Aero-engine casing inner cavity processing technology

Abstract

This invention relates to the field of machining technology, and discloses a machining process for the inner cavity of an aero-engine casing. The inner cavity of the casing includes multiple bosses, each with an annular groove. Bosses located at the casing opening and some bosses located deep within the inner cavity have vertical holes penetrating the annular grooves on their back surfaces, with a portion of the vertical holes coinciding with the annular grooves. Some bosses have oblique holes penetrating the annular grooves on their back surfaces, with a portion of the oblique holes located at the edge of the inner cavity. Some bosses also have through holes penetrating the annular grooves on their back surfaces, with the diameter of the through holes being smaller than the width of the annular grooves. The vertical holes, oblique holes, and through holes are all machined using CNC machining. The vertical holes at the casing opening are machined using a drill bit with a multi-stage drilling process. The through holes are machined using a drill bit with a multi-stage drilling process and a double-edged blade. The oblique holes and other vertical holes are machined using a drill bit with internal cooling holes and a multi-stage drilling process and a double-edged blade. This process ensures that the dimensions of each hole are within acceptable limits, saves manpower, and improves efficiency.

Description

Technical Field

[0001] This invention relates to the field of thin-walled parts processing technology, specifically to a machining process for the inner cavity of an aero-engine casing. Background Technology

[0002] Many parts in aero-engines require drilling and milling in the annular groove to facilitate ventilation or position the outer ring and blades, such as turbine casings, power turbine casings, and low-pressure turbine casings.

[0003] Taking a certain model's turbine casing as an example, as shown in the instruction manual... Figure 1 As shown, the material is GH2132, and the part is a ring-shaped component with a large end diameter of φ674.8 and a small end diameter of φ605.5. The total length is 221.8 mm, and the average wall thickness is about 2.8 mm, making it a typical thin-walled component. The part has 7 bosses inside, each with an annular groove. Each groove has a small hole in or near it, totaling 411. There are 3 sets of tenons distributed on 6 layers of bosses (each set of tenons is distributed on two adjacent layers of bosses). Each layer of bosses has 23-27 tenons, which are slanted grooves 18-25 mm wide and about 2-6 mm deep. The tenons are machined by machining a pair of tenons on the upper and lower layers of bosses in a single cut.

[0004] Overall, the casing has a large volume of space, making the processing and inspection process quite complicated.

[0005] Figure 1 In the casing, the lower half of the 92 φ5.5 holes on the mounting edge of the small end and the 46 φ3 holes in the second layer of the small end are all half-holes (i.e., the holes overlap with the annular groove); and the 104 φ3 holes in the third and fifth layers of the small end have 1 / 4 of their circle at the edge of the part wall, while the 77 φ2.6 holes in the fourth and sixth layers are deep within the casing. Currently, all the small holes (411 in total) in the annular groove are machined on ordinary drilling machines, resulting in high labor intensity and low processing efficiency for operators; moreover, the part's process route is lengthy and cumbersome, leading to long processing cycles and tight production. In addition, since drilling is a manual process, it is very easy to make low-level human errors such as drilling the wrong hole, drilling the wrong hole, or drilling multiple holes; in recent years, such quality problems have occurred frequently, and the rate of incorrect machining remains high. Patent CN110497152A discloses a method for machining deep holes in a casing and its application. However, the deep hole machining on the casing is still done using a conventional drilling machine, which cannot fundamentally solve the above-mentioned problems.

[0006] Mortise and tenon joints Figure 2As shown, the tenon groove needs to be machined using an angle head. Due to the difficulty in machining the material and the easy wear of the cutting tool, the angle head needs to be moved to the tool setting device for tool setting every time the tool is changed. The angle head is bulky and difficult to carry, resulting in a lot of time spent setting the tool. Later, based on the characteristics of large dimensional tolerance (not applicable to small dimensional tolerance), it was improved to use a vernier caliper to measure the length for tool setting, but there are quality problems such as measurement and tool setting errors.

