating agent Substances 0.000 claims description 43
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 22
- 239000011701 zinc Substances 0.000 claims description 22
- 229910052725 zinc Inorganic materials 0.000 claims description 22
- CSDREXVUYHZDNP-UHFFFAOYSA-N alumanylidynesilicon Chemical compound [Al].[Si] CSDREXVUYHZDNP-UHFFFAOYSA-N 0.000 claims description 21
- 239000000498 cooling water Substances 0.000 claims description 5
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- 239000000463 material Substances 0.000 abstract description 23
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- ZTXONRUJVYXVTJ-UHFFFAOYSA-N chromium copper Chemical compound [Cr][Cu][Cr] ZTXONRUJVYXVTJ-UHFFFAOYSA-N 0.000 description 1
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- 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
- B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
-
- 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
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
Abstract
The invention discloses a resistance spot welding process method of a steel workpiece with a coating layer, which is characterized in that the steel workpiece to be welded is lapped, pressure is applied to the lapping position, and pressurization and maintenance are carried out; applying a first welding current to the lap joint, and enabling the first welding current to be continuously applied for a first time; then, removing the first welding current and keeping the first welding current for a second time; after keeping the second time, applying a second welding current to the lap joint, and enabling the second welding current to continuously apply for a third time; after lasting for the third time, slowly reducing the second welding current to 0 within the fourth time; wherein the second welding current is greater than the first welding current, and the sum of the first time and the second time is greater than or equal to 600 ms. The first welding current is output to destroy the coating layer, the second welding current is output to complete heating welding, a longer output stopping time sequence between the first welding current and the second welding current is set, the coating layer material is promoted to be discharged, the splashing is restrained, and a wider process window can be obtained.
Description
Technical Field
The invention belongs to the technical field of welding, and particularly relates to a resistance spot welding process method for a steel workpiece with a coating layer.
Background
In the resistance spot welding process, a phenomenon occurs in which molten base metal flies out from a joint surface of the overlapped plate material or flies out from a contact surface between the plate material and the electrode at the time of welding, which is called "spattering". After the splashing phenomenon occurs, the sputtered metal is attached to the surface of the electrode, so that the welding effect of the electrode is influenced, the electrode is frequently polished, and the service life of the electrode is shortened; and spatter generation is accompanied by internal defects of the spot welded joint, affecting the strength of the welded joint. The current at the time of spattering is generally referred to as spattering current or upper limit current, and the current for securing the reference nugget diameter is generally referred to as lower limit current. The current range between the upper and lower current limits is an important metric for evaluating resistance spot welding processes and is referred to as the process window.
In the production of automobile bodies today, the joining of the body panels is mainly carried out by resistance spot welding. The bearing function of each part of the vehicle body is different, and the selected plates are also different. For example, in order to satisfy safety protection and corrosion resistance for passengers, aluminum-silicon-coated hot-stamped sheet materials are often used for the B-pillar of the vehicle body, and galvanized sheet materials are often used for the cover members in order to meet the requirement of light weight.
The spatter generated during the manufacturing and welding of the car body influences the performance of the final welding joint, causes frequent electrode grinding and reduces the service life of the electrode; the sputtered metal is attached to the surface of the car body, so that the appearance of the car body surface is influenced, the metal needs to be removed at the later stage, and the production cost is increased. In the actual production line production, due to the current stability and consistency of the welding machine, the actual current value usually floats about ten percent above and below the set value, a wider process window is obtained, splashing is avoided, and the method has strong practical significance.
Disclosure of Invention
One of the technical problems to be solved by the invention is to inhibit the generation of splash and obtain a wider process window in the resistance spot welding process.
In order to solve the technical problem, the embodiment of the invention provides a resistance spot welding process method of a steel workpiece with a coating layer, which comprises the following steps:
overlapping the steel workpieces to be welded, applying pressure to the overlapped part, and pressurizing and maintaining;
applying a first welding current to the lap joint, and enabling the first welding current to be applied for a first time;
removing the first welding current after continuing the first time and maintaining for a second time;
after the second time is kept, applying a second welding current to the lap joint, and enabling the second welding current to be continuously applied for a third time;
after continuing the third time, slowly reducing the second welding current to 0 within a fourth time;
wherein the second welding current is greater than the first welding current, and a sum of the first time and the second time is greater than or equal to 600 ms.
Preferably, the pressing is maintained at a pressure of 3-8 KN.
Preferably, the pulse peak value of the first welding current is 3-5.5 KA.
