In the process of machining magnesium alloys, the chips and fine powders produced have the risk of burning or exploding. The size of the chips generated in the initial processing stage is large. Due to the high thermal conductivity of magnesium, the friction heat generated can be quickly dissipated, so it is difficult to reach the ignition temperature, and accidents occur less at this stage. However, in the finishing stage, since the generated fine chips and fine powder have a large specific surface area, it is easy to reach the ignition temperature and cause a combustion or explosion accident.
During the processing of magnesium alloys, the factors that influence the temperature of the chips to reach the flash point or combustion are as follows.
a. Relationship between machining speed and cutting rate. Under any given set of conditions, there is a range of machining speeds and feed rates that can cause burning. The feed rate increases and the chip thickness increases, making it less likely to reach the ignition temperature. As long as the machining speed is low enough, chips of any size are unlikely to be ignited. If the machining speed is high enough, it is impossible to heat chips of any size to ignition temperature due to the short chip contact time with the tool.
b. The relative temperature of the environment. The higher the relative temperature, the greater the likelihood of fire.
c. The composition and state of the alloy. Single-phase alloys are less prone to misfires than multi-phase alloys. The more uniform the state of the alloy, the less likely it is to misfire.
d. Other factors. Feed rate or engagement is too low; dwell time during machining is too long; tool clearance and chip space are too small; high cutting speed is used without the use of cutting fluid; tool with nesting Sparks may occur when dissimilar metal core liners in castings collide; magnesium chips build up around or under machine tools, etc.