Welding method of Q355B and 42CrMo ultra-high strength heavy load eccentric shaft assembly

Abstract

The application discloses a welding method of a Q355B and 42CrMo super-high-strength heavy-load eccentric shaft assembly, and the welding method is as follows: the eccentric shaft assembly is respectively penetrated into corresponding welding displacement tooling at two ends, and the girth weld of the eccentric shaft assembly is adjusted to be located at a vertical position; before welding, electromagnetic induction cables are used to uniformly preheat predetermined areas on both sides of the weld area of the eccentric shaft assembly; arc breaking is used for backing, filling and continuous welding of a surface, the interlayer temperature is ensured to be not lower than a preheating temperature, and the welding process is limited to eccentric shaft assembly welding deformation through the weight of the workpiece and the rigidity constraint of tooling; immediately after welding, the workpiece is wrapped with heat preservation cotton, and the predetermined areas on both sides of the weld are spirally wound with electromagnetic induction cables for post-heating hydrogen removal treatment; after the welding heat preservation is finished, a predetermined time is left for magnetic powder detection. The welding method has the advantages of low welding process equipment cost, simple and convenient operation and stable welding quality, and can realize efficient and high-quality welding of the girth weld of the heterogeneous super-high-strength heavy-load eccentric shaft assembly at a vertical welding position.

Description

Technical Field

[0001] This invention belongs to the field of welding method technology and is particularly applicable to the welding production of dissimilar ultra-high strength heavy-duty eccentric shaft assemblies. Background Technology

[0002] 42CrMo, a commonly used ultra-high strength steel in engineering machinery, is characterized by high specific strength and hardness, and high hardenability. In particular, after quenching and tempering followed by surface hardening, it has a high fatigue limit and resistance to repeated impacts, making it suitable for manufacturing important parts with large cross-sectional dimensions and high mechanical performance requirements. However, its carbon equivalent is as high as 0.89%, resulting in poor weldability. After welding, the heat-affected zone is prone to producing a brittle and hard martensite structure with low plasticity, which can lead to cold cracking. Therefore, welding of 42CrMo materials requires strict adherence to preheating and heat preservation procedures to slow down the cooling gradient after welding and reduce the steel's tendency to become brittle and hard.

[0003] Taking a large-scale open-pit mine drilling equipment - a roller cone drilling rig - as an example, its rear axle assembly consists of a 42CrMo large round shaft and a Q355B support base, forming a heavy-duty eccentric structure (weighing more than 2 tons and longer than 4.8m). During the assembly of the whole machine, it is connected to the crawler beams on both sides through precision assembly, jointly supporting the box-shaped platform above and the weight of the whole machine. It has the characteristics of high requirements for coaxiality after welding, high requirements for static load impact, and high requirements for fatigue life.

[0004] The welding and manufacturing process of dissimilar ultra-high strength heavy-duty eccentric shaft assemblies composed of Q355B and 42CrMo presents four main technical challenges: First, the large cross-sectional dimensions of the large circular shaft make it difficult to ensure uniform preheating temperature. While localized heating using traditional flame methods can achieve the required preheating temperature on the shaft surface, the internal temperature remains low, especially below freezing, significantly increasing the likelihood of cold cracking after welding, leading to time-consuming and labor-intensive rework. Using a furnace for overall preheating ensures uniform heating temperature across the shaft cross-section, but requires a large furnace space (shaft length exceeds 4.8m), resulting in high equipment costs and inconvenient hoisting and transport of the heated heavy-duty shaft. Second, the eccentric shaft assembly is heavy (over 2 tons), making continuous rotating welding difficult. Especially for the circumferential weld, all-position welding not only demands high worker skill levels but also makes ensuring weld quality challenging. Using a positioner or roller frame for rotation is limited by the eccentric structure, requiring high compatibility with existing equipment and incurring high initial costs, making it unsuitable for discrete production models with multiple varieties and small batches. Third, the rear axle assembly has an open structure, resulting in significant welding deformation under high heat input and multi-layer continuous welding conditions, necessitating effective control of welding deformation during the welding process. Furthermore, the heavy-duty eccentric structure generates a large eccentric bending moment during rotation, limiting the possibility of leaving process allowances for the round shaft and performing post-weld machining to ensure coaxiality. Fourth, if conventional continuous arc welding is used for the climbing weld of the ultra-high strength heavy-duty eccentric shaft assembly's circumferential weld, high-current welding leads to excessively high molten pool temperature and deep weld penetration, causing molten iron to easily flow downwards under gravity, making weld formation difficult to control. Low-current welding results in lower overall heat input, making it prone to cold cracking along the hardened zone of the heat-affected zone, compromising weld quality.

