Cutting of Al-Alloys Using High-Pressure Coaxial Nozzle

Abstract

Aluminum alloys are used extensively in aerospace structures because of their high strength-to-weight characteristics. Unfortunately, these alloys are difficult to cut by laser processing. This behavior stems from: 1) their affinity for atmospheric gases, 2) their tendency to form high melting point reaction products and 3) the marked difference between their solidus and liquidus temperatures, which leads to formation of a mushy zone during cutting. This paper describes the results of a program directed toward improving CO2-laser cutting performance in aluminum alloys by optimization of cutting parameters. Tests were conducted with three gas-assist nozzle types: 1) a conventional coaxial nozzle, 2) a ring (annular) nozzle and 3) a high-pressure (to 15 bar) coaxial nozzle. The free flow field of the high-pressure nozzle was examined by schlieren photography. Micro and macro geometrical aspects of the cutting edge were examined using a test piece designed to provide information on cutting accuracy. Mechanical and corrosion tests of laser-cut samples were made and showed that postcutting heat treatment is required to restore tensile strength and avoid pitting corrosion in the heat-affected zone (HAZ) adjacent to the cut edge.