Application of diamond tools in optical glass processing

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

Diamond tools in this field mainly include milling and grinding wheels for milling planes and spherical surfaces in rough machining, edging wheels for edging, fine grinding discs and surface grinding discs, superfinishing discs and polishing discs in finishing machining; in addition, there are the following Saw blades for materials, etc.

1. Main types of diamond tools for optical glass processing

Milling grinding wheel

The milling and grinding of optical glass is the main method of rough machining, which is divided into plane and spherical grinding wheels. The diameter of the grinding wheel for plane milling is generally greater than 100mm, while the diameter of the grinding wheel for spherical milling is generally less than 100mm. The particle size of the grinding wheel is generally 60#～180#, the concentration is generally 50%～100%, and the binder is bronze.

Diamond edging wheel

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

Fine grinding discs, super fine grinding discs

Fine-grinding discs and super-finishing discs are used to finish rough-machined optical parts, so that they can fully demonstrate their optical properties when used. Fine grinding and super fine grinding have both flat and spherical processing. Bronze, iron-based, nickel-based or cobalt-based binders are generally used for fine grinding, while resin organic binders are generally used for ultra-fine grinding. The particle size of the finely ground sheet is generally in the range of 325/400 to 10/5, and the concentration is 100% to 35%, while the particle size of the superfine grinding sheet is generally in the range of 14/8 to 7/5, and the concentration is 50% to 25%.

polishing 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 fine grinding disc and a super fine grinding disc, the binder is resin, the abrasive is cerium oxide and a small amount of diamond powder.

 

2. Reasonable selection of diamond products in optical glass processing

The reasonable selection of diamond products in optical glass processing mainly refers to the shape, size, bond type, diamond particle size, diamond concentration, and bond Softness and hardness etc. to choose. The general selection principles are:

(1) Select the shape, size and precision of the diamond tool according to the processing method and the precision of the machine tool.

(2) Select the particle size of the diamond tool according to the allowance of the processing original and the roughness of the surface.

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

(4) Select the type of bonding agent according to the process of processing the workpiece and the grade of the workpiece, especially for fine grinding and super fine grinding. Bronze, nickel-based, cobalt-based and iron-based are generally selected for fine grinding; resin binders are selected for ultra-fine grinding. Bronze and nickel bases are selected for fine grinding of soft glass. For hard glass and viscous glass, iron-based and cobalt-based are selected.

(5) Select the softness and hardness of the diamond tool and the strength of the bond according to the grade, hardness and brittleness of the processed optical parts. In general, soft glass and glass with less brittleness choose lower hardness of the binder; the strength of the binder is lower. For hard and brittle glass, the hardness is higher; the bonding agent is stronger.

 

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: in terms of raw materials, the powder of the binder is getting finer and finer, generally the particle diameter is less than 40 μm, and some can reach below 10 μm, and all It is a pre-synthesized powder.

The particle size composition range of diamond is getting narrower, and the crystal shape is getting better and better, especially at the micropowder level, it tends to be almost equal bulk. Trace elements and compounds are added to various binders to improve their grinding efficiency. The distribution of diamond in the binder generally adopts granulation process or sufficient uniform mixing. Forming sintering adopts hot pressing sintering method with protective atmosphere.

The mold adopts high-precision and high-temperature-resistant metal molds. The fired blank has almost no pores, and the strength of the diamond is almost not reduced during the sintering process. The blanks produced must undergo strict finishing to ensure its shape and tolerance. At the same time to ensure its grinding sharpness.

 

4. Problems and countermeasures that some diamond tools are prone to occur in the process of optical glass processing

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

milling process

The following main problems often occur during milling and grinding:

(1) Poor roughness

(2) Glass breaking and chipping

(3) Unstable surface

(4) Low efficiency and deep scratches

 

These problems are mainly related to the particle size, concentricity, concentration, self-sharpening of the bond, and the life and durability of the grinding wheel. To solve these problems, analyze the manufacturing technology of the grinding wheel, and mainly adjust the strength of the bond and the concentration of diamond. and particle size, while the concentricity of the grinding wheel must be ensured. It is mainly to improve the holding strength of diamond and reduce the grinding hardness of the bond.

 

Fine grinding and super fine grinding and polishing process

Fine grinding, ultra-fine grinding and polishing are the most critical processes in optical glass processing, and they are also the processes most prone to quality problems. Diamond tools in this process are also the most difficult to manufacture, and the problems that are prone to occur in this process are mainly manifested as follows:

(1) The workpiece is prone to pitting

(2) The aperture is unstable and the aperture is irregular

(3) Poor surface roughness

(4) Broken edge or chipping of the workpiece

(5) Regular scratches or irregular scratches

(6) The grinding disc is easy to passivate

(7) Low cutting efficiency

 

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

(1) Select the appropriate diamond concentration, generally the diamond concentration is too high.

(2) Improve the self-sharpening of the binder, mainly to reduce its grinding hardness and uniformity, and reduce the segregation of low-melt materials.

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

(4) Reduce the dispersion of diamond particle size and the irregularity of shape. Large particles are never allowed, and at the same time, too many fine particles are not allowed.

(5) Add quasi-nanometer trace elements to the binder to change the properties of the binder.

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

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

(8) Reduce the pores in the pellets and reduce the crystal size of the binder.