A resistance spot welding process for plated steel sheets

Abstract

The application discloses a resistance spot welding process for plated steel sheet, and is characterized in that the welding current I and the total welding time WT are determined based on the following steps: obtaining the thickness t of the plated steel sheet and the resistivity p of the plated steel sheet; determining the corresponding thickness coefficient m based on the thickness t; determining the corresponding resistivity coefficient n based on the resistivity p; determining the welding current I of the resistance spot welding based on the thickness coefficient m and the resistivity coefficient n; determining the total welding time WT of the resistance spot welding based on the thickness coefficient m; wherein t0 represents the set reference thickness, and the value of t0 is 0.5 mm; the resistivity p0 represents the set reference resistivity, and the value of p0 is 10 μΩ·cm; I b represents the set reference current, which is the welding current of the plate material with the thickness of the reference thickness t0 and the resistivity of the reference resistivity p0, and the unit parameter of I min is KA; and WT0 represents the set reference welding time.

Description

Technical Field

[0001] This invention relates to a welding process, and more particularly to a resistance spot welding process. Background Technology

[0002] High-strength steel is characterized by high strength, high plasticity, and high toughness. It can reduce the weight of the vehicle body while improving the vehicle's collision safety.

[0003] However, high-strength steel generally contains more alloying elements and has a higher carbon equivalent, resulting in poorer weldability compared to ordinary mild steel. In resistance spot welding, this manifests as a narrower welding window, a greater risk of interface fracture, an increase in weld nugget defects (shrinkage cavities, porosity, hot and cold cracks), and materials above 1 GPa are prone to softening in the heat-affected zone. Furthermore, coated high-strength steel can exacerbate electrode wear, thereby reducing electrode life.

[0004] Due to the narrow welding window of high-strength steel, insufficient heat input makes it difficult to form a large weld nugget, easily leading to incomplete welds and insufficient load-bearing capacity. Conversely, excessive heat input easily causes spatter, resulting in more defects in the weld nugget. Excessive spatter reduces the weld nugget size, lowers weld strength, and affects the assembly accuracy of the parts. Therefore, selecting appropriate spot welding parameters is crucial when welding high-strength steel.

[0005] Furthermore, due to the wide variety of high-strength steels, the types of hand parts produced in actual production are even more complex, with variations in strength levels, plate thicknesses, and coating types, resulting in numerous joint combinations. In on-site production, the same welding torch is often used to weld many different types of joints, further increasing the difficulty of producing qualified spot welds.

[0006] Currently, the workload of outputting qualified process parameters is quite large. Generally, based on the basic information of the plate material (strength, thickness, whether it has a coating), we gradually explore each process parameter and find the weldable range, and then test the strength, metallographic formation, hardness, and electrode life of the weld.

[0007] This shows that while the traditional process provides an accurate and comprehensive evaluation of the various spot welding properties of the material, the evaluation cycle is long, generally requiring 5-15 working days, and involves a large workload, consuming 5-10 million cubic meters of material. 2 The materials used are varied. At OEM (Original Equipment Manufacturer) sites, it's common to see different materials being lapped and spot-welded together. The types of components are also more complex, with variations in strength levels, plate thickness, and plating types. If traditional methods are used to develop spot-welding processes, it would involve a significant workload and impact production schedules.

[0008] To improve the welding quality of weld joints under complex working conditions and to produce suitable spot welding processes, improvements are generally made in three aspects: process parameters, welding equipment, and auxiliary materials. Existing patent literature covers these areas, including:

[0009] For example, Chinese patent document CN108015401A, published on May 11, 2018, entitled "Resistance Spot Welding Method for Galvanized High-Strength Steel with Good Joint Performance," discloses a resistance spot welding method for galvanized high-strength steel with good joint performance. It uses a three-pulse method to obtain a resistance spot welded joint of galvanized high-strength steel with good joint performance and effectively suppresses liquid metal embrittlement (LME) cracks generated during spot welding of high-strength galvanized steel sheets, increasing the probability of button breakage at the weld point during destructive testing. However, it is unknown whether it is applicable to materials with low LME sensitivity.

[0010] For example, Chinese patent document CN116586732A, published on August 15, 2023, entitled "A resistance spot welding process for three-layer steel plates and the electrodes used therein", discloses a resistance spot welding process for three-layer steel plates and the electrodes used therein. This Chinese patent document solves the problem that the outer low-resistance steel plate cannot form a qualified weld nugget with the high-resistance steel plate by setting electrodes with different end face areas on the upper and lower sides. However, it is not suitable for joint materials with similar resistance.

