Manufacturing process of high-stress suspension springs and their high-stress suspension springs

Abstract

This invention discloses a manufacturing process for a high-stress suspension spring and the high-stress suspension spring thereof. The manufacturing process includes: a spring coiling step: cold coiling spring steel wire to form a preliminary finished spring; the spring steel wire is surface-softened steel wire; a tempering step: tempering the preliminary finished spring; a hot pressing and shot blasting step: hot pressing the tempered preliminary finished spring and then shot blasting it; a cold shot blasting step: shot blasting the hot-pressed and shot-blasted preliminary finished spring at room temperature; and a stress shot blasting step: shot blasting the preliminary finished spring compressed to a set height H1; H1 = H0 - 2ΔL, ΔL = L1 - L0, L1 is the current length of the preliminary finished spring after cold shot blasting, L0 is the target length of the preliminary finished spring after stress shot blasting, and H0 is obtained according to the following formula: τ = K*(L1 - H0)*(Dm / 2) / Wt + K*(L1 - H0) / A. Suspension springs manufactured using this process combine high strength and ductility, resulting in a long fatigue life.

Description

Technical Field

[0001] This invention relates to spring manufacturing technology. Background Technology

[0002] Most car suspension springs are steel coil springs, which are connected to the body and chassis components through upper and lower spring seats to provide weight support. During driving, they use inherent stiffness or variable stiffness to generate length deformation to resist wheel bounce caused by uneven road surfaces and adjust the vehicle height to improve driving comfort.

[0003] Against the backdrop of new energy vehicles impacting the automotive industry, the demand for traditional gasoline-powered vehicles is gradually being replaced by new energy vehicles. The core of new energy vehicles consists of the motor, battery, and electronic control system, collectively known as the "three electrics." While replacing the power system of traditional internal combustion engine vehicles, the three electrics significantly increase the weight of the entire vehicle. In order to simultaneously meet the load stiffness requirements and compensate for the power issues caused by the increased vehicle weight, various components, including suspension springs, need to be weight-reduced, resulting in a substantial increase in the maximum working stress and working stress amplitude of the springs.

[0004] Currently, the strength of the steel wire material in springs is at a relatively high level. The higher the material strength, the lower the reduction of area. These two factors are opposite and cannot be guaranteed at the same time. However, both of these factors play an important role in the fatigue life of springs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a manufacturing process for a high-stress suspension spring. The suspension spring manufactured by this process has both high strength and ductility, and has a long fatigue life.

[0006] Another technical problem to be solved by the present invention is to provide a high-stress suspension spring.

[0007] The manufacturing process of the high-stress suspension spring according to an embodiment of the present invention includes:

[0008] Spring coiling process: The spring steel wire is cold-coiled to form the initial finished suspension spring; the spring steel wire used is surface-softened steel wire;

[0009] Tempering step: Temper the rolled initial finished spring;

[0010] Hot pressing and shot blasting steps: The tempered pre-finished spring is first hot pressed, and then shot blasted.

[0011] Cold shot blasting process: The initial finished spring after hot pressing and hot shot blasting is shot blasted at room temperature;

[0012] Stress shot blasting steps: The pre-finished spring compressed to a set height H1 is shot blasted; H1=H0-2ΔL, ΔL=L1-L0, L1 is the current length of the pre-finished spring after cold shot blasting, L0 is the target length of the pre-finished spring after stress shot blasting, and H0 is calculated according to the following formula: τ=K*(L1-H0)*(Dm / 2) / Wt+K*(L1-H0) / A, where K is the spring stiffness, Dm is the mean diameter of the spring, Wt is the torsional section modulus of the spring steel wire, A is the cross-sectional area of ​​the spring steel wire, τ is the working stress of the pre-finished spring when it is compressed to a height H0, and τ is set as the sum of δs and σ, where δs is the shear yield strength of the spring steel wire, and σ is the surface residual compressive stress superimposed on the pre-finished spring by the cold shot alone.

[0013] Preferably, the aforementioned tempering step is as follows: the rolled initial-finished spring is placed in a tempering furnace for tempering, the tempering temperature T is controlled between 390℃ and 430℃, and the tempering time t follows the formula: t=T*r 2 / C, r is the radius of the spring steel wire in mm, t is in seconds, T is in °C, C is the tempering coefficient, and C is an empirical constant.

[0014] On the other hand, the high-stress suspension spring according to an embodiment of the present invention is manufactured by the aforementioned manufacturing process.

[0015] 1. The embodiments of the present invention use surface-softened steel wire material to produce high-stress suspension springs. Since the surface hardness of the surface-softened steel wire is lower than that of the steel wire core, the ductility of the steel wire is improved, the fatigue life of the product is extended, and the strength of the product can be taken into account at the same time, which can meet the requirements of vehicle manufacturing to maintain quality and reduce weight.

