CMT automatic welding method for unequal-thickness frame welding

Abstract

The invention relates to the technical field of different-thickness welding, in particular to a CMT automatic welding method for unequal-thickness frame welding, CMT automatic welding is conducted on two aluminum alloy frames with different thicknesses, parameters of CMT automatic welding include that the welding groove angle is 45-60 degrees, the offset is 0-2 mm, the wire feeding speed is 4.5-6 m / min, the welding speed is 40-60 cm / min, and a welding plate is obtained; the two aluminum alloy frames with different thicknesses are a thin frame with the thickness of 2-3mm and a thick frame with the thickness of 3-50mm; according to the method, the welding groove angle, the welding offset, the wire feeding speed and the welding speed are adjusted according to the thickness difference of the two borders with different thicknesses, a proper welding parameter interval is determined, it is ensured that welding heat input is matched with the heat capacity of the borders with different thicknesses, metal on the two sides of a welding seam is fully fused, and the welding quality is improved. And welding defects such as incomplete fusion and cracks caused by non-uniform heat input are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of differential thickness welding, and in particular to a CMT automatic welding method for welding frames of unequal thickness. Background Art

[0002] During the research process, we generally study the welding of materials of equal thickness (that is, the thickness of the parent material is equal), and there is not much research on the welding of materials of different thickness. However, in the actual production process, due to the functional requirements of the product, the product structure will be very complex, so a large amount of welding of aluminum alloys with different thickness will occur.

[0003] In the process of welding aluminum alloy with different thickness, under the same heat input, due to the strong thermal conductivity of aluminum alloy and the strong heat dissipation capacity of thick plate, the temperature at the same position is lower. Therefore, under the same process and the same position, the thin plate has melted into liquid, while the thick plate has not reached the melting point, resulting in the situation that under the same heat input conditions, the thick plate has shallow melting depth and the thin plate has deep melting depth. For example, when a 2.3mm thin plate is butt welded with a solid thick plate, the thick plate side is opened 2mm deep, with a 45° welding groove, the thin plate side has a longitudinal melting depth of 2.3mm (weld penetration), and the thick plate side is almost not fused. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a CMT automatic welding method for welding frames of unequal thickness.

[0005] A CMT automatic welding method for welding frames of unequal thicknesses comprises the following steps:

[0006] S1. Border cleaning:

[0007] Clean two aluminum alloy frames with different thickness;

[0008] The two aluminum alloy frames with different thicknesses are a thin frame with a thickness of 2 to 3 mm and a thick frame with a thickness of 3 to 50 mm;

[0009] S2, CMT automatic welding:

[0010] Perform CMT automatic welding on two aluminum alloy frames with different thicknesses, wherein the parameters of the CMT automatic welding include: welding groove angle 45-60°, offset 0-2 mm, wire feeding speed 4.5-6 m / min, welding speed 40-60 cm / min, and obtaining a welded plate;

[0011] S3. Heat treatment:

[0012] After the CMT automatic welding is completed, the welded plate obtained in step S2 is annealed.

[0013] Furthermore, in step S1, the method for cleaning the frame is: firstly degrease the surfaces of the two frames with absorbent cotton balls, then put the two frames into alcohol for cleaning, and then rinse with clean water and dry, and the cleaning is completed.

[0014] Note: The absorbent cotton balls can effectively absorb and remove these oil stains, and prevent the oil stains from being decomposed by heat during welding to produce welding defects such as pores and inclusions.

[0015] Furthermore, in step S2, the wire feeding speed and welding speed of the CMT are adjusted accordingly according to the thickness of the thin frame, and the adjustment method is as follows:

[0016] When the thickness of the thin frame is 2-2.5 mm, the wire feeding speed is 4.5-5.5 m / min and the welding speed is 45-60 cm / min;

[0017] When the thickness of the thin frame is 2.5-3mm, the wire feeding speed is 5-6m / min and the welding speed is 40-55cm / min.

[0018] Note: Frames of different thicknesses absorb and transfer heat differently during welding, and the wire feeding speed and welding speed determine the total amount of heat. Therefore, adjusting the wire feeding speed and welding speed can ensure that the weld metal is fully melted and avoid weld defects caused by excessive or insufficient heat input, such as lack of fusion and cracks. Adjusting the wire feeding speed helps maintain a stable arc and proper droplet transition, further improving welding quality.

