CN107598715A - Large-caliber special-shaped plane machining method - Google Patents

Abstract

The invention discloses a large-diameter special-shaped plane processing method, which comprises the following steps: forming processing, grinding, rough polishing, ring polishing machine polishing, and polishing finishing; cutting and forming the rough blank, and forming and processing to meet the accuracy requirements of the designed external dimension, using Laser tracker or three-coordinates are used for external dimension and surface shape detection; grinding is processed by traditional methods or CNC small tools (or robots), and laser tracker or three-coordinates are used for surface shape detection; surface shape detection equipment is used to detect optical mirrors , according to the actual processing difficulty of the mirror surface and the requirements of the construction period, polishing and finishing can further improve the surface quality of the mirror surface through small numerical control tools (including magnetorheological or ion beam), and the final inspection of the mirror surface quality meets the design requirements. The invention provides a new method for processing large-caliber special-shaped plane mirrors, which lays a foundation for the processing of larger large-diameter special-shaped plane mirror optical elements, and has great practical engineering application value.

Description

A method for machining large-caliber special-shaped planes

technical field

The invention relates to the technical field of plane processing, in particular to a large-caliber special-shaped plane processing method.

Background technique

High-power giant laser devices often use a large number of high-precision large-diameter and ultra-large-diameter planar optical components, and large-diameter and high-precision planar optical components. In all laser equipment, a large number of high-precision, large-diameter optical components are required, including irregular shapes. shaped optical components.

The continuous slow-speed ring polishing machine is called Continuous Polishing Machine for short. It is an important plane polishing technology. It mainly highlights its processing advantages for special-shaped and ultra-thin flat mirror windows. Influenced by many factors. Ring polishing machine polishing is referred to as ring polishing: ring polishing is a polishing method that can achieve higher surface accuracy and better surface roughness, and is widely used in various optical polishing fields. With the continuous development of polishing technology, many new processes and methods have emerged, such as magnetorheological polishing technology, ion beam polishing technology, laser polishing technology and other new high-precision polishing technologies.

At present, the processing technologies of large-aperture flat mirrors for optical components at home and abroad mainly include traditional classical large-plate processing, continuous ring polishing machine polishing, CCOS, online electrolytic grinding, magnetorheological polishing, ion beam polishing, jet polishing, and single-point diamond fly cutting. optical plane, etc. As far as the country is concerned, the processing level of high-precision large-diameter flat mirrors, especially large-diameter flat mirrors, is still relatively weak, and is limited by processing and testing equipment and other conditions.

After forming, grinding and initial polishing process, ring polishing machine is generally used for polishing, ring polishing or a combination of ring polishing and numerical control to complete the final precision polishing. The ring polishing process has always been the bottleneck in the cold processing process line of large-diameter planar optical components. Its manufacturing cost and man-hours account for more than half of the entire manufacturing process. The processing results basically determine the quality of optical components. Therefore, the ring polishing machine polishing process has become The key process of the production line of large aperture flat optical components.

At present, the processing control methods of large-scale ring throwing machines in China are relatively backward, mainly because there are relatively few parameters that can be adjusted and controlled by the equipment, and the relationship between equipment adjustment parameters and production quality is not clear enough.

The polishing mold of the ring polishing machine is ring-shaped, and the polishing disc, the correction disc and the workpiece disc rotate in the same direction. The correction disc performs real-time flattening on the polishing die to correct the surface shape of the polishing die, and the workpiece is free-floating on the ring-shaped polishing die. Polishing, the workpiece is polished by a continuous and uniform polishing mold, so as to obtain extremely low surface roughness and high surface accuracy. In recent years, with the continuous increase in the diameter of optical components, large-caliber components with meter-scale dimensions have appeared. This type of component has large size, high processing index requirements, high demand for component output, and extremely high requirements for processing technology. However, ring polishing machine polishing technology is still the main processing method for large-diameter components in current engineering production. However, the current The polishing process of the ring polishing machine is mainly suitable for the processing of small and medium-caliber optical components, and the processing technology of large-diameter reflective components is less involved, and the processing technology and testing corresponding to the increase of the component caliber are not a simple copy of the small-caliber component technology and testing. There are new phenomena and new difficulties unique to the processing and testing of large-diameter components.

