The outer diameter of the screw is easy to be roughly ground flat, so one of the most commonly used methods for refurbishing screws is the fine grinding process. Fine grinding is also known as fine grinding. It is an important process between the two major processes of rough grinding and polishing. The purpose of fine grinding is to ensure that the workpiece achieves the required surface shape accuracy, dimensional accuracy and surface roughness before polishing. Therefore, the quality of fine grinding has a very significant impact on polishing. The methods of fine grinding are divided into…
The outer diameter of the screw is easy to be roughly ground flat, so one of the most commonly used methods for refurbishing screws is the fine grinding process. Fine grinding is also known as fine grinding. It is an important process between the two major processes of rough grinding and polishing. The purpose of fine grinding is to ensure that the workpiece achieves the required surface shape accuracy, dimensional accuracy and surface roughness before polishing. Therefore, the quality of fine grinding has a very significant impact on polishing. The methods of fine grinding are divided into fine grinding with abrasive grains and fine grinding with diamond. The former is called classical fine grinding, also known as free grinding. The latter is called high-speed fine grinding.
Classification of fine grinding methods
Fine grinding can generally be divided into granular abrasive grinding method and fixed abrasive grinding method. The latter can be further divided into: forming surface shape tools and mold forming methods. Fine grinding with abrasive grains, also known as the classical method, involves gradually grinding glass with a metal forming mold (usually brass) and adding emery in the middle. Each time the abrasive particle size is changed, a ball mill with a different curvature radius must be replaced. For processing convex lenses, the abrasive particle size becomes increasingly fine, and accordingly, the curvature radius of the earth mode will also become smaller and smaller. The fixed abrasive fine grinding method is also known as high-speed fine grinding of diamond or micro-powder fine grinding. The so-called high-speed fine grinding of shot plates by forming method refers to the process of gluing small round plates made of bronze substrate containing diamond particles in a certain arrangement into spherical or planar shapes. The most commonly used method is to perform milling and grinding processing on glass. High-speed fine grinding by Fan Cheng method is exactly the same as spherical milling grinding. The only difference is that the diamond particle size of the grinding wheel is a little finer.
Technical requirements for fine grinding
I. Requirements for geometric surface shape accuracy
The geometric surface requirements for optical finishing are generally very high, often at the micrometer level of precision. To achieve such high precision, it can only be gradually improved through the fine grinding process, thus preparing for the final polishing process. In classical polishing, the surface geometry after fine grinding is 4 to 8 Newtonian interference rings worse than that of the polished part, approximately 2 microns. In modern high-speed polishing, only two Newtonian interference circles can be differed, approximately 0.5 microns. It should be noted here that in actual production, the surface shape after fine grinding should have a low aperture. At this time, for convex lenses, the radius of curvature should be larger, while for concave lenses, the opposite is true, and the radius of curvature should be smaller.
II. Surface roughness requirements
The surface roughness of the optical glass after rough grinding is relatively large, that is, the degree of surface concavity and convexity is very serious. The surface left after grinding with corundum in the processing of granular abrasives often has a glass surface damage layer of about 30 microns and a surface roughness RZ of less than 6 microns. The surface of the fixed abrasive processing is often processed by diamond grinding wheels, with a surface damage layer of about 50 microns and a surface roughness RZ of less than 0.9 microns.
One of the purposes of fine grinding is to reduce the degree of concavity and convexity on the surface of optical glass, so that it can be polished and removed. Under the current circumstances, it is believed that after processing with corundum using loose abrasive materials, the damage layer is below 12 microns and the roughness is below 0.4 microns. When processing fixed abrasives, the damage layer after processing with W10 diamond shot is less than 8 microns, and the surface roughness Rz is less than 0.35 microns.