A method of forming an axle housing

Abstract

The application discloses a kind of bridge housing forming methods, it is related to the technical field of automobile parts manufacturing, comprising the following steps: S1, blank preparation: tubular blank is processed into the bridge housing blank of preform with middle part arched shell and two end straight sections;S2, annealing treatment: bridge housing blank of preform is annealed heat treatment;S3, cold drawing: the two end straight sections of bridge housing blank of preform after annealing treatment are respectively axially cold drawn, so that the wall thickness of two end straight sections is plastic thinning, and reaches preset target wall thickness.The application can be wall thickness thinning to two end straight sections of bridge housing by subsequent cold drawing plastic processing technology, and realizes accurate wall thickness control.

Description

Technical Field

[0001] This invention relates to the field of automotive parts manufacturing technology, specifically a method for forming an axle housing. Background Technology

[0002] Currently, automotive axle housings on the market are mainly manufactured using two processes: 1. Stamping and welding: Multiple stamped parts are welded together to form the bridge housing. The disadvantages of this method are: numerous welding steps and high welding costs; difficulty in controlling weld quality, leading to welding defects; and susceptibility to oil leakage at the weld, affecting reliability and service life.

[0003] 2. Hydraulic-filled integrated molding (internal high-pressure molding): The axle housing is formed in one step using a hydraulic bulging process. The advantages of this method are no weld seams and strong integrity, but it has the following prominent problems: During the molding process, the material in the axial feeding areas at both ends of the tube blank flows towards the center under the effect of the diameter reduction process, resulting in a significant increase in the wall thickness of the straight pipe sections at both ends of the molded axle housing, with an increase of up to 40% or more. For axle housings used in passenger cars and light trucks, which are small in size and lightweight, excessive wall thickness at both ends causes serious material waste and weight increase. Given the current severe cost pressures and lightweight development trend in the automotive industry, this material redundancy directly affects the product's market competitiveness.

[0004] In the existing technology, in order to solve the problem of uneven wall thickness after liquid filling molding, mechanical processing (such as turning) is generally used to remove excess material. However, this method has low material utilization, high processing cost, and may disrupt the material fiber flow direction. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bridge shell forming method, which reduces the wall thickness of the straight sections at both ends of the bridge shell through subsequent cold drawing plastic processing, thereby achieving precise wall thickness control.

[0006] The objective of this invention is achieved through the following technical solution: a bridge shell molding method, the method comprising the following steps: S1. Precast blank preparation: The tubular blank is processed into a bridge shell precast blank with a central arched shell and straight sections at both ends through a liquid-filled integral molding process.

[0007] S2. Annealing treatment: Annealing heat treatment is performed on the bridge housing preform to eliminate work hardening caused by the liquid filling integral molding process and improve the plasticity of the material.

[0008] S3. Cold drawing: At room temperature, the straight sections at both ends of the annealed bridge housing preform are axially cold drawn using a drawing die to plastically reduce the wall thickness of the straight sections at both ends to achieve the preset target wall thickness. The preset target wall thickness is determined based on the CAE strength analysis, stiffness analysis and fatigue life simulation results of the bridge housing, ensuring that the thinned bridge housing meets all performance requirements.

[0009] S4. Post-processing: The bridge shell that has been cold-drawn is shaped, machined and surface-treated to obtain the finished bridge shell.

[0010] The tubular billet can be made of low-carbon alloy steel pipe, Q345 material or material with equivalent mechanical properties.

[0011] In step S2, the bridge shell preform is placed in a continuous drum heat treatment furnace for complete annealing. The annealing heat treatment temperature is 20-50℃ above the Ac1 line of the material [if Q345 material is used for tubular billets, its Ac1 temperature (austenite initiation temperature) is usually 730-740℃, and the annealing heat treatment temperature is 750℃-790℃]. The holding time is 1-3 hours, followed by furnace cooling or furnace cooling to obtain a uniform ferrite + pearlite structure.

