Introduction
With the development of technology, cutting fluids of various types have been developed in recent decades to improve the efficiency of process machining. According to the manufacturing industry, water-soluble cutting fluids are one of the most important cutting fluids among all types of cutting fluids. The performance of the cutting fluid is mostly associated with the molecule composition and raw material selection. Water-soluble cutting fluid is a fluid that uses water as a base solvent and is made up of some organic additives and specific inorganic additives in order to improve its effectiveness. This article is aimed to define the performance of water-soluble cutting fluid and the criteria of raw material selection.
composition of water-soluble cutting fluid
Water-soluble cutting fluid is the most used type of cutting fluid. It is a complex mixture of natural substances and synthetic substances, which includes synthetic oils, fatty acids, surfactants, inorganic salts and combinations of these. The composition of the water-soluble cutting fluid comprises of 20-30% of synthetic oil, 4-6% of fatty acid, 2-4% of surfactants, 3-4% of inorganic salts, and other components such as defoamers, biocides and corrosion inhibitors.
Synthetic oils are synthetic hydrocarbons or esters. It includes polyalkylene glycol, polyol fatty acid esters, polyglycerol fatty acid esters and so on. Its main role is to decrease the frictional resistance between the tool and the chip by lubricating their surfaces. Moreover, synthetic oils have excellent antifoaming qualities and oxidation stability.
Fatty acids, such as oleic acid, linoleic acid and palmitic acid, are used to reduce the adhesion force between the tool and the chip. They have the functions of detergency, anti-wear and anti-corrosion. Furthermore, they can prevent chips from welding onto the cutting tool.
Surfactants such as anionic surfactants, cationic surfactants and nonionic surfactants are used to reduce the surface tension of the cutting fluid. They form ions and micelles in solution, which can modify the surface of the cutting area.
Inorganic salts are mostly composed of borate salts, phosphate salts, chlorides, sulfates, carbonates and nitrates. Their function is to give the water–soluble cutting liquid a greater water miscibility and surface active properties, as well as offering corrosion protection and cooling.
Performance of water-soluble cutting fluid
Cooling
The primary role of a cutting fluid is to reduce the constant tool surface temperatures that result from friction force between the cutting tool and the workpiece by increasing the surface wetting during the cutting cycle. The cutting fluid cools down the tool and the workpiece, reducing their temperatures to below their melting points, preventing the deposits on the tool face.
Lubrication
The cutting fluid also acts as a lubricant to reduce the shearing force during cutting, thereby reducing the adhesion force between the tool and the chip thus reducing the friction between them. This significantly reduces the energy required to machine, therefore improving the tool life.
Cleaning and chip removal
The cutting fluid can also clean the machine surfaces, inhibiting the growth of bacteria and favourable to chip evacuation, because the fluid and chips form a slurry. This will further prevent blockage and pollution of the cutting area, and improve the chip breaking performance.
Anti-Corrosive
Water-soluble cutting fluid can offer corrosion prevention to the machined surface by forming a lubricating film on both the cutting tool and the workpiece, which will prevent them from direct contact and as a result, prevent corrosion of the machined surface.
Raw Material Selection
In order to ensure the highest performance of the water-soluble cutting fluid, it is very important to select the most suitable raw material. The criteria usually taken into consideration are the base oil, the oil properties and compatibility, the corrosion inhibition additives, and the viscosity modifier.
Base oil
The base oil is the main component of the cutting fluid, and it plays the role of forming a lubricating film between the cutting tool and the chip, hence the base oil should be chosen accurately to reduce the machining cost. Synthetic hydrocarbons, esters, and vegetable oil can be used as the base oil. Synthetic hydrocarbons are more resistant to oxidation and have better antifoaming characteristics than esters and vegetable oils, while vegetable oils are more eco-friendly. The selection of the base oil should always be tailored to the customers’ needs.
Oil Properties and Compatibility
It is also important to choose the oil properties and compatibility that best meet the machining needs. The oil properties should be selected depending on the type of the machined material. For example, if the machined material is steel and is difficult to be cut, then high lubricity, wear protection, and extreme pressure (EP) will be needed for the cutting fluid to perform its best. Furthermore, if the oil and water are incompatible, then corrosion or deposits on the surface of the machined material might happen, which will drastically reduce the service lifetime of the tools and the machined surfaces.
Corrosion Inhibition Additives
The corrosion inhibitors are useful protection for the machined surfaces and the cutting tools, because they capable to form a lubricating film on their surfaces and inhibit the potential corrosion from happening. The selection of an appropriate corrosion inhibitors has to consider the compatibility nature between the oil and water, because the corrosion inhibitors are usually compounds which have low solubility in both oil and water.
Viscosity Modifier
Viscosity modifier is a compound that lower the kinematic viscosity of the oil and water. Its purpose is to reduce energy used in machining, resulting in reducing machining cost. The selection of the viscosity modifier has to be done carefully, so it is determined by machining conditions such as cutting pressure, cutting speed, and chip removal rate.
Conclusion
The performance of a water-soluble cutting fluid mainly depends on its composition of its raw material. The raw material selection also has to be tailored to the customers’ needs in order to achieve the highest performance of the cutting fluid. The four criteria which are taken into accounts for raw material selection are the base oil, the oil properties and compatibility, the corrosion inhibition additives, and the viscosity modifier. By following these criteria, the most cost-effective cutting fluid can be produced.
