A method for processing a thin-walled cylindrical workpiece

Abstract

The application discloses a processing method of a thin-wall cylinder workpiece, and the method comprises the following steps: rough turning a blank; quenching and tempering the rough-turned blank, wherein the surface hardness of the quenched and tempered blank is HRC28~32, the circumferential tensile strength is greater than or equal to 980MPa, and the elongation after fracture is 12%; spinning the quenched and tempered blank; annealing the spun blank; and finish turning the annealed blank to form the thin-wall cylinder workpiece. The method reduces the deformation defects after spinning, saves the multiple correction processes, reduces the processing cost, and shortens the production cycle.

Description

Technical Field

[0001] This application relates to the field of metal processing technology, and in particular to a method for processing thin-walled cylindrical workpieces. Background Technology

[0002] Thin-walled cylindrical workpieces are typically used as the main structure of pressure vessels, towers, and other equipment, providing pressure-bearing space and withstanding internal pressure and external loads. They are widely used in high-pressure conditions in fields such as chemical and petroleum industries. Therefore, these workpieces not only need to have good pressure-bearing capacity but also require high machining accuracy.

[0003] Currently, the processing of thin-walled cylindrical workpieces typically employs a process of spinning followed by quenching and tempering. This involves spinning the forged blank into shape and then performing quenching and tempering. However, the alternating hot and cold temperatures during the quenching and tempering process can easily lead to deformation defects in the workpiece, such as excessive ellipticity, bending, and bulging. These defects often require multiple corrections, and each correction necessitates re-entering the workpiece into the furnace for tempering, resulting in high processing costs and long production cycles. Summary of the Invention

[0004] This application provides a processing method for thin-walled cylindrical workpieces, which solves the technical problems of high processing costs and long production cycles caused by the need for multiple corrections in the existing process routes for thin-walled cylindrical workpieces.

[0005] This application provides a method for processing a thin-walled cylindrical workpiece, comprising: rough turning a blank; quenching and tempering the rough-turned blank, wherein the surface hardness of the quenched and tempered blank is HRC28~32, the circumferential tensile strength is ≥980MPa, and the elongation after fracture is 12%; spinning the quenched and tempered blank; annealing the spun blank; and finish turning the annealed blank to form a thin-walled cylindrical workpiece.

[0006] In one possible implementation, the tempering treatment of the rough-turned blank includes: sequentially performing oil quenching at 880-900°C and high-temperature tempering at 520-560°C on the rough-turned blank.

[0007] In one possible implementation, the spun and tempered blank includes: continuously spinning the tempered blank in multiple passes.

[0008] In one possible implementation, a spinning wheel with a fillet radius of 2 to 6 mm is used during spinning, the angle of attack of the spinning wheel is 10° to 25°, and a mandrel with a surface roughness Ra≤1.6μm is used; during spinning, the spindle speed of the spinning machine is 120 to 160 r / min, and the feed ratio is 0.15 to 0.18 mm / r.

[0009] In one possible implementation, annealing the spun blank includes: holding the spun blank at 430±10℃ for 2 hours and then cooling it.

[0010] In one possible implementation, after annealing the spun blank, the method further includes: performing non-destructive testing on the annealed blank; the finish turning of the annealed blank includes: finish turning the blank that has been determined to be intact by non-destructive testing.

[0011] This application provides a method for processing thin-walled cylindrical workpieces. The method employs a process route of first quenching and tempering followed by spinning. The surface hardness of the quenched and tempered blank is HRC28–32, the circumferential tensile strength is ≥980 MPa, and the elongation after fracture is 12%. This ensures that spiral cracks and longitudinal tears will not occur when spinning the quenched and tempered blank, and spinning enhances the surface hardness and circumferential tensile strength of the blank. Since this method does not involve quenching and tempering after spinning, it reduces the occurrence of deformation defects after spinning, saves on multiple correction processes, lowers processing costs, and shortens the production cycle. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 A flowchart illustrating a method for processing thin-walled cylindrical workpieces according to some embodiments of this application. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0015] This application provides a method for processing thin-walled cylindrical workpieces, such as... Figure 1 As shown, the method includes steps S101 to S105.

[0016] Step S101: Rough turning of the blank. For example, the blank is forged from alloy structural steel 30CrMnSi.

[0017] Specifically, in step S101, a CNC lathe and / or a conventional lathe are used to turn the blank to prepare an initial blank that meets the initial geometric dimensions and surface quality requirements of the subsequent high-strength spinning process. Furthermore, rough turning can remove the surface oxide scale, decarburized layer, and micro-defects from the forged blank, obtaining a relatively uniform and smooth initial surface. This reduces or eliminates the potential for surface defects to become crack initiations during subsequent large-deformation spinning, ensuring the stability of the spinning process.

