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지르코니아 분말의 치밀화와 소결거동 : II. 소결거동
박홍채,김겸,김영우,이윤복,오기동,Park, H.C.,Kim, K.,Kim, Y.W.,Lee, Y.B.,Oh, K.D.,Riley, Frank L. 한국세라믹학회 1993 한국세라믹학회지 Vol.30 No.6
Sintering behaviour of zirconia powders prepared by different processing treatment was discussed. About >99% densities of theoretical were obtaiend on sintering at 140$0^{\circ}C$ for 2h in case of 300MPa uniaxially cold-pressed compact. But the lower densities were obtained on sintering above this temperature due to abnormal grain growth enabling the tetragonal to monoclinic phase transformation during cooling resulted in microcracks. All kinds of different dried powders exhibited nearly the same shrinkage behaviour with end-point shrinkage between 19 and 20%, and had maximum shrinkage rate (0.99~1.27%/min) around 120$0^{\circ}C$. During whole sintering process densification was mainly governed by grain growth and rearrangement of agglomerates. Heterogeneous abnormal grain growth and abrupt decrease in shrinkage were observed when continuous interagglomerate pore collapsed into isolated pores.
박기동(K. D. Park),송정한(J. H. Song),이혜진(H. J. Lee),이근안(G. A. Lee),이낙규(N. K. Lee),이형욱(H. W. Lee),나승우(S. W. Ra) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
There have been strong demands for micro size screw with high precision due to miniaturization and integration trends for electronic products such as Hard Disk Drives. The thread rolling process for screw manufacturing are lower unit cost, reduced material utilization, and superior mechanical properties compared to the machining process. But little work has been done on the thread rolling of micro size screw. In this paper, we investigate thread rolling process using Finite Element Analysis (FEA) and parameter study for screw. In this paper, we investigate thread rolling process using Finite obtain the material property and to implement into the FE tool for the numerical simulation. In case that parameter of relative position of dies is half length of pitch for maintaining the continuous thread profiles, we found that shear friction factor was 0.9 during the thread rolling process using FEA. We are trying to develop the thread rolling process using the FE-simulation to manufacture screws which have been commonly produced from the industrial level fabrication at present.
AZ31B 합금판재 성형관련 기초물성 실험 및 해석 연구
김세호(S. H. Kim),박기동(K. D. Park),장정호(J. H. Jang),김경태(K. T. Kim),이형욱(H. W. Lee),이근안(G. A. Lee),김기풍(K. P. Kim),이용신(Y. S. Lee) 한국소성·가공학회 2008 소성가공 : 한국소성가공학회지 Vol.17 No.7
In this paper, tension tests and formability tests are performed to construct a database related to mechanical properties and the formability of the AZ31B Mg alloy sheet. A forming test with a hemi-spherical punch is conducted at varying temperatures to establish a forming limit diagram. In order to verify the applicability of the analysis using the conventional flow hardening model, a finite element analysis is performed on the hemi-spherical punch forming process and the results are compared with experimental ones. The study investigates problems involving a computational analysis that does not consider flow softening of the magnesium alloy at elevated temperatures.