A welding method for a ship's bulbous bow

Abstract

This invention provides a welding method for a ship's bulbous bow, comprising: machining a V-shaped bevel on the outer side of the bulbous bow; assembling the bulbous bow by welding and fixing it to the inner side of the bulbous bow using positioning components; installing a ceramic gasket on the inner side of the bulbous bow, with the center of the ceramic gasket facing the back of the V-shaped bevel; installing a water-cooled slider on the front of the V-shaped bevel; using a flexible rail-mounted gas-electric welding trolley; formulating welding parameters for gas-electric all-position welding technology, including power supply polarity changes, welding wire distance, torch angle, oscillation width, and dwell time; performing single-sided welding with double-sided forming in gas-electric all-position welding; and inspecting the weld. This invention improves the assembly bevel form, changing from an inner Y-shaped bevel to an outer V-shaped bevel; and uses single-sided welding with double-sided forming in one step gas-electric all-position welding technology, reducing operational difficulty, improving the working environment, enhancing operational quality, and increasing operational efficiency.

Description

Technical Field

[0001] This invention belongs to the field of ship welding technology, and specifically relates to a welding method for a ship's bulbous bow. Background Technology

[0002] During shipbuilding, to reduce wave-making resistance during high-speed navigation, a large, elongated bulbous bow is designed at the very front of the ship. This not only increases speed but also provides excellent hull balance, and more importantly, it acts as a sonar dome. The bulbous bow sections (F001 & F002) are sealed joints connecting the bow tip, made of low-alloy high-strength steel. The outer plate welding method is as follows:

[0003] a) Assemble the inner Y-shaped bevel with a blunt edge of 2-3mm and no gap, and fix it by spot welding on the side of the outer plate.

[0004] b) Perform electric welding (4 passes) inside the bulbous bow using CO2 semi-automatic welding.

[0005] c) Use carbon arc gouging to clean the roots and create a U-shaped bevel on the outside of the bulbous bow.

[0006] d) Perform electric welding (2 passes) using CO2 semi-automatic welding at the U-shaped bevel on the outside of the bulbous bow.

[0007] After the bulbous bow is assembled, it connects to the bow tip structure of the hull, forming a sealed internal space. Workers enter the bulbous bow through the bow tip to perform construction work. After installation, welding work is required in the sealed internal space, as well as manual carbon arc gouging for root cleaning and beveling on the outside. The inner space of the bulbous bow is sealed and contains the hull structure; therefore, the welding work on the inner side constitutes a large proportion of the workload and is relatively difficult. The work generates a large amount of smoke and dust in a short period of time, creating a harsh environment. The existing technology has the following problems:

[0008] 1. The assignment is difficult.

[0009] The construction workers were engaged in welding in a confined space inside the bulbous bow, with obstacles from the hull structure. The high-tech work involved included flat welding, climbing welding, vertical welding, and overhead welding in all positions, making the welding operation difficult.

[0010] 2. Poor working environment

[0011] The inner butt joint of the bulbous bow requires four multi-pass welding operations. A large amount of welding fumes swirl inside the bulbous bow space where the air does not circulate, resulting in a harsh working environment for the workers.

[0012] 3. Poor work quality

[0013] The high difficulty and harsh working environment of all-position welding operations make it impossible to achieve the desired welding quality. After welding, the first pass rate of bulbous bows was only 86% on average after UT and MT inspection, resulting in a large amount of rework.

[0014] 4. Low work efficiency

[0015] The bulbous bow assembly and welding process takes eight days, which is time-consuming and inefficient. Summary of the Invention

[0016] The purpose of this invention is to provide a welding method for a ship's bulbous bow that is easy to manufacture and highly efficient.

[0017] This invention provides a welding method for a ship's bulbous bow, the method comprising:

[0018] Step S1: Machin a V-shaped bevel on the outer side of the bulbous bow;

[0019] Step S2: The bulbous bow assembly is fixed by welding positioning components to the inner side of the bulbous bow;

[0020] Step S3: Install a ceramic liner on the inside of the bulbous bow, with the center of the ceramic liner facing the back of the V-shaped bevel, and install a water-cooled slider on the front of the V-shaped bevel.

[0021] Step S4: Using a flexible rail-specific gas-electric welding trolley, formulate the welding parameters for gas-electric all-position welding technology, including the power supply polarity change, welding wire distance, gun angle, oscillation width, and dwell time, and perform single-sided welding with double-sided forming using the gas-electric all-position welding method.

[0022] Step S5: Inspect the weld.

[0023] Optionally, in step S1, the bevel angle of the V-shaped bevel is between 25° and 30°, the assembly gap is 8mm-12mm, and the blunt edge is 0mm.

[0024] Optionally, in step S2, the positioning element includes a Π-shaped card plate;

[0025] The bulbous bow assembly uses positioning components welded and fixed to the inner side of the bulbous bow, including: according to the V-shaped bevel processed by design, installing Π-shaped clamping plates on the back of the V-shaped bevel joint and fixing them by welding, with one Π-shaped clamping plate installed for every 250mm-300mm gap in the weld bevel.

[0026] Optionally, the welding method in step S4 includes:

[0027] The welding torch is clamped by a gas-electric vertical welding auxiliary carriage and the welding is carried out in all positions with gas and slag protection from the lower end of the bulbous bow to the upper end along a fixed gear flexible track next to the weld. During welding, a fiber ceramic liner is pasted on the back of the V-groove joint and a U-shaped groove water-cooled slider is used to support the molten pool and force it to form on the front of the groove.

