Thin floor milling using moving air jet support with controllable flow direction

Overcut or poor surface quality will easily during thin floor milling due to its low rigidity. Machining with the assistance of mobile support device is an important and frontier manufacturing method for milling the thin floor of a pocket on the thin-walled workpiece. Existed mobile support devices that provide positive contact pressure can effectively avoid the poor surface quality which caused by the vibro-impact vibration between the workpiece and the milling cutter but not the overcut. Besides, inappropriate support element will lead to surface damage to the backside of the floor. This paper proposes a new supporting method to overcome the aforementioned problems encountered during milling the thin floor of a pocket on the thin-walled workpiece. The method utilizes a directionally controllable high-pressure air jet to provide adaptive support for thin-walled workpiece and the air jet support synchronously follow the motion of the milling cutter. Specifically, when milling with a high level of axial depth of cut, the direction of the high-pressure air jet is controlled to flow away from the floor to generate a sucking pressure, which applies a pulling force on the floor to counteract the axial milling force and thus inhibits overcut behavior. On the other hand, when milling with a low level of axial depth of cut, the direction of the high-pressure air jet is controlled to flow toward the floor to generate a positive pressure, which applies a push force to prevent cutter-workpiece impact vibration and thereby improve surface quality of the machined surface. An experimental platform is constructed to verify the feasibility of proposed method. Milling experiments under conditions of no air jet support, air jet support with positive pressure and air jet support with sucking pressure are conducted based on the built platform. Force signals, surface roughness and part accuracy are compared and the critical depth of cut for the transition from vibro-impact vibration behavior to overcut behavior is revealed. The results indicate that the high-pressure air jet with controllable flow direction is effective to suppress the vibro-impact vibration and overcut behaviors during thin floor milling process. It also successfully avoids damage of the backside of the floor caused by the rigid support element, improving both machining accuracy and surface quality. The findings validate the feasibility of the proposed method. The developed method expands the applicability of current milling processes with mobile support devices assistance and provides some valuable insights for the design and optimization of air jet support with controllable flow direction.