Optimization of variable pitch milling tools for improved chatter stability

Chatter is an important problem in machining operations which causes poor surface quality, increased tool wear, failure of cutting tool and even machine tool, and excessive noise during machining hence reduced productivity. Chatter vibrations can be suppressed by variable pitch tools and higher chatter-free axial depth cuts can be obtained by the selection of proper tool geometry. This paper presents an efficient method for the selection of optimum pitch angle variation for improved productivity. Optimization is performed by the maximization of the chatter-free axial depth cut using the frequency domain solution of the milling stability. The sensitivity of the optimization method to the variations in the tool point FRF is investigated and it is shown that the proposed method is not sensitive to the tool point FRF variations which makes the proposed method much more robust and reliable compared to existing approaches. Finally, the performance of the optimized tools is experimentally verified through chatter tests and it is shown that a 100 % increase in chatter-free axial depth can be obtained by the specially designed variable pitch tools.