HIGH SPEED MACHINING USING CRYOGENICS
In conventional
machining processes when we go for high speed excessive heat is generated
during the chip formation process, which increases the temperature of cutting
tool and accelerates tool wear. Conventionally cutting fluid is used to cool
and lubricate cutting process. However conventional cooling process has
inherent health and environmental problems .In addition to this a process
should facilitate longer tool life ,higher cutting speed ,better work surface,
less built up edge, easier chip breaking and lower production cost.
Cryogenic machining is
one such process in which above mentioned features are present. Cryogenic
machining uses Liquid Nitrogen (LN2) as a coolant. LN2 has a boiling point of
-199 degree centigrade. It has been observed that at cryogenic temperatures
tool materials get harder and stronger. A micro nozzle is formed between tool
face and chip breaker and LN2 is passed through it. The chip breaker helps to
lift chip so that the jet reaches the hottest spot i.e. tool chip interface. At
this point LN2 absorbs heat and evaporates producing gas cushion causing
lubrication effect. This localized cryogenic cooling reduces the tool face
temperature, enhances its hardness, so less wear rate .The lubrication effect
reduces friction and tool wear.
This new cryogenic machining eliminates the built up
edge (BUE) problem on tools because cold temperature reduces possibility of
chips welding to tool. So the process will allow high speed cutting without
built up edge. In addition to various advantages of the cryogenic machining,
the paper discloses the comparison of cryogenic machining with conventional
process in the aspects of tool life, productivity, and production cost
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