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Investigation into Machine Tool Chatter Vibrations

Contact : André Preumont

The work aims to explore regenerative machine tool chatter in the milling and turning processes and its suppression by active control.

Principle

The feedback model of regenerative chatter, developed by Merrit, is followed for development of two mechatronic simulators for the instability. The closed loop feedback model is shown in Fig 1.

Fig 1 : Merrit’s representation for regenerative chatter phenomenon

The closed loop interaction between the structural dynamics of the machine tool system and the cutting process is the guiding principle behind the development of the demonstrators. The idea for milling is shown in the following figure. Investigations on chatter in actual machining conditions may be complex. Mechatronic simulators provide an alternative and simplified approach to study the characteristics and the prospects of active control of the instability.

Fig. 2 : Modal filters output : a) undamaged, b) damaged

The concept behind the hardware in the loop demonstrator is shown in Figure 3. A real cantilever simulates the MDOF structural dynamics of the machine tool system while the periodic regenerative cutting process is simulated in a DSP board.

Fig. 3: Conceptual model for demonstrator for milling

Fig. 4 shows the photograph of the demonstrator for milling. Chatter control is accomplished by implementing a local acceleration feedback strategy, using a collocated accelerometer and an active mass damper (manufactured by Micromega Dynamics ).

Fig. 4: Demonstrator for milling

Results

Experimental stability lobe diagrams with and without active damping for the various milling operations are shown in Fig. 5.

Fig. 5: Experimental stability lobe diagrams for up and downmilling operations