CUTTING FLUIDS: Function, Classification, Selection & Evaluation

What is the main function of cutting fluid?

The main function of the cutting fluids is: 
1. Cool the tool and workpiece (cooling effect). 
2. Reduce the friction between the tool and workpiece (lubrication effect).
3. Remove chips (flushing effect).
4. Provide a safe working environment (non misting, non-toxic, non-flammable, non-smoke).

How is the classification of cutting fluids?

Actually all cutting fluids currently in use belong to one of the following types: 

1. Air:
Compressed air with pure air jets or air mixed with liquid can be used to cool the machining area. 

2. Water-based cutting fluid:
Water, soluble oils, emulsions and chemical solutions or synthetic liquids form cooling lubricants. 

3. Clean the oil:
Mineral oil, fatty oil, compound oil, high pressure oil (EP) and multi-purpose oil. 

4. Liquid nitrogen.
Use liquid nitrogen with a temperature of -196°C as the cutting fluid for difficult-to-cut materials. 

It is also used to cool tubular workpiece or to cool tools through internal channels that supply nitrogen under pressure or by flooding the cutting area. 

Cutting fluid contains many additives, such as emulsifiers, antioxidants, fungicides, surfactants, additives, corrosion inhibitors or agents to prevent foam foaming. 

Cutting fluid accounts for 15% of shop production costs.

The cost of purchasing, maintaining, and disposing of cooling lubricants is more than twice the cost of tools. 

Dry cutting or increased tool wear will increase tool costs; however, compared with traditional methods using cutting fluids, manufacturing costs can be reduced. 

Despite the advantages, the use of cutting fluids also has potential environmental problems. 

Cutting fluids is carried away by cutting chips and wettable powder and contaminates machine tools, floors and workers. 

A part of the liquid evaporates into the air, and a part also flows into the ground. 

Cutting fluids has a direct impact on economic and ecological processing. 

Intensive contact between production employees and cutting fluids can cause skin and respiratory diseases, and increase the risk of cancer. 

This is mainly caused by the components and additives of the cooling lubricant and the resulting reaction products and particles. 

How is the selection of cooling lubricant done?

When selecting cooling lubricants for environmentally friendly production, the following points must be observed (Byrne and Scholta, 1993): 

The composition of cooling lubricants must not have any negative impact on the health of mechanic or the environment. 

The cutting fluid must not produce pollutants during use. 

Multifunctional oil can be used for hydraulic system, for slide way lubrication and as coolant and lubricant in processing, it should have minimum evaporation behavior. 

Cooling and lubrication should be applied in such a way to minimize the volume of fluid used. 

Need to use online sensors to continuously monitor the cutting fluids and machine environment. 

Through proper maintenance and maintenance of cutting fluid, the water requirement of emulsion can be reduced, thereby saving costs. 

How is the evaluation of cutting fluids done?

The purpose of  machining is to produce acceptable parts as quickly and cheaply as possible. 

There are many factors that affect the processing cost, such as the machine tool, the selected tool and the cutting fluid used. 

When evaluating cutting fluid during machining, the aspects discussed in the following sections must be considered. 

1. Lubricant flow 
Assume that the cutting fluid is divided into four paths during the machining process. 

Unfortunately, spoiled or contaminated cutting fluids are the most common waste during machining; due to their oil content and possible other chemical additives, these are classified as hazardous waste. 

Therefore, it is important to avoid or reduce this waste to avoid the cost of frequent replacement and disposal. 

Contaminants in these cutting fluids may include chips, machined parts, dust and other particles, and moisture in non-aqueous solutions. 

However, the most destructive contaminant is miscellaneous oil, which can interfere with the coolant, promote bacterial growth and cause undesirable residues on cutting tools. 

Cutting fluid must be used to achieve acceptable tool life.

Liquids and particles exposed to high temperatures will evaporate.

Emissions into the atmosphere therefore represent a complex mixture which can be as follows: 

Vapors due to elements of the workpiece and cutting tool material.

Vapors from surface deposits on the parts to be machined.

Vapors from cutting fluids.

2. Disposal 

Disposal is increasingly becoming the second most important factor in choosing new removal fluids. 

This importance is mainly due to the increasing costs and liabilities associated with these liquids. 

Whether using on-site waste treatment and disposal or paid disposal methods, waste handlers should provide detailed information on product components that may adversely affect the waste treatment process, which may result in increased company costs.

What are the health hazards associated with cutting fluids?

Cutting fluid has a negative impact on the health of operators, manifested in skin diseases, respiratory system and lung diseases. 

Workplace health hazards and skin problems are the most common in the metal and ceramic industries. 

There are 3 forms of occupational dermatitis: 

1. Irritant contact dermatitis, accounting for 50-80% of all cases. It is caused by contact with fluid that damage the skin. 

2. Allergic contact dermatitis, which accounts for 20-50% of all cases. This type of dermatitis is caused by workers who are allergic to chemicals and usually cannot be cured.

3. Exposure to mist caused by cutting fluid will increase workers susceptibility to respiratory diseases.

This depends on the amount of chemicals and particles in the generated mist. 

Factors such as operator hygiene, facility cleanliness, and air quality all contribute to the possibility of worker dermatitis. 

Several factors that cause skin irritation are: 

The high pH of cutting fluid (8.5) compared to 5.5-6 of human skin.
Certain metals, such as nickel, chromium and cobalt.
Microbial contamination of cutting fluid.

Surfactant cooling used in lubricants.

What are the advantages of cutting fluids?  

Increase tool life by cooling the cutting edge.

Decrease tool-chip friction by providing a lubricant between chip and tool.

Provide better finish on the workpiece.

Reduce forces on the tool and hence economize in power consumption.

What are the disadvantages of cutting fluids?  

Environmental impact.

Worker health hazardous.

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