Resistance spot welding method and process for flanging of aluminum alloy vehicle door

Abstract

The invention relates to the technical field of resistance spot welding, and discloses an aluminum alloy vehicle door flanging resistance spot welding method and process which comprises the following steps that firstly, a 6061 aluminum alloy vehicle door flanging part is cleaned, and oil stains and oxides on the surface are removed; step 2, preparing a copper-based alloy electrode cap made of a CuAl2O3 material, wherein the top end of the electrode cap is provided with a spherical surface structure and is provided with a transition curved surface and a conical surface; and thirdly, preheating treatment is conducted through a self-adaptive current adjusting system, and preheating current is adjusted based on the thickness of the oxidation film so that the surface oxidation film can be removed. By using the CuAl2O3 material electrode cap and the refined electrode design, uniform pressure distribution in the welding process is ensured, stable contact conditions are provided in a narrow flanging area, welding defects are effectively avoided, extrusion force in the welding process is more suitable for nugget forming due to precise multi-section pressure control, and the welding quality is improved. Therefore, the quality and the consistency of welding spots are improved.

Description

Technical Field

[0001] The invention relates to the technical field of resistance spot welding, and in particular to a method and process for resistance spot welding of aluminum alloy vehicle door flanging. Background Art

[0002] Aluminum alloy has become an important material in the automotive manufacturing field due to its light weight, high strength and good thermal conductivity, especially in car body parts such as doors and engine hoods. Compared with traditional steel, aluminum alloy can significantly reduce the weight of the car body, improve fuel economy and handling performance. However, aluminum alloy faces some special technical challenges in the resistance spot welding process.

[0003] First, aluminum alloys are prone to generate oxide films in the air, which have high melting points and high resistance characteristics, increasing the contact resistance during welding, resulting in uneven temperature and affecting the formation of welds. At the same time, the high thermal conductivity and large thermal expansion coefficient of aluminum alloys easily lead to heat loss during welding, and shrinkage cavities and cracks are easily generated during the cooling process, affecting the strength and quality of welding. In addition, the width of the flanging area of ​​aluminum alloys is relatively small, only 10mm-12mm, while the diameter of conventional aluminum alloy spot welding electrode caps is 19mm-20mm, which makes it difficult for traditional electrode caps to adapt. The pitting and adhesion problems between the electrode cap and the workpiece will also shorten the electrode life and increase production costs.

[0004] In the prior art, the improvement methods for aluminum alloy resistance spot welding mainly include optimizing welding parameters, using improved electrode materials, and adding auxiliary welding processes, but there are still problems of insufficient consistency and stability in mass production. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method and process for resistance spot welding of aluminum alloy vehicle door flanges, which solves the problem of unstable welding quality caused by oxide film, high thermal conductivity and insufficient electrode adaptability in resistance spot welding of aluminum alloy vehicle door flanges.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: a method and process for resistance spot welding of aluminum alloy door flanges, comprising the following steps:

[0007] Step 1: Clean the flange of the 6061 aluminum alloy door to remove surface oil stains;

[0008] Step 2: Use a CuAl2O3 alloy electrode cap, the top of which is provided with a spherical structure, a transition curved surface and a conical surface;

[0009] Step 3: Preheating is performed by an adaptive current regulation system, and the preheating current is adjusted based on the oxide film thickness to remove the surface oxide film;

[0010] Step 4: Implement multi-stage pressure control during spot welding, including initial pressurization, main welding pressurization and post-weld pressure maintenance;

[0011] Step 5: Use segmented pulse current for welding, with different current size and time for each segment, and set cooling time between pulses;

[0012] Step 6. To ensure the appearance quality of the weld, during the welding process, the center line of the electrode cap must be perpendicular to the workpiece surface, and its maximum deflection angle must be ≤3°;

[0013] Step 7. Finally, use ultrasonic wave to detect the quality of solder joints, record the welding parameter data, and adjust the parameters of subsequent solder joints.

[0014] Moreover, the workpiece to be welded needs to be preheated so that the oxide film on the surface of the aluminum alloy can be melted under the action of the preheating current, thereby reducing the contact resistance between the electrode and the plate interface, increasing the contact area, and increasing the heat conduction capacity; the preheating current is selected to be 10kA-12kA.

[0015] Moreover, the preheating time is adjusted to 60-80ms according to the thickness of the oxide film.

[0016] Moreover, the top spherical radius of the electrode cap is R3 mm, the intermediate transition curved radius is SR40 mm, and it has a 30° conical structure.

