Environmentally-Friendly Machining Temperature Analysis for Reaming with Minimum Quantity Lubrication

摘要

Metalworking processes often employ cutting fluid as a means of cooling, lubrication and chip evacuation. Traditionally, the approach in industry has been to apply a high volume of coolant to the cutting zone, thus 'flooding' the tool and work piece. While flood coolant is effective at reducing thermal expansion in the work piece and increasing tool life, it is costly in terms of the environment, worker health and operating costs (Klocke & Eisenblatter, 1997).rnOne alternative to flood coolant is minimum quantity lubrication (MQL). In MQL, a small amount of air and oil mist is delivered to the cutting zone (Stoll et al., 2006). Often, environmentally-friendly oil can be used, such as vegetable oil or a synthetic ester (Stoll et al., 2006). There are three common delivery system types for MQL: single-channel through tool, dual-channel through tool, and external. In the single-channel system, the oil and air is mixed at the base of the spindle and travels as a mist through the spindle to the tool tip. In a dual-channel system, the oil travels through a lance in the spindle, while the air travels outside the perimeter of the lance. The air and oil mix inside the tool holder. The third option is to deliver the MQL mist through external jets, similarly to flood coolant.rnSince MQL does not fully replicate the cooling effect of flood lubrication, it is of great importance to find ways to control the temperature during machining. This is particularly true for work piece materials with a high coefficient of thermal expansion,rnsuch as aluminum, where the thermal effects could be detrimental to part quality. While there has been considerable research in the area of MQL for operations such as turning, milling and drilling, there has been very little research for the reaming process. Reamed holes often require close geometric tolerances, so it is important to understand temperature mechanisms in reaming. One aspect of heat generation that has not been well documented is the effect of MQL delivery method.rnFor this research, temperature measurements were taken with an infrared camera during reaming spool bores of an aluminum automotive valve body. Temperature data was compared for single-channel and dual-channel MQL delivery systems. In addition, spindle power, surface finish and diameter data was collected from each set of experiments. Corresponding quality and spindle power data was collected from flood coolant experiments to establish a baseline for MQL performance.rnThe research shows that dual-channel MQL delivery system performed nearly equivalently or better than flood coolant in terms of quality and power consumption. The dual-channel MQL system was shown to be more effective at cooling the part and more robust than the single-channel MQL delivery system. Reasons for the difference in performance between the two systems are presented.