• Journal of Welding and Joining
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• v.28 no.5
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• pp.51-57
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• 2010

Brittle microstructure created in a heat affected zone (HAZ) during the welding of low alloy steel can be eliminated by post-weld heat treatment (PWHT). If the PWHT is not possible during a repair welding, the controlled bead depositions of multi-pass welding should be applied to obtain tempering effect on the HAZ without PWHT. In order to anticipate and control the tempering effect during the temper bead welding, the definition of temperature curve obtained from the analytical solution was suggested in this research. Because the analytical solution for heat flow is expressed as a mathematical equation of weld parameters, it may be effective in anticipating the effect of each weld parameter on the tempering in HAZ during the successive bead depositions. The reheating effect by the successive bead layer on the brittle coarse grained HAZ formed by earlier bead deposition was estimated by comparing the overlapped distance between the temperature curves in the HAZ. Three layered weld specimens of SA508 base metal with A52 filler were prepared by controlling heat input ratio between layers. The tempering effect anticipated by using the overlapped distance between the temperature curves was verified by measuring the micro-hardness distribution in the HAZ of prepared specimens. The temperature curve obtained from analytical solution was expected as a good tool to find optimal temper bead welding conditions.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.77-83
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• 2013

3D packaging technology using TSV (Through Silicon Via)has been studied in the recent years to achieve higher performance, lower power consumption and smaller package size because electrical line is shorter electrical resistivity than any other packaging technology. To stack TSV chips vertically, reliable and robust bonding technology is required because mechanical stress and thermal stress cause fracture during the bonding process. Cu pillar/solder ${\mu}$-bump bonding process is usually to interconnect TSV chips vertically although it has weak shape to mechanical stress and thermal stress. In this study, we suggest Insert-Bump (ISB) bonding process newly to stack TSV chips. Through experiments, we tried to find optimal bonding conditions such as bonding temperature and bonding pressure. After ISB bonding, we observed microstructure of bump joint by SEM and then evaluated properties of bump joint by die shear test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.667-672
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• 2016

This study presents results of an experimental investigation of the laser-arc, hybrid, butt welding process of SS400 structural steel. Welding parameters including laser power, welding current and speed were varied in order to obtain one-pass, full-penetration welds without defects. The conditions that resulted in optimal beads were identified. After welding, hardness measurements and microstructure observations were carried out in order to study weld properties. The mechanical properties of both the base material and welded specimen were compared based on the results of tensile strength measurements. The yield and tensile strengths were found to be similar.

• Special Issue of the Society of Naval Architects of Korea
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• 2006.09a
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• pp.112-121
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• 2006

The vertical displacement of a ship on the basis of the sea level is an important parameter for its stability and control. To indicate the displacement on operating conditions, "draft marks" are carved on the hull of the ship in various ways. One of the methods is welding. The position, shape and size of the marks are specified on the shipbuilding rules by classification societies to be checked by shipbuilders. In most cases, high-skilled workers do the welding along the drawing for the marks and welding bead becomes the marks. But the inaccuracies due to human errors and high labor cost increase the needs for automating the work process of the draft marks. In the preceding work, an indoor robot was developed for automatic marking system on flat surfaces and the work proved that the robot welding was more effective and accurate than manual welding. However, many parts of the hull structure constructed at the outdoor are cowed shapes, which is beyond the capability of the robot developed for the indoor works on the flat surface. The marking on the curved steel surface requiring the 25m elevations is one of the main challenges to the conventional robots. In the present paper, the robot capable of climbing vertical curved steel surfaces and performing the welding at the marked position by effectively solving the problems mentioned earlier is presented.

• Journal of Korean Society for Quality Management
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• v.45 no.4
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• pp.1003-1020
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• 2017

Purpose: The purpose of this study is to find the optimum working conditions for spot welding of wire Cu alloys to achieve high-level quality. The parts subject to spot welding are brush card assemblies, which are the main module of the electric movement method of the car seat. Methods: In this study, the signal-to-noise ratio(SN ratio) and the loss function [L(y)] are used as Taguchi method for dynamic characteristics. Results: The results of the study are as follows. First, the analysis of variance using SN ratio showed 6 significant factors(p = 0.1% or less) among 7 factors except press force. Second, the optimal design of the dynamic characteristics is the tip exchange cycle: 50,000 ea., the welding time is 110 ms, the pressing force is 11 kgf/cm2, the rise time is 40 ms, and the tip dressing is 3,000 ea., Tip angle is 12o and electric current is 1,800 A. Conclusion: The validity of the spot welding process of the manufacturer's brush card assembly was verified and proved to be consistent with the study results. The results of this study are expected to standardize the welding conditions and guarantee the quality level required by the customers.

