Cutting Fluids – Uses, Types, Properties, and Selection

Cutting fluid is a fluid that is mainly used to remove the heat produced during the metal cutting and other machining processes. It is also used as a lubricant in some cases.
They are also used for improving the cutting condition and also the tool life.
Cutting Fluids reduce the friction between the tool and the chip and between tool and workpiece.

If the right amount of cutting fluid is applied heat can be removed as soon as its generated.
So cutting fluid is necessary for increasing production efficiency.

Before the HSS was discovered, there was no problem in selecting the cutting fluids, and water was used as a coolant as machining was done at a much slower speed. But after HSS was discovered, water was not appropriate as the heat generated during machining was high due to high-speed machining. So, different cutting fluids were discovered and made for different machining processes and materials.
Cutting fluid can be in liquid or gaseous form. It is mainly used in metalworking processes like machining and stamping.
Cutting fluids are of various types like oils, oil-water emulsions, pastes, gels, etc.
Cutting Fluid can be referred to as cutting fluids, cutting oil, coolant, or lubricant based on the type of cutting fluid and on the context of its use.
Cutting fluids can be beneficial for most of the metalworking and machining processes.

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Uses of Cutting Fluids:

Cutting fluids can be used for different purposes. Some of its uses are listed below:

1 Used as a coolant:
The main function for which cutting fluids were discovered is for cooling the tool and the workpiece.
By cooling the tool and the workpiece, we can also minimize the tool wear, thermal expansion of the tool and get a good surface finish.

2 Used for lubrication:
Cutting fluids are also used for lubrication. By lubricating, chips and other contaminants can be easily removed from the workpiece.

3 Used for cleaning the machining area:
Cutting Fluids are also used as a cleansing agent and remove dust near and inside the cutting area. This dust removal is important as dust can cause uneven cutting.

4 Used to reduce friction:
Cutting Fluids also reduces the friction between the tool and the workpiece that keeps down the cutting forces and also reduces the heat generation.

5) It is used to improve the surface finish by protecting the newly generated surface from oxidation and corrosion.

6) It is used to prevent rusting.
7) It permits the use of high cutting speeds and larger metal removal rates.
8) It prevents the formation of built-up edges (BUE).
9) It is also used to remove the chips from the cutting zone.

Types Of Cutting Fluids:

Cutting Fluids is categorized into the following types:-

1) Straight Oil:
Straught oils are non-emulsifiable. These oils are used without dilution with water. The composition of this type of oil is a base mineral or petroleum oil. Examples of straight oils are paraffin oils,
naphthenic oils, vegetable oils.
In the system where environmentally friendly oil is required, vegetable oil is used as it is biodegradable.
Straight oils are best for lubrication but they cannot work as a good coolant because they have very poor cooling properties.

2) Soluble Oil:
Soluble Oil is made by mixing mineral oil, water, and coupling agents.
It provides good lubrication among the water-miscible fluids.
Soluble oils are used in machining both ferrous and non-ferrous metals when high cooling quality is required and chip bearing capacity is not much.
This soluble oil functions well in its diluted form and offers great lubrication in addition to heat transfer.
Soluble oils are the most widely used fluids in the industry and also they are very cheap.

3) Mineral Oils:
Mineral oils are generally found in high production machines which have high metal removal rates. As they have very good lubricating properties they are used in heavy cutting operations. The disadvantage of these oils is that they are corrosive and hence are not used for copper or its alloys.

4) Synthetic Fluids:

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As these are synthetic fluids, they do not contain mineral oil or petroleum. These are water-based fluids and water provides very good cooling properties. The problem with synthetic fluid is that it is not a good lubricant and also causes corrosion.
Corrosion or rusting can be prevented by adding rust inhibitors to synthetic fluids. Generally, synthetic fluids are used in grinding fluids.

5) Semi-Synthetic Fluids:
Semi-Synthetic fluid is made by combining synthetic fluid and soluble oils. For semi-synthetic fluid, about 5 to 20% mineral oil is emulsified with water to produce microemulsion. The size of the particles of microemulsion varies from 0.01 to 0.1 mm which can transmit all light easily.
Semi-synthetic fluids have very good cooling properties and its cost lies between the costs of synthetic fluid and soluble fluid. Some examples are molybdenum disulfide, graphite, wax stick, etc.

6) Solid and Paste Lubricants:
These lubricants are in the solid phase or in the form of a paste. These lubricants are put directly on the workpiece or the tool. Some examples of it are molybdenum disulfide, graphite, wax stick, etc.

7) Cutting Oil:
Cutting oil is made by mixing mineral oil and fatty oil. It is used as both coolant and lubricant.

Properties of good Cutting Fluid:

1) Cutting Fluid should have good antiwear properties.
2) It should not foam easily.
3) It should be chemically neutral and should not harm the machine and operator.
4) It should have high specific heat or high heat-absorbing capacity to dissipate the heat generated during machining.
5) It should be transparent so that the operator can be easily through it in the cutting area.
6) It should have a good lubricating property so that it can reduce the friction during machining.
7) It should be nontoxic and should not create any toxic fumes when it comes in contact with hot surfaces.
8) It should be odorless and should not create any bad smell at high temperatures.
9) It should have a low viscosity so that it can easily flow above the workpiece.
10) It should be non-corrosive to the workpiece and machine.
11) It should not gum the parts of the machine.
12) It should have a small molecular size to penetrate into the chip tool interface and allow rapid diffusion.
13) It should have a high flash point and should not burn due to heat produced during machining.

Selection Of Cutting Fluid:

Selection of cutting fluids in machining processes depends on various factors. The main factors according to which the cutting fluids are selected are given below:
i) Machining Process Type
Generally, more difficult machining processes more cutting fluids. The heavy machining processes like broaching or screwing with tap require heavy cutting oils. In horizontal broaching heavy cutting oils must be used but in the vertical broaching process, emulsions and solutions can be used.
For the threading and drilling process, the cooling characteristics of cutting fluid is more important.

ii) Workpiece Material
The next factor for the selection of cutting fluid is workpiece material. Cast iron and cast group of materials are brittle during machining and hence small chips are produced which does not cause much friction. So emulsion should be used as it increases surface finish and concentration should be kept between 10 to 15 percent.
For steel and stainless steel workpiece material, high pressure cutting oils should be used.
For machining of steel alloys, water-based cutting fluids are used as they are heat resistant and difficult to cut.

iii) Cutting Tool Material.

Another factor for the selection of cutting tool material is cutting tool material. High-speed steel cutting tools can be used with any type of cutting tool but when difficult to cut materials are cut, waterless cutting fluids are used with HSS cutting tools.
For tungsten carbide, the cooling characteristics of cutting fluid is more important as high heat is generated when it is used as cutting tool material.

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