Avoiding thermally induced warpage during machining of Ti-6Al-4V by using local cryogenic machining

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The aim of the research project is to compensate high cutting temperatures occurring during the milling of titanium using liquid nitrogen to enable a specific cryogenic cooling of the cutting tool. It is important to point out the sub-goal of only cooling the interaction zone, not the work piece or the environment. In the end, the process is to be adjusted to provide exactly the amount of cooling which is produced by the cutting process itself. So the aim is to allow high temperatures only in the shear zone where they are necessary to enable the cutting process. In order to achieve this goal it has to be analyzed how the cryogenic cooling with liquid nitrogen affects the characteristics of the cutting process. Therefore an existing and verified FE-simulation model for the cutting of Ti 6Al 4V will be upgraded to provide the cryogenic cooling of the cutting tool and its influence on chip formation, cutting forces and cutting temperatures without extensive experiments. Simultaneously the evaporation and expansion of the liquid nitrogen in the cutting tool will be analyzed very detailed. These processes highly depend on the geometry of the expansion chamber and affect intense the composition of the nitrogen, the temperature at the cutting edge and the consumption of nitrogen. It is an aim of this project to know the occurring processes and dependencies very detailed in order to be able to influence them specifically. With the use of orthogonal turning experiments the cryogenic FEM-model will be validated. To reach this main goal, the system of tool-nitrogen and work piece has to be designed to reach optimum cutting conditions regarding tool wear and quality of the material surface for the machining of Ti 6Al 4V at the same time. This implicates productive process parameters, low tool wear and high quality of the work piece surfaces at once. Due to the fact, that the use of liquid nitrogen as a cooling medium in cutting processes is not state of the art in industry the influences on cutting tool, machine tool and the environment by the cryogenic cooling are to be analyzed and quantified. As many parts of real applications are machined using milling operations, the results of the project will be transferred to the milling of slots and pockets with the beginning of the third year. The cryogenic machining of a real part is planned for the third and fourth year as well as strategies of compensation to provide an optimum of heat management during the milling of titanium.