Mitigation of chatter instabilities in milling by active structural control

Abstract

This report documents how active structural control was used to significantly enhance the metal removal rate of a milling machine. An active structural control system integrates actuators, sensors, a control law and a processor into a structure for the purpose of improving the dynamic characteristics of the structure. Sensors measure motion, and the control law, implemented in the processor, relates this motion to actuator forces. Closed-loop dynamics can be enhanced by proper control law design. Actuators and sensors were imbedded within a milling machine for the purpose of modifying dynamics in such a way that mechanical energy, produced during cutting, was absorbed. This limited the on-set of instabilities and allowed for greater depths of cut. Up to an order of magnitude improvement in metal removal rate was achieved using this system. Although demonstrations were very successful, the development of an industrial prototype awaits improvements in the technology. In particular, simpler system designs that assure controllability and observability and control algorithms that allow for adaptability need to be developed.

Analytical prediction of chatter stability for variable pitch and variable helix milling tools

“…Increasing the damping can be achieved by passive [5,6], semi-active [7][8][9] or fully active [10][11][12] means. Another seemingly elegant method is to attempt to break up the mechanism of regenerative chatter by rapidly varying the spindle speed [13,14].…”

Modelling and Simulation of a New Variable Stiffness Holder for Milling of Flexible Details

“…the use of cutting edge chamfers (Sellmeier and Denkena, 2012), using mechanical dampers (Kim et al, 2006) or smart materials (Rashid, 2005), robust optimum control (Moradi et al, 2013), active methods (i.e. active structural control (Dohner et al, 2004), active holder (Brecher et al, 2010), active damping (Ganguli et al, 2005;Parus et al, 2009;Kaliński and Galewski, 2014)), cutting with variable spindle speed (Soliman and Ismail, 1997; Kaliński and Galewski, 2011).…”

Optimisation of variable helix tool geometry for regenerative chatter mitigation

“…Chatter also causes lower machining quality, poor accuracy and surface finish, unpleasant noise and sound, accelerated tool wear, and can even damage the cutting spindle and machined part. Various approaches can be used to avoid the above catastrophic problems, such as active damping [1,2], passive damping [3,4], spindle speed variation [5,6,7] and variable pitch tools [8,9,10,11,12,13].…”