A method for fabricating a small-entrance, elliptical-gradient, large-deep cavity

Abstract

To address the issues of insufficient performance and high cost associated with integral casting and additive manufacturing methods for parts with small-entry elliptical gradient deep cavities, and the difficulties, low efficiency, and high cost of metal removal methods, this invention proposes a machining method for elliptical gradient deep cavities with small entry points. The method involves first rough drilling and rough turning to obtain a deep hole. Then, a step-by-step machining approach is adopted, dividing the part into regions and machining them axially and radially. First, the part is tilted to machine the regions on both sides of the major axis of the ellipse. Then, the part is turned upright to machine the regions on both sides of the minor axis of the ellipse. During the upright machining, a radial layering and thin-cutting fast-running method is used. Several layers are machined using the first toolpath until the machining residue in the undercut and triangular regions is removed. Then, a second toolpath is used for contour machining to obtain a gradient deep cavity with an elliptical cross-section. Finally, the gradient deep cavity is precision milled until its internal dimensions and surface roughness meet the design requirements.

Description

Technical Field

[0001] This invention belongs to the field of machining technology and relates to a machining method for a small-entry, elliptical, gradually increasing deep cavity. Background Technology

[0002] To meet the functional requirements of special pressure-bearing housings and pump valve components (e.g., for energy concentration), features with small inlets and large cavities are increasingly being used in product design. Common machining methods for achieving this feature include integral casting, additive manufacturing, and metal removal. However, integral casting suffers from drawbacks such as difficulty in demolding, high mold costs, long production cycles, and insufficient casting precision and performance to meet final usage requirements. Additive manufacturing is hampered by the immaturity of 3D printing technology for certain special materials, the high cost of 3D printing powder, and the inability to achieve the desired final performance. Therefore, for machining irregularly shaped cavity components with special performance requirements, forging is generally used, followed by metal removal to obtain the part's shape. Traditional CNC turning and milling are common for simple, regular, and similar shaped components, offering advantages such as low metal removal, short tool overhang, and good cutting feasibility. However, for components with a small inlet, elliptical gradient, and large deep cavity (e.g., [example missing]),... Figure 1-4 The processing conditions shown are rarely seen. The inner cavity of the small-entrance elliptical gradually widening deep cavity is vase-shaped, with a small upper opening and a large middle cavity. The diameter of the opening is 150-210mm, and the cavity depth is 700-1000mm. The opening of the cavity is a cylindrical cavity, and the main body of the cavity has a cross-section of an ellipse with gradually changing size, forming a large inverted cavity. The major axis of the ellipse is 220-310mm, and the minor axis is 150-220mm. The major axis is 1.5-2 times the minor axis. Because the small-entrance elliptical-gradient deep cavity is an irregular non-rotating body with a large deep cavity, it cannot be machined by traditional turning. If existing milling methods are used, the ratio of the tool head diameter to the tool shank diameter is about 1.5-2.5 times, the tool shank overhang ratio exceeds 12 times, the tool resistance is very high and the vibration is very serious, making normal cutting almost impossible. The machining efficiency is extremely low, the tool consumption is high, the manufacturing cycle is very long, and the manufacturing cost is very high. Therefore, the machining of parts with this feature is one of the challenges in the field of mechanical processing.

[0003] Patent document CN 117102815A discloses a method and tooling for machining irregularly shaped parts with elliptical internal cavities. Although it can machine irregularly shaped parts with elliptical internal cavities, this method ignores the adverse effects of machining residue generated during tilting machining on subsequent processes, and it uses traditional contour-following machining, therefore it cannot machine... Figure 1-4 The image shows a small-inlet, elliptical, gradually widening, deep cavity. Summary of the Invention

[0004] To address the technical problems of high costs and unmet performance requirements when using integral casting and additive manufacturing methods for parts with small-entrance elliptical gradient deep cavities, as well as the difficulties, low efficiency, and high costs associated with metal removal methods, this invention proposes a machining method for small-entrance elliptical gradient deep cavities.

[0005] The technical solution of this invention is:

[0006] A method for fabricating a small-entrance, elliptical-gradient, large-deep cavity, characterized by the following steps:

[0007] Step 1, rough drilling;

[0008] The small-entrance elliptical gradually increasing deep cavity to be processed is graded along the axial depth, and rough drilling is performed with a machining allowance to obtain n-level stepped holes distributed along the axial depth direction; n is 3-5.

