Machining method for transmission shaft of fuel pump

Abstract

The invention discloses a machining method for a transmission shaft of a fuel pump, and relates to the technical field of machining methods, the machining method comprises the following steps: S1, rough machining of an appearance: adopting a blank to remove allowance, so that a material structure is uniform; s2, quenching and tempering treatment, wherein the workpiece is pretreated, and the hardness of the core of the workpiece is improved; s3, semi-finish machining is conducted, specifically, the machining positioning reference is corrected, and the outer circle of the step is ground; s4, surface protection is conducted, specifically, nickel plating protection is conducted on the non-nitriding surface of the workpiece; s5, chemical heat treatment is conducted, specifically, nitriding treatment is conducted on the surface of the workpiece, and after nitriding treatment, first-time high-temperature tempering and second-time low-temperature destressing tempering are conducted in sequence so that the brittleness of a nitriding layer can be reduced and the grinding crack tendency can be eliminated; s6, finish machining, wherein the outer circle and the end face of the step subjected to nitriding treatment are ground; s7, surface treatment is conducted, specifically, the surface is subjected to chemical oxidation anti-corrosion treatment; s8, end face grinding, wherein the end face is ground, and the sealing performance of the sealing surface is improved; radioactive cracks generated in the subsequent grinding process are reduced, and the dimensional precision and stability are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transmission shaft processing methods, and more particularly to a processing method for a fuel pump transmission shaft. BACKGROUND

[0002] The transmission shaft is a core key component in an aviation fuel pump, one end of which is connected with an external shaft to continuously input torque, and the other end is connected with an impeller to drive it to rotate at high speed, for conveying aviation fuel. Meanwhile, the transmission shaft also needs to cooperate with a graphite bearing to realize dynamic sealing of fuel and the external environment. Therefore, the service working condition of the part is special and the environment is harsh, which puts forward extremely high requirements on its reliability, fatigue life and wear resistance and corrosion resistance. In order to realize these performances, the transmission shaft must have the characteristics of "hard outside and soft inside", that is, the surface has extremely high hardness and wear resistance, and the core part maintains sufficient toughness, which puts forward complex and professional requirements on the heat treatment process and the whole manufacturing process, forming a high technical barrier.

[0003] However, in the existing transmission shaft processing technology, the application of nitriding process faces a series of technical problems that have not been effectively solved. First of all, the surface layer formed after conventional nitriding treatment has high hardness and high brittleness, and there is significant residual stress inside. When subsequent grinding finishing is carried out, under the action of grinding force, these stress concentrations are released, which is easy to produce fine radioactive cracks (also known as ghost cracks) on the surface of the nitriding layer, especially in the end face area. Such cracks are highly concealed, and are often discovered during final detection or use, resulting in low part yield and serious safety hazards.

[0004] Secondly, the existing process lacks systematic regulation of the stress state before and after nitriding, as well as the matching finishing strategy; this leads to deformation of the part during processing, making it difficult to guarantee the flatness of the ground end face, and often resulting in over-difference phenomenon, which seriously affects the sealing effect of the part cooperating with the graphite bearing, and causes the risk of fuel leakage.

[0005] Therefore, how to provide a fuel pump transmission shaft processing method capable of effectively preventing radioactive cracks and effectively improving the yield is a problem that those skilled in the art need to solve. SUMMARY

[0006] Therefore, the present application provides a processing method for a fuel pump transmission shaft, aiming to solve the above technical problems.