• Journal of Korean Society for Quality Management
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• v.48 no.1
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• pp.51-68
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• 2020

Purpose: The primary objective of this research is to develop the optimal operating conditions as well as their associated design spaces for a Cryogenic Submerged Arc Welding(SAW) process by improving its quality and productivity simultaneously. Methods: In order to investigate functional relationships among quality characteristics and their associated control factors of an SAW process, a stepwise design of experiment(DoE) method is proposed in this paper. Based on the DoE results, not only a multi-dimensional design space but also a safe operating space and normal acceptable range(NAR) by integrating statistical confidence intervals were demonstrated. In addition, the optimal operating conditions within the proposed NAR can be obtained by a robust optimal design method. Results: This study provides a customized stepwise DoE method (i.e., a sequential set of DoE such as a factorial design and a central composite design) for Cryogenic SAW process and its statistical analysis results. DoE results can then provide both the main and interaction effects of input control factors and the functional relationships between the input factors and their associated output responses. Maximizing both the product quality with high impact strength and the productivity with minimum processing times simultaneously in a case study, we proposed a design space which can provide both acceptable productivity and quality levels and NARs of input control factors. In order to confirm the optimal factor settings and the proposed NARs, validation experiments were performed. Conclusion: This research may provide significant contributions and applications to many SAW problems by preparing a standardization of the functional relationship between the input factors and their associated output response. Moreover, the proposed design space based on DoE and NAR methods can simultaneously consider a number of quality characteristics including tradeoff between productivity and quality levels.

• Structural Engineering and Mechanics
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• v.88 no.3
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• pp.239-249
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• 2023

The Radial Point Interpolation Method (RPIM) has been proposed to overcome the difficulties associated with the use of the Radial Basis Functions (RBFs). The RPIM has the following properties: Simple implementation in terms of boundary conditions as in the Finite Element Method (FEM). A less expensive CPU time compared to other collocation meshless methods such as the Moving Least Square (MLS) collocation method. In this work, we propose an adaptive high-order numerical algorithm based on RPIM to simulate the thermoviscoplastic behavior of a material mixing observed in the Friction Stir Welding (FSW) process. The proposed adaptive meshfree RPIM algorithm adapts well to the geometric and physical data by choosing a good shape parameter with a good precision. Our numerical approach combines the RPIM and the Asymptotic Numerical Method (ANM). A numerical procedure is also proposed in this work to automatically determine an improved shape parameter for the RBFs. The efficiency of the proposed algorithm is analyzed in comparison with an iterative algorithm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.133-138
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• 2019

This study evaluated the tensile properties of SAPH440, a hot-rolled steel for automotive structural applications, based on GMAW lap welding, the welding current, the welding voltage, and the feed rate. Tensile tests were performed according to the joint parameters of the GMAW process, for which specimens were fabricated according to KS B ISO 9018 by lap welding. The bead appearance was observed in each condition, and the weldability was evaluated by the tensile test. Higher the welding current resulted in a deeper weld, but the tensile strength was not significantly different from when the parameter was fixed due to the fracture of the base material. When the current was higher than the voltage, as in the case of a welding current of 200 A and welding voltage of 17 V, a large amount of spatter is generated, the welding is unstable, and the welded part breaks. Higher the voltage resulted in the bead not causing defects in general, and it also affected the weldability. If the current and voltage were too low, the welding was not performed normally, and the tensile strength could not be measured. However, as the current increased, the increase of the voltage and the feed rate did not affect the tensile strength.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.322-325
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• 2000

In the previous report1), the grinding characteristics of quartz were investigated. In this paper, the grinding mechanisms of brittle materials including ceramics and quartz are modeled and a new parameter SDR(Surface roughness Direction Ratio) is proposed to characterize the grinding mechanisms of such materials. A set of experiments were performed to verify the effectiveness of the suggested parameter. The experimental results indicate that the plastic deformation is the dominant material removal mode at the grinding conditions which show the higher value of SDR. In the case of quartz, the material was removed by brittle fracture in a lower value of SDR and by plastic deformation in a higher value of it. SDR is not affected by wheel mesh size when brittle fracture occured. But in the plastic deformation case, SDR value increases with wheel mesh size.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.5
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• pp.70-75
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• 1999

Adaptive control in the robotic GMA(Gas Metal Arc) welding is employed to monitor the information about weld characteristics and process paramters as well as modification of those parameters to hold weld quality within the acceptable limits. Typical characteristics are the bead geometry composition micrrostructure appearance and process parameters which govern the quality of the final weld. The main objectives of this paper are to realize the mapping characteristicso f penetration through the learning. After learning the neural network can predict the pene-traition desired from the learning mapping characteristic. The design parameters of the neural network estimator(the number of hidden layers and the number of nodes in a layer) were chosen from an error analysis. partial-penetration single-pass bead-on-plate welds were fabricated in 12mm mild steel plates in order to verify the performance of the neural network estimator. The experimental results show that the proposed neural network estimator can predict the penetration with reasonable accuracy and gurarantee the uniform weld quality.