Method for processing a counterbore in a coating of an inner wall of a housing

Abstract

The application discloses a method for processing a counterbore of an inner wall coating of a casing, and belongs to the technical field of casing part machining of an aero-engine.The method comprises the following steps: installing an angle head on a machine tool, connecting an input end of the angle head with a main shaft of the machine tool, installing a processing cutter on an output end of the angle head, and setting an included angle between the input end and the output end of the angle head to 90 degrees; installing a special fixture on a numerical control machine tool with a swing head of the main shaft, setting a positioning center of the fixture as G54XY zero point, and setting an angular direction of the fixture as a positive direction of an X axis; installing a part on the fixture positioning circle, and fixing and clamping; adopting a buried drill and a buried cutting finish machining process to process the counterbore, wherein the buried cutting finish machining process comprises first-time buried cutting machining and second-time buried cutting machining, a machining allowance is left after the first-time buried cutting machining, and the second-time buried cutting machining is used to process the counterbore to a design size.The method has the effect of reducing the risk of peeling of the inner wall coating of the casing during the processing of the counterbore of the inner wall of the casing.

Description

Technical Field

[0001] This invention relates to the field of aero-engine component processing technology, and in particular, to a method for processing countersunk holes in the coating of the inner wall of a casing. Background Technology

[0002] The inner wall of an aircraft engine casing is coated with a special coating. Aircraft engines generate extremely high temperatures during operation. This coating protects the inner wall of the casing from high-temperature damage, improves the casing's heat resistance, and extends its service life. The inner wall of the casing has several guide vane holes and countersunk holes for assembly. These guide vane holes and countersunk holes require high precision and need to be machined using machine tools.

[0003] In the existing process of machining the countersunk holes on the inner wall of the casing, milling is used to machine the countersunk holes. A φ12 milling cutter is used to mill around the φ12.7 and φ17.2 countersunk holes clockwise to ensure the diameter and depth of the countersunk holes. However, during circumferential milling, the coating on the inner wall of the part is prone to peeling off, resulting in poor machining quality. Summary of the Invention

[0004] This invention provides a method for countersunk hole machining of the inner wall coating of a casing, in order to solve the technical problem that the inner wall coating of the casing is prone to peeling off during the countersunk hole machining process.

[0005] According to one aspect of the present invention, a method for machining countersunk holes in the inner wall coating of a casing is provided, comprising the following steps: installing an angle head on a machine tool, the input end of the angle head being connected to the machine tool spindle, and a machining tool being installed on the output end of the angle head, the included angle between the input end and the output end of the angle head being 90 degrees; installing a special fixture on a CNC machine tool with a spindle oscillating head, setting the positioning center of the fixture to the G54XY zero point, and setting the angular direction of the fixture to the positive direction of the X-axis; mounting the part on the positioning circle of the fixture and clamping it securely; and performing countersunk hole finishing by submerged drilling and submerged cutting, the submerged cutting finishing including a first submerged cutting and a second submerged cutting, leaving a machining allowance after the first submerged cutting, and machining the countersunk hole to the design size in the second submerged cutting.

[0006] Optionally, the feed rate of the second embedding machining is greater than the feed rate of the first embedding machining.

[0007] Optionally, in the second countersinking process, after the tool has reached the calibrated depth, the tool stops feeding and continues to rotate. After maintaining this position for a preset time, the tool exits the countersink.

[0008] Optionally, the countersunk hole includes a first countersunk hole and a second countersunk hole, the diameter of the first countersunk hole is larger than the diameter of the second countersunk hole, and the rotational speed of the first countersunk hole in the pre-cutting finishing process is lower than the rotational speed of the second countersunk hole in the pre-cutting finishing process.

[0009] Optionally, in the step of finishing the countersunk hole using submerged drilling, the worktable is rotated 180 degrees, which in turn drives the fixture and the housing to rotate synchronously, so that the opening of the countersunk hole to be processed faces downward. During processing, the tool processes the countersunk hole from bottom to top.

[0010] Optionally, before the step of finishing the countersunk hole using submerged drilling, the following steps are also included: raising the coordinates of the machining program by a preset dimension, and then running the CNC program to check whether the machining program is correct.

[0011] Optionally, the helix angle of the submerged drill used for submerged finishing is 20-30 degrees.

[0012] Optionally, the countersunk hole in the inner wall of the casing can be rough machined with a milling cutter before the coating is applied, and then the countersunk hole can be finished by embedding after the coating is applied.