[0007] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] A processing method for a fuel pump transmission shaft, comprising the following steps:

[0009] S1, rough machining of the outer shape: removing the excess amount of raw material to make the material organization uniform;

[0010] S2, tempering treatment: the workpiece is pretreated to improve the core hardness of the workpiece;

[0011] S3, semi-finishing: correcting the machining positioning reference, grinding the step outer circle;

[0012] S4, surface protection: the non-nitriding surface of the workpiece is plated with nickel for protection;

[0013] S5, chemical heat treatment: the workpiece surface is subjected to nitriding treatment, and after the nitriding treatment, first high-temperature tempering and second low-temperature stress relief tempering are sequentially performed to reduce the brittleness of the nitriding layer and eliminate the tendency of grinding cracks;

[0014] S6, finishing: grinding the step outer circle and end face after nitriding treatment;

[0015] S7, surface treatment: the surface is subjected to chemical oxidation corrosion protection treatment;

[0016] S8, end face grinding: the end face is ground to improve the sealing performance of the sealing surface.

[0017] Through the above technical scheme, the machining method of the fuel pump transmission shaft provided by the application establishes a unified high-precision reference through the semi-finishing of step S3, lays a reliable size and shape foundation for the entire manufacturing process; through the surface protection of step S4, the non-nitriding surface is plated with nickel to ensure the accurate local strengthening of the chemical heat treatment performance and avoid the destruction of the performance of the non-strengthening area; through the first high-temperature tempering in the chemical heat treatment of step S5, the excessive brittleness of the nitriding layer is effectively reduced, and the toughness is increased; through the second low-temperature stress relief tempering, the huge residual stress generated in the nitriding process is deeply eliminated. The two work together to reduce the radioactive cracks (ghost cracks) generated during subsequent grinding; after the workpiece is subjected to the above optimization treatment, the finishing of step S6 is performed, which can stably grind the high-precision shape, the precision machining reference established by S3 cooperates with the finishing of S6, and the final size precision and shape tolerance of the part are ensured, thereby significantly improving the product qualification rate, use reliability and sealing performance.

[0018] Preferably, in the fuel pump drive shaft machining method, in step S2, the workpiece is heated to 820-860℃, and held for 10-15 minutes; then heated to 950-955℃ again, and held for 70-75 minutes; and tempered within 8 hours after quenching. By limiting the specific process parameters of the quenching and tempering treatment, including the accurate temperature ranges of the two heating processes (820-860℃ and 950-955℃), the corresponding holding times (10-15 minutes and 70-75 minutes), and the requirement of tempering within 8 hours after quenching, the core structure of the workpiece is fully transformed into uniform and refined tempered sorbite, providing an ideal matrix structure for the subsequent nitriding treatment and laying the foundation for the overall mechanical properties of the part; the core hardness of the workpiece after quenching and tempering is specifically limited to the best range of HRC 30-37. This hardness range perfectly realizes the design requirement of "stiff outside and soft inside" for the drive shaft, ensuring that the core of the part has sufficient strength and hardness to withstand complex loads, while maintaining good toughness and impact resistance, providing strong support for the nitriding layer of the surface hardening.

[0019] Preferably, in the fuel pump drive shaft machining method, in step S3, the left-right feed transverse grinding method is used to grind the step outer circle, so that the coaxiality of the step outer circle relative to the center holes of the workpiece is not greater than 0.01mm. By using the left-right feed transverse grinding method and strictly controlling the coaxiality to be not greater than 0.01mm, a precise positioning system is established based on the two center holes before nitriding. This process not only ensures the accurate geometric relationship of each step outer circle, but more importantly, provides a unified machining reference for all subsequent processes, effectively avoiding error accumulation and laying a process foundation for obtaining high-precision products.

[0020] Preferably, in the fuel pump drive shaft machining method, in step S3, a finishing allowance of 0.03-0.05mm is left. By limiting the finishing allowance to 0.03-0.05mm, this parameter is carefully designed: it not only ensures that the nitriding layer has sufficient thickness to be retained after final machining to meet the wear resistance requirements, but also avoids excessive heat stress concentration due to excessive allowance, preventing the occurrence of grinding cracks from a process design perspective, achieving the best balance between nitriding effect and machining safety.

