A method of assembling a laser welded differential assembly

Abstract

The present application relates to the technical field of automobile differential, and particularly relates to an assembling method of a laser-welded differential assembly, a welding groove is formed along an axial direction at a connecting position of a main reduction driven gear and a differential housing, the main reduction driven gear and the differential housing are welded at the welding groove by a laser filler wire welding mode, and the welding groove is provided as an asymmetric structure, wherein a welding wire in the laser filler wire welding is a nickel-based welding wire, the welding groove is a Y-shaped groove in an asymmetric structure, the Y-shaped groove comprises a gear side slope surface and a housing side slope surface at an opening end, and the gear side slope surface and the housing side slope surface meet into a welding through hole extending along the axial direction at a side away from the opening. The present application provides a relationship of welding performance of the differential housing material, a method for calculating a carbon equivalent of spheroidal graphite cast iron welding, and a welding guidance method. The assembling between the differential housing and the main reduction driven gear is performed by the laser filler wire welding technology, so that the cost can be reduced, the light weight can be realized, and the reliability can be enhanced.

Description

Technical Field

[0001] This invention relates to the field of technology, specifically providing an assembly method for laser welding differential assemblies. Background Technology

[0002] In automotive transmissions, the differential assembly enables differential turning, transmits torque, and drives the vehicle. Specifically, torque needs to be transmitted from the main reduction gear to the differential, and then from the differential to the half-shafts and wheels, thus driving the vehicle. The assembly between the main reduction gear and the differential housing is crucial in the differential assembly. Currently, the assembly of the main reduction gear and the differential mainly uses a bolt-tightening method, which has the following disadvantages:

[0003] 1. The differential housing is often made of cast iron, while the main reduction and driven gears are often made of low carbon steel. When products made of these two materials are assembled by bolting, there are certain risks, whether the bolts are tightened manually or by automated equipment. The bolts are prone to loosening, the assembly efficiency is low when there are many bolts, and the product weight is large.

[0004] 2. The positioning error during bolt hole machining is relatively large, resulting in high production costs and certain assembly difficulties. Moreover, during operation, the bolts are subjected to significant shearing forces, making them vulnerable parts with high maintenance and replacement costs.

[0005] To avoid problems associated with bolt tightening assembly, laser welding has been developed in the prior art to assemble the differential housing and driven gear in the differential assembly.

[0006] 1. The utility model patent with patent number "202221037843.5" and patent name "an assembly method for laser welding differential assembly" includes a left differential housing, a right differential housing, a driven bevel gear and a gear transmission structure. The left and right differential housings are laser welded to form a hollow shell structure. The driven bevel gear is connected to the right differential housing by laser welding. This solution uses laser welding technology to connect the left and right differential housings and the driven bevel gear, which can eliminate the need for connecting bolts. It has the advantages of compact structure, light weight, simple manufacturing process, low cost and improved main reduction transmission efficiency.

[0007] 2. The invention patent application with patent number "202310271546.X" and patent name "Radial Differential Assembly, Assembly Method and Vehicle" includes a first housing, a driven gear, a second housing, a gear transmission structure, a first connecting part, a first weld, a second connecting part and a second weld. This solution can achieve the lightweighting of the radial differential assembly, improve the structural strength, and reduce the risk of cracking and weld failure of the weld in subsequent use.

[0008] While the aforementioned existing technologies can achieve the assembly of the differential housing and driven gear through laser welding, avoiding the problems associated with bolted connections, the structure is relatively complex, and the overall weight and manufacturing cost remain high. Therefore, designing a laser-welded differential assembly method that is simple in structure, lightweight, low in cost, and highly efficient is an urgent problem to be solved. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides an assembly method for laser-welded differential assemblies, which solves the problem of lightweighting the differential assembly, reduces production costs, and improves work efficiency and reliability.

[0010] The present invention provides an assembly method for laser welding differential assembly, which specifically involves: opening a welding bevel along the axial direction at the connection between the main reduction driven gear and the differential housing; welding the main reduction driven gear and the differential housing at the welding bevel using laser filler wire welding; and setting the welding bevel as an asymmetrical structure.

[0011] Furthermore, the welding wire used in laser filler wire welding is a nickel-based welding wire.

