Production process of anti-relaxation coil spring

Abstract

The present application relates to the technical field of metal spring manufacturing, and discloses a production process of anti-loose spiral spring, comprising the following steps: step one: spring steel wire raw material screening and pretreatment, selecting spring steel wire coils meeting the component requirements, carrying out surface rust removal and phosphating saponification treatment, and obtaining surface clean steel wire to be drawn; step two: matrix fiber organization orientation prefabricated drawing, carrying out three-step drawing treatment of room temperature pre-drawing, medium-temperature phase change temperature control treatment and warm drawing setting on the steel wire obtained in step one, and obtaining finished product steel wire with directional fibrous sorbite organization; the production process of the anti-loose spiral spring effectively improves the size precision of spring finished products through whole-process closed-loop management and control, ensures that the size parameters of the spring meet the design requirements, simultaneously enhances the size stability, is not prone to obvious deformation after long-term service, and effectively improves the fatigue resistance of the spring by the cooperation of gradient compressive stress field and strong and tough matrix.

Description

Technical Field

[0001] This invention relates to the field of metal spring manufacturing technology, specifically to a production process for an anti-relaxation helical spring. Background Technology

[0002] As a core component for shock absorption, reset, and energy storage, helical springs are widely used in various mechanical equipment. Stress relaxation during long-term service is the core failure mode. Under constant / alternating loads, springs will undergo irreversible plastic deformation, resulting in a decrease in free height, a decrease in stiffness, and dimensional deviations, ultimately leading to a decrease in equipment accuracy, shock absorption failure, or even safety accidents.

[0003] Existing anti-relaxation processes have the following core defects:

[0004] 1. Relying solely on post-molding high-pressure treatment and single heat treatment cannot improve creep resistance at the matrix level. The fundamental problem of dislocation slip remains unresolved, and the relaxation rate remains high during long-term service.

[0005] 2. After traditional coil spring molding, the tensile stress in the inner coil of the spring is concentrated and the stress distribution is extremely uneven. Subsequent processing cannot completely eliminate the molding internal stress, which becomes the core source of relaxation failure.

[0006] 3. Single surface treatments such as shot peening and nitriding cannot form a stable gradient compressive stress field, resulting in poor adhesion between the modified layer and the substrate. During service, the compressive stress decays rapidly, and the anti-relaxation effect is not sustained.

[0007] 4. Each process step is independent of the others and there is no related coupling effect. It is impossible to achieve full-chain anti-slack control from substrate to molding to surface, making it difficult to meet the service requirements of more than 10 years in high reliability scenarios. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a manufacturing process for anti-relaxation helical springs, which solves the problem that existing technologies, such as high-pressure treatment and single heat treatment, cannot improve creep resistance and dislocation slippage at the matrix structure level after the product is formed.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the present invention provides the following technical solution: a manufacturing process for an anti-relaxation helical spring, comprising the following steps:

[0012] Step 1: Screening and pretreatment of spring steel wire raw materials. Select spring steel wire coils that meet the composition requirements, and perform surface rust removal, phosphating and saponification treatment to obtain clean steel wires to be drawn.

[0013] Step 2: Oriented pre-drawing of matrix fiber structure. The steel wire obtained in Step 1 is subjected to a three-step drawing process: room temperature pre-drawing, medium temperature phase transformation temperature control treatment, and temperature drawing and shaping, to obtain a finished steel wire with oriented fibrous sorbite structure.

[0014] Step 3: Wire straightening and length cutting. The finished wire obtained in Step 2 is straightened by multiple rollers using a CNC straightening machine, and then cut to length according to the spring design dimensions to obtain the wire section to be rolled.

[0015] Step 4: Integrated winding and pre-compression aging. A CNC spring winding machine with a constant load pre-compression mechanism is used to wind and shape the steel wire segment. At the same time, constant load pre-compression and medium frequency induction segmented aging treatment are carried out simultaneously during the winding process to obtain the spring blank.

[0016] Step 5: Stress-relief annealing of spring blanks. The spring blanks obtained in Step 4 are placed in a mesh belt annealing furnace for low-temperature stress-relief annealing to eliminate residual processing stress.

[0017] Step Six: Spring Dimensioning and Shaping with Forced Pressing. A CNC hydraulic forced press is used to perform multiple fixed-load forced pressing shaping processes on the annealed springs to lock the spring's free height and stiffness dimensions.

[0018] Step 7: Ultrasonic surface nano-modification pretreatment. Using an ultrasonic surface nano-modification device, the spring obtained in Step 6 is subjected to full-coverage ultrasonic impact treatment to form a nanocrystalline modified layer on the spring surface.

[0019] Step 8: Step-by-step controllable shot peening strengthening treatment. Using a CNC shot peening machine, the spring treated in Step 7 is subjected to a two-step step-by-step shot peening treatment, first with coarse shot and then with fine shot, to form a gradient deformation strengthening layer on the surface of the spring.

[0020] Step 9: Low-temperature ion nitriding composite modification treatment. The spring treated in Step 8 is placed in a low-temperature ion nitriding furnace for low-temperature ion nitriding treatment to form a hardened nitriding layer on the surface of the spring, thus completing the construction of the gradient stress field.

[0021] Step 10: Finished product performance testing and sorting. The springs processed in Step 9 are subjected to full testing of dimensions, stiffness, stress relaxation rate, and fatigue life. They are then sorted according to design requirements to obtain the finished anti-relaxation helical springs.