[0013] Optionally, the cutting tools used for embedded cutting finishing are made of cemented carbide.

[0014] Optionally, the axial distance between the input and output ends of the angle head is 95mm, and the radial distance between the input and output ends of the angle head is 95mm.

[0015] In summary, this application includes at least one of the following beneficial technical effects:

[0016] 1. When finishing countersunk holes using the embedded cutting method, the machining path is a straight downward axial movement. This machining method makes the milling force mainly downward. When the milling force is mainly downward, it advances along the surface of the workpiece, consistent with the adhesion direction of the coating. This reduces the possibility of the coating being peeled off or lifted. Using a straight downward axial machining path reduces the shearing force in the lateral direction. Lateral force is an important factor causing coating to lift because it exerts lateral peeling pressure on the coating. This machining method can provide a more stable cutting process, reduce vibration between the workpiece and the tool, and thus reduce the risk of coating lifting.

[0017] 2. By installing an angle head on a machine tool, connecting its input end to the machine tool spindle, and installing a machining tool on its output end, it is possible to machine the sides of a workpiece or parts that are difficult to directly contact. Since the angle between the input and output ends of the angle head is 90 degrees, this allows the tool to machine perpendicular to the workpiece surface.

[0018] 3. Install a special fixture on the CNC machine tool and accurately align the fixture's positioning center as the G54XY zero point, and set the angular positioning to the positive X-axis direction to ensure the accuracy and repeatability of the machining.

[0019] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 This is a flowchart of a preferred embodiment of the casing inner wall coating countersinking machining method;

[0022] Figure 2 This is a schematic diagram of the angle head according to a preferred embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of countersunk hole machining using a milling cutter in the prior art;

[0024] Figure 4 This is a schematic diagram of a preferred embodiment of the present invention using submerged drilling to process countersunk holes;

[0025] Figure 5 This is a schematic diagram of the bottom-up drilling process in a preferred embodiment of the present invention.

[0026] Legend:

[0027] 1. Angle head; 2. Input end; 3. Output end; 4. Countersunk hole; 5. Submerged drill; 6. Milling cutter. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0029] The following is in conjunction with the appendix Figure 1-5 This application will be described in further detail.

[0030] This application discloses a method for machining countersunk holes in the coating of the inner wall of a casing.

[0031] Reference Figure 1 The method for machining countersunk holes in the inner wall coating of the casing includes the following steps:

[0032] Step S100: Install angle head 1 on the machine tool. The input end 2 of angle head 1 is connected to the machine tool spindle. The output end 3 of angle head 1 is equipped with a machining tool. The included angle between the input end 2 and the output end 3 of angle head 1 is 90 degrees.

[0033] Step S200: Install the special fixture on the CNC machine tool with the spindle tilting head, set the fixture positioning center to G54XY zero point, and set the fixture angular direction to the positive X-axis direction.

[0034] Step S300: Install the part on the positioning circle of the fixture and clamp the part in place.

[0035] Step S400: The countersunk hole 4 is precision machined by embedding drill 5. The embedding finishing process includes a first embedding machining and a second embedding machining. After the first embedding machining, a machining allowance is left. The second embedding machining processes the countersunk hole 4 to the design size.

[0036] By installing an angle head 1 on the machine tool and connecting its input end 2 to the machine tool spindle, while installing the machining tool on its output end 3, machining of the side or parts of the workpiece that are difficult to directly contact can be achieved. Since the included angle between the input end 2 and the output end 3 of the angle head 1 is 90 degrees, this allows the tool to machine perpendicular to the workpiece surface. Installing a special fixture on the CNC machine tool and accurately aligning the fixture's positioning center as the G54XY zero point, with angular positioning in the positive X-axis direction, ensures the accuracy and repeatability of the machining. Mounting the part on the positioning circle of the fixture and clamping it securely ensures the stability of the part during machining, reduces machining errors and vibration, and improves machining accuracy and surface quality. When using the recessed cutting method for finishing the countersunk hole 4, the machining path is a straight downward axial movement. This machining method allows… The milling force is mainly downward. When the milling force is mainly downward, it advances along the surface of the workpiece, which is consistent with the adhesion direction of the coating. This reduces the possibility of the coating being peeled off or lifted. The two-stage sinking machining strategy is adopted. The first sinking machining leaves a certain machining allowance, and the second sinking machining machines the countersunk hole 4 to the design size. This staged machining method helps to control the cutting load and improve machining accuracy. Most of the material is removed in the first machining, which reduces the burden of the second machining. This allows the second machining to focus more on achieving accurate dimensions and better surface finish, reducing the risk of coating peeling.

