1,721,204 research outputs found
Application of laser joining process for elimination of stair steps in steel laminate tooling
No full textLaminate tooling is a relatively fast and simple method of making large metal tools directly for various moulding processes in the rapid prototyping and manufacturing field. Metal sheets are usually cut, stacked, aligned and joined. In most cases, lasers are used only for the cutting of steel sheets in laminate tooling, but in this study, the use of the laser was expanded for improved laminate tooling. First, the laser was applied to eliminate the stair steps of steel laminates by filling them with molten filler metals. Then application of hard particles to molten filler metals for improved surface hardness of laminate tools was investigated. To achieve this goal, a CO2 laser system composed of a CO2 laser, a five-axis CNC table, an automatic feeding equipment of filler metal and flux and a personal computer was developed. Various experiments on filling stair steps and hardening were performed and the results were verified and estimated
High-precision digital microflow controllers using fluidic digital-to-analog converters composed of binary-weighted flow resistors
No full textThis paper presents digital microllow controllers (DMFC), where a fluidic digital-to-analog converter (DAC) is used to achieve high-linearity and fine-levels in flow-rate control for applications to precise biomedical dosing systems. The fluidic DAC, composed of binary-weighted flow resistance, is designed to control the flow-rate based on the ratio of the flow resistance to achieve finer flow-rate levels. The binary-weighted flow resistance has been specified by a serial or a parallel connection of an identical flow resistor to improve the linearity of the How-rate control by making the flow-resistance ratio insensitive to the size errors of flow resistors in micromachining process. We have designed and fabricated three types of 4-digit DMFC: Prototype S and P with serial and the parallel combinations of an identical flow resistor and Prototype V with width-varied flow resistors. In the experimental study, we perform static DMFC tests at forward and backward flow conditions as well as dynamic DMFC tests at pulsating flow conditions. The present DMFC shows the nonlinearity of 5.0% and finer flow-rate levels of 16(2(N)) for 4(N) digital valves. From the measured flow-rate deviation due to micromachining errors, Prototype S and P show 27.2 % and 27.6 % of the deviation measured from Prototype V, respectively; thus, verifying that Prototype S and P are less sensitive to the micromachining errors than Prototype V
Digital microflow controllers using fluidic digital-to-analog converters with binary-weighted flow resistor network
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A study on the plasma-augmented laser welding for small-diameter STS tubes
No full textLaser welding is an effective method to join small, thin parts, such as small stainless steel tubes. Laser power can be precisely adjusted to melt only a small part of the tubes, and the heat-affected zone can be controlled accurately. But laser welding systems are generally expensive; therefore, the welding speed is restricted by the maximal laser power capacity. Also, the laser welding method is very sensitive to the joint clearance and tolerance, and this makes laser welding difficult to obtain consistent welding qualities over time. Recently, solutions of these problems are being tried by introducing another heat source, such as a plasma arc. Additional plasma arc energy can make the overall welding speed faster, and sensitivity to the joint clearance can be reduced by the plasma arc. Plasma-augmented laser welding (PALW) is one of this kind of welding method, where a plasma arc is used to augment the laser welding. In this study, plasma arc welding (PAW) was added to the existing single-laser heat source to join the conventional V-grooved butt joint of thin stainless steel strips for manufacturing small-diameter stainless steel tubes. The effect of the welding speed enhancement was investigated by experiments and simulations. Finite element (FE) thermal analysis considering multiple reflections of a laser beam in the V-groove was conducted and verified
Abusive head traumas in 4 infants
Full text linkPediatric abusive head trauma (AHT) is a serious, repeated child abuse that causes grave brain damage. In Korea, AHT cases have been reported rarely, especially infants. We present 4 cases of AHT in infants diagnosed in our institution during last 2 years. We collected the demographic data, ophthalmologic examination, imaging study, and outcomes. The mean age was 7.2 months, and 2 infants were girls and the others were boys. All four were admitted with no history of head trauma, and among them 2 patients presented with an episode of seizure and respiratory arrest with no history of head trauma. The initial mental status was semi-coma in 3 cases, and stupor in 1 case. There were multiple retinal hemorrhages in both eyes in 2 cases; one had multiple old fractures on the extremities and another child showed multiple skull fractures. All patients underwent emergent surgery for acute bilateral subdural hemorrhages; 3 had craniotomy and another had burr-hole drainage. Two children expired and the other 2 are in vegetative status. The AHT has recently become more frequent in Korea so that neurosurgeons must alert AHT even in infants with head trauma. Copyright © 2020 Korean Neurotraumatology Society This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited
Measurement of tensile properties using filament wound ring specimens
No full textIn this study. the tensile properties of a filament wound ring specimens were evaluated by split disk test and compared to the theoretical values obtained by the rule of mixtures. The circumference-wound ring specimens were prepared from 4 types of material systems. The research results showed that the measured strengths of the composite systems were considerably lower than the theoretical values due to the local bending stresses around the split disk edges. For the measurement of elastic moduli of the filament wound ring specimens, the effect of friction oil the strain of the ring must be taken into account. But the effect of friction between the split disk fixture and the ring specimen can be eliminated by averaging the moduli for loading and unloading state with maintaining the same crosshead rates. The measured elastic moduli of ring showed very good agreement with the theoretical values
Development of DNA chip microarrayer
No full textA microarrayer system was developed mainly for manufacturing DNA chips. The 3-axis robot was designed to automatically collect samples from 96- or 384-well microtiter plates using up to 16 simultaneously moving pens and to deposit them on a surface-modified slide glass. This is followed by a wash/dry operation in a clean station. The cycle is repeated with a new set of samples. This system can deposit cDNA or oligonucleotides with spot intervals of 150 mu m and the spot size of 80 mu m, thus allowing a high density DNA chip containing about 5,000 spots per cm(2). The entire procedure is controlled by the Visual C++ program that was written in our laboratory by using a personal computer with Pentium 100 CPU
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