An alignment method for self-adaptive compensation machining of an integral box bottom with an ultra-large diameter-thickness ratio

Abstract

The present application discloses a alignment method for adaptive compensation machining of an integral box bottom with an ultra-large diameter-thickness ratio, which relates to the field of box bottom machining, and includes: coordinating the datum of the box bottom whose inner surface has been machined according to the theoretical dimensions. Taking the inner surface as the datum, after minimizing the error by tabulating the inner surface, the datum adjustment is completed; laser scanning the inner surface of the box bottom to obtain the actual inner surface, and using the actual inner surface as the machining datum; offsetting the machining datum according to the theoretical thickness of each part of the box bottom to obtain the machining outer surface; performing five-axis mirror milling on the machining outer surface, the milling adopts a constant milling path for the Z-axis and the A-axis, and adaptive real-time compensation is performed during the milling process. During the five-axis mirror milling process, accurate positioning of the machining basis of the box bottom is achieved, and only three axes are involved in the linkage during the milling process, greatly improving the response speed of real-time compensation and enabling high-precision machining of thin areas.

Description

Technical Field

[0001] The present application relates to the technical field of tank bottom processing, and in particular to an alignment method for adaptive compensation processing of an integral tank bottom with a super-large diameter-to-thickness ratio. Background Art

[0002] The manufacturing process of the tank bottom of the current rocket tank generally adopts the process of first forming a single melon slice 14 and thinning it with chemical milling, and then welding it into a tank bottom ring. The precision of chemical milling is not high, which is easy to produce quality problems such as orange peel and water ripples on the surface, and the surface consistency is poor. The surface of the melon slice 14 of the tank bottom of the current launch vehicle is out of tolerance by 30%. Figure 1 As shown, the box bottom is formed by welding melon segments 14, which are welded together to form a plurality of melon segments 14 and a top cover 12. There is a transition ring 13 at the bottom of the melon segment 14, and there are many welds 11. Affected by inherent welding defects and welding joint strength, the overall manufacturing quality and reliability of the box bottom are not high.

[0003] At present, there are two problems in the machining of the overall bottom of the box:

[0004] (1) Clamping rigidity problem: The existing clamping methods are mostly integral mold structure or local flexible support. The former is affected by the low mold adhesion rate due to the change of the mold surface, and the latter is affected by the discrete characteristics of the clamping position. Both cannot solve the problem of clamping rigidity.

[0005] (2) Surface error perception problem: Affected by the overall forming process and the deformation of the product itself, the overall bottom inner surface datum of the box often deviates too much from the theoretical value. Traditional machining cannot accurately perceive this type of deviation, resulting in a certain loss of machining accuracy.

[0006] (3) Mirror milling datum alignment problem: Mirror milling technology has been initially applied to the processing of box bottoms, but due to the mechanism of mirror milling equipment, the traditional alignment method of matching the workpiece with the machine tool coordinate system is no longer applicable. A new rapid alignment method is urgently needed to address the coordination problem of the dual motion mechanism of the support head and the follower head and the overall box bottom datum. Summary of the invention

[0007] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a method for aligning the adaptive compensation processing of the overall box bottom with a super-large diameter-to-thickness ratio, which can realize the milling clamping and alignment of the super-large diameter-to-thickness ratio transverse stiffness, and ensure the precise positioning, limited deformation, stiffness milling and no interference of the equipment of the overall box bottom.

[0008] Furthermore, adaptive compensation and alignment processing is achieved during the processing of the overall box bottom with an ultra-large diameter-to-thickness ratio of Φ3350mm, a minimum thickness of 1mm, and a wall thickness accuracy of ±0.1mm.

