Machining and laser-MIG composite welding combined machining method

Abstract

The invention discloses a machining and laser-MIG composite welding combined machining method. The machining and laser-MIG composite welding combined machining method comprises the steps that a sawtooth-shaped groove with specific geometric parameters is prepared in the edge of a to-be-welded medium-thickness plate in a machining mode; cleaning and rigidly clamping the groove area; laser-MIG composite welding is adopted for positioning spot welding; and finally, single-face welding and double-face forming laser-MIG composite welding is carried out. The geometric structure of the zigzag groove is beneficial to the reciprocating reflection of a laser beam in a groove gap, so that the penetrating power of a keyhole can be improved, the stability of the bottom of a molten pool can be enhanced, the probability of bottom humps can be reduced, and meanwhile, the accurate control and uniformity of an assembly gap can be realized. The method is suitable for the carbon steel plate with the thickness of 16-20 mm, welding humps, cracks and other defects can be effectively restrained, back auxiliary measures or the procedures of preheating before welding and heat preservation after welding are not needed, and the welding quality and the production efficiency are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding composite manufacturing, in particular to a machining and laser-MIG composite welding combined processing method suitable for medium-thick plates, and especially suitable for single-sided welding and double-sided forming process of carbon steel plates with thickness of 16-20 mm. BACKGROUND

[0002] With the development of parts in modern equipment gradually towards large-scale, integration, high performance, the welding problem of thick-walled components is increasingly prominent, becoming a key process in the manufacturing process of major equipment, and developing high-quality, efficient and reliable welding technology has become one of the key conditions to realize the manufacturing of large or super-large integral components and meet the needs of major equipment development. At present, the welding process of thick-walled components is gradually changing from manual welding to semi-automatic / automatic welding, but it still cannot meet the urgent needs of high-performance and high-efficiency manufacturing. For example, the welding position of submerged arc automatic welding is limited, which is generally used for welding flat plates, and when TIG / MIG / MAG or manual electrode welding is used to weld thick plates, the groove must be opened, which not only reduces the efficiency, but also easily causes welding defects. Therefore, it is urgent to develop advanced welding technology for welding thick-walled components.

[0003] As an advanced manufacturing process technology, laser welding or laser+arc composite welding has broad application prospects in the welding of medium-thick plates, but when the plate thickness exceeds 10 mm, double-sided welding or groove opening is generally required, which not only reduces the welding efficiency, but also limits the turning of the workpiece or the adjustment of the welding position, greatly limiting its application in actual production. Therefore, the single-sided welding and double-sided forming technology of thick plates shows great advantages.

[0004] At present, domestic and foreign experts and scholars have carried out a lot of research on the single-sided welding and double-sided forming of medium-thick plates by using laser+arc composite welding technology, and have successively proposed measures such as applying a magnetic field or a liner at the bottom of the welding part or applying a protective gas. Although some achievements have been made, the actual application effect is not good due to the limitation of specific production conditions. Especially for carbon steel plates with thickness exceeding 16 mm, there are few reported literatures on single-sided welding and double-sided forming, not to mention application in actual production. The main reasons are as follows.

[0005] 1. It is difficult to suppress the bottom hump defect. According to relevant literature and many experiments, when the single-sided welding and double-sided forming of the plate thickness exceeds 10 mm, the bottom hump defect is difficult to suppress, and when the single-sided welding and double-sided forming of the plate thickness exceeds 12 mm, the bottom hump defect is almost inevitable. Therefore, when the single-sided welding and double-sided forming of the plate thickness exceeds 16 mm, the bottom hump defect is more likely to occur.

