Free-form surface machining programming method and machining method

Abstract

The invention discloses a free-form surface machining programming method and a machining method.The machining programming method is embedded into a machine tool control system and controls a machine tool to machine a free-form surface through the machine tool control system, and the machining programming method comprises a modeling analysis module, a free-form surface optical equation establishing module and a free-form surface processing module, homogeneous coordinate transformation is carried out, a workpiece to be machined is transferred to a machine tool axis coordinate system, and a free-form surface model to be machined in the machine tool axis coordinate system is obtained; the track planning module is used for planning a tool contact track by using an equal-angle method according to a tool motion track, a to-be-machined free-form surface model under a machine tool axis coordinate system and machining parameters; the error compensation module is used for performing error compensation on the tool contact track by using a Z-direction compensation method according to the tool parameters to obtain a tool location point track; the programming module is used for programming a tool machining program according to the tool location point track; the user interface module is used for receiving the optical equation of the free-form surface to be machined, the machining parameters and the cutter parameters and displaying the machining progress and the machining result.

Description

Technical Field

[0001] The invention relates to the technical field of free-form surface machining, and in particular to a trajectory planning and tool radius compensation method for free-form surface machining. Background Art

[0002] Modern optical system design increasingly tends to use free-form optical components. These components have become core components in aerospace, national defense security, cutting-edge scientific instruments and other fields due to their excellent performance in optical performance, fluid dynamics performance and thermodynamic properties. They are widely used in cutting-edge projects such as diffractive optical components, astronomical observation telescopes, and inertial confinement nuclear fusion ignition systems. The surge in demand for free-form optical components has promoted the rapid development of free-form manufacturing technology, making it a core topic in manufacturing science research.

[0003] Free-form optical components refer to surfaces that do not have a unified rotational symmetry axis and cannot be processed continuously, and have the arbitrary characteristics of traditional processing and forming. In reality, most mechanical parts can be clearly expressed and conveyed by descriptive geometry and mechanical drawing. For example, surfaces composed of only elementary analytical surfaces such as planes, cylinders, cones, spheres, etc. Another type of mechanical parts cannot be composed of elementary analytical surfaces, but are composed of curve surfaces that change freely in complex ways, namely the so-called free-form curve surfaces, such as the appearance parts of airplanes, cars, and ships. Free-form curve surfaces cannot be clearly expressed by descriptive geometry and mechanical drawing, and their processing and manufacturing are more complicated. With the continuous improvement of the requirements of optical systems for high precision and low error, the demand for ultra-precision free-form components has become more urgent. However, the processing size of traditional free-form surfaces is mostly limited to more than 200mm, which cannot meet the requirements of ultra-precision. Therefore, the manufacturing of free-form optical components under ultra-precision requirements still faces huge challenges.

[0004] At present, in the field of ultra-precision optical component processing in China, grinding and polishing technology is mainly relied on, while the technology of using single-point diamond lathe to achieve one-time high-precision molding has yet to be broken through. The core of ultra-precision processing technology lies in two aspects: one is the research and development of high-performance CNC hardware systems; the other is the construction of software systems with highly automated programming capabilities. With the rapid development of integrated circuits and computer technology, modern CNC systems widely use very large-scale integrated circuits (VLSI), application-specific integrated circuits (ASIC) and digital signal processing (DSP) technology. The application of embedded hardware is driving CNC systems to develop in the direction of standardization and serialization. In contrast, the progress of CNC software systems lags behind slightly. The existing CNC software on the market, such as UG, Pro / E, SolidWorks, etc., has different communication protocols and operation methods, which brings great inconvenience to users' secondary development. Especially in the processing of free-form surface parts, mainstream commercial software such as UG, Pro / E, etc. lack automatic programming modules for such complex surfaces and cannot directly generate the required CNC programs. Therefore, it is necessary to conduct in-depth research on processing trajectory planning and automatic programming technology based on the unique properties of the surface. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a free-form surface machining program compilation method and a machining method, which adopts a modular design concept. After inputting the optical equation of the free-form surface to be machined, machining parameters, and tool parameters, the tool contact point trajectory is planned by the equal-angle method, and the tool contact point trajectory is error compensated by the Z-direction compensation method to obtain the tool position point trajectory, thereby effectively improving the machining accuracy of the free-form surface, and automatically compiling a machining program according to the tool position point trajectory. The machining plan can be quickly adjusted according to actual machining requirements to effectively improve the machining efficiency.

