Skeleton self-lubricating composite material part machining method, clamping device and grinding wheel

Abstract

The invention discloses a framework self-lubricating composite material part machining method, a clamping device and a grinding wheel, and belongs to the technical field of precision manufacturing. The method comprises the following steps: a reference correction step: carrying out clamp repair on the outer circle of a framework of a sintered composite blank to form a reference area, and clamping a trimmed soft claw in the reference area in a narrow surface line contact mode to correct the coaxiality of the blank and a machine tool spindle so as to process a precise axial reference surface; and a grinding machining step: adopting a CBN (Cubic Boron Nitride) grinding wheel with a porous structure to be matched with a high-pressure cooling system to grind the workpiece with the established reference surface. According to the method, the problems of benchmark missing and discontinuous machining of heterogeneous materials are effectively solved, and the product percent of pass and the machining efficiency are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of precision manufacturing technology for high-performance metal matrix composite materials. Specifically, it relates to a precision machining method, clamping device, and grinding wheel for a self-lubricating composite material part with a skeleton that can operate under high-temperature and unlubricated conditions above 800°C in a key component of aero-engines. Background Technology

[0002] Against the backdrop of the continuous pursuit of higher thrust-to-weight ratio and reliability in high-end equipment such as aero engines and gas turbines, the high-temperature self-lubricating composite inner end bushing, as a key friction pair component, adopts a nickel-based high-temperature alloy as the structural skeleton and a "sandwich" structure of composite self-lubricating material. It can simultaneously achieve excellent structural load-bearing and continuous self-lubricating function in extreme working conditions of high temperature above 800℃, high load and no additional lubrication.

[0003] However, this material system faces key technical challenges in its manufacturing process: The problem of missing sintering reference: Due to the influence of mold fitting clearance and material thermal expansion behavior during powder metallurgy, the self-lubricating material produces non-uniform wrapping and stress transfer on the skeleton during sintering, causing spatial orientation drift of the skeleton (typically manifested as radial offset of 0.05–0.15 mm and end face skew of 0.5°–2°). This offset makes the blank a "referenceless" blank, with inaccurate internal and external shapes, resulting in the inability to establish a reliable positioning reference in subsequent machining, such as... Figure 1 As shown, during the sintering process of the cold-pressed blank in the mold under high temperature and pressure, the axis of the composite skeleton rotates eccentrically, causing the axis of the blank formed after sintering to deviate from the original skeleton axis. Figure 2 As shown in the middle ring frame, the blank end face formed after sintering will also be uneven, which will lead to a series of processing quality problems such as uneven allowance distribution and coaxiality deviation, which seriously restrict the dynamic balance performance and service reliability of the component in high-speed and high-temperature environment.

[0004] The challenge of discontinuous machining of heterogeneous materials: Due to the inlay structure, the cutting tool needs to periodically and alternately cut the high-hardness (HRC≥40) high-temperature alloy region and the high-viscosity self-lubricating material region, enduring severe mechanical and thermal shocks. The cutting force fluctuation range is 2-3 times that of steady-state conditions, causing the tool life to plummet to 1 / 4 of that under continuous machining conditions. Significant stress concentration is observed at the interface between the skeleton part and the composite material, inducing microstructural damage and crack formation, such as... Figure 3 As shown, the inner surface of the part has many cracks; at the same time, the surface roughness of the machined part is difficult to control stably within Ra0.8μm, and the machining efficiency drops by more than 40%.

[0005] The aforementioned technical challenges together result in a product qualification rate of only about 40% for this type of component, and tool wear accounts for more than 35% of the total cost, which severely limits its large-scale application in next-generation aerospace equipment.

