Precision machining

Overview of Ultra Precision Machining Technology   

At present, ultra precision machining is aimed at achieving high-precision machining that cannot be achieved by existing ordinary precision machining methods. In terms of quantity, it involves machining sub micron or even nanometer sized shapes and sizes, and obtaining nanoscale surface roughness. However, the exact accuracy value that can be considered as ultra precision machining depends on factors such as part size, complexity, and susceptibility to deformation.   

Ultra precision machining mainly includes ultra precision cutting (turning, milling), ultra precision grinding, ultra precision grinding (mechanical grinding, mechanochemical grinding, polishing, non-contact floating grinding, elastic emission machining, etc.), and ultra precision special machining (electron beam, ion beam, and laser beam machining, etc.). All of the above methods can achieve dimensional accuracy, shape accuracy, and surface quality that ordinary precision machining cannot achieve. Each ultra precision machining method is selected based on the requirements of different parts.  

1. Ultra precision cutting processing  

The characteristic of ultra precision cutting is the use of diamond tools. Diamond cutting tools have a low affinity with non-ferrous metals, and their hardness, wear resistance, and thermal conductivity are excellent. They can also be sharpened very sharply (the arc radius of the cutting edge can be less than ρ zero point zero one μ m. General practical application ρ 0，05 μ m) Can process better than Ra0.01 μ The surface roughness of m. In addition, ultra precision machining also uses high-precision basic components (such as air bearings, air floating guides, etc.), high-precision positioning detection components (such as gratings, laser detection systems, etc.), and high-resolution micro feed mechanisms. The machine tool itself adopts measures such as constant temperature, vibration prevention, and isolation, as well as devices to prevent contamination of the workpiece. The machine tool must be installed in a clean room. The material used for ultra precision cutting must be uniform in texture and free from defects. In this case, processing oxygen free copper can achieve a surface roughness of Ba0.005 μ m. Processing φ 800mm aspherical lens with a shape accuracy of up to 0.2/ μ m。 Ultra precision machining technology is widely used in fields such as aerospace, optics, and civil use (see Table 1) and is developing towards higher precision     

2. Ultra precision grinding   

Ultra precision grinding technology has been developed on the basis of general precision grinding. Ultra precision grinding not only provides mirror level surface roughness, but also ensures accurate geometric shapes and dimensions. To this end, in addition to considering various process factors, it is also necessary to have high-precision, high stiffness, and high damping reference components, eliminate the impact of various dynamic errors, and adopt high-precision detection and compensation methods.   

At present, the processing objects of ultra precision grinding are mainly hard and brittle materials such as glass and ceramics. The goal of grinding processing is to achieve a smooth surface of 3-5 nm, which means that the required surface roughness can be achieved through grinding without polishing. As a nanoscale grinding process, machine tools are required to have high precision and stiffness, and brittle materials can be ductile ground. Nano grinding technology is an important and effective machining technology for gas turbine engines, especially for materials that require high fatigue strength, such as ceramic materials used in jet engine turbines of aircraft.   

In addition, the dressing technology of grinding wheels is also crucial. Although grinding is more effective than grinding in removing.

Material, but it is difficult to obtain a mirror surface when grinding glass or ceramics, mainly because the surface of the grinding wheel is easily blocked by chips when the particle size is too fine. The electrolytic online dressing (ELID) cast iron fiber binder (CIFB) grinding wheel technology invented by Dr. Ohmori, a scholar at the Japanese Institute of Chemistry, can effectively solve this problem.    

The current ultra precision grinding technology can process 0.0 1 μ M Roundness, O.1 μ M dimensional accuracy and Ra0.005 μ Cylindrical parts with a roughness of m can be machined to 0.03 by plane ultra precision grinding μ A flat surface of m/100mm.   
 

3. Ultra precision grinding   

Ultra precision grinding includes machining methods such as mechanical grinding, chemical mechanical grinding, floating grinding, elastic emission machining, and magnetic grinding. The spherical surface produced by ultra precision grinding has a non sphericity of 0.025ttm and a surface roughness of RaO.003 μ m。 The use of elastic emission processing can produce a mirror surface without any deterioration layer, with a roughness of up to 5A. The highest precision ultra precision grinding can produce a flatness of λ／ 200 parts. The key conditions for ultra precision grinding are almost vibration free grinding motion, precise temperature control, clean environment, and a small and uniform grinding agent. In addition, high-precision detection methods are also indispensable.