When the machining precision of ultra precision parts is nanometer, or even atomic unit (atomic lattice distance is 0.1 ~ 0.2 nanometer), the machining method of ultra precision parts can not adapt to it. It needs to use the method of special precision parts machining, that is, the application of chemical energy, electrochemical energy, thermal energy or electric energy, to make these energies exceed the binding energy between atoms, so as to remove the surface defects In order to achieve the goal of ultra precision machining, some atoms are attached, combined or lattice deformed. This kind of processing includes mechanical chemical polishing, ion sputtering and ion implantation, electron beam exposure, laser beam processing, metal evaporation and molecular beam epitaxy.
The characteristic of these ultra precision parts machining methods is that the amount of material removed or added to the surface layer can be controlled very finely. However, to obtain the machining accuracy of ultra precision parts, it still depends on precision machining equipment and precise control system, and uses ultra precision mask as the intermediary. For example, in VLSI plate making, electron beam is used to expose the photoresist (see lithography) on the mask to make the atoms of the photoresist polymerize (or decompose) directly under electron impact, and then the polymerized or unpolymerized parts are dissolved by the developer to make the mask. Electron beam exposure plate making requires ultra precision processing equipment with positioning accuracy of ± 0.01 micron.
General principles for drawing up process route of precision parts
There are two steps in the process planning of precision parts. First of all, draw up the process route of parts processing, and then determine the process size of each process, the equipment and process equipment used, as well as the cutting specification, man hour quota, etc. These two steps are interrelated and should be comprehensively analyzed.
The process route of precision parts processing is to make the overall layout of the process. The main task is to select the processing method of each surface, determine the machining sequence of each surface, and the number of processes in the whole process.
General principles of process planning
- Machining datum first
In the machining process of parts, the surface as the positioning datum should be machined first, so as to provide the precise datum for the subsequent process as soon as possible. It is called “benchmark first”.
- Division of processing stages
Machining quality requirements of the surface, are divided into processing stages, generally can be divided into rough machining, semi finishing and finishing three stages. The main purpose is to ensure the processing quality, to facilitate the rational use of equipment, to facilitate the arrangement of heat treatment procedures, and to facilitate the detection of blank defects.
- Face before hole
For parts such as box, bracket and connecting rod, the plane should be machined first and then the hole should be machined. In this way, the hole can be machined by plane positioning, the position accuracy of the plane and the hole can be ensured, and the machining of the hole on the plane is convenient.
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