[0006] The first object of the present invention is to provide a method for programming a free-form surface machining program, the method is embedded in a machine tool control system and controls a machine tool through the machine tool control system to machine a free-form surface on a workpiece to be machined, the method comprising:

[0007] A modeling and analysis module is used to establish a free-form surface model to be processed according to the optical equation of the free-form surface to be processed, and perform homogeneous coordinate transformation to transfer the workpiece to be processed to the machine tool axis coordinate system to obtain the free-form surface model to be processed in the machine tool axis coordinate system;

[0008] The trajectory planning module is used to plan the tool contact point trajectory of the tool machining by using the equal angle method according to the tool motion trajectory, the free-form surface model to be machined in the machine tool axis coordinate system and the machining parameters;

[0009] The error compensation module is used to perform error compensation on the tool contact point trajectory using the Z-direction compensation method according to the tool parameters to obtain the tool position point trajectory of tool processing;

[0010] A program compilation module is used to compile a tool processing program according to a tool position trajectory of tool processing;

[0011] The user interface module is used to interact with the user, receive the optical equation of the free-form surface to be processed, processing parameters, and tool parameters input by the user, and display the processing progress and processing results.

[0012] As a further improvement of the present invention, the method of establishing a model of the free-form surface to be processed according to the optical equation of the free-form surface to be processed includes: using a simulation tool to perform simulation modeling and analysis on the free-form surface to be processed according to the optical equation of the free-form surface to be processed to obtain the surface characteristics of the free-form surface to be processed, and establishing a model of the free-form surface to be processed.

[0013] As a further improvement of the present invention, the tool contact point trajectory of tool machining is planned by the equal-angle method according to the tool motion trajectory, the free-form surface model to be machined in the machine tool axis coordinate system and the machining parameters, including: according to the machining parameters, projecting the tool motion trajectory onto the free-form surface model to be machined in the machine tool axis coordinate system, and controlling the center angle between two adjacent tool contacts to be always equal, so as to obtain the tool contact point trajectory of tool machining.

[0014] As a further improvement of the present invention, the method of controlling the center angle between two adjacent tool contacts to be always equal to obtain the tool contact point trajectory of tool processing also includes: continuously adjusting the size of the center angle between two adjacent tool contacts to make the tool contact point trajectory of tool processing approach a continuous and smooth curve.

[0015] As a further improvement of the present invention, the tool motion trajectory is projected onto the free-form surface model to be processed in the machine tool axis coordinate system to obtain the tool contact point trajectory of the tool processing, including: obtaining the tool contact point trajectory of the tool processing by combining the tool motion trajectory equation and the free-form surface equation to be processed.

[0016] As a further improvement of the present invention, the error compensation of the tool contact point trajectory by the Z-direction compensation method is performed on the tool parameters to obtain the tool position point trajectory of the tool processing, including: compensation is performed in the Z direction of the tool contact point trajectory according to the curvature radius of the tool tip and the derivative of the tool contact point trajectory to obtain the tool position point trajectory of the tool processing after compensation; wherein the tool position point trajectory of the tool processing after compensation is located directly above the tool contact point trajectory;

[0017] The relationship between the Z-axis coordinate of the tool position point after compensation and the Z-axis coordinate of the original tool contact point is:

[0018]

[0019] Among them, z CL is the Z-axis coordinate of the tool position after compensation, z CP is the Z-axis coordinate of the original knife contact point, r tis the radius of curvature of the tool tip, f'(ρ CP )The derivative of the tool contact trajectory.

[0020] As a further improvement of the present invention, the method also includes a program detection module, which is used to import the tool processing program compiled by the program compilation module into the machine tool control system, control the program to run empty, and judge whether the program is wrong based on the tool operation trend and tool amplitude under the program running empty, and transmit the program to the machine tool control system after confirming that the program is correct.

[0021] As a further improvement of the present invention, when the program is run idle, the user interface module is also used to display the free-form surface model to be processed in the machine tool axis coordinate system and the tool position point trajectory of the tool processing when the program is run idle, so as to determine whether the program is wrong.

