21-03-2014, 10:54 AM
A new method for heat measurement during high speed machining
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ABSTRACT
The cutting temperature and temperature distribution along the rake face of cutting tool
and work piece is an essential factor in study of machining processes due to its effect on
surface quality, tool life, tolerances, metallurgical behavior and chip-removing rate. Several
methods have been introduced to measure temperature during machining, such as the
thermocouple technique, infrared camera and metallurgical methods. Each of these meth-
ods has some advantages and limitations. In this article, an infrared high-speed sensor with
specially designed software has been used to measure the transferred heat to the work
piece during high speed machining (HSM) of bronze alloys. The results revealed that this
system enhances accuracy and reduces the number of tests required.
Introduction
Metal cutting can be associated with high temperatures
in the tool-chip interface zone and hence the thermal
aspects of the cutting process strongly affect the accuracy
of the machining process. The deformation process is
highly concentrated in a very small zone and the tempera-
tures generated in the deformation zones affect both the
tool and the work piece [1]. High cutting temperatures
strongly influence tool wear, tool life, work piece surface
integrity, chip formation mechanism and contribute to
the thermal deformation of the cutting tool, which is con-
sidered amongst others, as the largest source of error in the
machining process [2]. Therefore measuring temperature
in machining process is an important issue in determining
the tool life, surface quality, work piece deflection, and
machining parameters such as the cutting speed and feed
rate.
Thermocouple
This method works on the principle that when two dis-
similar metals are joined together to form two junctions at
two different temperatures, an electromotive force (emf)
exists across the two junctions. The three laws of the ther-
moelectricity which are applicable to thermocouples are
given by the following:
1. The emf in a thermoelectric circuit depends only on the
difference in temperature between the hot junction and
the cold junction, and is independent of the gradients in
the parts making up the system.
2. The emf generated is independent of the size and resis-
tance of the conductors.
3. If the junction of two metals is at a uniform tempera-
ture, the emf generated is not affected by a third metal,
which is at the same temperature, used to make the
junction between the first two [9].
CONCLUSION
A new technique for heat measurement during high
speed machining is developed in this study. We could
determinate the critical speed (800 m/min) for Cu–Zn40–
Al12 by use of a high speed infrared sensor. Heat distribu-
tion of the work piece determined by measuring the tem-
perature of different points on the surface.