[0009] Step 2, rough machining;

[0010] The inner cavity profile of the n-level stepped hole obtained in step 1 is rough machined into a deep cavity, with a machining allowance reserved; the inner diameter of the deep cavity is smaller than and close to the length of the minor axis of the ellipse;

[0011] Step 3, rough milling;

[0012] Step 3.1 Divide the deep cavity obtained after rough turning in Step 2 into a first rough milling area and a second rough milling area for forming the regions on both sides of the major axis of the ellipse, and a third rough milling area and a fourth rough milling area for forming the regions on both sides of the minor axis of the ellipse.

[0013] Step 3.2 Divide the first and second rough milling areas into s-level machining depths along the axial direction. Tilt the part at a certain angle and rough mill the areas of different depths step by step to form the areas on both sides of the major axis of the ellipse; s is 3-5.

[0014] Step 3.3 Divide the third and fourth rough milling areas into 's' levels along the axial machining depth. Position the part upright and rough mill the different depth areas step by step. For the first depth area, use radial layering and thin-cut rapid-run machining method. First, use the first tool path to machine several layers until the machining residue generated in step 3.2 is removed. Then, use the second tool path for contour machining. For the remaining depth areas, before the machining depth exceeds the area of ​​machining residue generated in step 3.2, use the same machining method as the first depth area. After the machining depth exceeds the area of ​​machining residue generated in step 3.2, use the thin-cut rapid-run machining method to perform contour machining along an elliptical path. Finally, a gradually changing deep cavity with an elliptical cross-section is obtained. The first tool path consists of two elliptical arcs and two straight lines, with the two elliptical arcs and two straight lines facing each other. The second tool path is an ellipse.

[0015] Step 4, finish milling;

[0016] The elliptical cross-section of the gradually increasing deep cavity obtained in step 3 is processed into m levels along the axial direction. The inner cavity surface of each depth region is then finely machined to obtain the inner cavity dimensions and surface roughness that meet the design requirements; m is taken as 3-5.

[0017] Furthermore, n in step 1, s in step 3, and m in step 4 are all determined based on the required tool overhang ratio and the specifications and dimensions of commonly used tools.

[0018] Furthermore, in step 3.2, a thickened anti-vibration tool holder and a small-diameter rapid-feed milling cutter are used for milling.

[0019] Furthermore, in step 3.3, when machining the different depth regions in the third and fourth rough milling areas, acceleration and deceleration are applied to regions with different cutting widths:

[0020] When the cutting width is greater than or equal to 75% of the tool diameter, it indicates that the cutting width is too large. In this case, the cutting speed should be reduced to 30-50% of the normal cutting speed.

[0021] When the cutting width is less than or equal to 50% of the tool diameter, it indicates that the cutting width is too narrow. In this case, the cutting speed should be increased to 100-150% of the normal cutting speed.

[0022] When the cutting width is 50-75% of the tool diameter, it indicates that the cutting width is appropriate, and machining should be performed at the normal cutting speed.

[0023] Furthermore, in step 4, a horizontal boring and milling machine is used to perform axial rotary milling from near the minor axis of the ellipse to near the major axis of the ellipse.

[0024] Furthermore, in step 3.2, the turntable of the horizontal four-axis machining center is used to tilt the part at a certain angle.

[0025] Furthermore, in step 3.3, when machining the first-level depth area in the third and fourth rough milling areas, a small-diameter saw blade head + coarse tool bar with short overhang is first used to machine the first radial layer. As the radial depth of cut increases, the tool is replaced with a large-diameter saw blade head + fine tool bar to meet the requirements of large radial depth of cut.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention changes the traditional milling process and tool path, adopting a method of dividing the machining area into small-entry elliptical gradually large-deep cavities and decomposing the machining process in the axial and radial directions step by step. The entire machining process makes full use of the advantages of deep hole drilling machines, horizontal lathes, horizontal boring and milling machines and horizontal four-axis machining centers, and effectively combines them.

[0028] Because the cutting tool is very prone to jamming when it is near the major axis of the ellipse and in the corner area, the workpiece contour and the covering surface are large, and the cutting resistance is high. Therefore, when machining elliptical cavities, this invention makes full use of a horizontal four-axis rotary table instead of a traditional boring and milling machine. The area with the largest machining allowance of the elliptical cavity undercut is preferentially machined by the rotation strategy of the horizontal four-axis rotary table to remove the large allowance. This avoids the situation where the cutting tool has an excessively large covering surface, severe tool jamming and vibration, and tool breakage when the cutting tool is near the major axis of the ellipse. This ensures that the subsequent circumferential milling is smooth and does not jam.