[0019] Furthermore, according to the change of the thickness difference, the offset and groove angle are adjusted accordingly. The adjustment method is as follows:

[0020] When the difference thickness is ≤ 0.5 times the thickness of the thin frame, the offset is 0-1 mm, the groove angle is 45-55°, and a longitudinal magnetic field with an intensity of 10-15 mT is applied;

[0021] When the difference thickness is greater than 0.5 times the thickness of the thin frame, the offset is 0.5 to 2 mm, the groove angle is 50 to 60 degrees, and the longitudinal magnetic field is adjusted to a transverse magnetic field with an intensity of 8 to 12 mT.

[0022] Note: Frames of different thicknesses transfer heat differently during welding. Under the same heat condition, thin frames have lower heat dissipation rate and faster heating speed, while thick frames have higher heat dissipation rate and slower heating speed. In order to balance the welding temperature of the two, it is necessary to adjust the total heat absorbed by the two. The offset and groove angle determine the heat ratio. Adjusting the offset and groove angle can ensure that the metal on both sides of the weld is fully melted to avoid weld defects caused by uneven heat input distribution, such as lack of fusion and cracks. When the thickness difference is small, the heat transfer rate of thin and thick frames is relatively close. At this time, the offset range is small, which makes the welding temperatures formed by the thin and thick frames closer, so that both sides are fused more evenly; when the thickness difference is large, the thickness of the thick frame causes its heat dissipation rate to be faster, then A lower welding temperature can easily lead to a situation where the thin frame has already been melted while the thick frame has not yet been melted. Therefore, the offset range is relatively large, so that the thick frame obtains a higher heat input and the thin frame is relatively lower, so that the welding temperature of the thin frame and the thick frame is more even; applying a longitudinal magnetic field helps to improve the characteristics of the welding arc. A stable arc can transfer heat to the welding part more accurately, thereby improving the accuracy and quality of welding; a transverse magnetic field can change the flow direction and pattern of liquid metal in the welding pool. In the case of a large thickness difference, this adjustment of the magnetic field helps to make the liquid metal in the molten pool more evenly distributed in the transverse direction, avoiding uneven flow of liquid metal between thick and thin frames, further improving the forming quality of the weld, and making the weld transition smoother at frames of different thicknesses.

[0023] Furthermore, before performing step S2, the thick frame is first subjected to pre-welding treatment, and the method of the pre-welding treatment is as follows:

[0024] The welding surface of the thick frame is remelted to form a molten pool, and low melting point powder is added to the molten pool, wherein the distribution structure of the low melting point powder in the molten pool is wavy, the distance from the wave crest to the wave trough is 70-80% of the thickness of the thick plate, and the thickness of the wave is 0.4-0.6 mm, and then the welding surface of the thick frame is solidified to obtain a low melting point surface;

[0025] Then, laser holes are made on the low melting point surface, the depth of the holes is 0.1-0.3 mm, the laser power is 1.5-2.5 kW, and the pre-welding treatment is completed.

[0026] Note: Due to the high thickness of the thick frame, the overall heat dissipation efficiency is fast and the melting rate is slower than that of the thin frame. Remelting with low-melting-point aluminum alloy can reduce the melting point of the thick frame welding side to a certain extent, thereby reducing the heat input required for melting the thick frame, and making the melting depth of the two more balanced. The low-melting-point powder is designed with a wavy distribution pattern to improve the heat conduction efficiency, so that the welding surface reaches the required temperature faster and is easier to balance with the temperature of the thin frame. The hole gap can also reduce the heat dissipation efficiency of the thick frame side.

[0027] Furthermore, the low melting point powder is 7 series aluminum-zinc alloy powder with a particle size of 50 to 60 μm.

[0028] Note: The melting point of the welding wire is lower than that of the two frames, so it is easy to lower the melting point of the welding side of the thick frame.

[0029] Furthermore, the two aluminum alloy frames with different thicknesses are both made of 6061-T6 material.

[0030] Description: 6061-T6 aluminum alloy material has good welding performance, high strength, good toughness and excellent forming performance.

[0031] Furthermore, in step S2, the welding wire used for the CMT automatic welding is 4043 welding wire.

[0032] Description: Compared with 5 series welding wire, welding wire (4043) has better welding performance and is not prone to thermal cracks (especially at the arc closing position); it matches the composition of 6 series aluminum alloy and has better welding compatibility; the weld toughness is better after welding.

[0033] Furthermore, in step S3, the annealing treatment temperature is 300-350°C, the heating rate is 5-10°C / min, and the holding time is 2-3h.

