Repeated positioning precision verification method for quick-change fixture for ultra-precision machining

Abstract

The invention discloses a quick-change clamp repeated positioning precision verification method for ultra-precision machining, and relates to the technical field of ultra-precision machining. Selecting a quick-change clamp, and adjusting the quick-change clamp according to the characteristics of the workpiece; a blank is installed, and a spherical workpiece is machined and milled in the first procedure; the spherical workpiece is detached to be subjected to film plating or coating treatment; re-installing the quick-change clamp to ensure that the spherical workpiece is positioned consistently, and cutting a plurality of circular planes on the spherical workpiece through secondary processing; observing the spherical workpiece, and calculating the normal error of each circular plane according to the diameter of the circular plane; the optimal fitting parameter is found by minimizing the sum of squares of errors, and the repeated positioning error of the quick-change clamp is obtained by analyzing the normal error of each circular plane. The repeated positioning precision of the quick-change clamp is verified by adopting a mode of carrying out multi-process machining on a workpiece structure with a round plane on a sphere, so that the precision and the consistency in the machining process are ensured, and personal errors are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-precision machining, and in particular to a method for verifying the repeat positioning accuracy of a quick-change fixture used for ultra-precision machining. Background Art

[0002] Ultra-precision machining technology is a high-precision machining technology that has gradually matured with the advancement of science and technology and industrial development. It plays a vital role in manufacturing high-performance, high-precision, high-quality parts and devices. It can achieve micron-level or even nanometer-level surface accuracy and surface roughness, and has special requirements for machine tools, the complexity of the surface of the workpiece, clamping tools and other conditions.

[0003] For ultra-precision machining, workpieces are generally produced in small batches, and for some workpieces, they need to be removed from their positions for other processing during the machining process and need to be repeatedly disassembled and clamped. If the error between each disassembly and assembly cannot be controlled, the machining accuracy cannot be ensured. In this case, the machine tool needs to be equipped with a high-precision quick-change device. The quick-change device has a standardized and unified interface, does not require complex positioning and adjustment steps, and can easily achieve high-precision positioning and locking, repeated clamping, and multi-station conversion, and control the error generated in the machining process to the micron level. It is an important part of maintaining high efficiency without losing precision during the machining process.

[0004] Currently, there are quick-change fixtures for ultra-precision machining, and the most critical indicator for measuring the accuracy of quick-change fixtures is the repeatability accuracy, which can describe the consistency that the quick-change fixture can achieve during repeated use. The Chinese invention patent with publication number CN113695936B and publication date June 21, 2022 discloses a secondary clamping process method for thin-walled spherical shell-like micro-components, which solves the problems of low reliability and low repeatability accuracy of secondary clamping. Through the zero-point quick-change positioning system and high-resolution CCD camera monitoring, the accuracy of clamping and repeatability accuracy are improved, thereby improving the accuracy and surface quality of micro-pit structure processing. Based on this process method, the present invention can verify the repeatability accuracy of quick-change fixtures of different sizes, specifications and structures in actual processing, and provide a strong judgment basis for the selection of different types of quick-change fixtures in multi-process processing. Summary of the invention

[0005] In order to solve the problem that in multi-process machining, the workpiece needs to be clamped and positioned multiple times, and the traditional clamping method is difficult to ensure high-precision repeated positioning, resulting in a decrease in machining accuracy, the present invention provides a method for verifying the repeated positioning accuracy of a quick-change fixture for ultra-precision machining, which adopts a method of performing multi-process machining on a workpiece structure with a circular plane on a sphere to verify the repeated positioning accuracy of the quick-change fixture, which helps to ensure accuracy and consistency in the machining process and reduce human errors.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for verifying the repeatable positioning accuracy of a quick-change fixture for ultra-precision machining, comprising the following steps:

[0007] S1. Selection and adjustment of quick-change fixtures

[0008] Choose a quick-change fixture that needs to be verified for accuracy in multi-process processing. The quick-change fixture should be able to achieve repeated positioning in the X, Y and Z directions, and adjust the quick-change fixture according to the characteristics of the workpiece;

[0009] S2, first process

[0010] The blank is mounted on a quick-change fixture, and the blank is milled into a spherical workpiece for the first process. After the first process is completed, the initial state of the spherical workpiece is recorded using a measuring tool;

[0011] S3. Disassembly and processing of workpieces

[0012] After the first process is completed, the spherical workpiece is removed from the quick-change fixture and plated or coated;

[0013] S4, Secondary Processing

[0014] The processed spherical workpiece is reinstalled on the quick-change fixture, and the positioning of the spherical workpiece is ensured to be consistent with that in the first process by adjusting the quick-change fixture, and then a secondary process is performed to cut multiple circular planes on the spherical workpiece;

