Biomedical Engineering Reference
In-Depth Information
Keywords
: Diamond Tools, Medical Materials, Compact Bone
1.
I
NTRODUCTION
A micromachining technique is described that easily removes bone
without destroying the natural features of the surface of bone. One technique
that shows much promise in machining bone is ultra high-speed milling. This
technique has been shown to produce micro and nano scale structures in the
same way as a conventional machine tool produces macroscale features. A
special requirement of machining at such small scales is the need to increase
the rotational speed of the cutting tool. The cutting speed of the cutting tool is
given by the following equation:
V
r
(1)
where V is the cutting velocity (m/s), r is the cutting tool radius (m) and ω is
the rotational speed in (radians/s). From this relationship it can be seen that as
the cutter diameter reduces in size to create micro and nano scale features the
rotational speed must dramatically increase to compensate for the loss of
cutting speed at the micro and nanoscale. At the present time, the fastest
spindle commercially available rotates around 460,000 rpm under no-load
conditions.
Research is currently underway to improve the performance of air turbine
spindles where the initial aim is to reach 1,400,000 rpm [1]. Strain rates
induced at these high speeds cause chip formation mechanisms to be
significantly different than at low speeds. Additionally, it is now possible to
experiment at the extreme limits of the fundamental principles of machining at
ultra high speed and at the micro and nano scales using known theories of
machining. This paper discusses the use of these theories at the microscale and
at high strain rates and discusses the use of a model of initial chip formation
during high strain rate deformation at the microscale.
2.
M
ICROMACHINING
Following the development of modified equations proposed by Shaw [2],
the equations will be applied to a 6 flute end milling cutter with a shank of