[0034] Note: If the heating temperature is not high enough or the holding time is insufficient, the residual stress in the welded structure may not be fully eliminated, which will reduce the fatigue life and bearing capacity of the structure; if the heating temperature is too high, it may cause overheating or even burning of the material, thereby causing the strength and toughness of the material to decrease.

[0035] Compared with the existing welding method for frames of unequal thickness, the beneficial effects of the present invention are:

[0036] (1) According to the thickness difference between two frames of unequal thickness, this method adjusts the welding groove angle, welding offset, wire feeding speed and welding speed to determine the appropriate welding parameter range, ensure that the welding heat input matches the heat capacity of frames of different thicknesses, thereby achieving full fusion of the metals on both sides of the weld and avoiding welding defects caused by uneven heat input, such as lack of fusion and cracks.

[0037] (2) This method uses frames of different thicknesses to transfer heat differently during welding. Under the same heat condition, thin frames have a lower heat dissipation rate and a faster heating rate, while thick frames have a higher heat dissipation rate and a slower heating rate. In order to balance the welding temperatures of the two, it is necessary to adjust the total heat absorbed by the two. The offset and groove angle determine the heat ratio. Adjusting the offset and groove angle can ensure that the metal on both sides of the weld is fully melted, avoiding weld defects such as lack of fusion and cracks caused by uneven distribution of heat input. When the thickness difference is small, the heat transfer rates of the thin frame and the thick frame are relatively close. At this time, the offset range is small, which makes the welding temperatures formed by the thin frame and the thick frame closer, so that both sides are fused. When the thickness difference is large, the thickness of the thick frame causes its heat dissipation rate to be faster, and the welding temperature is lower, which may easily lead to the situation that the thin frame has already melted deeply while the thick frame has not yet melted deeply. Therefore, the offset range is relatively large, so that the thick frame obtains a higher heat input and the thin frame is relatively lower, so that the welding temperature of the thin frame and the thick frame is relatively even; the transverse magnetic field can change the flow direction and pattern of the liquid metal in the welding molten pool. When the thickness difference is large, the adjustment of this magnetic field helps to make the liquid metal in the molten pool more evenly distributed in the transverse direction, avoid the uneven flow of liquid metal between the thick and thin frames, further improve the forming quality of the weld, and make the weld transition smoother at frames of different thicknesses.

[0038] (3) Due to the high thickness of the thick frame, the overall heat dissipation efficiency of this method is fast, while the melting rate is slower than that of the thin frame. Remelting with low-melting-point powder can reduce the melting point of the thick frame welding side to a certain extent, thereby reducing the heat input required for melting the thick frame, thereby making the melting depth of the two more balanced. In addition, the hole gap formed by laser drilling can also reduce the heat dissipation efficiency of the thick frame side. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the penetration structure diagram of Example 11 in Exploration 2 of the present invention;

[0040] Figure 2 It is the penetration structure diagram of the comparative example 1 in the exploration 2 of the present invention;

[0041] Figure 3 It is the penetration structure diagram of the comparative example 2 in the exploration 2 of the present invention;

[0042] Figure 4 It is the penetration structure diagram of the comparative example 3 in the exploration 2 of the present invention;

[0043] Figure 5 It is the melting depth structure diagram of the comparison example 4 in the exploration 2 of the present invention. DETAILED DESCRIPTION

[0044] In order to further illustrate the method adopted by the present invention and the effect achieved, the technical solution of the present invention will be clearly and completely described in combination with experiments below.

[0045] Embodiment 1: A CMT automatic welding method for welding frames of unequal thickness, comprising the following steps:

[0046] S1. Border cleaning:

[0047] Cleaning two aluminum alloy frames with different thicknesses; the two aluminum alloy frames with different thicknesses are a thin frame with a thickness of 2.5 mm and a thick frame with a thickness of 30 mm;

[0048] The two aluminum alloy frames with different thickness are both made of 6061-T6 material. The method for cleaning the frames is: firstly degrease the surfaces of the two frames with absorbent cotton balls, then put the two frames into alcohol for cleaning, then rinse with clean water and dry, and the cleaning is completed;

[0049] S2, CMT automatic welding:

[0050] CMT automatic welding is performed on two aluminum alloy frames with different thicknesses. The parameters of the CMT automatic welding include: welding groove angle 52°, offset 1 mm, wire feeding speed 5.2 m / min, welding speed 50 cm / min, and 4043 welding wire is selected to obtain a welded plate;

[0051] S3. Heat treatment:

[0052] After the CMT automatic welding is completed, the welded plate obtained in step S2 is subjected to annealing treatment, wherein the annealing temperature is 325° C., the heating rate is 8° C. / min, and the holding time is 2.5 h.

