A method for improving the performance of resistance spot welded joints on pickled plates

Abstract

This invention discloses a method for improving the performance of resistance spot welded joints on pickled plates, comprising the following steps: Step 1, determining the current and preheating time; Step 2, determining the pulse time; Step 3, determining the current value and tempering time; Step 4, determining the time; Step 5, determining the welding pressure; Step 6, determining the holding pressure time; Step 7, resistance spot welding; wherein in Step 1, the preheating current I is determined according to the plate thickness. P With preheating time t P The size; where in step two above, three-pulse welding is used, and the pulse time t is determined according to the plate thickness. w In step three above, the current value I of the tempering pulse is determined. t With tempering time t t The purpose of using tempering pulses in this invention is to slow down the cooling rate of the welded joint, thereby reducing residual stress at the joint and improving joint performance. At the same time, this method has the advantages of suppressing spatter, increasing the welding process window, changing the joint failure mode, and improving joint performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding technology, in particular to a method for improving the performance of a resistance spot welded joint of a pickled plate. BACKGROUND

[0002] Pickled plates are mainly used in automobile girders, cross members, wheels, including rims, cab inner plates, carriage plates, etc. At present, pickled plates are widely used in the automobile manufacturing industry, and the spot welding process is also relatively mature. However, some pickled plates with high strength have large internal holes in the narrow window during spot welding. In addition, when using the existing pickled plate welding process to weld pickled plates with high strength, the joint shear tensile failure mode is often interface failure, which seriously affects the mechanical properties of the joint, thereby preventing the pickled plates from being applied to automobile production. Therefore, there is an urgent need to develop a method for improving the performance of a resistance spot welded joint of a pickled plate. Therefore, how to improve the performance of the pickled plate joint has become the key to better application and promotion. SUMMARY

[0003] The purpose of the present application is to provide a method for improving the performance of a resistance spot welded joint of a pickled plate to solve the problems raised in the background.

[0004] To achieve the above purpose, the present application provides the following technical scheme: a method for improving the performance of a resistance spot welded joint of a pickled plate, comprising the following steps: step one, determining the current and preheating time; step two, determining the pulse time; step three, determining the current value and tempering time; step four, time determination; step five, welding pressure determination; step six, dwell time determination; step seven, resistance spot welding;

[0005] In the above step one, the preheating current I P and the preheating time t P are determined according to the thickness of the plate.

[0006] In the above step two, three-pulse welding is used, and a pulse time t w is determined according to the thickness of the plate.

[0007] In the above step three, the current value I t and the tempering time t t of the tempering pulse are determined.

[0008] In the above step four, the preheating pulse and welding pulse cooling interval time t c1 , welding pulse interval time t c2 , and welding pulse and tempering pulse cooling interval time t c3 are determined according to the thickness of the plate.

[0009] In the above step five, the welding pressure P is determined according to the strength of the steel plate.

[0010] wherein in the above step six, the pressure holding time t is determined according to the strength of the steel plate h , 100ms≤t h ≤250ms;

[0011] wherein in the above step seven, the medium frequency DC spot welding machine is used to implement resistance spot welding according to the above determined parameters and in the time sequence of pre-pressing, pre-heating, welding, tempering and pressure holding.

[0012] Preferably, in the above step one, the pre-heating current I P is in the range of 10kA≤I P ≤15kA; and the pre-heating time t P is in the range of 20ms≤t P ≤40ms.

[0013] Preferably, in the above step two, the pulse time t w is in the range of 200ms≤t w ≤240ms; and the three-pulse welding current relationship is I w1 =I w2 -2=I w3 -4.

[0014] Preferably, in the above step three, the calculation formula is I t =0.5I w3 , and the tempering time 150ms≤t t ≤200ms.

[0015] Preferably, in the above step four, the relationship among the welding pulse cooling interval time t c1 , the welding pulse interval time t c2 , and the welding pulse and tempering pulse cooling interval time t c3 is 20ms≤t c1 =t c2 =t c3 ≤40ms.

[0016] Preferably, in the above step five, the welding pressure P is selected in the range of 5-6.5kN.

[0017] Compared with the prior art, the method for improving the performance of the spot-welded joint of the pickled plate has the advantages that the method is particularly suitable for the pickled plate with high strength, the iron oxide scale on the surface of the pickled plate is removed by using a large current and a short time pulse, so that the content of the iron oxide scale in the nugget is greatly reduced, the surface spatter caused by long-time continuous heating is avoided by using a welding current with gradually increasing three pulses, and the nugget size is further increased, the cooling speed of the joint after welding is reduced by using a tempering pulse, the residual stress at the joint is reduced, and the joint performance is improved, the method has the advantages of inhibiting spatter, increasing the welding process window, changing the failure mode of the joint, and improving the joint performance, and the pickled plate can be better applied to the automobile manufacturing field. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 The method flow chart of the present application is shown in the figure.