[0028] Optionally, in step S3, installing the ceramic gasket includes:

[0029] When installing the ceramic gasket, the ceramic gasket should be tightly fitted to the beveled steel plate inside the bulbous bow, with no gaps between the ceramic gaskets. The grooved end of the ceramic gasket should be tightly fitted to the back of the beveled steel plate of the bulbous bow and aligned. The ceramic gasket should be fixed by pressing it with iron wedges through the holes of the Π-shaped clip plate.

[0030] Optionally, the water-cooled slider is installed on the slider clamping mechanism of the welding carriage. The slider clamping mechanism is adjusted so that the water-cooled slider is in close contact with the edge of the V-groove steel plate on the outer front of the bulbous bow. As the welding carriage moves left and right, the slider clamping force is adjusted, and the water-cooled slider moves in close contact with the groove surface, so that the water-cooled slider supports the molten pool and forces the gas-electric all-position weld to form.

[0031] Optionally, in step S4, the welding sequence includes: dividing the bulbous bow into two hemispheres from 1 o'clock to 12 o'clock positions on the clock face based on the cross-sectional shape of the bulbous bow, and separating the hemispheres at 6 o'clock and 12 o'clock positions; performing gas-electric all-position welding with gas and slag protection in the direction of the lower end of the two hemispheres upward; welding one hemisphere and then welding the other hemisphere in the direction of the lower end upward; and adjusting relevant parameters according to different positions.

[0032] Optionally, in step S4:

[0033] The cross-sectional shape of the bulbous bow divides it into positions from 1 o'clock to 12 o'clock on a clock face. To ensure the formation of the back side of the weld in the overhead and oblique overhead positions during gas-electric all-position welding, the power supply adopts the DC positive polarity method, while the other positions adopt the DC reverse polarity method.

[0034] Optionally, in step S4:

[0035] The wire extension length for gas-electric all-position welding is 30mm to 35mm.

[0036] Optionally, after the bulbous bow is completed by gas-electric all-position welding, welding inspection, testing, and performance measurement are performed, as follows:

[0037] Visual inspection revealed that the weld was well formed on both sides, with no welding defects found. The appearance inspection was qualified. 100% UT+RT+MT non-destructive testing of the weld was carried out 24 hours after welding, and the results were qualified.

[0038] Mechanical properties of the welded joints on the test plate: Tensile and bending tests were conducted. The average tensile strength of the welded joint using the gas-electric all-position welding method was 523 MPa. The strength of the welded joint met the minimum tensile strength requirement of 490 MPa for matching the strength of the base material. Impact tests were also conducted on the welded joints.

[0039] The beneficial effects of this invention are as follows:

[0040] As can be seen from the above solutions, the embodiments of the present invention provide a method for welding a bulbous bow of a ship. Compared with the prior art, this new method has the following advantages:

[0041] 1. Reduce the difficulty of the assignment

[0042] Through methodological innovation, the amount of welding work done by construction workers in the confined space inside the bulbous bow has been greatly reduced. At the same time, mechanized and automated welding operations have lowered the skill requirements for welders and reduced the difficulty of welding operations.

[0043] 2. Improve the working environment

[0044] By optimizing the method, manual CO2 welding of multiple layers and multiple passes in the confined space inside the bulbous bow was avoided, which reduced the amount of smoke and dust generated in the confined space of the bulbous bow and improved the working environment for workers.

[0045] 3. Improve work quality

[0046] Through method optimization, a gas-electric all-position welding method for mechanized and automated single-sided welding and double-sided forming of the bulbous bow curved segment outer plate was realized. The reduction in welding difficulty and the improvement of the working environment led to improved welding quality. After welding, the average first-pass yield of the bulbous bow reached 100% after UT, RT, and MT inspections, which is 13.2% higher than the original method's first-pass yield of 86.8%.

[0047] 4. Improve work efficiency

[0048] The original method of welding the bulbous bow required an 8-day work cycle, while the current method only requires 1 day, reducing the work cycle by 4 days and significantly improving efficiency. Attached Figure Description

[0049] Figure 1 This is a flowchart of a ship bulbous bow welding method according to an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the bulbous bow bevel according to an embodiment of the present invention;

[0051] Figure 3 These are the front and side views of the Π-type card code plate according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the installation of the Π-type card code board according to an embodiment of the present invention;

[0053] Figure 5 This is a first welding state diagram according to an embodiment of the present invention;

[0054] Figure 6 This is a schematic diagram of the welding sequence according to an embodiment of the present invention;

[0055] Figure 7 This is a schematic diagram of the welding power source polarity according to an embodiment of the present invention.

[0056] Figure 8 This is a schematic diagram of the ceramic gasket installation according to an embodiment of the present invention;

[0057] In the diagram, 1. Bulbous bow; 2. Π-shaped locking plate; 3. Ceramic gasket; 4. Weld seam; 5. Molten pool; 6. Water-cooled slider; 7. Welding torch; 8. Iron wedge. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0059] This invention designs a welding method for the bulbous bow of a ship. Under the premise of meeting the weld quality requirements, it optimizes the operation process and improves the assembly bevel form, changing the inner Y-type to the outer V-type bevel. Based on the curve changes of the outer plate of the bulbous bow, it develops a single-sided welding double-sided one-time forming gas-electric all-position welding technology. It formulates welding processes and operation methods for the bulbous bow gas-electric all-position welding, including changes in welding power source polarity, welding wire position, welding torch angle, oscillation width, front and rear dwell time, welding sequence, welding parameters, etc., in different welding positions. This reduces the difficulty of operation, improves the working environment, enhances the quality of operation, and increases the efficiency of operation.