[0022] Preferably, the three-step drawing process described in step two is as follows: the deformation per pass in the room temperature pre-drawing is controlled at 8%-12%, and the drawing speed is controlled at 15-25 m / min; the medium-temperature phase transformation temperature control process uses a tubular continuous heating furnace, with the heating temperature controlled at 450-500℃ and the holding time controlled at 8-15s, to achieve ultra-fine pearlite lamellars inside the steel wire; the heating temperature for warm drawing and shaping is controlled at 350-400℃, the deformation per pass is controlled at 5%-8%, and the total deformation is controlled at 18%-25%; during the drawing process, an online metallographic monitoring device is used to sample and monitor the microstructure in real time to ensure the continuity and orientation of the sorbite fiber structure, and to refine the grain size to below 2μm.

[0023] Preferably, the multi-roller straightening in step three uses a 7-13 roll CNC straightening machine, with the tilt angle of the straightening rolls controlled at 1.5°-3° and the straightening speed controlled at 10-20m / min. The straightness of the straightened steel wire is ≤0.1mm / m. The fixed-length cutting uses a servo-guided shearing machine, with the cutting length tolerance controlled within ±0.2mm and the perpendicularity of the cut end face ≤0.05mm, to avoid end face misalignment during rolling.

[0024] Preferably, the CNC spring coiling machine with a fixed load preloading mechanism described in step four has an axial servo preloading cylinder coaxially mounted at the end of the spring coiling spindle. The pressure control accuracy of the preloading cylinder is ≤ ±0.5%. During coiling, after each coil of spring is completed, the preloading cylinder applies an axial preload of 30%-50% of the rated load to the coiled spring coil, and the holding time is controlled at 2-5 seconds. At the same time, a ring-shaped medium-frequency induction heating coil is used to synchronously segmentally heat the newly coiled spring coil, and the heating temperature is controlled at 280-320℃. The holding time is completely synchronized with the preloading holding time, realizing the integrated completion of coiling, preloading, and aging. After coiling, the pitch tolerance of the spring blank is controlled within ±0.1mm, and the inner diameter tolerance is controlled within ±0.15mm.

[0025] Preferably, the low-temperature stress-relief annealing treatment described in step five uses a mesh belt continuous annealing furnace, with high-purity nitrogen gas introduced into the furnace as a protective atmosphere, and an oxygen content of ≤50ppm to avoid oxidation and decarburization of the spring surface; the annealing temperature is controlled at 380-420℃, the holding time is controlled at 30-45min, and after annealing, forced air cooling is used to room temperature, with the cooling rate controlled at 5-10℃ / s.

[0026] Preferably, the constant load pressure shaping process described in step six uses a CNC servo hydraulic pressure press. The pressure load is 120%-150% of the spring's rated working load, the holding time for each pressure press is controlled at 10-30 seconds, and the number of pressure presses is 3-5 times. During the pressure press process, a high-precision laser displacement sensor is used to monitor the spring's free height in real time. The free height deviation after each pressure press is ≤0.05mm, and the free height tolerance of the final finished spring is controlled within ±0.2mm, and the stiffness tolerance is controlled within ±3%.

[0027] Preferably, the ultrasonic surface nano-sizing treatment described in step seven uses an ultrasonic frequency of 20-30kHz, an impact needle diameter of 2-5mm, and an impact amplitude of 30-50μm. The spring is clamped on a CNC rotary table with a rotation speed controlled at 5-15r / min. The ultrasonic impact gun moves along the spring axis at a speed of 2-5mm / s, and the angle between the impact gun and the spring surface is controlled at 45°-60°. The inner ring, outer ring, end face, and pitch gap of the spring are subjected to full-coverage impact treatment. After treatment, the thickness of the nanocrystalline layer on the spring surface is controlled at 50-100μm, and the surface grain size is ≤100nm.

[0028] Preferably, in step eight, the two-step shot peening process is as follows: the first step, coarse shot peening, uses cast steel shot with a diameter of 0.6-0.8 mm, a shot peening intensity of 0.3-0.4A, a shot peening coverage of 100%, and an effective shot peening reinforcement layer depth ≥0.2 mm; the second step, fine shot peening, uses stainless steel shot with a diameter of 0.2-0.3 mm, a shot peening intensity of 0.15-0.25A, and a shot peening coverage of 200%; the shot peening process uses a CNC multi-gun shot peening machine, and the spring rotates with the rotating fixture in a planetary motion to ensure that there are no dead angles in the inner ring and pitch of the spring, and the surface roughness Ra of the spring after shot peening is ≤1.6 μm.

[0029] Preferably, in the low-temperature ion nitriding treatment described in step nine, the vacuum degree in the nitriding furnace is controlled at 50-100 Pa, the working atmosphere is a mixture of ammonia and hydrogen in a volume ratio of 3:1; the nitriding temperature is controlled at 400-450℃, and the holding time is controlled at 4-6 h; after treatment, the thickness of the nitrided layer on the spring surface is controlled at 0.1-0.2 mm, the surface hardness is ≥650 HV, and the overall dimensional deformation is ≤0.03 mm.

[0030] Preferably, the stress relaxation rate test in step ten is performed using a high-temperature spring relaxation testing machine. The testing conditions are: ambient temperature of 120℃, application of the spring's rated working load, heat preservation and load preservation for 1000 hours, and a relaxation rate ≤1.2% is considered qualified. The fatigue life test is performed using an electromagnetic resonant spring fatigue testing machine, with an alternating load of 30%-70% of the rated working load, and 10^7 cycles. No fracture is considered qualified. After testing, an automatic sorting machine is used to classify and sort the springs according to their size and performance parameters, and reject unqualified products.