[0021] Preferably, in the above-mentioned fuel pump transmission shaft processing method, in step S4, the nickel plating thickness is greater than 50 μm; and stress relief annealing is performed before and after the nickel plating; the stress relief annealing temperature is 190-210°C, the holding time is 120-180 min, and the cooling is performed in air. By stipulating the nickel plating thickness to be greater than 50 μm and combining the stress relief annealing (190-210°C, 120-180 min holding time) before plating with specific parameters, the double protection effect is achieved: the sufficient plating thickness ensures the reliable protection of the non-nitriding surface; and the stress relief annealing eliminates the previous processing stress and effectively prevents the hydrogen embrittlement risk in the electroplating process, thereby improving the overall safety performance of the part.

[0022] Preferably, in the above-mentioned fuel pump transmission shaft processing method, in step S5, the nitriding treatment is performed at 500°C±5°C, and the nitriding time is 800 min; the first high-temperature annealing temperature is 500-510°C, the holding time is 90 min, and the protective rapid cooling is performed; the second low-temperature stress relief annealing temperature is 190-210°C, the holding time is 540-600 min, and the cooling is performed in air. The innovative double annealing process is specified as an accurate parameter system, including the nitriding treatment (500°C±5°C, 800 min), the first high-temperature annealing (500-510°C, 90 min, rapid cooling), and the second low-temperature stress relief annealing (190-210°C, 540-600 min, air cooling). The combination of these parameters is optimized to effectively achieve the technical effect of reducing the brittleness of the nitriding layer and eliminating the residual stress, and is the core process guarantee for solving the "ghost crack" problem.

[0023] Preferably, in the above-mentioned fuel pump transmission shaft processing method, the nitriding thickness is 0.2-0.3 mm, and HV≥700. The friction pair and the sealing surface of the transmission shaft have extremely high wear resistance and load capacity as required by the design. This technical effect directly achieves the design goal of "external rigidity" of the part, and provides performance guarantee for long service life and high reliability.

[0024] Preferably, in the above-mentioned fuel pump transmission shaft processing method, in step S6, the grinding wheel material is white corundum when grinding the outer circle, the 45° oblique infeed method is adopted, and the grinding wheel linear speed is 30 m / s; and the oscillation grinding method is adopted when grinding the end face. In view of the characteristics of the optimized nitriding layer, the special grinding parameter combination (white corundum grinding wheel, 45° oblique infeed, 30 m / s linear speed, oscillation grinding) in the finishing stage is stipulated. These specially matched process parameters can achieve efficient and stable processing of the modified nitriding layer, effectively prevent secondary defects such as surface scratches and burns, and ensure the dimensional accuracy.

[0025] Preferably, in the above-mentioned fuel pump transmission shaft machining method, in step S6, the outer circle and end face jump after grinding is not greater than 0.01mm, and the end face flatness is not greater than 0.008mm. By limiting the shape and position tolerance requirements (outer circle and end face jump ≤0.01mm, end face flatness ≤0.008mm) after finishing, the machining precision is quantified to provide a technical guarantee for ensuring the precise fit of the transmission shaft and related parts, especially laying a precision foundation for subsequent seal surface grinding.

[0026] Preferably, in the above-mentioned fuel pump transmission shaft machining method, in step S8, 8μm diamond grinding liquid is used for grinding the end face, and the grinding disc rotation speed is 14r / min. Extremely high end face flatness and excellent surface quality can be obtained, and such finishing effect effectively ensures that the transmission shaft end face forms a dynamic sealing interface with the mating part, reduces fuel leakage, and improves the qualified rate of air tightness detection.

[0027] Through the above technical solution, compared with the prior art, the present application provides a fuel pump transmission shaft machining method, which has the following beneficial effects:

[0028] 1. The present application effectively reduces the technical problem of radioactive cracks (ghost cracks) in the manufacturing of fuel pump transmission shafts through the combination of nitriding treatment and double tempering core processes. The first high-temperature tempering effectively reduces the brittleness of the high-hardness nitriding layer, and the second low-temperature stress relief tempering deeply eliminates internal residual stress, which reduces the generation of cracks in the subsequent fine grinding process. At the same time, the systematic process design, including the reference unification and micro-allowance control in the semi-finishing stage, reliable nickel plating protection of non-nitriding surfaces, and fine grinding parameters matching the modified nitriding layer, collectively ensures that the part maintains extremely high dimensional stability and shape accuracy throughout the entire machining process.

