Manufacturing process of flat wire spring

Abstract

The invention discloses a manufacturing process of a high-strength fatigue-resistant flat wire spring. The manufacturing process comprises six key steps of drawing, spring coiling, annealing, grinding, pre-pressing and shot blasting. After an SUS631 stainless steel round wire is subjected to drawing forming, the content of retained austenite is reduced to be lower than 5% through a gradient annealing process at the temperature of 480-620 DEG C, and the stress relaxation resistance is remarkably improved by combining 5-10 times of progressive pre-pressing treatment with the loading rate being smaller than or equal to 10 mm / min. A pre-cooling medium of 0.1-0.5 mm is innovatively adopted to carry out shot peening strengthening with the coverage rate of 200-300% in the environment of 20-25 DEG C, a gradient residual compressive stress layer is formed through multi-angle impact of 30-90 degrees, surface microcracks are effectively closed, and the influence of a decarburized layer is reduced. According to the process, the spring has the characteristics of high strength, excellent high and low temperature resistance, ultra-long fatigue life and stress relaxation resistance.

Description

Technical Field

[0001] This application relates to the technical field of springs, and more specifically, it relates to a manufacturing process for flat wire springs. Background Art

[0002] Due to its unique cross-sectional shape and mechanical properties, flat wire springs are widely used in the electronics industry in scenarios that require high space utilization, stable contact pressure, or special mechanical responses.

[0003] Flat wire springs are widely used, so springs are required in many extreme fields. For example, in high-temperature environments of 85 to 200 °C such as in transformers, electric meters, engine ECUs, turbocharger sensors, spring connectors in battery management systems (BMS), and in low-temperature environments of -50 °C - (-200 °C) such as circuit connection springs in satellites or deep space probes, support structures for superconducting coils in liquid helium environments, and battery contact springs in polar communication base stations. Currently, flat wire springs have a problem of rapid attenuation in high-temperature or low-temperature environments, resulting in a low service life of the equipment. Therefore, there is an urgent need to propose a process for manufacturing flat wire springs to reduce the attenuation of flat wire springs in high-temperature and low-temperature environments and improve the service life of the equipment. Summary of the Invention

[0004] To solve the problem that the attenuation of flat wire springs is relatively rapid in high-temperature and low-temperature environments, resulting in a low service life of the equipment, this application provides a manufacturing process for flat wire springs.

[0005] A manufacturing process for flat wire springs includes the following steps:

[0006] Step S1: Drawing, forming a flat wire by drawing a metal round wire, and the metal round wire is selected as SUS631 stainless steel;

[0007] Step S2: Spring coiling, coiling the flat wire into a spring according to the helix direction, prefabricated height, outer diameter, and number of turns, and clamping the two ends of the spring; Annealing, placing the obtained flat wire in a temperature environment of 480 °C - 620 °C, keeping it warm for 1 - 2 h, cooling it at a rate of 5 °C / min to 350 °C and then keeping it warm for 30 min, and then air-cooling to room temperature;

[0008] Step S3: Annealing, placing the obtained flat wire in a temperature environment of 480 °C - 620 °C, keeping it warm for 1 - 2 h, cooling it at a rate of 5 °C / min to 350 °C and then keeping it warm for 30 min, and then air-cooling to room temperature;

[0009] Step S4: Grinding, grinding the two end faces of the spring to make the two end faces of the spring flat and perpendicular to its own axis;

[0010] Step S5: Preloading. Apply pressure along the axial direction of the spring to cause plastic deformation of the spring. The loading rate is ≤ 10 mm / min, the number of pressurizations is 5 - 10 times, and each pressurization compresses the spring to the required length and holds for 5 - 30 minutes. Also, the unloading rate each time is the same as the loading rate.

[0011] Step S6: Shot peening. Under a pressure of 0.2 - 0.6 MPa, shot peen the spring for 1 - 5 minutes, with a shot peening coverage rate of 200% - 300%, a shot peening angle of 30° - 90°, a shot peening medium diameter of 0.1 - 0.5 mm, and the temperature in the shot peening chamber is maintained at 20 - 25°C, and the medium is pre-cooled to -10°C.

[0012] Preferably, the tensile strength of the SUS631 stainless steel is selected to be 1400 - 1800 MPa.

[0013] Preferably, the drawing process adopts a three-gradient shape-controlled drawing process. The first gradient uses a drawing die with a film hole compression ratio of 18% and is carried out in an environment of 80°C ± 10°C. The second gradient uses a drawing die with a film hole compression ratio of 12% and is carried out in an environment of 280°C ± 10°C. The third gradient uses a drawing die with a film hole compression ratio of 6% and is carried out at room temperature.