[0029] When rough milling the first and second rough milling areas to form the regions on both sides of the major axis of the ellipse, the rotation strategy of the turntable is used to tilt the part at a certain angle for machining. This can reduce the constraint of the deep cavity inlet on the tool diameter, so that a thickened anti-vibration tool holder + small diameter rapid feed milling cutter can be used to replace the T-type tool, which effectively reduces the tool overhang ratio and cutting resistance.

[0030] When machining to form the areas on both sides of the minor axis of the ellipse, a radial layering and thin-cutting fast-running machining method is adopted, and two different tool paths are used. First, the first tool path is used to machine several layers until the machining residue in the undercut area and triangular area is removed. Then, the second tool path is used for contour machining. This effectively solves the problem of excessive coverage of the tool with the workpiece contour and high cutting resistance when the tool is close to the major axis of the ellipse and in the corner area, thus avoiding the phenomenon of tool jamming and rapid tool breakage.

[0031] When machining in the correct orientation, the saw blade is applied to the undercut cavity machining, replacing the general T-type tool. The radial layering and thin-cut fast running method is adopted to reduce cutting resistance and vibration, and extend tool life. At the same time, acceleration and deceleration are applied to different cutting width areas to improve machining efficiency and reduce machining costs.

[0032] Through the above measures, the present invention achieves high-efficiency and low-cost processing of small-entry elliptical-gradient large-depth cavities. Attached Figure Description

[0033] Figure 1 This is an example of a part with a small inlet, gradually elliptical, deep cavity (isoaxial projection).

[0034] Figure 2 yes Figure 1 A cross-sectional diagram along the major axis of the ellipse.

[0035] Figure 3 yes Figure 1 A cross-sectional diagram along the minor axis of the ellipse.

[0036] Figure 4 yes Figure 2 A cross-sectional view of the maximum undercut position perpendicular to the axial direction.

[0037] Figure 5 This is a schematic diagram of the rough drilling (deep hole drilling) process.

[0038] Figure 6 This is a schematic diagram of the roughing process.

[0039] Figure 7 This is a schematic diagram showing the division of the rough milling area.

[0040] Figure 8 This is a schematic diagram of the rotation of the turntable when rough milling the left and right regions of the major axis of an ellipse.

[0041] Figure 9 This is a schematic diagram of the rotational machining of the first-depth region in the left area of ​​the major axis of the ellipse during rough milling.

[0042] Figure 10 This is a schematic diagram of the rotary machining of the secondary depth region in the left area of ​​the major axis of the ellipse during rough milling.

[0043] Figure 11 This is a schematic diagram of rotary machining of the three-level depth region on the left side of the major axis of the ellipse during rough milling.

[0044] Figure 12 This is a schematic diagram of the machining of the first-level depth region in the rough milling area on both sides of the minor axis of the ellipse.

[0045] Figure 13A This is a schematic diagram of the radial partitioning of the first-level depth region and the first tool path in the rough milling region on both sides of the minor axis of the ellipse.

[0046] Figure 13B This is a schematic diagram of the radial partitioning of the first-level depth region and the second tool path in the rough milling region on both sides of the minor axis of the ellipse.

[0047] Figure 14 This is a schematic diagram of the radial partitioning and machining path speed variation of the second and third depth regions in the rough milling area on both sides of the minor axis of the ellipse.

[0048] Figure 15 This is a schematic diagram of the machining of the second-level depth region in the rough milling area on both sides of the minor axis of the ellipse.

[0049] Figure 16 This is a schematic diagram of the machining of the three-level depth region on both sides of the minor axis of the ellipse during rough milling.

[0050] Figure 17 This is a schematic diagram of the tool path for precision milling of internal cavities.

[0051] Figure 18 This is an isometric schematic diagram of the tool path for precision milling of internal cavities.

[0052] Figure 19 This is a schematic diagram of the axial depth partitioning of the precision milled inner cavity. Detailed Implementation

[0053] To make the technical solution of the present invention clearer and easier to understand, the following description is provided in conjunction with the accompanying drawings and specific examples. Figure 1-4 The invention will be described in detail using the machining of the shown part as an example.