[0005] Therefore, there is an urgent need for a welding method that is low in cost, simple and convenient to operate, and provides stable welding quality to reduce the labor intensity of workers. This method should achieve efficient and high-quality welding of ultra-high strength heavy-duty eccentric shaft components while simultaneously ensuring uniform preheating temperature, rapid workpiece flipping, effective control of welding deformation, and high reliability of post-weld quality. Summary of the Invention

[0006] This invention provides a welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly to overcome the shortcomings of the prior art.

[0007] This invention is implemented according to the following technical solution:

[0008] A welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly includes the following steps:

[0009] a) Workpiece flipping: Insert the corresponding welding positioning fixtures into both ends of the eccentric shaft assembly to adjust the circumferential weld of the eccentric shaft assembly to be in the vertical position;

[0010] b) Preheating: Before welding, use an electromagnetic induction cable to uniformly preheat the predetermined areas on both sides of the weld zone of the eccentric shaft assembly.

[0011] c) Eccentric shaft welding: The welding process adopts interrupted arc for the root pass and fill pass, and continuous welding for the cover pass, ensuring that the interpass temperature is not lower than the preheating temperature. During the welding process, the welding deformation of the eccentric shaft assembly is limited by the workpiece's own weight and the rigidity of the tooling.

[0012] d) Post-heating hydrogen removal treatment: Immediately after welding, wrap the workpiece with heat insulation cotton and spirally wrap electromagnetic induction cable around the predetermined area on both sides of the weld to perform post-heating hydrogen removal treatment.

[0013] e) Magnetic particle inspection: After the welding insulation is completed, magnetic particle inspection is performed after a predetermined time.

[0014] In some embodiments, in step b, a medium-to-high frequency electromagnetic induction cable is used to uniformly preheat a 150mm area on both sides of the weld zone of the eccentric shaft assembly to 250-300°C before welding, with a heating rate of 150°C / h and a preheating holding time of 2h.

[0015] In some embodiments, in step d, immediately after welding, a heat insulation layer of about 40 mm thick is wrapped around the workpiece, and high-frequency electromagnetic induction cable is spirally wound 150 mm on both sides of the weld for post-heating hydrogen removal treatment. The post-heating temperature is 200-300℃, and the post-heating insulation time is 6 hours.

[0016] In some embodiments, the length of the spiral-wound induction heating cable needs to be greater than 20m, otherwise it cannot output full power. The excess induction cable needs to be spirally coiled in a non-metallic area.

[0017] In some embodiments, in step c, the current for the intermittent arc root pass welding is 250-300A, the weld thickness is 4-5mm, and the welding wire moves in a straight line; the current for the intermittent arc fill pass welding is 250-300A, the weld thickness is 4-5mm, and the welding wire oscillates in a small crescent shape; the current for the continuous cover pass welding is 180-200A, and a sawtooth oscillation is used. The welding process always maintains a short arc, moves quickly in the center of the weld bead, but pauses slightly on both sides of the bevel to melt 1-2mm of the edges on both sides of the bevel, and fills the arc crater with backfire when the arc is closed.

[0018] In some embodiments, step c uses gas metal arc welding, the current polarity is DC reverse polarity, the welding position is vertical welding, the welding wire is φ1.2mm ER50-6 welding wire, the shielding gas is 80%Ar+20%CO2, and the gas flow rate is 15~20L / min.

[0019] In some embodiments, in step d, after the welding heat preservation is completed, the sample is placed for 48 hours for magnetic particle testing.

[0020] In some embodiments, in step a, slings are used to bind both ends of the round shaft respectively, so that one end of the round shaft is slowly inserted into the welding positioning fixture, and then the other end of the round shaft is moved to bind the other end and slowly inserted into the welding positioning fixture on the other side. After both welding positioning fixtures on both sides have reached the designated position, they are slowly placed on the work platform; the eccentric shaft assembly is rotated using a crane to allow it to rotate freely in the bushing of the positioning fixture, and is fixed to the work platform with tie rods to place the circumferential weld in the designated welding position.