[0012] The cold drawing process uses a hydraulic press to provide drawing force. The nominal pressure of the hydraulic press is 100 tons, which can provide sufficient drawing force to cause plastic deformation of the material. The hydraulic press can be a 100-ton horizontal special hydraulic press.

[0013] The drawing die is made of cemented carbide. The inner hole of the drawing die includes an inlet cone angle, a sizing band, and an outlet cone angle. The inlet cone angle is 8-15°, and the length of the sizing band is 2-3 times the target wall thickness. The cold drawing thinning rate is 20-35%. The thinning rate is precisely controlled by controlling the drawing force and drawing speed.

[0014] Step S4 also includes hydraulic shaping, end face turning, flange welding, shot peening and coating of the bridge housing after cold drawing.

[0015] The beneficial effects of this invention are: 1. This invention achieves active and precise wall thickness control: it breaks through the limitation of uncontrollable wall thickness distribution at both ends of the straight section after diameter reduction and liquid filling molding. By actively and precisely thinning the redundant wall thickness at both ends through subsequent cold drawing, the wall thickness distribution is more in line with the theoretical design, thus overcoming the inherent defects of traditional liquid filling molding process.

[0016] 2. The present invention achieves significant weight reduction effect: by reducing the wall thickness at both ends, the weight of a single axle housing can be reduced by about 5 kg, with a weight reduction ratio of up to about 25%, which makes a significant contribution to the overall vehicle weight reduction and is conducive to reducing energy consumption and emissions.

[0017] 3. This invention has significant economic benefits: it improves material utilization, directly saving 15-20% of raw material costs; at the same time, it reduces the amount of subsequent machining, lowering processing costs; and the overall manufacturing cost can be reduced by 10-15%.

[0018] 4. This invention ensures the reliability of product performance: the target wall thickness is set based on CAE analysis to ensure that the thinned bridge shell meets the requirements in terms of strength, stiffness and fatigue life; the annealing treatment eliminates work hardening, improves the plasticity of the material, and avoids cracking defects that may occur during the cold drawing process; the cold drawing process causes work hardening of the material, which improves the strength and surface hardness of the thinned area.

[0019] 5. This invention improves the surface quality of the product: the cold drawing process makes the bridge housing surface smoother, and the roughness Ra value can reach below 1.6μm, which is better than the surface quality of hot working.

[0020] 6. Strong technological feasibility and easy industrialization: The equipment required for the core cold drawing process (100-ton hydraulic press) is highly versatile and cost-controllable; process parameters are easy to control and product quality is stable; it is easy to integrate into existing production lines to achieve large-scale production.

[0021] 7. Significant environmental benefits: Reduces material and energy consumption, in line with the concept of green manufacturing. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the wall thickness distribution of the finished bridge shell obtained by cold drawing and thinning of the precast bridge shell blank. Detailed Implementation

[0023] 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, not all, of the embodiments of the present invention. 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. Therefore, the following detailed description of the embodiments of the present 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 present invention without inventive effort are within the scope of protection of the present invention.

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] In one embodiment of this application: Manufacturing of a light truck axle housing: like Figure 1 As shown, a bridge shell forming method includes the following steps: S1. Precast Billet Preparation: Seamless steel pipe of Q345B material is selected as the original billet, with an outer diameter of φ168mm, a wall thickness of 4mm, and a length determined according to product requirements. The tubular billet is reduced in diameter at both ends and then placed in a liquid-filling molding mold. It is processed into a bridge shell precast billet with a central arched shell and straight sections at both ends through an internal high-pressure forming process. Main process parameters: Initial liquid injection pressure: 20MPa; Final forming pressure: 120MPa; Wall thickness distribution after forming: Central arched area: 2-2.5mm; Straight section areas at both ends: 6.5-7.5mm.

[0026] S2. Annealing treatment: The bridge shell preform is placed in a continuous drum heat treatment furnace for complete annealing; Annealing temperature: 860℃; Holding time: 1 hour; Cooling method: Cool to 100℃ in the furnace and then air cool.