[0054] Reference Figure 5-19 The method for processing a small-entrance, elliptical, gradually increasing deep cavity provided by this invention specifically includes the following steps:

[0055] Step 1, rough drilling.

[0056] The small-entrance elliptical gradually tapering deep cavity to be machined is graded along its axial depth. A rough drilling process is performed on the cross-sectional contour line obtained by sectioning along the axial direction of the deep cavity at the minor axis of the ellipse, with machining allowances reserved in both the axial and radial directions. This results in n-level stepped holes distributed along the axial depth direction, where n is 3-5, with the specific value determined based on the required tool overhang ratio and commonly used tool specifications. The reserved machining allowance refers to the safe machining allowance reserved in both the axial and radial directions of the cross-sectional contour line obtained by sectioning along the axial direction of the deep cavity at the minor axis of the ellipse for subsequent machining processes. For example... Figure 5 As shown, in this embodiment, the following is... Figure 1 The small-entrance elliptical gradient deep cavity on the part shown is divided into three levels. After rough drilling at the specified position on the surface of the part using a deep hole drill, the first-level stepped hole, the second-level stepped hole, and the third-level stepped hole are obtained. A machining allowance of 3-5mm is reserved in both the axial and radial directions of the cross-sectional contour obtained by cutting along the axial direction of the deep cavity at the minor axis of the ellipse.

[0057] Step two, rough machining.

[0058] Sufficient machining allowance is reserved in both the axial and radial directions of the cross-sectional contour obtained by sectioning along the axial direction of the large deep cavity at the minor axis of the ellipse for subsequent machining processes. The inner cavity profile of the n-level stepped hole obtained in step one is rough-turned to obtain a deep cavity. This deep cavity can be a deep cavity with or without a stepped surface, and its inner diameter is smaller than and close to the length of the minor axis of the ellipse. In this embodiment, a horizontal lathe is used for rough turning. Figure 5 The inner cavity profiles of the first, second, and third stepped holes are designed, and a machining allowance of 2-3 mm is reserved on each side of the axial and radial sides of the cross-sectional contour obtained by sectioning along the axial direction of the large deep cavity at the minor axis of the ellipse. The deep cavity obtained after rough turning is as follows: Figure 6 As shown.

[0059] Step 3: Rough milling.

[0060] First, the deep cavity obtained after rough turning in step two is divided into four regions to be rough milled, including the first and second rough milling regions for forming the regions on both sides of the major axis of the ellipse, and the third and fourth rough milling regions for forming the regions on both sides of the minor axis of the ellipse. Then, the first and second rough milling regions are rough milled to form the regions on both sides of the major axis of the ellipse, and the third and fourth rough milling regions are rough milled to form the regions on both sides of the minor axis of the ellipse, finally obtaining a gradient deep cavity with an elliptical cross section.

[0061] During rough milling, the deep cavity machining area needs to be divided into 's' levels according to the tool overhang ratio required for the axial machining depth, and machined level by level. As the machining depth increases, the tool holder needs to be extended. 's' is 3-5, and the specific value is determined based on the required tool overhang ratio (e.g., 3 times the diameter, 3-6 times the diameter, 6-10 times the diameter, 10-15 times the diameter, etc.) and combined with the specifications and dimensions of commonly used tools.

[0062] like Figure 7 As shown, the rough milling sequence in this embodiment is: first rough milling area - second rough milling area - third rough milling area - fourth rough milling area, thereby forming the left side region near the major axis of the ellipse - the right side region near the major axis of the ellipse - the front side region near the minor axis of the ellipse - the rear side region near the minor axis of the ellipse in sequence.

[0063] in:

[0064] 1) Rough mill the first and second rough milling areas to form the regions on both sides of the major axis of the ellipse:

[0065] Reference Figure 7-11The machining process employs a horizontal four-axis machining center with rotation. By using the turntable rotation strategy of the horizontal four-axis machining center, the part is tilted at a certain angle to reduce the constraint of the deep cavity entrance on the tool diameter, so that a thickened anti-vibration tool holder and a small-diameter rapid-feed end mill can be used to mill the first and second roughing areas, forming the left and right sides of the ellipse near the major axis, with a machining allowance of 1-1.5mm on each side. During machining, the first and second roughing areas on the deep cavity are divided into three levels according to the axial machining depth. As the axial machining depth increases, the tool holder is extended to process the first-level, second-level, and third-level depth areas step by step.

