• Journal of Powder Materials
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• v.29 no.4
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• pp.309-313
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• 2022

In this study, additive manufacturing of a functionally graded material (FGM) as an alternative to joining dissimilar metals is investigated using directed energy deposition (DED). FGM consists of five different layers, which are mixtures of austenitic stainless steel (type 316 L) and low-alloy steel (LAS, ferritic steel) at ratios of 100:0 (A layer), 75:25 (B layer), 50:50 (C layer), 25:75 (D layer), and 0:100 (E layer), respectively, in each deposition layer. The FGM samples are successfully fabricated without cracks or delamination using the DED method, and specimens are characterized using optical and scanning electron microscopy to monitor their microstructures. In layers C and D of the sample, the tensile strength is determined to be very high owing to the formation of ferrite and martensite structures. However, the elongation is high in layers A and B, which contain a large fraction of austenite.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.7-13
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• 2002

A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies" Requirements for Approval of $CO_2$ Laser Welding Procedures" Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to $-50^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.ximum hardness.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.222-228
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• 2002

A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies′ Requirements for Approval of $CO_2$ Laser Welding Procedures". Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to -5$0^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.51-56
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• 2002

The weld seam tracking system for arc welding process uses various kinds of sensors such as arc sensor, vision sensor, laser displacement sensor and so on. Among the variety of sensors available, electro-magnetic sensor is one of the most useful methods especially in sheet metal butt-joint arc welding, primarily because it is hardly affected by the intense arc light and fume generated during the welding process, and also by the surface condition of weldments. In this study, a dual-electromagnetic sensor, which utilizes the induced current variation in the sensing coil due to the eddy current variation of the metal near the sensor, was developed for arc welding of sheet metal I-butt joints. The dual-electromagnetic sensor thus detects the offset displacement of weld line from the center of sensor head even though there's no clearance in the joint. A set of design variables of the sensor was determined far the maximum sensing capability through the repeated experiments. Seam tracking is performed by correcting the position of sensor to the amount of offset displacement every sampling period. From the experimental results, the developed sensor showed the excellent capability of weld seam detection when the sensor to workpiece distance is near less than 5 ㎜, and it was revealed that the system has excellent seam tracking ability for the I-butt joint of sheet metal.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.34-38
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• 2003

It has been used many kinds of horizontal butt-welding methods at block-to-block erection stage in shipbuilding companies. For examples, some companies use conventional FCAW process with one side or both sides groove joint welding, others use carriage with torch holder type mechanized welding method. Although lots of efforts were done until now, some problems in quality and productivity still remain in ship's hull welding. In this study, we have attempted to raise productivity and quality on horizontal position of welding with following 3 items. 1) Prepare groove condition with no root gap for making easy fit-up work. 2) Develop improved MAG (100% $CO_2$ gas shielding) welding process with solid wire for making sound root bead from one side. 3) Develop and apply quite new automatic welding carriage. The stability of new welding process was confirmed by conducting mechanical tests of weldments to verify the soundness of weldments.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.23-29
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• 2001

In this study, a preview-sensing visual sensor system is constructed far weld seam tracking in GMA welding. The visual sensor system consists of a CCD camera, a diode laser system with a cylindrical lens, and a band-pass-filter to overcome the degrading of image due to spatters and/or arc light. Among the image processing methods, Hough transform method is compared with the central difference method from a viewpoint of the capability for extracting the accurate feature position. As a result, it was revealed that Hough transform method can more accurately extract the feature positions and it can be applied to real time weld seam tracking. Image processing which includes Hough transform method is carried out to extract straight lines that express laser stripe. After extracting the lines, weld joint position and edge points are determined by intersecting the lines. Even though the image includes a spatter trace on it, it is possible to recognize the position of weld joint. Weld seam tracking was precisely implemented with adopting Hough transform method, and it is possible to track the weld seam in the case of offset angle is in the region of $\pm$ $15^{\circ}$.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.39-44
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• 2003

The welded specimens were made by butt welding of the 2 wires of 50mm length using the pulsed YAG laser. The laser welded wires were tested for investigating the shape memory effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was Investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.100-100
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• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.280-288
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• 2016

This study proposes improved welding tools for magnesium alloys. Two types of tools were used for friction stir welding (FSW). The effect of the welding tools on the FSW joints was investigated with a fixed welding speed of 200mm/min and various rotation speeds of 400 to 800 rpm. After FSW, the joints were cross-sectioned perpendicular to the welding direction to investigate the defects. A tensile test and Vickers hardness test were conducted to identity the mechanical properties of the joints. Defects were observed when the rotation speed was 400 rpm, regardless of the welding tool, and the amount of defects tended to decrease with increases in rotational speed. Defect-free welds were obtained when the rotation speed was 800 rpm. The best weld quality was acquired using the C type welding tool. The rotation speed of 800 rpm and welding speed of 200 mm/min produced the best joining properties. The ultimate tensile strength, yield strength, and elongation of the welded region were 90.0%, 69.1%, and 83.2% those of the base metal, respectively.

• Composites Research
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• v.36 no.6
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• pp.441-447
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• 2023

Recently, as demand for high-strength, lightweight materials has increased, there has been great interest in joining with metals. In the case of mechanical bonding, such as bolting and riveting, chemical bonding using adhesives is attracting attention as stress concentration, cracks, and peeling occur. In this paper, surface treatment was performed to improve the adhesive strength, and the change in adhesive strength was analyzed. For the adhesive strength test were conducted with Carbon Fiber Reinforced Plastic(CFRP), CR340(Steel), and Al6061(Aluminum), and laser and plasma surface treatment were used. After plasma surface treatment, the adhesive strength improved by 7.3% and 39.2% in CFRP-CR340 and CFRP-Al6061, respectively. CR340-Al6061 was improved by 56.2% in laser surface treatment. Surface free energy(SFE) was measured by contact angle after plasma treatment, and it is thought that the adhesion strength was improved by minimizing damage through a chemical reaction mechanism. For laser surface treatment, it is thought that creates a rough bonding surface and improves adhesive strength due to the mechanical interlocking effect. Therefore, surface treatment is effect to improve adhesive strength, and based on this paper, the long-term fatigue test will be conducted to prevent fatigue failure, which is a representative cause of actual structural damage.