In mechanical cutting, there are several methods used when using CNC machine tools, including turning, milling, drilling, and boring. The amount of material removed is divided into three categories: roughing, semi-finishing and finishing.
The cutting tool materials used can be classified into five types: high-speed steel, hard alloy, ceramic, diamond and cubic boron nitride.
The machine tools used can be divided into four categories: those that require oil-based cutting fluids, those that do not, single-piece small batch production tools, and batch or automatic production lines (flexible manufacturing systems ).
It is important to note that different cutting methods have different cutting characteristics for the same metal and can result in varying levels of processing difficulty.
For example, when using Q235 carbon steel as material, it can be challenging to machine threads while ensuring the desired surface roughness quality index. The finishing process is more challenging than roughing.
Difficult cutting processes often require higher quality cutting fluids. Proper use of cutting fluid can ensure processing quality, extend tool life and improve processing efficiency.
Rough Machining
Cutting fluid selection must take into account several factors, such as the machine tool, cutting tool and machining process. The type of cutting fluid, whether oil-based or water-based, is determined according to safety and waste fluid treatment limitations.
If fire prevention and safety are prioritized, water-based cutting fluids should be considered. When choosing water-based fluids, waste emission issues must be taken into consideration and companies must have waste treatment facilities. For some operations, such as grinding, water-based cutting fluids are often the only option. For machining processes using carbide tools, oil-based cutting fluids are typically preferred.
For high-speed machine tools that require the use of oil-based cutting fluids, it is not advisable to switch to water-based cutting fluids as this may affect machine performance. After considering these factors, the appropriate type of cutting fluid can be decided. Once the type of primary cutting fluid has been determined, a secondary selection can be made based on the machining method, required precision, surface roughness, and other factors. If the cutting fluid chosen does not meet expectations, it must be reevaluated, the cause of the problem identified and corrected, and a final decision made.
Suitable situations for oil-based and water-based cutting fluids
With a wide variety of cutting fluids available, improper selection can lead to adverse results. Water-based cutting fluids should be chosen in the following situations:
- Locations with potential fire hazards due to oil-based cutting fluids.
- High-speed, high-feed cutting situations where the cutting area reaches high temperatures, produces intense smoke and poses a fire risk.
- Cases where workflow considerations of previous and subsequent processes require the use of water-based cutting fluids.
- When there is a need to reduce machine contamination and dirt caused by oil splashes and mist, thus maintaining a clean operating environment.
- For cost considerations, if the machining of certain materials and parts does not require high surface quality, general water-based cutting fluids can meet the requirements and significantly reduce costs.
Oil-based cutting fluids should be considered in the following situations:
- When tool durability has a significant impact on the cost-effectiveness of cutting (for example, when the tool is expensive, difficult to sharpen, or time-consuming to assemble and disassemble).
- For high-precision machine tools where water ingress is absolutely prohibited to avoid corrosion.
- When machine tool lubrication and cooling systems are easily connected and there is no equipment or conditions available for treating waste fluids.
Cutting Fluid Considerations
- Cutting fluids must not have a strong odor or contain additives that are harmful to humans, ensuring user safety.
- Cutting fluids must meet lubrication management and equipment protection requirements, i.e., they must not corrode metal parts of the machine tool, damage seals and paintwork, or leave hard, sticky deposits on machine tool guides, ensuring the safety and normal operation of the machine tool. the equipment.
- Cutting fluids must provide rust prevention between part processes and must not corrode the part. Sulfur-containing cutting fluids should not be used for machining copper alloys. PH neutral cutting fluids should be used for aluminum alloys.
- Cutting fluids must have excellent lubricating and cleaning performance. Choose cutting fluids with a high maximum seizing load (PB value), low surface tension and good performance proven through cutting tests.
- Cutting fluids must have a long service life, especially important for machining centers.
- Cutting fluids must accommodate a variety of processing methods and part materials.
- Cutting fluids must be low polluting and have waste fluid treatment methods.
- Cutting fluids should be reasonably priced and easy to mix. Users can select the cutting fluid that meets the requirements of their machining process and is priced appropriately after initial selection and testing in their factory.
Final thoughts
Proper use of cutting fluids plays a crucial role in improving machining efficiency, improving machining quality, extending tool life, and reducing overall costs during NC cutting.
However, cutting fluids can pose health risks to the operator and contribute to environmental pollution through the disposal and discharge of waste fluids.
To support green production, it is important for operators to explore alternative methods that minimize or eliminate the use of cutting fluids.
Industrial and research organizations must continue to develop cutting fluids with improved performance, green credentials, versatility and affordability to meet users' needs.
Machine tool managers, process technicians and operators must stay informed and actively promote the use of new cutting fluids and environmentally friendly cooling and lubrication technologies in production. This will ensure that the most appropriate cutting fluids and technologies are used in practice.