General caliber exceeds Millimeter plane mirror processing can be rough blank→rough grinding forming→small tool grinding or classical large plate grinding→small tool polishing or classical large plate rough polishing→ring polishing machine polishing→magnetorheological processing or ion beam processing or small tool and ring Polishing machine combined with polishing finishing→coating, so as to realize the method of large-caliber special-shaped flat mirror processing technology.

Research on the processing technology and detection methods of large-diameter special-shaped planes has become a difficulty and hot spot in large-diameter special-shaped plane optical processing.

Contents of the invention

When processing special-shaped flat mirrors, it is easy to produce astigmatism and edge collapse, which seriously affects the accuracy of the entire surface shape. Sometimes in order to obtain a good surface shape, the mirror shape has to be changed. In response to this situation, we combined the characteristics of special-shaped mirrors on the continuous polishing machine, explored a set of processing technology, and made effective improvements in the process structure of the polishing machine. Keeping the synchronous rotation of the calibration disc and the workpiece is the key to realize the continuous and uniform grinding of the plane. For this reason, improving various process factors is the key point to obtain a high-precision surface shape. In view of the deficiencies in the prior art, the purpose of the present invention is to propose a method for processing an optical large-diameter special-shaped plane mirror. This article mainly involves the polishing process of a continuous ring polishing machine.

In order to achieve the above object, the technical solution of the present invention is: a large-caliber special-shaped plane processing method, comprising the following steps:

Step 1), cutting and forming the rough blank, forming and processing, using a laser tracker or three-coordinates to carry out external dimension, surface shape, and detection to meet the design external dimension requirements;

Step 2), Grinding: use traditional methods or CNC small tools (or robots) to process, abrasive particles are ground from coarse to fine, and use laser tracker or three-coordinate for surface shape detection;

Step 3), rough polishing: Polishing (pre-stage) adopts traditional methods or CNC small tool (or robot) processing methods, using traditional methods or CNC small tools to process, polishing and controlling the surface shape of the mirror surface, so as to ensure the accuracy of rough polishing surface shape. Meet the requirements of interferometer for interference detection;

Step 4), ring polishing machine polishing:

Late polishing adopts ring polishing machine polishing: that is, continuous polishing process method, including asphalt polishing disc preparation, polishing disc casting and initial molding, polishing disc grinding, calibration plate, separator, counterweight and other technological factors;

Step 5), polishing and finishing: according to the quality of the mirror surface, the actual processing difficulty and the requirements of the construction period, it can be transferred to small numerical control tools such as magnetorheological processing or ion beam processing, and finally the ring polishing machine can be used for smooth polishing processing, using interference The instrument is used for repeated testing, and the quality of the surface shape meets the requirements of the mirror surface design.

Further, the large-diameter special-shaped flat mirror refers to a diameter of 200-2000mm and a thickness of 5-300mm.

Further, in the step 4) continuous polishing process: a separator is used. In order to ensure better surface shape accuracy, we designed and manufactured a separator whose outer diameter does not exceed two-fifths of the diameter of the rubber plate. The inner ring of the separator is similar to the shape of the workpiece, and the size is enlarged according to the overall shape of the workpiece ( For example, 2-35mm), add a protective rubber pad to the inner ring wall.

Further, different separators are selected according to the shape of the workpiece: if the shape of the workpiece is circular, the inner ring of the separator is also circular, that is, a general classic separator is selected, and the size of the inner ring only needs to be able to put the workpiece into the inner ring of the separator Just; if the shape of the workpiece is oval, the inner ring of the separator is also oval, that is, the selected separator improved type 1; if the shape of the workpiece is polygonal, the inner ring of the separator is also polygonal, that is, the selected separator improved type 2 . If the shape of the workpiece is polygonal, the inner ring of the separator is also polygonal. In order to minimize the uneven grinding of the major axis and the minor axis and protect the corners of the workpiece from chipping, try to avoid astigmatism and edge collapse of the workpiece. If the phenomenon occurs, the inner ring of the separator is modified as follows in the improved type 2 of the separator, and each edge corner of the separator is chamfered with a radius of R, that is, the improved type 3 of the separator is selected.