[0053] Example 2: This example differs from Example 1 in that the wire feeding speed is 4.5 m / min and the welding speed is 60 cm / min.

[0054] Example 3: This example is different from Example 1 in that the wire feeding speed is 6 m / min and the welding speed is 40 cm / min.

[0055] Embodiment 4: This embodiment differs from Embodiment 1 in that the welding groove angle is 45° and the offset is 0 mm.

[0056] Embodiment 5: This embodiment differs from Embodiment 1 in that the welding groove angle is 60° and the offset is 2 mm.

[0057] Embodiment 6: This embodiment is different from Embodiment 1 in that the two aluminum alloy frames with different thicknesses are a thin frame with a thickness of 3 mm and a thick frame with a thickness of 50 mm.

[0058] Embodiment 7: This embodiment is different from Embodiment 1 in that the two aluminum alloy frames with different thicknesses are a thin frame with a thickness of 2 mm and a thick frame with a thickness of 3 mm.

[0059] Embodiment 8: This embodiment differs from Embodiment 1 in that, in step S2, the wire feeding speed and welding speed of the CMT are adjusted accordingly according to the thickness of the thin frame, and the adjustment method is as follows:

[0060] When the thickness of the thin frame is 2-2.5mm, the wire feeding speed is 5m / min and the welding speed is 52cm / min;

[0061] When the thickness of the thin frame is 2.5 to 3 mm (it can be understood that 2.5 mm is not included), the wire feeding speed is 5.5 m / min and the welding speed is 48 cm / min.

[0062] Example 9: The difference between this example and Example 8 is that when the thickness of the thin frame is 2-2.5 mm, the wire feeding speed is 4 m / min and the welding speed is 45 cm / min; when the thickness of the thin frame is 2.5-3 mm, the wire feeding speed is 6 m / min and the welding speed is 55 cm / min.

[0063] Example 10: The difference between this example and Example 8 is that when the thickness of the thin frame is 2-2.5 mm, the wire feeding speed is 4.5 m / min and the welding speed is 60 cm / min; when the thickness of the thin frame is 2.5-3 mm, the wire feeding speed is 5 m / min and the welding speed is 40 cm / min.

[0064] Embodiment 11: This embodiment differs from Embodiment 8 in that the offset and groove angle are adjusted accordingly according to the change in the thickness difference. The adjustment method is as follows:

[0065] When the difference thickness is ≤ 1.5 times the thickness of the thin frame, the offset is 0.5 mm, the groove angle is 50°, and a longitudinal magnetic field with an intensity of 12 mT is applied;

[0066] When the difference thickness is greater than 1.5 times the thickness of the thin frame, the offset is 1.5 mm, the groove angle is 55°, and the longitudinal magnetic field is adjusted to a transverse magnetic field with an intensity of 10 mT.

[0067] Example 12: This example differs from Example 11 in that, when the difference thickness is ≤ 1.5 times the thickness of the thin frame, the offset is 0 mm, the groove angle is 45°, and a longitudinal magnetic field with an intensity of 10 mT is applied.

[0068] Example 13: This example differs from Example 11 in that, when the difference thickness is ≤ 1.5 times the thickness of the thin frame, the offset is 1 mm, the groove angle is 55°, and a longitudinal magnetic field with an intensity of 15 mT is applied.

[0069] Example 14: This example differs from Example 11 in that, when the difference thickness is greater than 1.5 times the thickness of the thin frame, the offset is 0.5 mm, the groove angle is 50°, and the longitudinal magnetic field is adjusted to a transverse magnetic field with an intensity of 8 mT.

[0070] Example 15: This example differs from Example 11 in that, when the difference thickness is greater than 1.5 times the thickness of the thin frame, the offset is 2 mm, the groove angle is 60°, and the longitudinal magnetic field is adjusted to a transverse magnetic field with an intensity of 12 mT.

[0071] Embodiment 16: This embodiment is different from Embodiment 11 in that, before performing step S2, the thick frame is first subjected to pre-welding treatment, and the method of pre-welding treatment is as follows:

[0072] The welding surface of the thick frame is remelted to form a molten pool, and then a low-melting-point powder is added to the molten pool, wherein the low-melting-point powder adopts 7-series aluminum-zinc alloy powder (7005) with a particle size of 54-57 μm, and the distribution structure of the low-melting-point powder in the molten pool is wavy, and the distance from the wave crest to the wave trough of the wave shape is 75% of the thickness of the thick plate, and the thickness of the wave shape is 0.5 mm, and then the welding surface of the thick frame is solidified to obtain a low-melting-point morphology;

[0073] Then, laser holes are made on the low melting point morphology, the depth of the holes is 0.2 mm, the laser power is 2 kW, and the pre-welding treatment is completed.