[0015] S5. Workpiece observation and error analysis

[0016] Use the image acquisition camera to observe the spherical workpiece after secondary processing, record the diameter of the cut circular plane, and calculate the normal error of each circular plane according to the diameter of the circular plane. The calculation formula is: Normal error = |Theoretical distance between the circular plane and the center of the sphere - actual distance between the circular plane and the center of the sphere|, where the distance between the circular plane and the center of the sphere needs to be calculated based on the radius of the circular plane and the radius of the sphere. The calculation formula is:

[0017] S6. Calculation of repeated positioning error

[0018] The best fitting parameters are found by minimizing the sum of squares of the errors, assuming that the actual circular plane diameter is the camera observation value y i , the theoretical circular plane diameter is the model prediction value error Then the minimum sum of squares of errors is expressed as:

[0019]

[0020] By analyzing the normal errors of each circular plane, the minimum repeatable positioning errors of the quick-change fixture in the X, Y and Z directions are obtained.

[0021] Furthermore, a single-arc-blade single-crystal diamond milling cutter is used in the first processing step, and the tool path is spiral.

[0022] Furthermore, during the secondary machining, a circular plane is cut on the spherical workpiece along the vertices in the directions of X+, X-, Y+, Y- and Z+ of the machine tool coordinate system respectively.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts a method of performing multi-process processing on a workpiece structure with a circular plane on a sphere on an ultra-precision machine tool to verify the repeat positioning accuracy of the quick-change fixture, firstly performs off-site coating or coating treatment on the spherical workpiece processed in the first process, and then repeatedly clamps it for secondary processing to obtain multiple circular planes on the sphere, and uses an in-situ detection method to detect the processed circular plane, and performs geometric calculations on the detection results to obtain the repeat positioning accuracy of the quick-change fixture and its error vector, which helps to ensure the accuracy and consistency of the processing process and reduce human errors. It can verify the repeat positioning accuracy of quick-change fixtures of different sizes, specifications and structures in actual processing, provide a strong judgment basis for the selection of different types of quick-change fixtures in multi-process processing, and provide strong support for high-precision and high-efficiency production in the manufacturing industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the repeated positioning process of the quick-change fixture in the method of the present invention;

[0025] Figure 2 It is a schematic diagram of the principle of the circular plane normal error analysis in the method of the present invention;

[0026] Figure 3 is a physical picture of the System 3R zero-point quick-change fixture in the embodiment;

[0027] Figure 4 It is a physical picture of the fast travel fixture developed by Harbin Institute of Technology in the embodiment;

[0028] Figure 5 It is a diagram of the actual installation state of the two clamps in the embodiment;

[0029] Figure 6 is a schematic diagram of a target shape of secondary processing in an embodiment;

[0030] Figure 7 is a schematic diagram of the milling trajectory of the secondary processing in the embodiment;

[0031] Figure 8is a plan view of repeated positioning milling of the System 3R zero-point quick-change fixture in the embodiment;

[0032] Fig. 9 It is a plan view of repeated positioning milling of the rapid accompanying fixture in the embodiment. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] like Figure 1-2 As shown in the figure, a method for verifying the repeatability of positioning accuracy of quick-change fixtures for ultra-precision machining is used. Figure 1 As shown, the following steps are included:

[0035] S1. Selection and adjustment of quick-change fixtures

[0036] Choose a quick-change fixture that needs to be verified for accuracy in multi-process processing. The quick-change fixture should be able to achieve repeated positioning in the X, Y and Z directions. The chuck and base of the quick-change fixture are positioned and connected through the end gear plate. Adjust the parameters of the quick-change fixture according to the characteristics of the workpiece, including the clamping force and the position of the positioning claw, to meet different processing requirements;

[0037] S2, first process

[0038] The blank is mounted on a quick-change fixture and the first process is performed to mill the blank into a spherical workpiece. A single-arc-edge single-crystal diamond milling cutter is preferably used, and the tool path is a spiral type. After the first process is completed, a measuring tool is used to record the initial state of the spherical workpiece, including size and position;

[0039] S3. Disassembly and processing of workpieces

[0040] After the first processing is completed, the spherical workpiece is removed from the quick-change fixture and plated or coated to prepare for secondary processing;

[0041] S4, Secondary Processing

[0042] The processed spherical workpiece is reinstalled on the quick-change fixture, and the positioning of the spherical workpiece is ensured to be consistent with that in the first process by adjusting the quick-change fixture. Then, a secondary process is performed on the spherical workpiece to cut a circular plane at each vertex along the X+, X-, Y+, Y- and Z+ directions of the machine tool coordinate system;

