Method for cold drawing spring wire in the form of an ellipse in cross section

Abstract

The application provides a cold drawing forming method of spring steel wire with an elliptical cross section, and the steps are as follows: sequentially performing peeling, annealing, shot blasting and electrolytic phosphating treatment on round steel wire to form a 5-8 mu m thick phosphating film on the surface of the round steel wire; designing at least three passes of elliptical drawing dies and installing and positioning the dies; wherein the single-pass compression rate of the round wire is less than or equal to 25%, the single-pass compression rate of the elliptical wire is less than or equal to 16%, and the compression rate difference between adjacent passes is less than or equal to 5%; the drawing speed is 1.5-1.8 m / s; a horizontal drawing tank with a chrome-plated and polished surface is used, the tank diameter D of the horizontal drawing tank is greater than or equal to 100*a, wherein a is the major axis of the elliptical cross section spring steel wire; and the spring steel wire is arranged and wound along the axial direction of the horizontal drawing tank. The application can ensure that the size precision, surface quality and mechanical properties of the elliptical cross section spring steel wire meet the use requirements of springs, and simultaneously improve the production efficiency and reduce the production cost.

Description

Technical Field

[0001] This application relates to the field of metal wire drawing technology, and in particular to a cold drawing forming method for spring steel wire with an elliptical cross-section. Background Technology

[0002] Elliptical cross-section springs are widely used in high-performance applications such as valve springs for high-power engines due to their advantages in installation space, stress distribution, and lightweight design. However, the multi-pass cold drawing process for elliptical cross-section steel wire is far more difficult than that for circular cross-section steel wire. Existing technologies mainly suffer from the following problems: 1) Cross-sectional accuracy is difficult to control, easily leading to lateral bending, distortion, and out-of-tolerance dimensional deviations; 2) Surface defects such as "bamboo-like" patterns and microcracks are easily generated during the drawing process, seriously affecting the fatigue life of the spring; 3) Poor process stability, rapid die wear, and difficulty in achieving high-efficiency and high-consistency mass production.

[0003] Therefore, developing a forming process that can simultaneously guarantee the dimensional accuracy, surface quality, mechanical properties, and production stability of elliptical cross-section steel wire has significant engineering application value. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art.

[0005] This application proposes a cold drawing forming method for spring steel wire with an elliptical cross section. By optimizing the design of the elliptical cross section parameters and the mold cavity structure, and by designing precise directional control for continuous multi-pass drawing of the elliptical cross section, high precision, high stability, and mass production of the elliptical cross section steel wire are achieved. This ensures that the dimensional accuracy, surface quality, and mechanical properties of the finished steel wire meet the requirements for spring use, while improving production efficiency and reducing production costs.

[0006] According to an embodiment of this application, a cold drawing method for spring steel wire with an elliptical cross-section is proposed, comprising the following steps:

[0007] The round steel wire is subjected to peeling, annealing, shot blasting and electrolytic phosphating in sequence to form a phosphating film with a thickness of 5-8 μm on the surface of the round steel wire;

[0008] Design at least three elliptical drawing dies and install and position the drawing dies; wherein, the single-pass compression ratio of round wire is ≤25%, the single-pass compression ratio of elliptical wire is ≤16%, and the difference in compression ratio between adjacent passes is ≤5%;

[0009] A horizontal wire drawing can with a chrome-plated and polished surface is used. The diameter of the horizontal wire drawing can is D≥100×a, where a is the major axis of the elliptical cross-section of the spring steel wire. The spring steel wire is arranged, wound, and coiled along the axial direction of the horizontal wire drawing can.

[0010] In some embodiments, the carbon content of the round steel wire is 0.51-0.67%;

[0011] And / or; during the stripping process of the round steel wire, the reduction in the cross-section of the round steel wire is controlled to be 0.27mm-0.33mm.

[0012] In some embodiments, the drawing die has a progressive cavity structure; wherein the cavity of the drawing die for each pass includes an inlet area, a working area, a sizing area, and an outlet area; and the cavity tolerance of the drawing die for each pass is 1 / 2 of the spring steel wire tolerance, to compensate for an elastic rebound of 0.005-0.01mm.

