A method for machining, clamping, aligning and coordinating the allowance of large conical shell parts
By engraving continuous lines and marking points on large-diameter conical shell parts, and combining coordinate measuring machine (CMM) and virtual space mapping, the problems of accurate alignment and allowance coordination of conical shell parts were solved, improving alignment accuracy and reducing allowance loss.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TIANJIN AEROSPACE CHANGZHENG ROCKET MFGCO
- Filing Date
- 2023-11-10
- Publication Date
- 2026-05-26
AI Technical Summary
Existing machining methods cannot meet the requirements for accurate alignment and allowance coordination of large-diameter conical shell parts. Traditional methods suffer from low alignment accuracy, large allowance loss, and inability to judge the allowance status in a timely manner.
A benchmark coordination method based on blank inspection and iterative allowance optimization is adopted. By engraving continuous lines and marking points on the blank, combined with coordinate measuring machine and virtual space mapping, the accurate alignment and allowance coordination of the conical shell part are achieved.
It improves alignment accuracy and minimizes the loss of allowance caused by alignment deviation, thus achieving precise clamping and alignment of conical shell parts and allowance coordination.
Smart Images
Figure CN117400061B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of allowance coordination for conical box-shaped parts, and in particular relates to a method for coordinating allowances during machining and clamping of large conical shell-shaped parts. Background Technology
[0002] The rear bottom of the new-generation manned launch vehicle's propellant tank features a 45° conical structure, with a large end diameter of approximately 4.6m, a small end diameter of 2.1m, and a height of approximately 1.2m. Both ends are open-shell structures. A high-density orthogonal grid is evenly distributed across the outer surface of the shell structure, with a grid thickness of 4mm at the bottom and 20mm at the top. This part is manufactured using a monolithic forming method. The preform, after being integrally formed, has certain allowances in the internal and external dimensions, as well as in the height direction. These allowances need to be removed through machining to achieve the final product's shape and position accuracy control.
[0003] Based on the product structure and actual condition of the blank, the machining plan adopts a "turning first, milling later" process route. Turning completes the internal and external contour machining of the conical shell part, while milling completes the mesh feature machining. In the first machining process, the most important task is to clamp and align the blank and coordinate the allowances, that is, to find the optimal position for the part on the blank and ensure that the machining coordinate system of the CNC machine tool matches that optimal position.
[0004] Due to limitations in sheet metal thickness imposed by the forming process, as well as factors such as thickness reduction during forming and precision control after forming, the allowance for the blank enveloping the product is often quite tight. This places high technical demands on the alignment accuracy and allowance coordination level of such parts. Traditional machining alignment methods often cannot meet the processing requirements of this type of product.
[0005] For clamping, alignment, and allowance coordination of large-diameter conical shell parts, existing solutions mainly rely on the common on-machine four-point alignment method. This method utilizes four symmetrically distributed points to perform four-point circular and leveling on a lathe. However, this method has the following main problems:
[0006] (1) The alignment accuracy is not high, and the allowance loss is large. The blank after integral forming often has large deviations in shape and position dimensions, and the overall roundness and flatness are poor. When aligning through the datum transferred by integral forming, the datum itself often changes significantly, resulting in large deviations when using it as a datum for alignment. At the same time, relying solely on four-point alignment cannot take into account the overall situation, and the error is large.
[0007] (2) The allowance cannot be determined after alignment. After four-point alignment, it is impossible to make a timely estimate of the overall allowance of the blank to guide subsequent processing. This alignment method is often suitable for processing parts with large allowance margins, but it cannot meet the precise alignment requirements of large-diameter conical shell integral forming parts.
[0008] In summary, there is still no effective solution for precision alignment and allowance coordination in the machining of large-diameter conical shell parts. Summary of the Invention
[0009] In view of this, the present invention aims to propose a method for coordinating the clamping and alignment allowance in the machining of large conical shell parts, which effectively solves the engineering problem of insufficient allowance at the bottom of the cone. Based on this method, the alignment accuracy can be improved and the allowance loss caused by alignment deviation can be minimized.
