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Application of diamond tools in optical glass processing
Nov 15 , 2019

With the rapid development of the information industry, optical components are widely used in various electronic devices, and the precision and quality of their processing are becoming higher and higher. Traditional processing techniques and tools are difficult to meet their processing requirements, especially in diamond tools. Regardless of the increasingly specialized requirements of its structure and intrinsic quality, the pertinence requirements are getting stronger and stronger. Therefore, the transformation of the traditional diamond tool structure and the improvement of the internal quality in this field are becoming more and more important.


The diamond tools in this field mainly include milling grinding wheels for milling planes and spheres in roughing, edging wheels for edging, fine grinding and surface grinding in finishing, super-finished and polished sheets; Saw blades for materials, etc.


1. Main types of diamond tools for optical glass processing

Milling wheel

Milling of optical glass is the main method of roughing, which is divided into flat and spherical milling wheels. The diameter of the surface milling grinding wheel is generally greater than 100mm, while the diameter of the spherical milling wheel is generally less than 100mm. The grinding wheel granularity is generally 60#~180#, the concentration is generally 50%~100%, and the bonding agent is bronze.


Diamond edging wheel

The diamond edging wheel is mainly used for grinding the outer circle of optical parts. The geometry and dimensions are shown in Figure 2 and Table 2. There are two kinds of bonding agents, one is electroplated nickel-based bonding agent, and the other is sintered bronze bonding. Agent. Its particle size is generally 230/270 -M28/20, the concentration is 100%-200% for electroplating, and 50%-100% for bronze.


Fine grinding disc, super fine grinding sheet

Fine and super-finished sheets are used to finish the rough-processed optical parts to fully demonstrate their optical properties. Fine grinding and super finishing have both surface and spherical processing. The fine grinding sheet generally uses a bronze, iron-based, nickel-based or cobalt-based bonding agent, and the super-fine grinding generally uses a resin organic bonding agent. The size of the refining sheet is generally 325/400~10/5, and the concentration is 100%~35%, while the superfine refining sheet is generally in the range of 14/8~7/5, and the concentration is 50%~25%.


Polished sheet

Polishing sheets are mainly used to improve the surface finish of optical parts, ensure a certain aperture, and reduce the processing of surface deterioration layers. The main shape is like a refining sheet and a super-refining sheet, the binder is a resin, and the abrasive is cerium oxide and a small amount of diamond powder.


2. Reasonable selection of diamond products in optical glass processing

The reasonable choice of diamond products in optical glass processing mainly refers to the shape and size, bonding agent type, diamond particle size, diamond concentration and bonding agent of diamond tools according to the shape, grade, processing quality requirements and processing technology of the processed optical glass components. Select the hardness and so on. The general selection principle is:


(1) Select the shape and accuracy of the diamond tool according to the machining method and the accuracy of the machine tool.

(2) Select the particle size of the diamond tool according to the remaining amount of the processed original and the roughness of the surface.

(3) Select the concentration of diamond according to the size of the workpiece and the processing procedure and the coverage ratio of the diamond tool, especially for fine grinding and super finishing.


(4) Select the type of bonding agent according to the process of machining the workpiece and the grade of the workpiece, especially for fine grinding and super finishing. For fine grinding, bronze, nickel-based, cobalt-based and iron-based are generally selected; superfine grinding is selected as a resin binder. The finishing of soft glass is selected from bronze and nickel. Hard glass and more viscous glass are selected from iron and cobalt.


(5) Select the hardness and bond strength of the diamond tool according to the grade, hardness and brittleness of the machined optical parts. In general, the soft glass and the brittle small glass selection binder have lower hardness; the binder strength is smaller. The hardness of the hard and brittle glass is higher; the strength of the bonding agent is larger.


3. The latest manufacturing technology of diamond tools for optical glass

At present, the manufacturing technology of diamond tools in this field is getting higher and higher, mainly in the following aspects: raw materials, the binder powder is getting finer and finer, the general particle diameter is less than 40μm, and some can reach below 10μm, and both It is a pre-synthesized powder.


The particle size composition of diamond is becoming narrower and narrower, and the crystal form is getting better and better, especially in the micronized level. A small amount of elements and compounds are added to various binders to improve the efficiency of grinding. The distribution of diamond in the binder generally employs a granulation process or sufficient uniform mixing. The forming and sintering is carried out by a hot press sintering method having a protective atmosphere.


The mold adopts a high-precision and high-temperature resistant metal mold. The burned blank has almost no pores, and the strength of the diamond is hardly reduced during the sintering process. The manufactured blank is subjected to strict finishing to ensure its profile and tolerance. At the same time ensure its sharpness.


4. Problems and countermeasures of some diamond tools in the process of optical glass processing

Diamond tools often have various problems during use, which affect the yield and efficiency of processing, and have a great impact on production costs and product performance. This is mainly reflected in the manufacturing technology and intrinsic performance of diamond tools.


Milling process

The following major problems often occur during milling:

(1) roughness difference

(2) hitting glass and crashing

(3) Profile instability

(4) Low efficiency, deep scratches


These problems are mainly related to the particle size, concentricity, concentration of the grinding wheel, the self-sharpness of the bonding agent and the life and durability of the grinding wheel. Solving these problems is analyzed from the manufacturing technology of the grinding wheel, mainly adjusting the strength and diamond concentration of the bonding agent. And the particle size, and the concentricity of the grinding wheel must be guaranteed. Mainly to improve the holding strength of the diamond and reduce the grinding hardness of the bonding agent.



Fine grinding and super finishing and polishing process

Fine grinding, super-finishing and polishing processes are the most critical processes for optical glass processing, and are the most prone to quality problems. The diamond tools in this process are also the most difficult to make.


The problems that are easy to occur in this process are as follows:

(1) The workpiece is prone to pitting

(2) Aperture instability and irregular aperture

(3) poor surface roughness

(4) The workpiece is broken or collapsed

(5) Regular scratches or irregular scratches

(6) The grinding disc is easy to passivate

(7) Low cutting efficiency


Most of these problems are related to the quality of diamond tools and should be improved from the following aspects:

(1) Select a suitable diamond concentration, which is generally higher than the diamond concentration.

(2) Improve the self-sharpness of the bonding agent, mainly to reduce the grinding hardness and uniformity, and to reduce the segregation of low-melt.

(3) Reduce the coverage ratio of the diamond sheet, reduce the grinding surface area ofthe diamond pellet, or increase the chip space.

(4) Reducing the dispersion of the diamond particle size and the irregularity of the shape. Never allow large particles, and do not allow more fine particles.

(5) The quasi-nanoscale trace elements are added to the binder to change the properties of the binder.

(6) Add a small amount of fine particle abrasive to the grinding fluid.

(7) Improve the water resistance and temperature resistance of the resin and improve its thermal conductivity.

(8) Lowering the pores in the pellet and reducing the crystal size of the binder.

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