A method for controlling the surface roughness of a bore of a part

Abstract

The application discloses a part inner hole surface roughness control method, which comprises turning, grinding, shot blasting and abrasive polishing steps in sequence. The surface roughness is controlled within Ra0.4 before shot blasting, and the surface roughness is controlled within Ra0.8 after shot blasting. In the abrasive polishing step, the part is placed in a grinding finishing device for polishing. The grinding finishing device comprises a rotatable barrel, the barrel contains abrasive, the part is fixed in the barrel and rotates with the barrel, and a vibration generator is arranged in the barrel to excite the abrasive to vibrate and roll. The abrasive polishing step comprises first polishing and second polishing, and the abrasive size and the barrel rotating speed are different in the first polishing and the second polishing. The control method can achieve the required roughness of the inner hole surface, the polishing removal amount of the shot blasting layer is controlled within 0.002 mm, the surface temperature of the part during polishing is far lower than 538 DEG C, and the shot blasting layer will not relax stress.

Description

Technical Field

[0001] This invention relates to the field of machining technology, and more specifically, to a method for controlling the surface roughness of the inner hole of a part. Background Technology

[0002] The turbine connecting shaft on an aircraft engine is part of the engine's turbine component, as shown in the instruction manual. Figure 1 As shown, it is used to connect the compressor rotor and the gas turbine rotor, transmitting the power generated by the gas turbine rotor to the compressor rotor to drive the compressor. As shown in the figure, surface A of the part is the nut mounting surface, which can be regarded as the inner hole surface. This surface needs to be shot peened, and the final surface roughness requirement is Ra0.4.

[0003] In routine operations, the aforementioned nut assembly surface requires turning, grinding, and shot peening. The surface roughness after shot peening is generally between Ra1.0 and Ra1.6. Further machining is needed to reduce surface roughness. According to enterprise standards, after shot peening, a small amount of material can be removed from the peened area, but the material removal should not exceed 10% of the arc height. Furthermore, it should be ensured that shot peening marks are visible under a 10x magnifying glass, and the surface heat generated during machining should not exceed the heat treatment temperature of 538℃. Currently, the conventional methods for reducing the roughness of the shot-peened surface are polishing with metallographic sandpaper or machining the shot-peened layer using conventional grinding methods. However, experiments have shown that both methods generate a large amount of heat during processing, causing stress relaxation in the shot-peened layer; and metallographic sandpaper polishing is extremely inefficient, severely impacting assembly progress.

[0004] Statistics show that the pass rate of nut assembly is less than 40% because the machining process conditions of the nut assembly surface cannot meet the roughness requirement of Ra0.4.

[0005] Patent CN112404913A discloses a processing method for integral titanium alloy bladed disks. By adjusting the processing route, the method adopts "rough and fine one-time milling forming → vibration finishing → blade laser strengthening → blade shot peening → supplementary vibration finishing". In particular, the blade milling forming is changed to one-time clamping and positioning to process the final blade shape, which significantly improves the geometric dimensions and surface condition forming quality of the blade; manual polishing is eliminated, which increases the product processing efficiency by 50%; and the consistency and stability of the final state of each blade are guaranteed, with a product qualification rate of 90%.

[0006] The aforementioned patent addresses the surface forming quality of the blades by adjusting the overall blade machining process. However, the surface roughness is ensured through a combination of rough grooving and hybrid milling with appropriate allowances and cutting parameters. This step precisely shapes all blade geometry, providing a solid foundation for subsequent finishing and strengthening processes. The vibration finishing operation can be achieved using only traditional abrasive machining. Furthermore, since the machining of this part involves external surface processing, the overall change in the machining process is convenient and feasible.

