Some of the Problems associated with Conventional Machine Tool Structures:
Limited degrees of freedom: Most of the common conventional machine tools
have about three degrees of freedom. Some of the modern conventional machines
have upto five degrees of freedom, but the arrangement is not very efficient.
The lack of degrees of freedom is a tangible limitation in the present
competitive manufacturing environment. The development of flexible manufacturing
systems and agile manufacturing stresses on machine tools which can perform
a wide variety of machining operations. An ideal machine tool is envisioned
as a cutting tool free enough for any spatial movement. This can be achieved
with a six degree of freedom machine tool.
Problems of Heavy Mass: Problems of rigidity frequently arise due to accelaration
and decelaration of heavy masses. Increasingly as an effort is being made
to produce light and portable machine tools, this factor assumes greater
Accuracy: The movements of the machine tool are dependent on linear ways
and bearings. During the life of a machine as these wear out the accuracy
of the machine is affected. This has an important bearing on the concept
of volumetric accuracy. In a conventional three-axis we have 21 position
variables to consider.
Vibration and Stiffness Problems: As the structures are composed of heavy
parts and are not very symmetrical this factor has a great effect on machine
tool performance. Individual axes take unproportional amount of forces.
Fixturing Requirements: In conventional machine tools as the degrees of
freedom are limited the fixturing requirements are large. Special tools
are needed for various purposes like machining thin wall sections or when
parts of workpiece surface are inaccessible. The need for extra tools and
fixtures increases machining time and cost to a great degree for applications
which require them.