In the process of metal cutting, in order to improve the cutting efficiency, improve the accuracy of the workpiece, reduce the surface roughness of the workpiece, extend the service life of the tool and achieve the best economic effect, it is necessary to reduce the cutting efficiency, improve the precision of the workpiece, reduce the surface roughness of the workpiece, extend the service life of the tool and achieve the best economic effect, It is necessary to reduce the friction between the tool and the workpiece, the tool and the chip, and take away the heat generated by the deformation of the material in the cutting area in time. To achieve these goals, on the one hand, the machining efficiency of metal cutting can be improved rapidly by developing high hardness and high temperature resistant tool materials and improving the geometry of tools, such as carbon steel, high-speed steel carbide and ceramics and other cutting tools and the use of transposing tools; On the other hand, the cutting efficiency can be improved obviously by using the cutting (grinding) cutting fluid with excellent performance, the surface roughness of the workpiece can be reduced, the service life of the tool can be prolonged, and the cutting fluid effect with good and economic benefits can be obtained as follows:
1) Rust prevention
During the cutting process, if the workpiece contacts with the corrosive medium caused by the decomposition or oxidation deterioration of water and cutting fluid, such as sulfur, sulfur dioxide, chloride ion, acid, hydrogen sulfide, alkali and other contacts, the parts contacting the machine tool and cutting fluid will also suffer corrosion. During the storage period after the workpiece is processed or during the process storage, If the cutting fluid does not have a certain rust resistance, the workpiece will be corroded by the water in the air and the corrosion medium, resulting in chemical corrosion and electrochemical corrosion, which will cause the workpiece to rust. Therefore, it is required that the cutting fluid must have a good anti rust performance, which is one of the most basic properties of cutting fluid. Titanium alloy cutting oil, stainless steel cutting oil, deep hole drilling cutting oil and stamping drawing oil generally have certain rust resistance. If the storage period between processes is not long, rust prevention additives can be added, because the anti-wear performance of cutting oil will be reduced by adding barium petroleum sulfonate and other rust prevention additives in cutting oil.
2) Cooling effect
The cooling effect is to take the cutting heat away from the solid (tool, workpiece and chip) by convection heat exchange and vaporization of cutting fluid, reduce the temperature of cutting area, reduce the deformation of workpiece, and maintain the hardness and size of the tool.
The cooling effect is also related to the foam. Because the air inside the foam is air, the thermal conductivity of the air is poor, and the cooling effect of the foam cutting fluid will be reduced. Therefore, the synthetic cutting fluid containing surfactant generally contains a small amount of emulsified silicone oil, which acts as a defoaming agent.
Recent research shows that the ion-based water-based cutting fluid can quickly eliminate the static charge caused by strong friction during cutting and grinding by ion reaction, and the combined workpiece does not produce high heat, and has a good cooling effect. These ion-based cutting fluids have been widely used as high-speed grinding and strong grinding coolant. The effect of oil additives is limited to the condition of low temperature. When the temperature exceeds 200 ℃, the adsorption layer of oil-based agent is damaged and the lubrication is lost. Therefore, cutting fluid containing oil additive is used in low speed and precision cutting. In high speed and heavy cutting, cutting fluid containing extreme pressure additive should be used. The so-called extreme pressure additive is a number of compounds containing sulfur, phosphorus and chlorine. These compounds react with metal at high temperature to produce iron sulfide, iron phosphide, iron chloride, etc. with low shear strength, thus reducing cutting resistance, reducing friction between tool and workpiece, tool and chip, making cutting process easy to carry out. Cutting fluid with extreme pressure additive can also inhibit the formation of chip forming and improve the surface roughness of workpiece.
3) Cleaning function
In the process of metal cutting, cutting, iron powder, grinding debris, oil pollution and other things are easy to adhere to the surface of the workpiece, tools and grinding wheels, which affect the cutting effect, and make the workpiece and machine tool dirty, so the cutting fluid must have a good cleaning function. For oil-based cutting fluid, the lower the viscosity, the stronger the cleaning ability, especially the cutting fluid containing light components such as diesel oil and kerosene, Permeability and cleaning performance is better. The water-based cutting fluid containing surfactant has better cleaning effect. On the one hand, it can absorb various particles and sludge, and form an adsorption film on the surface of the workpiece to prevent particles and sludge from adhering to the workpiece, tool and grinding wheel. On the other hand, it can penetrate into the interface of particle and oil pollution adhesion to separate particles and oil from the interface, and take away with cutting fluid, Thus, it can be used for cleaning. The cleaning effect of cutting fluid should also be shown in the good separation and settlement of chip, grinding, iron powder, oil pollution, etc. After the circulating cutting fluid is returned to the cooling tank, the chips, iron powder, grinding chips, particles and other substances can settle on the bottom oil pollution of the container and other substances suspended on the liquid surface, so as to ensure that the cutting fluid can still be kept clean after repeated use, and ensure the processing quality and prolong the service cycle.
4) Lubrication
In cutting, the friction between the tool and the cutting tool and the surface of the workpiece is produced. The cutting fluid is the lubricant to reduce the friction. In the aspect of cutting tools, because the tool has a back angle in the cutting process, the contact pressure between the tool and the processed material is lower than that of the front tool surface. Therefore, the friction lubrication state of the rear cutter surface is close to the boundary lubrication state. Generally, the material with strong adsorption, such as oil agent and extreme pressure agent with reduced shear strength, can effectively reduce friction. The lubrication of cutting fluid is superior to water-based cutting fluid, and the oil-based cutting fluid with oil-based and extreme pressure additives is better. Oil additives are usually long-chain organic compounds with extreme pressure groups, such as high fatty acids, alcohols, animal and vegetable oils. Oil based additive is a layer of lubricating film formed on the metal surface by polarity base adsorption, which reduces the friction between the tool and workpiece, tool and chip, thus reducing cutting resistance, prolonging tool life and reducing the surface roughness of workpiece.
In addition, in addition to the above lubrication effects, the recent research shows that cutting can directly penetrate into the tiny cracks on the metal surface, which changes the physical properties of the processed materials, thus reducing the cutting resistance and making the cutting process easy to carry out