[0010] To achieve the above objectives, the technical solution of the present invention is implemented as follows:
[0011] A method for coordinating the clamping and alignment allowances in the machining of large conical shell parts, the clamping and alignment method includes the following steps;
[0012] S1, Forming reference transfer; A continuous engraving line is made at the large end of the blank by the forming process to transfer the rough reference of the forming process;
[0013] S2. Machining alignment marks: Place the conical shell part with the large end down and the small end up on the lathe table, and mark 8 points evenly at the same height on the large end with "cross lines".
[0014] S3. Blank Inspection: Place the part with the large end facing up and the small end facing up on a coordinate measuring machine platform, and measure the shape of the blank using coordinate points.
[0015] The main task is to measure some data;
[0016] a. Coordinate point set Q of the blank's outer surface t , denoted as {X t(u.v) ,Y t(u.v) Z t(u.v)}, where u = 1, 2, ... 20 represents 20 measurements taken at 100 mm intervals along the busbar direction. v = 1, 2, ... 16 represents 16 measurements evenly distributed along the circumferential direction. In total, there are 320 measurement points.
[0017] b. Set of machining alignment markers Q b That is, {X} bi ,Y bi Z bi}, i = 1, 2, 3…8;
[0018] c. Forming reference point set Q c That is, {X} ci ,Y ci Z ci}, i = 1, 2, 3, 4. A planar mechanism is determined based on three points, and a verification point is added; here, any four points on the three-dimensional forming baseline can be measured.
[0019] Furthermore, the above-mentioned points are processed in reverse. First, the coordinate point set Q of the blank's outer surface is used. t Generate 20 circumferential spline curves (U-curves) and 16 generatrix spline curves (V-curves).
[0020] The U and V curves are used to generate a mesh surface in reverse to obtain the outer contour surface; the outer contour surface is offset inward to the minimum thickness of the actual blank to obtain the limit inner shape surface of the blank; the generation of the inner and outer blank surfaces completes the blank inspection.
[0021] S4. Optimization of allowance; The blank inspection only completes the contour generation, but the relative optimal position and orientation of the blank and the theoretical model are still the key factors that determine the allowance; Therefore, this invention provides a blank allowance optimization method based on a coarse datum.
[0022] Specifically, it includes the following steps;
[0023] S41. Position the theoretical coordinate system MCS. The origin of the coordinate system is at the center of the large end of the theoretical model. The XYZ directions are consistent with the theory. All subsequent operations on the MCS are considered as joint operations on the MCS and the theoretical model.
[0024] S42. Next, the set of forming reference points Q detected... c Create a coarse reference plane using three points, and then define the Z-axis of the MCS. MCS Adjust it to align with the normal direction of the reference plane. Set the rotation center (X) of the theoretical model... MCS Y MCS Z MCS Adjust it to coincide with the center of the large end contour of the blank. This completes the precise rounding and rough leveling of the theoretical model in the blank;
[0025] S43. Move the MCS along Z MCS The direction is shifted vertically. During this shift, the envelopment of the blank changes linearly. Taking any cross-section as an example, when the envelopment allowance K... v When a turning point occurs, that point is the optimal point; let Z be the value at that moment. MCS Coordinates can be used to complete the rough leveling of the upper and lower references;
[0026] S44. Analyze the envelope of the theoretical model and the blank contour at this point, according to the following rules: (X...) MCS Z MCS The plane is the cutting plane, and it moves along Z at a certain frequency i. MCS Rotate the cutting plane along the axis to obtain each cutting plane in the Z-axis. MCS +X in height MCS Directional envelope margin K vi+ and -XMCS Directional envelope margin K vi- Define pose threshold ΔK i =|K vi+ -K vi -|, this threshold represents the degree of attitude deviation. Find the maximum attitude threshold for each cutting plane, and then set Y... MCS The direction is consistent with the normal of the cutting plane;
[0027] S45, local fine-tuning, moving the MCS around the Y MCS Axial K vi+ and K vi Rotate the MCS to the side with the larger value in the matrix, with a single rotation angle of 0.2° and a maximum of 2°. Simultaneously, rotate the MCS along the Z-axis. MCS Make a slight vertical translation adjustment, with an adjustment range of ±5mm;
[0028] S46. Repeat steps S41-S45 until the pose threshold ΔK is reached. i When the deceleration is less than 0.2, the iteration process is terminated; the current MCS is recorded.
