Machining Chatter Analysis Machining Chatter Analysis
Accurate prediction of machining chatter in high speed machining has been the focus of this project. Both frequency and time domain models have been developed and used to predict machining chatter. The current stability lobe prediction capability covers milling, longitudinal turning, face turning and boring processes.
In milling, the three dimensional characteristics and the rotational effect of the cutter are taken into account for stability prediction. The extensive experimental validation has been performed and the results indicate the model can accurately predict machining chatter.
In turning and boring cases, process non-linearity and cross-coupling due to three dimensional tool geometry is accounted for. The models consider cutting tool geometry, cutting process non-linearity, cutting parameters and structural dynamics of the machining system. Recently, the tool wear model has been added to the stability lobe prediction model, thus allowing for time-dependent stability lobe prediction as wear progresses.
A few illustrative samples of the project are given below.
GUI of the frequency domain stability lobe program Stability lobing diagram predicted by the program
Dynamic cutting forces and vibrations are generated by the developed mechanistic
time-domain process simulation
software. The software provides comprehensive cutting force and vibration
signatures or peak-to-peak amplitude values over a range of cutting conditions. The
generated results can be used to determine the stable regions of machining by looking at
force and vibration amplitudes as shown below.
 |
 |
Simulated Vibration Amplitude |
Simulated Peak to Peak Force Amplitude |
The turning and boring simulation prediction models which account for cross-coupling and
process non-linearity provide a rather unknown unstable-stable-unstable chatter
behavior. Machining is unstable under a certain depth of cut during finish
machining, above which it becomes stable before it becomes unstable with continual
increase in depth of cut.
This modeling capability provides a systematic means of avoiding chatter during a finishing operation.
Machining is known to be most stable when the cutter excitation frequency becomes close to
the dominant
natural frequency of the underlying structural system.
Based on the low frequency undulation frequency which exists when the cutter excitation
frequency nears the natural frequency, the change in the system natural frequency can be
accurately detected and chatter control can be accomplished. The uniqueness of this
approach is that it needs only a low bandwidth force transducer and it is very simple to
implement.
Chatter during machining is related to the dynamics of the structure. Many
structural elements exhibit non-linear behavior. In order to model such non-linearity, a
new experimental modal analysis procedure using complex modal angle has been developed.
An interactive software allows for extraction of modal parameters and modal angles
(system delay parameter) from measured frequency response functions, which are used as
input to the machining simulation and chatter prediction programs.
In addition, procedures for estimating joint stiffness and damping parameters have been
developed, with which the
system dynamic response, in conjunction with a finite element model, can be predicted and
used for chatter analysis.
See the related section on taper joint parameter identification.
[ Welcome ] [ Research ] [ Education
] [ Laboratories ] [ Collaboration ]
© 2000 Purdue ME Manufacturing Laboratories