Combined polishing processing method for chalcogenide glass aspheric surface

Abstract

The invention discloses a combined polishing machining method for a chalcogenide glass aspheric surface. The combined polishing machining method comprises the following steps that S1, the surface damage depth of the chalcogenide glass aspheric surface is obtained; s2, whether the surface damage depth is larger than 100 nm or not is judged, if yes, the step S3 is executed, and if not, the step S4 is executed; s3, a small grinding head is used for polishing and shaping till the surface damage depth is smaller than 100 nm; s4, acquiring the surface shape precision of the chalcogenide glass aspheric surface; s5, judging whether the surface shape precision is smaller than the target precision or not, if yes, executing the step S7, and if not, executing the step S6; s6, magneto-rheological polishing and shaping are used, and the step S1 is executed; and S7, a small grinding head is used for polishing and fairing, and the process is finished. According to the method, the chalcogenide glass scrapping risk can be reduced, and the chalcogenide glass surface shape precision can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of aspheric optical element processing, and in particular to a combined polishing processing method for a chalcogenide glass aspheric surface. Background Art

[0002] Optical systems are evolving towards ultra-precision, complexity and integration, and complex curved optical workpieces are called the core of ultra-precision optical systems. Among them, complex surfaces are mainly aspheric surfaces. Due to its unique curved surface configuration, it is difficult to achieve high precision with the help of traditional polishing methods. At the same time, chalcogenide glass has gradually been widely recognized and applied in complex optical systems due to its excellent infrared optical properties. However, chalcogenide glass is brittle, soft and easy to crack, which makes it difficult to process to high precision. When facing large-diameter chalcogenide glass, single-point turning cannot guarantee its high surface accuracy, which creates the risk of workpiece size deviation, thereby increasing product production costs and even the risk of scrapping.

[0003] Due to the characteristics of chalcogenide glass itself, it is difficult to process, has high added value of lenses, high risk of lens scrapping, and long processing cycle, which makes it different from general materials such as window glass. The processing of chalcogenide glass itself is technically difficult, especially the ultra-precision aspheric processing of chalcogenide glass.

[0004] At present, the mainstream solution for ultra-precision machining of chalcogenide glass aspheric surfaces is ultra-precision single-point turning technology, which uses a fixture to fix the workpiece transferred from the previous process on the rotating air-floating spindle, and uses a single-point turning tool to turn the aspheric surface contour trajectory. Ultra-precision single-point turning can produce precision optical components with micron and submicron surface accuracy and nanometer surface roughness. Smooth diamond blades can produce optical surfaces with low residual stress and roughness, but single-point diamond turning is a complex material removal process with the characteristics of small cutting depth and large strain rate. In addition, ultra-precision single-point turning technology has limited machining accuracy for large-diameter aspheric chalcogenide glass, and each machining is a de-massing process, which easily causes thickness size deviations and leads to workpiece scrapping. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a combined polishing processing method for a chalcogenide glass aspheric surface which can reduce the risk of chalcogenide glass being scrapped and can improve the surface shape accuracy of the chalcogenide glass.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A combined polishing method for a chalcogenide glass aspheric surface comprises the following steps: S1. Obtaining the depth of surface damage on the aspheric surface of chalcogenide glass; S2, determine whether the surface damage depth is greater than 100nm, if yes, proceed to step S3, otherwise proceed to step S4; S3, use a small grinding head to polish and modify the surface until the depth of damage is less than 100nm; S4, obtaining the surface shape accuracy of the chalcogenide glass aspheric surface; S5, determine whether the surface accuracy is less than the target accuracy, if yes, execute step S7, otherwise execute step S6; S6, using magnetorheological polishing to perform shaping, and executing step S1; S7. Use a small grinding head to polish and smooth. Finished.

[0007] As a further improvement to the above technical solution: In step S1, the damage is a scratch or a pit.

[0008] In step S1, a white light interferometer is used to measure the depth of the surface damage.

[0009] In step S3, when the small grinding head is polishing and trimming, the polishing liquid used is a diamond polishing liquid with a particle size of 50nm to 300nm, and the air pressure is 0.04 to 0.06MPa.

