Cryogenic Milling of Aluminium-lithium Alloys: Thermo-mechanical Modelling towards Fine-tuning of Part Surface Residual Stress

Cryogenic cooling is emerging nowadays as an effective method for high performance machining, improving the machining efficiency as well as the surface integrity of the machined parts. Aluminium–lithium (Al-Li) alloys will likely become the material of choice over composites as the fuselages of the aircraft due to its higher strength-to-weight ratio and excellent corrosion resistance. We study the influence of liquid nitrogen (LN2) cryogenic cooling in milling process on surface residual stress of the generated Al-Li alloy parts. The model of the intrinsic thermo-mechanical coupling characters during cryogenic milling process is developed, which determines the cutting temperatures and forces related to the process parameters. Models and experimental results indicate that the cutting forces change little, while cutting temperatures do much under the LN2 cryogenic cooling and conventional dry milling operations respectively. Then the residual stresses of part surfaces after milling under the two different conditions are measured. Measured results show that the residual compression forces(negative values) under the LN2 condition is much less than those under the dry milling operations. This states clearly that the cutting temperatures contribute much more than the cutting forces to the part surface residual stresses.