[0060] See Figure 1 This invention provides a welding method for a ship's bulbous bow 1, the method comprising:

[0061] Step S1: Machin a V-shaped bevel on the outer side of the bulbous bow 1; the bevel angle of the V-shaped bevel is between 25° and 30°, the assembly gap is 8mm-12mm, and the blunt edge is 0mm.

[0062] Specifically, in combination Figure 2The bevel design of the bulbous bow 1 is improved from the original Y-shaped bevel on the inner side of the bulbous bow 1 to a V-shaped bevel on the outer side of the bulbous bow 1. Based on the 18mm thickness of the DH36 high-strength steel plate of the bulbous bow, in order to achieve gas-electric all-position welding with single-sided welding and double-sided forming, the bevel angle is 25-30°, the assembly gap is 8-12mm, and the blunt edge is 0mm.

[0063] Step S2: The bulbous bow 1 is assembled and fixed to the inner side of the bulbous bow 1 by welding positioning components; the positioning components include a Π-shaped locking plate 2;

[0064] The assembly of the bulbous bow 1 uses positioning components welded and fixed on the inner side of the bulbous bow 1, including: according to the V-shaped bevel processed by design, installing Π-shaped clamping plates 2 on the back of the V-shaped bevel joint and fixing them by welding, with one Π-shaped clamping plate 2 installed for each gap of 250mm-300mm in length at the bevel of the weld 4.

[0065] Specifically, in combination Figure 3 and Figure 4 The assembly method of the bulbous bow 1 includes: according to the V-shaped bevel manufactured according to the design, the Π-shaped positioning clip plate 2 is installed on the inner side of the bulbous bow 1 (the back of the V-shaped bevel joint) by welding. The size of the Π-shaped positioning clip plate required for assembly is 200x120x15mm. One Π-shaped clip plate 2 is installed for each gap of 250-300mm in length of the weld seam 4 bevel. The Π-shaped clip plate 2 is welded firmly to ensure that the bevel plane does not have any misalignment.

[0066] Step S3: Install ceramic pads 3 inside the bulbous bow 1, with the center of ceramic pads 3 facing the back of the V-shaped bevel. Install water-cooled sliders 6 on the front of the V-shaped bevel. Installing ceramic pads 3 includes: when installing ceramic pads 3, ceramic pads 3 are tightly attached to the bevel steel plate inside the bulbous bow 1, and there is no gap between ceramic pads 3. The grooved end of ceramic pads 3 is tightly attached to the back of the bevel steel plate of the bulbous bow 1 and centered. Ceramic pads 3 are fixed by pressing the holes of the Π-shaped clip plate 2 with iron wedges 8.

[0067] Step S4: Using a flexible rail-specific gas-electric welding trolley, the welding parameters for gas-electric all-position welding technology, including the power supply polarity changes, welding wire distance, gun angle, oscillation width, and dwell time, are determined. Single-sided welding with double-sided forming is performed using the gas-electric all-position welding method. The welding method includes: using a gas-electric vertical welding auxiliary trolley to clamp the welding gun 7, and performing gas-electric all-position welding with slag protection from the lower end of the two hemispheres of the bulbous nose 1 upwards along the gear-type flexible rail fixed beside the weld seam 4. During welding, a fiber ceramic liner is pasted on the back of the V-groove joint, and a U-shaped groove water-cooled slider 6 is used to support the molten pool 5 on the front of the groove for forced forming. The water-cooled slider 6 is installed on the slider clamping mechanism of the welding carriage. The slider clamping mechanism is adjusted so that the water-cooled slider 6 is in close contact with the edge of the V-groove steel plate on the outer front of the bulbous bow 1. As the welding carriage moves left and right, the slider clamping force is adjusted, and the water-cooled slider 6 moves close to the groove surface, so that the water-cooled slider 6 supports the molten pool 5 and forces the gas-electric all-position weld 4 to form. The welding sequence includes: dividing the bulbous bow 1 into two hemispheres from 1 o'clock to 12 o'clock positions based on the cross-sectional shape of the bulbous bow 1, and then separating the hemispheres at 6 o'clock and 12 o'clock positions. The gas-electric all-position welding is carried out in the order of gas-slag protection with the lower end of each hemisphere facing upwards. After welding one hemisphere, the other hemisphere is welded with the lower end facing upwards. The relevant parameters are adjusted according to different positions. The cross-sectional shape of the bulbous bow 1 divides it into clock face positions from 1 o'clock to 12 o'clock. During welding, to ensure the back surface formation of weld seam 4 in the overhead and inclined overhead positions of the gas-electric all-position welding, a DC positive polarity method is used, while a DC reverse polarity method is used for other positions. The wire extension length for gas-electric all-position welding is 30mm to 35mm.