[0010] In step S3, the number of times the small grinding head polishes and reshapes is multiple times, and the air pressure value Pn of a certain polishing and reshape of the small grinding head is set to be Pn+1, and Pn≥Pn+1 is satisfied.

[0011] In step S6, the process parameters of magnetorheological polishing and shaping are: ribbon pressing depth of 0.3 mm, polishing wheel speed of 180 rad / min, viscosity of 180 mPa·s, and flow rate of 60 L / H.

[0012] In step S7, the air pressure value when the small grinding head is polishing and smoothing is not greater than the air pressure value when the small grinding head is polishing and shaping in step S3.

[0013] In step S7, the polishing liquid used when the small grinding head is polished and smoothed is a diamond polishing liquid with a particle size of 50nm to 300nm, the air pressure used is 0.008 to 0.012MPa, and the speed is 800 to 1200mm / min.

[0014] Compared with the prior art, the advantages of the present invention are: The method of the present invention adopts magnetorheological polishing and small grinding head polishing. Magnetorheological polishing is a kind of ultra-precision polishing. Since it relies on the shear force between a ribbon and a workpiece for polishing, magnetorheological lines are easily formed on the surface of a relatively soft material such as chalcogenide glass. Polishing with a small grinding head for shaping or smoothing can improve the surface shape of the chalcogenide glass while ensuring its surface shape target accuracy and surface quality, thereby obtaining a chalcogenide optical element with better surface shape accuracy and better surface quality, reducing the risk of scrapping the chalcogenide glass, and being suitable for small-batch production in the field of polishing ultra-precision processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a process flow chart of the present invention.

[0016] Figure 2 It is a surface accuracy diagram of Example 1 of the present invention.

[0017] Figure 3 It is a photo of the product processed in Comparative Example 1 of the present invention.

[0018] Figure 4 It is a photo of the product processed in Comparative Example 2 of the present invention.

[0019] Figure 5 It is a photo of the product after processing of Comparative Example 3 of the present invention.

[0020] Figure 6 It is a photo of the product after processing of Comparative Example 4 of the present invention.

[0021] Figure 7 It is a photo of the processed product of Comparative Example 5 of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0023] Example 1 The processing object of this embodiment is a biconvex chalcogenide glass piece with a D127mm (effective aperture D120mm) and a vertex curvature radius of 700.29±0.3mm. The surface shape target accuracy RMS is required to be less than 35nm, where the quadratic coefficient K=-6. For the relevant process route, please refer to Figure 1 .

[0024] The operation steps of the processing method of this embodiment are as follows: Step 1: Use the DUI profilometer to detect the aspheric surface shape of the chalcogenide glass after front-end processing, rotate 120° respectively, evaluate whether the surface shape distribution is consistent, use a three-wave lamp in a black box to detect its aspheric surface finish, and use a white light interferometer to measure the depth of surface damage (in the present invention, surface damage refers to scratches or pits).

[0025] Step 2: Determine whether the depth of the damage (scratches or pits) on the aspheric surface of the chalcogenide glass is greater than 100 nm. If there are scratches or pits with a depth greater than 100 nm on the aspheric surface of the chalcogenide glass, use a small grinding head to polish and shape until there are no scratches or pits, and then execute step S3; otherwise, directly execute step S3.

[0026] In this step, it is found that the depth of the damage on the aspheric surface of the chalcogenide glass is greater than 100nm, so a small grinding head is used for polishing and shaping. In this embodiment, the process parameters for polishing and shaping with a small grinding head are a diamond polishing liquid with a particle size of 100nm and an air pressure of 0.05Mpa.

[0027] Step 3: Determine whether the surface accuracy is less than the target accuracy requirement. If it is greater, perform step 1 after using magnetorheological polishing for shaping. Otherwise, perform step 4.

[0028] In this embodiment, it is found that the surface accuracy RMS is greater than 35 nm, so magnetorheological polishing is used.

[0029] In this embodiment, magnetorheological polishing and shaping are performed twice and small grinding head polishing and shaping are performed three times.

