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

该研究项目的目的是补偿在使用液氮铣削钛的过程中出现的高温，以实现刀具的特定低温冷却。重要的是要指出，子目标是只冷却相互作用区，而不是工件或环境。最后，调整工艺，以提供与切割工艺本身所产生的冷却量完全相同的冷量。因此，这样做的目的是只允许剪切区的高温，在那里高温是实现切割过程所必需的。为了实现这一目标，必须分析液氮低温冷却对切割过程特性的影响。因此，现有的、经过验证的Ti6Al4V刀具有限元仿真模型将被升级，以提供刀具的低温冷却及其对切屑形成、切削力和切削温度的影响，而不需要进行大量的实验。同时，对液氮在刀具中的蒸发和膨胀过程进行了详细的分析。这些工艺高度依赖于膨胀室的几何形状，并对氮气的组成、切削处的温度和氮气的消耗产生强烈影响。这个项目的目的是非常详细地了解发生的过程和依赖关系，以便能够具体地影响它们。利用正交车削试验对低温有限元模型进行了验证。为了达到这一主要目标，刀具-氮气和工件系统必须设计成同时达到刀具磨损和材料表面质量的最佳切削条件。这意味着生产工艺参数、低刀具磨损和高质量的工件表面同时存在。由于在切割过程中使用液氮作为冷却介质在工业上并不是最先进的，因此对低温冷却对刀具、机床和环境的影响进行了分析和量化。由于实际应用的许多部件都是使用铣削操作进行加工的，因此该项目的结果将在第三年开始时转移到槽和凹槽的铣削上。实际零件的低温加工计划在第三年和第四年进行，以及补偿策略，以在钛的球磨过程中提供最佳的热管理。

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.