[0022] The second object of the present invention is to provide a free-form surface processing method. After the above-mentioned processing program compilation method is embedded in the machine tool control system, the machine tool is controlled by the machine tool control system to process the free-form surface. The method comprises:

[0023] Input the optical equation of the free-form surface to be processed, processing parameters, and tool parameters;

[0024] Modeling and analyzing the free-form surface to be processed, planning the tool contact point trajectory of tool processing, and performing error compensation on the tool contact point trajectory to obtain the tool position point trajectory of tool processing;

[0025] According to the tool position trajectory of tool processing, the tool processing program of the free-form surface to be processed is automatically compiled;

[0026] Import the tool processing program into the machine tool control system, fix the workpiece to be processed on the machine tool, and control the machine tool to process the free-form surface through the machine tool control system.

[0027] As a further improvement of the present invention, after the tool processing program is imported into the machine tool control system, the program is controlled to run empty first, and whether the program is wrong is judged based on the tool operation trend and tool amplitude during the empty program running. After confirming that the program is correct, the workpiece to be processed is fixed on the machine tool.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] By modeling and analyzing the free-form surface to be processed, using the equal-angle method to track the tool contact point trajectory, and using the Z-direction compensation method to perform error compensation on the tool contact trajectory to obtain the tool position point trajectory, the processing accuracy is effectively improved and the processing results are highly consistent with the design expectations.

[0030] Through modular design, after inputting the free-form surface optical equations, processing parameters, and tool parameters, the processing program is automatically compiled to effectively improve the processing efficiency. The processing plan can also be quickly adjusted according to actual processing needs to meet complex free-form surface processing tasks.

[0031] Through program dry run detection, the safety and reliability of the machining process can be improved, machining accidents caused by program errors can be effectively prevented, and the safety of equipment and workpieces can be effectively guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the method for programming free-form surface machining;

[0033] Figure 2 It is a schematic diagram of the layout of a single-point diamond turning machine tool;

[0034] Figure 3 It is a schematic diagram of machining trajectory using equal angle method;

[0035] Figure 4 This is a schematic diagram of machining trajectory using the equal arc length method;

[0036] Figure 5 Schematic diagram of the comparison between the ideal trajectory and the actual trajectory;

[0037] Figure 6 Schematic diagram of machining trajectory for generating free-form surface using equal angle method;

[0038] Figure 7 It is a schematic diagram of tool tip radius compensation;

[0039] Figure 8 This is the schematic diagram of normal compensation;

[0040] Fig. 9 This is the schematic diagram of Z-direction compensation;

[0041] Fig.10 It is a schematic diagram of the program detection process;

[0042] Fig.11 It is the turning trajectory diagram of the inclined plane;

[0043] Fig.12 This is a schematic diagram of the plane difference between the points collected by the three-coordinate measuring machine and the inclined plane model;

[0044] Fig.13 It is the turning trajectory diagram of the sinusoidal surface;

[0045] Fig.14 The measurement results of the three-dimensional coordinate measuring machine for the sinusoidal surface;

[0046] Fig.15 Tool path diagram for XY polynomial free-form surface;

[0047] Fig.16 Data point cloud of XY polynomial free-form surface collected by high-precision profilometer. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments 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 part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0050] This embodiment provides a method for programming a free-form surface machining program. The method is embedded in a single-point diamond turning machine control system and controls the machine tool through the machine control system to machine a free-form surface on a workpiece to be machined. Single-point diamond turning is an ultra-precision machining technology specifically used for machining high-precision optical components and complex surfaces. Through high-precision CNC technology and extremely sharp diamond tools, sub-micron-level machining accuracy and nanometer-level surface roughness can be achieved. For the layout of the single-point diamond turning machine, please refer to Figure 2 The machine tool consists of three main axes: two linear axes (X and Z) and one rotary axis (C). The X and Z axes are mounted on hydrostatic guideways, while the C axis is mounted on the X axis and supported by air hydrostatic bearings. During machining, the tool is mounted on the Z axis. As the C axis rotates and the X axis feeds, the tool moves helically relative to the workpiece. At the same time, the Z axis reciprocates in the cutting depth direction to achieve machining of free-form surfaces. In this way, complex and precise machining tasks can be completed through the horizontal feed of the X axis and the rotation of the C axis, combined with the vertical adjustment of the Z axis.