[0019] Fig. 2 The welding timing chart of the present application is shown in the figure. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. 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.

[0021] Please refer to Figs. 1-2 The present application provides an embodiment: a method for improving the performance of the spot-welded joint of the pickled plate, comprising the following steps: step one, determining the current and preheating time; step two, determining the pulse time; step three, determining the current value and tempering time; step four, time determination; step five, welding pressure determination; step six, dwell time determination; and step seven, resistance spot welding.

[0022] In the above step one, the welding material is a 2.0mm 780HE pickled plate with a small amount of iron oxide scale on the surface, the pre-pressing time is 300ms, a medium-frequency direct-current spot-welding machine is used, the preheating current I p =15kA is determined according to the thickness of the iron oxide scale, and the preheating time t p =20ms.

[0023] In the above step two, three-pulse welding is used, and the single-pulse welding time t w =220ms is determined according to the thickness of the plate.

[0024] In the above step three, the tempering current I t =0.5I is selected.w3 ; select tempering time t t = 180 ms;

[0025] wherein in the above step four, the cooling time interval t is determined according to the plate thickness c1 = t c2 = t c3 = 30 ms;

[0026] wherein in the above step five, the welding pressure p = 6 kN is selected according to the strength of the steel plate;

[0027] wherein in the above step six, the holding time t is selected according to the strength of the pickled plate h = 250 ms;

[0028] wherein in the above step seven, the resistance spot welding is performed by using a medium frequency direct current spot welding machine according to the above determined parameters and in the time sequence of pre-pressing, pre-heating, welding, tempering and holding, and the resistance spot welding process window of 2.0 mm 780HE obtained based on the welding parameters is 2.5 kA, which is much larger than the standard requirement of greater than 1 kA; the shear performance of the joint is greater than 30 kN, and the failure mode is all nugget pull-out, and there is no spatter on the surface.

[0029] Based on the above, the advantages of the present application are that when the present application is used, it has the following significant advantages: 1. It is suitable for all pickled plates, especially pickled plates with higher strength; 2. It can effectively suppress surface spatter; 3. The internal structure of the nugget is uniform without obvious holes; 4. The welding process window is significantly increased; 5. The joint failure mode is all nugget pull-out, and the joint mechanical performance is significantly improved.

[0030] It is apparent to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the above description, and it is intended to encompass all changes falling within the meaning and scope of the equivalent elements of the claims. Any reference signs in the claims should not be considered as limiting the claims involved.

Claims

1. A method of improving the performance of an acid wash sheet resistance spot welded joint comprising the steps of: Step one, determine the current and preheating time; step two, determine the pulse time; step three, determine the current value and tempering time; step four, time determination; step five, welding pressure determination; step six, pressure holding time determination; step seven, resistance spot welding; characterized in that: wherein in the above step one, the preheating current I is determined according to the plate thickness P and the size of the preheating time t P ; wherein in step two above, a three pulse welding is used, and a pulse time t is determined according to the thickness of the plate w ; wherein in step three above, the current value I of the tempering pulse is determined t with the tempering time t t ; wherein in the above step four, the preheat pulse and the welding pulse cooling interval time tc1, the welding pulse interval time t c2 , the welding pulse and the temper pulse cooling interval time tc2 are determined according to the plate thickness c3 ; In the above step five, the welding pressure P is determined according to the strength of the steel plate; wherein in the above step six, the pressure holding time t is determined according to the strength of the steel sheet h , 100 ms ≤ t h ≤ 250 ms; In the above step seven, a medium frequency direct current spot welding machine is used to implement resistance spot welding according to the determined parameters and the time sequence of pre-pressing, preheating, welding, tempering and pressure holding; The preheating current I P in the step one has a magnitude in the range of 10 kA ≤ I P ≤ 15 kA; the preheating time t P has a magnitude in the range of 20 ms ≤ t P ≤ 40 ms; The pulse time t w in the second step is in the range of 200 ms ≤ t w ≤ 240 ms; the three-pulse welding current relationship is I w1 = I w2 - 2 = I w3 - 4. In step three, the calculation formula is: I t = 0.5I w3 , the tempering time 150 ms ≤ t t ≤ 200 ms; In the fourth step, the welding pulse cooling interval time t c1 , the welding pulse interval time t c2 , the welding pulse and tempering pulse cooling interval time t c3 The relationship between them is 20ms≤t c1 = t c2 = t c3 ≤40ms; In the above step five, the welding pressure P is selected in the range of 5-6.5 kN.

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