Preferably, the first time is 200-.
Preferably, the second time is 300-.
Preferably, the pulse peak value of the second welding current is 6-9.5KA, and the third time is 300-600 ms.
Preferably, the fourth time is 80-240 ms.
Preferably, the method further comprises the following steps:
after the second welding current is gradually reduced to 0, the joint is kept pressurized, and cooling water is introduced to the joint.
Preferably, the steel workpiece with the coating comprises a zinc coating steel workpiece and an aluminum-silicon coating steel workpiece; wherein the coating thickness of the zinc coating steel workpiece is 10-35 μm, and the coating thickness of the aluminum-silicon coating steel workpiece is 20-50 μm; the sum of the thicknesses of the zinc coating steel workpiece and the aluminum-silicon coating steel workpiece is 2-4 mm.
The resistance spot welding process method firstly adopts the first welding current to destroy the coating layer, then utilizes the second welding current to finish the heating welding, and sets the output stop for a longer time between the first welding current and the second welding current to promote the discharge of the coating layer material, thereby reducing the influence of the coating layer material on the heating welding, inhibiting the occurrence of splashing, obtaining a wider process window and ensuring the practicability of the welding process in the actual production.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the technology or prior art of the present application and are incorporated in and constitute a part of this specification. The drawings expressing the embodiments of the present application are used for explaining the technical solutions of the present application, and should not be construed as limiting the technical solutions of the present application.
FIG. 1 is a schematic flow diagram of a process for resistance spot welding of a steel workpiece with a coating in accordance with an embodiment of the present invention;
FIG. 2 is an explanatory schematic view of a process implementation apparatus of the resistance spot welding process method according to an embodiment of the invention;
FIG. 3 is a schematic diagram of a welding current output timing sequence for a resistance spot welding process in accordance with an embodiment of the present invention;
FIG. 4 is a graph comparing the maximum tensile and shear forces of a spot weld in comparative experiment 1 using a resistance spot welding process according to an embodiment of the present invention and a comparative example;
fig. 5 is a graph comparing the maximum tensile and shearing force of the welding spot in comparative experiment 2 and the resistance spot welding method using the embodiment of the invention.
Detailed Description
The following detailed description of the embodiments of the present invention will be provided with reference to the accompanying drawings and examples, so that how to apply the technical means to solve the technical problems and achieve the corresponding technical effects can be fully understood and implemented. The embodiments and the features of the embodiments can be combined without conflict, and the technical solutions formed are all within the scope of the present invention.
In the manufacturing production of automobile bodies, resistance spot welding of coated steel workpieces is involved, such as welding of DP950 galvanized coating plates and aluminized silicon 1500MPa hot stamping plates. The inventors studied the resistance spot welding performance of such a welding relation and found that:
in the existing welding process, after welding current is switched on, the plating layers of the two materials are sequentially melted to form a molten coating. Because the zinc coating and the aluminum-silicon coating have differences in thickness, melting point, boiling point, resistivity and the like, the zinc coating is firstly melted, the aluminum-silicon coating is then melted, and the coating in a partial molten state is extruded and discharged under the pressure action of the welding electrode.
Then under the action of welding current, the heat input is continuously increased, the temperature reaches the boiling point of zinc, the liquid zinc is vaporized, and at the moment, coating materials in three states of molten aluminum silicon, molten zinc and vaporized zinc exist at the interface, and the coating materials in the three states cannot be well discharged. In the subsequent process of forming the weld nugget, the coating material which is not discharged influences the heat input effect of the welding current, so that the heat input is uneven, further, the splashing occurs at a smaller current, the performance of the final welding joint is influenced, and the process window is narrower.
Therefore, the invention provides a resistance spot welding process method of a steel workpiece with a coating layer, which adopts a double-pulse mode, and a certain welding retention time is set between two pulses to promote the discharge of a coating material in spot welding, thereby avoiding the occurrence of splashing and obtaining a wider process window.
For example, in the manufacture of vehicle bodies, commonly used sheet materials are zinc-coated sheet materials and aluminum-silicon coated sheet materials subjected to hot stamping. In the aluminum silicon coated plate subjected to hot stamping treatment, the coating material and a steel substrate are subjected to alloy reaction, so that an intermetallic compound and an iron-based solid solution are easily formed, and an oxide is formed on the surface. The zinc-plated coated sheet also has an oxide containing zinc as a main component formed on the surface thereof. Such intermetallic compounds and oxides serve to improve the corrosion resistance of the plate, but at the same time are liable to cause spattering at the time of resistance spot welding.
