Productivity improvement through chatter-free milling in workshops

Abstract

High-speed machining has improved performance in manufacturing sectors such as the aeronautical, automotive, and mould and die industries. However, one problem of reaching such high speeds is the self-excitation of the spindle-tool system during the machining process. This so-called chatter vibration produces several negative effects: a reduction in surface quality and accuracy, and in tool and spindle life. Nowadays, it is still the most common limitation to increased productivity and quality of metal-removal operations. Although theoretically calculated stability-lobe diagrams can be used to calculate stable cutting conditions, some uncertainties affect the accuracy of this solution. This paper presents a method based on experimental tests where an inclined plane in the workpiece is machined at several spindle speeds. The gradual increase of the axial depth of cut allows the milling to be interrupted when chatter is detected. The final result is that the stability lobes are machined in the workpiece. This method can be used for process optimization and avoiding trial and error tests to determine optimal depths of cut and spindle speeds. The creation of a database with the optimal cutting conditions for a given spindle-tool holder-tool system can help the computer aided manufacturing (CAM) programmer select the cutting conditions that maximize the material removal rate and avoid vibration problems. The method presented is especially suitable for small- and medium-sized workshops where operators are unfamiliar with analytical methods or modelling techniques. It is an interesting way of saving money that does not require complex knowledge, and can easily be applied without additional costs owing to its simplicity.