What are the mechanical processes in precision processing of ceramics?

At present, the most common application of ceramic precision processing technology is mechanical processing, such as grinding, grinding, polishing, etc. This chapter will comprehensively introduce the methods and corresponding theories in mechanical processing of structural ceramics.

The forms of grinding processing can be divided into surface grinding, internal cylindrical grinding, cylindrical grinding, and coreless grinding.

1. Grinding process and mechanism

Diamond grinding wheels are generally used for grinding. The reason why diamond grinding wheels remove material is because when the diamond abrasive grains cut the workpiece, the material in front of the cutting edge of the abrasive grains is squeezed. When the stress value exceeds the endurance limit of the ceramic material, the pressure is released and micro-forms are formed. .

On the other hand, when abrasive grains cut artificial parts, due to the effects of compressive stress and frictional heat, the material under the abrasive grains will produce localized flow to form a deformation layer. When the abrasive grains scratch, the deformation layer is decorroded from the workpiece to form chips due to the disappearance of stress.

In short, crushing chips are easily generated during rolling grinding, resulting in grain boundary fractures. Some ceramic surfaces will also be damaged by a mixture of plastic flow and crushing chips. The surface will have obvious strip-shaped wear marks, that is, it will be broken along the grain boundary. Type damage. After the surface grain layer is broken, it gradually falls off under the action of rolling. Then the new surface grains are broken again, rolled and then pierced off. After repeated grinding, the machining allowance of the material can be removed to achieve a ceramic surface that meets the quality.

2. Main factors of grinding processing

Process parameters: (1) Grinding wheel grinding speed (2) Workpiece speed (3) Grinding depth (4) Grinding ratio Diamond grinding wheel: (1) Metal bond diamond grinding wheel (2) Resin bond diamond grinding wheel (3) Ceramic bonded diamond grinding wheel

3. How to select grinding conditions

When selecting grinding conditions, the cutting depth of abrasive grains is one of the criteria. When rough grinding, the cutting depth of the abrasive is appropriately larger, but if the cutting depth of the abrasive is too large, the corresponding workpiece speed and the cutting depth of the abrasive tool will also be too large, and the rotational speed of the abrasive tool (grinding wheel) will inevitably decrease. This There is a risk of the workpiece collapsing. If the rotational speed of the grinding tool is too high, the grinding temperature will increase, the workpiece will undergo thermal cracking, and the grinding tool loss will increase.

In the ceramic grinding process, wet grinding is usually used, and it is better to use water-soluble substances as the grinding fluid. When the grinding fluid becomes sticky due to wear debris, it is still effective to use a large amount of water to precipitate the grinding debris. If the grinding debris in the grinding fluid is removed by filtration or other methods, it is very effective in reducing the wear of the grinding tool. In order to reduce the oxidation wear of diamond and pay attention to lubricity and other reasons, non-water-soluble grinding fluid is sometimes used.

4. Effect of grinding processing on ceramic materials

(1) Material strength (2) Surface phase transformation (3) Residual stress (4) Surface roughness


Ceramic grinding processing method

Ceramic grinding is a kind of machining that is more refined than grinding. It is a processing method that uses grinding tools and abrasives to remove an extremely thin layer of ceramics from the surface of the workpiece. In grinding processing, when the grinding parameters are properly selected, a flower-like texture of 1μm/m and a surface roughness of Ra<0.3μm can be achieved.

From the perspective of material removal mechanism, grinding processing is a processing method between brittle damage and elastic removal.

Grinding can be used to process flat surfaces, internal and external cylindrical surfaces, internal and external conical surfaces, four-convex spherical surfaces, threads and toothed surfaces. When grinding, add abrasive to the grinding tool (made of a material softer than the workpiece) and the surface of the workpiece to be ground. Under a certain pressure, the grinding tool and the workpiece make complex relative movements, and the abrasives in the abrasive will embed into the surface of the grinding tool. The surface of the workpiece that has been finely machined is cut in relative motion. The grinding process is accompanied by chemical effects. In addition, the movement trajectory is not repeated, the surface of the workpiece is processed evenly, and the uneven convex parts are cut off again and again, and the surface roughness is reduced. Decrease gradually.

According to the use of abrasives, grinding can be divided into three situations: wet grinding, dry grinding and semi-dry grinding. Grinding methods include external cylindrical grinding, internal cylindrical grinding and surface grinding. Cylindrical grinding is generally performed on the basis of fine grinding or fine turning, and there are two methods: manual grinding and mechanical grinding. Inner circle grinding needs to be done after fine grinding, usually by hand. Surface grinding is generally performed after fine grinding. Manual grinding is often used for single-piece small batch production, while mechanical grinding can be used for large-scale production. The grinding equipment is simple but a high accuracy and Ra can be obtained. The surface is very small; and because it is carried out at low speed and low pressure, the heat generation is small and the workpiece deterioration layer is thin, but it generally cannot improve the position accuracy of the machined surface and other surfaces.
Grinding abrasives and surface roughness


Polishing processing is similar to grinding processing. It is also an ultra-precision processing method that uses free abrasives to produce micro-removal effects on the surface materials being processed to achieve processing effects. In the ultra-precision processing and complete processing of ceramic materials, especially in the precision processing of ceramic balls used in ceramic bearings, polishing processing plays an irreplaceable role. The mirror processing method of optical glass, optical materials such as sapphire, semiconductor materials such as silicon wafers and GaAs substrates, and ceramic materials such as alumina and silicon nitride is also often processed by polishing.

There are several theories about the polishing mechanism: ① mechanical trace removal theory; ② plastic flow theory; ③ chemical action theory. The micro-removal theory can be explained by the micro-cutting action of the abrasive tip to remove surface irregularities. Polishing using diamond abrasive paste and cloth wheel polishing machine is based on this mechanism. The material removal rate of grinding and polishing is closely related to the toughness of the material being processed. The higher the toughness, the lower the processing efficiency.