[0011] For example, Chinese patent document CN117798480A, published on April 2, 2024, entitled "A Method for Ensuring the Quality of Resistance Spot Welds on Steel Plates," discloses a method for ensuring the quality of resistance spot welds on steel plates. This Chinese patent document adjusts the welding pressure and current, performs welding and tear analysis on the samples, and plots the weldability range of the electrode pressure-welding current window. Although it ensures the quality of spot welding, it is inefficient and not applicable in the case of multi-joint combinations on site. Summary of the Invention

[0012] One objective of this invention is to provide a resistance spot welding process for coated steel sheets, which can be used to spot weld joints of coated steel sheets with different thicknesses and resistivities. This resistance spot welding process also solves the problem of difficulty in determining process parameters due to the complexity of the materials used in spot welding joints, thereby reducing workload and improving production efficiency.

[0013] To achieve the above objectives, the present invention provides a resistance spot welding process for coated steel sheets, which performs resistance spot welding based on a welding current I and a total welding time WT determined by the following steps:

[0014] Obtain the thickness t and resistivity ρ of the coated steel sheet;

[0015] Determine the corresponding thickness coefficient m based on the plate thickness t:

[0016]

[0017] Based on the resistivity ρ, determine the corresponding resistivity coefficient n:

[0018]

[0019] The welding current I for resistance spot welding is determined based on the thickness coefficient m and resistivity coefficient n.

[0020] I = I b +200KA×(mn);

[0021] The total welding time WT for resistance spot welding is determined based on the thickness coefficient m.

[0022] WT = WT0 + 65ms × m

[0023] Where t0 represents the set reference thickness, which is 0.5 mm; resistivity ρ0 represents the set reference resistivity, which is 10 μΩ·cm; I b This indicates the set reference current, which is the current used to obtain a weld nugget diameter greater than the minimum weld nugget diameter D for a plate with a plate thickness of reference thickness t0 and a resistivity of reference resistivity ρ0. min The welding current is expressed in kA; WT0 represents the set reference welding time.

[0024] In this invention, based on the inherent material property of resistivity and combined with the material thickness, a resistance spot welding process for coated steel plates is proposed. Based on the plate thickness t and the plate resistivity ρ, the corresponding thickness coefficient m and resistivity coefficient n are obtained, and the welding current I is determined according to m and n; the total welding time WT is determined based on the thickness coefficient m corresponding to the plate thickness t.

[0025] Furthermore, in the resistance spot welding process described in this invention, the minimum weld nugget diameter D min Determined based on the obtained plate thickness t:

[0026] When 0.5mm ≤ t < 1.3mm, D min =4.0mm;

[0027] When 1.3mm ≤ t < 1.9mm, D min =5.0mm;

[0028] When 1.9mm ≤ t < 2.6mm, D min =6.0mm;

[0029] When t≥2.6mm, D min=7.0mm.

[0030] Furthermore, in the resistance spot welding process described in this invention, the reference current I... b The value range is 7.2-8.4KA.

[0031] Furthermore, in the resistance spot welding process described in this invention, the value range of WT0 is 120-170ms.

[0032] Furthermore, in the resistance spot welding process described in this invention, in the step of obtaining the plate thickness t of the coated steel plate, when the joint assembly of the resistance spot weld has multiple layers of plates with different plate thicknesses t, the plate thickness t is obtained based on the following rule:

[0033] When the joint assembly of resistance spot welding has two layers of plates with different thicknesses t, the plate thickness t is taken as the smaller value.

[0034] When the resistance spot welding joint assembly has three layers of plates with different thicknesses t, the plate thickness t is taken as the median value of the plate thicknesses of each plate.

[0035] When the joint assembly of resistance spot welding has three or more layers of plates with different thicknesses t, the plate thickness t is taken as the average value of the thicknesses of each plate.

[0036] Furthermore, in the resistance spot welding process described in this invention, in the step of obtaining the resistivity ρ of the coated steel plate, when the materials in the joint assembly have multiple plates with different resistivity ρ, the resistivity with the maximum value ρ is taken as the obtained resistivity.

[0037] Furthermore, in the resistance spot welding process described in this invention, when the obtained plate thickness t ≥ 1.0 mm, multi-pulse welding is adopted, and the number of pulses N is determined based on the obtained plate thickness t:

[0038] When 0.5mm ≤ t < 1.1mm, N = 1;

[0039] When 1.1mm ≤ t < 1.3mm, N = 2;

[0040] When 1.3mm ≤ t < 1.9mm, N = 3;

[0041] When 1.9mm ≤ t < 2.4mm, N = 4;

[0042] When t≥2.4mm, N=5.

