Small-aperture large-depth plug welding method for repairing rail transit bogie

Abstract

The invention relates to the technical field of plug welding repair, in particular to a small-aperture large-depth plug welding method for repairing a rail transit bogie, which is suitable for a welding repair scene with the aperture not greater than 16mm and the depth-diameter ratio not less than 3. The method comprises the following specific steps that an exhaust hole penetrating through the bottom is formed in a plug welding hole, and inert gas is introduced to exhaust air in the hole; performing inverted-cone-shaped flaring processing on an inlet in the upper part of the plug welding hole; after the plug welding holes are uniformly preheated, a bottom-to-top layered stepped welding mode is adopted, and time is set for pause after welding of each layer is completed; welding is divided into a bottoming layer, a filling layer and a covering layer, and different welding parameters and track control modes are adopted respectively. According to the method, exhaust is assisted through the exhaust holes, operability is improved through the inverted conical openings, the molten pool is stabilized through layered heat control, welding quality and reliability are effectively improved, and the method is suitable for high-strength welding repair of key parts such as rail transit bogies.

Description

Technical Field

[0001] This invention relates to the field of plug welding repair technology, and more specifically to a small-diameter, deep-hole plug welding method for repairing railway bogies. Background Technology

[0002] With the rapid development of the rail transit industry, the bogie, as a key load-bearing and running system of a vehicle, has a crucial impact on train operation safety due to its structural integrity. During long-term service, the bogie frame, bolster, and other components are prone to fatigue cracks, threaded hole damage, and corrosion defects in areas of concentrated stress. To extend service life and reduce replacement costs, the industry commonly uses welding repair methods for local reinforcement or hole sealing. This is especially true for small-diameter holes (Φ10mm~Φ12mm) and high aspect ratio holes (depth exceeding 50mm), where plug welding is used for metallurgical repair, gradually becoming an important process in rail transit vehicle maintenance.

[0003] In traditional deep hole plug welding, the industry typically employs methods such as pre-setting venting holes, layered welding, and controlling heat input to improve weld density and structural strength. However, in practical applications, these measures often face numerous limitations: venting channels are easily blocked by weld slag, fusion is insufficient during welding, spatter adheres to the hole wall and is difficult to clean, and uneven heat distribution during welding leads to uncontrolled deformation, which can even result in the scrapping of the structure in severe cases.

[0004] In view of the above, in order to overcome the above technical problems, the present invention designs a small-diameter, deep plug welding method for the repair of rail transit bogies, thus solving the above technical problems. Summary of the Invention

[0005] The technical objective of this invention is to provide a small-diameter, deep plug welding method suitable for the repair of railway bogies, so as to improve welding quality and reliability and solve the problems of poor venting, poor fusion and thermal deformation.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: The present invention provides a method for small-diameter, deep plug welding for repairing railway bogies, wherein the small-diameter, deep method refers to a hole diameter ≤ 16 mm and a depth-to-diameter ratio ≥ 3; specifically, it includes the following steps: The biggest challenge in deep hole welding is the inability to timely expel the gas generated during the welding process, leading to porosity, incomplete fusion, and even spatter. To address this, a forced escape channel for the gas generated during welding is needed to prevent its accumulation and the formation of high-pressure bubbles within the hole. Therefore, the first step involves creating a bottom-through vent hole inside the plug weld hole. Inert gas is introduced into the plug weld hole to expel the air inside. The diameter of this vent hole is typically much smaller than the plug weld hole itself, ideally 1mm-2mm. This significantly reduces the gas pressure inside the hole, improves the wetting and spreading ability of the molten metal, and reduces the risk of porosity and incomplete fusion. It also helps to remove any volatile gases or impurities that may be present at the bottom of the hole.

[0007] Furthermore, the narrow entrance of a small-diameter hole makes it difficult to accurately deliver the welding torch or wire to the bottom of the hole, resulting in limited operating space. Arc concentration and spatter buildup at the entrance can easily occur. The surface tension of the molten pool also hinders its spread to the narrow sidewalls. To improve accessibility, the entrance is widened, allowing the welding torch / wire to penetrate the hole more smoothly, especially near the bottom, thus improving operational accuracy. The conical surface also helps guide the arc and molten pool, ensuring a more stable arc action on the hole wall and filler metal, improving sidewall fusion. Therefore, step two involves creating an inverted conical flare at the upper entrance end of the plug weld hole, forming a trumpet-shaped flared section.