[0051] See also Figure 1 , the method comprising:

[0052] The modeling and analysis module uses simulation tools (Math simulation tools such as Matlab) to simulate and model the free-form surface to be processed according to the optical equation of the free-form surface to be processed, so as to obtain the surface features of the free-form surface to be processed, and establishes a model of the free-form surface to be processed, performs homogeneous coordinate transformation, and transfers the workpiece to be processed to the machine tool axis coordinate system to obtain the free-form surface model to be processed in the machine tool axis coordinate system;

[0053] The trajectory planning module projects the tool motion trajectory onto the free-form surface model to be processed in the machine tool axis coordinate system according to the processing parameters. By combining the tool motion trajectory equation and the free-form surface equation to be processed, the size of the center angle between two adjacent tool contacts is continuously adjusted, and the center angle between two adjacent tool contacts is controlled to be always equal, so that the tool contact point trajectory of the tool processing approaches a continuous and smooth curve, so as to obtain the tool contact point trajectory of the tool processing;

[0054] The spiral equation of the tool motion trajectory is:

[0055] The cylindrical coordinate equation of the free-form surface to be processed is: z = f (r, θ)

[0056] By combining the spiral equation and the cylindrical coordinate equation of the free-form surface to be processed, the tool contact point trajectory of the tool processing can be obtained.

[0057] The equation expressions of some free-form surfaces are established in the Cartesian coordinate system, and coordinate transformation is required to transform them into the cylindrical coordinate system. The transformation formula is: x = r*cos(θ), y = r*sin(θ)

[0058] Among them, r, θ, and z are the radial distance, angle, and axial height in the cylindrical coordinate system, respectively, f is the tool feed speed, v is the spindle speed, and x and y are the coordinates in the Cartesian coordinate system.

[0059] According to the different discrete point selection methods, trajectory planning in the free-form surface processing process can be divided into two types: equal angle method and equal arc length method. Figure 3 , the central angle between two adjacent trajectory points is always equal. Under this method, the distribution of discrete points on the Z axis is based on the angle. The closer to the center of the workpiece, the denser the processing points. As the angle increases, the density of the points becomes sparser, and the arc length between two adjacent points also increases.

[0060] Please refer to the machining trajectory of the equal arc length method Figure 4 , the arc length between two adjacent cutting points is equal, the processing path is expanded according to the arc length, the processing points are sparsely distributed in the inner circle, and when approaching the outer circle, the arc length between the two processing points remains unchanged, showing a more uniform distribution in the outer circle of the workpiece.

[0061] The ideal turning process expects to obtain a continuous and smooth cutting path. However, in actual operation, the tool moves along the preset cutting path points, and the two points are connected by a straight line. Therefore, the actual cutting path is approximately composed of continuous broken lines, such as Figure 5 To ensure the machining accuracy of the free-form surface, we need to accurately control the position of the trajectory points so that the adjacent trajectory points are as close to the ideal curve as possible.

[0062] In this situation, the equal arc length method will cause frequent fluctuations in the C-axis speed due to the constant changes in the angles of adjacent cutting points, which puts higher requirements on the dynamic performance of the machine tool, affects the stability of the machine tool processing, and is not conducive to high-precision control. In ultra-precision turning, the X and Z linear axes need to work together with the C-axis for three-axis linkage processing. If the C-axis can move in steps at a fixed angle, it will help improve the stability of the processing system and accurately control the surface shape. Therefore, from this perspective, the use of the equal angle method for trajectory planning is more conducive to the implementation of the processing process. The processing trajectory of the free-form surface generated by the equal angle method is as follows: Figure 6 shown.

[0063] The error compensation module performs compensation in the Z direction of the tool contact point trajectory according to the curvature radius of the tool tip and the derivative of the tool contact point trajectory to obtain the tool position point trajectory of the tool processing after compensation; wherein the tool position point trajectory of the tool processing after compensation is located directly above the tool contact point trajectory.

[0064] After trajectory planning, trajectory compensation from the tool contact point to the tool center point is also required. The single-point diamond ultra-precision machining machine uses an ultra-hard diamond tool. The tip of the tool is not an ideal point, but an arc with a certain radius of curvature, such as Figure 7 As shown in the figure, there is a certain distance between the contact point between the diamond tool and the workpiece and the tool position point in the machining trajectory planning program. If the machining is performed only according to the tool contact point obtained by trajectory planning, there will be a large error between the actual machined workpiece and the ideal workpiece. Therefore, in order to achieve the high-precision requirements of surface machining, the radius factor of the diamond tool tip must be fully considered. Specifically, the tool radius compensation processing needs to be implemented on the calculated tool contact point path to derive the tool position point path, that is, the motion trajectory of the tool during the actual machining process.

