• Transactions of Materials Processing
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• v.30 no.3
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• pp.109-118
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• 2021

Recently, there has been an increased interest in the remanufacturing of mechanical parts using metal additive manufacturing processes in regards to resource recycling and carbon neutrality. DED (directed energy deposition) process can create desired metallic shapes on both even and uneven substrate via line-by-line deposition. Hence, DED process is very useful for the repair, retrofit and remanufacturing of mechanical parts with irregular damages. The objective of the current paper is to investigate the effects DED process parameters, including the effects of power and the scan speed of the laser, on deposition and residual stress characteristics for remanufacturing of mechanical parts using experiments and finite element analyses (FEAs). AISI 1045 is used as the substrate material and the feeding powder. The characteristic dimensions of the bead shape and the heat affected zone (HAZ) for different deposition conditions are obtained from the experimental results. Efficiencies of the heat flux model for different deposition conditions are estimated by the comparison of the results of FEAs with those of experiments in terms of the width and the depth of HAZ. In addition, the influence of the process parameters on residual stress distributions in the vicinity of the deposited region is investigated using the results of FEAs. Finally, a suitable deposition condition is predicted in regards to the bead formation and the residual stress.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.473-476
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• 2005

Mobility of tracked vehicles is dependent on performance of its power equipment and suspension systems. Especially, its road wheels, components of its suspension systems, play an important role in distributing the vehicle weight on the ground and preventing from misguiding tracks. In this study, the maximum force acted on multipurpose tracked vehicles driven on the worst condition was calculated. And then FE analyses were carried out to evaluate the strength of the road wheels under the maximum force condition. For quality evaluation of the road wheels, FE simulations and experimental works were carried out under specific slant loads. Residual deformation for the slant loads was investigated and commented upon.

• The Korean Journal of Ceramics
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• v.3 no.4
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• pp.257-262
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• 1997

Aluminum nitride(AIN) thin films were deposited on SiO$_2$/Si substrates by reactive sputtering for the application of SAW devices. The major deposition parameters such as pressure, nitrogen fraction, rf power, substrate distance were changed to find out the optimal condition for c-axis oriented thin films on an amorphous substrate. The effects of deposition parameters on the crystal structure, residual stress, and growth morphology of thin films were characterized by XRD, SEM, and TEM. The FWHM of (002) rocking curve of the films deposited at the proper condition was lower than 2.2$^{\circ}$(C=0.93$^{\circ}$). Cross-sectional TEM showed that self-aligned structure was developed just after slightly random growth at the initial stage. The frequency characteristics of test device fabricated from AIN thin films confirmed their piezoelectric property and applicability for SAW devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1468-1476
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• 1996

Surface integrity is dictated by the fabrication process of the metal part. In this work, steel specimens were prepared under various mechine conditions to achieve different degrees of deformation state. The tribological characteristics of the speciments were tested using a pin-on-disk type apparatus and other surface characterization tools. It is shown that though frictional characteristics are similar, the wear rate is significantrly affected by the properties of the surface. In the case of steel, surface cracks resulted in high wear despite the relatively high hardness of the specimen. Also, the sliding action were found to reduce the residual stress on the surface. These results indicate that there is a strong relationship between surface integrity and the tribological properties of steel, and therefore the machining condition should be optimized woth respect to tribological performance of a steel part.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.6 s.249
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• pp.615-621
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• 2006

Increased application of optical disks requires more improved dynamic stability of rotating disks. In this study, a new concept of controlling the processing conditions of injection molded disks was developed to improve vibration characteristics. The critical speed, which shows stiffness and dynamic stability of disk, is affected by the residual stress distribution; this varies as functions of distance from the gate and processing condition. The critical speed of disk was calculated with the initial stress taken into consideration, which was determined from injection molding simulation. Choosing melt temperature, mold temperature, filling speed and packing pressure as design parameters, critical speed is maximized with the method of response surface. It is shown that the stability of injection molded disk has been improved for the new condition obtained as a result of the study proposed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.5
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• pp.1-10
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• 2008

Residual stress caused in the weldments with high restraint force are often during welding observed in the weldments of large size nozzles or radial tanks. The reason is that quantitative analysis about thermal stresses during welding is lack for this weldments. To verify Finite Elements Method(FEM) theory, the temperature was measured with thermocouple in a real time in this paper. Also analysis of the thermal stress for welding condition is performed by ABAQUS program package on various welding condition in 304 stainless steel butt welding.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.932-938
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• 2002

