Sustainability and the careful use of resources entail a demanding conglomerate of requirements for component properties to improve efficiency and service life. For this reason, the use of high-temperature, difficult-to-cut materials is increasingly becoming the focus of science and industry. Due to their properties, difficult-to-cut materials place high demands on the machining process; in the case of Inconel 718, heat dissipation is particularly difficult due to the low thermal conductivity. The machining process must also become more efficient and resource-saving, whereby conventional cooling lubricant systems often reach their limits in deep hole drilling with tools of the smallest diameters in materials that are difficult to cut, as insufficient cooling capacity severely impairs process reliability. The cryogenic minimum quantity lubrication (cMQL) can significantly improve performance in deep hole drilling, but is dependent on the interaction between lubricant and CO ₂ . Cryogenic MQL using CO ₂ as a cryogenic medium offers an alternative, as very high cooling capacities can be achieved with low resource consumption. The aim of this work is to explore possible improvements for cryogenic minimum quantity lubrication in the deep hole drilling process with the smallest diameters, focusing on the interactions between the lubricant and liquid CO ₂ pressure and their influence on the machining process. A higher CO ₂ pressure has a positive effect, particularly with regard to the solubility of the lubricants in the liquid CO ₂ phase, and the extent to which this influence also has a positive effect on the machining process will be determined as part of these investigations.

Thin-walled aluminium castings, such as stator housings for electric motors, are susceptible to distortion during and after machining due to the superposition of residual stress states introduced by casting, heat treatment and cutting. This paper investigates the influence of T6 heat treatment on cutting forces and surface residual stresses in orthogonal cutting of the aluminium casting alloy AlSi7Mg0.3 and assesses the capability of a Coupled Eulerian–Lagrangian (CEL) model to predict them. Orthogonal cutting tests were conducted with a sharp polycrystalline diamond (PCD) tool at cutting speeds of v_c = 600, 900 and 1200 m/min and feeds of f = 0.05 to 0.15 mm, with at least three replicates per parameter combination (154 force measurements in total). Johnson–Cook parameters for both material conditions were derived from Split-Hopkinson pressure bar tests at temperatures of up to 500 °C. The T6 heat treatment increases the cutting force by 25–43% and the feed force by 7–44%, consistent with the higher flow stress of the T6 condition, while the scatter between replicates is below 5.5%. Surface residual stresses measured by X-ray diffraction are tensile in the cutting direction for both conditions (mean values of 45–147 MPa), and show no consistent dependence on cutting speed and at most a weak decrease with feed for the T6 condition; perpendicular to the cutting direction, the T6 condition exhibits significantly lower stresses than the as-cast condition. The CEL model reproduces the cutting force with mean deviations of approximately 10–15%, but overestimates the feed force and fails to predict the tensile surface residual stresses of the T6 condition. The friction formulation, the mass scaling and the constitutive description are identified as the main sources of error that must be addressed before the model can be used for distortion prediction in the process chain.