[0018] Step S102: The rough-machined blank is heat-treated. The surface hardness of the heat-treated blank is HRC28~32, the circumferential tensile strength is ≥980MPa, and the elongation after fracture is 12%.

[0019] The tempering process includes quenching and high-temperature tempering. Specifically, in one implementation of step S102, when quenching the blank, the blank is heated to the complete austenitizing temperature range of 880-900℃ and held at that temperature for a sufficient period to ensure complete dissolution of carbides and homogenization of austenite composition. Then, it is oil-quenched to obtain a high-hardness martensitic structure. When tempering the blank at high temperature, the quenched blank is tempered at a temperature range of 520-560℃, held at that temperature, and then air-cooled or slowly cooled after being removed from the furnace.

[0020] To ensure the smooth progress of the subsequent spinning process and achieve the expected performance, it is necessary to accurately control the surface hardness, circumferential tensile strength and elongation after fracture of the blank after quenching and tempering. In the embodiments of this application, the hardness of the quenched and tempered blank is precisely controlled within the range of HRC28~32, the circumferential tensile strength is ≥980MPa, and the elongation after fracture is 12%.

[0021] After the quenching and tempering treatment described in step S102, the blank obtains a tempered sorbite structure. This tempered sorbite structure consists of uniformly dispersed fine-grained cementite particles embedded in a ferrite matrix, providing a substrate that combines high strength and good toughness. Compared to the annealed state, the tempered sorbite structure has a higher initial dislocation density. Furthermore, the tempered sorbite structure does not contain austenite, and subsequent spinning strengthening will not produce strain-induced martensitic transformation. The strengthening effect after spinning mainly comes from the synergistic effect of pure dislocation strengthening, subgrain strengthening, deformation texture strengthening, and residual compressive stress strengthening. Step S103: Spin-formed and tempered blank.

[0022] After the blank is spun in step S103, it achieves cold working strengthening by relying on the high dislocation matrix to generate dislocation entanglement, subgrain refinement, fiber texture and residual compressive stress. This strengthens without phase transformation, which increases the surface hardness of the blank and significantly enhances its circumferential load-bearing capacity.

[0023] Furthermore, when the blank is extruded and plastically deformed in step S103, it springs back and forms a high-amplitude residual compressive stress, which can offset the working tensile stress, inhibit crack initiation, and significantly improve fatigue life. This is an important reason why the spun blank is fatigue-resistant and crack-resistant after quenching and tempering.

[0024] For the existing conventional quenching and tempering 30CrMnSi cold spinning process, the plasticity allowance of the sorbite matrix after quenching and tempering is low. The industry-standard safety limit for single-pass thinning is 25%, and the total thinning rate exceeds 45%. In addition, low-temperature stress-relieving annealing at 380-420℃ must be added between passes to eliminate dislocation entanglement and accumulated cold working internal stress, and to prevent spiral cracks and longitudinal tears in the cylinder wall.

[0025] To overcome the aforementioned total thinning rate and eliminate the time occupied by annealing between passes, in one implementation of step S103, the tempered blank is spun in multiple consecutive passes without the need for low-temperature stress-relief annealing between passes, thus achieving continuous large deformation. In this embodiment, "multiple passes" refers to two or more passes.

[0026] For example, a blank with a hardness of HRC28-32 after tempering and an initial wall thickness of 13.6 mm is continuously spun in one pass to a target wall thickness of 2.9 mm. The first pass reduces the wall thickness from 13.6 mm to 7.0 mm, with a single-pass thinning rate of 48.53%. The second pass reduces the wall thickness from 7.0 mm to 2.9 mm, with a single-pass thinning rate of 58.57%. The overall thinning rate from the original blank to the finished product reaches 78.68%. This breakthrough overcomes the conventional limitation that "the single-pass thinning rate of tempered alloy structural steel should not exceed 25%, and inter-pass annealing is required if the total thinning rate exceeds 45%"; after the above two-pass spinning, the surface hardness of the blank is increased to HRC40~43, the hardness increment ΔHRC is about 8~11, the circumferential tensile strength of the blank is increased by 35%~45%, the circumferential load-bearing capacity is significantly enhanced, and a residual compressive stress of 350~550MPa is formed on the inner surface of the blank, which effectively inhibits the initiation and propagation of fatigue cracks.

[0027] In one implementation of step S103, a spinning wheel with a fillet radius of 2 to 6 mm is used during spinning, the angle of attack of the spinning wheel is 10° to 25°, and a mandrel with a surface roughness Ra≤1.6μm is used; during spinning, the spindle speed of the spinning machine is 120 to 160 r / min, and the feed ratio is 0.15 to 0.18 mm / r.