[0017] Moreover, the multi-stage pressure control includes:

[0018] Initial pressure: 1.8 kN initial pressure is applied for 30 ms;

[0019] The main welding pressure is increased to 2.2kN and lasts for 50ms;

[0020] After welding, the pressure is maintained at 2.1kN for 150-200ms.

[0021] Moreover, the segmented pulse current welding wherein comprises the following steps:

[0022] The initial pulse current is set to 22kA and lasts for 30ms;

[0023] The main welding section pulse, the current is set to 25kA, lasting 40ms;

[0024] In the final pulse segment, the current was set to 27 kA and lasted for 10 ms.

[0025] Moreover, a cooling interval of 10 ms is set during the pulse welding process.

[0026] Moreover, the welding quality detection includes:

[0027] Non-destructive testing of welds using ultrasonic testing equipment to detect nugget depth, diameter and uniformity;

[0028] The inspection data is transmitted to the quality monitoring system, the welding parameters of each weld are recorded, and the parameters of subsequent welds are adjusted according to the inspection results.

[0029] The present invention provides a method and process for resistance spot welding of aluminum alloy door flanging, which has the following beneficial effects:

[0030] 1. The present invention ensures uniform pressure distribution during welding by using CuAl2O3 material electrode cap and refined electrode design. Stable contact conditions are provided in the narrow flange area, effectively avoiding welding defects. In addition, precise multi-stage pressure control makes the extrusion force during welding more suitable for nugget formation, thereby improving the quality and consistency of the weld.

[0031] 2. The present invention uses an adaptive current regulation system to dynamically adjust the preheating current according to the thickness of the oxide film. This adaptive preheating treatment can fully remove the oxide film on the surface of the aluminum alloy, reduce the welding contact resistance, and make the welding current more evenly transmitted to the molten core, avoiding the fluctuation of the weld quality caused by the uneven oxide film.

[0032] 3. The present invention effectively controls the temperature rise rate by applying segmented pulse current welding, gradually increasing the welding current and setting a cooling interval between each segment. It reduces overheating, avoids external spatter and welding spot burnout, significantly improves welding appearance and electrode life, and makes the welding process more stable.

[0033] 4. The center line of the electrode cap of the present invention needs to be perpendicular to the workpiece surface, and its maximum deflection angle is ≤3°, so that the electrode and the workpiece surface always maintain the best contact angle during welding, preventing the weld from being uneven due to angle deviation, and improving the quality stability and consistency of the weld.

[0034] 6. The present invention uses ultrasonic nondestructive testing technology to monitor the nugget depth, diameter and uniformity of the weld in real time, and feeds the test data back to the quality monitoring system for automatic parameter adjustment. Automated quality monitoring and parameter optimization reduce human intervention, improve the consistency of welds during the production process, and make the process suitable for mass production.

[0035] 7. The present invention is particularly suitable for a thin plate thickness combination of 1.2mm+2.0mm, which solves the adaptation problem of conventional electrode caps when welding aluminum alloy in a narrow flanged area, making the application of aluminum alloy in the door structure more flexible and expanding the application prospects of aluminum alloy materials in lightweight automotive structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1It is a schematic diagram of the process of the present invention;

[0037] Figure 2 A schematic diagram of the maximum allowable offset angle of the electrode of the present invention;

[0038] Figure 3 Schematic diagram of the electrode cap dimensions of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Please see attached Figure 1 -Attached Figure 3 The embodiment of the present invention provides a method and process for resistance spot welding of aluminum alloy door flange, comprising the following steps:

[0041] Step 1: Workpiece cleaning

[0042] In this embodiment, the purpose of the workpiece cleaning process is to remove oil and dust on the surface of the aluminum alloy to reduce contact resistance and ensure the cleanliness and conductivity of the welding area. Cleaning is a basic step in the entire welding process and directly affects the stability of subsequent welding and the quality of the weld.

[0043] 1.1 Cleaning agent selection

[0044] Use a neutral detergent (such as industrial alcohol or special metal cleaning agent) to clean the surface of 6061 aluminum alloy plate.

[0045] 1.2 Cleaning process

[0046] First, apply the cleaning agent evenly on the surface of the workpiece, let it stand for 1-2 minutes to decompose the surface oil and impurities, and then wipe it gently with a soft cloth or dust-free cloth. To ensure thorough cleaning, rinse it twice with distilled water.

[0047] After cleaning, place the workpiece in a dry area and allow it to air dry naturally or use dry air flow to avoid any detergent residue.

