A welding method for reducing defects of end welds in FAB submerged arc automatic welding

Abstract

The application discloses a welding method for reducing end weld joint defects of FAB submerged arc automatic welding, which comprises the following steps: step 1, welding opening and groove cleaning before welding; step 2, welding the two ends of the weld joint by adopting restraint welding; step 3, laying filler metal in the groove; step 4, laying the submerged arc welding trolley track to the position parallel to the center line of the groove, and welding; step 5, after the welding is completed, carrying out X-ray or ultrasonic flaw detection inspection according to the requirements of the weld joint, and removing the defects. By optimizing the welding process parameters and the laying height of the filler metal of the FAB welding, the application effectively avoids or reduces the repair workload of the end weld joint defects, improves the weld joint quality and construction efficiency, and can be applied to the FAB butt joint welding of various ships with a thickness of greater than or equal to 6 mm.

Description

Technical Field

[0001] This invention belongs to the field of shipbuilding welding technology, and specifically relates to a welding method for reducing defects in the weld ends of FAB submerged arc automatic welding. Background Technology

[0002] FAB welding involves applying a cured flux or a fiber-ceramic backing to the back side to form the weld. For plates thicker than 6mm, additional metal is added to the groove to improve welding efficiency. Submerged arc welding is performed using a single electrode from the front side of the groove, achieving single-sided, single-pass welding with double-sided forming. During FAB welding, the thickness of the additional metal added to the groove is generally determined by the plate thickness. Two types of filler metal are used: iron powder and scrap welding wire. No additional filler metal is added when the plate thickness is less than 6mm or the gap between 6mm plates is 0mm-2mm. However, filler metal is required when the plate thickness is greater than 6mm or the gap between 6mm plates is 3mm or more. The height of the filler metal depends on the groove size, gap, and plate thickness. During filler metal placement, it is essential to ensure that the height and flatness of the filler are uniform, meaning the height of the filler metal should be approximately consistent along the weld length. Figures 1 to 2 As shown.

[0003] like Figure 3 As shown, in the FAB submerged arc welding process, unstable parameters and low heat input during the arc initiation and termination phases of the root pass weld result in poor weld formation and uneven transition within a 500mm range at both ends, leading to defects such as cracks or lack of fusion. These defects persist throughout the entire root pass weld. Current processes require the filler metal height at the weld ends to be consistent with that of the intermediate welds. The large filler metal volume at the ends of the root pass weld results in a significant proportion of its thickness to the total plate thickness. Because the proportion of welding defects along the plate thickness is large, a substantial amount of rework is required after welding. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a welding method for reducing defects in the end weld of FAB submerged arc welding. By adjusting the filler metal laying height and welding process parameters of the end weld, the proportion of defective end welds in the plate thickness direction is reduced or eliminated, thereby reducing the rework of the end welds.

[0005] The objective of this invention is achieved through the following technical solution: a welding method for reducing weld defects at the weld end of FAB submerged arc welding, comprising the following steps:

[0006] Step 1: Before welding, bevel the groove and clean it.

[0007] Step 2: Weld both ends of the weld using restraint welding;

[0008] Step 3: Lay filler metal inside the bevel;

[0009] Step 4: Lay the submerged arc welding trolley track parallel to the center line of the bevel and begin welding;

[0010] Step 5: After welding is completed, X-ray or ultrasonic testing is performed on the weld according to the requirements, and defects are removed.

[0011] Preferably, in step 1, an I-bevel is opened when the thickness of the plate to be welded is 6mm-7mm, and a V-bevel is opened when the thickness of the plate to be welded is 7mm or more.

[0012] Preferably, in step 2, the specific method for constraining the weld ends is as follows: install arc-starting and arc-extinguishing plates at both ends of the weld, and weld the weld from the inside of the bevel to the arc-starting plate end or the arc-extinguishing plate end to fix it.

[0013] Preferably, the dimensions of the restraint weld are selected based on the thickness of the plate to be welded.

[0014] Preferably, in step 3, the filler metal height at the start and end positions of the weld is 5mm, and the height gradually increases from the end to the middle. At a distance of 200mm from the end, the filler metal height increases to the standard height, and the laying process needs to ensure a smooth transition of the filler metal.

[0015] Preferably, in step 4, the welding wire is perpendicular to the surface of the workpiece to be welded, and then the welding wire is aligned so that the tip of the welding wire and the guide infrared tracking point are aligned with the center of the bevel before welding begins.

[0016] Preferably, in step 4, the welding parameters and the wire extension change with the height of the filler metal, and the welding current increases accordingly as the metal height increases during the welding process.

[0017] Preferably, in step 5, X-ray or ultrasonic testing is performed according to the weld requirements. Ultrasonic testing is performed on the arc-stopping position, the beginning and end, and the cross or T-joint positions during the welding process. If there are welding defects at the beginning and end, carbon gouging is performed on the back of the weld to remove the defects. After cleaning, repair welding is performed.