[0006] Currently, patent CN107635720A discloses a method and grinding machine for grinding the outer and inner contours of a workpiece in a single clamping state. While this method ensures that the machining of the inner and outer surfaces is completed in a single clamping operation, avoiding datum conversion errors, it relies on the workpiece itself having a stable and reliable initial datum (such as an internal concave cavity), centered and clamped by the hollow tip of the tailstock and the spindle box. This method completely fails to solve the "lack of sintering datum" problem addressed by this invention. That is, for "datumless" blanks whose inner and outer contours are inaccurate due to sintering deformation, the clamping method in this prior art not only cannot correct the issue but may also introduce additional stress or clamping errors due to forced clamping. Furthermore, this patent does not address the intermittent machining challenges of heterogeneous material combinations such as high-temperature alloys and self-lubricating materials, nor its dedicated grinding process.

[0007] In summary, existing technologies lack a systematic solution for reconstructing a reference for sintered blanks without a reference, while simultaneously achieving efficient and low-damage precision machining of heterogeneous materials. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for machining self-lubricating composite material parts, a clamping device, and a grinding wheel. This addresses the problems of low machining accuracy, high tool wear, and low yield rates caused by the lack of sintering references, intermittent machining of dissimilar materials, and difficulties in controlling surface integrity during the precision manufacturing of high-temperature alloy and self-lubricating composite material parts. Through the implementation of this invention, high-precision, high-efficiency, and low-damage machining of such parts can be achieved, improving product yield and service reliability, and meeting the stringent requirements of high-end equipment such as aero-engines for high-performance friction pair parts.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for processing self-lubricating composite material parts with a skeleton, comprising the following steps: Reference calibration steps: The outer circle of the skeleton of the sintered composite blank is clamped to form a reference area, and the modified clamping device is used to clamp the blank in the reference area by line contact to correct the coaxiality between the blank and the machine tool spindle, thereby machining an axial reference surface. Grinding process: A porous CBN grinding wheel, in conjunction with a high-pressure cooling system, is used to grind the workpiece on which the reference surface has been established.

[0010] Secondly, the present invention provides a clamping device for implementing the above method, including a chuck and a soft claw, the soft claw being disposed on the chuck, and the inner side of the soft claw being provided with an annular narrow protrusion band, the narrow protrusion band being configured to form line contact with the outer circle of the blank skeleton after clamping and trimming.

[0011] Thirdly, the present invention provides a grinding wheel for implementing the above method, which is a porous composite bonded CBN grinding wheel with a porosity of 12-16%.

[0012] Compared with the prior art, the present invention has at least the following beneficial effects: This invention utilizes an innovative "datum correction" technology to align the external contour of the blank with the machine tool spindle axis, thereby simultaneously correcting the spatial orientation of the internal skeleton and machining a unique and precise axial datum surface. This provides a stable and reliable positioning datum for subsequent machining, fundamentally eliminating quality problems such as uneven allowances and out-of-tolerance coaxiality caused by a lack of datum, and increasing the product qualification rate of such components from the current approximately 40% to over 95%.

[0013] The "grinding" process employed in this invention, through the combination of a specialized porous CBN grinding wheel and optimized parameters, replaces macroscopic intermittent cutting with micro-uniform cutting by agglomerates of abrasive grains, completely suppressing machining vibration and cutting force fluctuations. Simultaneously, the high-porosity grinding wheel structure and high-pressure cooling technology effectively prevent wheel clogging and maintain the wheel's self-sharpening properties. Ultimately, this achieves stable surface roughness control within Ra0.8μm, increases machining efficiency by over 50%, and significantly reduces tool wear costs.