[0013] In some embodiments, the ratio of the major axis a to the minor axis b of the elliptical cross-section of the spring steel wire is 1.2-1.5, and the fillet radius r is 0.3-0.8 mm; the tolerance of the major axis a and the minor axis b is controlled at ±0.02 mm, corresponding to the tolerance of the die cavity of the drawing die at ±0.01 mm.

[0014] In some embodiments, the angle α of the inlet region is 15-20°, the length L1 is (3-5)×b, and the inner wall roughness Ra≤0.05μm;

[0015] The angle β of the working area is 8-12°, and the length L2 is (0.8-1.2)×a;

[0016] The length L3 of the sizing zone is (0.5-0.8)×b;

[0017] The angle γ of the outlet area is 25-30°, and the length L4 is (2-3)×b; where a is the major axis of the elliptical cross-section of the spring steel wire; and b is the minor axis of the elliptical cross-section of the spring steel wire.

[0018] In some embodiments, the round steel wire is first drawn in multiple passes and then drawn into elliptical wire, wherein the drawing speed is 1.5-1.8 m / s; the compression rate of the round wire in a single pass is ≤25%; when the diameter of the drawn round steel wire is equal to the major axis dimension of the first elliptical drawing die plus 0.20 mm, aging treatment is performed for more than 48 hours, and then elliptical wire drawing is performed; during the elliptical wire drawing process, the compression rate of the elliptical wire in a single pass is ≤16%, and the difference in compression rate between adjacent passes is ≤5%.

[0019] In some embodiments, composite lubrication is performed during the drawing process of the round steel wire; this includes covering the inlet area of ​​the drawing die with calcium-based lubricating powder, using the phosphating film to form a continuous lubricating film with a thickness ≥2μm in the working area of ​​the drawing die, and controlling the temperature of the horizontal wire drawing can to be less than 40°C.

[0020] In some embodiments, the die sleeve of the drawing die is machined with a positioning keyway, the direction of which is consistent with the major axis of the die hole ellipse and mates with the positioning key of the wire drawing machine die base.

[0021] In some embodiments, the thickness of the chrome plating on the surface of the horizontal wire drawing can is 5-10 μm, and the surface roughness Ra ≤ 0.2 μm; the height H of the end flanges of the can is equal to the short axis b + (2-3) mm.

[0022] In some embodiments, the positioning keyway ensures that the long axis deviation of the drawing die for each pass is ≤0.5°, and the coaxiality between the centerline of the drawing die and the centerline of the spindle of the wire drawing machine is ≤0.01mm / m.

[0023] Compared with existing elliptical cross-section steel wire drawing processes, this application has the following significant advantages:

[0024] 1. Significantly improved dimensional accuracy: Through precise elliptical cross-section parameter design, mold cavity springback compensation, and mold installation positioning, the long / short axis tolerance of the finished steel wire can be stably controlled within ±0.02mm, effectively avoiding problems such as side bending and cross-section distortion, and meeting the accuracy requirements of valve springs for high-power engines;

[0025] 2. Stable and reliable product performance: Multi-pass progressive drawing, reasonable compression ratio and speed control, combined with a composite lubrication scheme, effectively avoids defects such as "bamboo pattern" and micro-cracks, and the fatigue life of the steel wire can reach 10 years. 7 No breakage occurred during the second cycle, and the mechanical properties meet the requirements for high-temperature and high-frequency vibration use of valve springs;

[0026] 3. High process stability: Optimized mold cavity structure, mold material and heat treatment process improve the wear resistance and impact resistance of the mold and reduce the risk of mold breakage; optimized wire drawing can layout avoids steel wire extrusion deformation.

[0027] 4. High production efficiency: The multi-pass continuous drawing process improves production efficiency compared to single-pass drawing, enabling mass production while reducing production costs.

[0028] 5. Strong applicability: The process parameters can be flexibly adjusted according to different specifications of elliptical cross-section steel wire, and it can be applied to other fields that require high-precision elliptical cross-section steel wire.

