The metalworking fluids applied in machining processes basically have three characteristics.
- Cooling effect
- Lubrication effect
- Taking away formed chip from the cutting zone.
Selecting a metalworking fluid for a particular application and workpiece material involves a consideration of several factors:
- Specific manufacturing process.
- Workpiece material.
- Tool or die material.
- Processing parameters.
- Compatibility of the fluid with the tool and die materials and the workpiece.
- Surface preparation required.
- The method of applying the fluid.
- The removal of the fluid and cleaning of the workpiece after processing.
- Contamination of the fluid by other lubricants, such as those used to lubricate machinery.
- Storage and maintenance of fluids.
- Treatment of waste lubricant.
- Biological and environmental considerations.
- Costs involved in all of the factors listed here.
In selecting an oil as a lubricant for metalworking, it is important to investigate its viscosity, temperature, and pressure characteristics. Low viscosity can have significant detrimental effects and cause high friction and wear. The particular function of a metalworking fluid-whether it is primarily a lubricant or a coolant also must be taken into account. Water-based fluids are very efficient refrigerants, but as lubricants, they are not as useful as oils. It is estimated that water-based fluids are used in 80 to 90% of all machining operations.
Some of the specific requirements for metalworking fluids are as follows:
- They should not leave any harmful residues that could interfere with operations.
- They should not stain or corrode the workpiece or the equipment.
- Periodic inspection is necessary to detect deterioration caused by bacterial growth, accumulation of oxides, chips, wear debris and general degradation and breakdown due to temperature and time. The presence of wear particles is of particular importance because they cause damage to the system; proper inspection and filtering are thus essential.
After the completion of manufacturing operations, workpiece surfaces usually have lubricant residues; these need to be removed before further processing, such as welding or painting. Oil-based lubricants are more challenging and expensive to remove than water-based fluids.