[0007] The three sets of tenons and slots are divided into groups S1, S2, and S3 from the small end to the large end of the housing. The machining process is divided into roughing and finishing. After roughing the 27 evenly distributed tenons and slots in group S3, groups S2 and S1 are then machined. After all tenons and slots are roughed, finishing is performed. During the roughing process, most of the excess material is removed, resulting in a large cutting force, which makes the reducer sleeve prone to deformation. Due to wear of the roughing tool, it is necessary to replace the tool for finishing. When replacing the tool, the operator failed to notice that the reducer sleeve was deformed and directly measured the tool overhang with a depth gauge after tool replacement. Because the depth gauge was measured on the deformed reducer sleeve, the distance from the tool tip to the end face of the reducer sleeve could not be accurately measured, resulting in the actual tool overhang being larger than the measured value (see the instruction manual appendix). Figure 3 The bottom of the tenon groove is machined by tip milling. The tip position is determined by measuring the tool overhang value and inputting it into the machine tool for compensation, thus ensuring the distance from the bottom of the tenon groove to the center. If the measured tool overhang value is too small, it will cause overcutting at the bottom of the S3 group tenon groove, resulting in the bottom surface to center dimension exceeding the tolerance. At the same time, the finishing of each row of tenons grooves is done by the same program, and each program stops after the entire circle of tenons grooves is machined. After the first tenon groove in each row is machined, the dimensions cannot be measured, and the incorrect measurement of the tool overhang value is not detected in time, resulting in the entire groove depth exceeding the tolerance. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a processing technology that can improve the processing accuracy and efficiency of various holes and tenons in the inner cavity of aero-engine casing.

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

[0010] A machining process for the inner cavity of an aero-engine casing includes multiple bosses, each with an annular groove. Bosses located at the casing opening and some bosses deep within the cavity have vertical holes penetrating the annular grooves on their back sides, a portion of which coincides with the annular grooves. Some bosses have oblique holes penetrating the annular grooves on their back sides, a portion of which is located at the edge of the casing cavity. Some bosses also have through holes penetrating the annular grooves on their back sides, the diameter of which is smaller than the width of the annular grooves. Tenon grooves are formed on multiple bosses from top to bottom within the casing cavity, with each pair of adjacent bosses forming a group. The vertical holes, oblique holes, and through holes are all CNC machined. The vertical holes at the casing opening are machined using a drill bit with a multi-stage drilling process. The through holes are machined using a drill bit with a multi-stage drilling and double-edge cutting. The oblique holes and other vertical holes are machined using a drill bit with internal cooling holes and a multi-stage drilling and double-edge cutting process.

[0011] Furthermore, the drill bit material is an ultra-fine particle cemented carbide with a nano-scale TiALN coating.

[0012] Furthermore, the drill bit used to machine the through hole located deep inside the casing is of a one-piece structure, with a thickened drill neck diameter and a drill tip angle of 140°.

[0013] Furthermore, the number of internal cooling holes on the drill bit with internal cooling holes is 1 to 2.

[0014] Furthermore, the process sequence for machining the vertical holes, oblique holes, and through holes is as follows: first, machine the through holes deep within the inner cavity; then, machine the vertical holes located at the opening end of the casing; then, machine the remaining vertical holes; then, machine the oblique holes; and finally, machine the through holes near the opening end of the casing.

[0015] Furthermore, the total length of the drill bit used to process the inclined hole and the through hole is not less than 80 mm, the overhang length is 50-53 mm, the machining linear speed is 20-25 m / s, and the feed is 40-50 mm / r.

[0016] Furthermore, the total length of the drill bit used for machining vertical holes located deep within the cavity is not less than 80 mm, the overhang length is 56-58 mm, the machining linear speed is 20-25 m / s, and the feed is 40-50 mm / r.

[0017] Furthermore, the machining life of the drill bit is designed to machine at least two housings per tool.

[0018] Furthermore, the tool setting method for mortise and tenon machining is as follows: add a tool setting position on the fixture for clamping the housing, fix the tool setting coordinate values ​​on the fixture, and use a tool setting block for tool setting.

[0019] Furthermore, for the burrs at the intersection of the oblique hole and the annular groove, a deburring fixture is designed. The deburring fixture includes a connector connected to a grinding air gun and a grinding rod set on the connector. The end of the grinding rod has a groove for clamping grinding material. The deburring fixture is rotated by the grinding air gun controlling the connector.

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

[0021] The holes inside the casing are now machined using CNC instead of traditional drilling. CNC machining combines multiple traditional processes, reduces the process route, significantly saves machining time, and improves machining efficiency. At the same time, by improving the cutting tools and optimizing the cutting parameters, problems such as unstable drilling, drill drift, poor tool rigidity, and poor cooling and chip removal are effectively solved, ensuring the quality of the machining of each hole size.