[0014] Preferably, the preloading is 2 - 3 times of static preloading and 3 - 5 times of dynamic preloading.

[0015] Preferably, the final shot peening medium in step S3 is steel shot, ceramic shot, and glass beads. Coarse shot peening is carried out for 2 minutes using 0.5 mm steel shot, fine shot peening is carried out for 1.5 minutes using 0.3 mm ceramic shot, and final shot peening is carried out for 0.5 minutes using 0.1 mm glass beads.

[0016] The beneficial technical effects of this application are as follows: By selecting SUS631 stainless steel as the base material, the flat wire has good high and low temperature resistance, corrosion resistance and high strength, which is beneficial for the spring to have high strength while being relatively resistant to high and low temperatures and corrosion. The coiled spring operation realizes spring forming. Through an innovative annealing process, the retained austenite content of the SUS631 stainless steel material is reduced to less than 5%, eliminating internal stress and stabilizing the structure, making the spring not easily deformed at high and low temperatures. The grinding operation is convenient for improving the reliability during spring installation. Through preloading treatment, the spring is formed into the required length, and the strategy of slow loading and multiple loading enhances the anti-relaxation ability of the spring, reducing attenuation during long-term use. By impacting the spring surface with shot peening medium, plastic deformation occurs on the surface layer while the inner layer remains elastic, forming a residual compressive stress layer on the spring surface to offset the tensile stress during work, delaying the initiation and propagation of fatigue cracks, and significantly improving the fatigue life. Using a shot peening medium of 0.1 - 0.5 mm can close or reduce defects such as microcracks and scratches on the spring surface, and reduce the negative impact of the decarburized layer, improving surface hardness and strength, enhancing the anti-deformation ability, and improving the load-bearing performance. Description of the Drawings

[0017] Figure 1 It is a flowchart of the manufacturing process of a flat wire spring according to this embodiment. Detailed Embodiments

[0018] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0019] Refer to Figure 1, A manufacturing process for a flat wire spring, comprising the following steps. Step S1: Drawing. A wire drawing machine is used to draw a metal round wire with a diameter of 1.33 mm ± 0.015 mm into a flat wire with a thickness of 0.79 mm ± 0.01 mm and a width of 1.6 mm ± 0.01 mm. The metal round wire is made of SUS631 stainless steel with a tensile strength of 1400 - 1800 MPa. The wire drawing process adopts a three-gradient shape control drawing process. Specifically, in the first gradient, a drawing die with a film hole compression ratio of 18% is used and carried out in an environment of 80℃ ± 10℃. In the second gradient, a drawing die with a film hole compression ratio of 12% is used and carried out in an environment of 280℃ ± 10℃. In the third gradient, a drawing die with a film hole compression ratio of 6% is used and carried out at room temperature. By selecting SUS631 stainless steel with a tensile strength of 1400 - 1800 MPa as the base material, SUS631 stainless steel has good high and low temperature resistance, corrosion resistance and high strength, so that the formed spring has high strength while being relatively resistant to high and low temperatures and corrosion. Combining with the three-gradient shape control drawing process (18% / 12% / 6% compression ratio gradient), the microstructural density is significantly improved while maintaining the high strength of the material. Through experimental verification, this process can refine the grain size of the flat wire to above ASTM 12 level, and the hardness deviation of the cross section ≤ 3%, effectively avoiding the stress concentration and microcrack problems caused by traditional single drawing. It should be noted that during the drawing process, after each stage of drawing, a measuring tool is used to measure the size of the flat wire to ensure that the flat wire is within the specified range after each drawing, and the surface quality of the flat wire is inspected to prevent surface scratches and wrinkles caused by die wear;

[0020] Step S2: Spring coiling. The flat wire is installed on a numerical control spring coiling machine, and the flat wire is coiled into a spring according to the helix direction, preformed height, outer diameter and number of turns by the numerical control spring coiling machine. The two ends of the spring are tightened. In this embodiment, the helix direction of the spring is clockwise, the preformed height is 25 ± 0.5 mm, the outer diameter is 8.0 mm ± 0.01 mm, and the number of turns is 9.5 turns;