[0030] The process parameters for the first magnetorheological polishing and shaping are: pressure depth of 0.3mm ribbon pressure depth, polishing wheel speed of 180rad / min, viscosity of 180 mPa·s, flow rate of 60L / H, and the polishing liquid here is magnetorheological fluid. After the first magnetorheological polishing and shaping, the shape and finish after processing are detected. The surface magnetorheological traces are measured by white light interferometer. There are still scratches with a depth of more than 100nm. The small grinding head polishing and shaping process uses a diamond polishing liquid with a particle size of 100nm, and the air pressure is 0.03MPa. The same process parameters are used for the small grinding head polishing and shaping process three times and then returned for detection. The scratch depth at the corresponding position is less than 100nm. The surface shape accuracy is detected and it is found that its value is still greater than the target accuracy requirement. Then the second magnetorheological polishing and shaping is carried out (with the same process parameters as the first magnetorheological polishing and shaping). After the second magnetorheological polishing and shaping, the shape has been reduced to the target accuracy RMS24.61nm, and there are magnetorheological traces on the surface.

[0031] Step 4: After confirming that the surface shape accuracy RMS of the workpiece after magnetorheological polishing has reached the target accuracy, use a small grinding head to polish and smooth it. Adjust the process parameters of the small grinding head to polish and smooth it to a diamond polishing liquid with a particle size of 100nm, an air pressure of 0.01MPa, and a feed speed of 1000mm / min. After the small grinding head polishes and smoothes it twice, detect the processing mirror finish in the black box to determine whether the finish meets the technical requirements. The detection mirror surface shape accuracy RMS is RMS32.785nm. Figure 2 shown.

[0032] In the present invention, the purpose of the small grinding head polishing and shaping in step 2 is different from the purpose of the small grinding head polishing and smoothing in step 4. In step 4, since the surface shape accuracy of the chalcogenide glass surface is in place, but due to the magnetorheological polishing and shaping in step 3, magnetorheological lines exist on the surface of the chalcogenide glass, and the small grinding head polishing and shaping is required to gently remove the magnetorheological lines on its surface. In step 2, since the damage on the surface of the chalcogenide glass is greater than 100nm, the main purpose of the small grinding head polishing and shaping is to repair the smoothness. That is to say, if the surface damage is deep, the small grinding head is used for polishing and shaping. If the surface shape accuracy reaches the target accuracy and the surface damage is less than 100nm, the small grinding head is used for polishing and smoothing.

[0033] The air pressure during the polishing and shaping by the small grinding head in step 2 is greater than the air pressure during the polishing and smoothing by the small grinding head in step 4, and the speed during the polishing and smoothing by the small grinding head in step 4 should not be too high, and it is only necessary to gently remove the magnetorheological lines on the surface.

[0034] The present invention ensures the surface quality of aspheric optical elements while ensuring the surface accuracy of aspheric surfaces, reduces the risk of scrapping workpieces due to thickness tolerance of chalcogenide glass in the previous process, and can achieve ultra-precision machining of aspheric surfaces of chalcogenide glass with larger apertures (aperture>100mm), with the machining surface accuracy RMS reaching λ / 20.

[0035] Comparative Example 1 The processing method of this comparative example only adopts magnetorheological treatment (without small grinding head polishing), that is, comprises the following steps: Step 1: Detect the surface accuracy of the D127 biconvex aspheric chalcogenide glass workpiece; Step 2: Determine whether the surface accuracy of the workpiece is less than the target accuracy requirement. If so, proceed to step 3. Otherwise, use magnetorheological polishing to modify the shape. The ribbon pressing depth during magnetorheological polishing is 0.5 mm.

[0036] Step 3: Check the surface finish of the D127 biconvex aspheric chalcogenide glass workpiece.

[0037] In this comparative example, magnetorheological polishing and shaping is directly used, and the magnetorheological polishing and shaping process parameters are: ribbon pressure depth of 0.5 mm, polishing wheel speed of 180 rad / min, viscosity of 180, flow rate of 60 L / H, and the polishing liquid is magnetorheological liquid.

[0038] Results: Figure 3 As shown, there are many pits or scratches visible to the naked eye in the red circle, and the surface quality of the chalcogenide glass is poor and cannot meet the requirements.