[0029] S5, Reference Mapping; The MCS obtained through the margin optimization process is the optimal reference for the product; Mapping this reference from virtual space to real space is a crucial process; The set of alignment markers Q for machining. b The point coordinates mapped to the MCS coordinate system are recorded as Q. b-MCS Let its Z coordinate be Z. b-MCS-i , i = 1, 2, 3…8; pass this value to the machine operator.
[0030] S6. Physical alignment: Through machine tool operation, leveling and shimming operations are performed on the raw workpiece to ensure that the relative positions of the 8 marked points of the machining are aligned with the Z-axis. b-MCS-i The relative positions of the eight provided points are kept consistent, thus achieving a consistent mapping relationship between the optimal reference MCS and the machine tool coordinate system.
[0031] Furthermore, the evaluation method for physical alignment includes the following steps:
[0032] S61. Calculate and adjust the target baseline drop. 8 Z b-MCS-i Subtract the minimum value Z b-MCS-min The relative height deviation of each point is obtained;
[0033] S62. The operator adjusts the blank products according to this deviation to make them as consistent as possible. The actual reference drop is measured by the machine tool dial indicator after adjustment. And calculate the adjustment deviation
[0034] S63. Repeat the above process until... If the average value is less than 0.5mm, it is considered to be accurately aligned; This is considered an evaluation method for clamping and alignment.
[0035] This invention provides a method for coordinating the clamping and alignment allowances in the machining of large conical shell parts. Addressing the precise alignment problem in the machining of large-diameter conical shell parts for storage tank bottoms, this invention effectively solves the engineering challenge of insufficient allowance at the conical bottom. It designs a datum coordination method based on blank inspection and iterative allowance optimization, and a clamping, alignment, and evaluation method based on datum mapping and physical alignment. Based on these inventions, a precise alignment and evaluation method for conical shell parts based on coordinate measuring machine (CMM) and virtual-real space mapping can be achieved, effectively improving alignment accuracy and minimizing allowance loss due to alignment deviations. Attached Figure Description
[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:
[0037] Figure 1 This is a schematic diagram of the conical shell part according to an embodiment of the present invention;
[0038] Figure 2 This is a schematic diagram of the 320 measuring points described in an embodiment of the present invention;
[0039] Figure 3 This is a schematic diagram illustrating the precise rounding and rough leveling of the theoretical model described in this embodiment of the invention in the blank.
[0040] Figure 4 This is a schematic diagram of the rough leveling of the theoretical model described in the embodiment of the present invention on the upper and lower reference surfaces of the blank. Detailed Implementation
[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.
[0042] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention 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 of the invention. Furthermore, the terms "first," "second," etc., 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 with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0043] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0044] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0045] A method for coordinating the clamping and alignment allowances in the machining of large conical shell parts, the clamping and alignment method includes the following steps;
[0046] S1, Forming reference transfer; A continuous engraving line is made at the large end of the blank by the forming process to transfer the rough reference of the forming process;
[0047] S2. Machining alignment marks: Place the conical shell part with the large end down and the small end up on the lathe table, and mark 8 points evenly at the same height on the large end with "cross lines".
[0048] S3. Blank Inspection: Place the part with the large end facing up and the small end facing up on a coordinate measuring machine platform, and measure the shape of the blank using coordinate points.