[0021] Step S3, Annealing. The spring obtained in step S2 is placed in a temperature environment of 480℃ - 620℃ and kept warm for 1 - 2 h. In this embodiment, the preferred holding temperature is 480℃ and the holding time is 1 h. Then it is cooled at a rate of 5℃ / min to 350℃ and kept warm for 30 min, and finally air-cooled to room temperature to anneal the spring. The annealing process in this embodiment reduces the retained austenite content of the SUS631 stainless steel material to less than 5%, eliminates the internal stress of the spring, stabilizes the structure, and is beneficial for the spring not to deform easily at high and low temperatures;

[0022] Step S4: Grinding. Use a spring grinder to grind and grind the two end faces of the made spring, so that the two end faces are flat and perpendicular to its own axis. During grinding, it should be noted that the amount of grinding each time should not be too large to prevent the spring from overheating and deforming. The grinding operation is convenient for improving the reliability of the spring during installation;

[0023] Step S5: Preloading. Install the ground spring on a spring preloading machine. The spring is statically preloaded 2 - 3 times (selected as 3 times in this embodiment) and then dynamically preloaded 3 - 5 times (selected as 5 times in this embodiment) through the spring preloading machine. The static pressure is to apply a constant pressure to the spring to compress the spring to 21.75 ± 0.5 mm and keep it for 30 minutes. The pressure loading rate is 10 mm / min, the pressure is 170 N, and the unloading rate is 10 mm / min. The dynamic pressure is to apply a cyclic load to the spring using an alternating load. Specifically, a pressure of 150 N is used, and the spring is compressed to 21.75 ± 0.5 mm at a pressure loading rate of 10 mm / min and kept for 2 minutes. Then, at the same loading rate, the spring is compressed to 21.75 ± 0.5 mm with a pressure of 160 N and kept for 2 minutes. Finally, at the same loading rate, the spring is compressed to 21.75 ± 0.5 mm with a pressure of 170 N and kept for 2 minutes, and then the cycle repeats. The number of cycles for each dynamic load is 5 times, and the unloading rate for each time is 10 mm / min. Through the innovative static-dynamic combined preloading process of static plus dynamic, the misalignment and rearrangement of spring grains and grain boundary strengthening are realized, which is beneficial to the spring maintaining a high fatigue life in high and low temperature environments;

[0024] Step S6: Shot Peening. After the spring is ultrasonically cleaned or chemically cleaned to remove stains, dust and other impurities on the material surface, the spring is placed in a shot peening device for shot peening treatment. Specifically, the temperature in the shot peening chamber is maintained at 20 - 25 °C, and 0.5 mm steel shot is sprayed on the spring surface at a pressure of 0.45 Mpa, the spraying angle is 45°, the coverage rate is 200%, and the spraying time is 2 min. The steel shot is pre-cooled to -10 °C to achieve rough shot peening of the spring. Then, 0.3 mm ceramic shot is sprayed on the spring surface at a pressure of 0.25 Mpa, the spraying angle is 75°, the coverage rate is 180%, and the spraying time is 1.5 min. The ceramic shot is pre-cooled to -10 °C to achieve fine shot peening of the spring. Finally, 0.1 mm glass shot is sprayed on the spring surface at a pressure of 0.15 Mpa, the spraying angle is 90°, the coverage rate is 150%, and the spraying time is 0.5 min. The glass shot is pre-cooled to -10 °C to achieve final shot peening of the spring. The composite shot peening process (three-stage treatment of steel shot + ceramic shot + glass beads) used in this step forms a gradient strengthening layer on the surface: surface nanocrystalline layer (<50 nm) + subsurface twin layer (200 - 500 nm) + dislocation strengthening layer (1 - 2 μm), which significantly improves the comprehensive performance of the spring in an extreme stable environment.

[0025] The spring prepared by the above process and the springs of the same specifications commercially available were subjected to elastic force detection, close compression detection, high and low temperature fatigue life test, salt spray test and comparison. The results are as follows:

[0026] Elastic force detection: In the first stage of the test, the spring prepared by the process of the present application and the commercially available spring were respectively placed on a high-precision dynamometer, and the spring was compressed to 17.9 mm. The elastic force value of the spring prepared by the process of the present application was 35 N, and the elastic force value of the commercially available spring was 35 N; in the second stage of the test, the spring was continuously compressed to 11.7 mm. The elastic force value of the spring prepared by the process of the present application was 95 N, and the elastic force value of the commercially available spring was 95 N.

[0027] Close compression detection: The spring prepared by the process of the present application and the commercially available spring were both compressed to the close compression height of 9.2 mm and maintained for 10 s. The spring prepared by the process of the present application had no deformation, fracture, or abnormal coiling, while the commercially available spring showed deformation.