[0006] 2. For laser-arc hybrid welding of medium-thick plates exceeding 16mm in thickness, when performing single-sided welding with double-sided forming, several challenges arise regardless of whether a gapless weld or a pre-existing assembly gap is used. With a gapless weld, either the weld is incomplete or easily leaks, forming a bottom hump defect. Using a pre-existing assembly gap also presents several problems: 1) Precise control of the assembly gap dimensions is difficult. The thicker the plate, the lower the gap tolerance, thus requiring precise dimensions. However, due to deformation during assembly clamping and locating spot welding, precise control is challenging. In actual products, assembly tolerances and spatial positioning further complicate matters, making precise gap control even more difficult. 2) Uniformity of the assembly gap is difficult to control. Due to locating spot welding and welding deformation during the welding process, the thicker the plate, the greater the deformation. This causes changes in the dimensions before and after the assembly gap, affecting weld quality. 3) Installation and adjustment of the assembly gap are time-consuming and labor-intensive. Given the high precision requirements of the assembly gap dimensions, assembly efficiency is extremely low. 4) If laser cutting is used to process a sawtooth-shaped bevel, it will cause some burn damage to the sawtooth shape at the bottom of the bevel. Slight burn damage has little impact on the accuracy of the bevel gap, but the thicker the plate, the greater the burn damage. Especially when the plate thickness exceeds 16mm, the laser cutting burn damage is too large, making it difficult to guarantee the dimensional accuracy of the cut. At the same time, it is difficult to clean the oxides and cutting residue at the cut.

[0007] 3. Applying a magnetic field, a backing, or a protective gas to the bottom of the workpiece during welding would greatly limit its application in actual production, as many actual welded products do not have the conditions to apply a magnetic field, a backing, or a protective gas.

[0008] 4. When the plate thickness reaches about 20mm, in order to prevent defects such as cracks and porosity, heat treatment measures such as preheating before welding and heat preservation after welding are often required. This greatly limits its application in actual production. However, many actual welded products do not have the conditions for preheating before welding and heat preservation after welding. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a combined machining and laser-MIG welding processing method. This method uses machining to prepare a serrated bevel with specific geometric parameters, ensuring precise dimensions of the assembly gap and uniformity of the bevel gap, thus improving assembly efficiency. It also prevents variations in the assembly gap size caused by welding deformation. Furthermore, this serrated bevel facilitates the reciprocating reflection of the laser beam within the serrated gap and allows the laser beam to easily penetrate to the bottom of the workpiece, thereby increasing the keyhole penetration depth. This reduces the total energy input of the laser-MIG welding, preventing cracks that may occur in plates of a certain thickness during welding, suppressing hump defects, and eliminating the need for preheating and post-weld insulation processes required during welding.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a combined machining and laser-MIG hybrid welding method, comprising the following steps: S1. Using mechanical processing, sawtooth-shaped bevels are machined on the butt joint edges of the two medium-thick plate specimens to be welded. S2. Place the two plates to be welded with their beveled edges facing each other and clamp them together so that the bevels on the two plates are aligned and the mating surfaces are tightly fitted. Clean the bevels and surrounding areas with acetone before and after clamping. S3. Use laser-MIG composite welding process to perform positioning spot welding on the mating parts of the clamped plates. S4. Using laser-MIG composite welding process, single-sided welding and double-sided forming welding are performed on the joints of the plates after positioning electric welding.

[0011] Furthermore, in step S1, the medium-thick plate specimen is a carbon steel plate with a thickness range of 16mm < δ ≤ 20mm.

[0012] Furthermore, the geometric parameters of the sawtooth bevel satisfy the following: the top opening width S1 is 0.5-0.8 mm, the top width S2 is 0.08-0.12 mm, the bottom width S3 is 0.2-0.4 mm, and the tooth height H is 0.5-0.7 mm.

[0013] By controlling the dimensions of the serrated bevel within the above range, and ensuring that the carbon steel plate thickness is within the range of 16mm < δ ≤ 20mm, a qualified welded joint can be obtained, which can ensure the precise size and uniformity of the required gap.

[0014] Furthermore, in step S2, the medium-thick plate is rigidly clamped using a tooling fixture, and the top widths of the bevels of the two plates to be welded are tightly fitted together.

[0015] Furthermore, in step S3, the positioning spot welding process parameters are as follows: laser power of 3000-5000W, defocusing amount of -2--4mm, laser deflection angle of 5°, welding wire diameter of 1.2mm, welding speed of 1.0-1.5m / min, wire feed speed of 6-11.5m / min, welding current of 200-314A, shielding gas of high purity Ar, gas flow rate of 15-20L / min, and wire spacing of 2-3mm.

[0016] Spot welding mainly serves to secure the test piece before welding. The parameter settings should meet the requirements for spot welding of carbon steel plates with a thickness of 16mm < δ ≤ 20mm. The goal is to ensure that the spot weld on the test piece is firm, but not to penetrate the test piece completely, and to avoid forming a large spot weld that could affect the subsequent welding process.

