A method for processing engine valve spring

Abstract

The present invention discloses a method for processing an engine valve spring that can solve the problem of valve spring fracture. The processing method includes: spring wire material inspection → winding → stress relief tempering → induction heating quenching, induction heating tempering → end face grinding → chamfering → shot peening → painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging; in the spring wire material inspection step, the content of non-metallic inclusions in the spring wire material is controlled to improve the purity of the steel used for the spring wire; in the induction heating quenching step, the valve spring is first induction heated and then oil quenched; in the induction heating tempering step, the valve spring is first induction heated and then air cooled to room temperature. The engine valve spring processing method of the present invention improves the quality of the F-type engine valve spring and solves the quality problems of the existing engine valve spring early fatigue fracture leading to engine explosion pressure and fire.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile engines, and in particular relates to a method for machining an engine valve spring. Background Art

[0002] The valve spring is an important component of the engine. Its function is to overcome the inertia of the valve and transmission parts during the valve closing process to ensure that the valve is seated in time and fits tightly. As the engine's performance such as specific power and specific torque increases, the requirements for valve spring fatigue strength are increased to ensure the normal operation of the engine.

[0003] However, in the actual production in the early stage, due to the influence of practical factors such as the valve spring production process and quality control, the valve spring of the F-type engine developed in the early stage showed early fatigue fracture during the engine's 500h rated power bench test, resulting in quality problems such as engine explosion and fire. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for processing engine valve springs, improve the quality of F-type engine valve springs, and solve the quality problems of early fatigue fracture of existing engine valve springs leading to engine explosion and fire.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is: a method for processing an engine valve spring, the processing method comprising: spring wire material inspection → winding → stress relief tempering → induction heating quenching, induction heating tempering → end face grinding → chamfering → shot peening → painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging; in the spring wire material inspection step, the content of non-metallic inclusions in the spring wire material is controlled to improve the purity of the steel used for the spring wire; in the induction heating quenching step, the valve spring is first induction heated and then oil quenched; in the induction heating tempering step, the valve spring is first induction heated and then air cooled to room temperature.

[0006] Furthermore, the non-metallic inclusions in the spring wire material include Class A inclusions, Class B inclusions, Class C inclusions, Class D inclusions and Class DS inclusions, and the levels of Class A inclusions, Class B inclusions, Class C inclusions, Class D inclusions and Class DS inclusions are all ≤0.5.

[0007] Furthermore, the minimum total length of the Class A inclusions is sulfides less than 38 μm, the minimum total length of the Class B inclusions is alumina less than 17 μm, the minimum total length of the Class C inclusions is silicates less than 18 μm, the maximum number of Class D inclusions is spherical oxides is 1, and the minimum diameter of the DS inclusions is a single particle is 13 um.

[0008] Furthermore, the device used for induction heating includes: a coil, an inductor and a power supply, the coil is wound around the outside of the inductor, the valve spring is placed in the inductor, the coil is connected to the power supply, the coil is energized, and the inductor performs induction heating on the valve spring.

[0009] Furthermore, the specific operation of the induction heating quenching is: placing the valve spring in the inductor, connecting the power coil and the inductor to induction heat the valve spring, the induction heating temperature of the valve spring is 850±10°C, and the heating time is 15±1 second; then using oil rapid cooling quenching, controlling the oil temperature to 20-60°C, which can completely eliminate the tensile stress generated by winding and obtain a quenched martensitic metallographic structure with high hardness.

[0010] Furthermore, the specific operation of the induction heating tempering is: induction heating the quenched valve spring to 405±15°C, keeping it warm for 60 minutes, and then cooling it to room temperature by air. Tempering can obtain higher elastic limit, strength limit and fatigue strength, and maintain appropriate toughness, promote the precipitation of extremely fine carbides from the quenched martensite, and gather at the martensite grain boundaries. The metallographic structure after tempering is tempered troostite.

[0011] Furthermore, the technical requirements for the microstructure formed after the induction heating tempering are: the tempered troostite grade is qualified for 1-3, among which grade 1 is fine tempered troostite, grade 2 is relatively fine tempered troostite, and grade 3 is relatively coarse tempered troostite; the tempered troostite is not allowed to have a full decarburization layer, and the maximum depth of the surface decarburization layer is 0.017mm.