[0029] 2. The present application realizes precise control of the "outer rigid and inner soft" characteristics of the transmission shaft. Through the optimized quenching and tempering process, the core hardness of the workpiece is stabilized to HRC30~37, achieving strong and tough matrix performance (inner soft); the precise nitriding process ensures that the surface obtains a hardened layer of 0.2~0.3mm with a hardness not less than 700HV (outer rigid); finally, through high-precision grinding and end face grinding, the key mating surfaces (each step outer circle and sealing end face) of the transmission shaft have a jump amount not greater than 0.01mm, and the end face flatness is within 0.008mm, and the precision grinding ensures the extremely high flatness of the sealing surface, thereby ensuring the air tightness requirement. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only aim to explain part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative work fall within the protection scope of the present application.

[0031] Figure 1 The flow chart of the processing method of the fuel pump transmission shaft provided by the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative work fall within the protection scope of the present application.

[0033] Referring to the accompanying drawings, Figure 1 the processing method of the fuel pump transmission shaft is disclosed in the embodiments of the present application, which comprises the following steps:

[0034] S1, rough machining of the outer shape:

[0035] A rough bar is adopted, clamped by a general jaw, and most of the excess is removed by turning to preliminarily form the outer circles of each step and the lightening hole. The purpose of this step is to make the internal organization of the material uniformly change in the subsequent quenching and tempering process.

[0036] S2, quenching and tempering:

[0037] This step is a preliminary heat treatment, aiming to stabilize the internal organizational structure of the raw material and increase the hardness of the core of the part to the predetermined range. The specific implementation method is as follows:

[0038] ①The part is vertically placed in a vacuum furnace to avoid bending and deformation due to self-weight during heating.

[0039] ②The part is subjected to stepwise heating treatment: first heated to 820-860℃, and kept for 10-15min; then heated to 950-955℃ again, and kept for 70-75min.

[0040] ③After the keeping, quenching is performed, and tempering is performed within 8 hours after the quenching is completed.

[0041] ④After the treatment is completed, corundum powder is used to blow the surface of the part to remove the oxide layer and clean the workpiece, and improve the surface bonding force of the subsequent chemical heat treatment.

[0042] After the above processing, the hardness of the workpiece core is stably improved to HRC 30-37, and the performance requirements of the "inner softness" base are realized.

[0043] S3, semi-finishing:

[0044] The core task of this step is to correct the machining positioning reference, and to reserve an accurate finishing allowance for the subsequent chemical heat treatment surface.

[0045] Reference correction: adopt two center clamping methods, use left and right feed horizontal grinding method to grind each step outer circle. This method can effectively correct the position relationship of each step outer circle and the axis of the two end center holes, ensure that the coaxiality of each outer circle relative to the two end center holes is not more than 0.01mm, so as to achieve the purpose of uniform positioning machining reference.

[0046] Forming machining: adopt gear shaping machine to perform profiling machining on the inner spline of the transmission shaft end.

[0047] Allowance control: for all surfaces that need to be chemically heat treated, a uniform finishing allowance of 0.03mm-0.05mm is left.

[0048] S4, surface protection:

[0049] In order to prevent the non-nitriding surface from being nitrided in the subsequent process, it needs to be reliably protected.

[0050] Nickel plating protection: the non-nitriding surface of the workpiece is treated by electroplating nickel, and the thickness of the nickel plating layer is required to be greater than 50μm.