[0012] Furthermore, the differential housing is made of ductile iron, and the carbon equivalent formula for ductile iron is: CE=C*P / Ni% / 10+Mn / 6+Si / 24;

[0013] Where P is the pearlite content, Ni% is the Ni content in the nickel-based welding wire used, C is carbon, Mn is manganese, and Si is silicon.

[0014] When CE≤0.4, ductile iron has good weldability.

[0015] When CE≥0.5, ductile iron requires preheating welding, and the welding temperature should not be lower than 75℃.

[0016] Furthermore, the nickel content in the nickel-based welding wire is ≥60%.

[0017] Furthermore, the welding bevel is set as an asymmetrical Y-shaped bevel; the Y-shaped bevel includes a gear side bevel and a housing side bevel located at the opening end. The gear side bevel and the housing side bevel converge on the side away from the opening to form a welding through hole extending axially. The included angle between the gear side bevel and the wall of the welding through hole and the included angle between the housing side bevel and the wall of the welding through hole are different.

[0018] Furthermore, the gear side slope and the wall of the welded through hole, as well as the housing side slope and the wall of the welded through hole, are all connected by a circular arc transition.

[0019] Furthermore, guide surfaces are provided at the openings of the gear side slope and the housing side slope, and the guide surfaces are inclined from the inside of the welding groove toward the outside and away from the center line L of the welding groove.

[0020] Furthermore, the distance between the gear side slope and the center line L of the welding groove is d1, the distance between the housing side slope and the center line L of the welding groove is d2, the total distance of the welding groove (3) is d, d1+d2=d, d1>d2 and d1=0.55d to 0.9d.

[0021] Furthermore, the diameter of the nickel-based welding wire is K, with d = 0.8K to 1.2K.

[0022] Furthermore, the angle between the guide surface on one side of the shell side slope and the center line L of the welding groove is β, and the angle between the guide surface on one side of the gear side slope and the center line L of the welding groove is α, where 20°<α<80° and 20°<β<80°.

[0023] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0024] 1. In this solution, the differential housing and the main reduction driven gear in the differential assembly are assembled using laser wire filling welding technology. Two different materials, ductile iron (the material of the differential housing) and low carbon steel (the material of the main reduction driven gear), are welded together as a whole. The welding method is axial welding, and the bevel is set in the axial direction. The welding depth and width can meet the requirements of general passenger vehicles. It has strong versatility, can reduce production costs, achieve lightweighting, and improve work efficiency and reliability.

[0025] 2. Due to the large number of specific grades or types of ductile iron used for differential housings, and the fact that the chemical composition and microstructure of the same grade are not entirely the same, the welding performance of the differential housing side will vary significantly. Usually, carbon equivalent is used to evaluate the welding performance of low alloy steel. However, since the carbon content of ductile iron is significantly higher than that of low carbon steel, and nickel-based welding wire is used for filler welding, the original carbon equivalent calculation formula is not applicable to ductile iron. In this solution, the carbon equivalent formula for ductile iron is derived based on welding performance, which can improve welding performance and reduce costs.

[0026] 3. The welding groove in this solution is an asymmetrical Y-shaped groove. Compared with the traditional symmetrical Y-shaped groove or V-shaped groove, it can reduce welding deformation, improve welding efficiency, and reduce welding costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the differential assembly provided in an embodiment of the present invention;

[0028] Figure 2This is a schematic diagram of the laser welding structure between the differential housing and the main reduction driven gear in the differential assembly provided by an embodiment of the present invention;

[0029] Figure 3 This is a data table for calculating carbon equivalent.

[0030] The reference numerals in the attached drawings include: 1. Main reduction driven gear, 2. Differential housing, 3. Welding bevel, 4. Gear side bevel, 5. Housing side bevel, 6. Welding through hole, 7. Guide surface, 8. Differential, 9. Planetary shaft, 10. Exhaust groove, 11. Exhaust hole. Detailed Implementation

[0031] The appendix will be referenced below. Figure 1-3 Embodiments of the present invention are described below. In the following description, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1-3 The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and do not constitute a limitation thereof.

[0033] like Figure 1 As shown, the differential assembly includes a differential 8, a differential housing 2, a main reduction driven gear 1, etc. The differential 8 includes a half-shaft gear, a planetary gear, and a planetary shaft 9. Figure 1 The axis S shown in the diagram is the central axis of planetary axis 9, and the following axis is the direction of the central axis S.