[0043] S5. Workpiece observation and error analysis

[0044] Use the image acquisition camera to observe the spherical workpiece after secondary processing, record the diameter of the cut circular plane, and combine Figure 2 As shown in the figure, the normal error of each circular plane is calculated according to the diameter of the circular plane. The calculation formula is: Normal error = |Theoretical distance between the circular plane and the center of the sphere - actual distance between the circular plane and the center of the sphere|, where the distance between the circular plane and the center of the sphere needs to be calculated according to the radius of the circular plane and the radius of the sphere. The calculation formula is: Thus, the normal error of the corresponding circular plane is calculated according to the detected circular plane diameter;

[0045] S6. Calculation of repeated positioning error

[0046] The best fitting parameters are found by minimizing the sum of squares of the errors, assuming that the actual circular plane diameter is the camera observation value y i , the theoretical circular plane diameter is the model prediction value error Then the minimum sum of squares of errors is expressed as:

[0047]

[0048] By analyzing the normal errors of each circular plane, the minimum repeatability error of the quick-change fixture in the X, Y, and Z directions can be obtained. Then, it can be evaluated whether the repeatability error of the quick-change fixture meets the machining accuracy requirements. If the error exceeds the allowable range, the quick-change fixture is adjusted and the experiment is repeated until the requirements are met.

[0049] Example

[0050] This example verifies the repeatability of two types of fixtures. One is the System 3R zero-point quick-change fixture of the MacroNano series 3R-600.84-3N model. Figure 3 As shown in the figure, the fixture reference surface is made of cemented carbide, including four X, Y direction positioning claws and four Z direction positioning claws and their matching reference plates to achieve high-precision positioning in all directions, with a multiplied clamping function, its fixed indexing position is 4×90°, and the required air pressure is 6±1bar; the other is a high-precision fast accompanying fixture developed by the Institute of Precision Engineering of Harbin Institute of Technology, combined with the actual picture Figure 4 As shown, it realizes repeated positioning in the X, Y, and Z directions through high-precision end gear discs, and the number of teeth used in the end gear discs is 18. A larger number of end gear disc teeth has a better equalization effect, which can effectively reduce the possibility of excessive overall error due to excessive deviation of a single meshing tooth.

[0051] In the quick-change device repeatability positioning accuracy verification experiment, the blank is first installed on the accompanying component, and then the accompanying component is installed on the base of the two fixtures for the first process. Figure 5 As shown, part (a) shows the System 3R zero-point quick-change fixture, and part (b) shows the quick-change fixture developed by Harbin Institute of Technology.

[0052] After the first processing, the blank is milled into a semi-spherical workpiece with a radius of 2.5mm. Then the accompanying components of the two fixtures are disassembled from the machine tool together with the workpiece, and epoxy resin glue is applied to the workpiece and left to dry. After drying, it is clamped on the quick-change fixture again for secondary processing. It is advisable to use a single-arc blade single-crystal diamond milling cutter with a spiral tool path. The target shape of the secondary processing is combined with Figure 6 As shown, the milling trajectory is combined with Figure 7 As shown, the trajectory is 2.51mm over the semicircular sphere with a circular plane 0.02mm away from the spherical surface.

[0053] The circular planes of the two groups of experiments were observed using an image acquisition camera, and the diameters of the detected circular planes were marked to observe the results and diameter sizes. The repeated positioning milling plane of the System 3R zero-point quick-change fixture was combined with Figure 8 As shown, the fast follow-up fixture developed by Harbin Institute of Technology combines repeated positioning and milling of planes Fig. 9 As shown in the two figures, part (a) shows the Z+ direction plane, part (b) shows the X+ direction plane, part (c) shows the Y+ direction plane, part (d) shows the X- direction plane, and part (e) shows the Y- direction plane.

[0054] The observed circular plane diameter detection results are sorted out to calculate the normal error of each circular plane. Normal error = |theoretical distance between the circular plane and the center of the sphere - actual distance between the circular plane and the center of the sphere|, where the distance between the circular plane and the center of the sphere needs to be calculated based on the radius of the circular plane and the radius of the sphere. The calculation formula is: Therefore, the normal error of the corresponding circular plane is calculated according to the detected circular plane diameter, and the calculation results are shown in Table 1:

[0055] Table 1 Quick-change fixture repeatability error (unit: μm)

[0056]

[0057] In Table 1, the first half of the plane number is the group number. Group 1 is the data of the experiment using the System 3R zero-point quick-change fixture, and Group 2 is the data of the experiment using the fast travel fixture developed by Harbin Institute of Technology. The second half of the plane number is the plane code, and numbers 1 to 5 represent the Z+ direction plane, X+ direction plane, Y+ direction plane, X- direction plane, and Y- direction plane, respectively.

