As is recognised widely, tool wear is a major problem in machining of difficult-to-cut titanium alloys. Therefore, it is of significant interest and importance to understand and determine quantitatively and qualitatively tool wear evolution and the underlying wear mechanisms. The main aim of this paper is to investigate and analyse wear, wear mechanisms along with surface and chip generation of uncoated and TiAlN coated carbide tools in a dry milling of Ti6Al4V alloys. Quantitative flank wear and roughness were measured and recorded. Optical and SEM observations of tool cutting edge, machined surface and chips were conducted. Results show that the TiAlN coated tool exhibits approximately 44% longer tool life than the uncoated tool at a cutting distance of 16 m. A more regular progressive abrasion between the flank face of tool and workpiece is found to be the underlying wear mechanism. The TiAlN coated tool generates smooth machined surface with a 31% lower roughness than the uncoated tool. As is expected, both tools generate the serrated chips; however, burnt chips with blue colour are noticed for the uncoated tool as the cutting continues further. The results are shown to be consistent with observation of other researchers, and further imply that the coated tools with appropriate combination of cutting parameters would be able to increase the tool life in cutting of titanium alloys.
One of the concerns in improving the quality of minority education in multicultural nations is how to choose the appropriate types of learning for different ethnic groups, especially when such decision can be constrained their cultural diversity. This paper aims to analyze the effect of cultural differences on selecting types of learning for ethnic minorities; thus, recommending some ethic-specific policies to better utilize the manpower resources in the Northwest region of Vietnam. Questionnaires were employed to survey 250 people from 6 ethnic minority groups, whose population is over one million locating in three provinces in the Northwest border region of Vietnam. The study also conducted 20 in-depth interviews with management teams of different educational institutions and corporations. The results show that ethnic-cultural factors including gender, customs, ethnic relations, and marriage age have determined the choice of learning types in higher education levels. From those points, this paper suggests development interventions so that ethnic-cultural factors do not reduce the ability to pursue higher
We present a numerical investigation of the breakup and freezing of a pendant hollow water drop beneath a cold curved surface. The drop contains a bubble surrounded by a shell of water that forms at an outer wetting angle of θo with the surface. The freezing begins on the cold curved surface and evolves in the direction of gravity. As it freezes, the water accumulates and forms a bulbous end at the bottom of the drop. Breakup can occur, inducing a daughter water drop. As a result, the freezing process of the remaining hollow drop attached to the surface takes less time, and the frozen drop shrinks. However, this breakup has no effect on the bubble. The various parameters under consideration include the Bond number Bo, the Stefan number St, the size of the bubble, and the angle θo. It is found that the breakup of the drop during freezing takes place for increasing Bo (from 0.1 to 3.0), increasing θo (from 60° to 120°), decreasing St (in the range of 0.01–0.64), or decreasing bubble size. On the other hand, the shape of the curved surface has little influence on the breakup of the drop. Phase diagrams of θo vs Bo and of St vs Bo are also presented to provide a more general picture of the breakup and freezing of the water drop.
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