In the present embodiment, the workpiece lap joint to be welded is formed of the first steel workpiece with the zinc plating layer and the second steel workpiece with the aluminum-silicon plating layer, and the resistance spot welding process proposed by the present invention is performed on the workpiece lap joint.
The present invention is also not limited to the production process and coating process of the welded steel materials, for example, the steel workpiece with the al-si plating layer is formed by hot press forming a hot-rolled steel sheet or a cold-rolled steel sheet, for example, the steel workpiece with the zn plating layer is a hot-rolled steel sheet or a cold-rolled steel sheet on which a metallic zn layer is formed, and for example, the zn plating process is hot-dip galvanizing, galvannealing, zn plating, or zn-fe plating.
The resistance spot welding method according to the embodiment of the present invention will be described with reference to a flowchart shown in fig. 1, a schematic explanatory view of an apparatus for carrying out the resistance spot welding process method according to the embodiment of the present invention shown in fig. 2, and a welding current output timing chart shown in fig. 3.
First, as shown in step S110 in fig. 1, a steel workpiece to be welded is lapped, and a workpiece lap joint body composed of a first steel workpiece 9 and a second steel workpiece 10 is interposed between spot welding electrodes 11a and 11b (shown in fig. 2). The pressure device 12 in fig. 2 supplies pressure, and the spot welding electrodes 11a, 11b apply pressure to and hold the lap of the work piece lap.
The first steel workpiece 9 and the second steel workpiece 10 constituting the workpiece attachment are a zinc-coated plate and an aluminum-silicon-coated plate, respectively. The spot welding electrodes 11a, 11b are typically of chromium copper with a circular top having a flat end face of a diameter, preferably in the range of 4-8 mm. In this example, the diameter of the flat end surface of the spot welding electrode was 6 mm.
As shown in fig. 2, the pressure is provided by a pressurizing device 12, and the pressure generation can be based on a servo motor or on compressed air. The spot welding electrodes 11a and 11b are held in opposition to each other to apply pressure to the workpiece lap, and the magnitude of the pressure output and the holding time are controlled by the pressure controller 8. Specifically, the pressurizing pressure in this embodiment is 3 to 8 KN.
The step S110 is provided for reducing the contact resistance by closely adhering the welding electrode to the workpiece joint and the steel workpieces constituting the workpiece joint. For example, the aluminum-silicon coating layer on the surface of the hot stamping plate with the aluminum-silicon coating layer has high hardness, the surface is microscopically uneven, the contact resistance after lapping is large, the splashing caused by unbalanced heat input at the moment of electrifying is easy to cause, and the contact resistance is reduced by pressing to ensure that each contact surface at the lapping part is closely attached. And during welding, the maintenance of pressure also promotes zinc expulsion and limits molten metal splashing.
Further, in order to ensure the effect of close contact between the welding electrode and the workpiece overlapping body and between the steel workpieces forming the workpiece overlapping body, the pressurization needs to be continued for a certain long time before the welding current is output, the time sequence in the time is called a pre-tightening stage, and similar to the prior art, the duration time of the pre-tightening stage is generally 300-600 ms. The pressurization is also maintained during the welding after the pretensioning phase.
After the step S110, the step S120 shown in fig. 1 is continued, the spot welding electrode outputs a first welding current, the first welding current acts on the lap joint of the workpiece lap joint, a current path is formed between the spot welding electrodes 11a and 11b, and the coating layer of the steel workpiece to be welded is damaged through the current thermal effect.
Fig. 3 is a schematic diagram showing the output timing of the welding current, in step S120, the first welding current is a power frequency alternating current, the pulse peak intensity of the first welding current is I1, the first welding current is continuously applied for a first time t1, in step S120, the coating layer is melted and vaporized, and a part of the melted coating layer is discharged under pressure.
Thereafter, the process S130 shown in fig. 1 is continued, and the spot welding electrode is in the welding current output state as shown in fig. 3, and the output of the first welding current is stopped, and the spot welding electrode is kept for the second time t2, and the plating layer broken in the previous process in the time sequence of t2 is completely discharged from the welding portion. To guarantee the expulsion effect, the sum of the first time t1 and the second time t2 is greater than or equal to 600 ms.
It is understood that the specific selection of t1, t2, and I1 in the above steps S120 and S130 is related to the coating material and the coating thickness. In a specific application scene, the preferable range of the thickness of the zinc coating is 10-35 μm, and the preferable range of the thickness of the aluminum-silicon coating is 20-50 μm. A preferred range of t1 is 200ms to 700 ms. A preferred range of t2 is between 300ms and 600 ms. I1 preferably ranges from 3 to 5.5 KA.
