Biomedical Engineering Reference
In-Depth Information
out for each design using FLUENT software. The results revealed that
changes in the rotor, inlet, and outlet geometries affect the pressure
distribution on the rotor significantly. The optimum design was identified
based on the lowest pressure variation on the rotor surface obtained from
the FLUENT results. Spinning the rotor at very high speeds provides a
new direction in the development of mechanical micromachining.
Keywords
: High-speed spindles, micromachining, medical materials
1.
I
NTRODUCTION
The major components of a high-speed air turbine spindle are: bearings,
rotor, stator, and spindle shaft. To drive a high-speed spindle a motor, or
compressor, is integrated with the spindle shaft. Bearings provide stability at
high speeds to prevent chatter and poor surface finish and to permit accurate
cutting tool paths. The speed of the spindle depends on the rotational speed of
the rotor. The spindle shaft, rotor, and bearings must be held in a housing.
High-pressure compressed air enters into the housing of the spindle from the
compressor through a pneumatic connector. The compressed air enters the
housing through the shaft and rotates the rotor of the spindle. The micro
cutting tool, which is attached to the center of the rotor, rotates with the speed
of the rotor and cuts the workpiece more quickly than conventional spindles.
The rotor is supported by an air bearing, which provides stability to the rotor
and also transmits the necessary torque. Recent studies on high-speed spindles
are described in references [1-4].
In high speed machining with high-speed spindles, the pressure variation
on the rotor surface is of vital importance. The pressure coefficient is defined
as the difference between the highest and lowest pressure on the rotor surface,
normalized by the imposed inlet pressure. Pressure coefficient determines
pressure variation exerted by high-speed compressed air on the rotor and for
the optimum design of the rotor, the pressure coefficient should be as low as
possible as the large values of pressure coefficient indicate high pressure
variations, which could cause the severe imbalance of the load and
deformation of the rotor and this generates failure of the rotor. Various designs
of rotor for different rotational speeds are proposed and fluid analysis of rotors
has been carried out with a computational fluid dynamics (CFD) software
package called FLUENT. Pressure coefficients of rotors were calculated and
