Laser TIG (Tungsten Inert Gas) hybrid welding process for stainless steel automobile fuel tank

Abstract

The invention discloses a laser TIG (Tungsten Inert Gas) hybrid welding process for a stainless steel automobile fuel tank, which comprises the following steps of: (a) pretreating the end joint surface of a stainless steel sheet to be welded; (b) a workpiece is clamped through a clamp; (c) adopting a paraxial composite welding gun layout; (d) setting laser working parameters; and (e) the welding gun walks in the downhill direction of 5-10 degrees at the welding speed of 30 mm / s. A laser TIG hybrid welding mode is adopted, and laser can increase the fusion depth of a welding seam of an end joint surface, so that the fatigue strength of a welding seam joint is improved; the electric arc can increase the coverage area of a heat source on base metal, so that the fault tolerance rate is increased, plasma generated by laser can be absorbed by the electric arc, the energy of the electric arc is increased, and the welding speed is increased. According to the method, standardized reference is provided for laser TIG hybrid welding through parameter threshold limitation.

Description

Technical Field

[0001] The present invention relates to the technical field of laser welding of automobile products, and in particular to a laser TIG composite welding process for a stainless steel automobile fuel tank. Background Art

[0002] Currently, automobile fuel tanks are manufactured using resistance seam welding, where the welds are welded at the overlap of the end surfaces. This method requires the width of the end surface of the fuel tank to be made very large (greater than 50mm), which increases the weight of the vehicle. At the same time, the flange takes up a large space, reducing the storage capacity of the fuel tank.

[0003] If the welding location is changed to the end joint, the width of the end joint will be significantly reduced, thereby increasing the storage capacity of the tank and improving the space utilization of the tank. However, changing to an end joint increases the welding difficulty and requires higher precision of the parts. Laser welding or arc welding alone cannot meet stable production requirements. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a laser TIG hybrid welding process for a stainless steel automobile fuel tank.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A laser TIG hybrid welding process for a stainless steel automobile fuel tank comprises the following steps:

[0007] (a) Pre-treat the end surface of the stainless steel sheet to be welded to ensure that the surface roughness Ra ≤ 1.6 μm and there is no oily oxide layer;

[0008] (b) Clamp the workpiece with a fixture, control the end-joint surface matching gap to be ≤0.1mm, the misalignment to be ≤0.3mm, and apply a clamping force of >10 tons;

[0009] (c) A paraxial hybrid welding gun layout is used: the laser is incident vertically on the workpiece (incident angle 90°), the TIG welding gun is at a 60° push angle to the workpiece, the laser is in front, the arc is behind, and the distance between the laser and arc is 2 mm;

[0010] (d) Set the laser power to 2000 W, the defocus distance to 0 mm, the continuous mode, the TIG current to 90 A, the voltage to 15 V, the DC mode, and the shielding gas flow rate to 15 L / min;

[0011] (e) Move the welding gun in a downhill direction of 5-10° at a welding speed of 30 mm / s.

[0012] Preferably, the determination of the filament spacing in (c) must meet the following requirements: the laser acts on the front of the molten pool so that the keyhole is filled with the molten pool and the plasma is absorbed by the arc; when the spacing deviation is greater than ±1 mm, spatter or penetration defects occur.

[0013] Preferably, the TIG welding gun in (c) uses a tungsten electrode with a diameter of 2.4 mm, and the height of the tungsten electrode is strictly controlled within the range of 2±0.5 mm. A height deviation of >±1 mm will result in a decrease in arc stiffness or tungsten inclusion defects.

[0014] Preferably, the welding speed in (e) can be other speeds, but when the welding speed is ≤40 mm / s, a combination of laser pulse mode (frequency 450 Hz, duty cycle 50%) and arc pulse mode (frequency 70 Hz, amplitude 3 A) is adopted; when the welding speed is ≥60 mm / s, it is switched to a combination of laser continuous mode and arc DC mode.

[0015] Preferably, the contact surface width of the clamping block is 2 mm, and when clamping, it is necessary to ensure that the misalignment of the workpiece during 360° rotation is maintained at ≤0.3 mm.

[0016] Preferably, when the stainless steel sheet is 304 stainless steel with a thickness of ≤1.5 mm, the weld after welding meets the following requirements: pull-off force > 4000 N, deformation ≤ 0.5 mm / m, porosity < 0.5 per cm, and positive and negative pressure alternating fatigue strength > 10,000 times.