[0029] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 This is a flowchart of a cold drawing forming method for spring steel wire with an elliptical cross-section according to this application. Detailed Implementation

[0032] Embodiments of this application are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, this application includes all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0033] According to embodiments of this application, a cold drawing method for spring steel wire with an elliptical cross-section is proposed, such as... Figure 1 As shown, it includes the following steps:

[0034] S1: The round steel wire is subjected to peeling, annealing, shot blasting and electrolytic phosphating in sequence to form a phosphating film with a thickness of 5-8μm on the surface of the round steel wire;

[0035] S2: Design at least three elliptical drawing dies and install and position the drawing dies; wherein, the single-pass compression rate of round wire is ≤25%, the single-pass compression rate of elliptical wire is ≤16%, and the difference in compression rate between adjacent passes is ≤5%;

[0036] S3: A horizontal wire drawing can with a chrome-plated and polished surface is adopted. The diameter D of the horizontal wire drawing can is ≥100×a, where a is the major axis of the elliptical cross section of the spring steel wire; the spring steel wire is arranged, wound and wound along the axial direction of the horizontal wire drawing can.

[0037] In S1, the carbon content of the round steel wire is 0.51-0.67%. This means that round steel wire with a carbon content of 0.51-0.67% is selected as raw material for peeling. During the peeling process, the reduction in cross-section of the round steel wire is controlled to be 0.27mm-0.33mm to remove the surface oxide layer and defects, ensuring a smooth surface. The peeled round steel wire is then annealed to eliminate internal stress and improve plasticity, laying the foundation for subsequent cold drawing. Next, shot blasting is used to remove residual oxide scale and impurities from the surface of the round steel wire, further purifying the surface. Finally, the round steel wire is electrolytically phosphated using a zinc-based phosphating solution to form a dense phosphate film 5-8μm thick on its surface, which adsorbs lubricating grease and ensures subsequent lubrication.

[0038] In S2, at least three elliptical drawing dies are designed. To meet the performance requirements of the spring steel wire (stiffness, installation space, stress distribution), key parameters of the elliptical cross-section are defined: the ratio of the major axis (a) to the minor axis (b) of the spring steel wire is controlled between 1.2 and 1.5. This is verified through spring steel wire stress simulation to avoid the round steel wire bending during drawing if the ratio is too large, and the stress optimization advantage of the elliptical cross-section cannot be reflected if the ratio is too small. In addition, the major and minor axes of the elliptical cross-section of the spring steel wire are designed with rounded corners r, set to 0.3-0.8mm, to avoid stress concentration at the sharp corners of the cross-section that could lead to cracking during drawing, and to match the bending radius during spring coiling. Finally, the cavity tolerance of the drawing die is stricter than that of the spring steel wire, taking 1 / 2 of the spring steel wire tolerance. The major / minor axis tolerance of the spring steel wire is controlled at ±0.02mm, corresponding to a cavity tolerance of ±0.01mm for the drawing die, used to compensate for the 0.005-0.01mm elastic rebound of the steel wire after drawing.

[0039] In some embodiments, the drawing die has a progressive cavity structure; wherein the cavity of each drawing die includes an inlet area, a working area, a sizing area, and an outlet area. For example, this embodiment adopts a multi-pass (3-5 passes) progressive cavity structure, and the cavity structure of each drawing die is designed according to "progressive deformation", wherein the cavity of each drawing die includes an inlet area, a working area, a sizing area, and an outlet area. The design points and functions of each area are as follows:

[0040] The angle α of the entrance area is 15-20°, the length L1 is (3-5)×b, and the inner wall is polished with a roughness Ra≤0.05μm; this guides the wire to enter smoothly and reduces friction and scratches at the entrance.

[0041] The working area has an angle β of 8-12° (β is slightly larger on the major axis side of the ellipse to ensure uniform deformation), and a length L2 of (0.8-1.2)×a; to achieve plastic deformation of the wire, control the deformation rate, and avoid excessive local stress leading to cracks;

[0042] The length L3 of the sizing zone is (0.5-0.8)×b; the size is consistent with that of the spring steel wire (including springback compensation) to ensure the cross-sectional dimensional accuracy of the spring steel wire and correct minor deviations in the deformation zone;

[0043] The angle γ of the exit area is 25-30°, and the length L4 is (2-3)×b; where a is the major axis of the elliptical cross-section of the spring steel wire; and b is the minor axis of the elliptical cross-section of the spring steel wire.