[0007] The machining of the nut assembly surface of the turbine connecting shaft is an internal surface machining process. The turning, grinding, and shot peening processes cannot be fundamentally changed. Therefore, how to ensure that the surface roughness of the nut assembly meets the assembly requirements while following the traditional process route is a problem that urgently needs to be solved. Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the difficulty in controlling the surface roughness of the inner hole of a part, and to provide a control method that ensures the surface roughness meets the requirements without changing the overall process route.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for controlling the surface roughness of an inner hole of a part, wherein the inner hole of the part has an outer circle and a flange mounting edge, the control method includes turning, grinding, shot peening and abrasive polishing steps performed sequentially on the surface, the surface roughness before shot peening is controlled within Ra0.4 and the surface roughness after shot peening is controlled within Ra0.8; in the abrasive polishing step, the part is placed in an abrasive finishing device for polishing, the abrasive finishing device includes a rotatable barrel containing abrasive, the part is fixed in the barrel and rotates with the barrel, the barrel is equipped with a vibration generator to stimulate the abrasive to vibrate and tumble; the abrasive polishing step includes a first polishing and a second polishing, the abrasive size and barrel rotation speed used in the first polishing and the second polishing are different.

[0011] Furthermore, the grinding wheel finishing equipment contains multiple material cylinders, which can revolve around the center of the grinding wheel finishing equipment.

[0012] Furthermore, the abrasive used for the first polishing is a first triangular prism structure with an equilateral triangle cross-section. The abrasive finishing time is 80–90 min, the rotation speed of the barrel itself is 270–350 r / min, and the revolution speed of multiple barrels is 55–65 r / min.

[0013] Furthermore, the abrasive used for the second polishing is a second triangular prism structure with an equilateral triangle cross-section. The side length of the cross-section of the second triangular prism structure is greater than that of the cross-section of the first triangular prism structure. The abrasive finishing time is 80–90 min, the rotation speed of the barrel itself is 380–420 r / min, and the revolution speed of multiple barrels is 75–85 r / min.

[0014] Furthermore, before abrasive polishing of the parts, a peelable coating is applied to the parts that do not require polishing for protection.

[0015] Furthermore, the grinding step uses a special fixture to hold the part, and the grinding wheel used in the grinding step has a large-diameter short rod. The grinding parameters for the grinding step are: the turbine connecting shaft speed is 25-35 r / min, the grinding wheel linear speed is 18-20 m / s, the rough grinding feed is 0.012-0.016 mm, the rough grinding remaining amount is 0.08-0.12 mm, and the finish grinding feed is 0.008-0.012 mm.

[0016] Furthermore, the special fixture includes a disc, a positioning ring, and a bushing. The positioning ring is fitted around the outer periphery of the end of the part away from the surface. A stop is provided on the outer circular surface of the positioning ring, and the stop is arranged facing the surface. The disc is fitted on the stop, and the end face of the disc facing the surface has a stepped groove. One end of the bushing is in close contact with the stepped groove, and the other end is in contact with the outer circle of the part and the flange mounting edge.

[0017] Furthermore, the grinding wheel grit size used in the grinding step is 80.

[0018] Furthermore, the grinding wheel is a P40X40X13SA80KV grinding wheel.

[0019] Furthermore, the processing parameters for the shot peening step are as follows: shot peening intensity: F12.5~17.5A; shot flow rate: 5Kg / min; spray angle: 85°; nozzle moving speed: 100mm / min; shot size: ZG18; shot peening distance: 100±10mm; air source pressure: 0.35MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This control method adds an abrasive polishing process only after shot peening of the parts. By imposing strict requirements on the surface roughness after grinding and shot peening, it provides a prerequisite for the nut assembly surface roughness to meet the standard after abrasive polishing. In the abrasive polishing operation, a combination of the part's rotation and revolution is specially designed to make the abrasive and the inner hole surface have more and closer contact, so that the amount of shot peening removed is within 0.002mm.