[0017] The longitudinal seam of the 304 stainless steel fuel tank welded by the laser TIG composite welding process of the aforementioned stainless steel automobile fuel tank has uniform weld penetration without hump, end surface fusion rate ≥98%, and no opening defect.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Regarding existing technologies: For automotive fuel tank end joints, if only TIG welding is used, the welding speed is slow and the heat input is high, resulting in severe welding deformation. If only laser welding is used, high workpiece matching accuracy is required (the gap requirement is <0.1mm), and the stamping error of the fuel tank shell is likely to cause welding deviation, resulting in a small process window.

[0020] The present invention utilizes laser TIG hybrid welding, combining the advantages of both processes to achieve a "1+1>2" effect. The laser increases the penetration depth of the end-joint weld, thereby improving the fatigue strength of the weld joint (according to experimental data, a 1mm end-joint automobile fuel tank exhibits greater fatigue strength at a penetration depth of 2-3mm). The arc increases the heat source's coverage of the base material, thereby improving fault tolerance. Furthermore, the plasma generated by the laser is absorbed by the arc, increasing the arc's energy and welding speed.

[0021] 2. This invention integrates various core parameters through detailed process parameter cross-tests, defines the gap / misalignment threshold (0.1mm / 0.3mm), filament spacing (2mm), tungsten pole height (2mm), etc., and covers the optimal process combination.

[0022] The key parameter tolerances (±1mm for filament spacing and ±0.5mm for tungsten electrode height) were verified, and their necessity was disproven by combining defects. The dynamic switching rules for pulse / continuous mode were defined (speed thresholds of 40 / 60mm / s). The clamping method and parameters (2mm clamping block width and rotation misalignment control) were also defined. The applicable material conditions (≤1.5mm 304 stainless steel) and welding quality indicators were also defined.

[0023] That is, the present invention provides a standardized reference for laser TIG hybrid welding by defining parameter thresholds. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the construction principle of the laser TIG hybrid welding process for stainless steel automobile fuel tanks proposed in the present invention;

[0025] Figure 2-1 Schematic diagram of the welding position of the transverse weld seam when the laser TIG hybrid welding process of the present invention is applied;

[0026] Figure 2-2 Schematic diagram of the welding direction of the laser TIG hybrid welding process of the present invention applied to the transverse weld;

[0027] Figure 3-1 Schematic diagram of the welding position of the vertical weld when the laser TIG hybrid welding process of the present invention is applied;

[0028] Figure 3-2 Schematic diagram of the welding direction of the laser TIG hybrid welding process of the present invention applied to a vertical weld;

[0029] Figure 4 This is a diagram showing the welding effect of the laser TIG hybrid welding process of the present invention under the condition that the misalignment is too large;

[0030] Figure 5 This is a diagram showing the welding effect of the laser TIG hybrid welding process of the present invention under the condition that the matching gap is too large;

[0031] Figure 6-1 This is a schematic diagram of the welding construction of the laser TIG hybrid welding process of the present invention under the condition that the wire spacing is 2 mm;

[0032] Figure 6-2 This is a schematic diagram of the welding operation of the laser TIG hybrid welding process of the present invention under the condition that the wire spacing is less than 2 mm;

[0033] Figure 6-3This is a schematic diagram of the welding construction of the laser TIG hybrid welding process of the present invention under the condition that the wire spacing is greater than 2mm. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the present invention in conjunction with specific implementation methods, but does not constitute any limitation to the present invention.

[0035] Reference Figure 1 The laser TIG hybrid welding test used an Aotai WSM-400R TIG welding machine with a maximum output current of 400A and adjustable pulse / DC. The laser was a Chuangxin MFSC2000X with a maximum output laser power of 2000W, a fiber core diameter of 200 microns, and adjustable continuous / pulse. The laser head was a Xinghong HP30I with a collimation: focusing ratio of 100:400. The focal spot size was 0.8mm. The two heat sources were off-axis, with the laser perpendicular to the workpiece and the TIG welding gun at a 60-degree push angle to the workpiece ( Figure 1 In the figure (α), the laser is in front and the arc is behind, and the arc is guided by the laser. Figure 1 Where d1 is the tungsten electrode height, d2 is the laser height, d3 is the filament spacing, d4 is the tungsten filament extension length, and α is the arc push angle.

[0036] When used, there are two welding directions of welds: ① horizontal, such as Figure 2-1 and Figure 2-2 ② Vertical, as shown Figure 3-1 and Figure 3-2 shown.

[0037] Example 1:

[0038] This embodiment mainly examines the effects of the matching gap (vertical distance between the parent materials on both sides of the butt joint) and the misalignment (height deviation of the parent material surfaces on both sides of the butt joint) of the parent material end surfaces on laser TIG hybrid welding.