[0068] Specifically, in combination Figures 5 to 7 Using a dedicated welding auxiliary carriage (EGW), the welding torch 7 is clamped and the gas-electric all-position welding with slag protection is performed from the lower end of the two hemispheres of the bulbous bow 1 upward along the gear flexible track fixed beside the weld seam 4. During welding, a fiber ceramic liner is pasted on the back of the V-groove joint, and a U-shaped groove water-cooled slider 6 is used to support the molten pool 5 on the front of the groove to force it into shape, so as to achieve the welding method of single-sided welding and double-sided forming in gas-electric all-position welding.

[0069] 1) Welding materials:

[0070] ① Fiber-coated ceramic welding gasket: This is used for one-time welding of the inner bevel back of the bulbous bow 1, ensuring the height and width of the back weld 4. The appearance dimensions of the fiber-coated ceramic gasket groove are required as follows: width 43mm, height 10mm, groove width 14mm, and groove arc depth 1.5mm. Because the bulbous bow 1 has linear curved surface segments, in order to ensure the quality of gas-electric all-position welding, the front of the ceramic welding gasket groove needs to be protected with a layer of fiber. The technical performance of the ceramic is: sulfur <0.05%, phosphorus <0.1%, moisture absorption ≤0.4%, bulk density ≥1.75g / cm3, flexural strength ≥83g / cm2, 180° peel force ≥20N / 2.5cm, and refractoriness 1300℃.

[0071] ② Flux-cored welding wire: The bulbous bow outer plate is made of Class D high-strength hull structural steel. 3Y grade flux-cored welding wire is used for gas-electric all-position welding. The composition of the flux-cored welding wire meets the following requirements: carbon ≤ 0.05%, sulfur < 0.004%, phosphorus < 0.007%, silicon ≤ 0.90%, manganese ≤ 2.0%, copper ≤ 0.35%, nickel ≤ 0.30%, molybdenum ≤ 0.35%, vanadium ≤ 0.08%.

[0072] ③ Gas: The bulbous bow outer plate is made of Class D high-strength hull structural steel. The gas used for all-position gas-electric welding is CO2 gas, and its purity must be greater than 99.9%.

[0073] 2) Welding process parameters and welding operation design:

[0074] (I) The main welding process parameters for all-position gas-electric welding of bulbous bow include: welding sequence, welding power polarity, welding torch angle, wire extension length, welding current, arc voltage, welding speed, wire swing amplitude and dwell time, etc.

[0075] (1) Welding sequence

[0076] Based on the cross-sectional shape of the bulbous bow 1, the bulbous bow 1 is divided into two hemispheres. The welding sequence of gas-electric all-position welding is to perform gas-slag protected all-position welding on the lower end of the two hemispheres of the bulbous bow 1 in the upward direction. After welding one hemisphere, the lower end of the other hemisphere is then welded in the upward direction.

[0077] (2) Welding power source polarity

[0078] The cross-sectional shape of the bulbous bow 1 divides it into clock face positions 1 to 12 o'clock. During welding, in order to ensure the formation of the back side of weld seam 4 in the overhead and oblique overhead positions (i.e., the 6 o'clock to 4 o'clock and 6 o'clock to 8 o'clock positions on the clock face of the bulbous bow 1) of the gas-electric all-position welding, the power supply adopts the DC positive polarity method (i.e., the base material of the bulbous bow 1 is connected to the positive terminal of the welding power supply, and the welding gun 7 is connected to the negative terminal). For other positions, the DC reverse polarity method is used for welding (i.e., the base material of the bulbous bow 1 is connected to the negative terminal of the welding power supply, and the welding gun 7 is connected to the positive terminal).

[0079] (3) Welding torch angle

[0080] The angle of the gas-electric all-position welding torch 7 is adjusted according to different welding positions, and whether the angle is suitable directly affects the formation and defects of the weld 4 on both sides. The angle of the welding torch 7 for each position is shown in the angle of the specific welding operation of the bulbous bow 1.

[0081] (4) Wire extension length

[0082] For gas-electric all-position welding, the wire extension length is 30-35mm. If the wire extension is too long, the resistance heat increases, the melting rate is too fast, and overheating and burn-out are likely, resulting in severe spatter and poor shielding, affecting the stability of the welding process and causing poor weld formation. If the wire extension is too short, it can easily lead to blockage of the shielding gas outlet, resulting in poor shielding and affecting weld quality.

[0083] (5) Welding current

[0084] Gas-electric all-position welding, due to its high current density, exhibits a droplet-like transfer pattern. Its characteristics include minimal spatter, stable arc combustion, and high deposition rate; therefore, selecting an appropriate current is crucial. Both excessively high and insufficient welding currents will negatively impact the stability of the welding process and the quality of the weld bead formation. For welding currents at various positions on the bulbous bow 1, please refer to the welding parameters for specific positions on the bulbous bow 1.

[0085] (6) Arc voltage

[0086] The arc voltage selected for gas-electric all-position welding must match the welding current. Excessively high arc voltage will result in excessive spatter and severe undercut in weld seam 4, while excessively low arc voltage will cause unstable arc combustion. Therefore, while ensuring welding process stability and good weld seam formation, the arc voltage should be minimized as much as possible to prevent porosity and reduce the loss of alloying elements. For the arc voltages at various positions of the bulbous bow 1, please refer to the welding parameters for specific positions of the bulbous bow 1 welding operation.