[0031] (III) Beneficial Effects

[0032] Compared with the prior art, the present invention provides a manufacturing process for anti-relaxation helical springs, which has the following beneficial effects:

[0033] 1. The production process of this anti-relaxation helical spring is controlled in a closed loop throughout the entire process, which effectively improves the dimensional accuracy of the finished spring and ensures that all dimensional parameters of the spring meet the design requirements. At the same time, it enhances dimensional stability and is less prone to significant deformation after long-term service. With the combined effect of gradient compressive stress field and strong and tough matrix, the fatigue resistance of the spring is effectively improved. Compared with springs made by traditional processes, the fatigue life is greatly extended and the service reliability is higher.

[0034] 2. The manufacturing process of this anti-relaxation helical spring is compatible with various specifications and grades of spring steel wire, and has a wide range of applications. It can meet the application needs of different fields such as automobiles, rail transportation, precision instruments, and aerospace. It is highly practical. The springs prepared by this process have excellent anti-relaxation performance and can effectively suppress stress relaxation during long-term service. It is significantly better than the relevant national standard requirements and can meet the long-term service requirements of high reliability scenarios. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] A manufacturing process for an anti-relaxation helical spring includes the following steps:

[0037] Step 1: Screening and Pretreatment of Spring Steel Wire Raw Materials

[0038] In the raw material selection process, it is necessary to select the corresponding grade of spring steel wire (such as 60Si2CrVA, 55CrSiA, 304 stainless steel, etc.) based on the actual service scenarios of the spring. The chemical composition of the steel wire must meet the GB / T1222 standard, and the surface must be free of defects such as cracks, folds, and rust. The original structure must be a uniform sorbite structure.

[0039] The surface pretreatment should be carried out according to the following procedure: First, the steel wire coil is mechanically derusted by shot blasting machine to completely remove the surface oxide scale; then, it is placed in a phosphating tank for phosphating treatment, with the phosphating temperature controlled at 50-60℃ and the phosphating time at 10-15 minutes, so that a uniform phosphating film is formed on the surface of the steel wire; finally, saponification treatment is carried out, with the saponification temperature maintained at 70-80℃ and the saponification time at 5-10 minutes, to form a lubricating layer to reduce the frictional resistance in the subsequent drawing process;

[0040] After pretreatment, the diameter tolerance of the steel wire is checked with a micrometer to ensure that it meets the requirements for subsequent drawing, and finally a clean and well-lubricated steel wire is obtained for drawing.

[0041] Step 2: Oriented pre-drawing of matrix fiber structure

[0042] This step is the core innovation point 1. The core objective is to achieve directional toughening of the matrix structure through three-step drawing. The supporting hardware includes a continuous drawing unit, a tubular continuous heating furnace, and an online metallographic monitoring device.

[0043] In the room temperature pre-drawing stage, the steel wire to be drawn is loaded into the continuous drawing unit to complete the first pass of room temperature drawing. The deformation amount of the pass is controlled at 8%-12%, and the drawing speed is 15-25m / min. Dislocations are introduced through cold deformation to prepare for subsequent phase transformation refinement.

[0044] In the medium-temperature phase change temperature control process, the pre-drawn steel wire is directly fed into a tubular continuous heating furnace, and the heating temperature is controlled at 450-500℃ and held for 8-15 seconds. Through precise temperature control, the pearlite lamellae are made ultra-fine while avoiding grain growth, laying the foundation for the formation of fiber structure.

[0045] In the warm drawing and shaping stage, the phase transformation treated steel wire is cooled to 350-400℃ and sent to the second warm drawing unit. The deformation amount per pass is 5%-8%, and the total deformation amount is controlled at 18%-25%. The warm deformation achieves the directional arrangement of dislocations, forming a continuous and directional fibrous sorbite structure.

[0046] During online monitoring, the online metallographic monitoring device takes samples every 5 minutes to monitor the internal structure of the steel wire in real time, ensuring the continuity of the sorbitic fiber structure, refining the grain size to below 2μm, and directly removing unqualified steel wires to ensure that the matrix meets the creep resistance standards.

[0047] Step 3: Straightening and Cutting the Wire to the Length

[0048] The hardware required for this step is a 7-13 roller CNC straightening machine and a servo-guided shearing machine.

[0049] In the multi-roller straightening operation, the finished steel wire is fed into the CNC straightening machine. The number of straightening rollers and the tilt angle are adjusted according to the wire diameter. The tilt angle is controlled between 1.5° and 3°, and the straightening speed is 10-20m / min. The bending stress of the steel wire is eliminated by continuous straightening with multiple rollers. After straightening, the straightness of the steel wire is ≤0.1mm / m, which avoids the spring coil from becoming eccentric during winding.

[0050] In the length-cutting stage, the straightened steel wire is fed into a servo-guided shearing machine. The cutting parameters are set according to the unfolded length designed by the spring to ensure that the cutting length tolerance is controlled within ±0.2mm and the perpendicularity of the cut end face is ≤0.05mm. After cutting, the end face burrs are removed to obtain the steel wire segment to be rolled.

[0051] Step 4: Integrated rolling and pre-compression aging

[0052] This step is the second core innovation point. The supporting hardware is a self-developed CNC spring coiling machine with a constant load preload mechanism. The core structure includes a spring coiling spindle, a wire feeding mechanism, a forming tool, a coaxial servo preload cylinder, a ring-shaped medium frequency induction heating coil, and a CNC control system.