[0027] S3. Cold Drawing: A 100-ton horizontal hydraulic press is used to axially cold draw the straight sections at both ends of the annealed bridge housing preform, causing plastic thinning of the wall thickness at both ends to achieve the preset target wall thickness; Equipment configuration: Hydraulic press nominal pressure: 1000kN; Drawing speed: 10-15mm / s; Drawing die: Carbide material, 12° guide cone angle, 20mm sizing band length; Process: a. Fix one end of the bridge housing precast blank to the hydraulic press worktable.

[0028] b. Insert the other end into the drawing die.

[0029] c. Start the hydraulic press, and the piston rod pulls the axle housing preform through the mold.

[0030] d. Control the pull-out force within the range of 600-800kN.

[0031] e. The drawing process is completed in one pass, reducing the wall thickness from 7.5mm to 6.8mm.

[0032] f. Process the other end in the same way.

[0033] g. The same method is used to achieve the required thickness through multiple drawing operations.

[0034] S4. Post-processing: The bridge shell that has been cold-drawn is subjected to the following processing to obtain the finished bridge shell.

[0035] Hydraulic alignment: Using a special alignment mold, the straightness of the axle housing is corrected under a pressure of 500kN.

[0036] End face machining: Turn both ends to ensure the perpendicularity and length of the end faces.

[0037] Flange welding: Welding the flanges at both ends.

[0038] Shot peening: Use φ0.8mm cast steel shot, shot peening intensity 0.35C.

[0039] Coating treatment: After phosphating, epoxy powder is electrostatically sprayed.

[0040] S5. Finished product inspection.

[0041] The above description is merely an embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for forming a bridge shell, characterized in that: Includes the following steps: S1. Precast blank preparation: The tubular blank is processed into a bridge shell precast blank with an arched shell in the middle and straight sections at both ends; S2. Annealing treatment: Annealing heat treatment of bridge housing preforms; S3. Cold drawing: The straight sections at both ends of the annealed bridge housing preform are axially cold drawn to plastically reduce the wall thickness of the straight sections at both ends and achieve the preset target wall thickness.

2. The bridge shell forming method according to claim 1, characterized in that: In step S1, the tubular blank is processed into a bridge shell preform with a central arched shell and straight sections at both ends by a liquid-filled integral molding process.

3. The bridge shell forming method according to claim 2, characterized in that: The tubular blank is made of low-carbon alloy steel pipe.

4. The bridge shell forming method according to claim 1, characterized in that: In step S2, the bridge housing preform is placed in a continuous drum heat treatment furnace for complete annealing.

5. The bridge shell forming method according to claim 1, characterized in that: In step S3, at room temperature, the straight sections at both ends of the annealed bridge housing preform are axially cold-drawn using a drawing die, so that the wall thickness of the straight sections at both ends is plastically reduced and reaches the preset target wall thickness.

6. The bridge shell forming method according to claim 5, characterized in that: Cold drawing uses a hydraulic press to provide the drawing force, and the nominal pressure of the hydraulic press is 100 tons.

7. The bridge shell forming method according to claim 6, characterized in that: The hydraulic press is a 100-ton horizontal special hydraulic press.

8. The bridge shell forming method according to claim 5, characterized in that: The drawing die is made of cemented carbide. The inner hole of the drawing die includes an inlet cone angle, a sizing band, and an outlet cone angle. The inlet cone angle is 8-15°, and the length of the sizing band is 2-3 times the target wall thickness.

9. The bridge shell forming method according to claim 1, characterized in that: It also includes step S4, which involves shaping, machining and surface treatment of the cold-drawn bridge shell to obtain the finished bridge shell.

10. A bridge shell forming method according to claim 9, characterized in that: Step S4 also includes hydraulic shaping, end face turning, flange welding, shot peening and coating of the bridge housing after cold drawing.

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