[0014] The establishment of a stable benchmark and the implementation of efficient machining processes have simplified and integrated the original multi-step, iteratively aligned machining routes. The finishing process has been streamlined, reducing the overall machining cycle by approximately 20%, thus overcoming the production bottleneck of inefficiency caused by multi-step machining for this type of part. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the missing reference state of sintered blanks in the prior art; Figure 2 This is a physical image of a part that lacks a reference standard in the existing sintered blank technology; Figure 3 This is a schematic diagram of defects in parts after machining in the prior art; Figure 4 This is a schematic diagram of the clamping reference in an embodiment of the present invention; Figure 5 This is a schematic diagram of the three-dimensional structure of the soft claw in an embodiment of the present invention; Figure 6 This is a three-dimensional structural diagram of the soft claw holding the blank in an embodiment of the present invention; Figure 7 This is a three-dimensional cross-sectional view of the soft claw holding the blank according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the diameter of the colored soft claw in an embodiment of the present invention; Figure 9 This is a schematic diagram of the wear of a traditional CBN grinding wheel in the existing technology; Figure 10 Here are schematic diagrams of the novel porous composite agent CBN grinding wheel according to an embodiment of the present invention; (a) is a schematic diagram of the state after processing with the grinding wheel, and (b) is a schematic diagram of the grinding wheel structure; Figure 11 This is a schematic diagram of the processing route before and after the improvement of the embodiments of the present invention. Detailed Implementation

[0017] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0018] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] This invention provides a method for processing self-lubricating composite material parts with a skeleton, a clamping device, and a grinding wheel.

[0020] This invention illustrates the machining of a high-temperature alloy-self-lubricating composite material inner end bushing for an aero-engine using an example. The specific machining steps include: Step 1: Reference Calibration Fitting reference: such as Figure 4As shown, the sintered composite blank 100 is first subjected to a finishing process. The blank consists of a high-temperature alloy skeleton 1 and self-lubricating coatings 2 sintered on both sides. Using manual or mechanical tools, the outer diameter of the original high-temperature alloy skeleton is repaired according to its design. A reference area 3 is established, ensuring that the roundness of the outer diameter within a 2mm length range at a position symmetrical to the axial center of the high-temperature alloy skeleton 1 is controlled within 0.02mm. This reference area is crucial for providing precise constraints for subsequent clamping. The self-lubricating composite material in other areas is ground radially to a depth 0.1-0.2mm below the surface of the central high-temperature alloy skeleton 1. This operation prevents excessive deformation of the soft material during clamping, which could interfere with the accurate positioning of the rigid skeleton.

[0021] By using clamping, an irregular blank is pre-processed into an area with high-precision geometric features, creating a prerequisite for subsequent precision clamping.

[0022] Soft jaw preparation and profile trimming: This embodiment of the invention provides a dedicated clamping device for clamping the aforementioned composite blank 100. The clamping device includes a chuck and soft jaws, with the soft jaws disposed on the chuck. Preferably, the chuck is a three-jaw chuck. Figure 5 As shown, a three-jaw chuck with soft jaws is used. The chuck 4 is manipulated to close the soft jaws 5. At low speed, a cutting tool is used to machine a narrow annular protrusion 6, at least 2mm wide and with a groove 7 at one end, corresponding to the position where the skeleton is clamped, on the inner side of each soft jaw. The diameter ФA of the narrow protrusion 6 should be consistent with the diameter of the part base (i.e., the high-temperature alloy skeleton). The narrow protrusion 6 is configured to form line contact with the outer circle of the blank skeleton after being clamped and finished. For example, the thickness of the part base is 3mm-7mm, and the diameter is approximately 20mm. The dedicated clamping device provided in this embodiment of the invention consists of the chuck 4 and the soft jaws 5 mounted thereon with the narrow annular protrusion 6.

[0023] like Figure 8 As shown, a standard ring gauge 8 with a diameter matching the correction circle size of the blank skeleton is selected for coloring inspection. The soft jaws 5 clamp the standard ring gauge, and the colored area on the narrow raised band 6 is inspected. It is required that the area be no less than 95% to ensure the formation of a high-precision line contact clamping surface.

[0024] Ensure that the inner hole profile of the modified soft claw is highly coaxial with the machine tool spindle, with radial runout not exceeding 0.005mm.

[0025] This step creates a clamping surface that precisely matches the clamping reference area. The line contact formed by the narrow raised band can apply sufficient radial constraint force to correct the blank, while avoiding positioning errors that may be introduced by surface contact due to the microscopic unevenness of the blank, thus achieving "adaptive clamping".