[0039] Comparative Example 2 The processing method of this comparative example is substantially the same as that of comparative example 1, except that the parameters of magnetorheological polishing and shaping are different, and specifically includes the following steps: Step 1: Detect the surface accuracy of the D127 biconvex aspheric chalcogenide glass workpiece; Step 2: Determine whether the surface accuracy of the workpiece is less than the target accuracy requirement. If so, proceed to step 3. Otherwise, magnetorheological polishing is used for shaping. The ribbon pressing depth during magnetorheological polishing is 0.3 mm.

[0040] Step 3: Detect the surface finish of the D127 biconvex aspheric chalcogenide glass workpiece; In this comparative example, magnetorheological polishing and shaping were directly used. The magnetorheological polishing and shaping process parameters were as follows: ribbon pressure depth of 0.3 mm, polishing wheel speed of 180 rad / min, viscosity of 180 mPa·s, flow rate of 60 L / H, and the polishing liquid was the same magnetorheological liquid.

[0041] Results: Figure 4 As shown, the surface quality of the chalcogenide glass has improved significantly, but there are still many magnetorheological lines (in the red circle).

[0042] Comparative Example 3 The processing method of this comparative example is substantially the same as that of Example 1, and adopts magnetorheological polishing and shaping and small grinding head polishing and shaping processes. The difference is that: this comparative example adopts cerium oxide polishing liquid with a concentration of 30% during small grinding head polishing and shaping, and specifically comprises the following steps: Step 1: Check the finish of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 2: Determine whether the depth of the surface damage (scratches or pits) of the workpiece to be processed is greater than 100nm. If so, perform polishing with a small grinding head and then perform step 2, otherwise proceed to step 3; Step 3: Detect the surface accuracy of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 4: Determine whether the surface shape accuracy of the workpiece is less than the target accuracy requirement. If so, proceed to step 5. Otherwise, perform step 4 after using magnetorheological polishing to correct the shape. Step 5: Check the surface finish of the D127 biconvex aspheric chalcogenide glass workpiece.

[0043] In this comparative example, magnetorheological polishing and shaping were used, and the magnetorheological polishing and shaping process parameters were as follows: ribbon pressure depth of 0.3 mm, polishing wheel speed of 180 rad / min, viscosity of 180 mPa·s, flow rate of 60 L / H, the polishing liquid was the same magnetorheological liquid, and when a small grinding head was used for polishing and shaping, the small grinding head polishing and shaping process parameters were 0.05 MPa air pressure, and a cerium oxide polishing liquid with a concentration of 30% was used for polishing.

[0044] Results: Figure 5As shown, it was found that the polishing effect was not good, the surface finish did not show obvious improvement, magnetorheological lines still existed (in the red circle), and there were even obvious polishing disc marks on the surface (in the red box).

[0045] Comparative Example 4 The processing method of this comparative example is roughly the same as that of comparative example 3, except that the process parameters of the small grinding head polishing and shaping are different. This comparative example uses a diamond liquid with a particle size of 500nm, and the operating steps are as follows: Step 1: Check the finish of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 2: Determine whether the depth of the surface damage (scratches or pits) of the workpiece to be processed is greater than 100nm. If so, perform polishing with a small grinding head and then execute step 2, otherwise proceed to step 3; Step 3: Detect the surface accuracy of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 4: Determine whether the surface accuracy of the workpiece is less than the target accuracy requirement. If so, proceed to step 5. Otherwise, perform magnetorheological polishing and then perform step 4. Step 5: Check the surface finish of the D127 biconvex aspheric chalcogenide glass workpiece.

[0046] In this comparative example, magnetorheological polishing and shaping are used, and the magnetorheological polishing and shaping process parameters are: ribbon pressure depth of 0.3mm, polishing wheel speed of 180rad / min, viscosity of 180mPa·s, flow rate of 60L / H, polishing liquid is the same magnetorheological fluid, and when a small grinding head is used for polishing and shaping, the small grinding head polishing and shaping process parameters are 0.05Mpa air pressure, and diamond liquid with a particle size of 500nm is used for polishing.