[0065] Traditional normal compensation is to achieve tool radius compensation by adjusting the position of the tool in the direction of the surface normal. For its principle, please refer to Figure 8 .

[0066] For coordinates P CC (ρ CC ,θ,z CC ) of the tool contact point, if the tool radius is selected as r t , then the tool position coordinate P after compensation along the normal direction CL (ρ CL ,θ,z CL ) can be calculated by the following formula:

[0067]

[0068] It can be seen that normal compensation will generate compensation components on the X-axis and Z-axis of the machine tool. The compensation component of the X-axis will superimpose high-frequency motion on the machine tool slide that originally moves at a single speed, destroying the uniform motion of the X-axis. What's more, reciprocating motion of the X-axis will be generated around some turning points. Since the X-axis worktable is equipped with large mass components and has a large moment of inertia, this high-frequency motion of the X-axis is not only not conducive to the precise control of the machine tool, but also greatly reduces the service life of the machine tool.

[0069] In the slow tool servo machining system, the frequency response characteristics of the Z axis were considered at the beginning of the design, and it was used as the main motion axis of the machine tool. Therefore, before and after compensation, the superposition of high-frequency motion components on the Z axis has no effect on the servo characteristics of the Z axis and the entire machine tool. In view of the above characteristics of the machining machine tool, it is necessary to find a new tool arc radius compensation method to avoid superposition of high-frequency motion components on the X axis.

[0070] In order to solve the problem of repeated movement of the X axis, in this embodiment, a Z-direction compensation scheme is used to perform tool compensation on the free-form surface. The implementation idea of ​​the Z-direction compensation is as follows: Fig. 9 shown.

[0071] Assume that the tool position P after compensation CL (ρ CL ,θ,z CL ) is located at the contact point P of the compensated knife CP (ρ CP ,θ,z CP ) at Δz directly above, if machining is performed according to the compensated trajectory, the actual tool contact point will become P CN (ρ CN ,θ,z CN ), because the arc radius of the tool used in ultra-precision turning is extremely small, the difference between the actual tool contact point and the compensated tool position point on the polar radius can be ignored, and the radial curve can be considered to be at P CL and P CN The derivatives at are the same, so the relationship between the Z-axis coordinates of the tool position point after compensation and the Z-axis coordinates of the original tool contact point can be obtained:

[0072]

[0073] Comprehensive analysis shows that the distribution of discrete points generated by the Z-axis tool compensation algorithm for CNC machining meets the requirements of the motion characteristics of each axis of the slow-tool servo lathe. By superimposing the compensation component on the Z-axis direction of the machine tool, the problem of precision loss in the X-axis due to superimposed motion components is avoided. This algorithm can be applied to free-form surface turning.

[0074] By utilizing unique trajectory planning and error compensation strategies, surface scratches, ripples and other defects generated during the processing process are effectively reduced, and the surface finish after processing is significantly improved, reaching an ultra-precision level, which is of great significance for improving product performance and extending service life.

[0075] The program compilation module is used to compile the tool processing program according to the tool position point trajectory of the tool processing.

[0076] The program detection module is used to import the tool processing program compiled by the program compilation module into the machine tool control system, control the program to run empty, and judge whether the program is wrong according to the tool operation trend and tool amplitude under the program running empty. After confirming that the program is correct, the program is transmitted to the machine tool control system. Please refer to the program detection process Fig.10 .

[0077] The user interface module is used to interact with the user, receive the optical equation of the free-form surface to be processed, processing parameters, and tool parameters input by the user, and display the processing progress and processing results. When the program is running idle, the user interface module is also used to display the free-form surface model to be processed in the machine tool axis coordinate system and the tool position trajectory of the tool processing when the program is running idle, so as to determine whether the program is wrong.

[0078] By optimizing processing strategies and algorithms, unnecessary processing steps are reduced, time waste during processing is reduced, and the overall processing efficiency can be significantly improved and production costs can be reduced while ensuring processing quality.

[0079] The above method adopts a modular design concept and can flexibly respond to the processing needs of free-form surfaces of various complex shapes and sizes. There is no need to redesign the processing process. Only by entering the parameters into the system, the processing plan can be quickly adjusted to meet the customized requirements of small batch and multi-variety production, thereby enhancing market competitiveness.

