1,721,027 research outputs found
A study on heat source equations for the prediction of weld shape and thermal deformation in laser microwelding
No full textIn the area of laser welding, numerous studies have been performed in the past decades using either analytical or numerical approaches, or both combined. However, most of the previous studies were process oriented and modeled conduction and keyhole welding differently. In this research, various heat source equations that have been proposed in previous studies were calculated and compared with a new model. This is to address the problem of predicting, by numerical means, the thermomechanical behavior of laser spot welding for thin stainless steel plates. A finite-element model (FEM) code, ABAQUS, is used for the heat transfer and mechanical analysis with a three-dimensional plane assumption. Experimental studies of laser spot welding and measurement of thermal deformation have also been conducted to validate the numerical models presented. The results suggest that temperature profiles and weld deformation vary according to the heat source equation of the laser beam. For this reason, it is essential to incorporate an accurate model of the heat source
Prediction of laser-spot-weld shape by numerical analysis and neural network
No full textThe finite element method (FEM) and neural network were applied for predicting the bead shape in laser spot welding of type 304 thin stainless steel sheets. The parameters of pulsed Nd:YAG laser spot welding such as pulse energy, pulse duration, sheet metal thickness, and gap between sheets were varied for various experiments and numerical simulations. The penetration depth and nugget size of spot welds measured for specimens without gap were compared with the calculated results to verify the proposed finite element model. Sheet metal thickness, gap size, and bead shape of the workpiece without gap were selected as the input variables for the back-propagation learning algorithm of the neural network, while the bead shape of the workpiece with and without gap was considered as its output variable. Various combinations of stainless steel sheet metal thickness were considered to calculate the laser-spot-weld bead shape of the workpiece without gap, which was then used as the input variable of neural network to predict the bead shape for various gap sizes. This combined model of finite element analysis and neural network could be effectively applied for the prediction of bead shapes of laser spot welds, because the numerical analysis of laser spot welding for the workpiece with gap between two sheets is highly limited
Thermomechanical analyses of laser precision joining for optoelectronic components
No full textThermomechanical analyses in laser-spot-welding (LSW) technique for a dual-in-line (DIP) type package has been studied experimentally and numerically to predict post-weld-shift (PWS). Experimental results show that the PWS of optoelectronic component changes sensitively depending on process parameters such as laser energy, beam delivery position, weld joint design and so on. This indicates that the PWS in laser packaging can be minimized by properly controlling the process parameters. A finite element method (FEM) has been carried out on the analysis of the effect of laser parameters and geometry of joint variation on PWS in laser packaging. And experimental studies of laser spot welding and electronic speckle pattern interferometry (ESPI) have also been conducted to validate the numerical model. A satisfactory agreement between the experimental results and FEM calculations suggests that the FEM provides one of the effective methods for predicting the PWS and optimizing package design in LSW technique for optoelectronic packaging. By using the numerical method above this work has led to an understanding of the effect of laser energy variation and joint design on thermal distortion. Hence the PWS can be controlled to produce a reliable laser module with high yield and high performance
A study on the prediction of the laser weld shape with varying heat source equations and the thermal distortion of a small structure in micro-joining
No full textIn the area of laser welding, numerous studies have been performed the past decades using either analytical or numerical approaches, or both combined. However, most of previous studies were process oriented and modeled differently in conduction and keyhole welding. In this research, the results of calculation using various heat source equations that have been proposed in previous studies were compared to the predictions of a new model. This model treats the problem of predicting, by numerical means, the thermo-mechanical behavior of laser spot welding for thin stainless steel plates. A finite element code, ABAQUS, is used for the heat-transfer analysis with a 3D model. Experimental studies of the laser spot welding have also been conducted to validate the numerical models presented. The results suggest that the predicted temperature profiles and weld dimensions vary according to the heat source equation of the laser beam. For this reason, it is essential to incorporate an accurate description of the heat source. Thermal and mechanical analyses of the laser micro-welding of a small structure are performed from these results. (C) 2002 Elsevier Science B.V. All rights reserved.This work was supported in part by the Brain Korea 21 Project
Numerical and experimental study on the thermal damage of thin Cr films induced by excimer laser irradiation
No full textSingle-shot laser damage of thin Cr films on glass substrates has been studied to understand the cracking and peeling-off mechanism. A mathematical model is developed for the calculation of transient heat transfer and thermal stresses in Cr films during excimer laser irradiation and cooling, the transient temperature, and the stress-strain fields are analyzed by using a three-dimensional finite-element model of heat flow. The finite-element program ABAQUS, with user subroutines, is adopted to perform the numerical analysis. A KrF excimer laser is used in experiments as a source of UV radiation. Morphological inspection of damaged Cr films is carried out by using scanning electron microscopy and the threshold fluences for visible damages are investigated for various film thicknesses. According to the numerical analysis for the experimentally determined cracking and peeling-off conditions, cracking is found to be the result of the tensile brittle fracture due to the excessive thermal stresses formed during the cooling process, while peeling off is found to be the combined result of films bulging from the softened glass surface at higher temperature and the tensile brittle fracture during the cooling process. (C) 1999 American Institute of Physics. [S0021-8979(99)09720-0]