[0017] Further, in step S4, the welding process parameters are as follows: laser power of 12000~14000W, welding speed of 1.5~2.0m / min, defocusing amount of -2~-4mm, welding wire diameter of 1.2mm, wire feed speed of 11.5~15m / min, welding current of 322~402A, shielding gas of high purity Ar, gas flow rate of 15~20L / min, and wire spacing of 2~3mm.

[0018] The welding process parameter setting range is designed to meet the welding requirements of carbon steel plates with a thickness range of 16mm < δ ≤ 20mm. Within the range of the serrated bevel setting, qualified welded joints can be obtained by single-sided welding and double-sided forming welding.

[0019] Furthermore, in step S1, the machining is either gear hobbing or milling.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a method similar to gear hobbing in machining to process a bevel with a sawtooth shape at the welding point of the medium-thick plate specimen. By accurately controlling the opening width S1, top width S2, bottom width S3 and tooth height H of the bevel, the reserved assembly gap size can be accurately obtained. Moreover, the uniformity of the assembly gap can be well controlled. In the assembly, it is only necessary to ensure that the tooth height H at the bevel of the two test plates corresponds and contacts each other. In this way, in the subsequent positioning spot welding and welding process, the deformation caused by welding heat can be better resisted, thereby ensuring the uniformity of the assembly gap throughout the welding process.

[0021] (2) First, there is no need to measure the bevel gap during assembly; just clamp it. Second, the sawtooth-shaped bevel produced by machining eliminates the need to clean the bevel and surrounding area, such as oxides and cutting residues, compared to other processes like laser cutting. This can significantly improve processing efficiency.

[0022] (3) It can avoid the problem of excessive burn-off when using laser cutting to cut thick plate bevels. When the plate thickness exceeds 16mm, excessive burn-off will occur at the bottom when using laser cutting to cut the sawtooth bevel of carbon steel plate. Excessive burn-off will seriously affect the dimensional accuracy of the assembly gap, thus failing to guarantee the welding quality. Machining eliminates the burn-off problem and can accurately guarantee the dimensional accuracy of the assembly gap. After machining, there is no need to grind and clean the bevel.

[0023] (4) When using the machining + laser-MIG composite welding method, there is no need to add auxiliary energy field or pads to the back of the specimen. When the thickness of the welded plate reaches 20mm, there is no need for the preheating and heat preservation process required for thick plate welding, thus significantly expanding the scope of actual production application.

[0024] (5) The bottom hump defect of the weld is well controlled. The gap formed by the sawtooth bevel produced by machining is more conducive to the laser beam to reflect back and forth in the gap of the sawtooth bevel than the gap without gap or narrow gap, which improves the penetration depth of the laser keyhole, enhances the stability of the bottom of the molten pool, and greatly reduces the probability of bottom hump. Attached Figure Description

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Figure 1 This is a schematic diagram of the sawtooth bevel formed by machining in this invention; Figure 2 Metallographic image of the welded joint in Example 1; Figure 3 Metallographic image of the welded joint in Example 2; Figure 4 Metallographic image of the welded joint in Example 3; Figure 5 Metallographic image of the welded joint in Example 4 Figure 6 The image shows the metallographic diagram of the welded joint in Comparative Example 6. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 A Q235 steel plate specimen with a thickness of 18mm was selected, and a sawtooth-shaped bevel was machined at the weldable area of ​​the medium-thick plate using a method similar to gear hobbing in machining (see...). Figure 1 The parameter values ​​of each part of the sawtooth bevel are shown in Table 1.

[0029] Table 1. Parameter values ​​for sawtooth bevel. Next, the medium-thick plate specimen is clamped using tooling fixtures to ensure that the top width S2 corresponds and contacts each other. Before and after clamping, the bevel and surrounding area are cleaned with acetone.

[0030] After clamping, the 18mm thick Q235 steel plate specimen was first tack welded using laser-MIG hybrid welding. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other tack welding process parameters are shown in Table 2.

[0031] Table 2. Spot welding process parameters The 18mm thick Q235 steel plate specimen was then subjected to laser-MAG hybrid welding using a single-sided welding and double-sided forming method. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other welding process parameters are shown in Table 3.