[0012] Furthermore, the valve spring surface has a compressive stress within 300 μm to the sub-surface, the compressive stress on the valve spring surface is greater than 550 MPa, and the compressive stress at 50 μm of the sub-surface is greater than 750 MPa.

[0013] Furthermore, the chemical composition of the spring wire material used for the valve spring is: C: 0.50% to 0.60%, Si: 1.20% to 1.60%, Mn: 0.50% to 0.90%, Cr: 0.50% to 0.80%, P: ≤0.025%, S: ≤0.02%, and the rest is Fe; the spring wire hardness is: 530 to 600 HV, and the spring wire tensile strength is 1910-2010 N / mm 2 , the cross-sectional shrinkage rate of spring wire is ≥45%.

[0014] The advantages of adopting the technical solution of the present invention are:

[0015] 1. The present invention improves the purity of spring wire steel, reduces the content of non-metallic inclusions, controls the properties and requirements of non-metallic inclusions, and thus improves the fatigue strength of valve springs by controlling the type and content of non-metallic inclusions in spring wire materials.

[0016] 2. The present invention increases the compressive stress of the valve spring at 50 μm from the surface from |-922|MPa| to |-1045|Mpa by adding induction heating quenching and tempering processes; the tensile stress of the valve spring at a position 300 μm from the surface is converted into compressive stress, which can significantly improve the life of the valve spring under repeated high-stress working environment, improve the fatigue strength of the valve spring, and increase the fatigue safety factor of the valve spring by about 15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0018] Figure 1 This is a schematic diagram of a broken valve spring;

[0019] Figure 2 This is a schematic diagram of the macroscopic fracture of the valve spring;

[0020] Figure 3 Schematic diagram of the location of inclusions;

[0021] Figure 4 Schematic diagram of inclusion morphology and size;

[0022] Figure 5 This is a schematic diagram of DS inclusion level 1.5;

[0023] Figure 6 This is a schematic diagram of DS inclusion level 0.5;

[0024] Figure 7 It is a schematic diagram of induction heating;

[0025] Figure 8 It is a schematic diagram of valve spring pressure distribution when induction quenching and tempering are not added;

[0026] Fig. 9 Schematic diagram of valve spring pressure distribution during induction quenching and tempering.

[0027] The markings in the above figure are: 1, coil; 2, inductor. DETAILED DESCRIPTION

[0028] In the present invention, it is necessary to understand that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "planar direction", "circumferential", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation; be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0029] like Figures 1 to 9 As shown, in order to eliminate the valve spring breakage, the causes of valve spring breakage are analyzed:

[0030] 1. Fracture analysis: The fractured fifth intake valve spring is shown in Figure 1 The fracture position is in the second circle, the fracture surface is inclined, and the fracture originates from Figure 2 On the inside of the arrow, the instantaneous breaking area occupies about one-third of the entire cross-section. The larger the area occupied by the instantaneous breaking area, the greater the load on the valve spring.

[0031] The fracture was observed under a scanning electron microscope and it was found that the crack source was 0.15914 mm away from the surface. Figure 3 ; There is a single granular inclusion at the fracture source, with a diameter of 0.03452mm, Figure 4 ; There are fatigue striations in the extended area.

[0032] 2. Metallographic analysis: Take samples near the fracture and check for non-metallic inclusions in the polished state. Figure 5 According to GB / T10561, the single particle spherical (DS) category is 1.5.

[0033] 3. Cause of fracture: During the engine test, the 1st to 3rd turns of the valve spring are subjected to the greatest force, which easily forms a crack source at the 0.1591mm inclusion on the sub-surface, leading to fatigue fracture of the spring.

[0034] After comprehensive analysis, it is believed that the root cause of fatigue fracture is: the fatigue strength of the valve spring itself is low, which cannot withstand the high stress repeated working environment, and the presence of non-metallic inclusions at the sub-surface crack source.

[0035] The engine valve spring processing method of the present invention can solve the problem of valve spring fracture, and the processing method includes: spring wire material inspection → winding → stress relief tempering → induction heating quenching, induction heating tempering → end face grinding → chamfering → shot peening → painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging; in the spring wire material inspection step, the content of non-metallic inclusions in the spring wire material is controlled to improve the purity of the steel used for the spring wire; in the induction heating quenching step, the valve spring is first induction heated and then oil quenched; in the induction heating tempering step, the valve spring is first induction heated and then air cooled to room temperature. The engine valve spring processing method of the present invention improves the quality of F-type engine valve springs and solves the quality problems of early fatigue fracture of existing engine valve springs leading to engine explosion pressure and fire.