[0008] The flared structure alters the stress state of the molten pool metal, facilitating its downward and sidewall spread, thus improving forming and fusion. It also reduces inlet splashing and clogging: providing more space to accommodate potential splashes and lowering the risk of inlet blockage.

[0009] Single-pass continuous welding of deep holes can lead to excessive heat accumulation, causing severe workpiece deformation or even burn-through. Excessively large and deep weld pools are difficult to control, easily resulting in poor fusion, weld collapse, and severe spatter. The continuously increasing venting pressure, even with venting holes, can exceed the venting capacity due to excessively rapid deposition.

[0010] Step 3: After uniformly preheating the plug weld hole, insert the welding torch into the bottom of the plug weld hole to start welding; the welding method is layer welding, and pause for a set time after each layer is completed; control the heat input and heat accumulation, and the pause time allows heat to diffuse to the base material, significantly reducing the interlayer temperature, avoiding overall overheating and deformation, and reducing the heat-affected zone.

[0011] Welding resumes, pressing the new weld layer onto the highest point of the old weld layer, and the weld holes are filled in a stepped manner.

[0012] Based on the above, when the welding torch is inserted into the bottom of the plug weld hole to start welding, the plug weld hole is divided into a bottom layer, a filler layer and a cover layer for welding from bottom to top; the bottom layer and the filler layer start from the center of the bottom of the plug weld hole and are welded in a clockwise outward circular motion along the side wall, ending in the middle of the plug weld hole; the cover layer starts from the center of the bottom of the plug weld hole and is welded in a clockwise spiral outward, ending in the plug weld hole and leading to the base material.

[0013] Preferably, the specific parameters for the bottom layer are set as follows: current 150-180A, voltage 18-22V, welding speed 3-4mm / s, and calculated heat input 0.54-0.96KJ / mm.

[0014] Preferably, the specific parameters of the filler layer and the cover layer are set as follows: current 260-280A, voltage 28-30V, welding speed 4-5mm / s, and calculated heat input 1.16-1.68KJ / mm.

[0015] Based on the above, while meeting the requirements of layered welding and thermal control, a relatively high welding current is used in conjunction with a relatively slow welding speed. Under controllable heat input, a high current can increase the amount of weld deposited per pass, thereby improving efficiency.

[0016] Preferably, the number of layers in the layered welding is not less than 5, and the interlayer temperature is controlled below 180 degrees Celsius.

[0017] Preferably, during layered welding, a 2-10 second pause is performed after each layer is completed. This short pause helps stabilize the welding torch and reduces spatter. The entire plugging process is divided into multiple layers / passes, with a brief 2-10 second pause after each layer / pass is completed to allow time for the bottom vent to effectively expel the gas generated in that layer.

[0018] Furthermore, during the pause, the welding torch is held above the orifice or the workpiece is removed until the weld pool solidifies.

[0019] Preferably, the flaring angle is 5 to 10 degrees.

[0020] Preferably, the number of exhaust holes is 1-2, and the inner diameter is 1mm-2mm.

[0021] Preferably, the preheating temperature is 120 degrees Celsius to 150 degrees Celsius.

[0022] The beneficial effects of this invention are as follows: 1. This invention improves the venting conditions within the plug weld hole by setting a bottom-through vent in a small-diameter, deep plug weld hole and introducing inert gas during welding, combined with an inverted conical flaring structure, a bottom-up stepped layered welding method, and short-pause welding between layers. This enhances the stability of the molten pool and the accessibility of the sidewalls. Based on the above, it can significantly reduce the occurrence of defects such as porosity, lack of fusion, and spatter accumulation during deep hole welding, ensuring the metallurgical quality and overall forming quality of the weld, thereby meeting the high-strength, high-density, and high-reliability repair requirements of key components of rail transit bogies.

[0023] 2. This invention subdivides the welding process into a base layer, a filler layer, and a capping layer, and employs different welding parameters and trajectory control methods for each. Specifically, the base layer is welded clockwise and obliquely around the hole wall, and the capping layer is welded using a spiral unfolding method. This results in a more uniform distribution of arc energy and more precise control of the molten pool, avoiding phenomena such as collapse, shrinkage, or cracks in the middle of the weld caused by heat concentration or trajectory deviation. At the same time, it enhances the stability of the fusion interface and effectively ensures the mechanical properties and fatigue life of the welded joint.

