This thesis presents a theoretical and experimental investigation
into the design of extended length tool holders, with specific emphasis
on vibration damping and the attenuation of chatter in boring bars.
The theoretical strategy was to evaluate the general mechanics of
vibration characteristics, as applied to metal cutting operations. This
was used to provide an insight into possible control parameters, and
demonstrate a practical approach to the design and optimization of the
boring bar structure.
Consideration of vibration control parameters and its interaction
with functional specifications of the tool resulted in a modified
design of the tool holder. The design aspects were confined to passive
damping, to enable its application for practical use in industry.
Passive damping can be separated into two areas: Material specification
and system configuration. Both have been exploited here through the
development of a new material.
The theoretical design approaches were further examined through
metallurgical consideration. From this the practical aspects of
material development were confined to improving equivalent stiffness
through alloying elements and processing techniques. Research into
developing a Titanium Carbide (TiC) composite is detailed, involving
powder metallurgy under controlled processing conditions.
The experimented results indicate a 47.39% reduction in density,
combined with 27.14% improvement on its modulus of elasticity leading
to an increase in equivalent stiffness up to 84.59% compared to steel.
Although the results demonstrated considerable improvements of
mechanical properties and substantiate the suitability of such material
as a candidate for the bar material, even better properties were
obtained through Hot Isostatic Pressing (HIPing) process. A further
13.48% increase in elastic modulus lead to an improvement of 109.58 %
on the value of equivalent stiffness.
Experimental examination of tools, was confined to simple
internal turning operations (boring). This required the design of
fixtures for setting up the test rig. The experimental verification of
the combination boring bars was undertaken through comparative
stability performance, assessed from the attained machining quality
under varying machining conditions.
A computational verification of the combination boring bars was
performed using Finite Element Method. The dynamic compliance of the
tool was evaluated in the frequency range relevant to machine tool and
cutting processes for the fundamental mode with appropriate boundary
conditions. The computational and practical analyses, support the
conclusions implicit in the theoretical model, that the combination
approach to the design through material development and system
configuration offers high performance, practical devices.