The principles of cutting fluid selection must meet the requirements of cutting performance and performance, i.e. should have good lubrication, cooling, rust prevention and cleaning performance, to meet the process requirements, reduce tool loss, reduce surface roughness, reduce power consumption and improve production efficiency. At the same time, the stability of use should be considered. Therefore, the selection of cutting fluids should follow the following principles.

1、Cutting fluids should be free of irritating odours and do not contain additives harmful to the human body to ensure the safety of users.

2、The cutting fluid should meet the requirements of equipment lubrication and protection management, i.e. the cutting fluid should not corrode the metal parts of the machine tool, not damage the machine tool seals and paints, and not leave hard gelatinous deposits on the machine tool guides to ensure the safety and normal work of the equipment used.

3. The cutting fluid should meet the rust prevention requirements between work processes and not corrode the workpiece. When processing copper alloys, cutting fluids containing sulphur should not be used. When machining aluminium alloys, cutting fluids with a neutral pH value should be used.

4. The cutting fluid should have excellent lubricity and cleaning performance. Choose cutting fluids with high maximum non-card bite load value and small surface tension, and be evaluated by cutting fluid tests.

5, cutting fluid should have a long service life, which is particularly important for machining centres.

6、Cutting fluids should try to adapt to a variety of processing methods and a variety of workpiece materials.

7、Cutting fluids should be low pollution and have waste liquid disposal methods.

8, cutting fluid should be inexpensive and easy to prepare.

In summary, the user in the choice of cutting fluid, according to the specific processing situation of the enterprise, the first preliminary selection that the overall performance of 2 to 3 cutting fluids, after the actual trial, to determine the performance of the cutting fluid to meet the processing requirements, the price of the appropriate cutting fluid workpiece material performance is important to the choice of cutting fluid

　　Due to the poor machinability of stainless steel, the cooling, lubrication, penetration and cleaning performance of cutting fluids have higher requirements, commonly used cutting fluids are the following categories.

　　Sulphur oil: It is a cutting oil with sulphur as the extreme pressure additive. The cutting process can form a high melting point sulphide on the metal surface, and it is not easy to destroy at high temperature, has a good lubricating effect, and has a certain cooling effect, suitable for general turning, drilling, reaming and tapping. Sulphurised soybean oil is suitable for drilling, reaming and reaming processes.

　　The formula for direct sulphurised oil is: 98% mineral oil, 2% sulphur.

　　The formula for indirect vulcanised oil is: mineral oil 78% to 80%, vegetable oil or lard 18% to 20%, sulphur 1.7%.

　　Mineral oil such as motor oil and spindle oil: its lubricating properties are better, but its cooling and penetrating properties are poor and it is suitable for external round finishing.

　　Vegetable oil: such as vegetable oil, soybean oil, etc., its lubricating performance is better, suitable for turning threads and reaming, tapping and other processes.

　　Emulsions: have better cooling and cleaning properties. It also has a certain lubricating effect and can be used for rough turning of stainless steel.

　　During the cutting process, the cutting fluid nozzle should be aligned with the cutting area, or it is best to use high pressure cooling, spray cooling and other cooling methods.