[0034] An assembly method for laser-welded differential assemblies, wherein the laser welding positions are as follows: Figure 1 As shown at point H, the specific assembly method for the laser-welded differential assembly is as follows: Figure 1 , Figure 2 As shown, a welding bevel 3 is opened axially at the connection between the main reduction driven gear 1 and the differential housing 2. The main reduction driven gear 1 and the differential housing 2 are welded at the welding bevel 3 by laser filler wire welding. The welding wire in the laser filler wire welding is a nickel-based welding wire with a nickel content ≥60%.

[0035] The differential housing 2 is made of ductile iron, and the driven gear 1 of the main reduction gear is made of low-carbon steel. The carbon content of ductile iron is higher than that of low-carbon steel. Ni-based welding wire is used for filler welding. The original carbon equivalent calculation formula is not applicable to ductile iron. Based on the welding performance of ductile iron, a new carbon equivalent formula is summarized as: CE=C*P / Ni% / 10+Mn / 6+Si / 24, where P is the pearlite content, Ni% is the Ni content in the nickel-based welding wire used, C is carbon, Mn is manganese, and Si is silicon. When CE≤0.4, the welding performance of ductile iron is good. When CE≥0.5, ductile iron needs to be preheated for welding, and the welding temperature should not be lower than 75℃.

[0036] Figure 3 A partial data table for carbon equivalent calculation is shown, such as... Figure 3 As shown, when CE=0.399375, ductile iron has good weldability and can be welded; when CE=0.41475, whether ductile iron needs preheating for welding depends on the actual situation; when CE=0.502778, ductile iron needs preheating for welding, and the welding temperature should not be lower than 75℃.

[0037] like Figure 2 As shown, the welding bevel 3 is designed as an asymmetrical structure, specifically an asymmetrical Y-shaped bevel. The Y-shaped bevel includes a gear-side bevel 4 and a housing-side bevel 5 located at the opening end. The gear-side bevel 4 and the housing-side bevel 5 converge on the side away from the opening to form a welding through hole 6 extending axially. The end of the welding through hole 6 is connected to an exhaust groove 10, and the exhaust groove 10 is connected to an exhaust hole 11 that communicates with the outside, so as to discharge the hot gas generated during the welding process and reduce welding deformation.

[0038] The angles between the gear side slope 4 and the wall of the welded through hole 6, and between the housing side slope 5 and the wall of the welded through hole 6, are different, creating an asymmetrical structure between the gear side slope 4 and the housing side slope 5. Both the gear side slope 4 and the wall of the welded through hole 6, and the housing side slope 5 and the wall of the welded through hole 6, are transitioned by rounded arcs, as detailed below. Figure 2 As shown at point P, there are rounded chamfers R between the gear side slope 4 and the wall of the welded through hole 6, and between the shell side slope 5 and the wall of the welded through hole 6. Since the pearlite content in ductile iron is high, when the laser energy is focused on the pearlite, the chemical structure is easily transformed into brittle cementite or ledeburite, forming cracks. The two rounded chamfers R shown at point P can prevent stress concentration and carbon concentration, and can avoid or reduce the occurrence of the above-mentioned cracks.

[0039] like Figure 2As shown, guide surfaces 7 are provided at the openings of the gear side slope 4 and the housing side slope 5. The guide surfaces 7 are inclined from the inside of the welding groove 3 towards the outside, away from the centerline L of the welding groove 3. The guide surfaces 7 effectively reduce the transformation of the pearlite structure, further preventing cracking. Figure 2 As shown, the angle between the guide surface 7 on one side of the shell side slope 5 and the center line L of the welding groove 3 is β, and the angle between the guide surface 7 on one side of the gear side slope 4 and the center line L of the welding groove 3 is α, 20°<α<80°, 20°<β<80°, and α and β are preferably 45°.

