Ultra-precision machining technology

At present, precision and ultra-precision machining accuracy ranges from micron to submicron, and even nano, and is widely used in automobiles, home appliances, IT electronic information high-tech fields, and military and civilian industries.At the same time, the development of precision and ultra-precision machining technology has also promoted the development of machinery, molds, hydraulics, electronics, semiconductor, optics, sensor and measurement technology, and metal processing industries.
Precision and ultra-precision machining-Concept and scope
Precision machining
Generally, according to the machining accuracy, machining can be divided into three stages: general machining, precision machining, and ultra-precision machining.At present, precision machining refers to processing technology with a machining accuracy of 1~0.1µm and a surface roughness of Ra0.1~0.01µm, but this boundary is constantly changing with the progress of processing technology. Today’s precision machining may be tomorrow’s general machining.
The problem to be solved by precision machining is the machining accuracy, including shape and position tolerance, dimensional accuracy and surface condition; the second is the processing efficiency. Some machining can achieve better machining accuracy, but it is difficult to achieve high processing efficiency.
Precision and ultra-precision machining-classification
1. Traditional precision machining methods include belt grinding, precision cutting, honing, precision grinding and polishing.
a.Abrasive belt grinding is the processing of workpieces with blended fabrics glued with abrasives as abrasive tools. It belongs to the category of grinding and processing of coated abrasives. It has the characteristics of high productivity, good surface quality, and wide range of uses.
b.Precision cutting, also known as diamond tool cutting (SPDT), uses high-precision machine tools and single crystal diamond tools for cutting and processing. It is mainly used for precision machining of soft metals such as copper and aluminum that are not suitable for grinding, such as magnetic drums for computers, magnetic disks, and metal mirrors for high-power lasers. The accuracy is 1~2 levels higher than that of general cutting.
c.Honing, a honing head composed of oilstone sand strips, reciprocates along the surface of the workpiece under a certain pressure, and the surface roughness after processing can reach Ra0.4~0.1µ;m, preferably up to Ra0.025µ;m, mainly used for processing cast iron and steel, not suitable for processing non-ferrous metals with low hardness and good toughness.
d.Precision grinding and polishing Through the abrasive and processing fluid between the workpiece and the tool, the workpiece and the grinding tool make mechanical friction with each other, so that the workpiece reaches the required size and accuracy of the processing method.Precision grinding and polishing can achieve accuracy and surface roughness that cannot be achieved by other processing methods for both metal and non-metal workpieces. The roughness of the ground surface Ra≤0.025µ;m The processing metamorphic layer is very small, the surface quality is high, and the precision grinding equipment is simple. It is mainly used for plane, cylindrical surface, gear tooth surface and seal parts with sealing requirements. It can also be used for the finishing of gauges, measuring blocks, fuel injectors, valve bodies and spool.
e.Polishing is a kind of microfabrication of the surface of a workpiece using mechanical, chemical, and electrochemical methods. It is mainly used to reduce the surface roughness of the workpiece. The commonly used methods are: manual or mechanical polishing, ultrasonic polishing, chemical polishing, electrochemical polishing and electrochemical mechanical composite processing.After manual or mechanical polishing, the surface roughness of the workpiece Ra≤0.05µ;m can be used for polishing planes, cylinders, curved surfaces and mold cavities.The machining accuracy of ultrasonic polishing is 0.01~0.02µ;m, and the surface roughness is Ra0.1µ;M.The surface roughness of chemical polishing is generally Ra≤0.2µ;M.Electrochemical polishing can be increased to Ra0.1~0.08µm.
2. Precision machining includes processing technologies such as microfabrication, ultra-microfabrication, and finishing. Microfabrication technology refers to the processing technology of manufacturing micro-size parts;
Ultra-microfabrication technology refers to the processing technology for manufacturing ultra-small size parts. They are proposed for the manufacturing requirements of integrated circuits. Due to the small size, its accuracy is expressed by the absolute value of the processed size, rather than by the ratio of the processed size to the size error.
Finishing generally refers to processing methods that reduce surface roughness and improve the mechanical properties of the surface layer. It does not focus on improving machining accuracy. Typical processing methods include honing, grinding, ultra-finishing and chip-free processing.In fact, these processing methods can not only improve the surface quality, but also improve the machining accuracy.Finishing is a new term proposed in recent years. It corresponds to finishing. It refers to a processing method that not only reduces the surface roughness and improves the mechanical properties of the surface layer, but also improves the machining accuracy (including size, shape, and position accuracy).
3. Ultra-precision machining is the process of micro-cutting materials on ultra-precision machine tools and equipment using the strictly constrained relative movement between parts and tools to obtain extremely high shape accuracy and surface finish.The current ultra-precision machining refers to the processing technology where the dimensional accuracy of the processed parts is higher than 0.1µm, the surface roughness Ra is less than 0.025µm, and the resolution and repeatability of the positioning accuracy of the machine tool used are higher than 0.01µm, also known as submicron-level processing technology, and it is developing towards nano-level processing technology.

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