The Experimental and Theoretical Evaluation of an Indirect Cooling System for Machining

Abstract

Cutting fluids have been used in machining processes for many years to decrease the temperature during machining by spraying the coolant into the machining zone directly on the cutting tool and the part. This has the effect of decreasing the tool temperature, which increases tool life and improves the part quality. These benefits come with significant drawbacks. Cutting fluids are environmentally unfriendly, costly, and potentially toxic. An alternative that has been evaluated in this paper is an internal cooling system (ICS) for lathe turning, which cools the cutting tool using a very small amount of an inert, cryogenic working fluid routed through a microchannel heat exchanger (MHX) that is mounted beneath the cutting tool insert. The working fluid absorbs the heat generated during the machining process after which it is harmlessly vented to the environment. This indirect cooling technique results in an environmentally friendly machining process that uses no cutting fluids, enables increased processing speed, and reduces manufacturing costs. An approximate heat transfer model was developed and used to predict the tool life as a function of the tool cooling approach for various speeds. Machining experiments were completed to validate the heat transfer model and confirm that the ICS can significantly improve tool life relative to conventional flood cooling. The validated model was then used to evaluate alternative cooling approaches using the ICS. It was found that the use of a cryogenic working fluid can significantly improve tool life at all cutting speeds but that the latent heat capacity of the working fluid should exceed the expected maximum heat transfer rate into the tool. This work established that the ICS approach is an effective means to increase tool life without the disadvantages associated with external cryogenic cooling methods.

Environmentally conscious machining of difficult-to-machine materials with regard to cutting fluids

“…In the absence of cutting fluids in dry machining the generated heat should be dissipated by conduction through the chips, workpiece and cutting tool. An alternative to enhancing the heat conduction is indirect cooling of the cutting tool and/or workpiece using heat pipes [122,123], coolant through tools [123,124], cooling the workpiece [125][126][127], etc.…”

Minimum Quantity Lubrication (MQL) in Machining: Benefits and Drawbacks

“…Unfortunately, these fluids also share several negative characteristics. Many are costly to purchase; all are applied in volume; all must be periodically replaced; and, when improperly used and disposed off can lead to health and environmental issues [7], [8]. It is these negative characteristics that have prompted researchers to investigate alternative solutions to traditional cutting fluids and their method of application (flood cooling).…”

Indirect cooling of the cutting tool with a pumped two-phase system in turning of AISI 1045 steel

“…Despite the good results that have been reported, heat pipes are difficult to adapt to toolholders and to conventional cutting tools because they have to be placed in close proximity to cutting edges, thus reducing the use of this method. Alternative cooling methods may be feasible if the device is affordable and if it can be integrated with any conventional machine tool [26]. Ferri et al [27] and Sun et al [28] developed a toolholder with indirect cooling using a machined cemented carbide tool at its base, to which was attached a steel support with microchannels, creating a chamber between the bottom surface of the tool and the top of the support through which 0.3 l/min of water circulated.…”