[0044] To ensure the directionality of the elliptical cross-section, the drawing die installation requires strict positioning. The die sleeve of the drawing die is machined with a positioning keyway, the direction of which is consistent with the major axis of the elliptical die hole and mates with the positioning key of the wire drawing machine die holder. This ensures that the major axis direction of the die is consistent for each pass, with a deviation ≤0.5°. Then, calibration is performed using a dial indicator. The dial indicator is fixed to the main shaft of the wire drawing machine, with the indicator tip contacting the inner hole of the drawing die. The position of the drawing die is adjusted so that the coaxiality between the centerline of the drawing die and the centerline of the wire drawing machine main shaft is ≤0.01mm / m, preventing uneven force on the steel wire during drawing, which could lead to lateral bending and dimensional deviations.

[0045] In some embodiments, the round steel wire is first drawn in multiple passes and then drawn into elliptical wire, wherein the drawing speed is 1.5-1.8 m / s; the compression rate of the round wire in a single pass is ≤25%; when the diameter of the drawn round steel wire is equal to the major axis dimension of the first elliptical drawing die plus 0.20 mm, aging treatment is performed for more than 48 hours, and then elliptical wire drawing is performed; during the elliptical wire drawing process, the compression rate of the elliptical wire in a single pass is ≤16%, and the difference in compression rate between adjacent passes is ≤5%.

[0046] For example, multi-pass cold drawing forming adopts a step-by-step drawing method of "round wire drawing → elliptical wire drawing", with a total of 2-4 elliptical die drawing passes. The specific parameters are controlled as follows:

[0047] Following the principle of "larger first, smaller later, and uniformly decreasing", the single-pass compression rate of the round steel wire is ≤25%. After the round steel wire is drawn into a semi-finished product, it undergoes aging treatment for more than 48 hours, and then the elliptical wire is drawn. The single-pass compression rate of the elliptical wire is ≤16%, and the difference in compression rate between adjacent passes is ≤5% to avoid stress abrupt changes that could cause the steel wire to break or have surface defects. The diameter of the semi-finished round steel wire is equal to the diameter of the first elliptical die + 0.20mm.

[0048] The drawing speed is controlled at 1.5-1.8 m / s throughout the process to balance frictional heat and lubrication, avoiding excessive speed leading to "over-deformation" or "insufficient forming," or excessive speed leading to "bulging" or "localized oxidation," ensuring consistent material deformation within the die. In addition, composite lubrication is applied during the drawing process of round steel wire, including covering the entrance area of ​​the drawing die with calcium-based lubricating powder, using a phosphate film to form a continuous lubricating film with a thickness of ≥2μm in the working area of ​​the drawing die, and controlling the temperature of the horizontal wire drawing can to be less than 40℃ to reduce frictional wear between the die and the steel wire and avoid surface scratches.

[0049] In S3, the diameter D of the horizontal wire drawing can is ≥100×a, where a is the major axis of the elliptical cross-section of the spring steel wire. This avoids excessively small bending radius during wire winding, which could lead to plastic deformation and affect the fatigue life of the spring. The thickness of the chrome plating on the surface of the horizontal wire drawing can is 5-10μm, and the surface roughness Ra is ≤0.2μm. This improves wear resistance and reduces scratches on the wire surface. The height H of the end flanges of the can is equal to the minor axis b + (2-3) mm. For example, if b = 3.5 mm, H = 5.5-6.5 mm to prevent the wire from coming off. In addition, the arrangement of "major axis along the axial direction of the wire drawing can" is adopted to increase the contact area between the wire and the can surface, improve winding stability, and avoid slippage and extrusion deformation. Finally, the spring steel wire with an elliptical cross-section after drawing is guided and then wound onto the I-beam of the take-up device to complete the entire cold drawing forming process.

[0050] Therefore, this application optimizes the elliptical cross-section parameter design of the drawing die and the die cavity compensation scheme, combining the elastic rebound amount to precisely control the die cavity size of the drawing die, solving the technical problems of low cross-sectional accuracy, side bending, and distortion of spring steel wire. In addition, this application designs at least three-pass elliptical drawing dies, combined with reasonable compression ratio and drawing speed control, to avoid defects such as "bamboo pattern" and micro-cracks in spring steel wire, and improve the fatigue life of spring steel wire. At the same time, it adapts to the precise installation and positioning scheme of the drawing die to ensure the stability and installation accuracy of the die, and reduce surface scratches and dimensional deviations. Finally, by combining composite lubrication during the round steel wire drawing process with the optimized arrangement of horizontal wire drawing cans with chrome-plated and polished can surfaces, it balances surface quality and production efficiency, achieving damage-free, orderly winding and mass production of spring steel wire with an elliptical cross-section.

