Chip ignition in research on high-speed face milling AM50A magnesium alloy
The ignition of magnesium alloy chips is a problem during high speed dry machining in industry. It should be avoided in the practical production. Many factors including machining environment, material composition, tool geometry, cutting parameters etc. can influence the cutting processes. Among these factors, cutting parameters is one of most important elements to induce the ignition of magnesium alloys. AM50A is a commercial magnesium alloy which is widely used in industry. However, very few reports about the ignition conditions of AM50A magnesium alloy are available. In this paper, we investigated the ignition conditions of AM50A magnesium alloy at different cutting parameters. The relationship between ignition conditions and chip morphologies was further explored. The macro morphologies of the chips were observed by optical microscope and the micro structure were obtained by scanning electron microscope (SEM). It is found that the macro morphologies of chips can be characterized into powdered chip, tubular helical chip, acicular helical chip, and long belt chip, which correspond to the different ignition conditions. The powdered chips and acicular spiral chips are easily ignited. They have thinner lamellar thickness compared to the other two types of chips. These results may be used to analyze cutting process and prevent the chip ignition in dry machining magnesium alloy.
Chip Fragmentation in the Milling of AZ91HP Magnesium Alloy
This paper presents new approaches to safety assessment in the milling of magnesium alloy. The objective of the study is to determine the effect of milling parameters and end mill geometry on machining safety, defined as the minimum probability of chip self-ignition. The assessment of safety and effectiveness in the milling of magnesium must include analysis of chip fractions formed during the milling process. The paper presents the state of the art of magnesium alloy machinability in terms of chip formation (chip fragmentation). Furthermore, the paper investigates the correlation between the quantity of distinguished chip fractions and variations in the parameters vc and fz as well as in the rake angle γo. In addition, the results of the dimensions of individual chip fractions are reported. The study was conducted on AZ91HP magnesium cast alloy, and the milling process was performed using carbide tools with varying rake angles (γo = 5o and γo = 30o). It has been found that chip fragmentation increases by increasing the above parameters, i.e. the feed rate fz and the cutting speed vc. The observed chip fragmentation (the quantity of chip fractions) is lower at the tool rake angle γo = 30o. Finally, technological recommendations are formulated based on the quantity of chip fractions generated at particular settings. The results do not unequivocally demonstrate that chip dimensions increase or decrease by increasing the operational parameters of the milling process. In terms of their application, it is vital that machining processes be simultaneously effective and safe.
Integrated land degradation monitoring and assessment: Horizontal knowledge management at the national and international levels
The need for improved horizontal knowledge management at the national and international levels is essential for monitoring and assessment of land degradation and desertification. At the national level, governments utilise scientific, socio‐economic and technical data and information for strategic planning, priority setting and national environment and development planning. However, challenges including the lack of capacity and lack of collaboration and sharing of information across governments affect responses to and the effectiveness of monitoring and knowledge exchange, along with the ability to effectively implement treaties. At the international level, a number of Multilateral Environmental Agreements (MEAs) share cross‐sectoral themes related to research and monitoring, information exchange, technology transfer, capacity building and financial resources. The need for increased synergies stems from the similarities between the issues they address. Challenges for improving knowledge management at the international level include insufficient interaction between the scientific bodies of the various MEAs; duplication of reporting, monitoring and assessment efforts; limited knowledge management between the various assessments addressing ecosystems and biological diversity during the past decade; and insufficient collaboration between the United Nations Convention to Combat Desertification (UNCCD), the UN system and the international non‐governmental organisation (NGO) community. This paper examines these challenges and offers recommendations on how monitoring and assessment knowledge can be better managed at the national and international levels. Copyright © 2011 John Wiley & Sons, Ltd.