[0048] Logical relationship: Cleaning the workpiece surface helps reduce spatter during welding and reduce contact resistance, thereby ensuring the stability of welding quality. Immediately after cleaning, proceed to the next step, namely electrode cap preparation, to ensure that the workpiece surface is in an ideal state.

[0049] Step 2: Electrode Cap Preparation

[0050] In this embodiment, the material and shape design of the electrode cap directly affect the quality of the weld and the service life of the electrode cap. The electrode cap is made of CuAl2O3 copper-based alloy to enhance wear resistance and thermal conductivity. At the same time, the shape of the electrode cap is designed to combine a spherical surface and a conical surface to achieve uniform pressure distribution, which is suitable for narrow flange welding areas.

[0051] 2.1 Material selection and electrode cap manufacturing

[0052] The CuAl2O3 copper-based alloy is used as the main material of the electrode cap, which has good conductivity and high hardness and is suitable for high-temperature welding conditions. The CuAl2O3 particles are evenly mixed into the base material, effectively improving the material's wear resistance.

[0053] 2.2 Shape design

[0054] The top of the electrode cap is a spherical surface of R3 mm, with a transition surface of SR40 mm and a 30° cone surface. The spherical surface structure provides concentrated pressure, and the cone and curved surface ensure uniform distribution of pressure, which is suitable for a flange width of 10-12 mm.

[0055] Check whether the end surface of the electrode cap is flat. If there are pits or scratches, polish it with ultra-fine sandpaper to ensure good contact quality.

[0056] Logical relationship: The material and structural design of the electrode cap directly affect the pressure distribution and temperature control in the welding area. Therefore, after the electrode cap is prepared, it enters the preheating treatment to improve the conductivity of the aluminum alloy surface and ensure that the welding current can pass stably.

[0057] Step 3: Adaptive preheating

[0058] In this embodiment, the preheating treatment removes the oxide film on the surface of the aluminum alloy by adjusting the preheating current and time, reduces the contact resistance, and lays the foundation for the stable conduction of the welding current. This step is dynamically adjusted according to the thickness of the oxide film through an adaptive current regulation system, and the preheating current range is 10kA-12kA.

[0059] 3.2 Preheating current and time setting

[0060] The preheating current is adjusted in stages, gradually increasing or decreasing according to the thickness of the oxide film. The preheating current in the thick film area is high and the time is set to 80ms, while the current in the thin film area is low and the time is set to 60ms.

[0061] The surface temperature of the workpiece is monitored by a temperature sensor to ensure that the heating temperature does not exceed 150°C to avoid material damage due to overheating.

[0062] Logical relationship: Preheating can reduce the obstruction of the oxide film, improve the conductivity of the contact surface, and provide a uniform temperature basis for subsequent multi-stage pressure control. After preheating, immediately enter the pressure control stage to avoid surface temperature loss after preheating.

[0063] Step 4: Multi-stage pressure control

[0064] In this embodiment, the multi-stage pressure control provides pressure support at different stages for the welding process to meet the requirements of the formation of the weld nugget. The quality and structural stability of the weld nugget are ensured through the three stages of initial pressurization, main welding pressurization and post-weld pressure maintenance.

[0065] 4.1 Initial pressurization

[0066] After preheating is completed, the electrode cap applies an initial pressure of 1.8kN to the workpiece for 30ms to ensure close contact between the electrode and the workpiece surface and eliminate tiny air gaps.

[0067] After the initial pressurization, the uniformity of the electrode contact surface is monitored to ensure good contact. If uneven pressure occurs, the system will automatically make fine adjustments.

[0068] 4.2 Main welding pressurization

[0069] Before entering the main welding stage, the system increases the pressure to 2.2kN for 50ms. This pressure level ensures sufficient extrusion force during the nugget formation process.

[0070] During the main welding pressurization process, the contact surface pressure is detected by the pressure sensor. If there is a fluctuation, the system will immediately correct the pressure.

[0071] 4.3 Maintaining pressure after welding

[0072] After the welding current ends, the pressure of 2.1kN is maintained for 150-200ms to provide stable compression to the weld nugget during the cooling stage. The length of the pressure holding stage is determined by the thickness of the welded workpiece and the thermal conductivity of the material.

[0073] Logical relationship: Multi-stage pressure control ensures that the pressure changes in time during the welding process to adapt to the formation and cooling of the weld nugget. After maintaining the pressure, enter the pulse current welding stage to provide heat support to stabilize the weld nugget structure.