[0058] In order to average the data results of the same group, the error vector in the Z+ direction is taken as the repetitive positioning error in the Z direction, the average value of the vectors in the X+ direction and the X- direction is taken as the repetitive positioning error in the X direction, and the average value of the vectors in the Y+ direction and the Y- direction is taken as the repetitive positioning error in the Y direction. According to the above method, the vector sum of the repetitive positioning errors in the X, Y, and Z directions is the repetitive positioning error caused by multiple clamping.

[0059] Let E Z+ Indicates the repeatability error in the Z+ direction, E X+ Indicates the repeat positioning error in the X+ direction, E X- Represents the repeatability error in the X-direction, Indicates the repeat positioning error in the Y+ direction, Indicates the repeatability error in the Y-direction. For 1 set of System 3R zero-point quick-change fixtures and 2 sets of fast travel fixtures developed by Harbin Institute of Technology, the calculation method for repeatability error is as follows:

[0060] Repeatability error in Z direction:

[0061] E Z =E Z+

[0062] Repeatability error in X direction:

[0063]

[0064] Repeatability error in Y direction:

[0065]

[0066] The total repeatability error caused by multiple clamping is the vector sum of the errors in the X, Y, and Z directions. If we consider these errors as components of the vector, the total repeatability error E total It can be expressed as:

[0067]

[0068] Calculation shows that the averaged total repeatability error of the System 3R zero-point quick-change fixture is 2.191μm, while the averaged total repeatability error of the fast accompanying fixture developed by Harbin Institute of Technology is 2.546μm. In comparison, the accuracy of the fast accompanying fixture developed by Harbin Institute of Technology in actual processing is close to that of the System3R zero-point quick-change fixture, and the repeatability error is less than 3μm, which can meet the accuracy requirements of ultra-precision processing, verifying the practicability of the method of the present invention.

[0069] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other forms of assembly without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0070] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for verifying the repeatability of positioning accuracy of a quick-change fixture for ultra-precision machining, characterized in that: The following steps are involved: S1. Selection and adjustment of quick-change fixtures Select quick-change fixtures that need to be verified for accuracy in multi-process processing. The quick-change fixtures should be able to achieve repeated positioning in the X, Y and Z directions, and adjust the quick-change fixtures according to the characteristics of the workpiece; S2, first process The blank is mounted on a quick-change fixture, and the blank is milled into a spherical workpiece for the first process. After the first process is completed, the initial state of the spherical workpiece is recorded using a measuring tool; S3. Disassembly and processing of workpieces After the first process is completed, the spherical workpiece is removed from the quick-change fixture and plated or coated; S4, Secondary Processing The processed spherical workpiece is reinstalled on the quick-change fixture, and the positioning of the spherical workpiece is ensured to be consistent with that in the first process by adjusting the quick-change fixture, and then a secondary process is performed to cut multiple circular planes on the spherical workpiece; S5. Workpiece observation and error analysis Use the image acquisition camera to observe the spherical workpiece after secondary processing, record the diameter of the cut circular plane, and calculate the normal error of each circular plane according to the diameter of the circular plane. The calculation formula is: Normal error = |Theoretical distance between the circular plane and the center of the sphere - actual distance between the circular plane and the center of the sphere|, where the distance between the circular plane and the center of the sphere needs to be calculated based on the radius of the circular plane and the radius of the sphere. The calculation formula is: S6. Calculation of repeated positioning error The best fitting parameters are found by minimizing the sum of squares of the errors, assuming that the actual circular plane diameter is the camera observation value y i , the theoretical circular plane diameter is the model prediction value error Then the minimum sum of squares of errors is expressed as: By analyzing the normal errors of each circular plane, the minimum repeatable positioning errors of the quick-change fixture in the X, Y and Z directions are obtained.

2. The method for verifying the repeatability of positioning accuracy of a quick-change fixture for ultra-precision machining according to claim 1, characterized in that: The first processing step uses a single-arc blade single-crystal diamond milling cutter, and the tool path is spiral.

3. The method for verifying the repeatability of positioning accuracy of a quick-change fixture for ultra-precision machining according to claim 1, characterized in that: During the secondary machining, a circular plane is cut on the spherical workpiece along the vertices in the directions of the machine tool coordinate system X+, X-, Y+, Y- and Z+, respectively.

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