Modelling the cryogenic environment aided by CFD & FEM to provide optimized solutions for unconventional manufacturing of aerospace alloys

Abstract

The modern manufacturing industry needs to meet the growing demands of aerospace production, while adhering to increasingly strict environmental and sustainability constraints. Cryogenic machining is steadily gaining traction as an eco-friendly unconventional machining method, effectively improving the machinability of the workpiece by cooling and lubricating the cutting process. The increased demand in the aerospace industry requires using higher cutting speeds and feeds, which adversely affect the machinability of the already difficult-tomachine aerospace alloys. This makes the optimization of the cryogenic manufacturing process critical to ensuring a good machinability and a high-quality product. This research investigates the optimization of cryogenic manufacturing of aerospace materials such as titanium alloy Ti-6Al-4V and low carbon steel A36. The optimization varies the cryogenic nozzle position in terms of separation distance from the tool-chip interface and the inclination angle from the vertical to determine the combination that leads to the minimum cutting forces. The study begins with a Computational Fluid Dynamics (CFD) model, aided by the results of Finite Element Modeling (FEM), to simulate the cryogenic environment for each of the nozzle positions and determine the optimal cooling effect. Cryogenic turning tests are then conducted by varying the same nozzle positions to measure the cutting forces in each case and compare them to dry turning. For the case of optimal cryogenic turning, tool wear and surface integrity are compared to dry turning using optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). It is shown that the nozzle position with the smallest separation distance and smallest orientation angle from the vertical leads to the biggest reduction in cutting temperatures as well as cutting forces, and a correlation is drawn between the cryogenic cooling effect and cutting forces. The dominant parameter affecting machining process the most is the separation distance. The results from the CFD and FEM simulations are used to provide a better understanding of the cryogenic effect on the machining process in terms of cutting temperatures, convection coefficients, phase composition and pressure near the tool-chip interface. In addition, a reduction in workpiece surface roughness and tool wear are observed for the case of optimal cryogenic machining, with adhesion being the dominant wear mechanism observed in both conventional and cryogenic turning. This research proves the importance of optimizing the nozzle position in the cryogenic manufacturing system, which has a positive effect on the machinability of difficult-to-machine materials. Using the optimized cryogenic system presents a practical solution to improve the productivity in the aerospace industry and meet the increasing demand in an eco-friendly and sustainable way.