[0087] (7) Welding speed

[0088] The appropriate welding speed depends on the melting speed of the welding wire. The ideal welding speed is when the molten metal level in the water-cooled slide block 6 is at least 2-3 mm from the bottom of the air inlet. If the welding speed is too fast, the molten metal level in the slide block 5 will gradually drop, resulting in incomplete fusion at the upper end of the fillet weld 4, or even poor fusion on the back side of the fillet weld, leading to incomplete penetration defects. If the welding speed is too slow, the molten metal level in the water-cooled slide block 6 will rise, and the fusible pool 5 will roll forward, easily causing incomplete penetration defects. When the molten metal level in the pool 5 rises to the bottom of the air inlet, the arc combustion becomes unstable, potentially forcing the welding process to be interrupted. For welding speeds at various positions on the bulbous bow 1, please refer to the welding parameters for specific positions on the bulbous bow 1.

[0089] (8) Welding wire swing amplitude and dwell time

[0090] When using an oscillating device for gas-electric all-position welding, the arc is stable, spatter is minimal, the temperature across the weld section 4 is uniform, and the molten pool 5 exhibits improved metal crystallization with finer grains, which is beneficial for obtaining a dense weld 4 and aesthetically pleasing weld formation. The oscillation amplitude and dwell time are detailed in the specific welding operation instructions for the bulbous bow 1.

[0091] (II) Welding operations of gas-electric all-position welding

[0092] (1) Installation of fiber ceramic gasket: combined with Figure 8 When installing the liner, it is essential to ensure that the fiber liner is tightly attached to the beveled steel plate inside the bulbous bow 1, with no gaps between the liners. The grooved end of the fiber liner should be tightly attached to the back of the beveled steel plate of the bulbous bow 1 and aligned with it. The fiber liner should be fixed by pressing the Π-type clip plate 2 with iron wedges 8.

[0093] (2) Installation of water-cooled slider 6: The water-cooled slider 6 is installed on the slider clamping mechanism on the welding trolley. Adjust the upper and lower knobs of the slider clamping mechanism to ensure that the water-cooled slider 6 is in close contact with the edge of the V-groove steel plate on the outer front of the bulbous bow 1. As the flexible guide rail welding trolley moves left and right, adjust the appropriate pressure of the slider clamping knob. The water-cooled slider 6 moves close to the groove surface, so that the water-cooled slider 6 supports the molten pool 5 and forces the gas-electric all-position welding seam 4 to form.

[0094] (3) Welding:

[0095] Based on the cross-sectional shape of the bulbous bow 1, the bulbous bow 1 is divided into clock face positions 1 to 12 o'clock, and the two hemispheres are separated at positions 6 and 12 o'clock. The gas-electric all-position welding is carried out in the order of gas-slag protection welding with the lower end of the two hemispheres facing upwards. After welding one hemisphere, the lower end of the other hemisphere is welded in the upward direction. The relevant parameters are adjusted according to different positions.

[0096] ① Welding the cross-sectional shape of the bulbous bow 1 at the 6-5 o'clock position: This position is the arc initiation position. Before initiating the arc, adjust the welding power supply to use the DC positive polarity method. Adjust the welding torch 7 angle to tilt inward by 5-8°, the wire extension length to be 30-35mm, the wire to be 4-6mm from the bevel toe, the welding torch 7 swing amplitude to be 6-8mm, the bevel toe face dwell time to be 1.0-1.2sec, the V-bevel face dwell time to be 1.5-1.8sec, the swing speed to be 31mm / sec, the welding current to be 297-352A, and the arc voltage to be 30-36V (see Table 1 for specific parameters). Press the start button to start the arc with an intermittent arc initiation. After the molten pool 5 is established, press the wire swing button to start normal welding. The welding speed is automatic tracking (about 11cm / min). Weld the molten pool 5 to be 2-7mm from the shielding gas port of the slider. At the same time, use an insulating rod to remove the spatter in the shielding gas box of the water-cooled slider 6 at any time.

[0097] Table 1 Welding parameters

[0098]

[0099] ② Welding of the cross-sectional shape of bulbous bow 1 at positions 5-4 o'clock: When welding from position 6-5 o'clock to position 5 o'clock, the same DC positive polarity method is used for welding power supply, the wire extension length is 30-35mm, and the angle of welding torch 7 is slowly adjusted to tilt inward by 4-6°, the wire is 5-8mm from the bevel toe, the welding torch 7 swing amplitude is 4-6mm, the dwell time at the bevel toe face is 1.0-1.2sec, the dwell time at the V bevel face is 1.3-1.4sec, the swing speed is 31mm / sec, the welding current is 320-355A, the arc voltage is 34-38V (see Table 2 for specific parameters), and the welding speed is automatic tracking (about 12cm / min). Weld the molten pool 5 to the position 2-6mm from the protective gas port of the slider. At the same time, use an insulating rod to remove the spatter in the protective gas box of the water-cooled slider 6 at any time.

[0100] Table 2 Welding parameters

[0101]

[0102] ③ Welding of the cross-sectional shape of bulbous bow 1 at the 4-2 o'clock position: When welding from the 5-4 o'clock position to the 4 o'clock position, adjust the welding power supply to use DC reverse polarity, the wire extension length to be 30-35mm, slowly adjust the angle of the welding torch 7 to tilt inward by 3-4°, the wire to be 8-10mm from the bevel toe, the welding torch 7 swing amplitude to be 3-5mm, the bevel toe face dwell time to be 1.0-1.2sec, the V bevel face dwell time to be 1.1-1.3sec, the swing speed to be 30mm / sec, the welding current to be 340-370A, the arc voltage to be 36-40V (see Table 3 for specific parameters), and the welding speed to be automatic tracking (about 10cm / min). Weld the molten pool 5 to be 2-5mm from the shielding gas port of the slider. At the same time, use an insulating rod to remove the spatter in the shielding gas box of the water-cooled slider 6 at any time.