[0009] The technical solution of the present invention is:

[0010] An alignment method for adaptive compensation machining of an integral box bottom with an ultra-large diameter-thickness ratio, comprising:

[0011] Coordinating the datum of the box bottom whose inner surface has been machined according to the theoretical dimensions. Taking the inner surface as the datum, after minimizing the error by tabulating the inner surface, the datum adjustment is completed;

[0012] Laser-scanning the inner surface of the box bottom to obtain the actual inner surface, and taking the actual inner surface as the machining datum;

[0013] Offsetting the machining datum according to the theoretical thickness at each part of the box bottom to obtain the machining outer surface;

[0014] Performing five-axis mirror milling on the machining outer surface. The milling adopts a constant milling path for the Z-axis and A-axis, and adaptive real-time compensation is carried out during the milling process.

[0015] Minimizing the error by tabulating the inner surface with the inner surface as the datum includes:

[0016] S1: Hoisting the box bottom to the hollow position of the platform structure. There is a vise on the platform structure. The vise has an inner jaw and an outer jaw that can be telescopically extended along the radial direction of the hollow position. Fix the box bottom to the platform structure through the vise;

[0017] S2: Adjust the profiling vise, that is: make the outer jaw located outside the outer surface of the box bottom and keep it in a relaxed state, and adjust the position of the inner jaw so that the inner jaw is in contact with the inner surface to adjust the position of the inner surface of the box bottom;

[0018] S3: Minimize the error by tabulating the inner surface, that is, detect the radius at any several points at the lower end of the box bottom;

[0019] Repeat steps S2 and S3 until the radius difference at the several measured points is minimized, and the datum coordination is completed.

[0020] The number of the vises is 24, and the lengths of the inner jaws and the outer jaws are 50 mm, and the heights are 40 mm - 50 mm.

[0021] Determining the machining datum includes:

[0022] Tabulating and measuring the offset amount between the in-machine laser scanning device and the center of the inner support head. The in-machine laser scanning device is used for laser scanning and is installed on the inner support head;

[0023] The in-machine laser scanning device performs laser scanning on the inner surface to obtain the inner surface point cloud data;

[0024] Perform relative coordinate transformation on the inner surface point cloud data according to the offset amount between the in-machine laser scanning device and the center of the inner support head;

[0025] After importing the point cloud data converted from relative coordinates into reverse software for processing, the actual inner surface is obtained.

[0026] The adaptive real-time compensation method includes:

[0027] S1: The machine tool control system mills the bottom of the box with an initial thickness of W3 according to the preset target thickness W1. During the milling process, the ultrasonic thickness measuring device on the mirror support subsystem performs ultrasonic real-time thickness measurement to obtain the actual thickness W2. The difference between the actual thickness W2 and the target thickness W1 is the thickness deviation e(t);

[0028] S2: The adaptive compensation system calculates the normal required cutting depth u(t) to reach the target thickness at the current thickness through proportional regulation (Kp), integral regulation (Ki), and derivative regulation (Kd);

[0029]

[0030] where t is the current time; Kp, Ki, and Kd are tuned according to the empirical trial-and-error method;

[0031] S3: The control system uses the normal required cutting depth u to calculate the target cutting point (xt, yt, zt) in the Cartesian coordinate system at the current position and outputs it to the W-axis normal feed unit;

[0032] S4: The W-axis normal feed unit interpolates and calculates the feed amounts of each axis according to the target cutting point and outputs them to each axis execution unit to achieve normal feed compensation for thickness deviation compensation; After one compensation, repeat steps S1 - S4 to ensure the minimization of the thickness deviation e(t).

[0033] It is not greater than the current maximum adaptive compensation cutting depth Umax.

[0034] The constant milling paths of the Z-axis and A-axis include milling the thick area first and then the thin area. The milling path of the thick area is: extracting the circular thick area cross-section curves at a fixed frequency of the Z-axis, and milling them in sequence according to the order from top to bottom or from bottom to top along multiple thick area cross-section curves.

[0035] The method for obtaining the constant planning paths of the Z-axis and A-axis includes,

[0036] Dividing the single milling range boundary according to the characteristics of the thick and thin areas of the bottom of the box to obtain the thin area range;

[0037] Extracting the thin area cross-section curves in the thin area range at a fixed frequency of the Z-axis;

[0038] After setting the allowance for the thin area characteristics, cutting off the thin area characteristics after allowance setting in the thin area cross-section curves as the boundary trimming curves.

