Cutting fluids are the fluids which are generally applied while the machining (or cutting) operation is taking place.
Advantages of cutting fluids
The advantages of cutting fluids in machining operation are :
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.
Cool workpiece to maintain its dimensional accuracy, by reducing or eliminating distortion caused by heat generation.
Decrease the tendency to form a 'built-up edge'.
Flash away chips.
Lubricate guiding portions of tooling, such as a drill or pilot in a bush.
Discourage corrosion of newly machined surfaces.
Lubricate machine movements.
The requirements of a cutting fluid are :
The fluid should be efficient coolant and provide effective lubrication. It should be easy to handle, prepare and store. It should have optimum service life and minimum cost, and have no ill-effects on normal machine lubrication, and be non-injurious to health (non-toxic, non-fuming) and odourless. Further it should be non-corrosive to machine, tooling or component.
Types of cutting fluids
The four types of cutting fluids commonly used are described below in brief:
1. Aqueous fluids are usually emulsions, known as soluble oils. They are generally cheapest and find greatest use where coolant properties are the important factor, such as conventional cutting of metals with high speed steel tools.
2. Oil-type fluids are straight petroleum products, usually known as neat cutting oils or mineral oils. They are generally used when reduction of friction is important and the presence of the water in a soluble oil emulsion is undesirable. Heavy duty cutting can break down the emulsifier of a soluble oil, and the water would tend to flush out the natural lubrication of the machine. Oil-type fluids find considerable usage on automatic lathes.
3. Synthetic fluids form solutions, not emulsions, in water. These solutions are transparent, allowing operators to observe the cutting, and are mainly used on grinding machines.
4. Gaseous fluids, such as carbon dioxide, have limited application, due to high cost, but are occasionally used when liquids have to be avoided, such as when cutting an absorbent material
use of Additives in cutting fluids
It is very common to use additives to cutting fluids to obtain following qualities : act as a wetting agent; discourage foaming ; stabilize an emulsifier; discourage bacterial growth; act as a rust inhibitor ; act as an antiseptic. The most common additive is sulphur. It acts as en anti-weld agent discouraging the formation of the built-up edge and reacts with the chip to form solid lubricants on the chip surface.
Following principles must be followed as the principles of safe design of machines from consideration of accident prevention.
Dangerous moving parts should be enclosed.
Parts subject to wear, adjustment, and hand lubrication should be conveniently accessible.
Lubrication should wherever possible be automatic and continuous when the machine is in operation
Consideration should be given to individual drive so that hazards due to driving mechanism may be minimized.
Sharp contrast between light and shadow and glare in the vicinity of the point of operation should be considered, also the provision of integrally mounted lights and the probable position of independent lighting units.
Materials should be mechanically conveyed to, and removed from machine whenever possible.
Provision should be made for automatically conveying dust and gases away from machine.
Noise should be eliminated or reduced to the maximum extent.
Machine motions tiring to the eyes should be avoided.
Exterior shapes of any parts of the machines that requires frequent contacting or handling should be such as to facilitate convenience in handling and moving parts that cannot be enclosed should, as far as possible, be smooth in contour.
Weight of parts to be handled should be kept within the limits of convenience, or these parts should be so designed that they may be conveniently handled by mechanical means.
Throughout the design of the machine and its parts, consideration should be given to convenience in attaching accessories, chiefly point-of-operation guards or moving parts.
Consideration in design should be given to the external shape of the machine unit so that the danger of accident from tripping and falling and collision will be minimized. Corners may often be rounded to lessen the danger from accidental contact.
Liberal factors of safety should be used in determining the strength of parts.
Wherever manufacturing circumstances permit, point-of-operation guards should be installed by the builder of the machine so that it may be delivered to the purchaser in a fully guarded condition.
Consideration should be given to the safe location or isolation of machines that cannot be made safe otherwise.
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