Technical Information

Technical Information
Technical Information
Tunable Tooling System (TTS)
Tunable Tooling System (TTS)
Overview
When machining with extended length setups, undesirable regenerative vibrations
(chatter) can arise, causing poor surface finish, dimensional control issues, and
tool breakage. To avoid chatter, machine operators are generally forced to reduce
cutting parameters, which decreases metal removal rates and diminishes
productivity.
Cutting force fluctuates when chip thickness varies. This is caused by waves left
on the workpiece from the previous pass. These waves may create chatter when
the cutting tool and workpiece interact. Continued chatter can further produce
variation in cutting force, leading to more vibration. If not addressed, the
amplitude of vibration may eventually reach levels that cause the tool
to bounce out of the workpiece or even result in catastrophic failure.
This problem can be approached in many different ways. Chatter can be avoided
by drastically reducing cutting speeds to increase process damping (friction
between flank face and workpiece), which dissipates energy to reduce vibrations.
Another approach utilizes milling cutters that have inserts with differential
spacing. This minimizes the regenerative effect by creating a disturbance on the
wave pattern left on the workpiece. However, this approach provides limited
success as chip loads are no longer evenly distributed over the cutting edges and
may require the feed rate to be restricted. Also, because the spacing is not even,
the surface quality could be negatively affected.
While passive dampening improves the dynamic stiffness of an extended reach
tool, the damping mechanism will not perform the same with every machine.
Not only does the natural frequency of the tool affect its dynamic stiffness,
frequencies inherent to the machine do as well. Because machine tools have
their own dynamic signature, a tool that is tuned on one machine may not be
tuned on another. Unlike other products on the market that are pretuned,
Kennametal tunable boring bars and milling adapters are tunable. They allow
users to adjust the passive damper, optimally tuning the tool for a specific
machine or setup. This enables extended reach tooling to be retuned to match
a machine’s dynamic signature, even as it changes over time. A key benefit
of Kennametal’s tunable boring bars and milling adapters is that they can be
optimally tuned for any given setup. While Kennametal standard tunable
products come pretuned from the factory, it may be beneficial to further
optimize them once installed.
The problem with these solutions is that they do not allow high metal removal
rates to be maintained. To uphold high rates, the dynamic stiffness of the system
must be increased. Dynamic stiffness is proportional to the product of static
stiffness and damping ratio. Static stiffness can be increased through using
shorter setups or larger toolholder diameters. Materials with a higher modulus
of elasticity can also increase static stiffness.
The Kennametal Tunable Tooling System (TTS) provides a means for maximizing
the dynamic stiffness of boring bars and milling adapters by suppressing
vibrations with a passive dynamic absorber. TTS is designed with an internal mass
that vibrates close to the natural frequency of the most dominant vibration mode
in the system. The motion of the internal mass will dissipate energy and prevent
chatter. The overall result depends on a machine’s dynamic characteristics*
and the rigidity of the connection between tool and machine tool. Manufacturing
tolerances, preload, and wear may change the dynamic response of a machine
and adversely affect overall results.
*Machines from same builder and model are not dynamically identical.
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