[0040] like Figure 2 As shown, the distance between the gear side slope 4 and the centerline L of the welding groove 3 is d1, the distance between the housing side slope 5 and the centerline L of the welding groove 3 is d2, and the total distance of the welding groove 3 is d, where d1 + d2 = d, d1 > d2, and d1 = 0.55d to 0.9d. During welding, the laser spot is mainly concentrated on one side of the main reduction driven gear 1. If d is 1cm, d1 can be set to 0.65mm and d2 to 0.35mm, or d1 can be set to 0.7mm and d2 to 0.3mm; if d is 1.5cm, d1 can be set to 0.9mm and d2 to 0.6mm, but this ratio of asymmetric groove is not limited. Meanwhile, if the diameter of the nickel-based welding wire is K, d = 0.8K to 1.2K. In this embodiment, to obtain better welding results, d is set to be the same as the diameter K of the nickel-based welding wire. Those skilled in the art can also set other ratios of asymmetric groove according to actual needs. The welding depth d3 of the welding groove 3 is 3-8mm, which can meet the requirements of general passenger vehicles and has high versatility.

[0041] Meanwhile, during laser welding, axial ring groove laser welding is used, and the coaxiality of the positioning fixture during welding is ≤0.1mm. A protective cover is used during welding to prevent spatter from entering the differential 8 or adhering to the product surface. Argon gas protection is used during welding, with a protective gas flow rate of 15L / min. The main reduction driven gear 1 and the differential housing 2 are centered and interference-fitted to ensure gear accuracy. Gear grinding is performed after welding the main reduction driven gear 1 to the differential housing 2, further ensuring gear accuracy.

[0042] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0043] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for assembling a laser-welded differential assembly, characterized in that, A welding bevel (3) is opened axially at the connection between the main reduction driven gear (1) and the differential housing (2). The main reduction driven gear (1) and the differential housing (2) are welded at the welding bevel (3) by laser filler wire welding. The welding bevel (3) is set as an asymmetrical structure. The welding wire in the laser filler wire welding is a nickel-based welding wire. The differential housing (2) is made of ductile iron, and the carbon equivalent formula of ductile iron is: CE=C×P / Ni% / 10+Mn / 6+Si / 24; Where P is the pearlite content, Ni% is the Ni content in the nickel-based welding wire used, C is carbon, Mn is manganese, and Si is silicon. When CE≤0.4, ductile iron has good weldability; when CE≥0.5, ductile iron requires preheating for welding, and the welding temperature should not be lower than 75℃.

2. The assembly method for laser-welded differential assembly according to claim 1, characterized in that, The nickel content in nickel-based welding wire is ≥60%.

3. The assembly method of the laser-welded differential assembly according to any one of claims 1-2, characterized in that, The welding bevel (3) is set as an asymmetrical Y-shaped bevel; the Y-shaped bevel includes a gear side bevel (4) and a housing side bevel (5) located at the opening end. The gear side bevel (4) and the housing side bevel (5) meet on the side away from the opening to form a welding through hole (6) extending axially. The included angle between the gear side bevel (4) and the wall of the welding through hole (6) and the included angle between the housing side bevel (5) and the wall of the welding through hole (6) are different.

4. The assembly method for laser-welded differential assembly according to claim 3, characterized in that, The gear side slope (4) and the wall of the welded through hole (6) are connected by a circular arc, as are the shell side slope (5) and the wall of the welded through hole (6).

5. The assembly method for laser-welded differential assembly according to claim 4, characterized in that, Guide surfaces (7) are provided at the opening of the gear side slope (4) and the opening of the housing side slope (5). The guide surfaces (7) are inclined from the inside of the welding groove (3) toward the outside and away from the center line L of the welding groove (3).

6. The assembly method for the laser-welded differential assembly according to claim 5, characterized in that, The distance between the centerline L of the gear side slope (4) and the welding groove (3) is d1, the distance between the centerline L of the housing side slope (5) and the welding groove (3) is d2, the total distance of the welding groove (3) is d, d1+d2=d, d1>d2 and d1=0.55d to 0.9d.

7. The assembly method for the laser-welded differential assembly according to claim 6, characterized in that, The diameter of the nickel-based welding wire is K, with d = 0.8K to 1.2K.

8. The assembly method of the laser-welded differential assembly according to claim 7, characterized in that, The angle between the guide surface (7) on one side of the shell side slope (5) and the center line L of the welding groove (3) is β, and the angle between the guide surface (7) on one side of the gear side slope (4) and the center line L of the welding groove (3) is α, 20°<α<80°, 20°<β<80°.

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