Materials Science Forum Vols. 580-582

Abstract: The micromachining technique for the fabrication of Fe-36%Ni (Invar®) microgrooves using a novel laser-induced wet etching system with an optical fiber as the light waveguide and machining tool is investigated. Microgrooves fabricated at the optimal process conditions with the proposed etching system have good surface morphology and dimensional accuracy. It is shown that the variation of etch profiles such as etch width and depth depends significantly upon the process parameters. Fiber damage, which is attributed to macrobubbles, can be dramatically reduced by adjusting the distance between the workpiece surface and the fiber terminal. The effects of process parameters such as laser power, scan speed, and threshold distance on etch width, depth, and crosssectional profiles are reported and the optimal process conditions to fabricate Invar® microgrooves with excellent shape and size are provided. Also, the applicability of the Invar® microgrooves for the manufacturing of shadow mask for an organic light emitting diode (OLED) is demonstrated.

Abstract: A spacer grid assembly, which is an interconnected array of slotted grid straps welded at the intersections to form an egg crate structure, is one of the core structural components for the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The commercial spacer grid assembly is spot-welded at the crossing points of the intersections by a TIG welding, LASER beam welding or Electron beam welding method. In this study, a LASER beam welding apparatus and a method for an inner strap welding has been proposed to obtain a longer and finer weld line and a smaller weld bead size for a spacer grid assembly for a PWR fuel assembly. Also a rapid welding and excellent weld quality have been achieved by the proposed welding apparatus and method.

Abstract: In recent years, many of automotive companies are using laser welding in car body assembly shop. Even though laser welding is better than resistance spot welding in many points, its application has been limited in special manufacturing areas. This paper describes a new laser welding system named by Remote Welding System (RWS) developed at Hyundai Motor Company and comprised of fiber laser, industrial robot and remote welding head. In this technology, welding efficiency can be dramatically improved since its remote welding head where laser continuously finds next welding stitches in advance. Therefore, positioning time of laser is near to zero. It is a good solution for welding in mass production.

Abstract: Experiment, finite element method, and theoretical analysis were performed to understand the fatigue phenomena of stainless steel overlap joining panels of different thickness partially penetrated by Nd:YAG Laser welding. The fatigue life curves are obtained through fatigue tests with various levels of applied load. The fatigue life is related with parameters such as thickness of plates, bead width, gap size, and penetration depth through experiment. To understand the fatigue test results, the effects of local stresses around a weld bead are calculated by FEM and theoretical stress analysis as a guide to the laser welding process control.

Abstract: The authors have applied laser peening without coating (LPwC) to metallic materials. Compressive residual stress nearly equal to the yield strength of the materials was imparted on the surface. Accelerating stress corrosion cracking (SCC) tests showed that LPwC had a significant effect to prevent the SCC initiation of sensitized materials of SUS304, Alloy 600 and the weld metal, Alloy 182. Push-pull type fatigue testing demonstrated that LPwC drastically enhanced the fatigue strength of fillet-welded rib-plates of SM490A.

Abstract: Laser material processing is a very rapidly advancing technology for various industrial applications, because of its many advantages. A few of its major advantages, less yet better controlled heat input, have been successfully exploited for the very critical application of aluminum alloy welding. This study suggested the source of weld-defects and its solution methods in welding a lithium ion battery with pulsed Nd:YAG laser. In the experiment, battery case has changed over joint geometry from side welding to flat welding. In the case of an electrolyte inlet seal welding, welding was carried out after pressing an Al ball and the degree of eccentricity, the contact length and the gap are presented as major parameters. With the Al ball indent improvement, the eccentricity and the gap were reduced and the contact length was increased. As a result of an experiment, a sound weld bead shape and crack-free weld bead were obtained.

Abstract: Due to manifold variants of joining processes feasible by laser, new possibilities have opened up in product design. An economic application of laser technology is usually connected to a laser adapted modification of the part design and a laser system technology, which meets the requirements of the chosen process in an optimum manner. For this contribution, three applications have been chosen in order to demonstrate the versatility of the laser joining technology.

Abstract: This paper describes laser and hybrid welding phenomena for the production of a sound and deep weld. The penetration of laser weld beads depended upon the power and power density at low and high welding speeds, respectively. It was reveled that the weld fusion zone geometry was formed by keyhole behavior and melt flows. It was also understood that the production of sound welds without porosity was attributed to no bubble formation in TIG-YAG hybrid welding of stainless steel and the disappearance of bubbles from the molten pool surface in YAG-MIG hybrid welding of aluminum alloy.

Abstract: The CW CO2 laser weldability of various Al-Mg alloys was investigated in terms of weld strength, ductility, Vickers hardness, formability and solidification cracking tendency when both autogenous and wire feed welding were made. Tensile strength of the laser welds was lower than that of the corresponding base metals, and it was linearly proportional to the Mg content of the weld metal. Formability and ductility of Al-Mg alloy laser welds were lower than those of corresponding base alloys as well. As for the weld solidification structure, as the Mg content increased in the weld metal, more equiaxed grains developed. Hence, softening of weld metal and solidification cracking were decreased in the weld metal containing higher Mg. Solidification cracking of Al-Mg alloy laser welds showed the highest susceptibility at 1.6 to 1.9wt.% Mg, and it decreased with further increase of Mg content.