[0039] The allowance setting range of the thin area feature is the value of the machining tool radius.

[0040] The boundary cutting curve is a plurality of horizontal curves, and milling is performed in sequence along a plurality of horizontal lines in the order from top to bottom or from bottom to top.

[0041] In summary, the present application includes at least the following beneficial technical effects:

[0042] For the overall manufacturing process of the tank bottom, aiming at problems existing in traditional machining such as clamping stiffness, surface error perception, and datum alignment method, a rapid clamping device for the integrally formed tank bottom and a method for coordinating the turning and milling datum, a method for establishing the machining datum by in-machine laser scanning reverse reconstruction, and a method for transverse stiffness milling and adaptive compensation based on mirror support are proposed, which can solve problems such as transverse stiffness clamping, cutting, equal-thickness adaptive machining, and precision control of the overall tank bottom.

[0043] Through the planning of a specific milling path, which is combined with the adaptive compensation method, it is realized that only three axes participate in the linkage during the milling process, greatly improving the response speed of real-time compensation, enabling high-precision machining of thin areas, with the surface roughness reaching at least Ra6.3 and the precision also being stable at ±0.1 mm. Description of the Drawings

[0044] Figure 1 It is a schematic structural diagram of the welded tank bottom in the background technology;

[0045] Figure 2 It is a schematic diagram of the rapid clamping device for the overall tank bottom;

[0046] Figure 3 It is the stress and deformation situation of the tank bottom;

[0047] Figure 4 It is the coordination of turning and milling datum for mirror milling;

[0048] Figure 5 It is the online laser scanning reverse reconstruction;

[0049] Figure 6 It is a schematic diagram of the normal support head;

[0050] Figure 7 It is the thickness real-time compensation mechanism;

[0051] Figure 8 It is the W-axis parameter setting;

[0052] Figure 9 It is the milling real-time thickness measurement result;

[0053] Figure 10 It is a flowchart of the milling path planning method with constant Z-axis and A-axis;

[0054] Figure 11 In the figure, area ① is the traditional milling path, and area ② is the specific milling path with constant Z-axis and A-axis in this application.

[0055] Reference numerals: 11, weld seam; 12, top cover; 13, transition ring; 14, segment.

[0056] 21, inner jaw; 22, outer jaw. Detailed implementation manners

[0057] The following further describes the present application in detail with reference to the drawings and specific embodiments:

[0058] An alignment method for adaptive compensation machining of an integral bottom of an ultra-large diameter-thickness ratio box is disclosed in an embodiment of the present application. As Figure 2 shown, it includes:

[0059] Step 1: Datum coordination

[0060] S1: The follow-up support head returns to zero, the spindle head aligns with the follow-up head, and the position of the spindle head after alignment is set as the zero point of the workpiece coordinate system of the bottom of the box, and the X and Y axes of the workpiece coordinate system are set.

[0061] S2: Set the datum of the workpiece Z-axis with the lower end of the bottom of the box after the bottom of the box is installed in the clamping position as the datum.

[0062] The bottom of the box is installed in the clamping position. The clamping position includes a hollow platform structure and a plurality of profiling vises evenly distributed on the platform structure. The bottom of the box is fixed by the vises. Specifically, the spindle head is positioned on the surface of the platform structure, and the Z-axis datum is: the positioning position of the spindle head on the surface of the platform structure minus the elevation of the vise.

[0063] S3: Lift the bottom of the box to the clamping position. The vise is designed as a double-acting jaw that can expand and contract radially, including an inner jaw 21 close to the circular hollow position of the platform structure and an outer jaw 22 far from the hollow position of the platform structure. The inner jaw and the outer jaw can be adjusted movably along the radial direction of the circular hollow position of the platform structure. The clamping position of the jaw is designed as a cylindrical surface with a diameter of 3350 according to the overall bottom surface of the box.

