Effect of cutting speed on tool life in ultrasonic-assisted milling process

Machining processes are inherently involved with tool wear, which is an influential factor in cutting forces, surface roughness, and machining costs. In conventional machining of some materials, there are some limitations regarding rapid wear of tool and large machining forces. As a result, new machining techniques have been developed in recent years, among which is the ultrasonic-assisted machining. This machining method is a combination of ultrasonic vibrations with conventional machining process. The goal of this article is to compare the tool life in ultrasonic-assisted milling and conventional milling processes. In experimental tests, one-dimensional ultrasonic vibrations have been applied on workpiece in the feed direction of tool. By varying spindle speed, the width of flank wear land of cutting tool has been obtained in ultrasonic-assisted milling and conventional milling processes, and the results are compared with each other. Due to tool rotation, the direction of workpiece vibrations with respect to edge of cutting tool varies in time. Consequently, there is the possibility of improper and uncontrolled contacts between tool and workpiece. In order to examine this issue, the relative speed of workpiece in normal direction of tool flank surface has been obtained analytically, and the results have been used in explaining the experimental observations. The experimental results have shown that in spindle speeds of n = 500, 1000, and 2000 r/min, tool life in ultrasonic-assisted milling process is less than in conventional milling process; however, for spindle speed of n = 3150 r/min, due to change in tool wear mechanism and decrease of relative speed of workpiece in normal direction of tool flank surface, tool life in ultrasonic-assisted milling process becomes larger than that in conventional milling process.