[0043] Furthermore, in the resistance spot welding process described in this invention, when multi-pulse welding is used, the welding current I of each pulse segment is the same.

[0044] Furthermore, in the resistance spot welding process described in this invention, when multi-pulse welding is used, the welding time WT for each pulse segment is...N Same, WT N Satisfying the formula:

[0045]

[0046] Furthermore, in the resistance spot welding process described in this invention, when multi-pulse welding is used, the cooling time between each pulse segment is ≤50ms.

[0047] Furthermore, in the resistance spot welding process described in this invention, the welding pressure F of resistance spot welding is determined based on the obtained plate thickness t:

[0048] When 0.5mm≤t<1.1mm, the value of F ranges from 1.8 to 2.2 kN;

[0049] When 1.1mm≤t<1.3mm, the value of F ranges from 2.4 to 2.8 kN;

[0050] When 1.3mm≤t<1.9mm, the value of F ranges from 3.4 to 3.8 kN;

[0051] When 1.9mm≤t<2.4mm, the value of F ranges from 4.8 to 5.2 kN;

[0052] When t≥2.4mm, the value of F ranges from 6.8 to 7.2 kN.

[0053] Furthermore, in the resistance spot welding process described in this invention, the electrode end face shape used in resistance spot welding is spherical, and the diameter of the electrode end face is 5.0-10.0 mm.

[0054] Furthermore, in the resistance spot welding process described in this invention, the pre-pressure time before welding is 300-1500ms.

[0055] Furthermore, in the resistance spot welding process described in this invention, the holding time after welding is 100-600ms.

[0056] Another object of the present invention is to provide a resistance spot welded steel connector that has stable and excellent quality.

[0057] To achieve the above objectives, the present invention also provides a resistance spot welded steel connector, which is manufactured by the resistance spot welding process described above.

[0058] Furthermore, in the resistance spot welded steel connection joint described in this invention, the relationship between the diameter D of the weld nugget and the width d of the single-sided weld heat-affected zone satisfies: 4≤D / d≤10.

[0059] It should be noted that in this invention, the relationship between the diameter D of the melt nugget and the minimum melt nugget diameter Dmin mentioned above is D≥Dmin.

[0060] Furthermore, in the resistance spot welding steel connection joint described in this invention, the ratio of the electrode indentation depth t' to the plate thickness t of the plate on which it is located is 0 < t' / t ≤ 0.5.

[0061] Furthermore, in the resistance spot welded steel connection joint described in this invention, the ratio of the height T' of the weld nugget to the total plate thickness T is 0.3 ≤ T' / T < 0.8, where the total plate thickness is the sum of the thicknesses of the plates lapped together to form the resistance spot welded steel connection joint (for example, when the lapped joint has two layers of plates, T = t). A +t B When the lap joint has three layers of plates, T = t A +t B +t C ).

[0062] Compared with the prior art, the resistance spot welding process for coated steel plates described in this invention has the following advantages:

[0063] The resistance spot welding process for coated steel sheets described in this invention is based on the inherent material property of resistivity and, in combination with material thickness, proposes a resistance spot welding process for coated steel sheets. This resistance spot welding process allows for precise determination of spot welding parameters according to thickness and resistivity, flexibly addressing the complex and varied material joint combinations in automotive bodies, thereby obtaining qualified welds. It also significantly reduces the amount of experimentation required to find suitable process parameters and improves production efficiency. Attached Figure Description

[0064] Figure 1 This invention demonstrates the welding current I in the resistance spot welding process for coated steel sheets within the weldable range of the joint assembly (I0). min -I max A schematic diagram within the range of ).

[0065] Figure 2 A schematic diagram of a resistance spot welded steel joint obtained by the resistance spot welding process of coated steel plate described in this invention is shown. Detailed Implementation

[0066] The resistance spot welding process for coated steel plates described in this invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, this explanation and description do not constitute an undue limitation on the technical solution of this invention.

[0067] Resistivity is a physical quantity used to represent the electrical resistance of a material, reflecting its property of impeding the flow of electric current. In resistance spot welding, resistivity is a crucial property of the materials being welded, determining the magnitude of the resistance and thus affecting the heat generated during welding. Generally, metals with high resistivity generate heat easily but have poor thermal conductivity, requiring a smaller heat input; conversely, metals with low resistivity generate heat more slowly but have better thermal conductivity, requiring a larger heat input. Simultaneously, thickness is also a significant parameter determining the required welding heat input; generally, thicker joints require a greater welding heat input.