[0049] The main task is to measure some data;
[0050] a. Coordinate point set Q of the blank's outer surface t , denoted as {X t(u.v) ,Y t(u.v) Z t(u.v)}, where u = 1, 2, ... 20 represents 20 measurements taken at 100 mm intervals along the busbar direction. v = 1, 2, ... 16 represents 16 measurements evenly distributed along the circumferential direction. In total, there are 320 measurement points.
[0051]
[0052] b. Set of machining alignment markers Q b That is, {X} bi ,Y bi Z bi}, i = 1, 2, 3…8;
[0053] i 1 2 ... 8 <![CDATA[Alignment marking point Q b > (-208.9，2321.6，-1350) (-1755.3，1533.6，-1350) (1453.2，1822.3，-1350)
[0054] c. Forming reference point set Q c That is, {X} ci ,Y ci Z ci}, i = 1, 2, 3, 4. A planar mechanism is determined based on three points, and a verification point is added; here, any four points on the three-dimensional forming baseline can be measured.
[0055] i 1 2 ... 8 <![CDATA[Forming reference point Q c > (363.7，2150.4，-1203.2) (-2173.3，182.5，-1197) (2112.4，-542.3，-1201.9)
[0056] Furthermore, the above-mentioned points are processed in reverse. First, the coordinate point set Q of the blank's outer surface is used. t Generate 20 circumferential spline curves (U-curves) and 16 generatrix spline curves (V-curves).
[0057] The U and V curves are used to generate a mesh surface in reverse to obtain the outer contour surface; the outer contour surface is offset inward to the minimum thickness of the actual blank (35.3 mm) to obtain the limit inner shape surface of the blank; the generation of the inner and outer blank surfaces completes the blank inspection; because the thickness of the blank is not uniform, the worst case can be obtained by offsetting according to the minimum thickness.
[0058] S4. Optimization of allowance; The blank inspection only completes the contour generation, but the relative optimal position and orientation of the blank and the theoretical model are still the key factors that determine the allowance; Therefore, this invention provides a blank allowance optimization method based on a coarse datum.
[0059] Specifically, it includes the following steps;
[0060] S41. Position the theoretical coordinate system MCS. The origin of the coordinate system is at the center of the large end of the theoretical model. The XYZ directions are consistent with the theory. All subsequent operations on the MCS are considered as joint operations on the MCS and the theoretical model.
[0061] S42. Next, the set of forming reference points Q detected... cCreate a coarse reference plane using three points, and then define the Z-axis of the MCS. MCS Adjust it to align with the normal direction of the reference plane. Set the rotation center (X) of the theoretical model... MCS Y MCS Z MCS Adjust it to coincide with the center of the large end contour of the blank; this completes the precise rounding and rough leveling of the theoretical model in the blank, such as... Figure 3 As shown;
[0062] S43. Move the MCS along Z MCS The direction is shifted vertically. During this shift, the envelopment of the blank changes linearly. Taking any cross-section as an example, when the envelopment allowance K... v When a turning point occurs, that point is the optimal point; let Z be the value at that moment. MCS Coordinates can be used to complete the rough leveling of the upper and lower references, such as... Figure 4 As shown;
[0063] S44. Analyze the envelope of the theoretical model and the blank contour at this point, according to the following rules: (X...) MCS Z MCS The plane is the cutting plane, and it moves along Z at a certain frequency i. MCS Rotate the cutting plane along the axis to obtain each cutting plane in the Z-axis. MCS +X in height MCS Directional envelope margin K vi+ and -X MCS Directional envelope margin K vi- Define pose threshold ΔK i =|K vi+ -K vi- | This threshold represents the degree of attitude deviation. Find the maximum attitude threshold for each cutting plane, and then set Y... MCS The direction is consistent with the normal of the cutting plane;
[0064] S45, local fine-tuning, moving the MCS around the Y MCS Axial K vi+ and K vi- Rotate the MCS to the side with the larger value, with a single rotation angle of 0.2° and a maximum of 2°. Simultaneously, move the MCS along the Z-axis. MCS Make a slight vertical translation adjustment, with an adjustment range of ±5mm;
[0065] S46. Repeat steps S41-S45 until the pose threshold ΔK is reached. i When the deceleration is less than 0.2, the iteration process is terminated; the current MCS is recorded.