[0039] Parts with different base material matching gaps (0, 0.2, 0.5, 0.8, 1) and misalignment (0, 0.2, 0.5, 0.8, 1) were welded. The process parameters are shown in Table 1:

[0040] Table 1. Effect of matching gap and misalignment of the end surface of the parent metal on laser TIG hybrid welding

[0041]

[0042] After multiple composite tests, it was found that when the matching gap of the parent material is less than 0.1mm and the misalignment is less than 0.3mm, the welding effect is better. When the matching gap is greater than 0.1mm and the misalignment is less than 0.3mm, the welding effect is poor, and surface humps and weld openings appear.

[0043] When laser TIG hybrid welding the end joints of stainless steel thin plates (less than 1.5mm), the joint matching gap and misalignment of the end joint surface have a great influence on the weld. If the misalignment is too large, it will lead to the formation of a hump on the weld surface (such as Figure 4 ), this is because a large amount of misalignment will cause the molten pool to fluctuate, thus causing the weld formed by solidification to fluctuate, forming a surface hump defect. If the matching gap is too large, the weld end surface will not be fused, and the arc will be biased to one side due to the effect of magnetic conduction, causing the weld to be desoldered (such as Figure 5 ).

[0044] Example 2:

[0045] This example mainly examines the filament spacing ( Figure 1 The influence of d3) on laser TIG hybrid welding.

[0046] When other parameters remain unchanged, welding is performed with different wire spacings (0, 1, 2, 3, 4). The process parameters are shown in Table 2 below:

[0047] Table 2. Effect of wire spacing on laser TIG hybrid welding

[0048]

[0049] After multiple composite tests, it was found that the best welding effect was achieved when the wire spacing was 2 mm. When the wire spacing was 2 mm, the laser just acted on the middle front of the molten pool ( Figure 6-1 The keyhole just formed by the laser will be filled by the molten pool, and the plasma ejected from the keyhole will be absorbed by the arc, increasing the energy of the arc, achieving the complementary effect of the laser and the arc, making the welding process stable and spatter small. The filament spacing is greater than 2mm ( Figure 6-3 ) or less than 2mm( Figure 6-2 ) The welding effect is poor. If the value is too small, the laser will act on the center of the molten pool, reducing the stability of the keyhole and increasing spatter. In addition, there will be too much plasma in the center of the deep penetration, which will affect the penetration of the laser. If the value is too large, the laser will act on the outside of the molten pool, and the laser will be far away from the arc, which will not achieve a complementary effect.

[0050] Example 3:

[0051] This embodiment mainly examines the tungsten electrode height ( Figure 1 The influence of d1) on laser TIG hybrid welding.

[0052] When other parameters remain unchanged, the tungsten electrode height (1, 2, 3, 4, 5) is distributed for welding. The process parameters are as shown in Table 3:

[0053] Table 3. Effect of tungsten electrode height on laser TIG hybrid welding

[0054]

[0055] Results showed that a 2mm tungsten electrode height yielded the best welding results. The tungsten electrode height determines the arc length. If the tungsten electrode is too high, the arc length will be excessive, causing the arc to melt and resulting in poor weld fusion stability. If the tungsten electrode is too low, the arc coverage of the base metal will be reduced, thus reducing compatibility. If the tungsten electrode is too high, the tungsten electrode may contact the molten pool, causing tungsten burn and tungsten inclusions in the weld.

[0056] Example 4:

[0057] This example mainly examines the effects of laser continuous / pulse mode and arc DC / pulse mode on laser TIG hybrid welding.

[0058] When other parameters remain unchanged, laser continuous / pulse and arc DC / pulse modes are used for welding. The process parameters are shown in Table 4:

[0059] Table 4. Effect of pulse mode on laser TIG hybrid welding

[0060]

[0061] We found that laser pulses combined with arc pulses produced better results during slow welding. A combination of laser continuous welding and arc DC welding produced better results during fast welding. Analysis revealed that laser TIG hybrid welding requires the laser to form a keyhole, which is not conducive to keyhole stability during pulse welding. Pulsed arcs, on the other hand, promote deeper penetration compared to DC arcs, while DC arcs offer greater stability.

[0062] Example 5:

[0063] 1mm 304 stainless steel fuel tank longitudinal seam welding:

[0064] 1. Parts processing before welding: Use acetone to clean the area to be welded. If there is oil in the area to be welded, it will cause oxidation of the weld. Check whether there is an oxide layer on the end surface. If there is an oxide layer, it needs to be mechanically cleaned and mechanically polished to remove the oxide layer (Ra≤1.6μm).

