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RISS 인기검색어
- 검색키워드
- 저자 : Dave F. Farson (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Numerical analysis of weld pool oscillation in laser welding
조정호,Dave F. Farson,Kendall J Hollis,John O. Milewski 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.4
Volume of fluid (VOF) numerical simulation was used to investigate melt flow and volumetric oscillation of conduction-mode pulsedlaser weld pools. The result is compared to high speed video stream of titanium laser spot welding experiment. The total simulation timeis 10ms with the first 5 ms being heating and melting under constant laser irradiation and the remaining 5 ms corresponding to resolidificationof the weld pool. During the melting process, the liquid pool did not exhibit periodic oscillation but was continually depressedby the evaporation recoil pressure. After the laser pulse, the weld pool was excited into volumetric oscillation by the release ofpressure on its surface and oscillation of the weld pool surface was analyzed. The simulation model suggested adjusting thermal diffusivityto match cooling rate and puddle diameter during solidification which is distinguishable from previous weld pool simulation. Thefrequency continuously increased from several thousand cycles per second to tens of thousands of cycles per second as the weld poolsolidified and its diameter decreased. The result is the first trial of investigation of small weld pool oscillation in laser welding althoughthere have been several reports about arc welding.
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Analysis of penetration depth fluctuations in single-mode fibre laser welds
Cho, Jung-Ho,Farson, Dave F,Reiter, Matt J Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.11
<P>Penetration depth fluctuations of single-mode fibre laser welds made with long focal length optics and the effects of sinusoidal laser power modulations were studied. It was found that the welds had a high aspect ratio and were subject to spiking defects. The magnitude of the penetration fluctuations tended to be larger for deeper welds. The weld penetration profiles had positive maximal Lyapunov exponents and broadband, aperiodic power spectral densities with most of the signal power in the spectral band from 0 Hz to 1 kHz. The amplitude of the frequency response of the laser penetration to large amplitude laser power modulations decreased at rates varying from −20 to −60 dB decade<SUP>−1</SUP> at modulation frequencies from 100 Hz to 1 kHz. It was found that sinusoidal laser power modulation at frequencies from 900 Hz to 3 kHz decreased the aperiodic penetration fluctuations.</P>
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Weld pool flows during initial stages of keyhole formation in laser welding
Cho, Jung-Ho,Farson, Dave F,Milewski, John O,Hollis, Kendall J Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.17
<P>Weld pool transport phenomena during the transition from conduction-mode laser spot welding to keyhole laser spot welding of titanium were studied by numerical simulation. A range of laser powers were simulated and temperature dependent evaporation recoil pressure and cooling were applied as boundary conditions on the weld pool surface. Simulation results predicted a complex time-varying flow pattern during weld pool development. The surface-normal flow at the weld pool centre oscillated between upwards and downwards during the simulation time due to interaction of competing effects of evaporation recoil and surface tension pressures and laser heating and evaporation cooling. The results show that the laser weld pool flow dynamics play a key role during the transition from conduction-mode laser welding to keyhole welding.</P>
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Ultrashort Pulsed Laser Machining for Biomolecule Trapping
최해운,Dave F. Farson,L. James Lee,이호 한국광학회 2009 Current Optics and Photonics Vol.13 No.3
Ultrashort pulse laser drilling of polycarbonate track-etched membrane (pTEM) material was used to fabricate a mouse embryo cell trapping device. Holes with a diameter of 2 μm to 5 μm were fabricated on a 10 μm thick membrane using a femtosecond laser with a 150 fs pulse width and 775 nm wavelength and multiple-pulse irradiation. In cell trapping tests, the overall cell occupancy of the machined holes in the fabricated pTEM was found to be more than 80%. The results of a single pulse and multiple pulse irradiation were compared in terms of the surface quality. It was generally found that a single pulse with high energy was less desirable than irradiation with multiple pulses of lower energy.
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Characteristics of Sn-2.5Ag flip chip solder joints under thermal shock test conditions
양경춘,이성혁,김종민,최영기,Dave F. Farson,신영의 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.2
The interfacial reaction between Cu pad coated with Au/Ni and solder bump of flip chip package, using Sn97.5wt.%-Ag2.5wt%, was studied under thermal shock stress. All joints were subjected to thermal shock test with - 65℃/+150℃ temperature range. For the Sn-2.5Ag solder, a scallop-like (Cu,Ni)6Sn5 intermetallic compound was formed in the solder matrix after 20 cycles of thermal shock. (Cu,Ni)6Sn5 was detached from the interface as (Ni,Cu)3Sn4 grew underneath the (Cu,Ni)6Sn5 IMC(Intermetallic Compound), whereas the elements of Sn, Ni and Cu were moved by interdiffusion at the interface between solder alloy and Cu pad. The composition of the IMCs in the solder joints and elemental distribution across the joint interfaces were quantitatively measured with EPMA (electron probe micro analysis). Finally, it was found that the crack initiation point and its propagation path could be influenced by the thermal shock conditions, two underfills, and their properties.
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