[0036] The material grade of spring steel wire (referred to as spring wire) used in valve spring is VD SiCr in EN 10270-2, and the technical requirements are as follows:

[0037] 1. Chemical composition of spring wire: Spring wire grade VD SiCr meets the requirements of Table 1

[0038] Table 1 Chemical composition of spring wire (Wt%)

[0039]

[0040] 2. Mechanical properties of spring wire: tensile strength 1910-2010N / mm 2 , section shrinkage ≥ 45%;

[0041] 3. Spring wire hardness: 530~600HV.

[0042] The non-metallic inclusions in the spring wire material include Class A inclusions, Class B inclusions, Class C inclusions, Class D inclusions and DS inclusions. The levels of Class A inclusions, Class B inclusions, Class C inclusions, Class D inclusions and DS inclusions are all ≤0.5. Class A inclusions are sulfides with a minimum total length of less than 38μm, Class B inclusions are alumina with a minimum total length of less than 17μm, Class C inclusions are silicates with a minimum total length of less than 18μm, Class D inclusions are spherical oxides with a maximum number of 1, and DS inclusions are single particles with a minimum diameter of 13um.

[0043] Strictly control the type and content of non-metallic inclusions in spring wire, in accordance with the requirements of Table 2:

[0044] Table 2 Types and contents of non-metallic inclusions in spring wire materials

[0045] Non-metallic inclusion types Non-metallic inclusion level (GB / T 10561) A (sulfide) ≤0.5 level (minimum total length less than 38μm) B (alumina) ≤0.5 level (minimum total length less than 17μm) C (silicate) ≤0.5 level (minimum total length less than 18μm) D (spherical oxide) ≤0.5 level (maximum quantity 1) DS (single particle, diameter ≥13um) ≤0.5 level (minimum diameter 13um)

[0046] By controlling the type and content of non-metallic inclusions in the spring wire material, the purity of the steel used for the spring wire is improved, the content of non-metallic inclusions is reduced, and the properties and requirements of non-metallic inclusions are controlled, thereby improving the fatigue strength of the valve spring.

[0047] The device used for induction heating includes: a coil 1, an inductor 2 and a power supply. The coil 1 is wound around the outside of the inductor 2, the valve spring is placed in the inductor 2, the coil 1 is connected to the power supply, the coil is energized, and the inductor 2 performs induction heating on the valve spring.

[0048] The specific operation of spring wire material inspection is as follows: the chemical composition inspection of spring wire is carried out according to GB / T4336 method, the mechanical property inspection is carried out according to GB / T 228.1 method, the hardness is carried out according to GB / T 4340.1 method, and the non-metallic inclusions are carried out according to GB / T10561 method.

[0049] The specific operation of winding is: winding on the spring winding machine, visually without rust and damage; winding to the right.

[0050] The specific operation of stress relief tempering is: tempering in a tempering furnace, the tempering temperature is 400±10℃, keeping warm for 45 minutes, and then cooling to room temperature with air.

[0051] The specific operation of induction heating quenching is as follows: placing the valve spring in the inductor (2), connecting the power coil and the inductor to induction heat the valve spring, the induction heating temperature of the valve spring is 850±10°C, and the heating time is 15±1 second; then using oil rapid cooling quenching, controlling the oil temperature to 20-60°C, and the oil pool residence time is 10-20 minutes, which can completely eliminate the tensile stress generated by winding and obtain a quenched martensitic metallographic structure with high hardness.

[0052] The specific operation of induction heating tempering is: clean the quenched valve spring, and then perform induction heating after cleaning, induction heating to 405±15℃, and keep it warm for 60 minutes, and then use air dispersion cooling to room temperature. Tempering can obtain higher elastic limit, strength limit and fatigue strength, and maintain appropriate toughness, promote the precipitation of extremely fine carbides from the quenched martensite, and gather to the martensite grain boundary. The metallographic structure after tempering is tempered troostite.