[0028] When performing step S103, high-pressure extreme-pressure lubricating oil is used throughout the process to eliminate frictional heat at the spinning interface and reduce mold wear and micro-damage to the workpiece surface.

[0029] Step S104: Anneal the spun blank. Annealing can eliminate most of the residual stress generated by spinning, preventing deformation during subsequent processing or use.

[0030] In one implementation of step S104, the spun blank is kept at 430±10℃ for 2 hours and then cooled to release harmful tensile stress and retain the surface reinforcement residual compressive stress of the blank, thereby ensuring long-term dimensional stability.

[0031] Step S105: Finish-turn the annealed blank to form a thin-walled cylindrical workpiece.

[0032] Specifically, when performing step S105, firstly, using the process reference end face reserved after spinning as the positioning reference, the two end faces of the blank are precision machined to ensure the perpendicularity of the two end faces to the axis; then, the inner and outer cylindrical contours are semi-precision machined to correct the slight form and position deviations caused by the spinning process, leaving only a small amount of final precision machining allowance (e.g., 0.03~0.08mm); finally, a precision machining pass without tool marks is performed to machine the inner and outer diameters to the tolerances, coaxiality, and cylindricity required by the drawing in one go.

[0033] For example, when performing step S105 on a blank made of 30CrMnSi material, the tool and cutting parameters are matched as follows: TiAlN coated cemented carbide tools are used for external diameter finishing, and YA6 cemented carbide tools are used for internal diameter finishing to ensure tool wear resistance and impact toughness, and to avoid dimensional deviations caused by rapid tool wear during cutting; the cutting parameters adopt a strategy of "medium-high speed, small feed, and small depth of cut": the cutting speed is controlled at 120-160 m / min, the feed rate is 0.08-0.12 mm / r, and the single-sided depth of cut is controlled at 0.05-0.15 mm to avoid large depth of cut damaging the residual compressive stress layer on the inner surface of the cylinder; extreme pressure cutting oil is used for full cooling and lubrication throughout the machining process to reduce workpiece thermal deformation caused by cutting heat, while inhibiting the generation of built-up edge and ensuring the quality of the machined surface.

[0034] The spinning process can only guarantee the approximate wall thickness and outline of the thin-walled cylindrical workpiece. Step S105 is to perform final precision turning on the cylindrical blank that has a high-strength work-hardened structure, transforming it from a spun semi-finished product into a finished thin-walled cylindrical workpiece that meets all the dimensional accuracy, geometric tolerances and surface quality requirements of the drawings.

[0035] Furthermore, by employing a fine turning process with a small depth of cut, only a very thin surface machining allowance is removed, without damaging the high dislocation hardened layer and the inner surface residual compressive stress layer formed after spinning and annealing. This allows the thin-walled cylindrical workpiece to obtain accurate dimensions while fully retaining the high strength, high hardness, and high fatigue performance imparted by the previous processes.

[0036] After annealing the spun blank, the processing method for the thin-walled cylindrical workpiece further includes: performing non-destructive testing on the annealed blank. Step S105, the finishing turning of the annealed blank, includes: finishing turning the blank that has been determined to be intact through non-destructive testing.

[0037] After annealing, the internal stress of the blank has been fully released and redistributed, and the microstructure is stable. At this time, the test results can best reflect the final quality state after the spinning and annealing process. At the same time, the discovery of defects before precision turning can avoid the waste of time and materials in subsequent precision turning.

[0038] For example, when performing non-destructive testing on annealed blanks, an ultrasonic probe is used to perform a full-coverage scan along the axial and circumferential directions of the blank's cylinder. The scanning method employs either water immersion or direct contact with a high-viscosity coupling agent to ensure that the sound beam can effectively penetrate the thin wall and receive a clear bottom echo.

[0039] Step S105 specifically includes steps S201 to S203.

[0040] Step S201: Using the reserved process reference end face as the positioning reference, precision machine both end faces of the annealed blank.

[0041] In the spinning process, a process allowance section is reserved at the end of the blank. This allowance section does not participate in the deformation during the spinning process, and maintains good end face flatness and positioning accuracy. The end face of this allowance section is the reserved process reference end face.

[0042] During precision turning, the annealed blank is first clamped on the lathe chuck, using the reserved process reference end face as the axial positioning surface. Alignment is achieved using a dial indicator to ensure that the coaxiality deviation between the central axis and the lathe spindle rotation axis is controlled within a preset error threshold. Then, a carbide end-face turning tool is used to precision turn both end faces of the blank in sequence, removing irregular allowances from the spun ends, ensuring that the flatness, parallelism, and perpendicularity of the end faces to the cylinder's central axis meet the accuracy requirements of the drawing.