[0068] For materials of the same thickness and microstructure, generally, materials with higher strength have more alloying elements and internal crystal defects, resulting in higher resistivity. Therefore, to generate a weld nugget of the same diameter, they require less heat input and, assuming other spot welding process parameters are the same, less welding current. Conversely, materials with lower strength have fewer alloying elements and lower resistivity, requiring greater heat input to produce a weld nugget of the required size. Under the same spot welding process parameters, they require a greater welding current.

[0069] In this invention, based on the inherent material property of resistivity and considering the material thickness, a resistance spot welding process for coated steel plates is proposed. This process involves resistance spot welding based on a welding current I and a total welding time WT determined by the following steps:

[0070] 100: Obtain the thickness t and resistivity ρ of the coated steel sheet;

[0071] In some embodiments, in the step of obtaining the plate thickness t of the coated steel sheet, when the resistance spot welded joint assembly has multiple layers of plates with different plate thicknesses t, the plate thickness t is obtained based on the following rule:

[0072] When the joint assembly of resistance spot welding has two layers of plates with different thicknesses t, the plate thickness t is taken as the smaller value.

[0073] When the resistance spot welding joint assembly has three layers of plates with different thicknesses t, the plate thickness t is taken as the median value of the plate thicknesses of each plate.

[0074] When the joint assembly of resistance spot welding has three or more layers of plates with different thicknesses t, the plate thickness t is taken as the average value of the thicknesses of each plate.

[0075] In some implementations, in the step of obtaining the resistivity ρ of the coated steel sheet, when the materials in the joint assembly have multiple sheets with different resistivity ρ, the resistivity with the maximum value ρ is taken as the obtained resistivity.

[0076] In some specific implementations, the range of ρ can be between 5 and 80 μΩ·cm.

[0077] In some more specific implementations:

[0078] (1) When the joint assembly has two plates, for easy distinction, the two plates can be represented as A and B respectively, with corresponding plate thicknesses t. A t B ,but:

[0079] (a) When the two plates are of equal thickness, t = t A =t B；

[0080] (b) When the thicknesses of the two plates are different, t should be the smaller value;

[0081] (2) When the joint assembly has three layers of plates, t is taken as the middle value. For easy distinction, the three layers are represented as A, B, and C, and the corresponding plate thicknesses are t, respectively. A t B t C ,but:

[0082] (a) When the three-layer plate has the same thickness, t = t A =t B =t C ;

[0083] (b) When two layers of a three-layer board have the same thickness, if t A =t B Then regardless of t C The size, t = t A =t B ;

[0084] (c) When the three layers are all different in size, t is taken as the thickness of the middle layer.

[0085] (3) When the joint is larger than three layers, t is taken as the average value.

[0086] 200: Determine the corresponding thickness coefficient m based on the plate thickness t:

[0087]

[0088] Where t0 represents the set reference thickness, which is 0.5 mm.

[0089] 300: Determine the corresponding resistivity coefficient n based on the resistivity ρ:

[0090]

[0091] Wherein, resistivity ρ0 represents the set reference resistivity, which is 10 μΩ·cm.

[0092] 400: Determine the welding current I for resistance spot welding based on the thickness coefficient m and resistivity coefficient n.

[0093] I = I b +200KA×(mn);

[0094] Among them, I b This indicates the set reference current, which is the current used to obtain a weld nugget diameter greater than the minimum weld nugget diameter D for a plate with a plate thickness of reference thickness t0 and a resistivity of reference resistivity ρ0. min The welding current, with a unit parameter of KA.

[0095] Figure 1 The resistance spot welding process for coated steel sheets described in this invention uses the formula I = I b The range of welding current I is determined by +200KA×(mn). Figure 1 middle, I min To obtain the minimum current limit for the molten core diameter, I max This is the current value at which splashing occurs.

[0096] In some implementations, the reference current I b The value range is 7.2-8.4KA, and no splashing occurs within this range.

[0097] In some implementations, the minimum melt core diameter D min Determined based on the obtained plate thickness t:

[0098] When 0.5mm ≤ t < 1.3mm, D min =4.0mm;

[0099] When 1.3mm ≤ t < 1.9mm, D min =5.0mm;

[0100] When 1.9mm ≤ t < 2.6mm, D min =6.0mm;

[0101] When t≥2.6mm, D min =7.0mm.

[0102] In some specific embodiments, a DC spot welding machine can be used. In some specific embodiments, a medium-frequency DC spot welding machine is preferably used.

[0103] In some specific implementations, the determined process parameters are not affected by the overlapping sequence of the joint materials.