[0021] Beneficial effects of this invention:

[0022] Practice has shown that the welding method for ultra-high strength heavy-duty eccentric shaft components of this invention requires minimal initial equipment investment, allows for simple and convenient workpiece flipping, ensures uniform and consistent welding preheating temperature, controls welding deformation, does not require high welding skill levels from workers, and provides stable welding quality. This improves production efficiency and first-pass yield, reduces manufacturing costs, and effectively solves the problem of welding cracks and unstable welding quality in dissimilar ultra-high strength heavy-duty eccentric shaft components under simple conditions. Attached Figure Description

[0023] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0024] In the attached diagram:

[0025] Figure 1 This is a schematic diagram of the flipping of the ultra-high strength heavy-duty eccentric shaft assembly of the present invention;

[0026] Figure 2 This is a left view of the ultra-high strength heavy-duty eccentric shaft assembly of the present invention;

[0027] Figure 3 This is a schematic diagram of the welding of the ultra-high strength heavy-duty eccentric shaft assembly of the present invention (① root pass welding, ② filler weld, ③ cover weld).

[0028] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Implementation

[0029] 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. In the drawings, the same or similar symbols represent the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] like Figure 1 As shown, a welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly includes the following steps:

[0031] a) Workpiece flipping: Insert simple welding positioning fixtures into both ends of the eccentric shaft assembly to adjust the circumferential weld of the eccentric shaft assembly to be in the vertical position;

[0032] b) Preheating: Before welding, use a medium- and high-frequency electromagnetic induction cable to uniformly preheat the 150mm area on both sides of the weld zone of the eccentric shaft assembly to 250-300℃, with a heating rate of 150℃ / h and a preheating holding time of 2h.

[0033] c) Eccentric shaft welding: The welding process adopts interrupted arc for the root pass and fill pass, and continuous welding for the cover pass, ensuring that the interpass temperature is not lower than the preheating temperature. During the welding process, the welding deformation of the eccentric shaft assembly is limited by the workpiece's own weight and the rigidity of the tooling.

[0034] d) Post-heating hydrogen removal treatment: Immediately after welding, wrap the workpiece with a thermal insulation layer of about 40mm thickness, and spirally wrap medium and high frequency electromagnetic induction cable 150mm on both sides of the weld for post-heating hydrogen removal treatment. The post-heating temperature is 200-300℃ and the post-heating insulation time is 6h.

[0035] e) Magnetic particle inspection: After the welding insulation is completed, magnetic particle inspection is performed after 48 hours.

[0036] The specific steps of the above welding method are given below:

[0037] The first step is to rotate the workpiece to the designated welding position: Use slings to secure both ends of the round shaft, slowly inserting one end of the shaft into the welding positioning fixture. Then, move the shaft to the other end and slowly insert it into the welding positioning fixture on the other side. Once both welding positioning fixtures are in the designated positions, gently place the workpiece on the work platform. Use a crane to assist in rotating the eccentric shaft assembly, allowing it to rotate freely within the positioning fixture's bushing, until it is rotated to the designated position. Figure 1The circumferential weld is positioned as shown and fixed to the work platform with tie rods or other auxiliary materials, so that the circumferential weld is in the designated welding position.

[0038] The second step is preheating the eccentric shaft assembly before welding: Medium- and high-frequency induction cables are wrapped around both sides of the weld seam within a 150mm area for preheating the circumferential weld. The heating rate is 150℃ / h. After reaching 250-300℃, the temperature is held for 2 hours to ensure uniform heating of the large circular shaft cross-section. Figure 2 As shown.

[0039] The third step is the welding of the eccentric shaft assembly: The eccentric shaft assembly is welded using DC reverse polarity gas metal arc welding. 1.2mm ER50-6 welding wire is used, and the shielding gas is an argon-rich mixture of 80% Ar + 20% CO2. For the intermittent arc root pass, the current is 250-300A, the weld thickness is 4-5mm, and the welding wire moves in a straight line; for the intermittent arc fill pass, the current is 250-300A, the weld thickness is 4-5mm, and the welding wire moves in a small crescent shape; for the continuous cap pass, the current is 180-200A, using a sawtooth oscillation. Throughout the welding process, a short arc is maintained, moving quickly in the center of the weld bead, but pausing slightly on both sides of the bevel to melt 1-2mm of the bevel edges. When finishing the arc, the wire is reheated to fill the crater. Figure 3 As shown, it should be noted that the interval between arc interruption and arc initiation is short, not exceeding 1 second, to avoid slag inclusions in the weld. Adjacent weld waves overlap by 30% to 40%, forming a dense scaly pattern to ensure a beautiful weld formation.

[0040] The fourth step is post-heating hydrogen removal treatment: Immediately after welding, wrap the workpiece with a thermal insulation layer of about 40mm thickness, and then wrap the circumferential weld area with a medium-high frequency induction cable, maintain the post-heating temperature at 200-300℃, and keep it at this temperature for 6 hours to accelerate the escape of hydrogen from the weld and heat-affected zone, and further reduce the probability of cold cracking. The length of the spirally wound induction heating cable must be greater than 20m, otherwise it cannot output full power. The excess induction cable needs to be spirally coiled in the non-metallic area.