For example, in a preferred embodiment, the zinc coating is 28 μm thick, the aluminum-silicon coating is 35 μm thick, t1 is 300ms, t2 is 300ms, and I1 is 4 KA.
After the step S130, the process S140 in fig. 1 is continued, and the spot welding electrode outputs the second welding current to act on the lap joint of the workpiece lap joint as shown in fig. 3 in the welding current output state. The second welding current is power frequency alternating current and lasts for a third time t3, the pulse peak intensity of the second welding current is I2, and the pulse peak intensity of the second welding current is larger than that of the second welding current, namely I2 is larger than I1.
The second welding current is used for heating welding so as to enable a welding point at the lap joint of the workpiece lap joint body to be in a molten state. Due to the discharge of the plating material in the previous process and the additional preheating effect of the first welding current, the heat affected zone for heating welding in the process is larger, and the mechanical property of the final welding joint is improved.
It is understood that in the step S140, I2 and t3 are selected according to the thickness and material of the plate. In a specific application scene, the thickness of the steel plate with the zinc coating and plating layer is preferably 0.8-1.8mm, the thickness of the steel plate with the aluminum-silicon coating and plating layer is preferably 1-2mm, and the sum of the thicknesses of the two is 2-4 mm; accordingly, a preferred range of t3 is 300ms to 600ms, and a preferred range of I2 is 6-9.5 KA.
For example, in a preferred embodiment, the thickness of the steel sheet with zinc coating is 1.2mm, the thickness of the steel sheet with aluminum silicon coating is 1.8mm, t3 is 400ms, and I2 is 9 KA.
After the step S140, the process S150 in fig. 1 is continued, and after the second welding current lasts for the third time, the second welding current outputted by the spot welding electrode slowly decreases to 0 within the fourth time t4, which is shown in detail in the timing sequence shown in fig. 3. The slowly-falling welding current in the step S150 can slow down the cooling speed of the welding point at the lap joint, so that the molten welding point is gradually cooled to promote the uniform diffusion of the nugget area, and the mechanical property of the final welding joint is improved. A preferred range of t4 is 80-240 ms. For example, t4 is taken to be 200 ms.
Finally, as in the prior art, after the output of the resistance welder is reduced to zero, the lap joint is continuously pressurized for a period of time and continuously cooled, so that the welding spot forms a nugget.
Further, while the pressurization is maintained, circulating cooling water is supplied and flows out from the spot welding electrode through 14 in fig. 2 to cool the spot welding, thereby increasing the cooling rate of the spot welding to improve the mechanical properties of the final nugget. In this example, the flow rate of the cooling water was 2cm3/s。
After the pressurization is maintained for a certain period of time, the pressurization is removed and the welding operation of the welding spot of the workpiece lap is completed.
In addition, in the implementation device of the resistance spot welding process method of fig. 2, 7 is an alternating current power supply for supplying a welding current. Reference numeral 13 denotes a current controller for controlling the magnitude and timing of the welding current outputted from the spot welding electrode. It will be appreciated that fig. 2, 7, 8, 11a, 11b, 12, 13, 14, can be implemented by corresponding functional components of an existing resistance welder. Such as the single-phase ac resistance welder used in the process implementation of this embodiment.
In the spot welding process method provided by the invention, a first welding current with smaller current and longer duration is adopted firstly to ensure that the coating material at the contact interface of the workpiece lapping body is melted and partially removed under small heat input, and then a stop output time sequence with longer duration is set to ensure that the melted and vaporized coating material is completely discharged. Through the above steps, a wide current path is formed at the contact surface, and the occurrence of spatter is suppressed at a large second welding current. And then a second welding current with larger current and shorter electrifying time is used for obtaining a nugget with enough size to meet the welding performance. After the second welding current is finished, the cooling speed is ensured by slowly reducing the current, the carbon diffusion of a fusion area formed by different matrix tissues is promoted, the carbon diffusion tends to be uniform, and the toughness of a welding joint is improved.
The resistance spot welding process method of the steel workpiece with the coating can completely inhibit splashing and improve the appearance quality of the workpiece, thereby omitting the working procedure of cleaning burrs on the surface of the workpiece and improving the production efficiency. In addition, the resistance spot welding process method for the steel workpiece with the coating layer, which is provided by the invention, is adopted, and the output stopping process is set for a longer time, so that a better process window can be obtained under the condition of ensuring that the specified welding strength is obtained. The process window is defined as the difference between the current at which spatter occurs during welding and the current that ensures the reference nugget diameter.
