Three-axis single-point diamond ultra-precision turning method for flat-topped bifocal glasses mold

Abstract

The invention discloses a three-axis single-point diamond ultra-precision turning method for a flat-topped bifocal glasses mold, and provides an off-axis clamping and turning path design scheme for solving the flat-topped step machining problem caused by the curvature radius difference of a far-used large spherical surface and a near-used small spherical surface. The die is fixed at a specific off-axis distance to ensure that a flat-top step is horizontal and is directly turned by all cutting edges, so that interference of a rear angle and a side edge of a cutter is avoided; high-density sampling points (more than or equal to 15 points per millimeter) are adopted for near small spherical surface curvature sudden change and step areas, turning speed fluctuation is restrained, and surface consistency is improved; meanwhile, the turning area and the transition area are divided, smooth path transition is achieved in the transition area through linear interpolation tool location points, and residual tool marks are avoided. By combining the three-axis ultra-precision single-point diamond turning technology, high-quality machining with the step precision smaller than or equal to 1 micron and the surface roughness Ra smaller than or equal to 5 nm can be achieved, and the method is suitable for ultra-precision manufacturing of complex bifocal glasses molds.

Description

Technical Field

[0003] The invention relates to an ultra-precision turning method, in particular to an ultra-precision turning method of a flat-top bifocal mold using a three-axis single-point diamond lathe, providing a new technical solution for ultra-precision machining of complex bifocal molds. Background Art

[0005] Flat-top bifocals are the mainstream optical devices for correcting presbyopia. Their lenses need to have dual-focus functions of a large spherical surface for distance and a small spherical surface for near vision. In order to achieve dual-light zone optical performance, mold processing needs to reproduce the large and small spherical surface structures with high precision on a single substrate, and a flat-top step is formed at the junction of the two spherical surfaces (the step depth Δk is determined by R 1 , R 2 The manufacturing difficulty of this type of mold is: on the one hand, there are processing limitations of the flat-top step. Traditional ultra-precision turning uses coaxial clamping, and the side edge of the tool is easy to interfere with the right-angle surface of the flat-top step, resulting in cracking of the step edge or residual burrs, which is difficult to meet the right-angle transition requirements of the optical surface. Second, the speed control in the curvature mutation zone: the curvature radius of the large sphere and the small sphere is significantly different (usually R 2 <R 1 / 2) When turning a small spherical surface, the tool feed direction changes frequently. If the sampling point density is insufficient, it is easy to cause a sudden change in the turning speed, resulting in excessive surface waviness. The third is the smoothness defect of path planning. The conventional turning path directly switches at the junction of the spherical surface and lacks a transition zone design. The discontinuous tool trajectory will cause vibration or residual tool marks, affecting the mold surface accuracy.

[0006] In the prior art, patent CN201910286361 proposes a flat-top bifocal lens and manufacturing method for improving myopia and naked eye vision, which only deals with the design and manufacturing of the lens, and does not cover mold processing. Multi-axis linkage is used to compensate for the difference in spherical curvature, but the problem of direct turning of the flat-top step blade is not solved; patent JP202210987654B2 "A tool geometry parameter optimization method for bifocal glasses mold processing" reduces interference by optimizing tool geometry parameters, but loses step depth accuracy (error ≥ 20 μm). In addition, traditional CNC interpolation algorithms are prone to acceleration mutations in the curvature mutation area, which makes it difficult to meet submicron processing requirements.

[0007] Therefore, there is an urgent need for an ultra-precision turning method for flat-top bifocal glasses molds to simultaneously achieve high-quality processing of flat-top steps, stable turning of curvature mutation zones, and smooth transition of the entire path. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and propose an ultra-precision turning method for a flat-top bifocal glasses mold. Aiming at the problem of flat-top step processing caused by the difference in curvature radius between the large spherical surface for distance use and the small spherical surface for near use, an off-axis clamping and turning path design scheme is proposed.

[0010] The present invention adopts the following technical solution:

[0011] One is off-axis clamping. The off-axis clamping method involves fixing the mold workpiece on the spindle of the ultra-precision lathe at an off-axis distance L, adjusting the mold orientation so that the flat-top step is in the horizontal direction, that is, parallel to the X-axis, to ensure that the flat-top step is directly turned by the blade of the diamond tool; the off-axis distance L satisfies the condition of L>0.6D, and D is the mold diameter.

[0012] The second is the turning path, which includes discrete angle sampling planning and complete tool path design; the discrete angle sampling planning is divided into the following steps:

[0013] (1) According to the center position of the flat-top step, that is, the horizontal distance l and vertical distance (hP) from the mold center, combined with the large spherical curvature radius R 1 and the radius of curvature of the small sphere R 2 The step depth Δk is calculated by the difference between

[0014] (3)

[0015] Where d' is the radius of the small sphere, s is the distance between the center of the small sphere and the flat top, s=hP; h is the distance between the center of the small sphere and the X-axis, and P is the distance between the flat top and the X-axis.