[0051] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0052] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for cold drawing and forming a spring steel wire with an elliptical cross-section, characterized in that, Includes the following steps: The round steel wire is subjected to peeling, annealing, shot blasting and electrolytic phosphating in sequence to form a phosphating film with a thickness of 5-8 μm on the surface of the round steel wire; Design at least three elliptical drawing dies and install and position the drawing dies; wherein, the single-pass compression ratio of round wire is ≤25%, the single-pass compression ratio of elliptical wire is ≤16%, and the difference in compression ratio between adjacent passes is ≤5%; A horizontal wire drawing can with a chrome-plated and polished surface is used. The diameter of the horizontal wire drawing can is D≥100×a, where a is the major axis of the elliptical cross-section of the spring steel wire. The spring steel wire is arranged, wound, and coiled along the axial direction of the horizontal wire drawing can.

2. The cold drawing forming method according to claim 1, characterized in that, The carbon content of the round steel wire is 0.51-0.67%; And / or; during the stripping process of the round steel wire, the reduction in the cross-section of the round steel wire is controlled to be 0.27mm-0.33mm.

3. The cold drawing forming method according to claim 1, characterized in that, The drawing die has a progressive cavity structure; each drawing die cavity includes an inlet area, a working area, a sizing area, and an outlet area; and the cavity tolerance of each drawing die is 1 / 2 of the spring steel wire tolerance to compensate for 0.005-0.01mm of elastic rebound.

4. The cold drawing forming method according to claim 1, characterized in that, The ratio of the major axis a to the minor axis b of the elliptical cross-section of the spring steel wire is 1.2-1.5, and the fillet radius r is 0.3-0.8mm; the tolerance of the major axis a and the minor axis b is controlled at ±0.02mm, and the tolerance of the cavity of the drawing die is ±0.01mm.

5. The cold drawing forming method according to claim 3, characterized in that, The angle α of the entrance area is 15-20°, the length L1 is (3-5)×b, and the inner wall roughness Ra≤0.05μm; The angle β of the working area is 8-12°, and the length L2 is (0.8-1.2)×a; The length L3 of the sizing zone is (0.5-0.8)×b; The angle γ of the outlet area is 25-30°, and the length L4 is (2-3)×b; where a is the major axis of the elliptical cross-section of the spring steel wire; and b is the minor axis of the elliptical cross-section of the spring steel wire.

6. The cold drawing forming method according to claim 1, characterized in that, The round steel wire is first drawn in multiple passes and then drawn into an elliptical wire, with a drawing speed of 1.5-1.8 m / s; The compression rate of the round wire in a single pass is ≤25%. When the diameter of the drawn round steel wire is equal to the major axis dimension of the first pass elliptical drawing die plus 0.20mm, an aging treatment is performed for more than 48 hours before elliptical wire drawing. During the elliptical wire drawing process, the compression rate of the round steel wire in a single pass is ≤16%, and the difference in compression rate between adjacent passes is ≤5%.

7. The cold drawing forming method according to claim 3, characterized in that, The round steel wire drawing process involves compound lubrication, including covering the inlet area of ​​the drawing die with calcium-based lubricating powder, using the phosphate film to form a continuous lubricating film with a thickness ≥2μm in the working area of ​​the drawing die, and controlling the temperature of the horizontal wire drawing can to be less than 40℃.

8. The cold drawing forming method according to claim 1, characterized in that, The drawing die sleeve is machined with a positioning keyway, the direction of which is consistent with the major axis of the die hole ellipse and mates with the positioning key of the wire drawing machine die base.

9. The cold drawing forming method according to claim 4, characterized in that, The thickness of the chrome plating on the surface of the horizontal wire drawing can is 5-10μm, and the surface roughness Ra≤0.2μm; the height H of the end flanges of the can is equal to the short axis b + (2-3) mm.

10. The cold drawing forming method according to claim 8, characterized in that, The positioning keyway ensures that the long axis deviation of the drawing die for each pass is ≤0.5°, and the coaxiality between the centerline of the drawing die and the centerline of the main shaft of the wire drawing machine is ≤0.01mm / m.

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