The beneficial effects of obtaining a better process window are further explained by two sets of comparative experiments.
In comparative experiments 1 and 2, the peak current of the second welding current is set as a variable to perform resistance spot welding by fixing part of parameters, so that a lower limit current value for ensuring that a welding joint is used as a reference nugget diameter and an upper limit current value for preventing splashing are obtained, wherein the reference nugget diameter is
(t is the thickness of the thicker sheet material in the work being welded). The nugget diameter of the spot welded joint was measured by microstructure under LEICA microscope, and presence or absence of spatter was confirmed visually at spot welding.
In comparative experiments 1 and 2, the spot welding equipment is a compressed air pressurization type single-phase alternating current resistance electric welding machine, and the diameter of the flat end face of a spot welding electrode is 6 mm. The welded workpiece respectively adopts a hot-dip galvanizing coating DP590 industrial plate and an aluminized silicon coating 1500 MPa-level hot stamping industrial plate. Wherein the thickness of the zinc layer and the alloying thickness thereof is about 28um, the thickness of the aluminum-silicon coating and the alloying thickness thereof is about 35um, and the size is 30mm multiplied by 100 mm. The pressurizing pressure was 3.5KN and the cooling water rate was 2cm3/s。
In comparative experiments 1 and 2, the implementation case of experiment number 1 adopts the process method of the invention, the comparative case of experiment number 2 is used for comparison, the retention time is shorter, the thickness of the plate in comparative experiment 1 is 1.2mm, and the obtained experimental data are shown in table 1.
Table 1 experimental data comparing experiment 1
The DP590 sheet thickness was 1.2mm and the aluminum-silicon-plated hot-stamped sheet thickness was 1.8mm in comparative experiment 2, and the experimental data obtained are shown in Table 2.
Table 2 experimental data comparing experiment 2
As is clear from the comparative experimental data shown in tables 1 and 2, the process window of the example of test No. 1 is expanded by about 1 time as compared with the comparative example of test No. 2.
In addition, the maximum tensile shear (in KN) to the total thickness of the workpiece for the test No. 1 embodiment in tables 1 and 2 was greater than 5, and failure modes were that the nugget was pulled out and the tensile shear was almost close to the strength limit of the galvanized coated sheet. As shown in fig. 4 and 5, the maximum tensile and shearing force of the welding point of the embodiment is improved by about 10% compared with that of the comparative case under the same second welding current.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. A resistance spot welding process method of a steel workpiece with a coating layer comprises the following steps:
overlapping the steel workpieces to be welded, applying pressure to the overlapped part, and pressurizing and maintaining;
applying a first welding current to the lap joint, and enabling the first welding current to be applied for a first time;
removing the first welding current after continuing the first time and maintaining for a second time;
after the second time is kept, applying a second welding current to the lap joint, and enabling the second welding current to be continuously applied for a third time;
after continuing the third time, slowly reducing the second welding current to 0 within a fourth time;
wherein the steel workpiece with the coating comprises a zinc coated steel workpiece and an aluminum silicon coated steel workpiece, and the second welding current is greater than the first welding current, and the sum of the first time and the second time is set to be greater than or equal to 600 ms; the second time is set to 300-.
2. A resistance spot welding process as defined in claim 1 wherein said pressure maintained is 3-8 KN.
3. The resistance spot welding process of claim 1 wherein the first welding current has a pulse peak value of 3-5.5 KA.
4. The process of resistance spot welding as set forth in claim 1 wherein said first time is 200-700 ms.
5. The resistance spot welding process of claim 1 wherein the pulse peak of the second welding current is 6-9.5KA and the third time is 300-.
6. A resistance spot welding process as claimed in claim 1 wherein said fourth time is 80 to 240 ms.
7. The resistance spot welding process of claim 1, further comprising:
after the second welding current is gradually reduced to 0, the joint is kept pressurized, and cooling water is introduced to the joint.
8. A resistance spot welding process according to any one of claims 1 to 7 wherein said zinc coated steel work piece has a coating thickness of 10 to 35 μm and said aluminum silicon coated steel work piece has a coating thickness of 20 to 50 μm; the sum of the thicknesses of the zinc coating steel workpiece and the aluminum-silicon coating steel workpiece is 2-4 mm.
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