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PhD ThesisThe work reported in this thesis has been developed to predict and measure the
cutting forces in the gear hobbing process. A review of past research in this area
has highlighted the need to adopt a different approach to modelling the process in
order to predict the cutting forces. The hobbing process has been described using
six different co-ordinate systems and the kinematic relationships between these
systems established. A single rack profile has been used to represent the profile
of a single cutting tooth from the hob which was then extended to simulate the
hob itself.
When the hob gashes pass through the cutting region surfaces are generated
which, if mapped on a regular grid can give the basis to estimate the depth of cut,
i.e. the instantaneous chip thickness produced by that particular tooth. The
instantaneous cutting forces generated by that tooth then can be estimated by
using the concept of a specific cutting force of the workpiece material. The
estimation of cutting forces acting on a single tooth space was used to predict the
cutting forces produced during machining of a full gear, by assuming that the
forces acting in a particular tooth space are equal to those acting on the adjacent
tooth space at an equivalent instant in the cutting cycle. In order to validate
predicted results, a Churchill PH1612 hobbing machine was retrofitted with a
CNC control system at Newcastle University, utilising a programmable multi
axis controller (PMAC).
A specially made single toothed gear, and a full gear were machined, and cut on
this machine, and the cutting forces measured in real time using a 3-axis
dynamometer. The force signals produced by the dynamometer were measured
utilising a 12-bit ADC card. Code, written in C, was developed to perform the
many functions needed for the overall control of the machine, but additionally
was used to capture both the cutting forces and axis position data. The results of
the simulation and modelling have shown very good agreement with those
obtained experimentally
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