[0053] During the equipment commissioning phase, the steel wire segments are loaded into the spring coiling machine. The forming cutter, wire feeding speed, and spindle speed are adjusted according to the inner diameter, pitch, and number of turns of the spring design. At the same time, the pressure parameters of the pre-pressure cylinder and the medium-frequency heating temperature are set.

[0054] The integrated molding operation process is as follows: After the spring coiling machine is started, the wire feeding mechanism sends the steel wire into the molding station, and the main shaft rotates to drive the steel wire to be coiled into shape; after each coil of spring is completed, the main shaft pauses for 0.5 seconds, and the coaxially set pre-pressure cylinder immediately extends to apply axial pre-pressure of 30%-50% of the rated load to the coiled spring coil, and holds the pressure for 2-5 seconds; at the same time, the annular medium frequency induction heating coil heats the spring coil synchronously, and the temperature is controlled at 280-320℃. The heat holding time is completely synchronized with the pre-pressure holding time, realizing a closed-loop process of single coiling, single coil pre-pressure, and single coil aging.

[0055] After forming, repeat the above operation until all spring coils are rolled to obtain a spring blank. During the rolling process, the CNC system monitors the inner diameter and pitch of the spring in real time to ensure that the pitch tolerance is within ±0.1mm and the inner diameter tolerance is within ±0.15mm. This step eliminates the internal stress of forming in advance through pre-compression aging during the forming process, locks the spring size, and reduces the slack allowance from the source.

[0056] Step 5: Stress-relieving annealing of spring blanks

[0057] The hardware required for this step is a mesh belt continuous annealing furnace and a nitrogen protection system.

[0058] When loading, place the spring blanks evenly on the mesh belt of the annealing furnace, leaving a gap of more than 5mm between the springs to avoid them colliding and deforming during the heating process.

[0059] In the annealing process, the annealing furnace is started and high-purity nitrogen is introduced as a protective atmosphere. The oxygen content in the furnace is controlled to be ≤50ppm to prevent oxidation and decarburization of the spring surface. The furnace temperature is raised to 380-420℃ and held for 30-45 minutes to completely eliminate residual processing stress from the rolling and pre-pressing processes.

[0060] During the cooling stage, after the heat preservation is completed, the spring blank is taken out of the furnace with the mesh belt and rapidly cooled to room temperature by forced air cooling. The cooling rate is controlled at 5-10℃ / s to avoid softening of the structure caused by slow cooling.

[0061] Step Six: Fine-tuning and Shaping of Spring Dimensions

[0062] The hardware required for this step includes a CNC servo hydraulic high-pressure press and a high-precision laser displacement sensor.

[0063] During equipment commissioning, set the pressure parameters, holding time, and number of press cycles of the press according to the rated working load of the spring. Install positioning fixtures at the upper and lower positions of the press to ensure that the coaxiality of the spring is ≤0.1mm when it is compressed.

[0064] During the shaping and pressing operation, the spring is placed in the positioning fixture, the press is started, and a pressing load of 120%-150% of the rated working load is applied. After holding the pressure for 10-30 seconds, the pressure is released to complete one pressing operation. This operation is repeated 3-5 times. After each pressing, the laser displacement sensor detects the free height of the spring in real time to ensure that the height deviation after each pressing is ≤0.05mm.

[0065] In the dimensional inspection stage, after the strong compression is completed, the free height, inner diameter, pitch and stiffness of the spring are fully inspected to lock the spring dimensional accuracy and ensure that the free height tolerance is ≤ ±0.2mm and the stiffness tolerance is ≤ ±3%.

[0066] Step 7: Ultrasonic Surface Nanoforming Pretreatment

[0067] This step is the pre-process of core innovation point 3, and the supporting hardware includes ultrasonic surface nano-sizing equipment, CNC rotary table, and multi-axis linkage robotic arm.

[0068] When clamping, the spring is vertically clamped on the CNC rotary table. The tooling uses an elastic chuck to avoid damaging the spring end face.

[0069] The parameter settings must meet the following requirements: set the frequency of the ultrasonic equipment to 20-30kHz, the diameter of the impact needle to 2-5mm, and the impact amplitude to 30-50μm; set the rotation speed of the rotary table to 5-15r / min, the speed at which the robotic arm drives the impact gun to move along the spring axis to 2-5mm / s, and the angle between the impact gun and the spring surface to 45°-60° to ensure coverage of all areas of the inner ring, outer ring, end face, and pitch gap of the spring.

[0070] During the impact treatment stage, after the equipment is started, the rotary table drives the spring to rotate, and the impact gun moves at a constant speed along the spring axis to perform full-coverage ultrasonic impact treatment on the spring. Through high-frequency impact, severe plastic deformation is introduced on the surface of the spring to form a nanocrystalline layer with a thickness of 50-100μm and a surface grain size of ≤100nm, which lays the foundation for the subsequent gradient stress field construction.

[0071] Step 8: Step-by-step controllable shot peening enhancement treatment

[0072] This step is the core process of core innovation point 3, and the supporting hardware is a CNC multi-gun shot peening machine, a planetary rotary tooling, and a shot separation system.

[0073] During the clamping process, the spring is clamped onto a planetary rotary fixture. The fixture can drive the spring to rotate on its own axis and revolve around the sun simultaneously, ensuring that there are no shot-peening dead zones between the inner ring and pitch of the spring.

[0074] The first step is coarse shot peening. Cast steel shot with a diameter of 0.6-0.8mm is loaded, and the shot peening pressure is set to 0.5-0.6MPa, the shot peening intensity to 0.3-0.4A, and the shot peening coverage to 100%. Through the high-energy impact of coarse shot, a deformation-strengthening layer with a depth of ≥0.2mm is formed on the subsurface of the spring, introducing basic compressive stress.