[0022] For the machining of tenons and mortises, the tool setting method has been improved. The actual value of the distance L from the center of the mark to the tool setting surface is marked above the tool setting position on the fixture. The actual value of the fixture is regularly checked to ensure that the tool setting value is not affected by the wear of the fixture. This eliminates the need to move the angle head to the tool setting instrument for tool setting every time the tool is changed, saving manpower and improving efficiency. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of the casing described in the background art and embodiments;

[0024] Figure 2 This is a schematic diagram of the mortise and tenon structure described in the background art and embodiments;

[0025] Figure 3 This is a schematic diagram of the measurement value of the tool overhang after deformation of the variable diameter sleeve in the background art;

[0026] Figure 4 This is a schematic diagram of the drill bit structure used for machining the vertical hole at the opening end of the casing in Example 1;

[0027] Figure 5 This is a schematic diagram of the drill bit structure used for machining oblique holes and other vertical holes in Example 1;

[0028] Figure 6 This is a schematic diagram of the drill bit structure used for machining through holes in Example 1;

[0029] Figure 7 This is a schematic diagram of the improved tool setting method on the fixture in Example 1;

[0030] Figure 8 This is a schematic diagram of the burr-removing fixture described in Example 2;

[0031] Figure 9 for Figure 8 Sectional view of AA. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] This invention is based on Figure 1 Taking the aircraft engine casing structure as an example, a casing inner cavity machining process is provided, such as... Figure 1 As shown, the inner cavity of the casing includes multiple bosses 1, each with an annular groove 2. The bosses located at the casing opening and some bosses deep within the inner cavity have vertical holes 3 penetrating the annular grooves on their back sides, with a portion of the vertical holes 3 coinciding with the annular grooves 2. Some bosses have oblique holes 4 penetrating the annular grooves on their back sides, with a portion of the oblique holes 4 located at the edge of the inner cavity. Some bosses also have through holes 5 penetrating the annular grooves on their back sides, with the diameter of the through holes 5 being smaller than the width of the annular grooves 2. Multiple bosses in the inner cavity from top to bottom have tenons 6 (tenon structure see...). Figure 2 The tenon grooves are machined in groups of two adjacent bosses.

[0038] Example 1

[0039] In this embodiment, the vertical holes, oblique holes, and through holes of the casing are all machined using CNC machining. However, using traditional CNC machining methods presents the following difficulties for the casing in this embodiment:

[0040] 1) When using a regular twist drill made of M42 material and carbide to machine the vertical hole of the casing, the drill bit is prone to drifting due to uneven force.

[0041] 2) In the φ2.6 through hole and φ3 oblique hole deep in the casing, especially the φ3 oblique hole, 1 / 4 of the circle is at the edge of the part wall (i.e. the intersection of the oblique surface and the straight surface). During machining, the tool overhang is long, the rigidity is poor, and there is also the problem of unstable centering.

[0042] 3) These holes are all located in the casing annular groove, which hinders chip removal and causes the drill bit to easily squeeze and shake during machining;

[0043] 4) The feed cannot be adjusted by cutting resistance during machining, and the process washers cannot be manually adjusted during machining.

[0044] In this embodiment, to ensure that the casing can be smoothly and successfully machined on CNC equipment, the drill bit for machining each hole has been improved, as detailed below:

[0045] like Figure 4 As shown, the drill bit used for machining the φ5.5 vertical hole 3 located at the opening end of the casing is subjected to a group drilling process. Compared with ordinary drill bits, the group drill has a shorter chisel edge, an increased average rake angle, smoother drilling, a 30% to 52% reduction in axial resistance, a 12% to 32% reduction in drilling torque, significantly improved centering force, reduced drilling force, better chip breaking and removal, smoother drilling, reduced friction, easier entry of cutting fluid into the cutting zone, better cooling and lubrication, and lower drilling temperature. These advantages effectively solve the problems of instability and drill drift during drill bit machining, ensuring that the diameter of the φ5.5 vertical hole in the part is fully qualified.