[0064] The basis for the selection of the number and size of the vises is as follows:

[0065] Through finite element simulation, a gravitational acceleration of 9810 mm / s is applied to the integral bottom of the box 2For the gravity load, a uniform load of 7000 N is applied outside the outer fixture as the clamping force. To ensure that the clamping force of the fixture can be transmitted to the bottom of the tank, a fixed constraint is applied to the inner fixture, and five degrees of freedom of the outer fixture are restricted, only retaining the degree of freedom to move along the center of the bottom of the tank. Under the action of the uniform load, the outer fixture moves towards the center of the sphere, compressing the large section of the bottom of the storage tank, thereby transmitting the clamping force to the bottom of the tank and causing clamping deformation of the bottom of the tank.

[0066] As shown in Table 1 below, through calculation verification, when the number of fixtures is between 10 and 18, the comprehensive clamping deformation is optimal.

[0067] Table 1 Maximum stress and maximum deformation of the bottom of the tank under different numbers of profiling fixtures (initial profiling fixture length is 80 mm, height is 40 mm, clamping force is 7000 N)

[0068]

[0069] As shown in Table 2 below, through calculation verification, when the length of the fixture is 50 mm, the maximum stress and maximum deformation of the bottom of the tank are the smallest.

[0070] Table 2 Maximum stress and maximum deformation caused by fixtures of different lengths to the bottom of the tank. The initial number of fixtures is 3, the height of the fixture is 40 mm, and the clamping force is 7000 N

[0071]

[0072] As shown in Table 3 below, through calculation verification, as the height of the fixture increases, the clamping stress and deformation of the bottom of the tank increase. When the height of the fixture is less than 50 mm, the growth of the stress and deformation of the bottom of the tank is relatively slow. When the height of the fixture is greater than 50 mm, the stress and deformation of the bottom of the tank increase rapidly. In order to make the clamping stable and the clamping stress and deformation of the bottom of the tank as small as possible, the height of the fixture is selected to be 40 - 50 mm.

[0073] Table 3 Maximum stress and maximum deformation caused by fixtures of different heights to the bottom of the tank. The initial number of fixtures is 3, the length of the fixture is 50 mm, and the clamping force is 7000 N

[0074]

[0075] Based on the finite element model, by optimizing the length, height, and number of fixtures, the influence of single factors on the clamping stress and clamping deformation of the bottom of the tank is studied, and a high-rigidity clamping scheme is obtained, that is, selecting profiling fixtures, the length of the fixture is 50 mm, the height of the fixture is 40 - 50 mm, and the number of fixtures is 24.

[0076] S4: Adjust the profiling vise, i.e., place the outer jaws on the outside of the outer surface of the bottom of the box and keep them loose, and adjust the position of the inner jaws 21 so that the inner jaws 21 are in contact with the inner surface to adjust the position of the inner surface of the bottom of the box;

[0077] S5: Measure the inner surface to minimize the error, i.e., detect the radius at any several points at the lower end of the bottom of the box;

[0078] Repeat steps S4 and S5 until the radius difference at the several measured points is minimized to complete the datum coordination.

[0079] Step 2: Establish the machining datum by in-machine laser scanning reverse reconstruction

[0080] After the overall formed bottom of the box is clamped, due to factors such as forming error and hoisting and clamping deformation, there is a large deviation between its actual datum and the theoretical datum. Direct milling will inevitably lead to loss of precision. Therefore, achieving precise setting of the machining datum is an important prerequisite for precision machining of the overall bottom of the box with a large diameter-thickness ratio. This patent provides a method for determining the machining datum by in-machine laser scanning reverse reconstruction, including:

[0081] S1: The operator measures the offset between the in-machine laser scanning device and the center of the inner support head by dial indicator to facilitate subsequent unification of the scanning datum and the machining datum. Among them, the in-machine scanning device is used for laser scanning, the in-machine scanning device is installed on the inner support head, and the five-axis mirror milling equipment includes an inner five-axis support head (support subsystem) and an outer five-axis milling head (tool subsystem).

