Abstract
The machining of magnesium alloys poses the hazard of uncontrolled sparking or ignition. Machining safety indicators such as ignition time and temperature, unit mass of chips and their morphology are presented in this study. Different carbide end mill helix angles λ(s) = 20° and λ(s) = 50° were used. It was shown that the AZ91D alloy could be dry-milled within a wide range of machining parameters without the chip ignition hazard. Nonetheless, for a tool with 50° helix angle a powder chip fraction was observed. As a result of varying v(c) and f(z), smaller fragmentation of chips was observed for a tool with λ(s) 20°. The most desirable leading fraction A was, respectively, up to 84% for λ(s) 20° and up to 67% for λ(s) 50° (in the case of v(c) analysis); up to 87% for λ(s) 20° and up to 83% for λ(s) 50° (in the case of f(z) analysis). Morphological images of chips proved the risk-free range of the tested milling conditions up to 1200 m/min and 0.03 mm/tooth (the chips were free from partial melting and burn marks). The use of a test stand demonstrated that time to ignition was an effective parameter for performing simplified simulations of chip ignition.