Machining Safety in Dry Rough Milling of Casting Magnesium Alloy AZ91D Using Carbide End Mills with Different Geometries

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.