Application of modal analysis on machine tool for stability lobe diagram generation

Machining chatter is a major limiting factor affecting productivity. Machining chatter leads to increased tool wear, surface dimension errors, high surface roughness, increased noise levels etc. Machining chatter has been a topic of research since the 1950s and multiple chatter avoidance methods have been documented. One chatter avoidance technique involves choosing stable cutting parameters such as spindle speed and axial depth of cut. Stability lobe diagrams play a vital role in parameter selection as they graphically show the boundary between stable and unstable cutting parameters. To generate a stability lobe diagram, modal parameters of the machining system must be determined. In this paper, modal analysis is conducted on a machining system consisted of a vertical machining centre, end mill and workpiece to acquire modal parameters of the machining system. Using modal parameters, a stability lobe diagram was generated for an up-milling operation with a 5,77 mm (28.85 % of the tool diameter) radial depth of cut. Nine milling experiments were conducted to test the stability lobe diagram. The tests showed that the diagram was accurate in the stable and unstable regions while inaccuracies in form of chatter were observed at low spindle speeds near the stability limit.