[0080] This embodiment provides a free-form surface processing method. After the above processing program compilation method is embedded in a machine tool control system, the machine tool is controlled by the machine tool control system to process the free-form surface. The method includes:

[0081] Input the optical equation of the free-form surface to be processed, processing parameters, and tool parameters;

[0082] Modeling and analyzing the free-form surface to be processed, planning the tool contact point trajectory of tool processing, and performing error compensation on the tool contact point trajectory to obtain the tool position point trajectory of tool processing;

[0083] According to the tool position trajectory of tool processing, the tool processing program of the free-form surface to be processed is automatically compiled;

[0084] Import the tool processing program into the machine tool control system, first control the program to run empty, and judge whether the program is wrong based on the tool operation trend and tool amplitude during the program run. After confirming that the program is correct, fix the workpiece to be processed on the machine tool, and control the machine tool to process the free-form surface through the machine tool control system.

[0085] Compared with the prior art, the present invention has the following advantages:

[0086] By modeling and analyzing the free-form surface to be processed, using the equal-angle method to track the tool contact point trajectory, and using the Z-direction compensation method to perform error compensation on the tool contact trajectory to obtain the tool position point trajectory, the processing accuracy is effectively improved and the processing results are highly consistent with the design expectations.

[0087] Through modular design, after inputting the free-form surface optical equations, processing parameters, and tool parameters, the processing program is automatically compiled to effectively improve the processing efficiency. The processing plan can also be quickly adjusted according to actual processing needs to meet complex free-form surface processing tasks.

[0088] Through program dry run detection, the safety and reliability of the machining process can be improved, machining accidents caused by program errors can be effectively prevented, and the safety of equipment and workpieces can be effectively guaranteed.

[0089] Hereinafter, the three-axis ultra-precision machine tool Nanosys-1000 developed by Beijing Institute of Aeronautical Precision Mechanics is used to process an inclined plane, a sinusoidal surface, and an XY polynomial free-form surface on a workpiece to be processed, respectively, as three groups of experiments to verify the effect of the present invention.

[0090] The machine tool technical parameters and processing parameters are shown in Table 1:

[0091] Table 1

[0092]

[0093]

[0094] The specific experimental process is as follows:

[0095] Experiment 1: Bevel plane machining

[0096] The equation of the inclined plane can be expressed as:

[0097]

[0098] Turning a slope with an inclination angle of 0.02°, set the parameters in the inclined plane formula to: A = 0.00349, b = 0, use 20 × 20mm AL6061-T651 aluminum workpiece to carry out the turning experiment of the inclined plane, the cutting radius D is 15mm, and the cutting parameters are shown in Table 2:

[0099] Table 2

[0100] parameter Parameter Value Cutting radius 15mm X-axis feed speed (coarse) 0.3mm / r X-axis feed speed (precision) 0.1mm / r Z axis feed speed (coarse) 0.01mm Z axis feed speed (precision) 0.005mm C-axis speed 48r / min

[0101] The diamond tool is an ultra-precision arc diamond tool from the British company CONTOUR, model C1.0mLGC. The machine tool tool is aligned before processing, and the turning trajectory is as follows: Fig.11 shown.

[0102] The surface accuracy is measured by using a metrological three-dimensional coordinate measuring machine (CMM). Fig.12 The final measured surface accuracy is 3.5μm.

[0103] The roughness was measured using a Taylor Hobson PGL optics high-precision profilometer. The workpiece was fixed on a workbench and the roughness was measured at a distance of 1 μm. The final roughness of the inclined plane was measured to be 13.9 nm.

[0104] Experiment 2: Sinusoidal Surface Machining

[0105] The processing equation of the sinusoidal surface can be expressed as:

[0106]

[0107] The parameters in the sine surface formula are set to: A = 1, w = 1 / 8, j = 0, b = 0, and the AL6061-T651 aluminum workpiece with a radius of D = 30 mm is used for the turning experiment of the sine surface, and the Nanosys-1000 CNC optical processing machine is used. The workpiece is first rough-machined to quickly remove the workpiece allowance, and then the parameters are adjusted for precision machining. The cutting parameters are shown in Table 3:

[0108] Table 3

[0109] parameter Parameter Value Cutting radius 30mm X-axis feed speed (coarse) 0.3mm / r X-axis feed speed (precision) 0.1mm / r Z axis feed speed (coarse) 0.01mm Z axis feed speed (precision) 0.005mm C-axis speed 48r / min

[0110] The diamond tool parameters are ultra-precision arc diamond tools from the British CONTOUR company, model C1.0mLGC, tool arc radius is 1.044mm, tool waviness is 0.05μm. Before starting processing, the tool needs to be calibrated to accurately obtain the center point position of the machine tool to prevent overcutting. The workpiece is fixed on the spindle and rotates with the spindle. The cutting trajectory is as follows: Fig.13 As shown, the processing is carried out using a time-based control method.