The processing method of ring polishing machine has the following characteristics:

1) The workpiece moves with a compound trajectory, which has a homogenized polishing effect;

2) The pressure can be applied freely, which is convenient for surface shape correction;

3) The workpiece floats during the processing, without cementation and other clamping deformation, which can avoid heating damage to the workpiece during the loading process, and there is no deformation problem after the workpiece is lowered;

The speed is slow, and the thermal deformation of the workpiece is small.

Due to the above characteristics, ring throwing technology occupies a very important position in the manufacture of large-aperture, high-precision planar optical components.

The present invention has the following advantages:

1) Multiple filtration of asphalt will further improve the grade of mirror finish;

2) The improvement of the special-shaped workpiece separator solves the problems such as surface convexity and edge collapse when processing special-shaped mirrors.

3) The asphalt polishing disc is made by adding polytetrafluoroethylene powder, which enhances the elasticity and wear resistance of the polishing glue;

4) The weight metal plate uses flexible protection to reduce safety risks, the pressure distribution is more uniform, and the weight column is added to improve processing efficiency.

Description of drawings

Fig. 1 is the flow chart of processing method of large-diameter special-shaped plane mirror in the embodiment of the present invention;

Fig. 2 is a diagram of the relationship between the positions of the continuous annular polishing disc, the calibration disc and the workpiece in the embodiment of the present invention;

Fig. 3 is a continuous annular polishing separator (i.e. workpiece disc or ferrule) figure in the embodiment of the present invention;

Fig. 4 is the final inspection result of the plane three-mirror polishing of an oval 780×555mm thick 130mm fused silica light project in the embodiment of the present invention.

detailed description

The present invention will be further elaborated below in conjunction with the accompanying drawings and embodiments.

With reference to Fig. 1, a kind of large-diameter special-shaped plane processing method mainly comprises the following steps:

Step 1), cutting and forming the rough blank, forming and processing, and using a laser tracker or three-coordinates to detect the outer dimension and surface shape to achieve the designed outer dimension;

Step 2), Grinding: use traditional methods or CNC small tools (or robots) to process, abrasive particles are ground from coarse to fine, and use laser tracker or three-coordinate for surface shape detection;

Step 3), Rough polishing: Polishing (pre-stage) adopts traditional methods or CNC small tool (or robot) processing methods, using traditional methods or CNC small tools to process, polish and control the mirror surface shape to ensure the final surface shape accuracy of rough polishing Meet the requirements of interferometer for interference detection;

Step 4), ring polishing machine polishing: polishing (later stage), finishing adopts continuous polishing process method, including asphalt polishing disc preparation, polishing disc casting and initial molding, polishing disc grinding, calibration plate, separator, counterweight, etc. process factors;

Step 5), polishing and finishing: according to the quality of the mirror surface, the actual processing difficulty and the requirements of the construction period, it can be transferred to small numerical control tools such as magnetorheological processing or ion beam processing, and finally the ring polishing machine can be used for smooth polishing processing, using interference The instrument is used for repeated testing, and the quality of the mirror surface shape meets the requirements of the mirror surface design.

Wherein, the large-diameter special-shaped plane mirror refers to a maximum diagonal diameter of 200-2000 mm and a thickness of 5-300 mm.

Wherein, in the step 4) continuous polishing process: a separator is used. In order to ensure better surface shape accuracy, we designed and manufactured a separator whose outer diameter does not exceed two-fifths of the diameter of the rubber disc. The inner ring of the separator is similar to the shape of the workpiece, and the size is enlarged according to the overall shape of the workpiece (for example 2-35mm), add a protective rubber pad to the inner ring wall. Choose different separators according to the shape of the workpiece: if the shape of the workpiece is circular, the inner ring of the separator is also circular, that is, choose a general classic separator, the size of the inner ring only needs to be able to put the workpiece into the inner ring of the separator; If the shape of the workpiece is oval, the inner ring of the separator is also oval, that is, the improved type 1 separator is selected; if the shape of the workpiece is polygonal, the inner ring of the separator is also polygonal, that is, the improved type 2 separator is selected. If the shape of the workpiece is polygonal, the inner ring of the separator is also polygonal. In order to minimize the uneven grinding in the direction of the long axis and the short axis and protect the edge chipping, the inner ring of the separator is improved as follows, and each edge of the separator The corner is chamfered with a radius of R, that is, the improved type 3 separator is selected.