[0066] As shown in the table below, after 10 iterations, the pose threshold tends to stabilize, and the current MCS position is recorded.
[0067] iteration number i 1 2 ... 8 9 10 <![CDATA[Pose threshold ΔK i > 36.4 20.3 ... 1.5 1.3 1.25 deceleration \ 16.1 .... 0.5 0.2 0.05
[0068] S5, Reference Mapping; The MCS obtained through the margin optimization process is the optimal reference for the product; Mapping this reference from virtual space to real space is a crucial process; The set of alignment markers Q for machining. b The point coordinates mapped to the MCS coordinate system are recorded as Q. b-MCS Let its Z coordinate be Z. b-MCS-i , i = 1, 2, 3…8; pass this value to the machine operator.
[0069] i 1 2 ... 8 <![CDATA[Alignment mark point Z coordinate Z b-MCS-i > -1328.5 -1333.2 -1325.5
[0070] S6. Physical alignment: Through machine tool operation, leveling and shimming operations are performed on the raw workpiece to ensure that the relative positions of the 8 marked points of the machining are aligned with the Z-axis. b-MCS-i The relative positions of the eight provided points are kept consistent, thus achieving a consistent mapping relationship between the optimal reference MCS and the machine tool coordinate system.
[0071] Furthermore, the evaluation method for physical alignment includes the following steps:
[0072] S61. Calculate and adjust the target baseline drop. 8 Z b-MCS-i Subtract the minimum value Z b-MCS-min The relative height deviation of each point is obtained;
[0073]
[0074] S62. The operator adjusts the blank products according to this deviation to make them as consistent as possible. The actual reference drop is measured by the machine tool dial indicator after adjustment. And calculate the adjustment deviation
[0075]
[0076] S63. Repeat the above process until... If the average value is less than 0.5mm, it is considered to be accurately aligned; This is considered an evaluation method for clamping and alignment; after three final adjustments, The average value is 0.35mm, which completes the precise alignment.
[0077] This invention provides a method for coordinating the clamping and alignment allowances in the machining of large conical shell parts. Addressing the precise alignment problem in the machining of large-diameter conical shell parts for storage tank bottoms, this invention effectively solves the engineering challenge of insufficient allowance at the conical bottom. It designs a datum coordination method based on blank inspection and iterative allowance optimization, and a clamping, alignment, and evaluation method based on datum mapping and physical alignment. Based on these inventions, a precise alignment and evaluation method for conical shell parts based on coordinate measuring machine (CMM) and virtual-real space mapping can be achieved, effectively improving alignment accuracy and minimizing allowance loss due to alignment deviations.