[0022] This control method redesigns grinding and shot peening parameters to control the surface roughness of the inner hole of the part from the source. During the abrasive polishing process, the part is subjected to slight actions such as rolling, scratching and sliding of the abrasive in its free state. In addition, the cooling effect of the abrasive fluid keeps the surface temperature of the part far below 538°C. The shot peening layer will not experience stress relaxation. On the contrary, it can effectively improve the surface quality of the part after shot peening. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of the turbine connecting shaft described in Example 1;

[0024] Figure 2 This is a schematic diagram of the special clamp used in Example 1 to hold the turbine connecting shaft;

[0025] Figure 3 This is a schematic diagram of the turbine connecting shaft as described in Example 1 being clamped in the material barrel of the mold finishing equipment;

[0026] Figure 4a This is a schematic diagram of the turbine connecting shaft nut assembly surface after abrasive polishing as described in Example 1;

[0027] Figure 4b This is a schematic diagram of the turbine connecting shaft nut assembly surface before abrasive polishing as described in Example 1. Detailed Implementation

[0028] To clearly illustrate the technical features of this solution, the following detailed description, in conjunction with the accompanying drawings, will explain the technical solution in detail.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0030] Furthermore, it should be understood in the description of this application that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0032] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0033] Example 1

[0034] Provide a kind of Figure 1The method for controlling the surface roughness of the nut assembly surface 11 on the turbine connecting shaft (hereinafter referred to as the part) is shown. The nut assembly surface of the part has an outer circle 12 and a flange mounting edge 13. This control method starts from the improvement of the grinding process, the shot peening process, and the reprocessing after shot peening. It includes turning, grinding, shot peening, and abrasive polishing processes performed sequentially on the nut assembly surface 11 of the part. Among them, the grinding process improves the grinding wheel bar, grinding wheel material, and grinding parameters to control the surface roughness of the nut assembly surface within Ra0.4 before shot peening. The improvement of the shot peening process ensures that the surface roughness of the nut assembly surface is controlled within Ra0.8 after shot peening, so as to reduce the time and removal amount of subsequent abrasive polishing. In the abrasive polishing process, the part is placed in the abrasive finishing equipment for polishing. By adjusting the abrasive, grinding fluid, processing process, and parameters, the surface roughness of the nut assembly surface is finally achieved to meet the requirement of Ra0.4, while the heat generation temperature during the polishing process is controlled within a low range.

[0035] Specifically, the grinding wheel used in the grinding process has a large-diameter, short wheel shank, for example... Figure 1 If the diameter of the inner hole adjacent to the grinding end face of the part is φ45, then the diameter of the grinding wheel rod can be designed to be close to the diameter of the inner hole, which is φ35 (the diameter of the grinding wheel rod used in the traditional grinding process of this part is φ25). In addition, the rigidity of the grinding wheel rod can be maximized by reducing the length of the grinding wheel rod to prevent chatter from generating chatter marks, which would affect the surface quality of the part. For example, if the length of the grinding wheel rod is 200mm in the traditional grinding process, it can be reduced to 80mm.

[0036] To enhance the rigidity of part clamping, the grinding process uses a special fixture to hold the part, such as... Figure 2 As shown, the special fixture includes a disc 2, a positioning ring 3, and a bushing 4. The positioning ring 3 is fitted around the outer periphery of the end of the part away from the nut mounting surface 11. A stop is provided on the outer circular surface of the positioning ring 3, and the stop is arranged facing the nut mounting surface 11. The disc 2 is fitted onto the stop, and the end face of the disc 2 facing the nut mounting surface has a stepped groove. One end of the bushing 4 is in close contact with the stepped groove, and the other end is in contact with the outer circle 12 and flange mounting edge 13 of the part. The workpiece is positioned using the outer circle close to the grinding surface, supported by the workpiece flange surface, and evenly tightened using multiple bolts 5 to ensure the clamping stability of the workpiece.

[0037] In the grinding process, the grinding wheel grit size for this part is 60 in traditional machining. However, according to the part's machining requirements, a higher grit grinding wheel is needed to achieve a better surface roughness on the nut assembly surface. Therefore, in this embodiment, an 80 grit grinding wheel is selected, and the grinding wheel used is a P40X40X13SA80KV. The grinding parameters are shown in the table below:

[0038] Workpiece rotation speed Grinding wheel linear velocity rough grinding feed rate Residual amount after coarse grinding Fine grinding of feed rate 30r / min 18m / s 0.015 0.1mm 0.01

[0039] The surface roughness of the nut assembly surface of the part ground by the above parameters can be stably controlled within Ra0.4, and the surface condition is normal.

