This article presents an experimental study on how tool wear affects tool life, surface roughness, and burr formation in ultrasonic vibration-assisted micro-milling. Small amplitude of vibration (2 µm) is applied to the micro-tools to evaluate the cutting performance influenced by tool flank wear as the cutting lengths increase. Compared to conventional milling, lower tool wear and better surface quality are recorded when cutting speed is much less than the maximum vibration speed. It is found that the use of minimum quantity lubrication in ultrasonic vibration-assisted micro-milling can further improve cutting performance due to reduction in tool wear.

Near dry machining refers to the condition of applying cutting fluid at relatively low flow rates, on the order of $2–100ml∕h$, as opposed to the conventional way of using either a large quantity, typically of about $10l∕min$, as in wet machining; or no fluid at all, as in dry machining. One important expectation of applying fluids is to control the cutting temperature, which is an important parameter for tool life and part dimensional accuracy in machining processes. In this context, the understanding of cutting temperature variation corresponding to the near dry cooling and lubrication is of interest. This paper models the temperature distributions in the cutting zone under through-the-tool near dry cooling condition. The heat source method is implemented to estimate the cutting temperatures on the tool-chip interface and the tool-workpiece interface. For the temperature rise in the chip, the effects of the primary heat source and the secondary heat source were modeled as moving heat sources. For the temperature rise in the tool, the effects of the secondary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear, were modeled as stationary heat sources. For the temperature rise in the workpiece, the primary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear were modeled as moving heat sources. The model describes the dual effects of air-oil mixture in near dry machining in terms of the reduction of cutting temperature through the cooling effect, as well as the reduction of heat generation through the lubricating effect. To pursue model calibration and validation, embedded thermocouple temperature measurement in cutting medium carbon steels with uncoated carbide insets were carried out. The model predictions and experimental measurements show reasonable agreement and results suggest that the combination of the cooling and the lubricating effects in near dry machining reduces the cutting temperatures on the tool-chip interface by about 8% with respect to dry machining. Moreover, the cutting speed remains a dominant factor in cutting temperature compared with the feed and the depth of cut in near dry machining processes.