Compensation milling method for curved surface boundary reconstruction

Abstract

The invention discloses a compensation milling method for curved surface boundary reconstruction, and belongs to the field of numerical control precision machining of complex curved surface parts. The method aims to solve the problems of low efficiency, unstable quality and easy out-of-tolerance caused by the fact that tool connecting traces generated after complex curved surface milling depend on manual polishing and repairing in the prior art. The method comprises the steps that firstly, a small plane body model reflecting the actual tool mark appearance is obtained through machining simulation; secondly, intersecting the small plane body model with the theoretical curved surface model to obtain a discrete initial intersection line; then, representative points are selected from the discrete lines, and a continuous and smooth curve is reconstructed through a curve fitting algorithm to serve as a compensation boundary; and finally, an offset finish machining tool path is generated based on the boundary, and the butt-joint tool mark area is milled at a time. According to the method, the problems possibly caused by manual grinding are avoided, and the fairness and geometric accuracy of the curved surface switching area are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of high-precision milling technology for complex curved surfaces, and specifically to a compensatory milling method for reconstructing the boundaries of curved surfaces. Background Technology

[0002] In the manufacturing process of engine parts, when machining complex curved surface transitions, there is a problem of obvious tool marks caused by multiple tool joints. For example... Figure 1 As shown, the old method of processing was to use manual polishing, which was labor-intensive, the transition surface was not smooth enough, and there was a possibility of local out-of-tolerance situations.

[0003] Currently, simulation fitting is used to reconstruct the boundary of tool marks, thereby enabling rapid processing of tool marks and achieving smooth transitions at the tool mark points without dimensional deviations. For example, in the fabrication of steel structure nodes, to address the issues of machining accuracy and efficiency for small-angle intersecting nodes, Chinese invention patent CN102661046B proposes a method: 3D modeling is performed using computer-aided design (CAD) software, and the intersection line is accurately drawn using the equal arc length micro-sectioning method, and a solid template is fabricated; during the assembly stage, a ground plan is laid out and three-dimensional assembly is performed based on 3D projection; during the welding stage, a zoned welding strategy is adopted to ensure quality. However, this method focuses on geometric unfolding and cutting and assembly processes assisted by solid templates, without addressing the surface tool mark repair problem commonly found in subtractive machining such as CNC milling, which is caused by multiple tool joints.

[0004] On the other hand, in the field of surface finishing, especially in the process of robotic polishing of blades, to solve the problems of uneven machining allowance and tool marks caused by path splicing, Chinese invention patent CN113954102B discloses a path planning method based on offline programming. This method first selects a tool based on the surface characteristics of the blade, then calculates path parameters and generates an optimized robot motion trajectory, which is then verified through offline programming simulation and used in actual machining. Through a specific path planning algorithm, it aims to achieve uniform polishing coverage, reduce tool marks, and improve the consistency of surface quality. Although this technology directly addresses the surface quality problem of tool marks, its solution starts from the perspective of pre-optimization of path planning, avoiding the generation of tool marks by finely planning the initial machining path, rather than performing subsequent detection, analysis, and compensation repair of existing, obvious tool marks on already machined parts.

[0005] In summary, existing technologies have either made breakthroughs in the machining processes of specific geometries or optimized the pre-planning of machining paths to avoid problems. However, for tool marks that actually exist after CNC milling of complex curved surfaces, especially how to efficiently and accurately automatically identify their boundaries and generate targeted smooth compensation machining paths, there is still a lack of effective solutions. Therefore, there is an urgent need for a new method that can automatically reconstruct tool mark boundaries and generate accurate compensation toolpaths based on machining simulation results. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of tool marks appearing after machining the curved surface at the corner of a complex curved surface transition.