[0103] Table 3 Welding parameters

[0104]

[0105] ④ Welding of the cross-sectional shape of bulbous bow 1 at position 2-1 o'clock: When welding from position 4-2 o'clock to position 2 o'clock, the same DC reverse polarity method is used for welding power supply, the wire extension length is 30-35mm, and the angle of welding torch 7 is slowly adjusted to tilt inward by 8-10°, the wire is 12-14mm from the bevel toe, the welding torch 7 swing amplitude is 2-3mm, the dwell time at the bevel toe is 0.4-0.6sec, the dwell time at the V bevel face is 0.8-1.0sec, the swing speed is 30mm / sec, the welding current is 340-380A, the arc voltage is 36-39V (see Table 4 for specific parameters), and the welding speed is automatic tracking (about 8cm / min). Weld the molten pool 5 to the position 3-7mm from the protective gas port of the slider. At the same time, use an insulating rod to remove the spatter in the protective gas box of the water-cooled slider 6 at any time.

[0106] Table 4 Welding parameters

[0107]

[0108] ⑤ Welding of the cross-sectional shape of bulbous bow 1 at positions 1-12 o'clock: When welding from position 2-1 o'clock to position 1 o'clock, the same DC reverse polarity method is used for welding power supply, the wire extension length is 30-35mm, slowly adjust the angle of welding torch 7 to balance with the steel plate bevel, the wire is 13-15mm from the bevel toe, the welding torch 7 swing amplitude is 3-4mm, the dwell time at the bevel toe face is 0.2-0.5sec, the dwell time at the V bevel face is 0.6-1.0sec, the swing speed is 30mm / sec, the welding current is 340-400A, the arc voltage is 36-40V (see Table 5 for specific parameters), the welding speed is automatic tracking (about 7cm / min), and the weld pool 5 is welded to the position 3-8mm from the protective gas port of the slider. At the same time, an insulating rod should be used to remove the spatter in the protective gas box of the water-cooled slider 6 at any time.

[0109] Table 5 Welding parameters

[0110]

[0111] ⑥ The cross-sectional shape of the bulbous bow 1 is the same as the other side, which is hemispherical and welded using the same welding method. After both sides are welded, the upper and lower closed joints are cut into U-grooves with a length of 50-100mm using air gouging and then welded using CO2 semi-automatic welding. The reverse side of the joint is treated in the same way.

[0112] Step S5: Inspect weld 4. After the bulbous bow 1 is completed by gas-electric all-position welding, weld inspection, examination, and performance testing are performed as follows: Weld 4 is visually inspected and found to be well-formed on both sides, with no welding defects found. The appearance inspection is qualified. Weld 4 is subjected to 100% UT+RT+MT non-destructive testing 24 hours after welding, and the results are qualified. Mechanical properties of the welded joint on the test plate: Tensile and bending tests are conducted. The average tensile strength of the welded joint using gas-electric all-position welding is 523 MPa. The strength of the welded joint meets the minimum tensile strength requirement of 490 MPa for matching the strength of the base material. Impact test is performed on the welded joint.

[0113] Post-welding inspection:

[0114] After the gas-electric all-position welding of the bulbous bow was completed, welding inspection, testing, and performance determination were carried out in accordance with the classification society's "Welding and Materials," and all results were qualified, as detailed below:

[0115] ① Weld 4 was visually inspected and found to be well formed on both sides with no welding defects. The appearance inspection was qualified. Weld 4 was subjected to 100% UT+RT+MT non-destructive testing 24 hours after welding, and the results were qualified.

[0116] ② Mechanical properties of the welded joints on the test plate: Tensile and bending tests were conducted. The average tensile strength of the welded joint using the gas-electric all-position welding method was 523 MPa. The strength of the welded joint met the minimum tensile strength requirement of 490 MPa for matching the strength of the base material. Impact tests were also conducted on the welded joints, and the results were satisfactory.

[0117] The original bulbous bow 1 assembly and welding method is as follows:

[0118] a) The outer plate of the bulbous bow is fitted with an inner Y-shaped bevel, with a bevel angle of 35°, a blunt edge of 2-3mm, and no gap.

[0119] b) Manual CO2 semi-automatic welding was used for electric welding inside the bulbous bow (4 passes).

[0120] c) Use carbon arc gouging to clean the roots on the outside of the bulbous bow and create a U-shaped 45° bevel.

[0121] d) Manual CO2 semi-automatic welding was used to perform electric welding (2 passes) on the outer side of the bulbous bow.

[0122] The present invention provides a method for welding a bulbous bow as follows:

[0123] a) The original Y-shaped inner bevel has been improved to a V-shaped outer bevel, realizing single-sided welding and double-sided forming gas-electric all-position welding of the outer side. The bevel angle is 25-30°, reducing the amount of weld metal filling in the weld bevel; the bevel gap is 8-12mm, reducing the impact of precision assembly; the bevel blunt edge is 0-1mm.