[0075] The second step involves fine shot peening, replacing the stainless steel shot with 0.2-0.3mm diameter, setting the shot peening pressure to 0.3-0.4MPa, the shot peening intensity to 0.15-0.25A, and the shot peening coverage to 200%. Through the refined impact of the fine shot, surface defects caused by coarse shot peening are repaired, the surface structure is refined, and the surface finish is improved. At the same time, a high amplitude compressive stress is formed on the surface, which forms a gradient distribution with the subsurface compressive stress formed by the coarse shot.

[0076] In the post-treatment stage, after shot peening, compressed air is used to clean the residual shot and dust on the spring surface, and the surface roughness Ra is tested to be ≤1.6μm.

[0077] Step Nine: Low-Temperature Ion Nitriding Composite Modification Treatment

[0078] This step is the final stage of the core innovation point 3, and the supporting hardware includes a low-temperature ion nitriding furnace, a vacuum system, and a gas supply system.

[0079] When loading the furnace, hang the springs evenly on the racks inside the nitriding furnace, leaving a gap of more than 10mm between the springs to ensure that the atmosphere evenly covers all surfaces.

[0080] In the vacuum exhaust process, after closing the furnace door, start the vacuum system to evacuate the furnace to a vacuum level of 50-100 Pa, and check the furnace body's sealing performance to ensure there is no leakage.

[0081] During the ion nitriding treatment stage, a mixture of ammonia and hydrogen (volume ratio 3:1) is introduced to maintain a stable vacuum in the furnace; a high-voltage power supply is turned on to generate glow discharge, raising the furnace temperature to 400-450℃ and holding it at that temperature for 4-6 hours, thereby forming a uniform nitrided hardening layer on the spring surface through ion bombardment.

[0082] In the cooling and unloading stage, after the heat preservation is completed, the power and gas supply systems are turned off, the furnace is cooled to below 100℃, air is introduced to break the vacuum, and the modified spring is obtained after unloading. The thickness of the nitrided layer after treatment is 0.1-0.2mm, the surface hardness is ≥650HV, and the dimensional deformation is ≤0.03mm. This step, through low-temperature nitriding, solidifies the surface nanocrystalline layer and deformation-strengthening layer, forming a stable gradient compressive stress field, which significantly improves the surface's creep resistance and fatigue resistance.

[0083] Step 10: Finished Product Performance Testing and Sorting

[0084] The hardware required for this step includes a spring dimension measuring instrument, a stiffness testing machine, a high-temperature spring relaxation testing machine, an electromagnetic resonant fatigue testing machine, and an automatic sorting machine.

[0085] In the dimension and stiffness inspection process, a spring dimension measuring instrument is used to inspect the free height, inner diameter, total number of coils, and effective number of coils of the spring. At the same time, a stiffness testing machine is used to test the stiffness of the spring. Springs that meet the design tolerance requirements enter the next inspection process.

[0086] In the stress relaxation rate testing process, a high-temperature spring relaxation testing machine is used. The rated working load is applied to the spring at an ambient temperature of 120℃. After heat preservation and load preservation for 1000 hours, the stress relaxation rate is calculated. A relaxation rate ≤1.2% is considered qualified.

[0087] In the fatigue life testing process, an electromagnetic resonant spring fatigue testing machine is used to apply an alternating load of 30%-70% of the rated working load to the spring. The spring is considered qualified if it can withstand 10^7 cycles without breaking.

[0088] In the sorting and warehousing stage, an automatic sorting machine is used to classify and sort qualified springs according to their size and performance parameters, and reject unqualified products. Finally, the finished anti-relaxation coil springs are obtained, packaged, and stored in the warehouse.

[0089] Example 1: Anti-relaxation coil spring for automotive suspension system

[0090] This embodiment is designed for the damping scenario of passenger car suspension system. The anti-relaxation coil spring is made of 60Si2CrVA spring steel wire. The core design parameters are: wire diameter 14mm, spring inner diameter 60mm, free height 350mm, effective number of coils 6.5, total number of coils 8.5, and rated working load 12kN.

[0091] The production process in this embodiment strictly follows the aforementioned 10 core steps. The specific parameters of each key process are controlled as follows: In the matrix fiber structure orientation pre-drawing process, the room temperature pre-drawing pass deformation is controlled at 10%, and the drawing speed is set at 20m / min; the medium temperature phase transformation temperature control process adopts a tubular continuous heating furnace with a heating temperature of 480℃ and a holding time of 10s; the warm drawing and shaping process has a heating temperature of 380℃, a pass deformation of 7%, and a total drawing deformation controlled at 17%. The entire drawing process is monitored in real time by an online metallographic monitoring device to ensure the formation of a continuous, oriented, ultrafine fibrous sorbite structure inside the steel wire. In the integrated winding and pre-compression aging process, a CNC spring winding machine with a fixed load pre-compression mechanism is used. The pre-compression load is set to 40% of the spring's rated working load, and the single-turn pre-compression holding time is 3 seconds. The synchronously matched annular medium-frequency induction heating coil is heated to 300℃, and the heating and holding time is completely synchronized with the pre-compression holding time. The winding spindle speed is set to 10 r / min, realizing integrated closed-loop forming of single-turn winding, pre-compression, and aging. In the ultrasonic surface nano-scale pretreatment process, the ultrasonic equipment is set to a working frequency of 25 kHz, the impact needle impact amplitude is 40 μm, the CNC rotary table clamping the spring rotates at 10 r / min, and the ultrasonic impact gun moves at a speed of 3 mm / s along the spring axis, achieving full-surface impact coverage of the spring without dead angles. In the step-by-step controllable shot peening strengthening process, the first step uses 0.7mm diameter cast steel shot for rough shot peening with a shot peening intensity of 0.35A and a shot peening coverage of 100%. The second step uses 0.25mm diameter stainless steel shot for fine shot peening with a shot peening intensity of 0.2A and a shot peening coverage of 200%. Planetary rotary tooling is used throughout the process to ensure that there are no shot peening dead zones in the inner ring of the spring and the pitch gap. In the low-temperature ion nitriding composite modification process, the vacuum degree in the nitriding furnace is stably controlled at 80Pa, the working atmosphere is a mixture of ammonia and hydrogen with a volume ratio of 3:1, the nitriding temperature is set at 420℃, and the holding time is 5h to complete the final construction of the gradient stress field.