[0047] Results: Figure 6 As shown, it is found that the surface finish effect is improved but not obvious, magnetorheological lines still exist (in the red circle), and the upper limit of the final controllable finish is relatively low (the finish detection and evaluation of the present invention adopts the national standard GB / T1185-1989 (or GB / T 1185-2006), and the finish of the product of this comparative example cannot meet the target requirements specified in the national standard, but Example 1 can meet it).

[0048] Comparative Example 5 The processing method of this comparative example is roughly the same as that of comparative example 4, except that a diamond liquid with a particle size of 100 nm is used as the polishing liquid, and the specific operation steps are as follows: Step 1: Check the finish of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 2: Determine whether the depth of the surface damage (scratches or pits) of the workpiece to be processed is greater than 100nm. If so, perform polishing with a small grinding head and then perform step 2, otherwise proceed to step 3; Step 3: Detect the surface accuracy of the D127 biconvex aspheric chalcogenide glass workpiece to be processed; Step 4: Determine whether the surface shape accuracy of the workpiece is less than the target accuracy requirement. If so, proceed to step 5. Otherwise, perform step 4 after using magnetorheological polishing to correct the shape. Step 5: Check the surface finish of the D127 biconvex aspheric chalcogenide glass workpiece.

[0049] In this comparative example, magnetorheological polishing and shaping were used, and the magnetorheological polishing and shaping process parameters were as follows: ribbon pressure depth of 0.3 mm, polishing wheel speed of 180 rad / min, viscosity of 180 mPa·s, flow rate of 60 L / H, the polishing liquid was the same magnetorheological liquid, and when a small grinding head was used for polishing and shaping, the small grinding head polishing and shaping process parameters were 0.05 Mpa air pressure, and diamond liquid with a particle size of 100 nm was used for polishing.

[0050] Results: Figure 7 As shown in the figure, the time cost of surface finish control and the quality control of surface shape after processing are good, without magnetorheological lines or polishing disk marks, but the cumulative smoothing surface shape after processing changes greatly.

[0051] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A combined polishing method for a chalcogenide glass aspheric surface, characterized in that: The following steps are involved: S1. Obtaining the depth of surface damage on the aspheric surface of chalcogenide glass; S2, determine whether the surface damage depth is greater than 100nm, if yes, proceed to step S3, otherwise proceed to step S4; S3, use a small grinding head to polish and modify the surface until the depth of damage is less than 100nm; S4, obtaining the surface shape accuracy of the chalcogenide glass aspheric surface; S5, determine whether the surface accuracy is less than the target accuracy, if yes, execute step S7, otherwise execute step S6; S6, using magnetorheological polishing to perform shaping, and executing step S1; S7. Use a small grinding head to polish and smooth. Finished.

2. The combined polishing method according to claim 1, characterized in that: In step S1, the damage is a scratch or a pit.

3. The combined polishing method according to claim 2, characterized in that: In step S1, a white light interferometer is used to measure the depth of the surface damage.

4. The combined polishing method according to claim 1, characterized in that: In step S3, when the small grinding head is polishing and trimming, the polishing liquid used is a diamond polishing liquid with a particle size of 50nm to 300nm, and the air pressure is 0.04 to 0.06MPa.

5. The combined polishing method according to claim 4, characterized in that: In step S3, the number of times the small grinding head polishes and reshapes is multiple times, and the air pressure value Pn of a certain polishing and reshape of the small grinding head is set to be Pn+1, and Pn≥Pn+1 is satisfied.

6. The combined polishing method according to claim 1, characterized in that: In step S6, the process parameters of magnetorheological polishing and shaping are: ribbon pressing depth of 0.3 mm, polishing wheel speed of 180 rad / min, viscosity of 180 mPa·s, and flow rate of 60 L / H.

7. The combined polishing method according to claim 1, characterized in that: In step S7, the air pressure value when the small grinding head is polishing and smoothing is not greater than the air pressure value when the small grinding head is polishing and trimming in step S3.

8. The combined polishing method according to claim 7, characterized in that: In step S7, the polishing liquid used when the small grinding head is polished and smoothed is a diamond polishing liquid with a particle size of 50nm to 300nm, the air pressure used is 0.008 to 0.012MPa, and the speed is 800 to 1200mm / min.

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