[0040] To meet the requirement that the surface roughness of the nut assembly surface after shot peening should not exceed Ra0.8, i.e., the increase in surface roughness at this location after shot peening needs to be kept within Ra0.4, the processing parameters for the shot peening process in this embodiment are designed as follows:

[0041]

[0042] Abrasive finishing equipment includes a rotatable barrel containing abrasive material, such as... Figure 3 As shown, the part is fixed inside the barrel and rotates with it. Both ends and the middle section of the part are stably fixed within the barrel to prevent loosening and detachment during rotation. A vibration generator inside the barrel stimulates the abrasive to vibrate and tumble. To improve processing efficiency and achieve better polishing of the nut assembly surface, the grinding wheel finishing equipment has multiple barrels that revolve around the center of the equipment. The combination of rotation and revolution allows for more frequent and closer contact between the abrasive and the nut assembly surface.

[0043] Before abrasive polishing of parts, precision parts that do not require polishing and other shot-peeled surfaces should be coated with a peelable coating for protection. Specifically, DT-500 protective peelable coating can be used to prevent dimensional deviations caused by polishing.

[0044] The abrasive polishing process includes a first polishing and a second polishing. The abrasive structure is the same for both polishing processes, but the size and barrel rotation speed differ. The abrasive material is high-alumina ceramic with a triangular prism shape, and the abrasive slurry is HA-FC. The abrasive structure for the first polishing is defined as a first triangular prism structure with a cross-section of an equilateral triangle with a side length of 4mm. The abrasive finishing time is 80–90 min, preferably 90 min. The barrel rotation speed is 270–350 r / min, preferably 300 r / min, and the revolution speed of multiple barrels is 55–65 r / min, preferably 60 r / min.

[0045] The abrasive used for the second polishing is defined as a second triangular prism structure with a cross-section of an equilateral triangle with a side length of 8 mm. The abrasive finishing time is 80-90 min, preferably 90 min. The rotation speed of the barrel itself is 380-420 r / min, preferably 400 r / min. The revolution speed of multiple barrels is 75-85 r / min, preferably 80 r / min.

[0046] In the abrasive polishing process, the part is placed in a barrel filled with abrasive and multi-functional abrasive slurry. The part moves relative to the abrasive in a fixed state, and is subjected to micro-grinding effects such as rolling, scratching, and sliding by the abrasive. This reduces the surface roughness, smoothness, and surface integrity of the part, effectively improving its appearance, fatigue strength, wear resistance, and corrosion resistance. Furthermore, combined with the cooling effect of the abrasive slurry, the workpiece surface temperature is well below 538℃, ensuring that the polishing process does not damage the shot peening layer. The shot peening layer thickness is typically 0.1mm, and the polishing removal amount should not exceed 0.01mm. The removal amount in this abrasive polishing process can be controlled between 0.001mm and 0.002mm.

[0047] Figure 4a and Figure 4b The figure shows the state of the nut assembly surface before and after the abrasive polishing process. As can be seen from the figure, the surface roughness of the nut assembly surface obtained by the specially designed abrasive polishing process is greatly improved. After inspection, the surface roughness is within Ra0.4, which meets the technical requirements of the part.

[0048] Statistics show that when parts are processed using the control method of this embodiment, the surface roughness of the nut assembly surface can reach within Ra0.4, and the first-pass yield of the clamping nut assembly is increased to over 95%.

