Dynamics of Parallel
Machining Operations
Dr. Erdem Ozturk*, Omer Ozkirimli, Thomas J. Gibbons, Dr . Sam Turner
AMRC with Boeing, The University of Sheffield
*Tel: +44 (0) 1142226671, e-mail: [email protected]
Introduction
• Parallel (Simultaneous) machining
employs more than one cutting tool in
machining of a workpiece.
• Chatter vibrations which cause poor
surface quality are still a problem as
they are in single tool machining.
• Dynamical interaction among the tools
and workpiece complicates the
dynamic behaviour of the system
further.
• To determine the process parameters
that will result in stable processes,
process models for parallel machining
can be utilized.
• In this study, process models for
parallel turning, parallel milling and
parallel boring operations are
developed.
Parallel Turning
• Vibration waves by one tool affect the other tool (induce
regeneration)
• The second tool may absorb/amplify these vibrations
• Dynamic coupling through process and workpiece
• At least 100% increase in MRR
• Application: Shaft machining
Parallel turning on the different turrets
Vibration waves
Stability prediction for 2nd case
Axial depth of cut comparison
Advantages of
Simultaneous Machining
 More than %100 productivity
increase
Reduced cycle time compared to
machining processes with a single
tool, increased number of tools offers
the potential for increased material
removal rate (MRR)
 Deflection and vibration control
though load balancing
With right selection of process
parameters, load sharing and load
balancing among the cutting tools
result in increased process capability
especially in a flexible workpieces
such as thin walled parts.
Parallel Machining
Process Model
Parallel Milling
• Increased capability for thin wall machining
• Dynamic coupling through workpiece
• Tools stabilizing each other with the right selection of
parameters
• More than 150% increase in MRR is possible
• Application: Thin walled airframes, plate machining
Parallel milling Schematic [2]
Test Setup &
Tool and Workpiece FRFs
Parallel Boring
Parallel Boring Schematic
(Tool CAD Source: Sandvik)
References
[1] E. Ozturk, E. Budak, Modeling Dynamics of Parallel
Milling Processes in Time-Domain, (2010), Proceedings
of the 2nd CIRP Int. Conf., Process Machine Interactions,
Vancouver, Canada
[2] E. Budak, A. Comak, E. Ozturk, Stability and high
performance machining conditions in simultaneous
milling, (2013), CIRP Annals-Manufacturing Technology,
Vol 62, pp. 403-406
• Tool flexibility in 3 dimensions, radial, axial
and torsional.
• Insert geometry (radius, inclination, etc.)
incorporated into the model.
• Dynamic coupling through process and
workpiece
• Torsional flexibility causes phase alteration
during cutting.
• On going research
• Application: Shafts, deep and large bores
Stability Lobe Diagram for 2nd tool
ap,1=10mm & n1=4500rpm
Conclusion
• Dynamics of Parallel turning, milling
and boring are investigated.
• Stability models for these operations
are developed and predicted stability
limits are compared with experimental
results
• For parallel turning, with twin turret
configuration, band of stable cutting
parameters are identified leading to
productivity increase more than 100%.
• For parallel milling, the load sharing
and dynamic interaction through
flexible workpiece, increases stability
and productivity.
• For parallel boring, verification tests
are in progress currently.
 New machine tool designs and
replacements of machine tools with
high degree of freedom robots will
increase the application area of
parallel machining processes.