[0124] b) Using fiber ceramic liner 3, a single-sided welding double-sided forming welding method for gas-electric all-position welding is realized.

[0125] c) A dedicated welding auxiliary trolley is used. The curvature of the bulbous bow plate is connected to a high-temperature resistant, flexible, bendable, and magnetically attached track to achieve automatic welding of all positions of the curved surface segmented overhead, vertical, and flat welding joints.

[0126] d) A mechanized gas-electric all-position welding operation was carried out on the outer side of the bulbous bow 1. The welding process and operation methods were formulated for the changes in welding power polarity, welding wire position, welding torch angle, oscillation width, front and back dwell time, welding sequence, welding parameters and other welding processes for the gas-electric all-position welding of the bulbous bow 1 at different welding positions.

[0127] Compared with existing technologies, this new method has the following advantages:

[0128] 1. Reduce the difficulty of the assignment

[0129] Through methodological innovation, the amount of welding work done by construction workers in the confined space inside the bulbous bow 1 has been greatly reduced. At the same time, mechanized and automated welding operations have reduced the skill requirements for welders and the difficulty of welding operations.

[0130] 2. Improve the working environment

[0131] By optimizing the method, multi-layer and multi-pass manual CO2 welding in the confined space inside the bulbous bow 1 was avoided, which reduced the amount of smoke and dust generated in the confined space of the bulbous bow 1 and improved the working environment for workers.

[0132] 3. Improve work quality

[0133] Through method optimization, a gas-electric all-position welding method for mechanized and automated single-sided welding and double-sided forming of the curved segmented outer plate of the bulbous bow 1 was realized. The reduction in welding difficulty and the improvement of the working environment led to the improvement of welding quality. After welding, the average first-pass yield of bulbous bow 1 reached 100% after UT, RT and MT inspection, which is 13.2% higher than the first-pass yield of 86.8% of the original method.

[0134] 4. Improve work efficiency

[0135] The original method required an 8-day work cycle for welding the bulbous bow, while the current method only requires 1 day, reducing the work cycle by 4 days and significantly improving efficiency.

[0136] In summary, the present invention has the following beneficial effects:

[0137] a) The Y-shaped bevel inside the confined space of the bulbous bow 1 was improved to a V-shaped bevel on the outside. The reverse-cutting root cleaning process was improved to a single-sided welding double-sided forming gas-electric all-position welding technology with fiber ceramic pad 3. The operation process was optimized and the carbon arc gouging root cleaning process was reduced.

[0138] b) Innovative application of gas-electric all-position welding on bulbous bow, realizing the technological innovation of automatic all-position welding of curved sections of ships.

[0139] c) Develop a single-sided welding double-sided one-time forming gas-electric all-position welding technology, and formulate welding processes and operation methods for the bulbous bow 1 gas-electric all-position welding in different welding positions, such as changes in welding power polarity, changes in welding wire position, welding torch angle, oscillation width, front and back dwell time, welding sequence, and welding parameters, to avoid the occurrence of many arc-stopped joints in manual CO2 root welding, thereby reducing welding defects such as joint fast holes and fast hole microcracks.

[0140] According to passenger roll-on / roll-off ship statistics, the installation and welding of bulbous bow 1 requires (4 person-times of assemblers + 4 person-times of welders + 2 person-times of carbon planers + 2 person-times of grinders). Calculated based on a reduction of 4 days in the operation cycle of bulbous bow 1, the total time saved by bulbous bow 1 is: 6 people * 4 days * 8 hours / day * 45 yuan / time = 8640 yuan.

[0141] Based on the calculation of building 27 product ships per year, the annual cost savings are 8,640 yuan * 27 ships = 233,280 yuan.

[0142] In addition, the innovative application of gas-electric all-position welding in the bulbous bow can effectively improve quality and reduce welding rework, energy, and welding materials, resulting in huge and immeasurable cost savings.

