Machining of ultralight magnesium alloy AZ31

• Main Author: Wong, Benjamin Yu Zhi.
• Other Authors: Zhou Wei
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/50209
• Institution: Nanyang Technological University

Magnesium (Mg) and its alloys are widely used as structural material in many industries because of its low density (and lightweight properties), good machinability and high specific strength as well as recyclability. Even though magnesium alloys are popularly produced into cast parts or wrought products, some form of machining operations are still required. However, the concern with machining magnesium alloys is the risk of fire ignition of highly flammable small chips generated during dry machining. In this paper, the effect of cutting speed, cutting depth and feed rate on the ignition of AZ31B-H24 hard rolled magnesium alloy sheet during high speed face milling was investigated. The objective of this research project is to find ways to prevent ignition during high-speed machining of magnesium alloy AZ31B. It was discovered that different intensity or severity of ignition could be caused under different cutting parameters. At any fixed depth of cut, there was a certain range of cutting speed and feed rate where ignitions were found to be present. All ignitions were at minimum intensity when the cutting depth was 80 μm. In addition, the relationship between chips’ morphology and the intensity of ignition caused was explored. It is discovered that entangled or intertwined chips easily would most likely produce continuous sparks, a very severe form of ignition. Upon detailed mapping of ignition conditions, it was found that to prevent ignition at cutting depth less than 10μm, machining of AZ31B should not be done with the following parameter: 2000rpm ≤ cutting speed ≤ 6000rpm, 100 mm/min ≤ feed rate ≤ 800 mm/min. For cutting depth more than 10μm, machining should not be done with the following parameter: 2000rpm ≤ cutting speed ≤ 6000rpm, 100 mm/min ≤ feed rate ≤ 400 mm/min. Pneumatic gun can be used to prevent chip accumulation in order to change severe ignition into very minimal ignition or prevent ignition if the original ignition was either a major or minor sparks type of ignition. For future researches, ignition problems in machining magnesium alloys could be solved through determination of instantaneous cutting temperature of region surrounding the cutting area. This research results show potential and important information to avoid the occurrence of fire ring during dry face milling.