[0046] like Figure 5 As shown, the drill bits used for the inclined holes 4 at the third and fifth steps of the machining housing and the vertical holes 3 at the second layer are equipped with internal cooling holes (not shown) and subjected to group drilling and double-edge banding. The number of internal cooling holes on the drill bit is generally designed to be 1 to 2, and the path of the internal cooling holes is consistent with the path of the drill bit's spiral groove. Because the φ3 vertical hole is located deep inside the housing and the inclined hole is at the edge of the part's wall, the rigidity is poor during machining, the drill bit is prone to drifting, and the chip removal and cooling effects are poor. Therefore, the above-mentioned group drilling, double-edge banding, and internal cooling hole treatments for the drill bit bring many advantages: the internal cooling holes are ventilation grooves through which the cutting fluid passes during cutting, which cools the tool. At the same time, the coolant passing through these holes can flush away the iron chips sticking to the tool, reduce the tool's cutting temperature, and make the cutting process more stable. This effectively solves the problems of drill bit drifting, poor tool rigidity, and poor cooling and chip removal effects, ensuring that the diameter dimensions of the φ3 vertical hole and the inclined hole on the part are all qualified.

[0047] like Figure 6 As shown, the drill bit used for machining through hole 5 features a multi-drill and double-edge treatment to enhance chip removal and solve the problems of poor chip removal and rigidity during drilling. Because the φ2.6 through hole is deep within the housing, an excessively large drill shank diameter would obstruct the workpiece and result in excessive overhang and poor tool rigidity. Therefore, the drill bit in this area was changed from a welded type to a one-piece type. In areas where it doesn't obstruct the workpiece, the drill neck diameter was increased to ensure drill rigidity. Simultaneously, the drill tip angle was set to 140° to increase tip strength, effectively ensuring the φ2.6 through hole diameter met specifications.

[0048] All of the above drill bit materials are made of ultra-fine particle cemented carbide with a nano-level TiALN coating, which makes the drill bit hard to HRA92.1, giving it strong wear resistance and cutting performance.

[0049] The machining process for the aforementioned vertical holes, oblique holes, and through holes is as follows: First, machine the φ2.6 through hole deep within the inner cavity; then, machine the φ5.5 vertical hole located at the opening end of the casing; next, machine the φ3 vertical hole; then, machine the φ3 oblique hole; and finally, machine the φ2.6 through hole near the opening end of the casing (the large end of the casing). For machining the φ3 oblique hole and the φ2.6 through hole, the total length of the drill bit should be no less than 80 mm, with a cantilever length of 50–53 mm, a machining speed of 20–25 m / s, and a feed rate of 40–50 mm / r. For machining the φ5.5 vertical hole deep within the inner cavity, the total length of the drill bit should be no less than 80 mm, with a cantilever length of 56–58 mm, a machining speed of 20–25 m / s, and a feed rate of 40–50 mm / r. The drill bit life is designed to allow each tool to machine at least two casings.

[0050] The following is a comparison of the machining process flow of the aforementioned holes in the casing in this embodiment and the traditional machining process flow:

[0051]

[0052] As can be seen from the table above, this invention combines multiple processes by modifying ordinary drilling operations to CNC machining.

[0053] Example 2

[0054] This embodiment improves the tool setting method for mortise and tenon machining based on embodiment 1. Specifically, a tool setting position is added to the fixture for clamping the housing, the tool setting coordinate values ​​are fixed on the fixture, and a tool setting block is used for tool setting.

[0055] like Figure 7 As shown, the actual distance L from the center of the mark to the tool setting face is marked above the tool setting position on the fixture. The fixture's dimensions for this actual value are then regularly checked to ensure that the tool setting value is not affected by fixture wear. This effectively avoids the labor-intensive and inefficient problem of having to move the angle head to the tool setting device for tool setting every time a tool is changed.

[0056] When changing worn tools, first remove the worn tool and install a new CNC milling cutter according to the tool overhang requirements of the CNC adjustment card. Use a leveling fixture to align the tool setting edge perpendicular to the machine tool's +X axis (before machining, the leveling fixture and part center should be consistent with program G54). Then, move the angle head with the new tool to the tool setting edge designed in the fixture and use the tool setting fast tool (the setting method is the same as for CNC lathes). When designing the fixture, ensure that the distance from the tool setting edge to the fixture center + the distance from the angle head center to the bottom edge of the tool are less than the machine tool's rotation center distance. Otherwise, the machine tool will report an overtravel warning during tool setting. Input the fixed coordinate values ​​(the actual values ​​branded on the fixture, requiring periodic inspection) + the tool setting block dimensions into the corresponding tool compensation in the machine tool before continuing machining.