[0026] Blank clamping and preliminary centering: Remove the standard ring gauge 8, and place the sintered composite blank 100, which has undergone clamping treatment, into the prepared soft jaws 5, as follows. Figure 6 As shown.

[0027] like Figure 7 As shown, the chuck 4 includes a chuck base 41 and a chuck ratchet 42. The chuck ratchet 42 is mounted on the chuck base 41. The jaws 43 are hinged to the chuck ratchet 42. Soft jaws 5 are mounted on the jaws 43. By manipulating the chuck 4, the narrow protrusions 6 of the three soft jaws 5 are precisely clamped in the rounded reference area 3 in the middle of the blank skeleton, with a minimum clamping length of 2mm. Figure 7 As shown in the image. The edge of the clamping part is ground 2mm away from the edge of the self-lubricating coating 2 of the composite material, as shown in the image. Figure 7 As shown in the image.

[0028] Apply a clamping force of 15KN-20KN to make the narrow protrusion 6 slightly embed into the surface of the blank, and complete the initial active centering through the slight adaptive deformation of the material.

[0029] This step is based on the principle of static centering, which forces the macroscopic shape of the blank to coincide with the center of the machine tool spindle through uniform radial constraint. Given that the internal high-temperature alloy skeleton 1 and the external self-lubricating coating 2 are metallurgically bonded as a whole, and the skeleton itself has extremely high rigidity, the spatial orientation of the internal high-temperature alloy skeleton 1 is synchronously corrected after the external shape is precisely corrected.

[0030] Datum surface machining and datum establishment: Based on the initial centering of the blank, the end face turning process is performed. For example... Figure 7 As shown, a precision axial reference surface B, perpendicular to the central axis of the target skeleton and with a flat surface, is machined. This reference surface B is the only reliable axial reference for the current composite blank 100. All subsequent finishing processes will use this surface as the reference, realizing the transformation from a blank without a reference to a workpiece with a definite reference, and providing a stable and repeatable positioning reference for subsequent precision machining.

[0031] In this embodiment of the invention, "blank" specifically refers to an initial part that has been sintered and formed but has not yet undergone the reference correction step described in this invention. Its typical characteristic is that it lacks a reliable machining reference due to sintering deformation. "Workpiece" specifically refers to a semi-finished part that has undergone the reference correction step described in this invention and obtained a precision axial reference surface. This workpiece has a stable and reliable positioning reference and can be used for subsequent finishing.

[0032] Step 2: Grinding After the datum is established, the outer diameter and inner hole of the workpiece are precision machined. This embodiment of the invention focuses on the inner hole grinding.

[0033] Grinding wheel selection: This embodiment of the invention uses a special porous composite bonded CBN (cubic boron nitride) grinding wheel, combined with optimized grinding parameters and a high-pressure cooling system, to achieve micro-uniform cutting of the abrasive grains, replacing traditional turning processes. The porosity (large porosity) of the grinding wheel is 12-16%, the bond is ceramic N7, and the abrasive is cubic boron nitride. This grinding wheel is prepared through a unique secondary calcination process, ensuring uniform distribution, directional arrangement, and high bonding strength of the CBN abrasive grains. Figure 10 As shown in (b), its structure includes large air pores 200 and abrasive grains 300; its high porosity provides ample chip space and cooling effect. The special grinding wheel provided in this embodiment of the invention is the above-mentioned porous composite bonded CBN grinding wheel with high porosity and a specific binder.

[0034] The grinding process parameters can be set as follows: grinding wheel linear speed of 80–120 m / s; workpiece feed speed of 200–300 mm / min; radial depth of cut of 0.005–0.01 mm; grinding wheel speed of 25000 rpm to 30000 rpm, which is determined according to the diameter of the grinding wheel and the required linear speed.

[0035] Cooling system: Equipped with a high-pressure cooling system with a pressure of 10–15 MPa and a coolant flow rate of not less than 20 L / min to ensure sufficient cooling and effective chip removal.