[0007] The technical solution of this invention: a compensation milling method for reconstructing curved surface boundaries, comprising the following steps: Step S1: Obtain the machining simulation model: Simulate the CNC machining process of the part using CNC simulation software to generate a small planar model of the actual part after machining. Step S2: Extract the intersection boundary between theory and reality: retrieve the theoretical model of the part with the surface to be processed, and perform intersection calculation between the small planar body model obtained in step S1 and the theoretical model to obtain the intersection curve representing the initial boundary of the tool mark. The intersection curve is a set of multiple curve segments that are completely discontinuous. Step S3: Reconstruct the smoothing processing boundary: Select multiple sample points from the completely discontinuous intersecting curves in step S2, and use the selected sample points to generate a continuous smoothing curve through a curve fitting algorithm. This smoothing curve serves as the theoretical boundary for compensation processing. Step S4: Generate and execute the compensation toolpath: Based on the smooth curve in step S3, generate a single toolpath by offsetting along the surface normal or a specified direction. Use this toolpath to perform a one-time milling operation on the tool mark area to eliminate tool marks and ensure the smoothness of the surface transition.

[0008] Furthermore, in step S1, the tool marks at the curved surface transition between the small planar body model and the actual part are consistent.

[0009] Furthermore, the CNC simulation software includes UG software.

[0010] Furthermore, in step S3, the selected sample points meet the following requirements: no obvious distortion, centered position, and able to reflect the actual boundary trend of the tool mark, and the number of the sample points is not less than 5.

[0011] Furthermore, in step S4, the single tool path is offset downwards by a preset distance along the surface normal.

[0012] Furthermore, the preset distance is 0.05mm, and the generation direction of the single tool path is consistent with the curvature direction at the surface transition.

[0013] Furthermore, the part is an aero-engine part, the surface to be processed is a complex surface transition of the aero-engine part, the complex surface transition is a concave corner surface, and the tool marks are continuous defects formed after multiple tool-joining processes.

[0014] Furthermore, the one-time milling process is a CNC precision machining, in which the machining accuracy is fed back in real time by the CNC system to ensure that there are no dimensional deviations at the curved surface transition. The beneficial effects of this invention are as follows: using the method of obtaining a smooth boundary by reconstructing the boundary can effectively remove tool marks, reduce the labor cost required for manual polishing, and at the same time, avoid any dimensional deviations by simulating the toolpath generated by the boundary curve in advance. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the small planar body model obtained from the simulation; Figure 2 This is a schematic diagram of the simulation results of the part surface after compensation processing; Figure 3 This is a simulation diagram of the intersection between the small plane and the workpiece surface; Figure 4 This is a schematic diagram of the intersection curve between the small plane and the workpiece surface; Figure 5 yes Figure 4 Enlarged view of the intersecting curves in the middle; Figure 6 This is the result of selecting the midpoint and canceling the fitting of the intersection points; Figure 7 This is a schematic diagram of toolpath generation based on the fitted curve. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0018] A surface tool mark compensation milling method based on simulation and curve fitting, such as... Figures 1 to 7 As shown, the specific steps include: Step S1: Machining State Simulation and Model Acquisition. First, import the original CNC machining program of the part to be processed into UG software, and use its CNC machining simulation module to perform virtual machining. After the simulation is completed, the software generates a small planar model that reflects the surface morphology after actual machining. For example... Figure 1 As shown, at the corner surface transition of the model, raised tool marks caused by multiple tool changes or improper path connection can be clearly observed. The state of the model is consistent with the actual state of the part after machining.

[0019] Step S2: Extract the theoretical and practical boundaries, retrieving the ideal theoretical CAD model of the part. In the software, perform an intersection operation between the small planar body model obtained in Step S1 and the target surface requiring smoothing in the theoretical model. For example... Figure 3 and Figure 4 As shown, the calculation yields a spatial curve located at the intersection of the two points, i.e., the intersection curve. This curve represents the original, rough boundary of the tool mark. A magnified view of the local area (e.g.) Figure 5 As can be seen, this intersecting curve is not a smooth, continuous curve, but is composed of a large number of discontinuous, jagged micro-segments, and cannot be directly used to generate high-quality machining toolpaths.