[0043] Step S202: Semi-finish turning of the inner and outer cylindrical contours to correct slight shape and position deviations caused by the spinning process.

[0044] While spinning can achieve large deformation and thinning, the inherent forming characteristics of the spinning process inevitably result in slight dimensional and positional deviations in the blank after spinning, such as uneven wall thickness, roundness deviation, and generatrix straightness deviation. These deviations typically range from 0.05 to 0.15 mm. The purpose of semi-finish turning is to correct these deviations before final finish turning, making the cylinder profile more regular and creating uniform and stable machining allowances for the final finish turning.

[0045] During operation, first, using the outer diameter as a reference, a semi-finish turning tool is used to turn the inner hole along the entire axial length of the cylinder, removing minor scratches and local high points caused by the demolding of the spinning mandrel. This corrects the roundness and straightness of the inner hole to the accuracy requirements of the drawing. Then, using the inner hole as a reference, a semi-finish turning tool is used to turn the outer diameter, removing local annular protrusions and slight ellipticity caused by the spinning wheel, correcting the roundness of the outer diameter to the accuracy required by the drawing. After the semi-finish turning is completed, a final finishing allowance is left on both the inner and outer diameter surfaces.

[0046] Step S203: Perform a finish turning without tool marks to machine the inner and outer diameters to the tolerances, coaxiality, and cylindricity accuracy range required by the drawing, and obtain a thin-walled cylindrical workpiece.

[0047] After the inner and outer cylindrical semi-finish turning is completed and the allowance is uniform, the final tool mark-free finish turning is performed. Tool mark-free means that the finish turning is completed in one continuous pass without stopping, retracting, or changing the tool. The tool is fed from one end of the cylinder to the other at a constant speed, and the cutting state is stable and consistent throughout the process, avoiding the formation of tool step marks or sudden changes in cutting force on the workpiece surface due to interruption or tool change.

[0048] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0049] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for processing a thin-walled cylindrical workpiece, characterized in that, include: Rough machining of blank parts; The blank after quenching and tempering treatment and rough turning has a surface hardness of HRC28~32, a circumferential tensile strength ≥980MPa, and an elongation after fracture of 12%. The blank after spinning and quenching; The spun blank is then annealed. The blank after precision turning and annealing is formed into a thin-walled cylindrical workpiece.

2. The processing method for thin-walled cylindrical workpieces according to claim 1, characterized in that, The rough part after quenching and tempering treatment and rough turning includes: The rough-machined blanks are then subjected to oil quenching at 880–900°C and high-temperature tempering at 520–560°C.

3. The processing method for thin-walled cylindrical workpieces according to claim 1, characterized in that, The spun and tempered blank includes: The quenched and tempered blank is spun in multiple consecutive passes.

4. The processing method for thin-walled cylindrical workpieces according to claim 3, characterized in that, During spinning, a spinning wheel with a fillet radius of 2 to 6 mm is used, the angle of attack of the spinning wheel is 10° to 25°, and a mandrel with a surface roughness Ra≤1.6μm is used; During the spinning process, the spindle speed of the spinning machine is 120~160 r / min, and the feed ratio is 0.15~0.18 mm / r.

5. The processing method for thin-walled cylindrical workpieces according to claim 1, characterized in that, The annealing of the spun blank includes: The spun blank is kept at 430±10℃ for 2 hours and then cooled.

6. The processing method for a thin-walled cylindrical workpiece according to claim 1, characterized in that, After annealing the spun blank, the method further includes: The annealed blank was subjected to non-destructive testing. The blank after precision turning and annealing includes: precision turning of the blank that has been determined to be intact by non-destructive testing.

7. The method for processing thin-walled cylindrical workpieces according to claim 6, characterized in that, The non-destructive testing of the annealed blank includes: An ultrasonic probe was used to perform a full-coverage scan along the axial and circumferential directions of the annealed blank.

8. The processing method for a thin-walled cylindrical workpiece according to claim 1, characterized in that, The blank after precision turning and annealing forms a thin-walled cylindrical workpiece, including: Using the reserved process reference end face as the positioning reference, the two end faces of the blank after annealing are precision machined; Semi-finish machining of the inner and outer cylindrical contours is used to correct slight shape and position deviations caused by the spinning process. A precision turning process without tool marks is performed to machine the inner and outer diameters to the tolerances, coaxiality, and cylindricity accuracy ranges required by the drawings, thereby obtaining the thin-walled cylindrical workpiece.

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