[0036] By combining the aforementioned specialized grinding wheel with optimized high-power grinding process parameters and high-pressure cooling technology, macroscopic intermittent cutting was replaced by micro-uniform cutting of abrasive grains, thus completely suppressing cutting force fluctuations and machining vibrations.

[0037] The high porosity structure and high-pressure cooling of the grinding wheel effectively solve the problem of grinding wheel clogging caused by soft self-lubricating materials, improve the dressing ability of the grinding wheel, and thus improve grinding efficiency. Figure 9 As shown, when traditional CBN grinding wheels are applied to this composite material, they suffer from severe clogging, significant wear, and poor self-sharpening properties; while the grinding wheel provided in this embodiment of the invention, such as Figure 10 As shown in (a), after applying it to the composite material, the grinding wheel showed virtually no clogging or wear.

[0038] By optimizing the binder formulation and process parameters, the grinding wheel maintains good self-sharpening properties when cutting high-hardness, high-temperature alloys. This ultimately achieves stable surface roughness control within Ra0.8μm, while increasing machining efficiency by over 50% and significantly improving surface integrity.

[0039] Process integration: such as Figure 11As shown, the method described in this embodiment of the invention simplifies the original 10 finishing processes to 7 (the processes outlined in the box in the figure are the finishing processes). This is mainly because after datum calibration, the workpiece has a stable and reliable datum, reducing the intermediate processes of repeated alignment and datum conversion. Furthermore, the aforementioned "grinding" process itself combines rough turning, semi-finish turning, and fine grinding steps, significantly improving the efficiency of precision machining of parts.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing self-lubricating composite material parts with a skeleton, characterized in that, Includes the following steps: Reference calibration steps: The outer circle of the skeleton of the sintered composite blank is clamped to form a reference area, and the modified clamping device is used to clamp the blank in the reference area by line contact to correct the coaxiality between the blank and the machine tool spindle, thereby machining an axial reference surface. Grinding process: A porous CBN grinding wheel, in conjunction with a high-pressure cooling system, is used to grind the workpiece on which the reference surface has been established.

2. The method according to claim 1, characterized in that, The reference calibration step specifically includes: The sintered composite blank is trimmed to form a reference area with a roundness of no more than 0.02 mm at a position symmetrical to the center of the skeleton axis, and the self-lubricating composite material on both sides of the reference area is ground down to below the surface of the skeleton. A narrow annular protrusion is machined on the soft jaw of the clamping device, and the soft jaw is inspected and adjusted using a standard ring gauge to ensure that the narrow protrusion is coaxial with the machine tool spindle. The blank after being trimmed is placed into the soft jaws, so that the narrow protrusion is clamped on the reference area by line contact, and clamping force is applied to complete the centering. The axial reference surface is machined on the centered blank.

3. The method according to claim 2, characterized in that, The width of the annular narrow protrusion is not less than 2mm; when clamping, the minimum clamping length between the narrow protrusion and the reference area is 2mm.

4. The method according to claim 2, characterized in that, The applied clamping force is 15KN-20KN.

5. The method according to claim 1, characterized in that, In the grinding process, the porosity of the porous CBN grinding wheel is 12-16%.

6. The method according to claim 5, characterized in that, The grinding parameters for the grinding process are: grinding wheel linear speed 80-120 m / s, workpiece feed speed 200-300 mm / min, radial depth of cut 0.005-0.01 mm; the pressure of the high-pressure cooling system is 10-15 MPa, and the coolant flow rate is not less than 20 L / min.

7. A clamping device for implementing the method according to any one of claims 1-6, characterized in that, It includes a chuck and soft claws, the soft claws being disposed on the chuck, and the inner side of the soft claws having an annular narrow protrusion band, the narrow protrusion band being configured to form line contact with the outer circle of the blank skeleton after being clamped and trimmed.

8. The dedicated clamping device according to claim 7, characterized in that, The width of the narrow protrusion is not less than 2mm.

9. A grinding wheel for implementing the method according to any one of claims 1-6, characterized in that, The grinding wheel is a porous composite bonded CBN grinding wheel with a porosity of 12-16%.

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