Wherein, described step 4) in the continuous polishing process method, the asphalt polishing disk is prepared:

According to the use environment and polishing requirements, the asphalt glue selected for preparation must have sufficient rigidity, and at the same time ensure proper fluidity, abrasiveness and aging resistance. For rubber discs with super large diameters, it is generally selected and added with a certain proportion of PTFE micropowder to consider enhancing the elasticity and wear resistance of the polishing rubber. Heat the prepared asphalt to fully melt and filter.

Wherein, in the step 4) continuous polishing process method: polishing disc casting and initial molding, grinding:

Heat the prepared asphalt to fully melt and filter. Surround the granite platform with edge protection (50mm over the platform), turn the machine, pour the glue slowly from the two symmetrical directions of the granite rotating platform, then use a natural gas flame to burn off the surface glue bubbles, and continue to keep the spindle rotating until it is fully cooled. In order to save time and ensure the flatness of the rubber disc, the rubber disc can be initially formed by mechanical turning, and grooves are made on the rubber disc, for example, the square groove of a 2.5-meter rubber disc: the general facet is 65mm×65mm, and the groove width is 4～ 6mm; then dig out the center part of the rubber disc to make a circle about a quarter of the diameter of the rubber disc. The thickness of the rubber plate is appropriate, generally 15-35mm. Before loading the workpiece, the asphalt polishing disc must be ground with a calibration disc.

Wherein, the calibration plate in the step 4) continuous polishing process: in continuous polishing, the surface shape of the polishing disc is achieved by continuous grinding of the calibration plate. There is a cyclic relationship of trimming-processing-change-re-dressing among the calibration plate, polishing disc and workpiece. The ratio of the caliber of the large-diameter calibration plate to the caliber of the polishing disc is generally 0.52 to 0.62.

Among them, other process factors in the step 4) continuous polishing process method: in the grinding or polishing process, it should also be done: 1) the spindle speed of the machine tool is suitable, generally 0.3 to 1.5 rpm; 2) the ambient temperature is 20 ℃ ~ 26 ℃ (higher in summer, lower in winter), humidity 45% to 85%; 3) During the polishing process, it is necessary to regularly brush the polishing disc to produce a new polishing surface; 4) Control the concentration of the polishing solution and give way.

Wherein, the counterweight in the step 4) continuous polishing process method: due to the complex shape of the special-shaped mirror, the counterweight is similar to the shape of the workpiece, and the size is reduced by an appropriate amount (such as 2-35mm) according to the overall shape of the workpiece. In order to achieve uniform grinding, the counterweight The basic purpose of the machine is to balance the two directions of the long and short axes and the uneven grinding of the chamfered surface. The counterweight can be made of a metal plate to evenly contact the back of the workpiece at multiple points. The weight metal plate uses flexible protection, and the sponge is bonded to the weight plate to reduce safety risks.

Specific examples are as follows:

A method for machining a large-caliber special-shaped plane, comprising the following steps:

Step 1), cutting and forming the rough blank into the designed external dimensions, using a laser tracker or three-coordinates to detect the external dimensions and surface shapes to achieve the designed external dimensions;

Step 2), Grinding: Use a small tool copper fine grinding disc with a diameter of 110mm and an oval shape of 780mm×555mm thick 130mm fused quartz light. A certain item of flat three-mirror surface contact plus auxiliary materials for diamond grinding, and the CNC robot removes the formed by milling and grinding of the flat mirror For the damaged layer, the corundum particles are ground from coarse to fine. Use emery green sand W40 to remove the damaged layer. The removal amount is 0.05-0.10mm. Use emery green sand W20 to remove the damaged layer. The removal amount is 0.03-0.06mm. Use emery green sand W14 removes the damaged layer, the removal amount is 0.02-0.04mm, and the API laser tracker is used for online detection or three-coordinate detection.

