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김재구(Jaegu Kim),조성학(Sunghak Cho),장원석(Wonseok Chang),나석주(Suck-Joo Na),황경현(Kyunghyun Whang) 한국레이저가공학회 2007 한국레이저가공학회지 Vol.10 No.4
In this paper, we suggested the femtosecond laser processing using the mask which makes Gaussian spatial beam distribution to a normalized distribution by Fresenel diffraction. Holography pattern of the size of 320 × 320 ㎛² on the Cr thin film on glass substrate with a pixel size of 5 × 5 ㎛² was fabricated according to the pattern generated by the iterative Fourier transform algorithm (IFTA) algorithm. We analysed the damage threshold with an assumption the power distribution as Gaussian profile as 45 mJ/㎠, The regenerated image of letters through the diffractive pattern was well recognized at the screen.
Laser Assisted Additive Manufacturing by Rotating Metal Wire Feeder
김재구(Jaegu Kim),이창우(Chang-Woo Lee) Korean Society for Precision Engineering 2018 한국정밀공학회지 Vol.35 No.9
Chiefly, the metal wire-feed and laser additive manufacturing (AM) is a deposition process to produce larger mechanical parts required for aerospace, shipbuilding, automobile, and mold repair industries. The principal advantage of metal wire-feed AM is the high deposition rate compared to an assisted metal powder-feed AM, and metal powder-based fusion AM. During the wire-feed deposition process, the feed orientation is a critical parameter managed at all stages of processing. A better surface finish is attained when the melted wire flows smoothly through the process, and a wire feed direction that is utilized opposite to the deposition direction yields the best results. To improve the surface quality of metal 3D printing, we designed a rotating wire feeder, the feed direction of which varies with the direction of deposition; all free-form lines which thus exhibit identical surface qualities. Here, we use a rotating stage to orient the wire-feed direction according to the bead direction, a slip ring to supply electrical power to the feeder motor, and utilized two rotating channels on a plate to supply Ar gas and extract fumes safely during the processing stage. We evaluated the rotating wire feeder by building various parts as needed to the equipment.
김재구(Jaegu Kim) 강원대학교 기초과학연구소 1986 기초과학연구 Vol.3 No.-
선형화된 최소 초중력이론의 구조를 기약 초장을 이용하여 분석했다. superspin 3 / 2의 기약 초장은 선형화된 Weyl 초중력을 기술함을 보였다. 이 Weyl 초중력을 보조장과 결합하여 선형화된 Poincare 초중력을 구했다. The structure of the minimal supergravity is analyzed at linear level by using irreducible superfields. It is shown that the irreducible superfield with superspin 3 / 2 describes the linearized Weyl supergravity. The linearized Poincar'e supergravity is obtained by coupling the Weyl supergravity with compensating superfield.
김재구(JaeGu Kim),구동식(DongSik Gu),최병근(ByeongKeun Choi) 한국소음진동공학회 2011 한국소음진동공학회 학술대회논문집 Vol.2011 No.4
The acoustic emission (AE) technique is a well-known non-destructive test technique, both in research and for industrial applications. It is mainly used to monitor the onset of cracking processes in materials and components. Predicting and preventing the crack phenomenon has attracted the attention of many researchers and has continued to provide a large incentive for the use of condition monitoring techniques to detect the earliest stages of cracks. In this research, goal is in grasping features of AE signal caused by crack growth. The envelope analysis with discrete wavelet transform (DWT) is used to find the characteristic of AE signal. To estimate feature of divided into three by crack length, the time waveform and the power spectrum were generated by the raw signals and the transferred signal processed by envelope analysis with DWT.