True variable-depth milling

Abstract

When tool wears during machining, cost of the process increases. Rapid tool wear leads to even further contributions to process cost and hence must be taken well care of. Among the many forms of tool wear, notch wear is one that has a big effect on the tool change decision. When the tool contacts the workpiece, a high amount of impact is created where depth of cut is. With continuous machining operations such as turning, the impact may not be as important; however, with interrupted machining operations such as milling, repetitive impact between tool and workpiece occurs at every rotation. Therefore, notch wear can propagate rapidly when milling at a constant depth. When that happens, machine operator would be required to discard the tool and replace it with a fresh one. However, this may not have to be the case, if the depth of cut is varied throughout the milling process (variable-depth milling). Although different patterns of varying the depth of cut can be determined, the easiest route of continuously varying the depth of cut in increasing or decreasing direction should be as effective as any other. While varying the depth of cut, the direction of the variation is also found to have an effect on the end results. In this work, first the theoretical difference between end milling and variable-depth milling is discussed. Afterwards, benefit of using "true variable-depth milling" is explained. Then, machining experiments to quantify such benefits is detailed and the results are presented. It was found that when the same machining conditions were used to end-mill, variable-depth mill, and true variable-depth mill a workpiece, impact of notch wear can be minimized by continuously varying depth of cut in the right direction.