[0016] 2. The embodiments of the present invention include multiple shot blasting processes, and make the working stress when the spring is compressed to a height H0 in the stress shot blasting process equal to the sum of δs and σ, so that more residual stress can be superimposed on the spring surface, thereby improving the strength of the spring.

[0017] 3. This invention eliminates the cold pressing step in the traditional manufacturing process. By stress shot blasting, it simultaneously increases the residual compressive stress and compresses away excess length, thus eliminating the drawback that the cold pressing process (excessive compression after stress shot blasting) reduces the residual stress on the spring surface.

[0018] 4. By setting reasonable tempering parameters, the embodiment of the present invention improves the overall average hardness of the material and avoids the problem of reduced overall average hardness of the material due to surface softening caused by using traditional tempering parameters. Attached Figure Description

[0019] Figure 1 A schematic diagram of the cross-section of a surface-softened spring steel wire is shown.

[0020] Figure 2 This is a process flow diagram of one embodiment of the present invention. Detailed Implementation

[0021] To provide a clearer understanding of the performance and features of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings.

[0022] Currently, the manufacturing process for suspension springs with working stress below 1250MPa is as follows: cold coiling → tempering → hot pressing and shot blasting → cold shot blasting → cold pressing → painting. The manufacturing process for high-stress suspension springs (working stress 1250MPa~1300MPa) using oil-quenched and tempered steel wire is: cold coiling → tempering → hot pressing and shot blasting → stress shot blasting → cold pressing → painting. As the requirements for lightweight vehicles become increasingly stringent, the strength requirements for suspension springs are also increasing. However, excessively high material strength requirements can compromise the toughness of the suspension springs, thus affecting the product's fatigue life.

[0023] To balance the high strength and ductility of spring steel wire, the inventors considered using surface-softened spring steel wire as the raw material for high-stress suspension springs. This surface-softened spring steel wire is a high-strength induction-hardened and tempered spring steel wire, such as... Figure 1 As shown, its surface has a softening layer 91, the hardness of which is lower than the hardness of the core 92 of the spring steel wire.

[0024] The yield strength ratio of this surface-softened spring steel wire has been experimentally verified to be consistently greater than 90%, making it suitable for producing automotive suspension springs with a working stress not exceeding 1400 MPa, resulting in a weight reduction of more than 10%. The mechanical properties of this surface-softened spring steel wire are shown in the table below:

[0025]

[0026] The high-stress suspension spring described in this embodiment has a working stress greater than 1280 MPa and less than 1400 MPa. In some specific embodiments, the material grade of the surface-softened spring steel wire used in this application is SWI-210S.

[0027] Surface-softened steel wire materials have the following advantages: a) reducing the risk of spring coiling fracture with a small coiling ratio; b) delaying the onset of fatigue cracks; c) slowing the propagation rate of fatigue cracks; and d) reducing the impact of surface non-metallic inclusions on spring fatigue. However, surface-softened steel wire materials also have the following disadvantages when manufactured using traditional suspension spring production processes: a) stress-relief tempering can easily reduce the overall average hardness of the material; and b) the softened surface layer is not conducive to the superposition of residual stress from shot blasting.

[0028] To fully utilize the properties of surface-softened steel wire while overcoming manufacturing challenges, the inventors improved the conventional suspension spring manufacturing process. Compared to traditional suspension spring manufacturing processes, the process in this invention eliminates the cold pressing step and improves the stress shot blasting step. This allows the springs to directly reach the specified length after stress shot blasting, ensuring consistent length across multiple springs manufactured in batches. Conventional suspension spring manufacturing processes require a cold pressing step after stress shot blasting, compressing the spring at room temperature to achieve the desired length and ensure consistent length across multiple springs. The reason for eliminating the cold pressing step is that the inventors found that excessive compression after stress shot blasting causes internal yielding, significantly reducing the surface compressive stress superposition effect of stress shot blasting.

[0029] Please see Figure 2 The manufacturing process of a high-stress suspension spring according to an embodiment of the present invention includes: a spring coiling step, a tempering step, a hot pressing and shot blasting step, a cold shot blasting step, a stress shot blasting step, and a coating step.

[0030] The spring coiling step involves cold coiling spring steel wire using a spring coiling machine to form a preliminary finished suspension spring. The spring steel wire used is surface-softened steel wire. Preferably, the domestic grade of this surface-softened spring steel wire is SWI-210S.

[0031] Because the strength of the material has been increased, the overall hardness of the material has increased, requiring a more powerful coiling spring device for the same wire diameter and winding ratio.

[0032] The tempering step involves tempering the initially rolled springs to eliminate rolling stress.

