Papers by Keyword: Laser Welding

Abstract: Nowadays, dissimilar materials welding, especially between metal to plastics, has been become the hottest issue. The objective of the study is to investigate the effects of physical properties of plastics on the weldability and the quality of the dissimilar materials welding between SUS304 stainless steel and plastics. In experiment, the lap joint configuration with SUS304 put on the top was applied. The welding speed, focal position, and keeping period of weld after welding were varied. The results indicated that the decomposition temperature of plastics affected both weldability and quality of joint after welding. Moreover, crazing was a prominent property to be considered for long-term use of the dissimilar materials welding as the specimen could fracture by itself after a period of time without any application of the external load.

Abstract: Silicon carbide fiber reinforced silicon carbide composite (SiC/SiC composite) is expected as a potential replacement of the current Zircaloy fuel cladding in the light-water reactor because of its many superiorities, where it is necessary to develop the end-cap seal of SiC/SiC composite cladding. In this research, the applicability of diode laser irradiation for joining between Zircaloy and SiC/SiC composite tubes was examined based on the caulking method. As the method for fitting two tubes, the screw cutting was conducted for the inner face of Zircaloy tube and the outer surface of SiC/SiC composite. In addition, as a method to improve the joinability of Zircaloy and SiC/SiC composite, titanium nanopowder was inserted into a gap between two tubes. The laser beam irradiation was circumferentially applied to the outer surface of Zircaloy tube. Although the mechanical caulking joint was successfully produced, the airtightness was insufficient for the end-caps of SiC/SiC composite cladding. However, the good adhesion between Zircaloy and SiC/SiC composite was partially produced as the result of the generation of all proportional solid solution between titanium and zirconium. Namely, it can be concluded that the circumferential diode laser irradiation with inserting titanium nanopowder between Zircaloy and SiC/SiC composite tubes would have a good potential for producing the caulking joint of two tubes.

Abstract: The scope of this paper is to examine the improvement from laser welding by an innovative beam wobbling head towards the welding of tailored blanks parts, widely used in automotive to develop different stiffness aluminum components. For this purpose, butt joints and overlapping joints were produced from sheets made out of two industrial grades, i.e. AA-6082 T6 and AA-5754 H111 of different thickness. The technique was evaluated both with and without the use of a filler wire (AA-5556). The qualification of the welding process encompassed Non Destructive Testing (NDT) and mechanical testing. The results indicate that butt joints tend to fail within the base material (BM) of sheet with smaller thickness. On the contrary, the shear tests on lap joints highlighted a rupture mode occurring in the heat affected zone (HAZ) of the thin sheet. Remarkably, the wobbling process generally allows avoiding porosity when combined with an optimized set of welding parameters. Yet, a residual porosity was always detected in lap joints, varying with the size of the fused zone.

Abstract: The advantages of laser and hybrid laser-arc welding in production of welded structures from high strength steels are increase of efficiency due to rise of the welding rate by order; significant (3 – 5 times) decrease of heat input; reduction of weld size; receiving of fine grain structures in the welds and the heat affected zone increasing strength of the joint and reducing susceptibility to crack formation. Research of the peculiarities of laser and hybrid processes, their effect on weld formation, revealing the advantages and eliminating the disadvantages of laser and arc constituents of the heat sources are currently the main problems for the production engineers and researchers. Therefore, the aim of the investigation lies in determination of the effect of process mode parameters of the hybrid laser-arc and laser welding in high-strength steel welding on formation of the structure of the welded joint metal as well as the analysis of effect of this structure on their mechanical properties. The investigation was focused on the high-strength steel N-A-XTRA-70 which is widely used in European Union countries for manufacture of critical structures of different designations. A laboratory bench was developed for experiments. It was used for carrying out investigation on the process flow sheet which provided location of a consumable electrode arc at some distance ahead of a laser beam during welding proceeding. The laser irradiation source was Nd:YAG-laser DY 044 of ROFIN company (Germany). For the first time the results of carried investigations allowed determining the process modes of laser and hybrid laser-arc welding for producing quality and sound welded joints of the high-strength steel from the point of view of the structure formation and metal phase composition providing high indices of mechanical properties and crack resistance of the welded joints.