[0028] High and low temperature fatigue life test: The spring prepared by the process of the present application and the commercially available spring were both compressed to 11.7 mm and placed in a temperature control box. The temperature in the temperature control box was set to -25 °C and maintained for 3 hours. After 3 hours, the temperature was set to 70 °C and maintained for another 3 hours. The above operation was repeated five times. Then the spring was taken out for elastic force test. When the spring prepared by the process of the present application was compressed to 17.9 mm, the elastic force value was 33 N, and when compressed to 11.7 mm, the elastic force value was 92 N. When the commercially available spring was compressed to 17.9 mm, the elastic force value was 20 N, and when compressed to 11.7 mm, the elastic force value was 70 N. The elastic force attenuation rate of the spring prepared by the process of the present application was less than 5%, and the elastic force attenuation rate of the commercially available spring was much greater than 5%.

[0029] Salt spray test: The spring prepared by the process of the present application and the commercially available spring were both placed in a salt spray chamber, and the temperature was stably controlled at 35 ± 1 °C. The spray rate was controlled at 1 - 2 mL / (h·80 cm 2 ), and the spray solution was 5% NaCl solution with a pH of 6.5 - 7.2. The test period was 72 hours. The spring prepared by the process of the present application had no visible corrosion, and the corrosion grade was judged to be grade 10. The corrosion area of the commercially available spring was ≥ 5%, with obvious rust spots or coating peeling, and the corrosion grade was grade 3.

[0030] The spring prepared by the process of the present application has a lower attenuation amount in high and low temperature environments, and the spring prepared by the process of the present application has high corrosion resistance, which can improve the service life of the equipment.

[0031] Although the embodiments of the present application have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for a flat wire spring, characterized in that, It includes the following steps: Step S1: Drawing. A metal round wire is drawn to form a flat wire. The metal round wire is made of SUS631 stainless steel. Step S2: Spring coiling. The flat wire is coiled into a spring according to the helix direction, prefabricated height, outer diameter and number of turns, and the two ends of the spring are tightened. Annealing: The obtained flat wire is placed in a temperature environment of 480°C - 620°C, held for 1 - 2 h, cooled at a rate of 5°C / min to 350°C, then held for 30 min, and then air-cooled to room temperature. Step S3: Annealing. The obtained flat wire is placed in a temperature environment of 480°C - 620°C, held for 1 - 2 h, cooled at a rate of 5°C / min to 350°C, then held for 30 min, and then air-cooled to room temperature. Step S4: Grinding. The two end faces of the spring are ground to make the two end faces of the spring flat and perpendicular to its own axis. Step S5: Preloading. A pressure is applied to the spring along its axis to cause plastic deformation of the spring. The loading rate is ≤10 mm / min, the number of pressurizations is 5 - 10 times, each pressurization compresses the spring to the required length and holds for 5 - 30 minutes, and the unloading rate each time is the same as the loading rate. Step S6: Shot peening. Under a pressure of 0.2 - 0.6 MPa, the spring is shot peened for 1 - 5 min, and the shot peening coverage rate is 200% - 300%. The shot peening angle is 30° - 90°, the diameter of the shot peening medium is 0.1 - 0.5 mm, and the temperature of the shot peening chamber is maintained at 20 - 25°C, and the medium is pre-cooled to -10°C.

2. The manufacturing process of a flat wire spring according to claim 1, characterized in that: The tensile strength of the SUS631 stainless steel is selected to be 1400 - 1800 MPa.

3. The manufacturing process of a flat wire spring according to claim 1, characterized in that: The drawing process adopts a three-gradient shape control drawing process. The first gradient uses a drawing die with a film hole compression ratio of 18% and is carried out in an environment of 80°C ± 10°C. The second gradient uses a drawing die with a film hole compression ratio of 12% and is carried out in an environment of 280°C ± 10°C. The third gradient uses a drawing die with a film hole compression ratio of 6% and is carried out at room temperature.

4. The manufacturing process of a flat wire spring according to claim 1, characterized in that: The preloading is 2 - 3 times of static preloading and 3 - 5 times of dynamic preloading.

5. The manufacturing process of a flat wire spring according to claim 1, characterized in that: The final shot peening medium in step S3 is steel shot, ceramic shot and glass beads. Coarse shot peening is carried out with 0.5 mm steel shot for 2 min, fine shot peening is carried out with 0.3 mm ceramic shot for 1.5 min, and final shot peening is carried out with 0.1 mm glass shot for 0.5 min.

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