[0016] (2) Using the calculated depth Δk, the discrete angle sampling planning of turning is completed. When turning a large spherical surface for a long distance, the conventional tool sampling point density is used. When turning a small spherical surface for a short distance, the tool sampling point density is increased to 3 to 5 times the sampling angle of the large spherical surface for a long distance, so as to suppress the sudden change in turning speed caused by the flat-top step depth Δk, as follows: (4)

[0017] where θ 1 is the turning sampling angle of the near spherical surface, θ 2 It is the sampling angle of turning of the large sphere used far away;

[0018] The complete tool path design scheme is divided into two parts: the mold turning area and the path transition area. Because the mold is placed off-axis, the turning area generates continuous tool position points according to the far and near spherical curvature and the flat-top step depth in step (1). The transition area uses linear interpolation to connect the tool position points to ensure the smoothness of the path. Finally, the X-axis (radial feed), Z-axis (axial feed) and C-axis (workpiece rotation) of the lathe are controlled by three-axis linkage to complete the processing of the flat-top double-light mold.

[0019] The above-mentioned ultra-precision path can be divided into at least three equally divided mold turning areas according to the off-axis distance and the maximum rotation diameter of the lathe spindle. By using high-precision fixtures, the flat top line in each turning area can be aligned with the array angle direction. Adjacent mold turning areas are smoothly connected without breakpoints. One tool path can be used to complete the turning of at least three workpieces, thereby improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the processing design of double-light mold workpiece;

[0022] Figure 2 Side view of processing 3 array workpieces at one time;

[0023] Figure 3 It is a complete diagram of the ultra-precision turning tool path of the present invention;

[0024] Figure 4 It is a curve diagram of the die height Z value within a rotation cycle;

[0025] Figure 5 It is a distribution curve of the Z value rate change within a rotation period. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0028] Example 1

[0029] See attached Figure 1 In this embodiment, the diameter D of the dual-light mold is 75 mm, and the radius of curvature of the large sphere for far-field use is 132.405 mm; the diameter d of the small sphere for near-field use is 28 mm, the radius of curvature of the small sphere is 90 mm, and the mold off-axis distance L is 46.65 mm; the horizontal offset l between the flat top center and the mold center is 5 mm, and the vertical offset h is 11.5 mm, and the entire fixture size is 180 mm.

[0030] Turning path planning: Select the large sphere as equal-angle discrete sampling, that is, θ 2 is 0.6 degrees. According to formula (1), the center depth of the flat-top step is 0.154 mm, which is less than 200 um. Then θ 1 The sampling step is 0.2 degrees, the sampling step is 0.1 mm for rough turning and 0.005 mm for fine turning. The subsequent transition zone path takes the die edge sagittal height of 5.413 mm as the reference point, and 0.6 degree spiral linear interpolation is performed.

[0031] See attached Figure 2,In order to improve the turning efficiency, the mold array is clamped three times at once, and the flat top line of each mold is parallel to the indexing axes of 0 ,120 ,and 240 ,degrees, respectively, with an error of no more than 0.05 ,degrees.

[0032] Figure 3 and Figure 4 The following are the complete tool path diagrams for ultra-precision turning of three array molds and the mold sagittal height Z value curve diagram within a rotation cycle, i.e., 0~360°. As can be seen from the figure, the overall distribution is uniform. At 120 degrees, 240 degrees and 360 degrees, the Z value has a local jump due to the existence of flat-top steps. In order to reduce the following error and suppress the fluctuation caused by the steps, the sampling angle θ of the small sphere is selected. 1 is 0.2 degrees, see Figure 5 At the positions of 120 degrees, 240 degrees and 360 degrees, the Z value rate changes by 0.1 mm / °, the flat top is basically smoothly connected, there is no obvious sudden change in turning speed, and the difference between the maximum and minimum values ​​of the overall fluctuation does not exceed 0.5 mm / °.

Claims

1. A three-axis single-point diamond ultra-precision turning method for a flat-top bifocal glasses mold, characterized in that : The ultra-precision turning method includes off-axis clamping and turning path design. The off-axis clamping fixes the mold workpiece to the ultra-precision lathe spindle at an off-axis distance L, and adjusts the mold orientation so that the flat-top step is in a horizontal direction, that is, parallel to the X-axis, to ensure that the flat-top step is directly turned by the blade of the diamond tool; the off-axis distance L satisfies the condition of L>0.6D, where D is the mold diameter; The turning path includes discrete angle sampling planning and a complete tool path design scheme; the discrete angle sampling planning is divided into the following steps: (1) According to the center position of the flat-top step, that is, the horizontal distance l and the vertical distance (hP) from the mold center, the step depth Δk is calculated by combining the difference between the large spherical curvature radius R1 for distance and the small spherical curvature radius R2 for near. (1) Where d′ is the radius of the small sphere, s is the distance between the center of the small sphere and the flat top, s=hP; h is the distance between the center of the small sphere and the X-axis, and P is the distance between the flat top and the X-axis; (2) Using the calculated depth Δk, complete the turning discrete angle sampling; when turning the far large spherical surface, use the conventional tool sampling point density; when turning the near small spherical surface, increase the tool sampling point density to 3~5 times the far large spherical surface sampling angle to suppress the sudden change in turning speed caused by the flat-top step depth Δk, as follows: (2) Where θ1 is the turning sampling angle of the small sphere for near use, and θ2 is the turning sampling angle of the large sphere for far use; The complete tool path design scheme is divided into two parts: the mold turning area and the path transition area, which are designed simultaneously. Because the mold is placed off-axis, the turning area generates continuous tool position points according to the far and near spherical curvatures and the flat-top step depth in step (1), and the transition area uses linear interpolation to connect the tool position points to ensure the smoothness of the path. Finally, the X-axis (radial feed), Z-axis (axial feed) and C-axis (workpiece rotation) of the lathe are controlled by three-axis linkage to complete the processing of the flat-top double-light mold.

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