[0032] Table 3 Single-sided welding double-sided forming welding process parameters Example 2 A Q235 steel plate specimen with a thickness of 20mm was selected. A sawtooth-shaped bevel was machined at the weldable part of the medium-thick plate using a method similar to gear hobbing in machining. The parameter values ​​of each part of the sawtooth-shaped bevel are shown in Table 4.

[0033] Table 4. Parameter values ​​for sawtooth bevel Top opening width S1 (mm) Top width S2 (mm) Bottom width S3 (mm) Height of tooth H (mm) 0.8 0.1 0.3 0.6 Next, the medium-thick plate specimen is clamped using tooling fixtures to ensure that the top width S2 corresponds. Before and after clamping, the bevel and surrounding area are cleaned with acetone.

[0034] After clamping, the 20mm thick Q235 steel plate specimen was first tack welded using laser-MIG hybrid welding. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other tack welding process parameters are shown in Table 5.

[0035] Table 5. Positioning spot welding process parameters The 20mm thick Q235 steel plate specimen was then subjected to laser-MIG hybrid welding using a single-sided welding and double-sided forming method. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other welding process parameters are shown in Table 6.

[0036] Table 6 Single-sided welding double-sided forming welding process parameters Example 3 A Q235 steel plate specimen with a thickness of 17mm was selected. A sawtooth-shaped bevel was machined at the weldable part of the medium-thick plate using a method similar to gear hobbing in machining. The parameter values ​​of each part of the sawtooth-shaped bevel are shown in Table 7.

[0037] Table 7. Parameter values ​​for sawtooth bevels Next, the medium-thick plate specimen is clamped using tooling fixtures to ensure that the top width S2 corresponds. Before and after clamping, the bevel and surrounding area are cleaned with acetone.

[0038] After clamping, the 17mm thick Q235 steel plate specimen was first tack welded using laser-MIG hybrid welding. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other tack welding process parameters are shown in Table 8.

[0039] Table 8. Spot welding process parameters The 17mm thick Q235 steel plate specimen was then subjected to laser-MIG hybrid welding using a single-sided welding and double-sided forming method. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other welding process parameters are shown in Table 9.

[0040] Table 9 Single-sided welding double-sided forming welding process parameters Example 4 A Q235 steel plate specimen with a thickness of 19mm was selected. A sawtooth-shaped bevel was machined at the weldable part of the medium-thick plate using a method similar to gear hobbing in machining. The parameter values ​​of each part of the sawtooth-shaped bevel are shown in Table 10.

[0041] Table 10 Parameter values ​​for sawtooth bevel Next, the medium-thick plate specimen is clamped using tooling fixtures to ensure that the top width S2 corresponds. Before and after clamping, the bevel and surrounding area are cleaned with acetone.

[0042] After clamping, the 19mm thick Q235 steel plate specimen was first tack welded using laser-MIG hybrid welding. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other tack welding process parameters are shown in Table 11.

[0043] Table 11. Spot welding process parameters The 19mm thick Q235 steel plate specimen was then subjected to laser-MIG hybrid welding using a single-sided welding and double-sided forming method. The welding wire diameter was 1.2mm, the shielding gas was high-purity argon, the laser deflection angle was 5°, and other welding process parameters are shown in Table 12.

[0044] Table 12 Single-sided welding double-sided forming welding process parameters Comparative Example 1 Comparative Example 1 is a comparative test example of Example 1, and its difference from Example 1 is as follows: Instead of using a machining method similar to gear hobbing to create a sawtooth-shaped bevel at the weldable part of the medium-thick plate, the reserved assembly gap is 0.8mm, which is roughly equivalent to the assembly gap formed by the sawtooth-shaped bevel in Example 1.

[0045] The other steps and parameter settings are the same as in Example 1.

[0046] Comparative Example 2 Comparative Example 2 is a comparative test example of Example 1, and its difference from Example 1 is as follows: The serrated bevel was not machined at the welding point of the medium-thick plate, and no assembly gap was reserved.

[0047] The other steps and parameter settings are the same as in Example 1.

[0048] Comparative Example 3 Comparative Example 3 is a comparative test example of Example 1, and its difference from Example 1 is: The serrated bevel was not machined at the welding point of the medium-thick plate, and no assembly gap was reserved.

[0049] When performing laser-MIG hybrid welding on 18mm thick Q235 steel plate specimens using single-sided welding and double-sided forming, some welding process parameters were changed to ensure penetration. The single-sided welding and double-sided forming process parameters are shown in Table 13.

