In the cutting of the most hard and brittle non-me

2022-08-22
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Machining of hard and brittle non-metallic materials and rocks (Part 2)

grinding and polishing is one of the main methods for machining hard and brittle non-metallic materials. The grinding process is to produce abrasive and cutting fluid between the workpiece and the lapping tool, and then brittle fracture between the workpiece and the lapping tool to remove the allowance by mechanical friction or mechanochemical action, so that the workpiece can achieve the required machining accuracy and surface quality. The grinding of hard and brittle materials is different from the grinding of metals. It is processed by the abrasive under the action of external force, making the surface of the workpiece produce tiny cracks, and gradually expanding and collapsing, separated from the parent material. However, with the reduction of processing removal unit, the processing mechanism is also different. At the beginning of coarse abrasive grinding, it is mainly brittle failure. When using fine abrasive (below W5), the grinding is mainly plastic failure. Generally, the processing method of using hard grinding tools is called grinding, and that of using soft materials as grinding tools is called polishing. In precision machining, grinding and polishing are difficult to distinguish. The hard and brittle materials commonly ground and polished are shown in the table

9. What are the process parameters for grinding and polishing hard and brittle materials

in grinding and polishing, the grinding pressure, relative speed and machining accuracy, the hardness of grinding tools, and the particle size of abrasives are closely related to the grinding surface quality. The grinding pressure is small, the relative speed is low, and the machining accuracy is high. The abrasive particle size is small, the material of the grinding tool is soft, and the surface roughness after machining is small. With high pressure, high relative speed, large particle size of abrasive and hard material, the machining efficiency is high. See table for process parameters of grinding and polishing

10. What are the commonly used abrasives for grinding and polishing

Abrasives commonly used for grinding and polishing can be divided into general abrasives and special-purpose abrasives. General Abrasives include: silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconia (ZrO2), cerium oxide (CeO2), iron oxide (if Fe2O3 is damaged), chromium oxide (Cr2O3), diamond (c). Abrasives for special purposes include magnesium oxide (MgO), thorium oxide (ThO2), zinc oxide (ZnO), titanium oxide (TiO2), manganese oxide (MnO2), calcium carbonate (CaCO3), etc

ultra precision grinder

11 What are the methods and characteristics of ultra precision grinding and polishing

generally, the smaller the unit removed by machining or the smaller the role of machinery, the higher the quality of the machined surface. If grinding can remove materials in atomic or molecular units, the surface roughness can reach the nanometer (nm) level, and the processed metamorphic layer is very small or not. The abrasive particle size of various ultra precision grinding and polishing is generally below several microns. For ultra precision machining of semiconductor materials, abrasive with particle size of 0.02 M is often used. Distilled water or ionic water is generally used to prevent the workpiece from being oxidized and impurities in the grinding fluid from causing scratches on the processing surface. Various ultra precision grinding methods and characteristics are as follows:

(1) ultra precision grinding and polishing: its mechanism is to remove materials mainly by the mechanical action of abrasives. Various fine abrasives and soft abrasives are used during grinding. The grinding tools are cast iron, glass, ceramics and soft metal, and soft grinding tools or asphalt are used for polishing. The grinding fluid is oil, kerosene and water solution, and filtered water or distilled water is used for polishing. Grinding methods include manual grinding and mechanical grinding. The main processing objects are all kinds of hard and brittle materials

(2) grinding and polishing in liquid: it is carried out by immersing in the working liquid containing abrasive. It is mainly based on the mechanical action of abrasive, coupled with the cooling of liquid and the dispersion of abrasive. The processed workpiece is floating and moves in liquid. Grinding fluid is filtered water or distilled water. The grinding tool adopts soft materials such as synthetic resin or tin. The main processing objects are silicon wafers and other electronic materials

(3) chemical grinding and polishing: it is to remove the products of chemical reaction or hydration reaction in the process of workpiece processing, with the purpose of improving the processing efficiency. Its principle is to remove the products of chemical reaction by mechanical action. Use fine abrasive, water solution or pure water, non-woven fabric or glass plate and other grinding tools. It is mainly used for processing silicon and sapphire substrates

(4) EEM processing: its processing principle is that the high-speed rotating resin ball generates a certain pressure and air flow on the workpiece, and a working fluid containing abrasive is added between them to make the resin ball impact or wipe the surface of the workpiece for processing. This processing method can process any shape of surface, and the quality is very high, but the efficiency is very low

(5) floating grinding: it uses the principle of dynamic pressure effect of sliding bearings to make the grinding tool into a shape that is easy to produce dynamic pressure effect. When the workpiece moves relative to the rotary table, due to the dynamic pressure effect, the workpiece floats out of contact, and then enters the abrasive and cutting fluid through the gap for processing. This method can obtain high surface quality

honing machine

12 What are the other methods of processing hard and brittle materials

(1) honing: honing is not only suitable for metal, but also for precision machining of hard and brittle non-metallic materials. The honing rod is made of Al2O3 or diamond abrasive, the particle size is generally W28, and kerosene is used as honing fluid. The honing bar and the machined surface of the workpiece move relatively under a certain pressure. The greater the pressure, the higher the machining efficiency, but the greater the roughness of the machined surface

