I understand: the precision machining of CNC non-spherical lenses

From: Castech Wicker.com It is also belonging to the use of milling and grinding and polishing and other means to remove material removal machining method of the surface of the part surface material (MRP). Different are precision numerical controls are based on digital and quantitativeization of theoretical hypothesis and processing experience, and the computer control machining tool is ideal as the workpiece to do the ideal aspherical surface type scanning movement, \”point\” (or smaller area) in the process The contact is accurately removed from the surface of the part, which greatly enhances the processing accuracy and repeatability.

Based on minimal removal of material principles, we have \”best fit ball\” formed by the aspherical vertex and the edge point, as a non-spherical blank. After removing the \”excess\” material, \”correct\” is \”corrected\” into an aspherical surface. Figure 1 shows the MRP method for the aspherical process, where the red portion is the removal portion:

Fig. 1 MRP method is used aspherical schematic

Obviously, non-spherical lens The larger the diameter, the more materials that need to remove, the longer the processing time; the same, in the direction of the horizontal coordinate, the larger the offset of the aspherical surface and the spherical, the more \”steep\”, the surface is \”steep\”, processing The higher the cost is also the same.

An overview of the non-spherical precision numerical control method

The removal process is generally divided into two steps: First, the spherical blank milling is consissed by precision grinding wheels. The aspherical contour required by the facial equation is to ensure that the surface damage is as small as possible, the surface error should also be initially reached a certain precision; Secondly polishing, pre-throwing the milling and destroying layer completely extracted After that, it is repeatedly refined to refine the face until it fully meets the requirements of accuracy and finishness, as shown below:

Figure 2 CNC machine milling and polishing schematic

Spherical \”Open R\”

[ 123] Before wearing the best fit spherical lens, this process is consistent with the conventional spherical proof and the cutting and rolling circle.

Milling

belongs to the rigid removal, the precision grinding wheel is mainly a butterfly grinding wheel and a cup type grinding wheel according to the shape .

Figure 3 Precision grinding wheel [1]

The milling process is divided into two steps of rough grinding and fine grinding:

Raw grinding is the size of \”cow knife\” – coarse grinding wheel (such as D64 particle size) with large particle size The purpose is to quickly change the spherical blank to the aspherical contour, but the surface failure layer of the material at this time is deeper to polish;

So, the next needs refined grinding, \”small knife\” – fine grinding wheel (, Such as D20 particle size) Rear milling, so that the surface failure layer becomes smaller, when the surface is large (eg \u0026 gt; 3um), the introduction measurement data is corrected to a certain precision (such as \u0026 lt; 3um). The milling must be selected according to the size of the lens caliber, and the milling effect is best to achieve the equipment parameters such as the feed speed and the speed of the grinding wheel.

Polishing

To describe the polishing process, 1927 Preston proposed a famous Preston formula [2], That is: under certain conditions, the removal amount ΔZ of the surface material in the machining time can be described as:

k is a PRESTON constant, from relative speed Other factors other than pressure; ν is a relative speed of a surface (x, y) in transient (T) and polishing head; P is polishing pressure.

As can be seen from the formula, in the same case of and p, the removal amount ΔZ is proportional to the time T. This experience formula provides theoretical basis for our further numerical simulation and processing test.

Usually polished is also divided into two steps :

First

pre-polishing,

utilizes a polishing airbag and other tools (see Figure 4) The milling damage layer is completely extracted. In addition to the airbag, common other polishing tools include sponge pad polishing head, wheeled polishing and jet polishing.

Fig. 4 Different specifications of airbag polishing head and modulation tool If the surface is not reached,

is corrected to correct the polishing

, the specific process In order to: (1) Measure the surface surface error of the optical element, acquire the front-shaped data value;

(2) compares the error to the device to obtain this machining Periodic material removal distribution function ΔZ;

(3) Sets polishing parameters, calculates the residence time and optimization processing path, and the computer thus simulates polishing results. If you do not meet the requirements, re-select the polishing parameter again simulation;

(4) The simulation results are feasible, turn on a processing cycleFixed polishing;

(5) After the last cycle is completed, the workpiece surface is measured, and the surface data is provided for the next correction throwing peripheral, so repeatedly iterate until the surface precision requirements are met.

Fig. 5 Flow of non-spherical polishing process

4 [ 123]

Detects Indicators such as lightness Precision CNC Machining and size.

The price of CNC machine tools is expensive, and the removal rate of processing process is low. This is the main reason why this process is high and low capacity. This method is suitable for the production of high-small batch of non-spheroidized non-spherical products from DUV to IR on the surface precision and injury threshold.

Fujing Technology has advanced Optotech ultra-precision CNC milling and polishing equipment, in the Taylor Hobson contour Command \”Under the command, Fujing people constantly climb the non-spherical\” fine \”peak, all processing indicators are in the industry’s leading position:

Precision

Ultra High

Material DUV to IR Optical Glass [ 123]

Outer diameter tolerance ± 0.05 mm

± 0.02mm

center thick Tolerance

± 0.02mm

Eccentric

≤3 ‘

≤ 1′

Noodles (PV / IRR)

0.6um

0.06 um Waste (S / D) 60/40 10/5 Note: Coating can be customized according to customer needs Table 1 Fujing Technology non-spherical product routine VS. Ultra high precision indicators It is worth mentioning that

For special high-facing requirements for customers, our PV / IRR accuracy can be corrected to λ / 10 (@ 633nm)

. Below you share the number of non-poliless products of two Fujing TechnologyExample of processing.

High-precision \”Hemisphere\” processing example [

As mentioned earlier, the more \”steep\” surface of the aspherical surface, the larger the processing difficulty, the more difficult the surface is also repaired. For this example product, the outer diameter φ \u003d 30 mm (Ca \u003d 25.5 mm), our company is detained by 2D correction to IRR \u003d 0.191um, and the 3D process can significantly reduce costs. The product has achieved batch production, the test report is shown below:

LUPHOSCAN test report for \”over hemisphere\” products

Ultra-large diameter and ultra-high precision example

An outer diameter φ \u003d 170 mm, R \u003d 2000 parabolic lens, in the effective area (CA \u003d 155mm, intermediate hole φ \u003d 20 mm) processing index can achieve facade accuracy PV / IRR ≈ 70nm, RMSI \u003d 13 nm, inspection report is shown in Figure 7:

Figure 7 φ \u003d 170mm, r \u003d 2000 parabolic lens product LUPHOSCAN test report

[1] https://www.optotech.de/files/downloads/ products / catalogue_consumables_precision_optics_0.pdf

[2] Preston, FW (1927) The Theory and Design of Plate Glass Polishing Machines. Journal of the Society of Glass Technology, 11, 214-256.