[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for coordinating the clamping and alignment allowances during machining of large conical shell parts, characterized in that: The clamping and alignment method includes the following steps; S1, Forming reference transfer; A continuous engraving line is made at the large end of the blank by the forming process to transfer the rough reference of the forming process; S2, Machining alignment mark; Place the conical shell part with the large end down and the small end up on the lathe table, and mark the 8 points with "cross lines" evenly distributed at the same height on the large end. S3. Blank Inspection: Place the part with the large end down and the small end up on the coordinate measuring machine platform, and measure the shape of the blank using coordinate measuring machines. S4. Optimize the margin; find the relative optimal position and orientation between the blank and the theoretical model; The allowance optimization in S4 is a blank allowance optimization method based on a rough benchmark, which specifically includes the following steps; S41. Position the theoretical coordinate system MCS. The origin of the coordinate system is at the center of the large end of the theoretical model. The XYZ directions are consistent with the theory. All subsequent operations on the MCS are considered as joint operations on the MCS and the theoretical model. S42. Next, the set of forming reference points to be detected. Create a coarse reference plane using three points, and then... Adjust it to be aligned with the normal of the reference plane; set the rotation center of the theoretical model ( Adjust it to coincide with the center of the large end contour of the blank; this completes the precise rounding and rough leveling of the theoretical model in the blank. S43, Move the MCS along The direction is shifted vertically. During this shift, the envelopment of the blank changes linearly. Taking any cross-section as an example, when the envelopment allowance... When a turning point occurs, this point is the optimal point; set the value at this point. Coordinates can be used to complete the rough leveling of the upper and lower references; S44. Analyze the envelope of the theoretical model and the blank contour at this point, according to the following rules: The plane is a cutting plane, along a certain frequency i. Rotate the cutting plane along the axis to obtain each cutting plane in... + in height Directional envelope margin and- Directional envelope margin Define pose threshold This threshold represents the degree of attitude deviation; find the maximum attitude threshold value for each cutting plane, and then... The direction is consistent with the normal of the cutting plane; S45, local fine-tuning, moving the MCS around Axial Rotate the MCS to the side with the larger value, with a single rotation angle of 0.2° and a maximum of 2°; simultaneously, move the MCS along... The adjustment range is ±5mm; S46. Repeat steps S41-S45 until the pose threshold is reached. The iteration process is terminated when the deceleration is less than 0.
2. Record the current MCS; S5, Baseline Mapping: The MCS obtained through the margin optimization process is the optimal baseline of the product. This baseline is then mapped from the virtual space to the real space. Set of alignment marks for machining The point coordinates mapped to the MCS coordinate system are recorded as follows Take its Z coordinate as , i=1,2,3…8; S6. Physical alignment: The machine tool is used to level the blank, ensuring the relative positions of the eight marked points are aligned with the machine tool's alignment. The relative positions of the eight provided points are kept consistent, thus achieving a consistent mapping relationship between the optimal reference MCS and the machine tool coordinate system.
2. The method for coordinating the clamping and alignment allowances in the machining of large conical shell parts according to claim 1, characterized in that: In S3, the three-coordinate point measurement mainly measures the following data; a. Set of coordinate points on the outer surface of the blank , recorded as Where u=1,2,…20 represents 20 measurement points at 100mm intervals along the busbar direction; v=1,2,…16 represents 16 measurements evenly distributed along the circumferential direction; in total, there are 320 measurement points. b. Set of alignment marks for machining That is i = 1, 2, 3…8; c. Forming reference point set That is i=1,2,3,4; A plane mechanism is determined according to three points, and a verification point is added. Here, any four points on the three forming reference line can be measured.
3. The method for coordinating the clamping and alignment allowances in the machining of large conical shell parts according to claim 2, characterized in that: The point location is processed in reverse. First, the coordinate point set of the blank's outer surface is used. Generate 20 circumferential spline curves (U-curves) and 16 generatrix spline curves (V-curves). The U and V curves are used to generate a mesh surface in reverse to obtain the outer contour surface; the outer contour surface is offset inward to the minimum thickness of the actual blank to obtain the limit inner shape surface of the blank; the generation of the inner and outer blank surfaces completes the blank inspection.
4. The method for coordinating the clamping and alignment allowances in the machining of large conical shell parts according to claim 1, characterized in that: In step S5, the specific operation of datum mapping is the setting of alignment marker points for machining. The point coordinates mapped to the MCS coordinate system are recorded as follows Take its Z coordinate as , i=1,2,3…8; pass this value to the machine operator.
5. The method for coordinating the clamping and alignment allowances in the machining of large conical shell parts according to claim 1, characterized in that: In step S6; the evaluation method for physical alignment, Includes the following steps, S61. Calculate and adjust the target baseline drop. ,Will Subtract the minimum value The relative height deviation of each point is obtained; S62. The operator adjusts the blank products according to this deviation to make them as consistent as possible. The actual reference drop is measured by the machine tool dial indicator after adjustment. And calculate the adjustment deviation. ; S63. Repeat the above process until... The value of is regarded as the evaluation method for clamping and alignment.