[0037] Reference Figure 2In step S100, the axial distance between the input end 2 and the output end 3 of the angle head 1 is 95mm, and the radial distance between the input end 2 and the output end 3 of the angle head 1 is 95mm. The conventional axial distance between the input end 2 and the output end 3 of the angle head 1 is 150mm, and the radial distance is 120mm. This solution significantly improves the rigidity of the angle head 1 by shortening the length of its lever arm, effectively reducing vibration during processing, thereby improving the surface roughness of the countersunk hole 4 and reducing the possibility of coating peeling. On the one hand, shortening the lever arm enhances rigidity, making the material less prone to bending or deformation. Therefore, shortening the lever arm of the angle head 1 can improve the rigidity of the entire system, thereby reducing vibration during processing. On the other hand, the lever arm length is proportional to the vibration amplitude; the longer the lever arm, the greater the vibration amplitude; the shorter the lever arm, the smaller the vibration amplitude. Therefore, shortening the lever arm can effectively reduce the vibration amplitude and enhance the stability of the processing. Simultaneously, the force exerted by the tool on the workpiece during processing will generate a torque on the lever arm of the angle head 1. The longer the lever arm, the greater the torque produced by the same force, which leads to greater vibration. Shortening the lever arm can reduce this torque, thereby reducing vibration.

[0038] In step S100, after the tool is installed, the length and radius tool compensation values ​​of the CNC tool need to be calculated on the tool setter and input into the CNC machine tool. The main purpose is to ensure the accuracy and consistency of machining. This step allows the machine tool to accurately know the specific position and size of the tool, thereby accurately calculating the tool path in the CNC program. This effectively avoids machining deviations caused by tool clamping errors, ensuring that each machining operation can be performed according to the predetermined dimensions and trajectory.

[0039] In step S200, the special fixture is correctly installed on the spindle tilting head of the CNC machine tool, ensuring the alignment and secure fixation of the fixture and the spindle connection to prevent displacement during machining. The CNC machine tool is then turned on for initial positioning, roughly aligning the fixture with the expected working area. The fixture should be within the machine tool's working range. Appropriate measuring tools, such as edge levelers or probes, are used to accurately locate the fixture's positioning center. The coordinates of the located positioning center are input into the machine tool control system and set as the zero point of the G54 XY workpiece coordinate system. Next, the angular orientation of the fixture needs to be aligned, ensuring that a specific direction of the fixture is aligned with the positive X-axis direction of the machine tool. Once the fixture's angular orientation is set to align with the positive X-axis direction, the accuracy of this angular positioning needs to be reconfirmed to ensure that the workpiece positioning during machining is completely consistent with the program's expectations.

[0040] Reference Figure 3 and Figure 4In step S400, the feed rate of the second submerged cutting process is greater than that of the first submerged cutting process. Since the first processing has removed most of the excess material, the second processing is mainly to achieve accurate dimensions and a good surface finish. Therefore, the feed rate can be increased to improve processing efficiency while ensuring processing quality.

[0041] In the second sub-digging process, after the tool reaches the specified depth, it stops feeding and continues to rotate for a preset time before withdrawing from the countersunk hole 4. This continuous rotation after reaching the specified depth helps reduce cutting stress and heat generated during machining, minimizing thermal and stress deformation of the workpiece and maintaining machining accuracy. The tool's continuous rotation for the preset time allows for more detailed machining of the bottom and sidewalls of the countersunk hole 4. This further improves the surface quality of the countersunk hole 4, especially in precision machining requiring high surface finish and accurate dimensions. The tool slowly withdraws from the countersunk hole 4 after the preset time, reducing vibration or damage to the workpiece that could occur during rapid withdrawal and protecting the machined surface from scratches or damage.

