| Description |
Cutting fluids, typically an emulsion containing a lubricant within a larger cooling medium, are expected to reduce the cutting temperature at the interface between the chip and tool in machining, which improves both part quality and tool life. Traditionally, cutting fluids are applied as a flood, completely wetting the tool for maximum heat removal. However, flood coolant has adverse effects on both the environment and workplace safety, leading industry towards developing alternative solutions, such as dry and minimum quantity cutting fluid (MQCF) application. The capability of MQCF to access and cool the tool-chip interface is not completely understood or modeled with no ability to deliver a desired fluid volume to achieve a desired temperature or friction reduction. This research attempted to model and study dry, flood, and various levels of MQCF cooling targeted onto the rake face of the tool. Experiments were conducted to determine the effectiveness of each level of fluid condition, which could then be parameterized as an effective heat transfer coefficient, heff. The model created here is based off of an established dry analytical model and now expands its capabilities to model machining operations under varying levels of coolant application. The model presented in this thesis was validated with Oxley's model, which is widely accepted as the most comprehensive and accurate machining model for plain carbon steels. All machining parameters input into Oxley's model were held constant, but feed rate was increased from 0.05 mm/rev to 0.2 mm/rev. The model closely predicted the increase in average tool-chip interface temperature, but did not agree with the predicted average tool-chip interface temperatures. To determine heff, a near-orthogonal facing experiment on 1045 steel was conducted to measure the change in temperature under six cutting fluid conditions, including dry, MQCF (0, 150, 300, and 500 ml/hr of water mist supplied by compressed air), and flood (6 l/min of synthetic cutting fluid delivered as a water-based emulsion). Using a tool-work thermocouple to measure average tool-chip interface temperature, a decrease in temperature as the flow rate of fluid increased was measured. Cutting forces were largely constant during the experiment, indicating that the MQCF was primarily cooling and that temperature reductions observed were not due to any lubricating action. Increased coolant flow rate likely caused a larger temperature gradient in the chip, resulting in tightly coiled chips. Furthermore, cooling caused a significant reduction in contact length at the tool-chip interface, indicating that there is an indirect friction altering effect due to in-situ thermal changes at the tool-chip interface. With the aid of experimental measurements, the model calculated the temperature distribution at the interface between the chip and tool as well as discrete points in the chip and tool. The measured temperature decrease with coolant application could be used to solve for heff. The results from this research give insight into the minimum amount of cutting fluid needed to achieve a measurable temperature difference at the tool-chip interface. Additionally, this model can serve as a predictive machining tool to calculate temperature profiles for dry, flood, as well as minimized cutting fluid conditions. |