[0051] Stress relief annealing: before and after the nickel plating operation, stress relief annealing treatment is needed. Process parameters: heat to 190℃-210℃, hold for 120min-180min, then cool in air. This process is used to eliminate the stress generated by machining, and effectively prevent the hydrogen embrittlement problem caused by the invasion of hydrogen atoms in the electroplating process.

[0052] S5, chemical heat treatment:

[0053] This step is the core of improving surface performance and preventing "ghost crack", mainly including nitriding treatment and double tempering.

[0054] Preparation before nitriding:

[0055] Clean the parts and remove oil stains.

[0056] 60 minutes before loading the furnace, perform oxygen-free treatment on the surface of the parts and clean the furnace.

[0057] Nitriding treatment:

[0058] Rising temperature: After the parts are loaded into the nitriding furnace, nitrogen is first introduced into the furnace and the temperature is raised to 400℃. Then the nitrogen is turned off and only ammonia is introduced, and the temperature is continued to rise to 510℃.

[0059] Temperature holding: At the nitriding temperature of 500℃±5℃, the nitriding is maintained for 800 minutes.

[0060] Cooling: After the nitriding is completed, the workpiece is cooled to 450℃, and then inert gas (such as argon) is introduced for protective cooling.

[0061] First high-temperature tempering:

[0062] In a vacuum furnace, the workpiece is heated to 500℃-510℃ and held for 90 minutes. After the holding is completed, the furnace is cooled or transferred to a cooling chamber and backfilled with argon for rapid cooling to room temperature. The main purpose of this tempering is to reduce the excessive brittleness of the nitriding layer.

[0063] Second low-temperature stress relief tempering:

[0064] Immediately after, the workpiece is heated to 190℃-210℃ and held for 540-600 minutes, and then cooled to room temperature in air. This tempering aims to deeply eliminate the macroscopic stress remaining after nitriding and the first tempering.

[0065] Through this combined process, the risk of grinding cracks during finishing grinding due to the excessive hardness or uneven structure of the nitriding layer is effectively avoided. The final nitriding layer thickness is 0.2-0.3mm, the surface hardness HV≥700, and the design goal of "external rigidity" is achieved.

[0066] S6, finishing:

[0067] Final forming processing is carried out on the nitriding layer that has been optimized as described above.

[0068] Processing method: Use an external grinding machine, use two centers to clamp, grind the outer circle of each step and rely on the end face.

[0069] Accuracy requirement: Ensure that the runout of the outer circle and end face of each step after grinding is not more than 0.01mm, and the flatness of the ground end face is not more than 0.008mm.

[0070] Grinding parameters:

[0071] Grinding outer circle: the abrasive wheel material is white corundum (WA) with a granularity of 80 mesh, and a 45° oblique infeed method is adopted. The coarse grinding infeed amount is 0.05 mm / min, the semi-fine grinding infeed amount is 0.03 mm / min, and the fine grinding infeed amount is 0.005 mm / min; the coarse grinding allowance is 0.05 mm, the semi-fine grinding allowance is 0.03 mm, and the fine grinding allowance is 0.01 mm; the polishing time is 40 s, the workpiece rotating speed is 100 r / min, and the abrasive wheel linear speed is 30 m / s.

[0072] Grinding end face: the abrasive wheel material is white corundum (WA) with a granularity of 80 mesh, and a vibration grinding method is adopted. The coarse grinding infeed amount is 0.01 mm / min, the semi-fine grinding infeed amount is 0.005 mm / min, and the fine grinding infeed amount is 0.003 mm / min; the coarse grinding allowance is 0.05 mm, the semi-fine grinding allowance is 0.02 mm, and the fine grinding allowance is 0.01 mm; the polishing time is 40 s, the workpiece rotating speed is 100 r / min, and the abrasive wheel linear speed is 30 m / s.

[0073] Abrasive wheel treatment: because of the hardness difference of the finished surface, when the work surface with low hardness is ground, the copper bar is ground in advance with a well-trimmed abrasive wheel to remove the surface layer of abrasive grains with poor bonding force, passivate the cutting edge, and prevent the soft surface from being scratched.

