Methods for Prevention of Ignition during Machining of Magnesium Alloys

Abstract

Magnesium alloys have been increasingly used in automotive and aerospace components and in portable microelectronic devices due to their “ultralightness” and high specific strength. Machining is an important method used to process magnesium alloys. The advantages of machining over other processing methods such as die casting include reduction in power consumption and excellent surface finish. However, the ignition of chips presents a dangerous problem during machining. This problem has attracted considerable research interests. Though coolants can be used effectively to prevent ignition, the pollution of environment and reclamation of chips can not be resolved easily. Therefore, one better approach is to control the machining parameters for minimizing ignition hazard of magnesium alloy chips during dry machining. A systematic study was conducted for a few different magnesium alloys (including AM50A and AZ91D) to understand effect of cutting parameters (cutting speed, feedrate and depth of cut) on ignition of chips during face milling. It is interesting to find that for any fixed cut depth ignition in the forms of sparks, flares or ring of fire occurs only in the moderate cutting speeds and feedrates and can thus be easily prevented by adopting either higher or lower cutting speeds or feedrates. Chips produced in different machining conditions were collected and their morphology was analyzed to understand mechanisms of ignition.

Study of Chip Ignition and Chip Morphology After Milling of Magnesium Alloys

“…Chip ignition studies are conducted at depths of cut (1÷1000μm) that are rarely applied in industrial conditions. In the depth of cut range of 1÷80 μm, chip ignitron during machining was observed [6,7,20].…”

Analysis of chip fragmentation in AZ91HP alloy milling with respect to reducing the risk of chip ignition

“…To this end, we measured chip temperature in the cutting zone, the mean temperature of tool application surface and the temperature on the tool-workpiece contact [3,11]. It was equally important to examine the problem of chip ignition for machining processes run at small depths of cut and the so-called ignition point of a given type of Mg alloy [5,21]. The investigation into chip ignition during machining is connected with determination of the so-called "undeformed chip thickness."…”

Thermographic Study of Chip Temperature in High-Speed Dry Milling Magnesium Alloys

“…In recent works on magnesium alloys machinability, observation of chip ignition conditions for lower depth of cut values is recommended [15,16]. Flares, sparks as well as rings of flares (continuous flares) were observed during cutting.…”