[0111] In order to verify the effectiveness of the proposed processing method for sinusoidal surface processing, the surface roughness and surface accuracy of the workpiece after processing were measured and evaluated. The roughness was measured using a Taylor Hobson PGL optics high-precision profilometer, and the surface accuracy was measured using a metrological coordinate measuring machine (CMM). The measurement results of the CMM are shown in Figure 2. Fig.14 shown.

[0112] The contour shape of the sinusoidal workpiece was obtained by point acquisition using a three-dimensional coordinate measuring machine. By performing a difference analysis with the theoretical sinusoidal surface, the surface accuracy of the workpiece was found to be 3μm. At the same time, the roughness of the sinusoidal surface was measured using a Taylor Hobson PGL optics profilometer, and the roughness of the sinusoidal surface was measured to be 11.4nm.

[0113] Experiment 3: Polynomial Freeform Surface Machining

[0114] The XY polynomial free-form surface formula is as follows:

[0115]

[0116] According to the machine tool speed, the Z axis one circle motion trajectory, and the above XY polynomial free-form surface formula, the machine tool acceleration required for processing the free-form surface can be calculated and the machine tool acceleration can be set. At the same time, according to the tool radius compensation, linear compensation, etc., the tool trajectory of the XY polynomial free-form surface is finally obtained. The tool trajectory is as follows Fig.15 shown.

[0117] The off-axis parabola turning experiment was carried out using a 200×200mm AL6061-T651 aluminum workpiece. The cutting radius D was 150mm. The processing parameters are shown in Table 4:

[0118] Table 4

[0119] parameter Parameter Value Cutting radius 150mm X-axis feed speed (coarse) 0.3mm / r X-axis feed speed (precision) 0.1mm / r Z axis feed speed (coarse) 0.01mm Z axis feed speed (precision) 0.005mm C-axis speed 100r / min

[0120] The diamond tools are still ultra-precision arc diamond tools from the British company CONTOUR, and the machine tool tools are aligned before processing.

[0121] Since the surface features of the XY polynomial free-form surface are not obvious and cannot be measured using a three-dimensional coordinate measuring machine, the workpiece is measured using a Taylor Hobson high-precision profilometer. Data is collected at the longitudinal origin and 30 mm above and below the origin at intervals of 0.5 mm. Then, the workpiece is rotated 90 degrees counterclockwise and points are collected at the longitudinal origin and 30 mm above and below the origin at intervals of 0.5 mm. A total of 45,696 data points are collected. The collected point cloud is shown in the figure below. Fig.16As shown, the surface error obtained by Spatial View data software is 2μm. At the same time, the parabola is pulled 1μm by Taylor Hobson high-precision profilometer to measure the surface roughness of the XY polynomial free-form surface. The roughness of the XY polynomial free-form surface is 20.2nm.

[0122] The above experimental results show that the free-form surface processing technology proposed in this invention has high processing accuracy, excellent surface quality, high processing efficiency, and can meet the requirements of ultra-precision processing.

[0123] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for programming a free-form surface machining program, which is embedded in a machine tool control system and controls a machine tool to machine a free-form surface on a workpiece to be machined through the machine tool control system, characterized in that: The method comprises: A modeling and analysis module is used to establish a free-form surface model to be processed according to the optical equation of the free-form surface to be processed, and perform homogeneous coordinate transformation to transfer the workpiece to be processed to the machine tool axis coordinate system to obtain the free-form surface model to be processed in the machine tool axis coordinate system; The trajectory planning module is used to plan the tool contact point trajectory of the tool machining by using the equal angle method according to the tool motion trajectory, the free-form surface model to be machined in the machine tool axis coordinate system and the machining parameters; The error compensation module is used to perform error compensation on the tool contact point trajectory using the Z-direction compensation method according to the tool parameters to obtain the tool position point trajectory of tool processing; A program compilation module is used to compile a tool processing program according to a tool position trajectory of tool processing; The user interface module is used to interact with the user, receive the optical equation of the free-form surface to be processed, processing parameters, and tool parameters input by the user, and display the processing progress and processing results.