[0092] After the entire process of manufacturing was completed, the finished spring of this embodiment underwent comprehensive performance testing. The results are as follows: the free height tolerance of the finished spring was controlled within 350±0.15mm, and the stiffness tolerance was ±2.2%, both meeting the design accuracy standards; under an ambient temperature of 120℃ and a rated working load of 12kN, the stress relaxation rate after 1000h of heat preservation and load holding was 0.92%; after 10^7 cycles of alternating load within the rated range at room temperature, the stress relaxation rate was 0.75%; the fatigue life test reached 1.2×10^7 cycles without fracture, which fully meets the high reliability service requirements of passenger car suspension systems.

[0093] Example 2: Anti-slackening coil springs for rail transit bogies

[0094] This embodiment is designed for vibration reduction of bogies in rail transit vehicles. The anti-relaxation helical spring is made of 55CrSiA spring steel wire. The core design parameters are: wire diameter 22mm, spring inner diameter 120mm, free height 500mm, effective number of coils 8, total number of coils 10, and rated working load 35kN.

[0095] The production process in this embodiment strictly follows the aforementioned 10 core steps, and the specific parameters of each key process are controlled as follows: In the matrix fiber structure orientation pre-drawing process, the room temperature pre-drawing pass deformation is controlled at 9%, and the drawing speed is set at 18m / min; the medium temperature phase transformation temperature control treatment adopts a tubular continuous heating furnace with a heating temperature of 470℃ and a holding time of 12s; in the warm drawing and shaping process, the heating temperature is 370℃, the pass deformation is 6%, and the total drawing deformation is controlled at 15%. The entire drawing process is monitored in real time by an online metallographic monitoring device to ensure that the steel wire matrix forms a uniform and continuous orientation fibrous sorbite structure. In the integrated winding and pre-compression aging process, a CNC spring winding machine with a fixed load pre-compression mechanism is used. The pre-compression load is set to 45% of the spring's rated working load, and the single-turn pre-compression holding time is 4 seconds. The synchronously matched annular medium-frequency induction heating coil is heated to 310℃, and the heating and holding time is completely synchronized with the pre-compression holding time. The winding spindle speed is set to 8 r / min, realizing the integrated synchronous implementation of the winding, pre-compression, and aging processes. In the ultrasonic surface nano-scale pretreatment process, the ultrasonic equipment is set to a working frequency of 22kHz, the impact needle impact amplitude is 45μm, the CNC rotary table clamping the spring rotates at 8 r / min, and the ultrasonic impact gun moves along the spring axis at a speed of 2.5 mm / s, fully covering the inner coil, outer coil, end face, and pitch gap of the spring to complete the impact treatment. In the step-by-step controllable shot peening strengthening process, the first step uses 0.8mm diameter cast steel shot for rough shot peening with a shot peening intensity of 0.4A and a shot peening coverage of 100%. The second step uses 0.3mm diameter stainless steel shot for fine shot peening with a shot peening intensity of 0.25A and a shot peening coverage of 200%. Planetary rotary tooling is used throughout the process to ensure that there are no shot peening dead spots in any part of the spring. In the low-temperature ion nitriding composite modification process, the vacuum degree in the nitriding furnace is stably controlled at 70Pa, the working atmosphere is a mixture of ammonia and hydrogen with a volume ratio of 3:1, the nitriding temperature is set at 430℃, and the holding time is 5.5h to complete the construction of a stable gradient compressive stress field.

[0096] After the entire process of manufacturing was completed, the finished springs of this embodiment underwent comprehensive performance testing. The results are as follows: the free height tolerance of the finished springs was controlled within 500±0.18mm, and the stiffness tolerance was ±2.5%, which meets the dimensional accuracy standards of the rail transit industry; under an ambient temperature of 120℃ and a rated working load of 35kN, the stress relaxation rate after 1000h of heat preservation and load holding was 1.08%; after 10^7 cycles of alternating load within the rated range at room temperature, the stress relaxation rate was 0.81%; the fatigue life test reached 1.5×10^7 cycles without fracture, which fully meets the long-term high-load service requirements of rail transit bogies.

[0097] Example 3: Anti-relaxation helical spring for servo mechanism of precision instrument

[0098] This embodiment is designed for high-precision, low-relaxation scenarios in the servo reset mechanism of precision instruments. The anti-relaxation helical spring is made of 304 austenitic stainless steel spring wire. The core design parameters are: wire diameter 1.2mm, spring inner diameter 8mm, free height 45mm, effective number of turns 12, total number of turns 14, and rated working load 80N.

