flender group H3-HH-12B Helical gear reducer H3

Flender/Flender Gear Units/Helical gear reducer H3

drawn between two types of machine vibrations: separately excited and self-excited vibrations. Separately excited vibrations arecaused by disturbance forces arising inside or outside the machine. These vibrations are, for example, those which are introduced via the bed, are due to sub-assemblies of the machine (.. from imbalances), are caused by discontinuous cutting process. Resonant frequencies of the machine in the range of separately excited vibra- tions increase the risk of resonance. The higher the compliance of the machine atthe relevant excitation frequency, the greater is the effect of these vibrations. Unlike separately excited vibrations, self-excited vibrations are initiated not by external energy, but from within the process itself. The occurrence of self-excitedvibrations is closely correlated with the dynamic compliance behavior of themachine tool system. Probably the most frequent cause of self-excited vibrations is the regenerative effect which can occur in cutting processes as well as in grinding processes. Theregenerative effect stems from the excitation of vibrations in the machine structurein the region of pronounced resonant points. These are manifested in the form of waviness on the work piece surface. When the tool re-enters the waviness which has been cut previously, the excitation of the machine structure is repeated, possiblyleading to unstable process behavior if the system is not adequately damped. Evenminimal excitation forces, like cutting force noise which is always present, areenough to initiate the regenerative effect. Apart from system damping or thedynamic compliance behavior of the machine, process stability is also determinedby the chosen cutting parameters. The regenerative effect in cutting machinesoccurs only on the work piece side whereas the regenerative effect in grinding machines can also be induced by wear on the grinding wheel. knowledge of what causes vibrations is therefore of crucial importance. Machining tests