[0104] In some implementations, when the obtained plate thickness t ≥ 1.0 mm, multi-pulse welding is used, and the number of pulses N is determined based on the obtained plate thickness t:

[0105] When 0.5mm ≤ t < 1.1mm, N = 1;

[0106] When 1.1mm ≤ t < 1.3mm, N = 2;

[0107] When 1.3mm ≤ t < 1.9mm, N = 3;

[0108] When 1.9mm ≤ t < 2.4mm, N = 4;

[0109] When t≥2.4mm, N=5.

[0110] In some implementations, when multi-pulse welding is used, the welding current I is the same for each pulse.

[0111] In some implementations, when multi-pulse welding is used, the welding time WT for each pulse is... N Same, WT N Satisfying the formula:

[0112]

[0113] In some implementations, when using multi-pulse welding, the cooling time between each pulse segment is ≤50ms. In some implementations, the cooling time between each pulse segment can be further controlled to ≤30ms.

[0114] 500: The total welding time WT for resistance spot welding is determined based on the thickness coefficient m.

[0115] WT = WT0 + 65ms × m

[0116] WT0 represents the set baseline welding time.

[0117] In some implementations, the value of WT0 ranges from 120 to 170 ms.

[0118] In some implementations, the welding pressure F for resistance spot welding is determined based on the obtained plate thickness t:

[0119] When 0.5mm≤t<1.1mm, the value of F ranges from 1.8 to 2.2 kN;

[0120] When 1.1mm≤t<1.3mm, the value of F ranges from 2.4 to 2.8 kN;

[0121] When 1.3mm≤t<1.9mm, the value of F ranges from 3.4 to 3.8 kN;

[0122] When 1.9mm≤t<2.4mm, the value of F ranges from 4.8 to 5.2 kN;

[0123] When t≥2.4mm, the value of F ranges from 6.8 to 7.2 kN.

[0124] In some embodiments, the electrode end face of the resistance spot welding is spherical, with a diameter of 5.0-10.0 mm. In some embodiments, the diameter of the electrode end face can be further controlled between 6.0-8.0 mm.

[0125] In some embodiments, the pre-compression time before welding is 300-1500 ms. In some embodiments, the pre-compression time before welding can be further controlled between 500-1000 ms.

[0126] In some embodiments, the holding time after welding is 100-600 ms. In some embodiments, the holding time after welding can be further controlled between 150-300 ms.

[0127] The coated steel sheet used in this invention can be made of various materials with different strengths, including the connection between high-strength steel, the connection between high-strength steel and ordinary steel, and the connection between ordinary steel. The tensile strength of the coated steel sheet can be 200-2000MPa.

[0128] In some specific embodiments, the coating of the coated steel sheet includes, but is not limited to, hot-dip galvanizing, electro-galvanizing, zinc-iron alloy, zinc-aluminum-magnesium, and aluminum-silicon coatings.

[0129] Figure 2 A schematic diagram of a resistance spot welded steel connection joint manufactured using the resistance spot welding process of coated steel plate described in this invention is shown.

[0130] like Figure 2 As shown in the figure, "A" represents the upper plate, "B" represents the lower plate, "HAZ" represents the heat-affected zone, "NZ" represents the melt nugget, "D" represents the melt nugget diameter, and "d" represents the diameter of the melt nugget. L "d" indicates the width of the heat-affected zone on the left side, as shown in the figure. R "" indicates the width of the heat-affected zone on the right, as indicated by the label "t" in the diagram. A "" indicates the thickness of the upper plate, as indicated by the label "t" in the diagram. B "" indicates the thickness of the lower plate, as indicated by the label "t" in the diagram. A’ "" indicates the electrode indentation depth of the upper plate, labeled "t" in the figure. B’ "" indicates the electrode indentation depth of the lower plate, and the symbol "T'" in the figure indicates the height of the melt nugget.

[0131] To better illustrate the application of the resistance spot welding process for coated steel plates described in this invention, some embodiments are also provided for further explanation.

[0132] Examples 1-26

[0133] It should be noted that Examples 1-26 in this group are all joint combinations between coated plates, including connections between two-layer and three-layer plates, involving materials with different thicknesses, strengths, coatings, and resistivities. t and ρ are determined according to the principles for determining plate thickness and resistivity in the joint combination. Table 1 shows detailed information on the joint combinations of each example.

[0134] Table 1 lists the joint assembly material information for Embodiments 1-26 of the present invention.

[0135] Table 1.