[0053] The specific operation of end face grinding is as follows: grinding on a spring grinding machine, the grinding angle is 300°~330°, measured with a protractor;

[0054] The specific operation of chamfering the inner angle is as follows: chamfer the inner angle on the chamfering machine, the chamfer width is 0.45±0.15mm, and the chamfer angle is 45±15°;

[0055] The specific operation of shot peening is as follows: shot peening on the shot peening machine, first with a steel ball with a diameter of 0.7 mm, shot peening time of 30 minutes; then with a steel ball with a diameter of 0.4 mm, shot peening time of 15 minutes;

[0056] The specific operation of dotting paint is: dotting paint on the pad printer, the color of the color mark is yellow, the number of color marks is three circles, and the color mark position is in the middle of the side;

[0057] The specific operation of hot pressing is: hot pressing on a hot press machine, the hot pressing temperature is 260±10℃, and the hot pressing time is 15 minutes;

[0058] The specific operation of the full inspection is: full inspection on the detection machine, and the installation position elastic force F 1 (e.g. 230±9N), working position elastic force F 2 (e.g. 510±20N) test;

[0059] The specific operation of rust prevention is: immerse the anti-rust oil DW30X in the oil pool;

[0060] The specific operations of finished product inspection are: use micrometer to check the wire diameter, use vernier caliper and plunger to check the inner diameter, use vernier caliper and sleeve to check the outer diameter, rotation direction and total number of turns (such as 7.6 turns), and use dynamometer to check the installation position elastic force F1 and working position elastic force F2;

[0061] The specific packaging operations are: packing according to the packaging plan and passing the visual inspection.

[0062] The technical requirements for the microstructure formed after induction heating tempering are: the tempered troostite grade is 1-3, where grade 1 is fine tempered troostite, grade 2 is relatively fine tempered troostite, and grade 3 is relatively coarse tempered troostite; tempered troostite is not allowed to have a full decarburized layer, and the maximum depth of the surface decarburized layer is 0.017mm. Table 3 shows the tempered troostite grades specified in the JB / T 9129 standard.

[0063] Table 3 Tempered troostite grades

[0064] grade illustrate Level 1 Fine tempered troostite Level 2 Fine tempered troostite Level 3 Coarse tempered troostite Level 4 Coarse tempered troostite Level 5 Tempered troostite and a small amount of massive ferrite

[0065] The valve spring processed by the present invention has compressive stress within 300 μm from the surface to the subsurface, the compressive stress on the surface of the valve spring is greater than 550 MPa, and the compressive stress at 50 μm of the subsurface is greater than 750 MPa.

[0066] In view of the phenomenon that the valve spring fracture fatigue source originates from 300μm from the surface to the subsurface, it is stipulated that the range from the surface to the subsurface of the valve spring is compressive stress (the surface compressive stress is greater than 550MPa, and the compressive stress at 50um of the subsurface is greater than 750MPa) to improve the valve spring's ability to resist external loads.

[0067] The performance of the valve spring manufactured by the processing method of the present invention is as follows:

[0068] 1. Non-metallic inclusions in the spring wire used in the valve spring: reduced from DS1.5 before rectification to DS<0.5, such as Figure 5 and Figure 6 By comparison, the non-metallic inclusions meet the technical requirements; the microstructure of the processed valve spring is fine tempered troostite, corresponding to level 2 in Table 3, and the metallographic structure of the valve spring is qualified.

[0069] 2. Before the valve spring "end grinding" process, add induction heating quenching and tempering process, induction heating quenching, such as Figure 7 Schematic diagram; for valve springs that undergo induction heating quenching and tempering and those that do not undergo induction heating quenching and tempering, the typical values ​​of X-ray diffractometer-residual stress test are compared, see Table 4:

[0070] Table 4 Comparison of typical values ​​of residual stress test

[0071] project Before improvement After improvement (adding induction heating quenching and tempering) Distance from surface Stress test value Stress test value 3μm -576MPa -694MPa 50μm -922MPa -1045MPa 100μm -1011MPa -1051MPa 200μm -226MPa -317MPa 300μm 105MPa -164MPa

[0072] Note: In material engineering, compressive stress is negative (-) and tensile stress is positive (+)

[0073] It can be seen from Table 4 that the compressive stress of the valve spring at a distance of 50 μm from the surface increases from |-922|MPa to |-1045|MPa, and the tensile stress at a distance of 300 μm from the surface of the valve spring turns into compressive stress.

