Cutting Fluid Points to consider:
Cutting Fluid - Steel
Low tensile steels can be readily machined unlike the higher tensile steels which are more difficult to machine.
The higher tensile steels, such as stainless, tool and alloy steels require the use of some form of extreme pressure additive.
Staining is not a problem when machining steels.
Cutting Fluid - Cast Iron
Cast iron is easily machinable due to the presence of graphite, except for white cast iron which is strong and hard and difficult to machine.
Fluids with a low oil content must be used. For normal cast irons to minimise ‘drag out’ of oil by the fine swarf particles. Staining is not a problem when machining cast iron.
Cutting Fluid - Aluminium
Aluminium is a soft ‘draggy’ material, which can make it difficult to achieve a good surface finish. Lubricity additives, normally in the form of a fatty material, are necessary.
Additives containing chlorine or sulphur must be avoided as these will result in staining. Staining can be reduced by the incorporation of a passivator.
Cutting Fluid - Copper and Copper Alloys
These are generally soft, ‘draggy’ metals which are difficult to machine. Fluids should therefore contain some form of extreme pressure additive together with a
passivator. Insoluble copper soaps can be formed during the process, which will turn the fluid green and could exacerbate the tendency to staining.
Cutting Fluid - Titanium
Titanium can tend to work harden, and is usually cut at low speeds. Often used in aerospace work along with aluminium alloys and therefore an aluminium coolant is often
used a rationalisation product. Chlorine and sulphure extreme pressure agents should generally be avoided due to the potential for stress crack corrosion.
Cutting Fluid - Magnesium
Magnesium exhibits excellent machining properties, and a good surface finish can be readily obtained. Care must be taken as magnesium swarf can react exothermically (generating heat) with water.
The use of sulphurised additives must be avoided otherwise staining can occur.
Cutting Fluid - Nickel
Nickel and its alloys are prone to work-hardening so low cutting speeds are essential. Extreme pressure additives are necessary to ensure adequate machining performance. The use of sulphurised additives must be avoided otherwise staining can occur