[0074] Step 5: Segmented Pulse Current Welding

[0075] In this embodiment, the segmented pulse current welding controls the temperature rise rate through a multi-segment current heating method to ensure the temperature uniformity and welding quality during the nugget forming process.

[0076] 5.1 Initial pulse current

[0077] The initial pulse current is set to 22kA and lasts for 30ms. It is mainly used to preliminarily heat the contact surface of the workpiece to gradually increase the temperature.

[0078] 5.2 Main welding pulse

[0079] The main welding section current was set at 25 kA for 40 ms to provide the main heat support to form the nugget.

[0080] 5.3 Final pulse current

[0081] The final pulse current is set to 27kA and lasts for 10ms to complete the fine-tuning heating of the weld nugget and make the weld spot uniformly formed.

[0082] 5.4 Pulse Interval Cooling

[0083] A 10ms cooling time interval is set between each pulse to reduce the temperature fluctuation of the solder joint and avoid structural damage caused by overheating.

[0084] Logical relationship: The interval cooling of the pulse current and the segmented heating mode help to form a stable weld nugget. After welding, the angle calibration is performed immediately to ensure the accuracy of the contact between the electrode and the workpiece.

[0085] Step 6: Welding quality inspection

[0086] In this embodiment, the quality of the weld is detected by ultrasonic wave, and the depth, diameter and uniformity of the weld nugget are detected, so as to ensure the stability of the quality of the weld.

[0087] 6.1 Ultrasonic testing

[0088] Use an ultrasonic detector to perform non-destructive testing on each weld and collect data on the weld nugget depth, diameter and uniformity.

[0089] 6.2 Data Analysis and Feedback

[0090] The inspection data is transmitted to the quality monitoring system, which automatically records the welding parameters of each weld and adjusts the parameters of subsequent welds based on the inspection data.

[0091] Logical relationship: Through testing, the quality of solder joints is monitored in real time and parameter feedback is adjusted to ensure consistency in mass production. Quality testing is the final step of the process and provides a guarantee for the stability of the welding process.

[0092] This embodiment takes a combination of 1.2 mm and 2.0 mm thick 6061 aluminum alloy plates as the research object, and through experimental analysis and simulation verification, determines the optimal process parameters for resistance spot welding of aluminum alloy door flanges to ensure the quality of the weld core and welding consistency.

[0093] Table 16061 Chemical element composition (mass fraction, %)

[0094] element Si Fe Cu Mn Mg Cr Ni Zn Ti content(%) 0.95 0.23 0.066 0.12 0.37 0.036 0.004 0.002 0.027

[0095] Specific steps:

[0096] Sample preparation

[0097] 1.2mm and 2.0mm thick 6061 aluminum alloy plates were selected as experimental materials, and the materials conformed to ASTM B221 standard. To ensure the accuracy of the composition, the aluminum alloy plates were cut into small samples suitable for composition analysis.

[0098] Chemical composition analysis

[0099] The chemical composition of the aluminum alloy samples was detected by inductively coupled plasma optical emission spectrometry (ICP-OES). The test results showed that the content of each element in 6061 aluminum alloy was as shown in Table 1: silicon (Si) was 0.95%, iron (Fe) was 0.23%, copper (Cu) was 0.066%, manganese (Mn) was 0.12%, magnesium (Mg) was 0.37%, chromium (Cr) was 0.036%, nickel (Ni) was 0.004%, zinc (Zn) was 0.002%, and titanium (Ti) was 0.027%.

[0100] Repeated testing ensures data accuracy and performs data verification to ensure that the results meet design requirements.

[0101] Results: The composition data of 6061 aluminum alloy were obtained (Table 1), which provided a material basis for the subsequent optimization of welding process parameters.

[0102] Table 21.0mm+2.0mm 6061 plate thickness combination spot welding parameters

[0103]

[0104] Specific steps:

[0105] Choice of electrode cap

[0106] The electrode cap is made of CuAl 2O3 material and is Figure 1 The top of the electrode cap is a spherical structure with a curvature radius of R3 mm, a transition radius of SR40 mm, and a 30° cone surface to ensure uniform pressure distribution and stable welding contact.

[0107] Preheating current and time test

[0108] In order to remove the oxide film on the surface of aluminum alloy, the preheating current and time were tested. The preheating current range was set to 10-13kA, and the preheating time was gradually adjusted between 60-80ms.

[0109] Through repeated experiments, it was determined that a preheating current of 12kA and a preheating time of 80ms can effectively remove the oxide film, ensure the cleanliness of the aluminum alloy surface, and avoid the influence of the oxide film on the contact resistance.