[0074] Example 17: This example differs from Example 16 in that a low melting point powder with a particle size of 50 to 54 μm is added to the molten pool.

[0075] Example 18: This example differs from Example 16 in that a low melting point powder with a particle size of 57 to 60 μm is added to the molten pool.

[0076] Example 19: This example differs from Example 16 in that the distance from the crest to the trough of the wave shape is 70% of the thickness of the thick plate, and the thickness of the wave shape is 0.4 mm.

[0077] Example 20: This example differs from Example 16 in that the distance from the wave crest to the wave trough of the wave shape is 80% of the thickness of the thick plate, and the thickness of the wave shape is 0.6 mm.

[0078] Example 21: This example is different from Example 16 in that the depth of the hole is 0.1 mm and the laser power is 1.5 kW.

[0079] Example 22: This example differs from Example 16 in that the depth of the hole is 0.3 mm and the laser power is 2.5 kW.

[0080] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and is intended to illustrate the practical application effect of the present invention.

[0081] In order to illustrate the welding advantage of the present invention for welding frames of unequal thickness, the penetration depths of the unequal thickness frames welded in various embodiments are measured to obtain the penetration depth difference between the two unequal thickness frames. The smaller the penetration depth difference, the better the welding effect.

[0082] 1. Explore the influence of CMT welding parameters and the difference in thickness between the two frames on the difference in penetration depth.

[0083] Table 1 Difference in penetration depth of Examples 1 to 7

[0084]

[0085]

[0086] From the data in Table 1 and Figure 1 It can be seen that Figure 1 The penetration depth on both sides is more uniform, and the welding effect is better;

[0087] By comparing Examples 1 to 7, it can be seen that too little or too much heat input, too little or too much offset, and too little or too much thickness difference between the two frames will affect the welding temperature of the two frames, so that the uneven temperature on both sides leads to a deeper penetration difference, thereby affecting the welding effect. Since the influence of heat treatment on the penetration difference after welding is completed is relatively small, its data is not filled in Table 1. Therefore, in general, the parameter effect of Example 1 is better.

[0088] 2. Explore the effect of adjusting the wire feeding speed and welding speed of CMT according to the thickness difference on the depth of penetration.

[0089] Table 2 Difference in penetration depth of Examples 8 to 15 and Comparative Examples 1 to 6

[0090]

[0091] The difference between the comparative example 1 and the embodiment 11 is that the offset is 0 and the groove angle is 60°;

[0092] The difference between the comparative example 2 and the example 11 is that the offset is 2 and the groove angle is 45°;

[0093] The difference between the comparative example 3 and the example 8 is that the ratio of the wire feeding speed to the welding speed is less than 4.5 / 60;

[0094] The difference between the comparative example 4 and the embodiment 8 is that the ratio of the wire feeding speed to the welding speed is greater than 6 / 40;

[0095] The difference between Comparative Example 5 and Example 11 is that the magnetic field is always a longitudinal magnetic field;

[0096] The difference between Comparative Example 6 and Example 11 is that the magnetic field is always a transverse magnetic field;

[0097] From the results in Table 2 and Figures 2 to 5 It can be seen that the offset of Control Examples 1 and 2 exceeds the scope of the present application, resulting in a thick frame or a thin frame that is not melted. The heat input (ratio of wire feeding speed to welding speed) in Control Examples 3 and 4 exceeds the scope of the present application, resulting in a root that is not fully melted or collapse due to excessive penetration. The magnetic field of Control Examples 5 and 6 remains unchanged in the longitudinal or transverse direction, and the reduction in the penetration difference is slightly lower than that of Examples 8 to 15. Therefore, the change in the magnetic field has a certain effect.

[0098] By comparing Examples 8 to 15 with Examples 1 to 7, it can be seen that after further fine-tuning the wire feeding speed and the welding speed according to the thickness difference, the penetration difference is stabilized below 0.3 mm, and under the adjustment gap of each parameter, the penetration difference of each embodiment is more stable, and there is no situation where the penetration difference is too small or too large, and the penetration difference obtained by the parameters of Example 11 is the smallest, so the adjustment steps and parameters of Example 11 are relatively better.