[0050] Table 13 Welding process parameters for single-sided welding and double-sided forming The other steps and parameter settings are the same as in Example 1.

[0051] Comparative Example 4 Comparative Example 4 is a comparative test example of Example 1, and its difference from Example 1 is: By changing only the parameters of each part of the sawtooth bevel, as shown in Table 14, the parameter values ​​of each part of the sawtooth bevel are all lower than the corresponding parameter values ​​in Example 1, and also lower than the optimal parameter range values ​​of the sawtooth bevel.

[0052] Table 14 Parameter values ​​for sawtooth bevel The other steps and parameter settings are the same as in Example 1.

[0053] Comparative Example 5 Comparative Example 5 is a comparative test example of Example 1, and its difference from Example 1 is as follows: By changing only the parameters of each part of the sawtooth bevel, as shown in Table 15, the parameter values ​​of each part of the sawtooth bevel in the table are all higher than the corresponding parameter values ​​in Example 1, and also higher than the parameter range values ​​of the optimal sawtooth bevel.

[0054] Table 15 Parameter values ​​for sawtooth bevel The other steps and parameter settings are the same as in Example 1.

[0055] Comparative Example 6 Comparative Example 6 is a comparative test example of Example 2, and its difference from Example 2 is as follows: Instead of using a machining method similar to gear hobbing to create a sawtooth-shaped bevel at the weldable part of the medium-thick plate, the reserved assembly gap is 1.0 mm, which is roughly equivalent to the assembly gap formed by the sawtooth-shaped bevel in Example 1.

[0056] The other steps and parameter settings are the same as in Example 2.

[0057] Comparative Example 7 Comparative Example 7 is a comparative test example of Example 2, and its difference from Example 2 is as follows: The sawtooth-shaped bevel was not machined at the welding point of the medium-thick plate using machining methods, and no assembly gap was reserved.

[0058] The other steps and parameter settings are the same as in Example 2.

[0059] Comparative Example 8 Comparative Example 8 is a comparative test example of Example 2, and its difference from Example 1 is as follows: The serrated bevel was not machined at the welding point of the medium-thick plate, and no assembly gap was reserved.

[0060] When performing laser-MAG composite welding on a 20mm thick Q235 steel plate specimen using a single-sided welding and double-sided forming method, some welding process parameters were changed to ensure penetration. The single-sided welding and double-sided forming process parameters are shown in Table 16.

[0061] Table 16 Single-sided welding double-sided forming welding process parameters The other steps and parameter settings are the same as in Example 2.

[0062] Comparative Example 9 Comparative Example 9 is a comparative test example of Example 2, and its difference from Example 2 is as follows: By changing only the parameters of each part of the sawtooth bevel, as shown in Table 17, the parameter values ​​of each part of the sawtooth bevel are all lower than the corresponding parameter values ​​in Example 2, and also lower than the optimal parameter range of the sawtooth bevel.

[0063] Table 17 Sawtooth Bevel Parameter Values The other steps and parameter settings are the same as in Example 2.

[0064] Comparative Example 10 Comparative Example 10 is a comparative test example of Example 2, and its difference from Example 2 is as follows: By changing only the parameters of each part of the sawtooth bevel, as shown in Table 18, the parameter values ​​of each part of the sawtooth bevel are all higher than the corresponding parameter values ​​in Example 2, and also higher than the optimal parameter range of the sawtooth bevel.

[0065] Table 18 Sawtooth Bevel Parameter Values The other steps and parameter settings are the same as in Example 2.

[0066] Experimental performance testing The welded joints of the welded specimens in Examples 1-4 and Comparative Examples 1-10 were observed to assess the surface finish (whether defects such as incomplete penetration, lack of fusion, weld protrusion, depression, undercut, and bottom hump were present). Performing mechanical property testing and metallographic analysis on welded joints with obvious surface defects is meaningless; therefore, only some welded joints and base materials underwent mechanical property testing and metallographic analysis, as shown in Tables 19 and 20. Figure 2-5 As shown.