Step 3) Rough polishing: CNC robot CNC small tool grinding disc contacts the surface of the plane mirror and grinds the surface of the plane mirror with abrasive cerium oxide. Polishing is performed first, and a sample is used to control the surface shape of the mirror during the polishing process to ensure that the final surface shape of the rough polishing meets the requirements of Interferometer for interference detection;

Step 4), ring polishing machine polishing: rough polishing and finishing adopt continuous polishing process, including asphalt polishing disc preparation, polishing disc casting and initial molding, polishing disc grinding, calibration plate, separator, counterweight and other processes factor;

Separators used in continuous polishing process methods:

Separator principle: To ensure better surface accuracy. We designed and manufactured a separator with an outer diameter of Φ1006mm. The inner ring of the separator is elliptical, and the size is enlarged by 10mm as a whole according to the shape of the workpiece, and a protective rubber pad is added to the inner ring wall.

Preparation of asphalt polishing discs in continuous polishing process:

According to the use environment and polishing requirements, the asphalt glue selected for preparation must have sufficient rigidity, and at the same time ensure proper fluidity, abrasiveness and aging resistance. For rubber discs with large diameters, it is generally suitable to use self-made No. 1 asphalt rubber and add a certain proportion of polytetrafluoroethylene powder. The purpose of adding polytetrafluoroethylene powder is to consider enhancing the elasticity and wear resistance of the polishing rubber, which is ideal.

Polishing disc casting and initial molding:

Heat the prepared asphalt to fully melt and filter. Cover the edge of the granite platform with paper or other such as aluminum foil, turn the machine, you can use the spotlight to preheat the granite in advance, slowly pour the glue from the two symmetrical directions of the granite turning platform, and then use a natural gas flame to burn off the surface glue Continue to keep the main shaft rotating until it is fully cooled. In order to save time and ensure the flatness of the rubber plate, mechanical turning can be used to make the initial shape of the rubber plate. The thickness of the rubber plate is appropriate, about 30mm.

Grinding of the polishing disc in the continuous polishing process:

Before loading the workpiece, the asphalt rubber disc must be ground with a calibration disc. Open a square groove on the plastic plate, for example, the facet of a 2.5m plastic plate is generally 65mm×65mm, and the groove width is 4-6mm; The combined effect of this grooving to form uniform multiple small polished flats is very important.

Calibration plate in continuous polishing process method:

In continuous polishing, the surface shape of the polishing disc is achieved by the continuous grinding of the calibration plate. There is a cyclic relationship of trimming-processing-change-re-dressing among the calibration plate, polishing disc and workpiece. Experiments have proved that the feasible parameters of the diameter and weight of the large glass calibration plate are as follows: the ratio of the diameter of the calibration plate to the diameter of the polishing disc is generally 0.52-0.62, and the pressure applied between the calibration plate and the polishing disc is 2400-3400 Pa.

Counterweight in continuous polishing process:

Due to the complex shape of the special-shaped mirror, the counterweight is similar to the shape of the workpiece, and the size is reduced by an appropriate amount (for example, 10mm) according to the overall shape of the workpiece. In order to achieve uniform grinding, the basic purpose of the counterweight is to balance the two directions of the long and short axes and the unevenness of the chamfering surface For grinding, metal plates can be used as the counterweight, and multiple points evenly contact the back of the workpiece. The weight metal plate uses flexible protection, and the sponge is bonded to the weight plate to reduce safety risks. Two counterweight columns are added on the basis of the original counterweight plate, so that the counterweight can be added or subtracted according to the surface shape of the mirror surface, so as to improve the processing efficiency. The machining results showed that the counterweight worked well.

Other process factors in the continuous polishing process method:

During the grinding or polishing process, it should also be done:

1). The spindle speed of the machine tool is appropriate, generally 0.3 to 1.5 rpm;

2). The ambient temperature is 20°C-26°C (higher in summer and lower in winter), and the humidity is 45%-85%;

3). During the polishing process, the polishing disk needs to be brushed regularly to produce a new polishing surface.