[0099] The production process in this embodiment strictly follows the aforementioned 10 core steps. The specific parameters of each key process are controlled as follows: In the matrix fiber structure orientation pre-drawing process, the room temperature pre-drawing pass deformation is controlled at 11%, and the drawing speed is set at 22m / min; the medium temperature phase transformation temperature control process adopts a tubular continuous heating furnace with a heating temperature of 460℃ and a holding time of 8s; the warm drawing and shaping process has a heating temperature of 360℃, a pass deformation of 7%, and a total drawing deformation controlled at 18%. The entire drawing process is monitored in real time by an online metallographic monitoring device to ensure that a uniform and continuous ultrafine fibrous sorbite structure is formed inside the fine diameter steel wire. In the integrated coiling and pre-compression aging process, a CNC spring coiling machine with a constant load pre-compression mechanism adapted to fine-diameter steel wire is used. The pre-compression load is set to 35% of the spring's rated working load, and the single-turn pre-compression holding time is 2 seconds. The synchronously matched miniature annular medium-frequency induction heating coil is heated to 290℃, and the heating and holding time is completely synchronized with the pre-compression holding time. The coiling spindle speed is set to 15 r / min, achieving high-precision integrated processing and forming of fine-diameter springs. In the ultrasonic surface nano-sizing pretreatment process, the ultrasonic equipment is set to a working frequency of 28 kHz, the impact needle amplitude is 30 μm, the CNC rotary table for clamping the spring rotates at 12 r / min, and the ultrasonic impact gun moves at a speed of 4 mm / s along the spring axis. Combined with the dimensional characteristics of the fine-diameter spring, a full-coverage, non-destructive impact treatment is completed. In the step-by-step controllable shot peening strengthening process, the first step uses 0.6mm diameter cast steel shot for coarse shot peening with a shot peening intensity of 0.3A and a shot peening coverage of 100%. The second step uses 0.2mm diameter stainless steel shot for fine shot peening with a shot peening intensity of 0.15A and a shot peening coverage of 200%. Specialized micro-tooling is used throughout the process to prevent deformation of the small-diameter springs and ensure uniform shot peening across the entire spring surface. In the low-temperature ion nitriding composite modification process, the vacuum degree inside the nitriding furnace is stably controlled at 90Pa, the working atmosphere is a mixture of ammonia and hydrogen with a volume ratio of 3:1, the nitriding temperature is set at 410℃, and the holding time is 4 hours. This process completes the construction of the gradient hardening layer without affecting the spring's toughness.

[0100] After the entire process of manufacturing was completed, the finished spring in this embodiment underwent comprehensive performance testing. The results are as follows: the free height tolerance of the finished spring was controlled within 45±0.1mm, and the stiffness tolerance was ±1.8%, which meets the high-precision dimensional standards of precision instruments; under an ambient temperature of 80℃ and a rated working load of 80N, the stress relaxation rate after 1000h of heat preservation and load holding was 0.78%; after 10^7 cycles of alternating load within the rated range at room temperature, the stress relaxation rate was 0.63%; the fatigue life test reached 2.1×10^7 cycles without fracture, which fully meets the long-term stable service requirements of precision servo mechanisms.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for an anti-relaxation helical spring, characterized in that: Includes the following steps: Step 1: Screening and pretreatment of spring steel wire raw materials. Select spring steel wire coils that meet the composition requirements, and perform surface rust removal, phosphating and saponification treatment to obtain clean steel wires to be drawn. Step 2: Oriented pre-drawing of matrix fiber structure. The steel wire obtained in Step 1 is subjected to a three-step drawing process: room temperature pre-drawing, medium temperature phase transformation temperature control treatment, and temperature drawing and shaping, to obtain a finished steel wire with oriented fibrous sorbite structure. Step 3: Wire straightening and length cutting. The finished wire obtained in Step 2 is straightened by multiple rollers using a CNC straightening machine, and then cut to length according to the spring design dimensions to obtain the wire section to be rolled. Step 4: Integrated winding and pre-compression aging. A CNC spring winding machine with a constant load pre-compression mechanism is used to wind and shape the steel wire segment. At the same time, constant load pre-compression and medium frequency induction segmented aging treatment are carried out simultaneously during the winding process to obtain the spring blank. Step 5: Stress-relief annealing of spring blanks. The spring blanks obtained in Step 4 are placed in a mesh belt annealing furnace for low-temperature stress-relief annealing to eliminate residual processing stress. Step Six: Spring Dimensioning and Shaping with Forced Pressing. A CNC hydraulic forced press is used to perform multiple fixed-load forced pressing shaping processes on the annealed springs to lock the spring's free height and stiffness dimensions. Step 7: Ultrasonic surface nano-modification pretreatment. Using an ultrasonic surface nano-modification device, the spring obtained in Step 6 is subjected to full-coverage ultrasonic impact treatment to form a nanocrystalline modified layer on the spring surface. Step 8: Step-by-step controllable shot peening strengthening treatment. Using a CNC shot peening machine, the spring treated in Step 7 is subjected to a two-step step-by-step shot peening treatment, first with coarse shot and then with fine shot, to form a gradient deformation strengthening layer on the surface of the spring. Step 9: Low-temperature ion nitriding composite modification treatment. The spring treated in Step 8 is placed in a low-temperature ion nitriding furnace for low-temperature ion nitriding treatment to form a hardened nitriding layer on the surface of the spring, thus completing the construction of the gradient stress field. Step 10: Finished product performance testing and sorting. The springs processed in Step 9 are subjected to full testing of dimensions, stiffness, stress relaxation rate, and fatigue life. They are then sorted according to design requirements to obtain the finished anti-relaxation helical springs.

2. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The three-step drawing process described in step two is as follows: the deformation per pass in the room temperature pre-drawing is controlled at 8%-12%, and the drawing speed is controlled at 15-25 m / min; the medium-temperature phase transformation temperature control process uses a tubular continuous heating furnace, with the heating temperature controlled at 450-500℃ and the holding time controlled at 8-15s, to achieve ultra-fine pearlite lamellars inside the steel wire; the heating temperature for warm drawing and shaping is controlled at 350-400℃, the deformation per pass is controlled at 5%-8%, and the total deformation is controlled at 18%-25%; during the drawing process, an online metallographic monitoring device is used to sample and monitor the microstructure in real time to ensure the continuity and orientation of the sorbite fiber structure, and to refine the grain size to below 2μm.

3. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: Step 3, multi-roller straightening, uses a 7-13 roll CNC straightening machine. The tilt angle of the straightening rolls is controlled between 1.5° and 3°, and the straightening speed is controlled between 10-20 m / min. The straightness of the straightened wire is ≤0.1 mm / m. The fixed-length cutting uses a servo-guided shearing machine. The cutting length tolerance is controlled within ±0.2 mm, and the perpendicularity of the cutting end face is ≤0.05 mm to avoid end face misalignment during rolling.

4. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The CNC spring coiling machine with a fixed load preloading mechanism described in step four has an axial servo preloading cylinder coaxially installed at the end of the spring coiling spindle. The pressure control accuracy of the preloading cylinder is ≤±0.5%. During coiling, after each coil of spring is completed, the preloading cylinder applies an axial preload of 30%-50% of the rated load to the coiled spring coil, and the holding time is controlled at 2-5 seconds. At the same time, a ring-shaped medium-frequency induction heating coil is used to synchronously segmentally heat the newly coiled spring coil, and the heating temperature is controlled at 280-320℃. The holding time is completely synchronized with the preloading holding time, realizing the integrated completion of coiling, preloading, and aging. After coiling, the pitch tolerance of the spring blank is controlled within ±0.1mm, and the inner diameter tolerance is controlled within ±0.15mm.

5. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The low-temperature stress-relief annealing process described in step five uses a mesh belt continuous annealing furnace. High-purity nitrogen is introduced into the furnace as a protective atmosphere, with an oxygen content of ≤50ppm to prevent oxidation and decarburization of the spring surface. The annealing temperature is controlled at 380-420℃, and the holding time is controlled at 30-45min. After annealing, forced air cooling is used to bring the spring to room temperature, with the cooling rate controlled at 5-10℃ / s.

6. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The constant load pressure shaping process described in step six uses a CNC servo hydraulic pressure press. The pressure load is 120%-150% of the spring's rated working load. The holding time for each pressure press is controlled at 10-30 seconds, and the number of pressure presses is 3-5 times. During the pressure press process, a high-precision laser displacement sensor is used to monitor the spring's free height in real time. The free height deviation after each pressure press is ≤0.05mm. The free height tolerance of the final finished spring is controlled within ±0.2mm, and the stiffness tolerance is controlled within ±3%.

7. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The ultrasonic surface nano-sizing treatment described in step seven uses an ultrasonic frequency of 20-30kHz, an impact needle diameter of 2-5mm, and an impact amplitude of 30-50μm. The spring is clamped on a CNC rotary table with a rotation speed controlled at 5-15r / min. The ultrasonic impact gun moves along the spring axis at a speed of 2-5mm / s, and the angle between the impact gun and the spring surface is controlled at 45°-60°. The inner ring, outer ring, end face, and pitch gap of the spring are subjected to full-coverage impact treatment. After treatment, the thickness of the nanocrystalline layer on the spring surface is controlled at 50-100μm, and the surface grain size is ≤100nm.

8. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: Step 8 describes a two-step shot peening process. The first step, coarse shot peening, uses cast steel shot with a diameter of 0.6-0.8 mm, a shot peening intensity of 0.3-0.4A, a shot peening coverage of 100%, and an effective shot-peening reinforcement layer depth ≥0.2 mm. The second step, fine shot peening, uses stainless steel shot with a diameter of 0.2-0.3 mm, a shot peening intensity of 0.15-0.25A, and a shot peening coverage of 200%. The shot peening process uses a CNC multi-gun shot peening machine. The spring rotates with the rotating fixture in a planetary motion to ensure that there are no dead angles in the inner ring and pitch of the spring. After shot peening, the surface roughness Ra of the spring is ≤1.6 μm.

9. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: In step nine, the low-temperature ion nitriding treatment involves controlling the vacuum level in the nitriding furnace at 50-100 Pa, using a mixed gas of ammonia and hydrogen in a volume ratio of 3:1, controlling the nitriding temperature at 400-450℃, and holding the temperature for 4-6 hours. After treatment, the thickness of the nitrided layer on the spring surface is controlled at 0.1-0.2 mm, the surface hardness is ≥650 HV, and the overall dimensional deformation is ≤0.03 mm.

10. The manufacturing process of an anti-relaxation helical spring according to claim 1, characterized in that: The stress relaxation rate test described in step ten uses a high-temperature spring relaxation testing machine. The testing conditions are: ambient temperature of 120℃, application of the spring's rated working load, heat preservation and load preservation for 1000h, and a relaxation rate of ≤1.2% is considered qualified. The fatigue life test uses an electromagnetic resonant spring fatigue testing machine, with an alternating load of 30%-70% of the rated working load, and 10^7 cycles. It is considered qualified if the spring does not break. After the test, an automatic sorting machine is used to classify and sort the springs according to their size and performance parameters, and reject unqualified products.