[0020] Step S3: Smooth Boundary Reconstruction. To obtain usable processing boundaries, a series of sample points representing the overall boundary trend are selected manually or automatically using an algorithm from the discontinuous intersecting curves mentioned above. The selection principle is to avoid obvious distortion points and prioritize points in the middle of each small line segment, such as... Figure 6 The diagram shows a series of discrete points. Then, using the curve fitting function of UG software, a continuous and smooth curve passing through or approximating these points is generated based on these sample points (e.g., ...). Figure 6 (The smooth curve shown). This curve is the reconstructed ideal tool mark boundary.

[0021] Step S4: Compensation machining toolpath generation and execution. Using the smooth curve generated in step S3 as the driving boundary, a finishing allowance is offset along the surface normal. In this example, the offset distance is set to 0.05mm. Based on this, a single-path root-cleaning machining toolpath is generated, as follows: Figure 7 As shown. Finally, the toolpath is post-processed to generate a CNC program, and a one-time finish milling process is performed on the actual tool mark area of ​​the part on the machine tool, resulting in a smooth surface at the transition point, as shown. Figure 2 As shown.

[0022] Through the standard process of this embodiment, the discrete and rough original boundary of the tool marks is successfully transformed into a smooth and continuous theoretical machining boundary, and a precise compensation toolpath is generated accordingly. This method replaces the traditional manual polishing that relies on the craftsman's feel, standardizes and digitizes the machining process, fundamentally eliminates the risk of local deviations (overcutting or undercutting) caused by the uncertainty of manual operation, and ensures the geometric accuracy and surface smoothness of the corner transition surface.

[0023] The above provides a detailed description of the compensatory milling method for reconstructing curved surface boundaries provided by this invention. Specific examples have been used to illustrate the structure and working principle of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A compensatory milling method for reconstructing curved surface boundaries, characterized in that: Includes the following steps: Step S1: Obtain the machining simulation model: Simulate the CNC machining process of the part using CNC simulation software to generate a small planar model of the actual part after machining. Step S2: Extract the intersection boundary between theory and reality: retrieve the theoretical model of the part with the surface to be processed, and perform intersection calculation between the small planar body model obtained in step S1 and the theoretical model to obtain the intersection curve representing the initial boundary of the tool mark. The intersection curve is a set of multiple curve segments that are completely discontinuous. Step S3: Reconstruct the smoothing processing boundary: Select multiple sample points from the completely discontinuous intersecting curves in step S2, and use the selected sample points to generate a continuous smoothing curve through a curve fitting algorithm. This smoothing curve serves as the theoretical boundary for compensation processing. Step S4: Generate and execute the compensation toolpath: Based on the smooth curve in step S3, generate a single toolpath by offsetting along the surface normal or a specified direction. Use this toolpath to perform a one-time milling operation on the tool mark area to eliminate tool marks and ensure the smoothness of the surface transition.

2. The compensation milling method for surface boundary reconstruction according to claim 1, characterized in that: In step S1, the tool marks at the transition point between the small planar model and the actual part are consistent.

3. The compensation milling method for surface boundary reconstruction according to claim 1, characterized in that: The numerical control simulation software includes UG software.

4. The compensatory milling method for reconstructing curved surface boundaries according to claim 1, characterized in that: In step S3, the selected sample points meet the following requirements: no obvious distortion, centered position, and able to reflect the actual boundary trend of the tool mark. The number of sample points is not less than 5.

5. The compensation milling method for surface boundary reconstruction according to claim 1, characterized in that: In step S4, the single tool path is offset downwards by a preset distance along the surface normal.

6. The compensation milling method for surface boundary reconstruction according to claim 5, characterized in that: The preset distance is 0.05mm, and the generation direction of the single tool path is consistent with the curvature direction at the surface transition.

7. The compensation milling method for surface boundary reconstruction according to claim 1, characterized in that: The part is an aero-engine component, the surface to be processed is a complex surface transition point of the aero-engine component, the complex surface transition point is a concave corner surface, and the tool marks are continuous defects formed after multiple tool-joining processes.

8. The compensation milling method for surface boundary reconstruction according to claim 1, characterized in that: The one-time milling process is a CNC precision machining process. During the machining process, the machining accuracy is fed back in real time through the CNC system to ensure that there are no dimensional deviations at the curved surface transition.

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