[0057] Example 3

[0058] When machining the intersection of the oblique hole and the annular groove on the casing, residual burrs are easily generated, which are inconvenient to observe with the naked eye and require close inspection with a flashlight. Commonly used fitter tools (screwdrivers, grinding wheel heads, diamond dies, grinding wheels, etc.) cannot reach in to remove them, and it is not easy to observe them during removal. Because it is a thin-walled part, the difference in diameter between the oblique hole and the annular groove is also very small, and the center of the oblique hole is not in the center of the annular groove, so the chamfering tool cannot go down to remove the burrs. Furthermore, if the tools are sharp, they can easily damage the parts, causing defects in the appearance of the parts.

[0059] This embodiment addresses the aforementioned problem by designing a deburring fixture, such as... Figure 8 and Figure 9 As shown, the drill bit structure for processing the intersecting position is modified. The deburring fixture includes a connector 71 connected to a grinding air gun and a grinding rod 72 set on the connector. A 17mm long groove 73 is opened at the end of the grinding rod 72 to wrap fine sandpaper (i.e., grinding material). The connector 71 is connected to the interface of the fitter's grinding air gun. The deburring fixture is rotated by the grinding air gun. The fine sandpaper removes the burrs at the intersection during the rotation. The fine sandpaper can also protect the casing from tool damage.

[0060] Compared to traditional machining methods, this machining process combines processes, shortens the process route, and transforms hole machining from ordinary processes to CNC machining. At the same time, it optimizes cutting parameters and improves the tool setting method for tenon and groove machining. According to statistics, the machining time of a single part can be reduced from 84.38 hours to 56.9 hours. At the same time, it effectively improves the machining quality of the parts. Currently, the part machining qualification rate has increased from 93.2% to 99.5%.

[0061] 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 machining process for the inner cavity of an aero-engine casing, the inner cavity of the casing comprising multiple bosses, each boss having an annular groove; the bosses located at the opening end of the casing and some bosses located deep within the inner cavity have vertical holes penetrating the annular grooves on the back side of the bosses, a portion of the vertical holes coinciding with the annular grooves; some bosses have oblique holes penetrating the annular grooves on the back side of the annular grooves, a portion of the oblique holes being at the edge of the inner cavity of the casing; some bosses have through holes penetrating the annular grooves on the back side of the annular grooves, the diameter of the through holes being smaller than the width of the annular grooves; tenons are formed on multiple consecutive bosses from top to bottom within the inner cavity of the casing, the tenons being machined in groups of two adjacent boss layers, characterized in that… The vertical holes, oblique holes, and through holes are all CNC machined. The vertical holes located at the opening end of the casing are machined using a drill bit with a multi-stage drilling process. The through holes are machined using a drill bit with a multi-stage drilling process and a double-edged blade. The oblique holes and the remaining vertical holes are machined using a drill bit with internal cooling holes and a multi-stage drilling process and a double-edged blade. The machining sequence of the vertical holes, oblique holes, and through holes is as follows: first, machine the through holes deep inside the cavity; then, machine the vertical holes located at the opening end of the casing; then, machine the remaining vertical holes; then, machine the oblique holes; and finally, machine the through holes near the opening end of the casing.

2. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The drill bit material is an ultra-fine particle cemented carbide with a nano-scale TiALN coating.

3. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The drill bit used to machine the through hole located deep inside the casing is of a one-piece structure with a thickened neck diameter and a drill tip angle of 140°.

4. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The number of internal cooling holes on a drill bit with internal cooling holes is 1 to 2.

5. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The total length of the drill bit used to process the inclined holes and through holes shall not be less than 80 mm, the overhang length shall be 50~53 mm, the machining linear speed shall be 20~25 m / s, and the feed shall be 40-50 mm / r.

6. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The total length of the drill bit used for machining vertical holes located deep within the cavity shall not be less than 80 mm, the overhang length shall be 56~58 mm, the machining linear speed shall be 20~25 m / s, and the feed shall be 40-50 mm / r.

7. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The machining life of the drill bit is designed to machine at least two housings per tool.

8. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, The tool setting method for mortise and tenon machining is as follows: add a tool setting position on the fixture for clamping the housing, fix the tool setting coordinate values ​​on the fixture, and use a tool setting block for tool setting.

9. The machining process for the inner cavity of the aero-engine casing according to claim 1, characterized in that, For burrs at the intersection of the oblique hole and the annular groove, a deburring fixture is designed. The deburring fixture includes a connector connected to a grinding air gun and a grinding rod set on the connector. The end of the grinding rod has a groove for clamping grinding material. The deburring fixture is rotated by the grinding air gun controlling the connector.

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