Division III – Mechanical and Electrical Engineering
wbk Institute of Production Science
Simultaneous Whirling and Turning – Synchronized
Whirling for Simultaneous Turning and Whirling to
Increase Efficiency in Thread Production
Synchronized whirling is a type of whirling with increased
rotational speed of the workpiece. Exploiting this alteration on, a new process was developed for simultaneous
whirling and turning in order to enhance productivity of
machining of bone screws, see Fig. 1. Compared to conventional whirling, process time is reduced significantly by
parallelization of whirling and turning.
Conventional whirling is a machining process related to
form milling. The whirling head is a ring which rotates at
high speed with its cutting tools facing inwards. The whirling head envelopes the slowly rotating workpiece, see
Fig. 2. The envelopment of the workpiece results in a long
path of engagement between cutting tool and workpiece. This leads to favorable cutting conditions and often
renders a burr-free workpiece. The good cutting conditions
Figure 2: Process kinematics of thread whirling
also allow for machining of difficult-to-machine materials.
For this reason, whirling is used for production of threads
with high surface requirements, such as spindles for leadscrews and ball screws, pump screws, extruder screws, and
bone screws.
Figure 1: Simultaneous thread whirling and longitudinal turning in the production of bone screws.
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head are reduced considerably. The thread is machined from
the blank in a single integrated process step.
Increased Feed Rates through
Improved Cutting Conditions
Figure 3: Material removal at the thread of a bone screw.
In many cases, a portion of the material to be removed is
located above the outer diameter of the thread, see Fig. 3.
Cutting the material above the thread by turning allows
increasing the feed rate for whirling, while reducing wear of
the cutting tools. However, due to the low rotation speed of
the workpiece during whirling, turning is not possible at the
same time and requires an additional, preceding process step.
New Simultaneous Process
The new, simultaneous process was developed within the
framework of the joint research project “GeWinDe“. Unlike
conventional whirling, rotation speeds of tool and workpiece are synchronized according to the ratio of threads and
number of cutting tools in the whirling head. In between the
engagements of two consecutive cutting tools, the workpiece completes a whole revolution around its axis. This
allows rotating the workpiece fast enough for a turning
operation at the same time. The whirling tool only cuts the
thread, while the material beyond the outer diameter of the
thread is removed by turning. The removed material, process
forces, and, hence, wear of the cutting tools on the whirling
The kinematics adapted by synchronization result in a
change of the engagement path of the cutting tools with
the workpiece. Compared to conventional whirling, the
synchronized rotations of workpiece and tool enhance
the envelopment of the workpiece, see Fig. 4. The already
favorable cutting conditions of conventional whirling are
further improved. Kinematic roughness and cutting thickness decrease. Therefore, feed rates in rotary whirling can
be higher without increasing the load of the cutting tools or
the kinematic roughness. The integrated process of simultaneous whirling and turning significantly reduces production
time. The change in cutting conditions allows increasing the
feed rate, while the same surface quality is maintained and
tool load reduced.
Figure 4: Path of cutting tool engagement with the workpiece for
conventional whirling (a) and synchronized whirling (b).
Karlsruhe Institute of Technology
Kaiserstraße 12
76131 Karlsruhe, Germany
This research and development project is
funded by the German Federal Ministry
of Education and Research (BMBF)
within the Framework Concept
“Research for Tomorrow’s Production”
and managed by the Project Management Agency Karlsruhe (PTKA). The
author is responsible for the contents of
this publication.
Joint Project:
GeWinDe – Efficient whirling of threads through simultaneous turning
Project coordinator:
Project partners:
Karlsruhe © KIT 2017
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Jan Klose
wbk Institute of Production Science
Phone: +49 721 608-47865
Email: [email protected]