[0065] 2. Install the part into the fixture and check the fit between the part and the fixture. The misalignment must be less than 0.3mm, the gap less than 0.1mm, and the end faces of the part must be free of misalignment during a 360-degree rotation of the fixture. The pressure on the end faces of the part must be greater than 10 tons, and the width of the contact surface of the pressure block must be 2mm.

[0066] 3. Welding trajectory programming, laser incident angle 90 degrees, laser tilt angle 0 degrees, TIG welding gun arc angle 60 degrees push welding, laser in front and arc behind, wire spacing 2mm, welding trajectory moves along the downhill slope, slope 5-10 degrees.

[0067] 4. Input process parameters as shown in Table 5 below:

[0068] Table 5. Stainless steel tank longitudinal seam welding process parameters

[0069]

[0070] 5. Check that the above parameters match correctly and start formal welding.

[0071] 6. Test results

[0072] Weld strength: pull-off force> 4000N;

[0073] Deformation: ≤0.5mm / m;

[0074] Porosity: <0.5 / cm;

[0075] Fatigue strength: positive and negative pressure alternation> 10,000 times;

[0076] Air tightness: No leakage points after 35KPa pressure air tightness test.

[0077] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A laser TIG hybrid welding process for stainless steel automobile fuel tanks, characterized in that: The following steps are involved: (a) Pre-treat the end surface of the stainless steel sheet to be welded to ensure that the surface roughness Ra ≤ 1.6 μm and there is no oily oxide layer; (b) Clamp the workpiece with a fixture, control the end-joint surface matching gap to be ≤0.1mm, the misalignment to be ≤0.3mm, and apply a clamping force of >10 tons; (c) A paraxial hybrid welding gun layout is used: the laser is incident vertically on the workpiece (incident angle 90°), the TIG welding gun is at a 60° push angle to the workpiece, the laser is in front, the arc is behind, and the distance between the laser and arc is 2 mm; (d) Set the laser power to 2000 W, the defocus distance to 0 mm, the continuous mode, the TIG current to 90 A, the voltage to 15 V, the DC mode, and the shielding gas flow rate to 15 L / min; (e) Move the welding gun in a downhill direction of 5-10° at a welding speed of 30 mm / s.

2. The laser TIG hybrid welding process for a stainless steel automobile fuel tank according to claim 1 is characterized in that: The determination of the filament spacing in (c) above must satisfy the following requirements: the laser acts on the front of the molten pool so that the keyhole is filled with the molten pool and the plasma is absorbed by the arc; when the spacing deviation is greater than ±1 mm, spatter or penetration defects occur.

3. The laser TIG hybrid welding process for a stainless steel automobile fuel tank according to claim 1 is characterized in that: The TIG welding gun in (c) uses a tungsten electrode with a diameter of 2.4 mm, and the height of the tungsten electrode is strictly controlled within the range of 2±0.5 mm. A height deviation of more than ±1 mm will result in a decrease in arc stiffness or tungsten inclusion defects.

4. The laser TIG hybrid welding process for a stainless steel automobile fuel tank according to claim 1, characterized in that: The welding speed in (e) can be other speeds, but when the welding speed is ≤40 mm / s, a combination of laser pulse mode (frequency 450 Hz, duty cycle 50%) and arc pulse mode (frequency 70 Hz, amplitude 3 A) is adopted; when the welding speed is ≥60 mm / s, it is switched to a combination of laser continuous mode and arc DC mode.

5. The laser TIG hybrid welding process for a stainless steel automobile fuel tank according to claim 1, characterized in that: The contact surface width of the clamping block is 2 mm. When clamping, it is necessary to ensure that the misalignment of the workpiece during 360° rotation is maintained at ≤ 0.3 mm.

6. The laser TIG hybrid welding process for a stainless steel automobile fuel tank according to claim 1, characterized in that: When the stainless steel sheet is 304 stainless steel, with a thickness of ≤1.5mm, the weld after welding shall meet the following requirements: pull-off force > 4000N, deformation ≤0.5mm / m, porosity <0.5 / cm, and positive and negative pressure alternating fatigue strength >10,000 times.

7. A longitudinal seam of a 304 stainless steel fuel tank welded by the laser TIG hybrid welding process of a stainless steel automobile fuel tank according to any one of claims 1 to 6, characterized in that: The weld penetration is uniform and has no hump, the end surface fusion rate is ≥98%, and there is no opening defect.

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