[0041] Step 5, magnetic particle inspection: After the welding and heat preservation are completed, the surface is placed horizontally for 48 hours and then subjected to magnetic particle inspection.

[0042] As can be seen from the above, practice has shown that the welding method for ultra-high strength heavy-duty eccentric shaft components of the present invention requires a small initial investment in equipment, makes workpiece flipping simple and convenient, ensures uniform and consistent welding preheating temperature, controls welding deformation, does not require high welding skill levels from workers, and provides stable welding quality. This improves production efficiency and first-pass yield, reduces manufacturing costs, and effectively solves the problem of welding cracks and unstable welding quality that easily occur in dissimilar ultra-high strength heavy-duty eccentric shaft components under simple conditions.

[0043] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0044] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features found in other embodiments but not others, combinations of features from different embodiments are also within the scope of protection of this invention and form different embodiments. For example, in the embodiments described above, those skilled in the art can use them in combination based on known technical solutions and the technical problems to be solved by this application.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly, characterized in that, Includes the following steps: a) Workpiece flipping: Insert the corresponding welding positioning fixtures into both ends of the eccentric shaft assembly to adjust the circumferential weld of the eccentric shaft assembly to be in the vertical position; b) Preheating: Before welding, use an electromagnetic induction cable to uniformly preheat the predetermined areas on both sides of the weld zone of the eccentric shaft assembly. c) Eccentric shaft welding: The welding process adopts interrupted arc for the root pass and fill pass, and continuous welding for the cover pass, ensuring that the interpass temperature is not lower than the preheating temperature. During the welding process, the welding deformation of the eccentric shaft assembly is limited by the workpiece's own weight and the rigidity of the tooling. d) Post-heating hydrogen removal treatment: Immediately after welding, wrap the workpiece with heat insulation cotton and spirally wrap electromagnetic induction cable around the predetermined area on both sides of the weld to perform post-heating hydrogen removal treatment. e) Magnetic particle inspection: After the welding insulation is completed, magnetic particle inspection is performed after a predetermined time. In step c, the current for the intermittent arc root pass is 250-300A, the weld thickness is 4-5mm, and the welding wire moves in a straight line; the current for the intermittent arc fill pass is 250-300A, the weld thickness is 4-5mm, and the welding wire oscillates in a small crescent shape; the current for the continuous cover pass is 180-200A, using a sawtooth oscillation, maintaining a short arc throughout the welding process, moving quickly in the center of the weld bead, but pausing slightly on both sides of the bevel to melt 1-2mm of the edges on both sides of the bevel, and then reheating to fill the crater when the arc is closed. In step b, before welding, a medium- and high-frequency electromagnetic induction cable is used to uniformly preheat a 150mm area on both sides of the weld zone of the eccentric shaft assembly to 250-300℃, with a heating rate of 150℃ / h and a preheating holding time of 2h. In step d, immediately after welding, a thermal insulation layer of about 40mm thick is wrapped around the workpiece, and high-frequency electromagnetic induction cable is spirally wound 150mm on both sides of the weld for post-heating hydrogen removal treatment. The post-heating temperature is 200-300℃, and the post-heating insulation time is 6h.

2. The welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly according to claim 1, characterized in that: The length of the spiral-wound induction heating cable must be greater than 20m, otherwise it cannot output full power. The excess induction cable needs to be spirally wound in a non-metallic area.

3. The welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly according to claim 1, characterized in that: In step c, gas metal arc welding is used, the current polarity is reverse DC, the welding position is vertical welding, the welding wire is φ1.2mm ER50-6 welding wire, the shielding gas is 80%Ar+20%CO2, and the gas flow rate is 15~20L / min.

4. The welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly according to claim 1, characterized in that: In step d, after the welding insulation is completed, the sample is left to stand for 48 hours before magnetic particle testing.

5. The welding method for a Q355B and 42CrMo ultra-high strength heavy-duty eccentric shaft assembly according to claim 1, characterized in that: In step a, use slings to tie both ends of the round shaft, so that one end of the round shaft is slowly inserted into the welding positioning fixture, and then move the position to tie the other end of the round shaft and slowly insert it into the welding positioning fixture on the other side. After both welding positioning fixtures reach the designated position, slowly place it on the work platform; use a crane to assist in flipping the eccentric shaft assembly, so that it can rotate freely in the positioning fixture bushing, and fix it to the work platform with tie rods, so that the circumferential weld is in the designated welding position.

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