[0082] S2: Plan the scanning path in regions according to the theoretical inner surface;

[0083] S3: The in-machine laser scanning equipment scans the inner surface according to the fixed frequency and the scanning path planned in step S2 to obtain point cloud data;

[0084] S4: Perform relative coordinate transformation on the point cloud data according to the offset measured in S1 to unify the measurement and machining datum;

[0085] S5: Import the point cloud data after relative coordinate transformation in step S4 into reverse software for operations such as smoothing, noise reduction, surface-body conversion, segmentation, and sheet generation to obtain the reverse reconstructed sheet;

[0086] S6: Import the reverse reconstructed sheet into UG machining software. At this time, the relative datum is the machining datum. Based on this, the actual size of the inner surface in the clamped state, that is, the machining datum, can be obtained.

[0087] According to this method, the inner surface can be reverse reconstructed by in-machine laser scanning and used as the machining datum, and then the final thickness forming machining datum can be determined to achieve high-precision equal-thickness machining.

[0088] Further, afterwards, offset the machining reference according to the theoretical thickness of each part of the overall box bottom to generate a machining profile surface, and then perform milling machining according to the machining profile surface.

[0089] Step 3: Adaptive real-time compensation method during milling

[0090] Five-axis mirror milling is adopted for milling. The mirror support head and the quick clamping device clamping vise jointly provide stiffness support for the workpiece. Among them, 24 vises provide binding forces in the axial and up-down directions; the mirror support head provides continuous stiffness support in the normal direction, so that the transverse stiffness clamping and milling of the overall box bottom can be realized to ensure a thickness tolerance of ±0.1 mm.

[0091] As Figure 6 shown, the mirror support subsystem uses 6 rolling heads to provide normal support. The rolling heads are connected to cylinders and can adapt to the profile and provide stiffness and damping. To avoid the discretization of support, its support strategy is designed as mirror support, that is, during the milling process, the mirror support subsystem always maintains mirror symmetry with the tool subsystem, realizing the conversion from discretized stiffness support to continuous stiffness support, that is, transverse stiffness milling.

[0092] At the same time, although the mirror support subsystem realizes transverse stiffness milling, the diameter-thickness ratio of the overall box bottom can reach 3350 at most. Under the condition of sufficient and stable stiffness, the deformation caused by milling is still an indispensable consideration factor. Therefore, based on this, on the premise of transverse stiffness milling of mirror support, an adaptive compensation method based on real-time thickness measurement is designed.

[0093] As Figure 7 shown, the adaptive compensation method during milling includes:

[0094] And data is transmitted back and displayed on the panel through the DNC module of the machine tool. At the same time, the machine tool control system compares the measured thickness value with the target thickness value according to a certain filtering algorithm, and performs real-time compensation calculation through its thickness error. The control unit performs fine adjustment of the normal feed of the W normal expansion axis of the milling subsystem to compensate for the thickness deviation, realizing closed-loop thickness compensation control.

[0095] Specifically, the adaptive compensation method includes:

[0096] S1: The operator uses the adaptive compensation module macro instruction WCON(W1, Umax, W3), where W1 represents the target thickness, Umax represents the current maximum adaptive compensation cutting depth (an inherent parameter of the machine tool), and W3 represents the initial thickness. The machine tool control system mills according to the preset target thickness W1. Meanwhile, an ultrasonic thickness measuring device is provided on the mirror support subsystem. During the milling process, while the support subsystem provides support, it cooperates with the coupling agent to perform real-time ultrasonic thickness measurement to obtain the actual thickness W2. The difference between the actual thickness W2 and the target thickness W1 is the thickness deviation e(t).

[0097] S2:: The adaptive compensation system calculates the normal required cutting depth u(t) to reach the target thickness at the current thickness through proportional regulation (Kp), integral regulation (Ki), and derivative regulation (Kd).

[0098]

[0099] Where t is the current time; Kp, Ki, and Kd are tuned according to the empirical trial-and-error method.

