Interference- and chatter-free cutter posture optimization towards minimal surface roughness in five-axis machining

Five-axis CNC machining of sculptured surfaces plays a significant role in aerospace industry, such as blisk machining. The key issue involved is the determination of cutter posture in tool path planning. As the interference will cause the cutter to intrude the workpiece or machine tool and then seriously damage the cutter or machine tool, cutter posture must be well planned to avoid interference. Meanwhile, as the machined surface quality will be deteriorated inevitably when chatter arises, chatter must be eliminated as well. In this paper, posture accessibility and stability diagram (PASD) is firstly constructed by identifying interference- and chatter-free cutter postures based on geometric analysis and machining dynamic analysis. Furthermore, as surface roughness is an important characteristic to evaluate the surface properties of workpieces and should be generally minimized, its prediction model is also established for optimization. As is well known, surface roughness is mainly affected by cutter deflection due to inevitable cutter deformation force (CDF). By analyzing the relationship between surface roughness and maximum CDF, a novel surface roughness prediction model is proposed from a new viewpoint, i.e., the maximum CDF. Compared with the traditional prediction models considering only geometry, the proposed prediction model is much more straightforward, and the prediction results are more accurate (the average prediction error is only about 9.0%). This study reveals that the cutter posture has a great effect on surface roughness, which implies that surface roughness can be optimized from a new perspective (cutter posture). Finally, based on the proposed PASD and surface roughness prediction model, a new cutter posture optimization algorithm is proposed to minimize surface roughness. The algorithm considers both geometrical and dynamical constraints (interference and chatter) simultaneously, and it is verified by machining experiments under different cutter postures. According to the validation experiments, the proposed algorithm can effectively avoid the interference and chatter while minimizing the surface roughness (the optimized Ra is only 0.3589 mu m compared to normal one 0.5476 mu m). To the authors' best knowledge, it is the first time to optimize cutter posture by considering the following three aspects simultaneously: avoiding interference, eliminating chatter and reducing surface roughness. It will greatly improve the machined surface properties, while optimizing the utilization of the machine tool and cutter (extending their service life by avoiding various potential damages). This also will provide a new perspective that optimizes the machining process of complex and precise parts from cutter posture, which is of great significance to aviation and aerospace industries.