[0033] The rolled springs are then placed in a tempering furnace for tempering. The tempering temperature is controlled between 390℃ and 430℃, and the tempering time t follows the formula: t=T*r 2 / C, where r is the radius of the spring steel wire in mm, t is in seconds, T is in °C, C is the tempering coefficient, and C is an empirical constant. The above formula indicates that after determining the tempering temperature, a longer tempering time is needed for springs with thicker steel wires (the thicker the wire, the longer the heat conduction time to the core), to ensure that the core of the spring steel wire can fully eliminate residual stress without softening. This embodiment of the invention improves the overall average hardness of the material by setting reasonable tempering parameters, avoiding the problem of reduced overall average hardness due to surface softening caused by traditional tempering parameters. When the spring steel wire grade is SWI-210S, the value of C is 400.

[0034] The hot pressing and hot shot blasting process involves first hot pressing the tempered pre-finished springs, and then performing shot blasting.

[0035] In the hot-press shot blasting step, the shot diameter is between 0.8 and 1 mm, and the arc height of the Arman A-type test piece is greater than or equal to 0.45 mm. The initial finished spring is heated to >150℃ during hot-press shot blasting.

[0036] To avoid loss of spring compression force, which would reduce load and residual stress, it is preferable to control the free length tolerance after hot pressing within ±3mm.

[0037] The cold shot blasting process involves blasting the pre-finished springs, which have undergone hot shot blasting, at room temperature.

[0038] Because the subsequent stress shot blasting clamping method will block the upper and lower support rings from shot blasting the area, a cold shot blasting is required.

[0039] In the cold shot blasting process, the shot diameter is between 0.6 and 0.8 mm, and the arc height of the Arman A-type test piece is greater than or equal to 0.45 mm.

[0040] The stress shot blasting step involves shot blasting the pre-finished spring compressed to a set height H1; H1 = H0 - 2ΔL, ΔL = L1 - L0, where L1 is the current length of the pre-finished spring after cold shot blasting, L0 is the target length of the pre-finished spring after stress shot blasting, and H0 is calculated according to the following formula: τ = K*(L1-H0)*(Dm / 2) / Wt + K*(L1-H0) / A, where K is the spring stiffness, Dm is the mean diameter of the spring, Wt is the torsional section modulus of the spring steel wire, A is the cross-sectional area of ​​the spring steel wire, τ is the working stress of the pre-finished spring when it is compressed to height H0, and τ is set as the sum of δs and σ, where δs is the shear yield strength of the spring steel wire (material), and σ is the surface residual compressive stress superimposed on the pre-finished spring by the cold shot alone (the surface residual compressive stress is a negative value).

[0041] It should be noted that, in this field, the height of a spring in its free state (uncompressed) is usually referred to as its length.

[0042] In this embodiment, the shear yield strength δs of the spring steel wire is equal to 2 / 3 of the tensile strength of the spring steel wire (material). The above is an empirical formula obtained from compression tests.

[0043] When using surface softening material of grade SWI-210S, the tensile strength of the surface softening material is 2100 MPa, and the shear yield strength δs is equal to 1400 MPa. Under conditions where the spring is not subjected to other external forces, experiments show that for a pre-finished spring made of SWI-210S, after cold shot blasting (shot diameter between 0.6 and 0.8 mm), the cumulative residual compressive stress on the surface is approximately -500 MPa. Therefore, the working stress τ of the pre-finished spring when compressed to height H0 is set to +900 MPa.

[0044] Empirical formulas show that after a spring has yielded, for every 2K (2 stiffness units) of force added, the stress increases by 2*[(K*Dm / Wt)+(K / A)], causing plastic deformation on the surface to overcome a 1mm rebound. Therefore, the preload height H1 is set to H0-2ΔL. After shot blasting the initial finished spring compressed to the set height H1 (stress shot blasting), the free length decreases from L1 to L0.

[0045] Shot blasting strengthens the surface while also producing a certain degree of hardening, within a depth of 0-0.5 mm from the spring surface. This process may reduce the softening effect on the material surface. However, the superposition of residual stress has a positive effect on offsetting the tensile stress during spring operation. Therefore, the shot blasting time should be minimized while ensuring sufficient compressive stress superposition on the surface. Since the effective area of ​​residual stress is only within 0-0.5 mm of the surface, the area within 0.5 mm is all tensile stress, and the spring will rebound after the stress shot blasting is completed and unloaded.

[0046] The surface softening material has low surface hardness, and the softening layer acts as a speed bump for the shot blasting particles, resulting in poor superposition of residual compressive stress. This application sets up a stress shot blasting step, and makes the working stress when the spring is compressed to height H0 in the stress shot blasting step equal to the sum of δs and σ, achieving the effect of superimposing more residual stress in a short time.