[0100] S3: The control system uses the normal required cutting depth u to calculate the target cutting point (xt, yt, zt) in the Cartesian coordinate system at the current position and outputs it to the W-axis normal feed unit.

[0101] S4: The W-axis normal feed unit interpolates and calculates the feed amounts of each axis based on the target cutting point and outputs them to each axis execution unit to achieve normal feed compensation for thickness deviation compensation. After one compensation, steps S1 - S4 are repeated to ensure the minimization of the thickness deviation e(t).

[0102] In addition, since the follow-up support head of the mirror milling equipment has the function of real-time thickness measurement and tool cutting depth compensation, but the actual tool cutting is a dynamic process, the response speed of the cutting depth compensation determines the accuracy and quality of the cutting surface. At the same time, due to the existence of many complex thin area features on the overall box bottom, the traditional tool path is affected by the thin area features, and there is a situation where the five-axis interpolation response is too slow during processing, resulting in poor milling surface quality and unstable milling accuracy. Therefore, after establishing the machining base accuracy of in-machine laser scanning reverse reconstruction, it is necessary to plan the milling path of the compensation body.

[0103] Based on this, this patent sets a mirror milling path based on a fast response compensation strategy. To improve the response speed of the compensation, the milling path should minimize the number of linked axes as much as possible. Combining the rotary characteristics of the box bottom, based on this idea, a milling path with constant Z-axis and A-axis is designed. According to its strategy, in most of the milling process, only three axes participate in the interpolation linkage, greatly improving the real-time compensation response speed.

[0104] Such as Figure 10As shown, the milling path planning includes:

[0105] S1: First, divide the boundary of the single milling range according to the characteristics of the thick and thin areas at the bottom of the box;

[0106] S2: Extract the cross-sectional curve of the thin area at a fixed frequency of the Z-axis (the milling width of the tool) (at this time, the cross-sectional curve of the thin area is a complete and continuous curve);

[0107] S3: After setting a certain allowance for the thin area feature, use it as the boundary cutting curve (at this time, the cross-sectional curve of the thin area is cut off by the thin area feature to form the boundary cutting curve), and the allowance setting range of the thin area feature is the radius value of the machining tool;

[0108] S4: Use the boundary cutting curve to perform milling path conversion, and a constant Z-axis cutting can be achieved for most of the time;

[0109] S5: Finally, use five-axis reprocessing to set the tool axis direction so that it is always perpendicular to the machining surface. In this way, it can be ensured that during the milling process with a constant Z-axis, the tool axis direction is only C-axis linkage.

[0110] As Figure 11 shown, the area ① on the left is the conventional cutting path. The cutting path is affected by the thin area feature and is all five-axis linkage; the area ② on the right is the cutting path of this application. For most of the cutting time, the Z-axis and A-axis are constant, and only three axes are involved in the linkage, greatly improving the response speed of real-time compensation. The surface roughness reaches at least Ra6.3, and the accuracy is also stable at ±0.1 mm.

[0111] Although the present invention is disclosed above with preferred embodiments, it is not used to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined by the claims of the present invention.