[0136]

[0137]

[0138] Furthermore, it should be noted that embodiments 1-11, 13-20, 22, and 25-26 of the present invention use spherical electrodes with an electrode end face diameter of 6.0 mm; embodiments 12, 21, and 23-24 use spherical electrodes with an electrode end face diameter of 8.0 mm. The pre-compression time before welding in embodiments 1-7, 10-11, 14-18, and 26 is 500 ms; the pre-compression time before welding in embodiments 8-9, 13, 19-20, 22, and 25 is 800 ms; and the pre-compression time before welding in embodiments 12, 21, and 23-24 is 1000 ms. The holding time after welding in embodiments 1-7, 10-11, 14-18, and 26 is 200 ms; and the holding time after welding in embodiments 8-9, 12-13, and 19-25 is 250 ms.

[0139] Then, the welding pressure F and pulse N are determined based on t. The thickness coefficient m and resistivity coefficient n are calculated based on t and ρ, respectively. This allows for the determination of the range of welding current I and welding time WT. Within this range, a specific actual welding current I is selected. 实 And actual welding time WT 实 The detailed spot welding process for each embodiment is shown in Table 2.

[0140] Tables 2-1 and 2-2 list the specific process parameters for embodiments 1-26 of the present invention.

[0141] Table 2-1.

[0142] Example Thickness coefficient m resistivity coefficient n <![CDATA[WT N (ms)]]> Pulse number N CT(ms) 1 1.4 1.80 110 2 20 2 1.4 3.83 110 2 20 3 1.0 4.00 200 1 0 4 0.6 1.98 180 1 0 5 1.0 0.17 200 1 0 6 1.4 2.37 120 2 0 7 1.0 2.55 200 1 0 8 1.8 1.59 83 3 20 9 2.0 2.51 90 3 20 10 1.4 4.00 120 2 20 11 1.4 3.83 120 2 20 12 2.6 2.51 100 3 20 13 2.0 2.09 90 3 20 14 1.4 4.00 120 2 20 15 1.0 1.98 210 1 0 16 1.4 1.80 115 2 20 17 1.4 4.00 115 2 20 18 1.4 3.83 120 2 0 19 1.8 3.83 83 3 20 20 2.0 4.00 90 3 20 21 2.6 4.00 100 3 20 22 2.0 2.51 90 3 20 23 2.6 3.83 107 3 20 24 2.6 1.98 107 3 20 25 2.2 3.83 97 3 20 26 1.4 1.98 120 2 0

[0143] Table 2-2.

[0144]

[0145]

[0146] The minimum melting nucleus diameter D is determined based on t. min In the above embodiments, the reference current I b When the plate thickness is taken as the reference thickness t0 = 0.5 mm and ρ = 10 μΩ·cm, the weld nugget diameter meets the requirements (the weld nugget diameter meeting the requirements means that the minimum weld nugget diameter D is met). min The current is ≥4), and its value is 7.2-8.4KA; the reference welding time WT0 is the appropriate welding time when the plate thickness is the reference thickness t0=0.5mm, and its value is 120-170ms.

[0147] Table 3 lists the actual weld nugget diameter data of Examples 1-26 of the present invention, measured by metallographic method, using the spot welding processes listed in Tables 2-1 and 2-2.

[0148] Table 3.

[0149]

[0150]

[0151] As shown in Table 3, the results of each embodiment show D 实 All are greater than D min The solder joints in all embodiments were of acceptable quality.

[0152] Examples 27-46

[0153] Examples 27-46 all involve joint combinations between coated plates, including connections between two-layer and three-layer plates, involving materials with different thicknesses, strengths, coatings, and resistivities. The values ​​t and ρ are determined based on the principles for determining plate thickness and resistivity in the joint combination. Table 4 provides detailed information on the joint combinations of Examples 27-46.

[0154] Table 4 lists the joint assembly material information for Embodiments 27-46 of the present invention.

[0155] Table 4.

[0156]

[0157]

[0158] Furthermore, it should be noted that embodiments 27-35, 38-39, 41-42, and 44-46 of the present invention use spherical electrodes with an electrode end face diameter of 6.0 mm; embodiments 36-37, 40, and 43 use spherical electrodes with an electrode end face diameter of 8.0 mm. The pre-compression time before welding in embodiments 27-29, 31-35, 38, 41-42, and 45-46 is 500 ms; the pre-compression time before welding in embodiments 30, 39, and 44 is 800 ms; and the pre-compression time before welding in embodiments 36-37, 40, and 43 is 1000 ms. The holding time after welding in embodiments 27-29, 31-35, 38, 41-42, and 45-46 is 200 ms; and the holding time after welding in embodiments 30, 36-37, 39-40, and 43-44 is 250 ms.

[0159] Then, the welding pressure F and pulse N are determined based on t. The thickness coefficient m and resistivity coefficient n are calculated based on t and ρ, respectively. This allows for the determination of the range of welding current I and welding time WT. Within this range, a specific actual welding current I is selected. 实 And actual welding time WT 实 The detailed spot welding process is shown in Table 5.

