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Summary. The stability of the milling process is a state characterised by the non-occurrence of
the self-excited vibration or the extinction of the resulting vibration. The best-known prediction
method of the stability of the machine tool-clamping device-workpiece-tool system is the
determination of the stability lobes for fixed process conditions. They show the relationship of
rotational speed n usually as a function of the depth of cut ap, defining stable and unstable areas.
Experimental modal analysis is used to plot aforementioned stability lobe diagram [1,2].
The Doosan NHP 6300 five-axis milling centre was used for tests. The modal analysis set was
applied. The milling cutter diameter was d = 8 mm and the number of teeth was
z = 4. The EN AW-7050 T745 aluminium alloy, the feed per tooth fz = 0.1 mm/tooth, and the
milling width ae = 8 mm (corresponded to the diameter tool) were defined in the software.
Fig. 1 presents an example of the stability diagram for the tested cutting tool. Characteristic
increase in the width of the ranges of stable and unstable areas with the increase in rotational
speed n was observed. Additionally, it was found that at the depth of cut ap = 0.5 mm, regardless
of the rotational speed value n, process is stable.
Stability lobe diagram for the milling cutter with the diameter of d = 8 mm
In conclusion, the usefulness of the modal analysis to assess the stability of the milling process
was found. This analysis enables the selection of the optimal technological parameters as well
as it is also quick and easy to use.
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