High-speed machining drastically increases productivity and reduces manufacturing cost Providing fluid circulation through a cooling channel which gets circulated inside the motor housing seems to be an effective forced convection solves heating problem
3. 1.What is the need for employing
High-speed machining ?
High-speed machining drastically increases productivity and
reduces manufacturing cost, and has attracted the interest of
engineers for many years and why so ?
4. 2. How High speed machining
achieved ?
The spindle containing the machining tool acts as a motor shaft which is noting but
the rotating armature, therefore when motor windings are excited spindle-tool
rotates directly so that power transmission devices, such as belts and gears are
eliminated. Now the tool is capable of rotating in higher RPM which is proportional
to the motor excitation current. The RPM ranges for 30000 to 160000
5. Applications of high speed motor in
manufacturing
left – machining of aluminium, apple’s laptop keyboard sockets
Middle – high speed machined PCB board
Right – milling of sophisticated components
6. 3. Are there no problems
encountered in high speed
machining ?
Drawbacks are inevitable,
As in this case drawbacks lies in the fact that motor coupled to the spindle whose
impedance increases generating heat while continuous running, since the rate of
generation of heat at a point of time exceeds the heat dissipation rate the overall
system temperature raises as heat cant get rid off
This elevated temperature causes thermo-elasticity affecting tools performance to
machine
7. 4.What are the ways to suppress
these drawbacks ?
Increasing the heat dissipation rate i.e increased heat transfer through some means
is the only way
Providing fluid circulation through a cooling channel which gets circulated inside
the motor housing seems to be an effective forced convection
Using helical channel as a cooling duct seems more advantages
8. The physical model of the built-in
motorized spindle with a helical
channel
12. Assumptions made to simplify the
analysis
The heat generated per volume by the motor is distributed in the
middle of the inner housing
The thermal conductivity of the spindle housing, whose material is AISI
302 with a conductivity coefficient k = 16.3 W/m C, is isotropic and
temperature independent
The natural convection and radiation effects are ignored
The fluid is considered to be incompressible with constant physical
properties
The flow is assumed to be steady
13. Base of fluid dynamic analysis
The NAVIER-STOKES equation is the fundamental equation for fluid
dynamics
It governs the motion of fluids and can be seen as Newton’s second
law of motion for fluids
16. Results and discussion
The hot spots are concentrated near the center of the spindle axis
The spindle housing temperature increases when the heat source is increased
Water inside the channel are mixed well and quite uniform due to the swirl effect
generated by the helical channel
The average maximum temperatures along the spindle axis is decreased from 24.5 C
to 22.2 C when the water flow rate is increased
17. References
C.H. Chien, J.Y. Jang,
3-D numerical and experimental analysis of a built-in motorized high-
speed spindle with helical water cooling channel,
International Journal of Science direct, Applied Thermal Engineering 28
(2008) 2327–2336.