[0160] Tables 5-1 and 5-2 list the specific process parameters for embodiments 27-46 of the present invention.

[0161] Table 5-1.

[0162] Example Thickness coefficient m resistivity coefficient n <![CDATA[WT N (ms)]]> Pulse number N CT(ms) 27 1.4 2.50 110 2 20 28 1.4 1.80 135 2 20 29 1.0 3.83 210 1 0 30 2.2 2.09 97 3 20 31 0.6 2.51 180 1 0 32 1.0 3.28 210 1 0 33 1.4 2.12 120 2 20 34 1.0 2.37 210 1 0 35 1.4 4.00 120 2 20 36 2.6 1.59 100 3 20 37 2.6 2.51 100 3 20 38 1.4 2.12 120 2 20 39 1.8 1.59 90 3 20 40 3.0 2.09 85 4 20 41 1.0 3.30 210 1 0 42 1.4 1.44 120 2 0 43 3.0 2.09 85 4 20 44 1.8 3.83 83 3 20 45 0.6 2.12 180 1 20 46 1.0 2.12 210 1 0

[0163] Table 5-2.

[0164]

[0165]

[0166] In the above embodiments, the reference current I b When the plate thickness is taken as the reference thickness t0 = 0.5 mm and ρ = 10 μΩ·cm, the weld nugget diameter meets the requirements (the weld nugget diameter meeting the requirements means that the minimum weld nugget diameter D is met). min The current is ≥4), and its value is 7.2-8.4KA; the reference welding time WT0 is the appropriate welding time when the plate thickness is the reference thickness t0=0.5mm, and its value is 120-170ms.

[0167] Table 6 lists the actual weld nugget diameter D of Examples 27-46, obtained by welding according to the spot welding process parameters in Tables 5-1 and 5-2 and then measuring it using metallographic methods. 实 .

[0168] Table 6.

[0169] Example <![CDATA[D / d L ]]> <![CDATA[D / d R ]]> <![CDATA[t A ’ / t A ]]> <![CDATA[t B ’ / t B ]]> T' / T <![CDATA[D 实 (mm)]]> <![CDATA[D min (mm)]]> Remark 27 8.77 8.62 0.14 0.15 0.62 6.26 4 qualified 28 8.59 7.64 0.12 0.04 0.70 5.82 4 qualified 29 7.92 8.84 0.15 0.26 0.65 6.94 4 qualified 30 8.03 7.22 0.27 0.16 0.67 6.23 5 qualified 31 5.26 5.79 0.54 0.19 0.59 5.69 4 qualified 32 4.94 5.11 0.20 0.15 0.43 5.45 4 qualified 33 5.47 4.99 0.23 0.41 0.61 5.80 4 qualified 34 5.68 5.21 0.39 0.27 0.64 6.01 4 qualified 35 6.64 6.01 0.37 0.32 0.63 6.34 4 qualified 36 5.22 5.47 0.24 0.21 0.53 6.02 5 qualified 37 5.81 5.49 0.20 0.14 0.51 5.85 5 qualified 38 5.54 5.63 0.38 0.36 0.67 6.18 4 qualified 39 6.55 6.20 0.22 0.35 0.59 6.43 5 qualified 40 6.45 6.79 0.19 0.33 0.71 6.72 6 qualified 41 6.43 5.71 0.24 0.40 0.65 5.79 4 qualified 42 5.82 6.26 0.37 0.20 0.66 5.66 4 qualified 43 6.77 6.91 0.09 0.09 0.62 6.52 6 qualified 44 4.79 5.61 0.39 0.11 0.69 6.57 5 qualified 45 4.98 5.72 0.35 0.19 0.57 5.98 4 qualified 46 5.97 5.61 0.38 0.20 0.63 6.04 4 qualified

[0170] As shown in Table 6, the results show that D in Examples 27-46 实 All are greater than D min The weld quality is acceptable.

[0171] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0172] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A resistance spot welding process for coated steel plates, characterized in that, Resistance spot welding is performed based on the welding current I and total welding time WT determined by the following steps: Obtain the thickness t and resistivity ρ of the coated steel sheet; Determine the corresponding thickness coefficient m based on the plate thickness t: Based on the resistivity ρ, determine the corresponding resistivity coefficient n: The welding current I for resistance spot welding is determined based on the thickness coefficient m and resistivity coefficient n. I=I b +200KA×(m-n); The total welding time WT for resistance spot welding is determined based on the thickness coefficient m. WT = WT0 + 65ms × m Where t0 represents the set reference thickness, which is 0.5 mm; resistivity ρ0 represents the set reference resistivity, which is 10 μΩ·cm; I b This indicates the set reference current, which is the current used to obtain a weld nugget diameter greater than the minimum weld nugget diameter D for a plate with a plate thickness of reference thickness t0 and a resistivity of reference resistivity ρ0. min The welding current is expressed in kA; WT0 represents the set reference welding time.