2. A method for compiling a free-form surface machining program according to claim 1, characterized in that: The method of establishing a free-form surface model to be processed according to the optical equation of the free-form surface to be processed includes: using a simulation tool to perform simulation modeling and analysis on the free-form surface to be processed according to the optical equation of the free-form surface to be processed to obtain the surface features of the free-form surface to be processed, and establishing a free-form surface model to be processed.

3. A method for compiling a free-form surface machining program according to claim 1, characterized in that: The method of planning the tool contact point trajectory of tool processing by using the equal-angle method according to the tool motion trajectory, the free-form surface model to be processed in the machine tool axis coordinate system and the processing parameters includes: projecting the tool motion trajectory onto the free-form surface model to be processed in the machine tool axis coordinate system according to the processing parameters, and controlling the center angle between two adjacent tool contacts to be always equal to obtain the tool contact point trajectory of tool processing.

4. A method for compiling a free-form surface machining program according to claim 3, characterized in that: The method of controlling the center angle between two adjacent tool contacts to be always equal to obtain the tool contact point trajectory of tool processing also includes: continuously adjusting the size of the center angle between two adjacent tool contacts to make the tool contact point trajectory of tool processing approach a continuous and smooth curve.

5. A method for compiling a free-form surface machining program according to claim 3 or 4, characterized in that: The projecting of the tool motion trajectory onto the free-form surface model to be processed in the machine tool axis coordinate system to obtain the tool contact point trajectory of the tool processing includes: obtaining the tool contact point trajectory of the tool processing by combining the tool motion trajectory equation and the free-form surface equation to be processed.

6. A method for compiling a free-form surface machining program according to claim 1, characterized in that: The method of using a Z-direction compensation method to perform error compensation on the tool contact point trajectory according to the tool parameters to obtain a tool position point trajectory of tool processing includes: performing compensation in the Z direction of the tool contact point trajectory according to the curvature radius of the tool tip and the derivative of the tool contact point trajectory to obtain a tool position point trajectory of tool processing after compensation; wherein the tool position point trajectory of tool processing after compensation is located directly above the tool contact point trajectory; The relationship between the Z-axis coordinate of the tool position point after compensation and the Z-axis coordinate of the original tool contact point is: Among them, z CL is the Z-axis coordinate of the tool position after compensation, z CP is the Z-axis coordinate of the original knife contact point, r t is the radius of curvature of the tool tip, f'(ρ CP )The derivative of the tool contact trajectory.

7. A method for compiling a free-form surface machining program according to claim 1, characterized in that: The method also includes a program detection module, which is used to import the tool processing program compiled by the program compilation module into the machine tool control system, control the program to run empty, and judge whether the program is wrong according to the tool operation trend and tool amplitude under the program running empty, and transmit the program to the machine tool control system after confirming that the program is correct.

8. A method for compiling a free-form surface machining program according to claim 7, characterized in that: When the program is running idle, the user interface module is also used to display the free-form surface model to be processed in the machine tool axis coordinate system and the tool position trajectory of the tool processing when the program is running idle, so as to determine whether the program is wrong.

9. A method for machining a free-form surface, wherein the machining program compilation method according to any one of claims 1 to 8 is embedded in a machine tool control system, and the machine tool is controlled by the machine tool control system to machine the free-form surface, characterized in that: The method comprises: Input the optical equation of the free-form surface to be processed, processing parameters, and tool parameters; Modeling and analyzing the free-form surface to be processed, planning the tool contact point trajectory of tool processing, and performing error compensation on the tool contact point trajectory to obtain the tool position point trajectory of tool processing; According to the tool position trajectory of tool processing, the tool processing program of the free-form surface to be processed is automatically compiled; Import the tool processing program into the machine tool control system, fix the workpiece to be processed on the machine tool, and control the machine tool to process the free-form surface through the machine tool control system.

10. A free-form surface machining control method according to claim 9, characterized in that: After the tool processing program is imported into the machine tool control system, the program is controlled to run empty first, and the program is judged whether it is wrong according to the tool operation trend and tool amplitude during the empty run. After confirming that the program is correct, the workpiece to be processed is fixed on the machine tool.

Images