[0074] The stress distribution changes of valve springs with and without induction heating quenching and tempering are shown in Figure 8 and Fig. 9 Comparison: The compressive stress of the valve spring at 50μm from the surface increases from |-922|MPa| to |-1045|Mpa; the tensile stress of the valve spring at 300μ from the surface becomes compressive stress, which can significantly increase the life of the valve spring under repeated high-stress working environment, improve the fatigue strength of the valve spring, and increase the fatigue safety factor of the valve spring by about 15%.

[0075] The qualified valve spring after adjustment is assembled in accordance with the "Valve Spring Assembly Operation Instructions", which can ensure that the end face of the valve spring is flat against the lower seat of the spring (the spring is not allowed to tilt), and is carried on the F-type engine for 500 hours of rated power bench test without early fatigue fracture.

[0076] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for processing an engine valve spring, characterized in that: The processing method comprises: spring wire material inspection → winding → stress relief tempering → induction heating quenching, induction heating tempering → end face grinding → chamfering → shot peening → painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging; in the spring wire material inspection step, the content of non-metallic inclusions in the spring wire material is controlled to improve the purity of the steel used for the spring wire; in the induction heating quenching step, the valve spring is firstly induction heated and then oil quenched; in the induction heating tempering step, the valve spring is firstly induction heated and then air cooled to room temperature; the non-metallic inclusions in the spring wire material include Class A inclusions, The levels of Class B inclusions, Class C inclusions, Class D inclusions and Class DS inclusions, Class A inclusions, Class B inclusions, Class C inclusions, Class D inclusions and Class DS inclusions are all ≤0.5; the Class A inclusions are sulfides with a minimum total length of less than 38μm, the Class B inclusions are alumina with a minimum total length of less than 17μm, the Class C inclusions are silicates with a minimum total length of less than 18μm, the Class D inclusions are spherical oxides with a maximum number of 1, and the DS inclusions are single particles with a minimum diameter of 13um; the valve spring surface to sub-surface within 300μm is compressive stress, the valve spring surface compressive stress The stress is greater than 550MPa, and the compressive stress at 50um of the subsurface is greater than 750Mpa; the specific operation of the induction heating quenching is: placing the valve spring in the inductor (2), connecting the power coil and the inductor to induction heat the valve spring, the induction heating temperature of the valve spring is 850±10℃, and the heating time is 15±1 second; then using oil rapid cooling quenching, controlling the oil temperature to 20-60℃, which can completely eliminate the tensile stress generated by winding and obtain a quenched martensite metallographic structure with high hardness; the specific operation of the induction heating tempering is: induction heating the quenched valve spring to 405±1 5℃, and keep it warm for 60 minutes, and then cool it to room temperature by air. Tempering can obtain higher elastic limit, strength limit and fatigue strength, and maintain appropriate toughness, promote the precipitation of extremely fine carbides in the quenched martensite, and gather at the martensite grain boundary. The metallographic structure after tempering is tempered troostite; the technical requirements for the microstructure formed after induction heating tempering are: the tempered troostite grade is 1-3 to be qualified, among which grade 1 is fine tempered troostite, grade 2 is relatively fine tempered troostite, and grade 3 is relatively coarse tempered troostite; tempered troostite is not allowed to have a full decarburization layer, and the maximum depth of the surface decarburization layer is 0.017mm.

2. The engine valve spring processing method according to claim 1, characterized in that: The induction heating device comprises: a coil (1), an inductor (2) and a power source, wherein the coil (1) is wound around the outside of the inductor (2), the valve spring is placed in the inductor (2), the coil (1) is connected to the power source, the coil is energized, and the inductor (2) performs induction heating on the valve spring.

3. The engine valve spring processing method according to claim 2, characterized in that: The chemical composition of the spring wire material used for the valve spring is: C: 0.50% to 0.60%, Si: 1.20% to 1.60%, Mn: 0.50% to 0.90%, Cr: 0.50% to 0.80%, P: ≤0.025%, S: ≤0.02%, and the rest is Fe; the spring wire hardness is: 530 to 600 HV, and the spring wire tensile strength is 1910-2010 N / mm 2 , the cross-sectional shrinkage rate of spring wire is ≥45%.

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