[0024] 3. This invention also controls the interlayer temperature of layered welding below 180°C and sets a pause time of 2-10 seconds after each layer is welded, allowing the molten pool sufficient time to solidify and dissipate heat, thus avoiding excessive heat accumulation in the hole. Simultaneously, during the pause, removing or leaving the welding torch stationary suppresses thermal interference, which facilitates the removal of impurities and slag. This effectively reduces problems such as hole thermal deformation, coarse grains in the heat-affected zone, or embrittlement caused by continuous heat input, further improving the process stability and quality consistency of deep hole welding. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] The above and other aspects of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 This is a schematic diagram of the cross-sectional structure of the plug weld hole of the present invention; Figure 2 This is a schematic diagram of the method for initiating an arc inside a plug welding hole according to the present invention; Figure 3 This is a schematic diagram of the welding method for the underlayer and filler layers of the present invention; Figure 4 This is a schematic diagram of the layered welding process for the bottom layer of this invention; Figure 5 This is a schematic diagram of the overall welding of the underlayer, filler layer and cover layer of the present invention.

[0027] In the diagram: 1. Plug hole; 2. Vent hole; 3. Flared section; 4. Undercoat layer; 5. Filler layer; 6. Topcoat layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] The small-diameter, deep plug welding method for repairing rail transit bogies provided in this embodiment ensures sufficient penetration depth and sidewall fusion, especially guaranteeing the fusion quality at the bottom of the hole. While ensuring high metallurgical quality, high strength, and high fatigue performance of the welded joint, it precisely controls welding deformation, ensuring that the repaired bogie meets strict dimensional tolerances and safe operation requirements. Simultaneously, it improves process stability and operability, reducing excessive reliance on the individual skills of welders.

[0036] like Figures 1 to 5 As shown, this embodiment provides a small-diameter, deep-hole plug welding method for repairing rail transit bogies, applicable to welding repair scenarios of holes with a diameter less than or equal to 16mm and a depth-to-diameter ratio greater than or equal to 3. This method is particularly suitable for situations where hole sealing is required in critical components of rail transit bogies due to fatigue, corrosion, or thread failure.

[0037] The specific implementation steps provided in this embodiment are as follows: One or two vent holes 2 penetrating the base material are provided at the bottom of the plug weld hole 1 to be repaired. The inner diameter of the vent holes 2 is 1-2 mm. These vent holes provide a forced venting channel to reduce porosity or fusion defects caused by gas accumulation in the hole. Before welding, argon gas is continuously introduced into the plug weld hole 1 to dispel residual air and volatile gases in the hole, further reducing the risk of porosity formation.

[0038] The upper opening of the plug weld hole 1 is flared into an inverted conical shape to form a trumpet-shaped conical flared section 3, with the cone angle controlled between 5° and 10°. This flaring improves the accessibility of the welding torch wire feed, enhancing operability and observation. Furthermore, it helps guide the distribution of arc energy and the spread of molten metal in the weld pool, improving the fusion quality at the hole opening and providing a buffer space for spatter, preventing hole blockage.

[0039] Before welding, the base material area within a range of about 75mm centered on the plug weld hole 1 is uniformly preheated, and the temperature is controlled between 120℃ and 150℃ to avoid water vapor condensation, improve the stability of the initial molten pool, and reduce the adverse effects of thermal gradient on welding deformation.

[0040] The plug weld hole 1 is divided into multiple welding layers: a root pass 4, a filler pass 5, and a cap pass 6. The root pass 4 is welded with a current of 150A–180A, a voltage of 18–22V, a welding speed of 3–4 mm / s, and a heat input of 0.54–0.96 KJ / mm, ensuring complete penetration without burning through the vent hole 2. During the root pass 4 welding, the arc starts at the center of the hole bottom and is welded in a clockwise circular motion along the hole wall, ending at the center of the hole.

[0041] The current for filler layer 5 and capping layer 6 is 260A–280A, the voltage is 28–30V, the welding speed is 4–5mm / s, and the unit heat input is 1.16–1.68KJ / mm. Filler layer 5 continues to be welded using a diagonal circular welding method along the sidewall, moving upwards layer by layer. Capping layer 6 uses a spiral trajectory to gradually unfold from the center of the hole bottom to the outside of the hole opening, finally striking the arc at the surface of the base material and ending the arc to prevent heat concentration at the center of the weld from causing shrinkage cavities.

[0042] Based on the above, it is important to note that after completing each weld pass, pause for 2–10 seconds to allow the molten pool of the current pass to cool naturally and prevent heat accumulation. During the pause, the welding torch can be held above the orifice or temporarily removed, and the next pass can be welded only after the molten pool has initially solidified. This pause step facilitates gas escape, interpass temperature control, and spatter removal, significantly improving weld formation quality and overall stability.