(2) abrasive belt processing: abrasive belts for precision processing are mostly made of 25 ~ 75 m thick polyester film and coated with chromium oxide or iron oxide, aluminum oxide, silicon carbide and diamond powder with particle size of 0.3 ~ 30 m. There are banded, discoid, plate-shaped, cylindrical and special shapes. It mainly processes ceramic materials in electronic devices. In grinding, with the increase of speed, the grinding amount also increases, and the maximum speed can reach 40m/s. Water is generally used as grinding fluid, and the supply amount is about 3L/min. When grinding glass, the effect of using black silicon carbide is better than that of using green silicon carbide. When grinding hard materials with abrasive belt, diamond abrasive greatly reduces o, and the dispersion rate entering the material through these shortcomings is the best

(3) compound machining: it applies two or more machining methods with different machining principles to the machining process of the same surface. This method is called compound machining

① chemical mechanical processing. It uses mechanical action to activate the processing surface, so as to promote the chemical reaction. At the same time, the chemical action also promotes the deterioration or weakening of the processed surface, and makes the mechanical action easy to carry out, so as to achieve the purpose of processing. When various hard and brittle materials are processed by chemical machining, the key is to select the abrasive materials that produce solid state reaction and the liquid of chemical reaction. For example, using soft abrasives to process silicon, sapphire, etc. through solid-state reaction

② electrochemical machining. Hard and brittle non-metallic materials are generally non-conductive, but electrochemical machining can be carried out by properly adding conductive and electrolytic components to the processed materials. If tin is added to ceramics, the material will have electrolytic properties, and electrolytic grinding will be carried out

③ EDM. Some hard and brittle non-metallic materials, such as zrbi and Si3N4 tin, have conductivity, and SiC is a semiconductor, which can be processed by EDM. These materials can be ground by EDM combined with machining. For non-conductive hard and brittle materials, EDM in electrolyte should be used for machining. Such as diamond, ruby hole processing is the use of this principle

④ electrolytic EDM. For non-conductive hard and brittle materials, immerse them in the electrolyte to make the spark discharge between the metal electrode and the electrolyte. At this time, the materials placed near the electrode are processed

⑤ ultrasonic grinding. It combines ultrasonic and grinding to make the grinding wheel produce ultrasonic vibration, prevent the grinding wheel from blocking, reduce the grinding force, and improve the machining efficiency and surface quality

rock

13 What are the types of rocks

rocks have many excellent properties that cannot be compared with other materials. Such as good wear resistance, corrosion resistance, good accuracy retention, and its products have beautiful luster. After processing, stone can be made into precision flat plates and high-precision machine parts, such as the workbench and column of CMM. Stone can also be used as decorative materials for high-grade buildings to improve the aesthetic value of buildings

rocks can be divided into three categories according to their formation causes, namely magmatic rocks (also known as igneous rocks), sedimentary rocks and metamorphic rocks

(1) magmatic rock: under high temperature conditions, the use of tools for condensing iron from magma or lava flow is also the reason for the increase of iron content in molten aluminum. Rocks formed by crystallization are called magmatic rocks. Rocks solidified on the surface of magma eruption are called igneous rocks or extrusive rocks. Rocks whose magma solidifies in the deep crust are called intrusive rocks or plutonic rocks. Such as granite, diorite, gabbro, etc. The main minerals that make up magmatic rocks are quartz, potassium feldspar, pyroxene, amphibole, biotite, magnetite, pyrite, etc. Magmatic rocks have full crystal structure and semi crystal structure, and have high hardness and strength

(2) sedimentary rock: under surface conditions, rocks formed by the transformation of substances formed by weathering, biological action and some volcanism (such as transportation, sedimentation and fossilization) are called sedimentary rocks. It is characterized by bedding structure, and its hardness is lower than that of magmatic rock. The sedimentary rocks used for processing are mainly chemical rocks and clastic rocks. Chemical rocks include limestone, dolomite and anhydrite. Clastic rocks mainly include sandstone and breccia

(3) metamorphic rock: it is a rock formed by the change of the original rock mineral composition and structure due to the change of physical and chemical conditions. Metamorphic rocks mainly include schist and gneiss metamorphosed from granite and rhyolite, and marble metamorphosed from limestone and dolomite

stone processing industry, according to the basic characteristics of rocks, stones are divided into marble and granite. The so-called marble refers to metamorphic or sedimentary carbonate rocks and some silicate rocks containing a small amount of carbonate, such as marble, limestone, dolomite, serpentine, sandstone, quartzite and gypsum rock. All stones belonging to magmatic rock and metamorphic magmatic rock are collectively referred to as granite. It includes granite, syenite, diorite, gabbro, diabase, basalt and gneiss

rock

14 What are the basic physical properties of rocks

(1) relative density D: it is the ratio of the mass of the actual volume of rock to the mass of water of the same volume. The so-called actual volume of rock is the volume excluding pores

(2) unit weight: the unit weight of rock is the mass of rock per unit volume. The so-called unit volume is the total volume of rock including pores. The unit weight of rock is divided into dry unit weight and wet unit weight

(3) density: the density of rock is the mass of rock per unit volume

(4) porosity n: the porosity of rock refers to the ratio of the total volume of various fractures and pores of rock to the total volume of rock

(5) water absorption W: the water absorption of rock refers to the ratio of water absorption mass to dry mass of rock under atmospheric pressure

see table for physical properties of rock

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