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

[0019] This invention provides a welding method for reducing weld defects at the end of FAB (Fused Aperture Blower) submerged arc welding. By optimizing the height of the filler metal and adjusting welding process parameters, the height of defective welds at the end is avoided or reduced. Within a 200mm range at the end, the filler metal height at the start and end positions is set to 5mm, gradually increasing from the end towards the middle. At 200mm from the end, the filler metal height meets the process requirements. In this invention, the starting and ending currents are set to 650A-750A. As the metal height increases during welding, the welding current increases accordingly, solving the problem of deep root welds and excessive rework for end defects.

[0020] This invention effectively avoids or reduces the amount of rework for end weld defects by optimizing the welding process parameters and filler metal laying height of FAB welding, thereby improving weld quality and construction efficiency. It can be applied to FAB butt welding of various types of ships with a diameter of ≥6mm.

[0021] This invention improves welding quality and production efficiency by reducing defects in end FAB welds, while also bringing economic benefits in terms of resource conservation, personnel safety, and equipment reliability, thereby increasing the rate of automated welding and assembly efficiency in ships. Attached Figure Description

[0022] Figure 1 A cross-sectional view of the filler metal laying in the existing FAB welding technique;

[0023] Figure 2 A schematic diagram of the overall laying of filler metal in FAB welding in the prior art;

[0024] Figure 3 This is a schematic diagram showing the proportion of each weld bead at the end of a FAB weld in the prior art;

[0025] Figure 4 This is a flowchart of the FAB submerged arc automatic welding end weld defect removal method in this invention;

[0026] Figure 5 This is a schematic diagram of the welding bevel in an embodiment of the present invention;

[0027] Figure 6 This is a schematic diagram of the end restraint welding of a weld with a plate thickness of less than 7mm and a gap of 0mm-2mm in an embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of the end restraint welding of a weld with a plate thickness of less than 7mm and a gap of more than 2mm in an embodiment of the present invention;

[0029] Figure 8 This is a schematic diagram of arc-starting end restraint welding in an embodiment of the present invention with a plate thickness greater than or equal to 7mm;

[0030] Figure 9 This is a schematic diagram of arc-extinguishing end restraint welding in an embodiment of the present invention with a plate thickness greater than or equal to 7mm;

[0031] Figure 10 This is a schematic diagram of the optimized filler metal arrangement in an embodiment of the present invention;

[0032] Figure 11 This is a schematic diagram of V-groove welding in an embodiment of the present invention;

[0033] Figure 12 This is a schematic diagram of type I groove welding in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0035] Due to the instability of welding parameters during the arc initiation and termination phases of the FAB (Fused Arc Welding) root pass, incomplete fusion or crack defects may occur in the 500mm weld end. Because the root pass has a large filler content, its thickness constitutes a large proportion of the total plate thickness, resulting in a significant amount of rework for defective welds. To reduce this rework workload, the technical solution of this invention provides a welding method for reducing defects in the end welds of FAB submerged arc welding, such as... Figure 4 As shown, the method includes the following steps:

[0036] Step 1: Before welding, bevel the groove and clean it.

[0037] Step 2: Weld both ends of the weld using restraint welding;

[0038] Step 3: Lay filler metal inside the bevel;

[0039] Step 4: Lay the submerged arc welding trolley track parallel to the center line of the bevel and begin welding;

[0040] Step 5: After welding is completed, X-ray or ultrasonic testing is performed on the weld according to the requirements, and defects are removed.

[0041] like Figure 5 As shown, in one embodiment of the present invention, the bevel is cleaned and assembled before welding according to the process requirements. Impurities are removed by grinding within a 30mm range of the bevel. When the plate thickness is 6mm-7mm, an I-type bevel is opened, and when the plate thickness is 7mm or more, a V-type bevel is opened.

[0042] In one embodiment of the present invention, in step 2, when using restraint welding, arc-starting and arc-extinguishing plates need to be installed at both ends of the weld. The weld is fixed by welding from the inside of the bevel towards the arc-starting or arc-extinguishing plate end; this weld is called a restraint weld, which can prevent cracks from forming at the end of the formal weld. The specifications and dimensions of the restraint weld are differentiated according to the plate thickness. For restraint welds less than 7mm, the requirements are as follows: Figures 6 to 7 As shown, when the plate thickness is less than 7mm and the gap is in the range of 0mm-2mm: a restraint weld is made from the inside of the groove to the end of the arc-starting plate or the end of the arc-extinguishing plate, with a length of 150mm and a weld thickness of about 1mm-2mm; when the gap is greater than 2mm, a restraint weld is made with a length of 150mm and a weld thickness equal to the thickness of the base plate.

[0043] For bevel restraint welding of plates with a thickness of 7mm or more, the requirements are as follows: Figures 8 to 9 As shown, the restraint weld is a multi-layer, multi-pass weld. The arc-starting end requires two restraint welds, each 150mm long, with the second weld located 50mm from the arc-starting plate. The overall weld thickness is approximately 7mm-8mm. The arc-extinguishing end requires a restraint weld of 350mm in length, with the overall weld thickness being approximately 0mm-2mm less than the base material thickness. Each weld pass is staggered by 20mm from the previous one.