[0066] 2) Rough mill the third and fourth rough milling areas to form the regions on both sides of the minor axis of the ellipse:

[0067] Reference Figure 12-16 The turntable of the horizontal four-axis machining center is rotated to the correct position. The third and fourth rough milling areas on the deep cavity are divided into three levels according to the axial machining depth, and each level is machined sequentially.

[0068] For the first-level depth region, due to the preceding rotary machining, ... Figure 2 The inverted area shown and Figure 8 The triangular region shown has a large amount of residual material. Therefore, this invention uses a radial layering and thin-cutting high-speed processing method in the first-level depth region, and first employs the following... Figure 13A The first toolpath shown processes several layers until the residual material in the undercut and triangular areas is removed, and then... Figure 13B The second toolpath shown in the diagram performs contour machining, ultimately forming an elliptical surface. In this process, a small-diameter saw blade with a coarse tool holder and short overhang can be used to machine the first radial layer (around the circumference). As the radial depth of cut increases, the tool is replaced with a large-diameter saw blade with a fine tool holder to meet the requirements of a large radial depth of cut. The first toolpath consists of two elliptical arcs and two straight lines, with the two elliptical arcs and two straight lines positioned opposite each other. The second toolpath is elliptical in shape. Compared to traditional contouring toolpaths, the advantage of using two different toolpaths in this invention is that it avoids excessive tool-workpiece contour coverage and high cutting resistance near the major axis of the ellipse and in corner areas, thus preventing tool jamming and rapid tool breakage.

[0069] Furthermore, such as Figure 14As shown, when machining the first-level depth region, this invention also uses CNC-programmed machining programs to perform acceleration and deceleration processing for different cutting width regions. Specifically, when the cutting width is too large, the cutting speed is reduced to 30-50% of the normal cutting speed; when the cutting width is too narrow, the cutting speed is increased to 100-150% of the normal cutting speed; and when the cutting width is appropriate, machining is performed at the normal cutting speed. This effectively controls the cutting state of the tool as it advances to different regions, ensuring smooth and efficient operation. The determination of whether the cutting width is too large or too narrow is based on the ratio of the cutting width to the tool diameter. When the cutting width is less than or equal to 50% of the tool diameter, it is considered too narrow; when the cutting width is greater than or equal to 75% of the tool diameter, it is considered too large; and when the cutting width is between 50% and 75% of the tool diameter, it is considered appropriate.

[0070] After processing the first-level depth region, the second-level and third-level depth regions are processed sequentially. For the second-level and third-level depth regions, the radial layering and thin-cut rapid-run processing method can also be used, with acceleration and deceleration applied to regions of different cut widths; the difference from the processing method for the first-level depth region is:

[0071] For the second-level depth region, the undercut and triangular regions near the major axis of the ellipse are processed using two different toolpaths, just like the first-level depth region. As the processing depth increases, the residual material in the undercut and triangular regions decreases. The radial number of layers processed along the first toolpath can be gradually reduced until the depth continues to increase beyond the triangular and undercut regions. Then, only the elliptical toolpath is used for contouring.

[0072] For depth level three regions, contour machining can be performed using only an elliptical toolpath.

[0073] After all depth regions have been machined, a gradient deep cavity with an elliptical cross-section can be obtained.

[0074] Step 4: Finish milling.

[0075] The elliptical, gradually increasing deep cavity obtained in step three is divided into m-level axial depths. The inner cavity surfaces of each depth level are then precision machined to obtain the inner cavity dimensions and surface roughness that meet the design requirements. m is taken as 3-5, and the specific value is determined based on the required tool overhang ratio and the specifications of commonly used tools.

[0076] Reference Figure 17-19In this embodiment, the elliptical gradient deep cavity obtained in step three is divided into three depth regions along the axial depth: a first-level depth region, a second-level depth region, and a third-level depth region. In order to reduce the cutting resistance and tool deflection of the tool in the region near the major axis of the ellipse, the tool path is changed from circumferential contour milling to axial contour rotary milling. A horizontal boring and milling machine is used to sequentially cut from the region near the minor axis of the ellipse to the region near the major axis of the ellipse. This effectively avoids the cutting resistance and vibration phenomenon of the tool directly approaching the major axis of the ellipse, and finally obtains the internal cavity size and surface roughness required by the design.

