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질소가스를 이용한 Ti-6Al-4V의 레이저 표면 질화처리
황태우(T. W. Hwang),김재현(J. H. Kim),우영윤(Y. Y. Woo),길태동(T. D. Kil),문영훈(Y. H. Moon) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
Surface nitriding of Ti-6Al-4V can be achieved by laser melting in a flow of nitrogen gas, and high surface hardness values could be obtained. In this study, the effect of process parameters on surface nitriding of a Ti-6Al-4V alloy has been investigated to achieve higher surface hardness without process-induced cracks. The effects of process parameters were experimentally studied and process window is provided on the basis of microstructure, microhardness, and cracking of the nitride layers. It is shown that hardened layers having various depth and hardness can be obtained by controlling the processing parameters. High scanning speed coupled with lower nitrogen flow rate results in crack-free layer at the expense of both a lower hardness and a shallower melt depth.
우영윤(Y. Y. Woo),이민(M. Li),강형석(H. S. Kang),황태우,문영훈,T. W. Woo 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
The flexible roll forming process makes it possible to produce profiles with a variable width by controlling the roll stands with CNC. But profile with variable cross-sections by flexible roll forming has a shape defects, so called buckling. Buckling occurs due to the geometrical deviations which cause longitudinal residual stress in the transitional zones of the profile between the initial metal strip and the roll-formed profile. Therefore in this study, the effect of forming parameters of metal blank on the longitudinal and shape error which are affected by several parameters have been performed to prevent buckling. The parameter investigated in this study is the forming angle. For the flexible roll forming experiments, symmetrical U-sections are formed from advanced high strength steel (AHSS) blank. Numerical simulations by finite element analysis have also been performed to analyze strain variations during roll forming. The tracing of incremental strains at the edge may provide insights to solve buckling problems. From the analysis results, the behavior of buckling in flexible roll forming process can be predicted with relation between geometry parameters and longitudinal and shape error.