[0042] Countersunk hole 4 includes countersunk hole No. 1 and countersunk hole No. 2. The diameter of countersunk hole No. 1 is larger than that of countersunk hole No. 2, and the speed of the finishing pass for countersunk hole No. 1 is lower than that for countersunk hole No. 2. Different diameters of countersunk holes 4 have specific requirements for machining parameters. For larger diameters (countersunk hole No. 1), a lower speed is required to ensure the stability of the cutting process and reduce vibration. This is because larger diameters usually require more material to be removed, which puts more wear and strain on the tool. Lowering the speed helps to reduce the load on the tool, extend tool life, and maintain machining accuracy. For smaller diameters (countersunk hole No. 2), a higher speed can be used to improve machining efficiency and surface finish. This is because smaller diameters require less material to be removed, so the load on the tool is relatively smaller. Using a higher speed can effectively improve the material removal rate and the surface finish, thereby improving machining efficiency and quality. Therefore, selecting an appropriate speed according to different countersunk hole diameters and machining requirements is key to improving machining quality and efficiency. In actual processing, operators need to take into account specific processing requirements and material properties to optimize processing efficiency and accuracy.

[0043] In one specific implementation, the diameter of the first countersunk hole is 17.2 mm. The first embedded drill 5 is used for embedded cutting with S220F15. At this time, there is still tool deflection and vibration on the bottom surface of the countersunk hole 4. Then, the second embedded cutting is performed with S220F20, and the hole is held on the bottom surface for 2 seconds to complete the machining. The diameter of the first countersunk hole is 12.7 mm. The first embedded drill 5 is used for embedded cutting with S340F15. At this time, there is still tool deflection and vibration on the bottom surface of the countersunk hole 4. Then, the second embedded cutting is performed with S300F20, and the hole is held on the bottom surface for 2 seconds to complete the machining.

[0044] Reference Figure 5 In step 400, during the finishing machining of the countersunk hole 4 using the submerged drill 5, the worktable rotates 180 degrees, causing the fixture and housing to rotate synchronously, so that the opening of the countersunk hole 4 faces downwards. During machining, the tool processes the countersunk hole 4 from bottom to top. The main function of this design is to optimize the chip removal process. In this downward machining position, the chips can naturally fall from the machining area by gravity, thus avoiding chip blockage or re-cutting, improving machining efficiency and the quality of the countersunk hole 4. When the tool tip is downwards, the chips will accumulate at the bottom and need to be discharged from the opening of the countersunk hole 4. At this time, the chips may push up the coating; while when the tool tip is upwards, the chips fall directly downwards, and the generated chips will not accumulate at the bottom of the hole, thus not compressing the coating. At the same time, this downward machining method also reduces the accumulation of machining fluid, preventing it from stagnating inside the countersunk hole 4, which helps to cool the tool and workpiece more effectively, reduces machining heat, and also reduces the difficulty of chip and machining fluid removal. Furthermore, the bottom-up machining method helps reduce workpiece weight and fixture deformation, especially when machining longer or larger workpieces, helping to maintain the perpendicularity and dimensional accuracy of the countersunk hole 4. Finally, this flipping design not only reduces operator intervention when cleaning chips and machining fluid, improving machining safety, but also provides a more convenient machining method for workpieces with special shapes or sizes.

[0045] In step S400, before the step of finishing the countersunk hole 4 using the submerged drill 5, the following step is also included: raising the coordinates of the machining program by a preset dimension, and then test-running the CNC program to check whether the machining program is correct. The main purpose of this design is to verify the safety and accuracy of the program before actual machining, ensuring that the tool moves along the predetermined path without collision or misoperation. In this way, the operator can simulate the entire machining process without contacting the actual workpiece, checking for any potential errors in the program, such as trajectory errors, improper speed, or incorrect coordinate settings. This not only helps prevent damage to the workpiece or machine tool, but also improves machining efficiency and accuracy.

[0046] The helix angle of the embedded drill 5 used in embedded finishing is 20-30 degrees. In one specific embodiment, the helix angle of the embedded drill 5 is 25 degrees, while the helix angle of conventional embedded pin tools is 35 degrees. The size of the helix angle directly affects the distribution and direction of the cutting force. In tools such as end mills 6 or drills, the helix angle is the angle between the cutting edge and the tool axis. When the helix angle decreases, a major component of the cutting force is distributed more radially along the cutting edge, while the axial component is relatively reduced. Reducing the helix angle makes the main direction of the cutting force more radial, thereby reducing the axial component. In this solution, the helix angle is reduced to decrease the axial component caused by the helix angle of the end mill 6, thereby reducing the risk of coating flaking.