Claims

1. A processing method of a small-inlet elliptical gradually large deep cavity, characterized in that, Includes the following steps: Step 1, rough drilling; The small-entrance elliptical gradually increasing deep cavity to be processed is graded along the axial depth, and rough drilling is performed with a machining allowance to obtain n-level stepped holes distributed along the axial depth direction; n is 3-5. Step 2, rough machining; The inner cavity profile of the n-level stepped hole obtained in step 1 is rough machined into a deep cavity, with a machining allowance reserved; the inner diameter of the deep cavity is smaller than and close to the length of the minor axis of the ellipse; Step 3, rough milling; Step 3.1 Divide the deep cavity obtained after rough turning in Step 2 into a first rough milling area and a second rough milling area for forming the regions on both sides of the major axis of the ellipse, and a third rough milling area and a fourth rough milling area for forming the regions on both sides of the minor axis of the ellipse. Step 3.2 Divide the first and second rough milling areas into s-level machining depths along the axial direction. Tilt the part at a certain angle and rough mill the areas of different depths step by step to form the areas on both sides of the major axis of the ellipse; s is 3-5. Step 3.3 Divide the third and fourth rough milling areas into 's' levels along the axial machining depth. Position the part upright and rough mill the different depth areas step by step. For the first depth area, use radial layering and thin-cut rapid-run machining method. First, use the first tool path to machine several layers until the machining residue generated in step 3.2 is removed. Then, use the second tool path for contour machining. For the remaining depth areas, before the machining depth exceeds the area of ​​machining residue generated in step 3.2, use the same machining method as the first depth area. After the machining depth exceeds the area of ​​machining residue generated in step 3.2, use the thin-cut rapid-run machining method to perform contour machining along an elliptical path. Finally, a gradually increasing deep cavity with an elliptical cross-section is obtained. The first tool path consists of two elliptical arcs and two straight lines, with the two elliptical arcs and two straight lines facing each other. The second tool path is an ellipse. Step 4, finish milling; The elliptical cross-section of the gradually increasing deep cavity obtained in step 3 is processed into m levels along the axial direction. The inner cavity surface of each depth region is then finely machined to obtain the inner cavity dimensions and surface roughness that meet the design requirements; m is taken as 3-5.

2. The method of claim 1, wherein: In step 1, n, in step 3, and m in step 4 are all determined based on the required tool overhang ratio and the specifications of commonly used tools.

3. The processing method for a small-entrance, elliptical-gradient, large-depth cavity according to claim 1, characterized in that: In step 3.2, a thickened anti-vibration tool holder and a small-diameter rapid-feed milling cutter are used for milling.

4. The method for processing a small-entrance elliptical-gradient large-deep cavity according to any one of claims 1-3, characterized in that: In step 3.3, when machining the different depth regions in the third and fourth rough milling areas, acceleration and deceleration are applied to regions with different cutting widths: When 50% of the tool diameter < the cutting width < 75% of the tool diameter, the cutting width is appropriate, and machining should be performed at the normal cutting speed. When the cutting width is greater than or equal to 75% of the tool diameter, it indicates that the cutting width is too large. In this case, the cutting speed should be reduced to 30-50% of the normal cutting speed. When the cutting width is less than or equal to 50% of the tool diameter, it indicates that the cutting width is too narrow. In this case, the cutting speed should be increased to 100-150% of the normal cutting speed.

5. The processing method for a small-entrance, elliptical-gradient, large-depth cavity according to claim 4, characterized in that: In step 4, a horizontal boring and milling machine is used to perform axial rotation milling from near the minor axis of the ellipse to near the major axis of the ellipse.

6. The method for processing a small-entrance, elliptical-gradient, large-depth cavity according to claim 5, characterized in that: In step 3.2, the turntable of the horizontal four-axis machining center is used to rotate the part to tilt it at a certain angle.

7. The method for processing a small-entrance, elliptical-gradient, large-depth cavity according to claim 6, characterized in that: In step 3.3, when machining the first-level depth area in the third and fourth rough milling areas, a small-diameter saw blade head + coarse tool bar with short overhang is first used to machine the first radial layer. As the radial depth of cut increases, the tool is replaced with a large-diameter saw blade head + fine tool bar to meet the requirements of large radial depth of cut.

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