In structural applications, brittle materials such as soda-lime glasses and ceramics are usually subjected to multiaxial stress state. Brittle materials with cracks or damage by foreign object impacts are apt to fracture abruptly from cracks, because of their properities of very high strength and low fracture toughness. But in most cases, the residual strength of structural members with damage has been tested under uniaxial stress condition such as the 4-point bend test. Depending upon the crack pattern developed, the strength under multiaxial stress state might be different from the one under uniaxial. A comparative study was carried out to investigate the influence of stress state on the residual strength evaluation. In comparable tests, the residual strength under biaxial stress state by the ball-on-ring test was greater than that under the uniaxial one by the 4-point bend test, when a small size indendation crack was introduced. In the case that crack having an angle of 90deg. to the applied stress direction, the ratio of biaxial to uniaxial flexure strength was about 1.12. The residual strength was different from crack angles to loading direction when it was evaluated by the 4-point bend test. The ratio of residual strength of 45deg. crack to 90deg. one was about 1.20. In the case of specimen cracked by a spherical impact, it was shown that an overall decrease in flexure strength with increasing impact velocity, and the critical impact velocity for formation of a radial and/or cone crack was about 30m/s. In those cases that relatively large cracks were developed as compared with the case of indented cracks, the ratio of residual strength under biaxial stress state to one uniaxial became small.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.601-607
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• 2007

In order to maintain constant residual chlorine in sedimentation basin, It is necessary to develop real time prediction model of residual chlorine considering water treatment plant data such as water qualities, weather, and plant operation conditions. Based on the operation data acquired from K water treatment plant, prediction models of residual chlorine in sediment basin were accomplished. The input parameters applied in the models were water temperature, turbidity, pH, conductivity, flow rate, alkalinity and pre-chlorination dosage. The multiple regression models were established with linear and non-linear model with 5,448 data set. The corelation coefficient (R) for the linear and non-linear model were 0.39 and 0.374, respectively. It shows low correlation coefficient, that is, these multiple regression models can not represent the residual chlorine with the input parameters which varies independently with time changes related to weather condition. Artificial neural network models are applied with three different conditions. Input parameters are consisted of water quality data observed in water treatment process based on the structure of auto-regressive model type, considering a time lag. The artificial neural network models have better ability to predict residual chlorine at sediment basin than conventional linear and nonlinear multi-regression models. The determination coefficients of each model in verification process were shown as 0.742, 0.754, and 0.869, respectively. Consequently, comparing the results of each model, neural network can simulate the residual chlorine in sedimentation basin better than mathematical regression models in terms of prediction performance. This results are expected to contribute into automation control of water treatment processes.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.4
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• pp.23-28
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• 1990

This study is to investigate the magnitude, direction and distribution of residual stresses in surface ground plate according to working conditions. The specimens were made of structural carbon steel and were machined in various grinding conditions. These were divided in two groups; heat-treated materials and non-heat-treated materials. In each working condition, let the ground specimen generate displacements using deflection-etching techniques. At the same time, these displacements were precisely measured with electronic micrometer. Through the relation formula between the plane stress and strain, which was derived using these measured data, the values of residual stress are calculated, and the results are analyzed. These results are as follows : 1. According to the working conditions in this experiment, it can be seen that the distribution of residual stress generally had same trend and the maximum residual stress remained in 20~30 ((${\mu}m$) beneath the surface. 2. It is observed that compressive residual stress changes into tensile stress in 5~20 (${\mu}m$) beneath the surface. It is suggested that such phenomenon is originated from the friction effect in grinding process. 3. As the hardness increases by the heat treatment, residual stress increases. 4. As the fatigue strength increases by the compressive residual stress, it is desirable that the dowm feed and table feed reduce. 5. It can be seen that the more great the down feed and table feed increase, the more close the changing point, where the stress changed from compressive to tensile, is colse to the surface. This is due to the resultant effects of the grinding temperature and resistence are larger than the effect of the friction.

• Review of Korea Contents Association
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• v.14 no.3
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• pp.37-42
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• 2016