[0044] like Figure 10 As shown, in one embodiment of the present invention, in step 3, filler metal is laid in the bevel. The height of the filler metal at the start and end positions of the weld is set to 5 mm, and the height gradually increases from the end to the middle. At a distance of 200 mm from the end, the height of the filler metal increases to the standard height. The laying process needs to ensure that the filler metal transition is smooth.

[0045] like Figures 11 to 12 As shown, in one embodiment of the present invention, in step 4, the submerged arc welding trolley track is laid to a position parallel to the center line of the bevel and at a suitable distance. The straightness of the welding wire is checked. The welding wire should be perpendicular to the surface of the workpiece to be welded. Then, the welding wire is aligned so that the tip of the welding wire and the guide infrared tracking point are aligned with the center of the bevel before welding begins.

[0046] In this embodiment, the welding parameters and wire extension vary with the filler metal height. The starting and ending currents are set to 650A-750A. As the metal height increases during welding, the welding current increases accordingly. When the filler metal height remains constant, the welding current remains stable. The relationship between plate thickness, welding parameters, and filler metal height is shown in Table 1. During welding, the wire length is always maintained between 30-45mm.

[0047] Table 1 Welding process parameters

[0048]

[0049] In one embodiment of the present invention, in step 5, after welding is completed, X-ray or ultrasonic testing is performed on the weld according to the requirements. Ultrasonic testing is performed on the arc-stopping points, the beginning and end of the weld, and the cross-shaped or T-shaped joints, with a testing length of not less than 300 mm. If welding defects exist at the beginning or end, carbon gouging is performed on the back of the weld to remove the defects to a depth of 6-7 mm. After cleaning, repair welding is performed.

[0050] This invention helps reduce the material and time costs of rework and repair by reducing welding defects, thereby improving construction efficiency, reducing overall repair time, and saving material costs such as welding wire, carbon rods, and gas generated during repairs.

[0051] 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 reducing weld defects at the weld ends of FAB submerged arc welding, characterized in that: The method includes the following steps: Step 1: Before welding, beveling and cleaning the bevel. When the thickness of the plate to be welded is 6mm-7mm, open the I-type bevel. When the thickness of the plate to be welded is 7mm or more, open the V-type bevel. Step 2: Weld the two ends of the weld using restraint welding. The specific method for restraint welding the two ends of the weld is as follows: Install arc-starting and arc-extinguishing plates at both ends of the weld, and weld the weld from the inside of the bevel towards the arc-starting or arc-extinguishing plate end to fix it; the specifications and dimensions of the restraint weld are selected according to the thickness of the plate to be welded. When the plate thickness is less than 7mm and the gap is in the range of 0mm-2mm: weld one restraint weld from the inside of the groove to the end of the arc-starting plate or the end of the arc-extinguishing plate, with a length of 150mm and a weld thickness of 1mm-2mm; when the gap is greater than 2mm, weld one restraint weld with a length of 150mm and a weld thickness equal to the thickness of the base plate. When performing bevel restraint welding on plates with a thickness of 7 mm or more, the restraint weld is a multi-layer, multi-pass weld. The restraint weld at the arc-starting end consists of two welds with a length of 150 mm. The second weld is located within 50 mm of the arc-starting plate, and the overall weld thickness is 7 mm to 8 mm. The restraint weld at the arc-extinguishing end is 350 mm long, and the overall weld thickness is 0 mm to 2 mm less than the thickness of the base plate. Each weld is staggered from the previous weld by 20 mm. Step 3: Lay filler metal inside the bevel; In step 3, the filler metal height at the start and end positions of the weld is 5mm, and the height gradually increases from the end to the middle. At a distance of 200mm from the end, the filler metal height increases to the standard height. The filler metal transition needs to be smooth during the laying process. The starting current and ending current are set to 650A-750A. As the metal height increases during the welding process, the welding current increases accordingly. Step 4: Lay the submerged arc welding trolley track parallel to the center line of the bevel and begin welding; Step 5: After welding is completed, X-ray or ultrasonic testing is performed on the weld according to the requirements, and defects are removed.

2. The welding method for reducing weld defects at the end of FAB submerged arc welding as described in claim 1, characterized in that: In step 4, the welding wire is perpendicular to the surface of the workpiece to be welded, and then the welding wire is aligned so that the tip of the welding wire and the guide infrared tracking point are aligned with the center of the bevel before welding begins.

3. The welding method for reducing weld defects at the end of FAB submerged arc welding as described in claim 2, characterized in that: In step 4, the welding parameters and wire extension vary with the height of the filler metal. As the metal height increases during the welding process, the welding current increases accordingly.

4. The welding method for reducing weld defects at the end of FAB submerged arc welding as described in claim 3, characterized in that: In step 5, X-ray or ultrasonic testing is performed according to the weld requirements. Ultrasonic testing is performed on the arc-stopping position, the beginning and end, and the cross or T-joint positions during the welding process. If there are welding defects at the beginning and end, carbon gouging is performed on the back of the weld to remove the defects. After grinding clean, repair welding is performed.

Images