Claims

1. A centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio, wherein, The specific large diameter-thickness ratio is as follows: diameter Φ3350mm, the thinnest thickness 1mm, and wall thickness accuracy ±0.1mm; and it is characterized in that it includes: Coordinating the datum for the bottom of the box whose inner surface has been machined according to the theoretical dimensions. Taking the inner surface as the datum, after minimizing the error by tabulating the inner surface, the datum adjustment is completed. Laser-scanning the inner surface of the bottom of the box to obtain the actual inner surface, and taking the actual inner surface as the machining datum. Offsetting the machining datum according to the theoretical thickness at each part of the bottom of the box to obtain the machining outer surface. Performing five-axis mirror milling on the machining outer surface. The milling uses a constant milling path for the Z-axis and A-axis, and adaptive real-time compensation is carried out during the milling process. The said adaptive real-time compensation method includes: S1: The machine tool control system mills the bottom of the box with an initial thickness of W3 according to a preset target thickness W1. Meanwhile, during the milling process, the ultrasonic thickness measuring device on the mirror support subsystem performs ultrasonic real-time thickness measurement to obtain the actual thickness W2. The difference between the actual thickness W2 and the target thickness W1 is the thickness deviation e(t). S2: The adaptive compensation system calculates the normal required cutting depth u(t) for the current thickness to reach the target thickness through proportional regulation Kp, integral regulation Ki, and derivative regulation Kd. Where t is the current time; the proportional regulation Kp, integral regulation Ki, and derivative regulation Kd are tuned according to the empirical trial and error method. S3: The control system uses the normal required cutting depth u(t) to calculate the target cutting point (xt, yt, zt) in the Cartesian coordinate system at the current position, and outputs it to the W-axis normal feed unit. S4: The W-axis normal feed unit interpolates and calculates the feed amounts of each axis according to the target cutting point, and outputs them to each axis execution unit to realize the normal feed compensation for thickness deviation compensation. S5: After completing one compensation, repeat steps S1 - S4 to ensure the minimization of the thickness deviation e(t).

2. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 1, characterized in that: The minimizing the error by tabulating the inner surface with the inner surface as the datum includes: S1: Hoisting the bottom of the box to the hollow position of the platform structure. There is a vise on the platform structure. The vise has an inner jaw and an outer jaw that can be telescopically extended along the radial direction of the hollow position. The bottom of the box is fixed to the platform structure through the vise. S2: Adjusting the profiling vise, that is: making the outer jaw located outside the outer surface of the bottom of the box and keeping it in a relaxed state, and adjusting the position of the inner jaw so that the inner jaw is in contact with the inner surface to adjust the position of the inner surface of the bottom of the box. S3: Tabulating the inner surface to minimize the error, that is, detecting the radii at any several points at the lower end of the bottom of the box. Repeat steps S2 and S3 until the radius difference at the several measured points is minimized, and the datum coordination is completed.

3. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 2, characterized in that: The number of the vises is 24, and the lengths of the inner jaws and the outer jaws are 50 mm, and the heights are 40 mm - 50 mm.

4. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 1, characterized in that: Determining the said machining datum includes: Tabulating and measuring the offset amount between the in-machine laser scanning device and the center of the inner support head. The in-machine laser scanning device is used for laser scanning and is installed on the inner support head. The in-machine laser scanning device performs laser scanning on the inner surface to obtain the inner surface point cloud data. Performing relative coordinate transformation on the inner surface point cloud data according to the offset amount between the in-machine laser scanning device and the center of the inner support head. After importing the point cloud data after converting the relative coordinates into reverse software for processing, the actual internal shape surface is obtained.

5. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 1, characterized in that: The normal required cutting depth u(t) is not greater than the current maximum adaptive compensation cutting depth Umax.

6. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 1, characterized in that: The milling path with constant Z-axis and A-axis includes milling the thick area first and then the thin area. The milling path for the thick area is as follows: extract the circular thick area section curves at a fixed frequency of the Z-axis, and mill according to multiple thick area section curves in order from top to bottom.

7. The centering method for adaptive compensation machining of an integral box bottom with an extremely large diameter-thickness ratio according to claim 1, characterized in that: The method for obtaining the milling path with constant Z-axis and A-axis includes Dividing the single milling range boundary according to the characteristics of the thick and thin areas at the bottom of the box to obtain the thin area range; Extract the thin area section curves in the thin area range at a fixed frequency of the Z-axis; After setting the allowance for the thin area feature, cut off the thin area feature after setting the allowance in the thin area section curve as the boundary cutting curve.

8. A centering method for adaptive compensation machining of an integral bottom of a super-large diameter-thickness ratio, characterized in that: The allowance setting range for the thin area feature is the value of the machining tool radius.

9. A centering method for adaptive compensation machining of an integral bottom of a super-large diameter-thickness ratio, characterized in that: The boundary cutting curve is multiple horizontal curves, and milling is performed in order from top to bottom according to multiple horizontal curves.

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