[0043] Throughout the welding process, there are no fewer than five layers to ensure that each weld bead is fully fused and that there is sufficient space for gas to escape. The interpass temperature is monitored and controlled in real time to keep it below 180℃ to prevent thermal deformation, coarsening of the microstructure, or stress concentration caused by welding heat accumulation.

[0044] Throughout the entire process, Ar or Ar-CO2 mixed gas is used to protect the welding area. The gas flow rate is set 10%–20% higher than that of conventional welding to create a more stable protective atmosphere, prevent oxidation, and enhance arc control and forming effect.

[0045] After welding, the weld joint is subjected to non-destructive testing and geometric grinding to ensure that there are no shrinkage cavities, porosity, or cracks on the weld surface, the internal porosity is less than 1%, the sidewall fusion rate is not less than 98%, and the thermal deformation is controlled within 0.5 mm / m.

[0046] This embodiment effectively solves the problems of poor venting, unstable welding, insufficient fusion, spatter accumulation, and difficult-to-control thermal deformation during plug welding in scenarios with small diameter and large depth. It improves the metallurgical density of the weld, the controllability of operation, and the reliability of the weld joint, meeting the high-standard repair application requirements of rail transit.

[0047] Although one or more exemplary embodiments of this disclosure have been described with reference to the accompanying drawings, those skilled in the art will understand that various changes in form and detail may be made therein without departing from the spirit and scope of this disclosure as defined by the appended claims.

[0048] Although the present disclosure has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to the embodiments of the present disclosure, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of the present disclosure are all within the scope of protection claimed by the present disclosure.

[0049] The foregoing description is merely illustrative of this disclosure, and modifications may be made to the invention in light of the above detailed description. The terminology used in the appended claims should not be construed as limiting the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention will be fully defined by the appended claims, which will be interpreted according to established principles of claim interpretation.

Claims

1. A method for small-diameter, deep plug welding for repairing railway bogies, wherein the small-diameter, deep method refers to a hole diameter ≤ 16 mm and a depth-to-diameter ratio ≥ 3; characterized in that, Includes the following steps: An exhaust hole (2) is opened inside the plug weld hole (1) and extends through the bottom. Inert gas is introduced into the plug weld hole (1) to expel the air inside the plug weld hole (1). An inverted conical flare is made at the upper entrance end of the plug weld hole (1) to form a trumpet-shaped flare section (3). After uniformly preheating the plug welding hole (1), insert the welding torch into the bottom of the plug welding hole (1) to start layer welding. Pause for a set time after each layer of welding is completed. Welding resumes and the new weld layer is pressed onto the highest point of the old weld layer. Welding is then performed in a stepped manner to fill the plug weld hole (1).

2. The method for small-diameter, deep plug welding for repairing rail transit bogies according to claim 1, characterized in that: During welding, the plug weld hole (1) is divided into a bottom layer (4), a filler layer (5) and a cover layer (6) from bottom to top for welding. The bottom layer (4) and the filler layer (5) start from the center of the bottom of the plug weld hole (1) and are welded in a clockwise outward circular motion along the side wall, ending in the middle of the plug weld hole (1). The cover layer (6) starts from the center of the bottom of the plug weld hole (1) and is welded in a clockwise spiral motion outward, ending in the plug weld hole (1) and extending to the base material.

3. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 2, characterized in that: The specific parameters for the bottom layer (4) are set as follows: current 150-180A, voltage 18-22V, welding speed 3-4mm / s, calculated heat input 0.54-0.96KJ / mm.

4. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 2, characterized in that: The specific parameters of the filler layer (5) and the cover layer (6) are set as follows: current 260-280A, voltage 28-30V, welding speed 4-5mm / s, calculated heat input 1.16-1.68KJ / mm.

5. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 1, characterized in that: The number of layers in the layered welding is not less than 5, and the interlayer temperature is controlled below 180 degrees Celsius.

6. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 1, characterized in that: In layered welding, pause for 2-10 seconds after each layer is completed.

7. The method for small-diameter, deep-hole plug welding for repairing railway bogies according to claim 6, characterized in that: When pausing, keep the welding torch above the orifice or remove the workpiece until the weld pool solidifies.

8. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 1, characterized in that: The flaring angle is 5 to 10 degrees.

9. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 1, characterized in that: The number of exhaust holes (2) is 1-2, and the inner diameter is 1mm-2mm.

10. The method for small-diameter, deep plug welding for repairing railway bogies according to claim 1, characterized in that: The preheating temperature is 120 to 150 degrees Celsius.

Images