[0067] Table 19 Test results of welded joint specimens Table 20 Test results of the base material samples Sample type Tensile strength average / MPa Example 1 445 Example 2 430 Example 3 440 Example 4 433 As shown in Tables 19 and 20, in Examples 1-4, the tensile strength of the welded joints all exceeded 90% of the tensile strength of the base material. Except for a few areas with undercut, the weld reinforcement on the front side was generally uniform, with no obvious defects such as depressions. Similarly, no obvious defects such as bottom humps were observed on the back side of the weld. Overall, the weld formation was good, as indicated by metallographic analysis. Figure 2-5It can be seen that no obvious defects were found inside the weld, thus confirming that the multi-combination processing method of machining + laser-MIG composite welding is effective for carbon steel plates with a thickness of 16mm < δ ≤ 20mm when using single-sided welding and double-sided forming.

[0068] In Comparative Example 1, unlike Example 1, no serrated bevel was machined on the medium-thick plate to be welded, and the reserved assembly gap was 0.8 mm. The weld face showed unevenness and poor uniformity; the weld back showed discontinuous bottom hump drooping in some areas, and most areas were not fully penetrated. The reason for this was that sufficient assembly gap accuracy was not ensured during assembly, and the assembly gap changed due to thermal deformation during tack welding and welding. This change caused the gap to be too small in some areas, making it difficult for the welding heat to spread to the bottom of the specimen, and the laser keyhole was insufficient to penetrate the specimen, resulting in incomplete penetration in some areas. On the other hand, the gap was too large, causing the molten pool to be too wide and large, resulting in a hump drooping due to gravity.

[0069] Compared to Example 1, Comparative Example 2 did not use machining methods to process a serrated bevel at the welding point of the medium-thick plate, nor did it leave an assembly gap. The welding effect on the front side of the weld was good. Except for the slightly higher weld reinforcement, the reinforcement of the entire weld was uniform. However, the entire weld on the back side was not fully penetrated, indicating that the bottom of the specimen did not receive enough heat during welding and the laser keyhole penetration ability was severely reduced. The total energy of the laser and the electric arc was insufficient to penetrate the specimen.

[0070] Compared to Example 1, Comparative Example 3 did not use machining methods to create a serrated bevel at the weldable area of ​​the medium-thick plate, and no assembly gap was reserved. In order to penetrate the workpiece, some welding process parameters were changed, especially the laser power and welding current were increased, which increased the total input energy. The weld front area had more spatter, some areas were concave and some areas were convex. Some discontinuous humps appeared on the back of the weld, and some areas were not penetrated. This indicates that the laser keyhole penetration ability decreased during the welding of the test piece. Even with the increase in total energy, some areas were still not penetrated.

[0071] Comparative Example 4, compared to Example 1, only the parameters of each part of the serrated bevel were changed. The parameter values ​​of each part were all lower than the corresponding parameter values ​​in Example 1, and also lower than the optimal parameter range values ​​for the serrated bevel. The weld front showed poor formation, exhibiting an uneven surface. A small number of bottom humps appeared on the back of the weld, and most areas were not fully penetrated. This is because the assembly gap formed by the serrated bevel was too small. An excessively small gap makes it difficult for welding heat to extend to the bottom of the specimen, and the laser keyhole is insufficient to penetrate the specimen, resulting in most areas of the weld back being incompletely penetrated. The small number of bottom humps may be caused by heat accumulation or instability in the welding process.

[0072] Comparative Example 5, compared to Example 1, only the parameters of each part of the serrated bevel were changed. The parameter values ​​of each part were all higher than the corresponding parameter values ​​in Example 1, and also higher than the optimal parameter range for the serrated bevel. The weld face showed collapse and poor formation, while the weld back showed a discontinuous, large bottom hump. This was because the assembly gap formed by the serrated bevel was too large. An excessively large gap leads to an excessively wide surface weld, and the molten pool metal is prone to collapse under gravity, forming a deep pit and a large hump at the bottom of the weld.

[0073] Compared to Example 2, Comparative Example 6 did not use machining methods to process a serrated bevel at the welding point of the medium-thick plate. The reserved assembly gap was 1.0 mm. The weld front was uneven and had poor uniformity. On the back of the weld, there were some discontinuous bottom humps and some areas were not fully penetrated. The reasons were similar to those in Comparative Example 1.

[0074] Compared to Example 2, Comparative Example 7 did not employ machining methods to create a serrated bevel at the weldable area of ​​the medium-thick plate, nor did it leave any assembly gap. The weld reinforcement on the front side was excessively high, and the weld on the back side was not fully penetrated, indicating a significant decrease in the laser keyhole penetration capability during welding of the specimen.