[0099] 3. Explore the influence of pre-welding treatment on the penetration difference.

[0100] Table 3 Difference in penetration depth of Examples 16 to 22 and Comparative Examples 7 to 8

[0101]

[0102] The difference between Comparative Example 7 and Example 16 is that the distribution structure of the low melting point powder is linear;

[0103] The difference between Control Example 8 and Example 16 is that no laser pore making is performed;

[0104] From the results in Table 3, it can be seen that the control example 7 lacks the wavy distribution, and the control example 8 lacks the laser pore making, both of which weaken the distribution of the low melting point morphology. Therefore, compared with the examples 16 to 22, the reduction in the depth difference is smaller, and the wavy distribution and laser pore making have certain beneficial effects on reducing the melting point of the thick frame.

[0105] By comparing Examples 16 to 22 and Example 11, it can be seen that the penetration difference of Examples 16 to 22 is more stable and is stable within a lower penetration difference range, so the welding effect is more stable. In addition, by comparing Examples 16 to 22, each parameter that is too small or too large will affect the change in the melting point of the welding surface of the thick frame. Therefore, the parameter effect of Example 16 is relatively better.

Claims

1. A CMT automatic welding method for welding frames of unequal thickness, characterized in that: The following steps are involved: S1. Border cleaning: Clean two aluminum alloy frames with different thickness; The two aluminum alloy frames with different thicknesses are a thin frame with a thickness of 2 to 3 mm and a thick frame with a thickness of 3 to 50 mm; S2, CMT automatic welding: Perform CMT automatic welding on two aluminum alloy frames with different thicknesses, wherein the parameters of the CMT automatic welding include: welding groove angle 45-60°, offset 0-2 mm, wire feeding speed 4.5-6 m / min, welding speed 40-60 cm / min, and obtaining a welded plate; S3. Heat treatment: After the CMT automatic welding is completed, the welded plate obtained in step S2 is annealed.

2. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: In step S1, the method for cleaning the frame is: first degrease the surfaces of the two frames with an absorbent cotton ball, then put the two frames into alcohol for cleaning, and then rinse with clean water and dry, and the cleaning is completed.

3. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: In step S2, the wire feeding speed and welding speed of the CMT are adjusted accordingly according to the thickness of the thin frame. The adjustment method is as follows: When the thickness of the thin frame is 2-2.5 mm, the wire feeding speed is 4.5-5.5 m / min and the welding speed is 45-60 cm / min; When the thickness of the thin frame is 2.5-3mm, the wire feeding speed is 5-6m / min and the welding speed is 40-55cm / min.

4. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 3, characterized in that: In step S2, the offset and groove angle are adjusted accordingly according to the change of the thickness difference. The adjustment method is as follows: When the difference thickness is ≤ 0.5 times the thickness of the thin frame, the offset is 0-1 mm, the groove angle is 45-55°, and a longitudinal magnetic field with an intensity of 10-15 mT is applied; When the difference thickness is greater than 0.5 times the thickness of the thin frame, the offset is 0.5 to 2 mm, the groove angle is 50 to 60 degrees, and the longitudinal magnetic field is adjusted to a transverse magnetic field with an intensity of 8 to 12 mT.

5. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: Before performing step S2, the thick frame is first subjected to pre-welding treatment, and the method of the pre-welding treatment is as follows: The welding surface of the thick frame is remelted to form a molten pool, and low melting point powder is added to the molten pool, wherein the distribution structure of the low melting point powder in the molten pool is wavy, the distance from the wave crest to the wave trough is 70-80% of the thickness of the thick plate, and the thickness of the wave is 0.4-0.6 mm, and then the welding surface of the thick frame is solidified to obtain a low melting point surface; Then, laser holes are made on the low melting point morphology, the depth of the holes is 0.1-0.3 mm, the laser power is 1.5-2.5 kW, and the pre-welding treatment is completed.

6. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: The low melting point powder is 7 series aluminum-zinc alloy powder with a particle size of 50 to 60 μm.

7. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: The two aluminum alloy frames with different thicknesses are both made of 6061-T6 material.

8. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: In step S2, the welding wire used for the CMT automatic welding is 4043 welding wire.

9. A CMT automatic welding method for welding frames of unequal thickness as claimed in claim 1, characterized in that: In step S3, the annealing treatment temperature is 300-350°C, the heating rate is 5-10°C / min, and the holding time is 2-3h.

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