[0143] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A welding method for a ship's bulbous bow, characterized in that, The method includes: Step S1: Machin a V-shaped bevel on the outer side of the bulbous bow; Step S2: The bulbous bow assembly is fixed to the inner side of the bulbous bow by welding with positioning components; Step S3: Install a ceramic liner inside the bulbous bow, with the center of the ceramic liner facing the back of the V-shaped bevel, and install a water-cooled slider on the front of the V-shaped bevel. Step S4: Using a flexible rail-specific gas-electric welding trolley, formulate the welding parameters for gas-electric all-position welding technology, including the power supply polarity change, welding wire distance, gun angle, oscillation width, and dwell time, and perform single-sided welding with double-sided forming using the gas-electric all-position welding method. Step S5: Inspect the weld; In step S1, the bevel angle of the V-shaped bevel is between 25° and 30°, the assembly gap is 8mm-12mm, and the blunt edge is 0mm. In step S4, the welding sequence includes: dividing the bulbous bow into two hemispheres from 1 o'clock to 12 o'clock on the clock face based on the cross-sectional shape of the bulbous bow, and separating the hemispheres at 6 o'clock and 12 o'clock. The gas-electric all-position welding is carried out in the order of gas-slag protection with the lower end of the two hemispheres facing upwards. After welding one hemisphere, the other hemisphere is welded with the lower end facing upwards. The relevant parameters are adjusted according to different positions. In step S4: The cross-sectional shape of the bulbous bow divides it into clockwise positions from 1 o'clock to 12 o'clock. To ensure proper weld formation on the back side of the weld in the overhead and angled overhead positions during all-position gas-electric welding, a DC positive polarity method is used for the power supply, while a DC negative polarity method is used for other positions. Details are as follows: 1) Welding at the 6-5 o'clock position of the cross-sectional shape of the bulbous bow: This position is the arc starting position. Before starting the arc, adjust the welding power supply to use DC positive polarity, the welding torch swing amplitude is 6-8mm, the dwell time at the bevel toe end face is 1.0-1.2sec, the dwell time at the V bevel front face is 1.5-1.8sec, and the swing speed is 31mm / sec. 2) Welding of the cross-sectional shape of the bulbous bow at the 5-4 o'clock position: When welding from the 6-5 o'clock position to the 5 o'clock position, the welding power supply is DC positive polarity, the welding torch swing amplitude is 4-6mm, the dwell time on the bevel toe end face is 1.0-1.2sec, the dwell time on the V bevel front face is 1.3-1.4sec, and the swing speed is 31mm / sec; 3) Welding of the cross-sectional shape of the bulbous bow at the 4-2 o'clock position: When welding from the 5-4 o'clock position to the 4 o'clock position, adjust the welding power supply to use DC reverse polarity, the welding torch swing amplitude is 3-5mm, the dwell time on the bevel toe end face is 1.0-1.2sec, the dwell time on the V bevel front face is 1.1-1.3sec, and the swing speed is 30mm / sec; 4) Welding of the cross-sectional shape of the bulbous bow at the 2-1 o'clock position: When welding from the 4-2 o'clock position to the 2 o'clock position, the welding power supply adopts the DC reverse polarity method, the welding torch swing amplitude is 2-3mm, the dwell time of the bevel toe end face is 0.4-0.6sec, the dwell time of the V bevel front face is 0.8-1.0sec, and the swing speed is 30mm / sec; 5) Welding of the cross-sectional shape of the bulbous bow at positions 1-12 o'clock: When welding from position 2-1 o'clock to position 1 o'clock, the welding power supply adopts the DC reverse polarity method, the welding torch swing amplitude is 3-4mm, the dwell time at the bevel toe end face is 0.2-0.5sec, the dwell time at the V bevel front face is 0.6-1.0sec, and the swing speed is 30mm / sec; 6) The cross-sectional shape of the bulbous bow is the same as that of the other hemisphere, and it is welded using the same welding method.

2. The welding method for a ship's bulbous bow according to claim 1, characterized in that: In step S2, the positioning element includes a Π-shaped card code plate; The bulbous bow assembly employs positioning components welded and fixed to the inner side of the bulbous bow, including: according to the designed and processed V-shaped bevel, installing Π-shaped locking plates on the back of the V-shaped bevel joint and fixing them by welding, with one Π-shaped locking plate installed for every 250mm-300mm gap in the weld bevel.

3. The welding method for a ship's bulbous bow according to claim 2, characterized in that, The welding method in step S4 includes: The welding torch is clamped by a gas-electric vertical welding auxiliary carriage and the welding is carried out in all positions with gas and slag protection from the lower end of the bulbous bow to the upper end along a fixed gear flexible track next to the weld. During welding, a fiber ceramic liner is pasted on the back of the V-groove joint and a U-shaped groove water-cooled slider is used to support the molten pool and force it to form on the front of the groove.

4. The welding method for a ship's bulbous bow according to any one of claims 1 to 3, characterized in that, In step S3, installing the ceramic gasket includes: When installing the ceramic gasket, the ceramic gasket should be tightly fitted to the beveled steel plate inside the bulbous bow, with no gaps between the ceramic gaskets. The grooved end of the ceramic gasket should be tightly fitted to the back of the beveled steel plate of the bulbous bow and aligned. The ceramic gasket should be fixed by pressing it with iron wedges through the holes of the Π-shaped clip plate.

5. The welding method for a ship's bulbous bow according to claim 4, characterized in that: The water-cooled slider is installed on the slider clamping mechanism of the welding carriage. The slider clamping mechanism is adjusted so that the water-cooled slider is in close contact with the edge of the V-groove steel plate on the outer front of the bulbous bow. As the welding carriage moves left and right, the slider clamping force is adjusted, and the water-cooled slider moves close to the groove surface, so that the water-cooled slider supports the molten pool and forces the gas-electric all-position weld to form.

6. The welding method for a ship's bulbous bow according to claim 1, characterized in that, In step S4: The wire extension length for the gas-electric all-position welding is 30mm to 35mm.

7. The welding method for a ship's bulbous bow according to any one of claims 1 to 3, characterized in that: After the bulbous bow is welded in all positions using gas and electricity, welding inspection, testing, and performance evaluation are carried out, as follows: Visual inspection revealed that the weld was well formed on both sides, with no welding defects found. The appearance inspection was qualified. 100% UT+RT+MT non-destructive testing of the weld was carried out 24 hours after welding, and the results were qualified. Mechanical properties of the welded joints on the test plate: Tensile and bending tests were conducted. The average tensile strength of the welded joint using the gas-electric all-position welding method was 523 MPa. The strength of the welded joint met the minimum tensile strength requirement of 490 MPa for matching the strength of the base material. Impact tests were also conducted on the welded joints.

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