[0075] Compared to Example 2, Example 8 did not use machining to create a serrated bevel at the weldable area of ​​the medium-thick plate, nor was an assembly gap reserved. To achieve complete weld penetration, some welding process parameters were modified, particularly increasing the laser power and welding current, thus increasing the total input energy. However, partial incomplete penetration still occurred on the back of the weld, along with intermittent bottom humps and cracks within the weld. This indicates a decrease in laser keyhole penetration, leading to incomplete penetration in some areas. Furthermore, the increased total input energy, coupled with the lack of preheating and post-weld heat treatment, resulted in cracks appearing in the 20mm thick plate weld. Figure 6 As shown.

[0076] Comparative Example 9, compared to Example 2, only the parameters of each part of the serrated bevel were changed. The parameter values ​​of each part were all lower than the corresponding parameter values ​​in Example 2, and also lower than the optimal parameter range for the serrated bevel. The weld front showed poor formation, with unevenness, and a small number of bottom humps appeared on the back of the weld, with most areas showing incomplete penetration. The reasons are similar to those in Comparative Example 4.

[0077] Comparative Example 10, compared to Example 2, only changed the parameters of each part of the serrated bevel. The parameter values ​​of each part were higher than the corresponding parameter values ​​in Example 2, and also higher than the optimal parameter range for the serrated bevel. The weld face showed collapse and poor formation, while the weld back showed discontinuous, large-volume bottom humps. The reason is similar to that of Comparative Example 5.

[0078] As can be seen from Examples 1 and 2 and Comparative Examples 1-10, the serrated bevel produced by machining a method similar to gear hobbing can precisely control the size of the assembly gap. Compared with narrow gaps, no gaps, or gaps that are too large or too small (outside the range of serrated bevel parameters), this serrated bevel gap makes it easier to obtain high-quality welded joints under the condition of single-sided welding and double-sided forming welding using laser-MIG composite welding. There is no need to add auxiliary energy fields or backings to the back of the specimen. When the weld plate thickness reaches 20mm, the preheating and post-weld heat preservation processes required for thick plate welding are also eliminated.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A combined machining and laser-MIG hybrid welding method, characterized in that, Includes the following steps: S1. Using mechanical processing, sawtooth-shaped bevels are machined on the butt joint edges of the two medium-thick plate specimens to be welded. S2. Place the two plates to be welded with their beveled edges facing each other, and clamp them together so that the bevels on the two plates are aligned and the mating surfaces are tightly fitted. S3. Use laser-MIG composite welding process to perform positioning spot welding on the mating parts of the clamped plates. S4. Using laser-MIG composite welding process, single-sided welding and double-sided forming welding are performed on the joints of the plates after positioning electric welding.

2. The combined processing method according to claim 1, characterized in that, In step S1, the medium-thick plate specimen is a carbon steel plate with a thickness range of 16mm < δ ≤ 20mm.

3. The combined processing method according to claim 2, characterized in that, The geometric parameters of the sawtooth bevel are: top opening width S1 is 0.5-0.8 mm, top width S2 is 0.08-0.12 mm, bottom width S3 is 0.2-0.4 mm, and tooth height H is 0.5-0.7 mm.

4. The combined processing method according to claim 3, characterized in that, In step S2, the medium-thick plate is rigidly clamped using a tooling fixture, and the top widths of the bevels of the two plates to be welded are tightly fitted together.

5. The combined processing method according to claim 1, characterized in that, In step S3, the positioning spot welding process parameters are as follows: laser power is 3000~5000W, defocusing amount is -2~-4mm, laser deflection angle is 5°, welding wire diameter is 1.2mm, welding speed is 1.0~1.5m / min, wire feeding speed is 6~11.5m / min, welding current is 200~314A, and the wire spacing is 2~3mm.

6. The combined processing method according to claim 1, characterized in that, In step S4, the welding process parameters are as follows: laser power is 12000~14000W, welding speed is 1.5~2.0m / min, defocusing amount is -2~-4mm, welding wire diameter is 1.2mm, wire feeding speed is 11.5~15m / min, welding current is 322~402A, and the wire spacing is 2~3mm.

7. The combined processing method according to claim 1, characterized in that, In step S1, machining includes gear hobbing, milling, turning, and wire cutting.

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