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NOVEL TURNING TOOL WITH AN INTERNAL COOLING SYSTEM
[Thesis]. Manchester, UK: The University of Manchester; 2019.
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Abstract
High temperature developed during cutting process is an important factor that influences tool wear, decreases tool life and effects component’s quality. The metal cutting fluid used in industry causes environmental and health problems, and has low efficiency, while newer cooling methods such as cryogenic cooling and mist coolant are much more expensive. This thesis suggests a novel but simple design of an internally cooled cutting tool. Circulating water as the cooling fluid in a closed loop circuit contributes to reducing the pollution and health problems. Results from experimental works show that machining EN8 and titanium alloy with internal cooling can effectively reduce the insert temperature by 30% and the tool life when machining EN8 is doubled. A 3D fully coupled thermal-displacement model has been developed to simulate the turning process. This model is linked to a 3D thermal model the input conditions (contact region between the tool and chip, and the nodal heat loads) for which are obtained from the 3D mechanical model. The 3D fully coupled thermal-displacement model uses Johnson-Cook constitutive material model with a pure Lagrangian formulation, and the friction phenomena is modelled by the Coulomb law of friction. This model showed the cutting process in an intuitive way and the temperature distribution in the insert, contact area and the heat entering the insert were calculated. However, run times were excessive and this limited further development of the 3D fully coupled thermal-displacement model. Results from the fully coupled thermal-displacement model were fed into either the 3D thermal Abaqus model or CFD model. Both these models consider the cutting tool, with its internal cooling channel. In the 3D thermal model, the heat transfer coefficients of 14 the water at different temperatures were calculated by empirical equations whereas in the CFD model, the flow is simulated, and the heat transfer coefficients were calculated internally. Both the CFD and 3D thermal models yielded similar results, and both sets of results show agreement with experimental results. The CFD model, developed using STAR CCM+, provided a better insight into the cooling performance as it showed areas of the cooling channel where sub-cooled nucleate boiling occurred. Results obtained from the different models were verified with experimental values; in the experiments, the three components of the forces and temperatures were measured. A specially designed holder was machined from tool steel, and cooling channels were machined on the back face of the insert. The simulation and experimental results have shown that the maximum temperature on the rake face was reduced by an average of 213°C, which represents a reduction of 29%.