A study on a vision sensor based laser welding system for bellows
No full textWelded metal bellows are commonly manufactured by welding pairs of washer-shaped diaphragms of thin sheet metal. Two types of welding operations are required: inner edge welding to make pairs of diaphragms, and outer edge welding to form a bellows by welding the number of pairs. In this study, the inner and outer edges of bellows were welded by using a CW Nd:YAG laser. For the inner edge welding, the Nd:YAG laser beam was directed at an angle of 45 degrees to the edge because of the limited accessibility. In the outer edge welding, welded pairs were fixed on a jig and compressed axially. The difference between the center of the bellows and that of a jig shaft causes an eccentricity, while the tolerance between a motor shaft and a jig shaft causes a wobble-type motion. A vision sensor based on the optical triangulation was used for seam tracking. Two image processing algorithms that can find a bellows edge were developed for inner and outer edge welding. A geometrical modeling that describes the difference between the position of the Nd:YAG laser spot on a bellows edge and that of the laser diode stripe of the vision sensor was established. The seam tracking by a two-axis Cartesian robot was performed after the vision sensor determined the positional deviation in each sampling. Experiments were performed with 0.1 mm thick stainless steel bellows and 0.5 mm outer edges pitch. The seam tracking by the sensed positional deviation and geometrical modeling was performed successfully with an acceptable error
Near-field optical patterning on chloromethylated polyimide
No full textNear-field scanning optical microscopy (NSOM) coupled with laser is used in nano-scale processing to make nano-scale dots or nano-scale structure. Nano-sclae processing using NSOM coupled with laser can be applied to photo- chemical etching process on crstalline silicon, to additive processes on some polymers, to subtraction processes on SAMs and other polymers. And it can be used to change material's optical properties in nano-scale geometry. As above, nano-scale processing using NSOM coupled with laser has an advantage that it can be applied to various processes. In this work, by using NSOM coupled with 266nm UV laser, nanoscale patterns were fabricated on chloromethylated polyimide(CMPI) films coated on silicon wafer. CMPI undergoes a fast photolysis under UV light. So, in the case of pattern fabrication on CMPI it is possible to fabricate patterns without development process. Possibilities for SMPI to be applied to nano-scale patterns fabrication were demonstrated. Compared to usual lithographic processes, the process proposed in this work is simple because development, one of steps to fabricate nano-scale patterns, is not needed. And the finite-difference-time-domain (FDTD) method was employed to simulate the energy intensity distribution in the near-field. The simulation was executed for NSOM tip and UV laser. The influence of aperture size and tip-sample distance on the resolution of the lithographic process is discussed from the simulation results. Comparison of some simulation results with corresponding experimental results could confirm the validity of the simulation model proposed
Assessment of acoustic metawindow unit through psychoacoustic analysis and human perception
Full text linkAcoustic metamaterials (AMMs) have become so far a resourceful solution for standard materials’ physical limitations, and their tuneable acoustic properties have shown potential for noise reduction and absorption over standard materials. At the same time, the building's features’ ergonomics value has been discovered to play a key role in indoor well-being. So AMM-based design features, such as windows, should be not only assessed through physical parameters (SPL, IL, and TL) but also investigated by psychoacoustics and human perception. Therefore, the methodology presented in this paper has been developed by firstly measuring and recording a previously developed acoustic metawindow (AMW) unit effect over seven environmental sound recordings, and secondly, merging soundscape-based questionnaires (performed in laboratory and online) and analytical physical and psychoacoustic assessment of the AMW unit. A significant quantitative impact on Loudness, Roughness, and Sharpness was achieved through the AMW unit (between 1 and 15.58 times the just noticeable difference of each psychoacoustic parameter). Moreover, participants qualitatively perceived an effect of neutralisation over the seven sound recordings with the AMW unit effect. After pondering the soundscape rates of the environmental recordings with and without the AMW unit effect separately, a percentage comparison highlighted that the first resulted as 7% less chaotic than the second one, 8% less eventful, 9% less vibrant, 23% more monotonous, and 22% more uneventful. In addition, sound sources related to middle-high frequency resulted specifically neutralised. Finally, Loudness was reduced by the AMW unit effect for the same environmental noise recordings in both the quantitative (psychoacoustic parameters) and qualitative (soundscape descriptors) methods. This research could be the first step toward a tuneable AMMs-based window design from physical, psychoacoustic and human perception points of view, creating a new paradigm for natural ventilation/heating control combined with noise reduction systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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