4). Control the concentration of polishing liquid and the way of feeding;

Ring Polisher Polishing: Use The meter ring polishing machine can greatly reduce the low-frequency error, and further improve the surface shape accuracy and surface quality of the mirror surface. The sample process detection or zygo24-inch interferometer is used for splicing detection to monitor the surface shape accuracy of the mirror surface. The mirror surface shape after the rice ring polishing machine reaches a PV value of 0.46λ and an RMS value of 0.046λ;

Step 5), polishing finishing: According to the mirror surface shape quality, actual processing difficulty and construction period requirements, further improve the mirror surface precision and mirror surface quality, then use the CNC small tool combined with the ring polishing machine for finishing, and finally use the ring polishing machine Carry out smooth processing, so that the quality of the mirror surface meets the design requirements. Successfully completed the development of a flat three-mirror project with an oval shape of 780mm×555mm and a thickness of 130mm fused silica light weight. It passed the splicing detection of the zygo24-inch planar interferometer, and finally polished the surface shape: the edge is edged 5mm Reach PV value 0.263λ, RMS value 0.021λ.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the present invention shall fall within the scope of the present invention.

Claims (4)

1. a kind of heavy caliber special-shaped level processing method, it is characterised in that comprise the following steps：

Step 1), by blank excision forming, processing and forming, it is full to carry out appearance and size detection using laser tracker or three coordinates Appearance and size designed by foot；

Step 2), grinding：Using conventional method or numerical control small tool or processing of robots, abrasive grain grinding from coarse to fine, Surface testing is carried out using laser tracker or three coordinates；

Step 3), rough polishing：Early stage polishes generally use conventional method or numerical control small tool or processing of robots process, Throw bright and control mirror shape, ensure that rough polishing surface figure accuracy can meet that interferometer carries out interference detection；

Step 4), glass polishing machine polishing：

Later stage polishing is polished using glass polishing machine：It is continuous polishing process, including pitch lap is prepared, polishing disk casting With pre-profiling, the reconditioning of polishing disk, correcting plate, separator, counterweight technological factor；

Step 5), polishing refine：According to mirror shape quality, actual processing difficulty and construction period, numerical control unskilled labourer can be transferred to Tool processing, numerical control small tool include magnetorheological or ion beam, finally glass polishing machine can be used smoothly to be processed, using interferometer It is repeatedly detected, mirror shape quality reaches mirror design requirement.

A kind of 2. heavy caliber special-shaped level processing method according to claim 1, it is characterised in that the heavy caliber abnormity Level crossing refers to that diagonal bore is 200-2000mm, thickness 5-300mm.

3. a kind of heavy caliber special-shaped level processing method according to claim 1, it is characterised in that the step 4) is continuous In polishing process method：Used separator, to ensure to obtain preferable surface figure accuracy, separator is designed and produced, has been work Part disk or lasso, its general external diameter are no more than 2/5ths of lacquer disk(-sc) bore, and its inner ring is similar workpiece shapes, size Integrally expand according to workpiece shapes appropriate：4-35mm, in internal ring wall plus protection rubber cushion.

4. a kind of heavy caliber special-shaped level processing method according to claim 3, it is characterised in that selected according to workpiece shapes Select different separators：If workpiece shapes are circular, the inner ring of separator is also circular, that is, selects the classical separation of in general Device, as long as inner ring size can put workpiece into separator inner ring；If workpiece shapes are ellipses, the inner ring of separator And ellipse, the i.e. separator of selection improve 1 type；If workpiece shapes are polygons, the inner ring of separator is also polygon, I.e. the separator of selection improves 2 types；If workpiece shapes are polygons, the inner ring of separator is also polygon, in order to subtract as far as possible The grinding uneven with short-axis direction of small major axis and protection workpiece corner avoid chipping, avoid workpiece easily to produce astigmatism, side as far as possible Edge point produces the phenomenon of turned-down edge, and separator inner ring is done to be improved again, and it is R chamferings that each edge angle of separator is done into radius, that is, is selected Select separator and improve 3 types.