In the development process of cutting fluid technology, we can see two characteristics: firstly, the number of cutting fluid products is increasing, the types are becoming more complete, and the functions are becoming increasingly refined. There are corresponding cutting fluids corresponding to different machining methods. Secondly, the technology of cutting fluids is becoming more and more sophisticated, thus continuously improving machining efficiency.
In addition, with the rapid development of modern manufacturing and increasing attention to environmental protection, cutting fluid technology is also in a cycle of improvement and renewal, and new cutting processing technologies are constantly emerging.
The Development Status of Cutting Fluid Technology
Faced with the increasingly mature development of the cutting fluid market and the diversification of cutting fluid products, the International Organization for Standardization and some industrialized countries have formulated relevant classification standards for cutting fluids. The American Materials Association has established the classification standard for metal working fluids and related materials ASTM D2881-03, and the Japanese Standards Association also established a new cutting fluid standard JIS K2241 in 2000.
In 1989, China formulated the national standard GB/T7631.5-1989 "Classification of Lubricants and Related Products (L-Class) - Part 5: Group M (Metal Processing)", which divided metal processing lubricants into two major categories, namely the processing type that emphasizes lubrication and the processing type that emphasizes cooling. It is worth mentioning that, similar to the standards established by the American Materials Association, these classification standards in China include lubricants used in metal forming processes such as forging, stamping, drawing, and rolling, rather than the types of lubricants discussed in this article for removal of machining (i.e. cutting), so they will not be discussed in detail.
Although various classification standards vary, they are roughly divided into two categories based on the composition and state of cutting fluids: water-based and oil-based.
Water-based cutting fluids need to be diluted with water before use, and can be divided into emulsified cutting fluids, microemulsified cutting fluids, and synthetic cutting fluids based on their diluted state. The original emulsion of emulsified cutting fluid generally does not contain water, and the cutting fluid prepared with water is in an emulsion shape; The synthetic cutting fluid is generally oil-free and can be miscible with water. The prepared cutting fluid is mostly transparent; The oil content (i.e. the content of oily additives) in the microemulsion cutting fluid is relatively small, while the content of surfactants and inhibitors is relatively high. After being prepared with water, it appears as a semi transparent microemulsion with an appearance intermediate between the first two.
Oil based cutting fluid (also called cutting fluid) is generally used directly, and its basic component is base oil. According to different processing needs, various additives with different properties can form different kinds of cutting fluid. According to the difference between base oil and additives, oil-based cutting fluids can be roughly divided into pure mineral oil, pure synthetic oil, active extreme pressure cutting fluid, inactive extreme pressure cutting fluid and antifriction cutting fluid.
Cutting fluid technology
As mentioned above, the cutting fluid generally takes base oil or oil-based additives as the carrier. By adding a variety of additives with different properties and functions to the base oil or oil-based additives and mixing them, the original liquid of cutting fluid or water-based cutting fluid is formed. Therefore, additives are the core element in metal cutting fluid technology, and excellent additive formulations have become a necessary condition for enterprises to improve their brand market competitiveness.
The main functions of metal cutting fluid in mechanical removal processing are cooling, lubrication, cleaning, and prevention. Due to the convection and gasification of liquids, the temperature of the tool and workpiece surface can be reduced, thereby preventing burns and deformation of the workpiece surface.
At the same time, the cutting fluid cleans and removes the debris generated during cutting, avoiding it from being mixed between the workpiece and the tool for secondary cutting, which may affect the surface quality of the workpiece. In addition to water-soluble synthetic cutting fluids, other oil-based compounds (from base oil or oil-based additives) in the cutting fluids adsorb onto the surface of the workpiece through their polar groups and form an oil film, which reduces friction during the cutting process.
In cutting fluids containing extreme pressure additives, compounds composed of elements such as halogen, sulfur, and phosphorus react instantly with the metal on the surface of the workpiece under high temperature and pressure, forming a material layer with low shear resistance. This reduces friction while also preventing adhesion on the metal surface.
In addition, antioxidant (to prevent cutting fluid from being oxidized under high temperature and pressure), anti gasification agent (to prevent the cutting fluid from volatilizing and producing atomized liquid) and defoamer (to prevent the cutting fluid from producing foam during spraying and causing dry grinding) shall be added to the cutting fluid.
In water-based cutting fluids, there are also some special additives, such as inhibitors (to prevent metal corrosion), surfactants (to reduce the surface tension of the oil layer and change the interface state of the system), anti-corrosion and bactericidal agents (to prevent the growth of microorganisms from causing the cutting fluid to deteriorate), stabilizers (to protect the emulsified state), etc.
It is worth noting that when these additives are mixed into the cutting fluid to form the finished product, it is not only necessary to ensure that these substances do not undergo chemical reactions with each other, but also to ensure that the cutting fluid's performance in the workpiece processing remains stable and does not undergo unnecessary and irreversible chemical changes with the processed metal.
The Application of Cutting Fluids in Metal Processing
As mentioned earlier, different cutting fluids are applied to different cutting methods. Therefore, in the actual operation of cutting fluid, it is necessary to choose a suitable cutting fluid based on one's own situation.
Firstly, the selection of water-based cutting fluids and oil-based cutting fluids needs to be considered. Generally speaking, oil-based cutting fluid has higher price and superior comprehensive performance. For more expensive machine tools or if the workpiece is required to obtain better surface quality and greatly extend the service life of the tool, it is recommended to use cutting fluid; If machining efficiency and cost are the main reference factors, water-based cutting fluid can be selected.
Secondly, it is necessary to refer to the characteristics of the machine tool itself. Usually, machine tool manufacturers recommend some brands of cutting fluids for their own equipment because they consider the usage of cutting fluids when designing machine tools. For example, some open machine tools cannot use oil-based cutting fluid to avoid the dissipation of cutting fluid due to a large amount of volatilization.
Thirdly, due to the different materials of cutting tools and workpieces, their high temperature resistance, machinability index, hardness, etc. also vary. Therefore, different cutting fluids should be selected separately. For example, diamond cutting tools have a very high hardness, and in order to achieve good cooling effect, water-based cutting fluids are generally used; For machining workpieces with lower hardness, such as gears, it is necessary to use cutting fluids with higher viscosity to prevent surface scratches.
Fourthly, the specific processing method of metal cutting also requires the corresponding cutting fluid to cooperate with it. In contemporary mechanical processing, there are various cutting methods, such as turning, milling, drilling, broaching, grinding, etc. In terms of precision machining and heavy cutting, the operating method undoubtedly puts higher requirements on the cutting fluid.