[0110] Welding pressure test

[0111] Welding pressure directly affects the formation of the weld nugget. The experiment tested the effects of different pressures (from 1.8kN to 2.5kN) and observed the quality of the weld.

[0112] The experimental results show that a welding pressure of 2.2 kN can ensure the stable formation of the weld nugget while avoiding excessive burning, so 2.2 kN is selected as the optimal welding pressure.

[0113] Welding current and time test

[0114] By setting different welding currents (from 22kA to 27kA) and welding times (from 80ms to 120ms), the nugget formation and the strength of the weld were observed.

[0115] It was finally determined that a welding current of 25 kA and a welding time of 100 ms could produce a weld nugget with uniform size and strength that met the requirements, and therefore was selected as the optimal welding parameters.

[0116] Pressure maintenance time test

[0117] After welding, maintaining pressure can reduce shrinkage defects when the weld core cools. Through different holding time tests (ranging from 100ms to 250ms), it was determined that 200ms of pressure holding time is most suitable for reducing weld core cracks and ensuring stable weld quality.

[0118] Results: The optimal spot welding process parameters summarized according to the experimental results are shown in Table 2, namely, the preheating current is 12kA, the preheating time is 80ms, the welding pressure is 2.2kN, the welding current is 25kA, the welding time is 100ms, and the pressure maintenance time is 200ms.

[0119] Through the above experimental process, the composition data of 6061 aluminum alloy material (Table 1) and spot welding process parameters (Table 2) were obtained. The data in these two tables were obtained through systematic experiments and verification, providing reliable technical support for the process of aluminum alloy door flanging resistance spot welding. In practical applications, production settings can be made based on these parameters to ensure the quality and consistency of the welds.

[0120] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method and process for resistance spot welding of aluminum alloy door flanges, characterized in that: The following steps are involved: Step 1: Clean the flange of the 6061 aluminum alloy door to remove surface oil stains; Step 2: Use a copper-based alloy electrode cap made of CuAl2O3, the top of the electrode cap is provided with a spherical structure, a transition curved surface and a conical surface; Step 3: Perform preheating treatment through an adaptive current regulation system, and adjust the preheating current based on the oxide film thickness to remove the surface oxide film; Step 4: Implement multi-stage pressure control during spot welding, including initial pressurization, main welding pressurization and post-weld pressure maintenance; Step 5: Use segmented pulse current for welding, with different current size and time for each segment, and set cooling time between pulses; Step 6. To ensure the appearance quality of the weld, during the spot welding process, the center line of the electrode cap must be perpendicular to the workpiece surface, and its maximum deflection angle must be ≤3°; Step 7. Finally, use ultrasonic wave to detect the quality of solder joints, record the welding parameter data, and adjust the parameters of subsequent solder joints.

2. The aluminum alloy door flanging resistance spot welding method and process according to claim 1, characterized in that: The adaptive current regulation system automatically adjusts the preheating current, and the preheating current is selected to be 10kA-12kA.

3. The aluminum alloy door flanging resistance spot welding method and process according to claim 1, characterized in that: The warm-up time is 60-80ms.

4. The method and process for resistance spot welding of aluminum alloy door flange according to claim 1, characterized in that: The top spherical radius of the electrode cap is R3 mm, the intermediate transition curved radius is SR40 mm, and it has a 30° conical structure.

5. The aluminum alloy door flanging resistance spot welding method and process according to claim 1, characterized in that: The multi-stage pressure control includes: Initial pressure: 1.8 kN initial pressure is applied for 30 ms; The main welding pressure is increased to 2.2kN and lasts for 50ms; After welding, the pressure is maintained at 2.1kN for 150-200ms.

6. The aluminum alloy door flanging resistance spot welding method and process according to claim 1, characterized in that: The segmented pulse current welding method comprises the following steps: The initial pulse current is set to 22kA and lasts for 30ms; The main welding section pulse, the current is set to 25kA, lasting 40ms; In the final pulse segment, the current was set to 27 kA and lasted for 10 ms.

7. The method and process for resistance spot welding of aluminum alloy door flange according to claim 1, characterized in that: A cooling interval of 10 ms is set during the pulse welding process.

8. The method and process for resistance spot welding of aluminum alloy door flange according to claim 1, characterized in that: The welding quality inspection includes: Non-destructive testing of welds using ultrasonic testing equipment to detect nugget depth, diameter and uniformity; The inspection data is transmitted to the quality monitoring system, the welding parameters of each weld are recorded, and the parameters of subsequent welds are adjusted according to the inspection results.

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