2. The resistance spot welding process as described in claim 1, characterized in that, Minimum melt diameter D min Determined based on the obtained plate thickness t: When 0.5mm ≤ t < 1.3mm, D min =4.0mm; When 1.3mm ≤ t < 1.9mm, D min =5.0mm; When 1.9mm ≤ t < 2.6mm, D min =6.0mm; When t≥2.6mm, D min =7.0mm.

3. The resistance spot welding process as described in claim 2, characterized in that, Reference current I b The value range is 7.2-8.4KA.

4. The resistance spot welding process as described in claim 1, characterized in that, The value range of WT0 is 120-170ms.

5. The resistance spot welding process as described in claim 1, characterized in that, In the step of obtaining the plate thickness t of the coated steel sheet, when the resistance spot welded joint assembly has multiple layers of plates with different plate thicknesses t, the plate thickness t is obtained based on the following rules: When the joint assembly of resistance spot welding has two layers of plates with different thicknesses t, the plate thickness t is taken as the smaller value. When the resistance spot welding joint assembly has three layers of plates with different thicknesses t, the plate thickness t is taken as the median value of the plate thicknesses of each plate. When the joint assembly of resistance spot welding has three or more layers of plates with different thicknesses t, the plate thickness t is taken as the average value of the thicknesses of each plate.

6. The resistance spot welding process as described in claim 1, characterized in that, In the step of obtaining the resistivity ρ of the coated steel sheet, when the materials in the joint assembly have multiple plates with different resistivity ρ, the resistivity with the maximum value ρ is taken as the obtained resistivity.

7. The resistance spot welding process as described in claim 1, characterized in that, When the obtained plate thickness t ≥ 1.0 mm, multi-pulse welding is used, and the number of pulses N is determined based on the obtained plate thickness t: When 0.5mm ≤ t < 1.1mm, N = 1; When 1.1mm ≤ t < 1.3mm, N = 2; When 1.3mm ≤ t < 1.9mm, N = 3; When 1.9mm ≤ t < 2.4mm, N = 4; When t≥2.4mm, N=5.

8. The resistance spot welding process as described in claim 1, characterized in that, When using multi-pulse welding, the welding current I is the same for each pulse.

9. The resistance spot welding process as described in claim 1, characterized in that, When using multi-pulse welding, the welding time for each pulse (WT) is... N Same, WT N Satisfying the formula:

10. The resistance spot welding process as described in claim 1, characterized in that, When using multi-pulse welding, the cooling time between each pulse segment should be ≤50ms.

11. The resistance spot welding process as described in claim 1, characterized in that, The welding pressure F for resistance spot welding is determined based on the obtained plate thickness t: When 0.5mm≤t<1.1mm, the value of F ranges from 1.8 to 2.2 kN; When 1.1mm≤t<1.3mm, the value of F ranges from 2.4 to 2.8 kN; When 1.3mm≤t<1.9mm, the value of F ranges from 3.4 to 3.8 kN; When 1.9mm≤t<2.4mm, the value of F ranges from 4.8 to 5.2 kN; When t≥2.4mm, the value of F ranges from 6.8 to 7.2 kN.

12. The resistance spot welding process as described in claim 1, characterized in that, The electrode end face of the resistance spot welding electrode is spherical, and the diameter of the electrode end face is 5.0-10.0mm.

13. The resistance spot welding process as described in claim 1, characterized in that, The pre-compression time before welding is 300-1500ms.

14. The resistance spot welding process as described in claim 1, characterized in that, The pressure holding time after welding is 100-600ms.

15. A resistance spot-welded steel connection joint, characterized in that, It is manufactured by resistance spot welding as described in any one of claims 1-14.

16. The resistance spot-welded steel connection joint as described in claim 15, characterized in that, The relationship between the diameter D of the weld nugget and the width d of the heat-affected zone on one side of the weld is: 4≤D / d≤10.

17. The resistance spot welded steel connection joint as described in claim 15, characterized in that, The ratio of the electrode indentation depth t' to the thickness t of the plate on which it is located is 0 < t' / t ≤ 0.

5.

18. The resistance spot-welded steel connection joint as described in claim 15, characterized in that, The ratio of the height T' of the molten core to the total plate thickness T is 0.3 ≤ T' / T < 0.8.

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