[0047] Before applying the coating to the inner wall of the casing, the countersunk hole 4 is rough-machined using a milling cutter 6. After applying the coating, the countersunk hole 4 is then finished using a backfilling process. This design is primarily to ensure the machining accuracy of the countersunk hole 4 and the integrity of the coating. The roughing stage removes a significant amount of material, which can easily damage the coating. Therefore, performing roughing before coating reduces the damage to the coating during the machining process. This process of roughing, coating, and then finishing helps improve the overall manufacturing quality and performance of the component, while minimizing potential damage to the coating during machining.

[0048] In step S400, the cutting tool used for countersunk finishing is made of cemented carbide. Due to its high hardness, high strength, and good wear resistance, cemented carbide can maintain the sharpness of the cutting edge at higher cutting speeds, thereby improving machining efficiency and quality. In one specific embodiment, based on the depth of the countersunk hole 4, a tool with a total length of 65mm and a cutting edge length of 20mm is selected to ensure sufficient tool rigidity.

[0049] In the conventional approach, a milling cutter 6 needs to be replaced after machining 3 housings. However, this approach allows the embedded drill 5 to machine 15 housings, thus reducing tool costs. The embedded drill 5 moves in a straight line from top to bottom, resulting in a short path and a diameter that is achieved in one pass. In contrast, the conventional approach uses milling, which requires a circular path and is longer. Therefore, this approach improves machining efficiency.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for machining countersunk holes in the inner wall coating of a casing, characterized in that, Includes the following steps: An angle head (1) is installed on the machine tool. The input end (2) of the angle head (1) is connected to the machine tool spindle. The output end (3) of the angle head (1) is used to install the machining tool. The included angle between the input end (2) and the output end (3) of the angle head (1) is 90 degrees. Install the special fixture on the CNC machine tool with the spindle tilting head, set the fixture positioning center to G54XY zero point, and set the fixture angular direction to the positive X-axis direction; Mount the part onto the positioning circle of the fixture and clamp the part securely. Before applying the coating to the inner wall of the casing, the countersunk hole (4) in the inner wall of the casing is rough machined with a milling cutter (6), and the countersunk hole (4) is then finished by embedding after applying the coating to the inner wall of the casing. The countersunk hole (4) is finished by submerged drilling (5). The submerged drilling finish includes a first submerged drilling process and a second submerged drilling process. After the first submerged drilling process, a machining allowance is left. The second submerged drilling process will machine the countersunk hole (4) to the design size. When the countersunk hole is finished by submerged drilling, the machining path direction is consistent with the adhesion direction of the coating. In the second sinking process, after the tool has reached the calibrated depth, the tool stops feeding and continues to rotate. After maintaining this position for a preset time, the tool exits the countersunk hole (4). In the step of using a submerged drill (5) to finish the countersunk hole (4), the worktable is rotated 180 degrees, which in turn drives the fixture and the housing to rotate synchronously, so that the opening of the countersunk hole (4) to be processed faces downward. During processing, the tool processes the countersunk hole (4) from bottom to top.

2. The method for machining countersunk holes in the inner wall coating of the casing according to claim 1, characterized in that: The feed rate for the second embedding machining is greater than the feed rate for the first embedding machining.

3. The method for processing countersunk holes in the inner wall coating of the casing according to claim 2, characterized in that: The countersunk hole (4) includes a first countersunk hole (4) and a second countersunk hole (4). The diameter of the first countersunk hole (4) is larger than that of the second countersunk hole (4). The rotational speed of the first countersunk hole (4) during the finishing process is smaller than that of the second countersunk hole (4).

4. The method for machining countersunk holes in the inner wall coating of the casing according to claim 1, characterized in that, Before the step of using a submerged drill (5) to finish the countersunk hole (4), the following steps are also included: Raise the coordinates of the machining program to a preset dimension, and then run the CNC program to check if the machining program is correct.

5. The method for machining countersunk holes in the inner wall coating of the casing according to claim 3, characterized in that: The helix angle of the embedded drill (5) used for embedded finishing is 20-30 degrees.

6. The method for machining countersunk holes in the inner wall coating of the casing according to claim 3, characterized in that: The cutting tools used for embedded cutting and finishing are made of cemented carbide.

7. The method for machining countersunk holes in the inner wall coating of the casing according to claim 1, characterized in that: The axial distance between the input end (2) and the output end (3) of the angle head (1) is 95mm, and the radial distance between the input end (2) and the output end (3) of the angle head (1) is 95mm.

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