[0049] Example 2

[0050] The difference between this embodiment and Embodiment 1 lies in the grinding parameters, as detailed in the table below:

[0051] Workpiece rotation speed Grinding wheel linear velocity Rough grinding feed rate Residual amount after coarse grinding Fine grinding of feed rate 25r / min 20m / s 0.012 0.08mm 0.008

[0052] Example 3

[0053] The difference between this embodiment and Embodiment 1 lies in the grinding parameters, as detailed in the table below:

[0054] Workpiece rotation speed Grinding wheel linear velocity Rough grinding feed rate Residual amount after coarse grinding Precision grinding feed rate 35r / min 18m / s 0.016 0.21mm 0.012

[0055] Comparative Example 1

[0056] This comparative example involves polishing the nut assembly surface using conventional abrasive methods after the shot peening process in Example 1. Final inspection revealed that the surface roughness at this location fell far short of the required Ra0.4.

[0057] Comparative Example 2

[0058] Similar to the example, this comparative example also involves sequentially turning, grinding, shot peening, and abrasive polishing of the nut assembly surface of the part. However, the turning, grinding, and shot peening processes are all performed using traditional methods, and the processing parameters for each process differ from those in Example 1. Ultimately, inspection revealed that the surface roughness at this location fell far short of the Ra0.4 requirement.

[0059] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of controlling the surface roughness of a bore of a part, the bore of the part having an outer circle and a flange mounting edge, the method comprising: The control method includes sequential steps of turning, grinding, shot peening, and abrasive polishing on the surface. Before shot peening, the surface roughness is controlled within Ra0.4, and after shot peening, the surface roughness is controlled within Ra0.

8. In the abrasive polishing step, the part is placed in an abrasive finishing device for polishing. The abrasive finishing device includes a rotatable barrel containing abrasive. The part is fixed inside the barrel and rotates with it. A vibration generator is installed inside the barrel to excite the abrasive to vibrate and tumble. The abrasive polishing step includes a first polishing and a second polishing, with different abrasive sizes and barrel rotation speeds used in the first and second polishing. The abrasive used for the first polishing is a first triangular prism structure with an equilateral triangle cross-section. The abrasive finishing time is 80-90 minutes, the rotation speed of the barrel itself is 270-350 r / min, and the revolution speed of multiple barrels is 55-65 r / min. The abrasive used for the second polishing is a second triangular prism structure. The cross-section of the second triangular prism structure is an equilateral triangle. The side length of the cross-section of the second triangular prism structure is greater than the side length of the cross-section of the first triangular prism structure. The abrasive finishing time is 80-90 min. The rotation speed of the barrel itself is 380-420 r / min. The revolution speed of multiple barrels is 75-85 r / min. The grinding step uses a special fixture to hold the part. The grinding wheel used in the grinding step has a large diameter short rod. The grinding parameters for the grinding step are: part rotation speed 25-35 r / min, grinding wheel linear speed 18-20 m / s, rough grinding feed 0.012-0.016 mm, rough grinding remaining material 0.08-0.12 mm, and finish grinding feed 0.008-0.012 mm. The special fixture includes a disc, a positioning ring, and a bushing. The positioning ring is sleeved on the outer periphery of the end of the part away from the surface. A stop is provided on the outer circular surface of the positioning ring, and the stop is arranged facing the surface. The disc is sleeved on the stop. The end face of the disc facing the surface has a stepped groove. One end of the bushing is in close contact with the stepped groove, and the other end is in contact with the outer circle of the part and the flange mounting edge. The grinding wheel used in the grinding step has a grit size of 80; the grinding wheel is a P40X40X13SA80KV grinding wheel; the processing parameters for the shot peening step are: shot peening intensity: F12.5~17.5A; shot flow rate: 5Kg / min; spray angle: 85°; nozzle moving speed: 100mm / min; shot size: ZG18; shot peening distance: 100±10mm; air source pressure: 0.35MPa.

2. The method of part bore surface roughness control of claim 1, wherein, The grinding wheel finishing equipment contains multiple material cylinders, which can revolve around the center of the grinding wheel finishing equipment.

3. The method of controlling the bore surface roughness of a part of claim 1, wherein, Before abrasive polishing, apply a peelable coating to the parts of the parts that do not require polishing for protection.

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