[0047] In the stress shot blasting process, the shot diameter is between 0.6 and 0.8 mm, and the arc height of the Arman A-type specimen is greater than or equal to 0.45 mm.

[0048] In this embodiment, the diameter of the shot used in the hot-press shot blasting step is larger than the diameter of the shot used in the cold shot blasting step and the stress shot blasting step. Using larger shot can obtain the peak value and depth of residual compressive stress, while using smaller shot can improve the residual stress and surface quality of the spring surface and subsurface.

[0049] The coating step involves applying a coating to the surface of the pre-finished spring to form the finished spring. Since both the pre-treatment and powder coating processes heat the spring, resulting in the loss of residual surface stress, it is necessary to control the drying temperature and time. In some specific embodiments, the coating temperature is less than or equal to 210°C, and the coating time does not exceed 40 minutes.

[0050] Furthermore, in mass production, a length screening process is performed after the cold shot blasting step and before the stress shot blasting step. The length screening process divides the pre-finished springs after cold shot blasting into multiple groups according to their length. The length difference between the longest and shortest springs in each group does not exceed a preset length difference threshold (this length threshold can be, for example, 2 mm). The current length L1 of all pre-finished springs in each group is assigned a fixed length value L2. This fixed length value L2 is greater than or equal to the length of the shortest spring in the group and less than or equal to the length of the longest spring in the group. This is done to facilitate the processing of L1 in the subsequent hot stress shot blasting step and improve production efficiency.

Claims

1. A manufacturing process for a high stress suspension spring, characterized by, include: Spring coiling process: Cold coiling of spring steel wire to form the initial finished product of suspension spring; The spring steel wire is made of surface-softened steel wire; Tempering step: Temper the rolled initial finished spring; Hot pressing and shot blasting steps: The tempered pre-finished spring is first hot pressed, and then shot blasted. Cold shot blasting process: The initial finished spring after hot pressing and hot shot blasting is shot blasted at room temperature; Stress shot blasting steps: The pre-finished spring compressed to a set height H1 is shot blasted; H1=H0-2ΔL, ΔL=L1-L0, L1 is the current length of the pre-finished spring after cold shot blasting, L0 is the target length of the pre-finished spring after stress shot blasting, and H0 is calculated according to the following formula: τ= K*(L1-H0)*(Dm / 2) / Wt+ K*(L1-H0) / A, where K is the spring stiffness, Dm is the mean diameter of the spring, Wt is the torsional section modulus of the spring steel wire, A is the cross-sectional area of ​​the spring steel wire, τ is the working stress of the pre-finished spring when it is compressed to a height H0, and τ is set as the sum of δs and σ, where δs is the shear yield strength of the spring steel wire, and σ is the surface residual compressive stress superimposed on the pre-finished spring by the cold shot alone.

2. The manufacturing process of high-stress suspension springs as claimed in claim 1, wherein, The manufacturing process of the high-stress suspension spring includes a coating step after the stress shot blasting step, in which the surface of the initial finished spring is coated.

3. The manufacturing process of high-stress suspension springs of claim 1, wherein, The manufacturing process of the high-stress suspension spring includes a length screening process performed after the cold shot blasting step and before the stress shot blasting step. The length screening process involves dividing the pre-finished springs after cold shot blasting into multiple groups according to their length. The length difference between the longest and shortest springs in each group does not exceed a preset length difference threshold. The current length L1 of all pre-finished springs in each group is assigned a fixed length value L2. This fixed length value L2 is greater than or equal to the length of the shortest spring in the group and less than or equal to the length of the longest spring in the group.

4. The manufacturing process for high-stress suspension springs as claimed in any one of claims 1 to 3, characterized in that, The tempering step is: putting the coiled primary product spring into a tempering furnace for tempering, the tempering temperature T is controlled between 390℃ and 430℃, and the tempering time t follows the formula: t=T*r 2 / C, r is the radius of the spring wire, the unit is mm, the unit of t is second, the unit of T is ℃, and C is the tempering coefficient, C is an empirical constant.

5. The manufacturing process of the high-stress suspension spring as described in claim 1, characterized in that, The diameter of the shot used in the hot-press shot blasting step is larger than the diameter of the shot used in the cold shot blasting step and the stress shot blasting step.

6. The manufacturing process of the high-stress suspension spring as described in claim 1, characterized in that, The working stress of the high-stress suspension spring is greater than 1280 MPa and less than 1400 MPa.

7. The manufacturing process of the high-stress suspension spring as described in claim 1, characterized in that, The shear yield strength of the spring steel wire is equal to 2 / 3 of the tensile strength of the spring steel wire.

8. A high-stress suspension spring, characterized in that, The high-stress suspension spring is manufactured using the manufacturing process described in any one of claims 1 to 7.

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