Generally, according to the processing accuracy, machining can be divided into three stages: general processing, precision processing and ultra precision machining. At present, precision machining refers to the machining accuracy of 1-0.1?; m. The surface roughness is ra0.1-0.01?; M processing technology, but this boundary is with the progress of processing technology, today's precision processing may be the general processing tomorrow. The first is the precision of machining, including the tolerance of shape and position, the accuracy of dimension and the surface condition; Second, processing efficiency, some processing can achieve better processing accuracy, but it is difficult to achieve high processing efficiency. Precision machining includes micro cnc machining services, ultra micro machining, finishing and other processing technologies. The traditional precision machining methods include belt grinding, precision cutting, honing, precision grinding and polishing.
1. Belt grinding is a kind of grinding tool which is made of a mixed cloth with abrasive, which belongs to the category of grinding with coated abrasive, which has the characteristics of high productivity, good surface quality and wide application range.
2. Precision cutting, also known as diamond cutting (SPDT), is mainly used for the precision processing of soft metals which are not suitable for grinding copper and aluminum, such as magnetic drum, disk and high power laser, which is 1-2 higher than that of general cutting.
3. Honing, honing head composed of oilstone sand bar moves back and forth along the surface of workpiece under certain pressure. The surface roughness after machining can reach ra0.4-0.1?; m. It is better to reach Ra0.025?; m. It is mainly used for processing cast iron and steel, and it is not suitable for processing non-ferrous metals with small hardness and good toughness.
4. Precision grinding and polishing is a machining method which can achieve the required size and precision by means of the abrasive and processing fluid between the workpiece and tool, the workpiece and the grinding tool. Precision grinding and polishing can achieve the precision and surface roughness that other processing methods can not achieve for metal and non-metallic workpiece. The roughness of the ground surface RA is less than 0.025?; M processing metamorphic layer is very small, surface quality is high, precision grinding equipment is simple, mainly used for plane, cylindrical surface, gear tooth surface and spouse parts with sealing requirements, and also can be used for the finishing of gauges, measuring blocks, fuel injection nozzles, valve body and valve core.
5. Polishing is a kind of micro machining on the surface of workpiece by means of mechanical, chemical and electrochemical methods, which is mainly used to reduce the surface roughness of workpiece. The common methods include: manual or mechanical polishing, ultrasonic polishing, chemical polishing, electrochemical polishing and electrochemical mechanical composite processing. The surface roughness Ra of workpiece after manual or mechanical polishing is less than 0.05?; m. It can be used for polishing plane, cylinder, surface and mold cavity. The precision of ultrasonic polishing is 0.01-0.02?; m. Surface roughness ra0.1?; m。 The surface roughness of chemical polishing is generally RA ≤ 0.2?; m。 The electrochemical polishing can be increased to ra0.1-0.08? m。 Ultra precision machining is a process of cnc machining which uses the relative movement of parts and tools with strict constraints to cut the material in a micro way to obtain high shape precision and surface finish. The current ultra precision machining refers to the dimension precision of the processed parts is higher than 0.1 μ m. Surface roughness Ra less than 0.025 μ m. The resolution and repeatability of the positioning accuracy of the machine tool are higher than 0.01 μ M processing technology, also known as submicron processing technology, is developing to nano level processing technology.
Ultra precision machining includes micro machining, ultra micro processing, finishing, finishing and other processing technologies. Micro machining technology refers to the manufacturing technology of small size parts; Ultra micro machining technology refers to the manufacturing technology of ultra small size parts. They are proposed for the manufacturing requirements of integrated circuits. Because of the small size, the precision is expressed by the absolute value of the cut-off dimension, rather than the ratio of the processed size to the size error. Finishing generally refers to the processing method of reducing surface roughness and improving mechanical and mechanical properties of surface layer, which does not focus on improving cnc machining accuracy. The typical processing methods include honing, grinding, super finishing and chip free processing. In fact, these machining methods can not only improve the surface quality, but also improve the machining accuracy. Finishing is a new term put forward in recent years. It is corresponding to finishing. It refers to the processing method which not only reduces surface roughness, improves mechanical properties of surface layer, but also improves machining accuracy (including dimension, shape and position precision.