Cryogenic cooling in machining processes
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23-12-2010, 12:59 PM

Presented by: Kulkarni Aniket P.

.pptx   10TH08F-Cryogenic cooling in machining processes.pptx (Size: 91.06 KB / Downloads: 167)

The cooling applications in machining operations play a very important role and many operations cannot be carried out efficiently without cooling.
Application of a coolant in a cutting process can increase tool life and dimensional accuracy, decrease cutting temperatures, surface roughness and the amount of power consumed in a metal cutting process .
Thus, it become mandatory to use coolant in machining operations.

Cutting fluids i.e. coolants
There are two categories
i)Conventional cutting fluids.
a)Water soluble cutting fluids
b)Mineral oils

ii)Cryogenic cutting fluids.
Here, liquid nitrogen is used as a cryogenic coolant.

Application of conventional fluids create some techno-environmental problems such as,
Environmental pollution due to chemical dissociation or break up due to high cutting temperature.
Biological (Dermatological) problems to operators coming in physical contact.
Water pollution & Soil contamination during disposal.
So, it is absolutely necessary to use an environmentally acceptable coolant in manufacturing industry.
For this purpose, liquid nitrogen as a cryogenic coolant has been explored.

Properties of N2
Triple point : 63.148 K
Normal Boiling Point :77.313 K
Critical Point : 126.19K
It is the most abundant gas, composes about four-fifths (78.03%) by volume of the atmosphere.
It is a colourless, odourless,tasteless and non-toxic gas.
These characteristics of liquid nitrogen have made it as a preferred coolant.
Cryogenic cooling approaches
Cryogenic cooling approaches in material machining could be classified into four groups
Cryogenic pre-cooling the of work piece.
Indirect cryogenic cooling.
Cryogenic spraying and jet cooling.
Cryogenic treatment.
Cryogenic pre-cooling the of work piece.
Here,aim is to cool work piece or chip to change properties of material from ductile to brittle because, the ductile chip material can become brittle when the chip temperature is lowered and become easy to dispose
This achieved by
Pouring the liquid nitrogen by continually onto the work piece.
Disadavatage of this method are,
High LN2 consumption
Dimensional changes may occur

Indirect cryogenic cooling
This method was also called conductive remote cooling.
Here,the aim is to cool the cutting point through heat conduction.
In this method, instead of tool tip, tool shank is cooled by LN2.
Hence,LN2 does not contact with the workpiece and it does not cause significant change in properties of the work piece , in addition, cooling effect is stable.
Disadvantages are : effect of this approach is highly dependent on
thermal conductivity of the cutting tool material,
the distance from the LN2 source to the

Cryogenic spraying and jet cooling.
The objective in this method is to cool cutting zone,particularly tool–chip interface with liquid nitrogen by using nozzles.
Here,workpiece will constant temperature and not subject to dimensional inaccuracy and geometrical Distortion
this localised cryogenic cooling reduces the tool
face temperature, enhances its hardness, and so reduces its wear rate;
This approach also embrittles the chip by
cold temperature and bend the chip with the chip breaker.

This cryogenic machining approach eliminates the BUE problem on tools because the cold temperature reduces the possibility of chips welding to the tool and the high pressure
cryogenic jet also helps to remove possible BUE formation
Therefore, it will produce better surface quality.
Cryogenic treatment
Cryogenic treatment is a process similar to heat treatment. In this method, samples are cooled down to cryogenic temperature and maintained at this temperaturefor a long time and then heated back to room temperature to improve wear resistance and dimensional stability of them.
However, the effect of the cryogenic treatment on cutting performance is not stable for all machiningapplications and cutting conditions, and there was not seen a comparison between cryogenic treatment and other cryogenic cooling approaches.
Effects of the cryogenic cooling in machining processes
The effect of cryogenic cooling on tool wear and tool life
Tool wear decreases considerably And tool life increases around four times , for steels.
The effect of cryogenic cooling on surface roughness and dimensional deviation
In application of indirect cryogenic cooling, the surface
rough nesses of materials machined with LN2 cooling were
found to be much better than the surface roughness of
materials machined without LN2 cooling after the same
length of cutting.
The effect of cryogenic cooling on friction
LN2 lubricated contact produced lower friction coefficient than the dry sliding contact and the emulsion-lubricated contact.

The effect of cryogenic cooling on cutting forces
Energy consumption in a cutting operation was associatedwith friction and cutting forces. So, it is significant being cutting forces less in terms of productivity and production cost in any machining process.
According to some researchers, cryogenic cooling did not significantly alter the cutting forces in machining of different materials.

When compared with dry cutting and conventional cooling, the most considerable characteristics of the cryogenic cooling application in machining operations
could be determined as enabling substantial improvement in tool life and surface finish-dimensional accuracy through reduction in tool wear through control of machining temperature desirably at the cutting zone.

Yakup Yildiz, Muammer Nalbant, A review of cryogenic cooling in machining processes,2008
N.R.Dhar,S.Paul,A.B.Chattopadhyay,“Machinig of AISI 4041 steel under croygenic cooling –Tool wear, surface roughness, dimensional variation”,2002
Cryogenic Engineering, Thomas M. Flynn

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