[0074] S7, surface treatment:

[0075] Chemical oxidation treatment is performed on all surfaces of the finished workpiece to form a dense corrosion-resistant oxidation film, thereby improving the corrosion resistance of the part in the aviation fuel environment.

[0076] S8, end face grinding:

[0077] The sealing end face of the transmission shaft is finally precisely ground to ensure its dynamic sealing performance.

[0078] Process parameters: the grinding medium is 8 μm diamond grinding liquid, the grinding disc surface roughness is Ra 0.02, and the grinding disc rotating speed is 14 r / min. The grinding liquid is added every 6 minutes, and each addition lasts for 3 seconds. The grinding disc and the workpiece produce relative motion.

[0079] Quality inspection: the flatness of the ground end face is measured by a flat crystal or a laser interferometer, and is controlled within 2 to 3 light bands, which can ensure that the transmission shaft is 100% qualified in the air tightness test in the assembly.

[0080] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0081] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for machining a fuel pump drive shaft, characterized in that, Includes the following steps: S1. Rough machining of the outer shape: Remove excess material using raw material to make the material structure uniform; S2. Heat treatment: Pre-treatment of the workpiece to improve the core hardness; S3, Semi-finishing: Correct the machining positioning datum and grind the outer circle of the step; S4. Surface protection: Nickel plating is applied to the non-nitrided surface of the workpiece for protection. S5. Chemical heat treatment: Nitriding treatment is performed on the surface of the workpiece. After nitriding treatment, a first high-temperature tempering and a second low-temperature stress-relieving tempering are performed in sequence to reduce the brittleness of the nitrided layer and eliminate the tendency of grinding cracks. S6. Finishing: Grinding and nitriding the outer circle and end face of the step after the step is finished; S7. Surface treatment: Chemical oxidation is applied to the surface for corrosion protection. S8. End face grinding: Grind the end face to improve the sealing performance of the sealing surface.

2. The method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S2, the workpiece is heated to 820℃-860℃ and held for 10min-15min; then heated again to 950℃-955℃ and held for 70min-75min; and tempered within 8 hours after quenching, so that the core hardness of the workpiece is increased to HRC30-37.

3. The method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S3, the outer circle of the step is ground by a transverse grinding method with left and right feed, so that the coaxiality of the outer circle of the step relative to the center holes at both ends of the workpiece is no more than 0.01mm.

4. The method for machining a fuel pump drive shaft according to claim 3, characterized in that, In step S3, a finishing allowance of 0.03mm to 0.05mm is left.

5. The method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S4, the nickel plating thickness is greater than 50 μm; and stress-relief tempering is performed before and after nickel plating; the stress-relief tempering temperature is 190℃-210℃, the holding time is 120min-180min, and then the plated plated is cooled in air.

6. The method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S5, the nitriding treatment is carried out at 500℃±5℃ for 800 min; the tempering temperature of the first high-temperature tempering is 500℃~510℃, held for 90 min, and then subjected to protective rapid cooling. The second low-temperature stress-relief tempering was performed at a tempering temperature of 190℃~210℃, held for 540min~600min, and then cooled in air.

7. A method for machining a fuel pump drive shaft according to claim 6, characterized in that, The nitriding thickness is 0.2–0.3 mm, and the HV is ≥700.

8. A method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S6, when grinding the outer diameter, the grinding wheel material is white corundum, a 45° angled feed method is used, and the grinding wheel linear speed is 30m / s; when grinding the end face, an oscillating grinding method is used.

9. A method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S6, the runout of the outer circle and end face of the step after grinding is no more than 0.01 mm, and the flatness of the end face is no more than 0.008 mm.

10. A method for machining a fuel pump drive shaft according to claim 1, characterized in that, In step S8, 8μm diamond polishing slurry is used on the polishing end face, and the polishing disc rotates at 14 r / min.

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