Abstract: Amongst the ultra high strength steels, the maraging steels have been noticed because they maintain the fracture toughness superior to other steels of their class. The main difference is the way they acquire resistance. While the conventional carbon steels raise their resistance by heat treatments forming harder phases such as martensite or bainitic constituents, the maraging steels harden by intermetallic particles precipitation. These steels are very promising for several applications, mainly for the aerospace or nuclear areas. In this work, tests of laser welding on a sample of maraging 300 steel, have been carried out, by applying aging at several times and temperatures and analyzing the influence of plasma treatment on the steel microstructure and resistance. The results are promising and show that this welding process is viable and can even be associated with nitriding to improve the surface characteristics. It was observed that the temperature choice and aging time are fundamental to reach high mechanical resistance levels. Temperature values about 480 oC and time 10,800 seconds proved to be suitable for this treatment. The loss of strength in the welded joints, after the aging treatment, was less than 10%. It was also noticed that when the plasma nitriding treatment is applied, aging occurs simultaneously, therefore it is important to select temperature and treatment time in order to optimized the aging process as well.

Abstract: This paper studies the ductile iron (DI) weldability using laser welding. For performing an Yb:YAG continuous laser was used, with a maximum power of 6 kW. The parametrical window power (P) - welding speed (S) was explored by carrying out the fusion lines on ductile iron plates without preheating, to determinate areas of weldability (complete penetration, correct geometry) to allow further characterization. The criteria for selection of focus areas were the geometry of the fusion lines and the absence of the welding defects. The unsatisfactory domains were characterized by: collapse of the melted metal, incomplete penetration, low fusion lines quality (geometry, compactness). In present study, several values of power and welding speed have been tested to identify their influence on geometry, compactness of the joints and mechanical properties. As result, the power-welding speed diagram for feasible domains of laser welding was generated.

Abstract: The transition towards renewable energy implicates more decentralized and time-dependent ways of energy generation. In order to deal with the resulting fluctuation in energy supply, local storage systems are necessary. Larger systems may consist of thousands of battery cells. Therefore, the reliable interconnection between the individual battery cells is the basic prerequisite for the production of these systems. It has been demonstrated that laser beam welding is a suitable process for the contacting of batteries. However, due to the high requirements regarding the heat input and the reproducibility of the joining process, further investigations are necessary. Within this work, experiments on pulsed laser beam welding of nickel-plated DC04 steel were conducted. Four different pulsed welding strategies were analyzed in a preliminary study in order to develop a method for obtaining suitable process parameters while reducing the amount of free parameters. Subsequently, a comparative study between the rectangular pulse, the shaped pulse, the spike pulse and the sloping pulse was carried out. The weld seam properties as well as the electrical and the mechanical properties of the connection joints were evaluated. The results presented in this paper indicate a high eligibility of pulsed laser beam welding as a joining process for the connection of battery cells. For all analyzed pulsed welding strategies a homogeneous weld seam without full penetration was observed. Similar electrical resistances for all strategies were measured despite the comparatively small total joint area for the discretely pulsed weld seams.

Abstract: The energy efficient, high-speed laser deep penetration welding process is a technology which is increasingly used for industrial applications. In order to guarantee weld seams of high quality a stable process needs to be established. Especially when welding aluminium alloys the weld quality is reduced due to occurring spatters which entails a loss of material. Solidified spatters remain on the surface of the specimen after welding and need to be cleaned for further processing steps. One method to change the process behaviour is beam shaping. In this work, a bifocal optic is used to produce two foci along the beam axis in order to manipulate the energy input into the keyhole. Bead-on-plate welds are produced in aluminium alloy EN AW-6082 and mild steel S235. For comparison, welding is conducted using standard optics. The spatter occurrence is compared when using these different beam shapes. While a reduced number of spatters per time are observed the spatter size increases when using the bifocal optic in this study.

Abstract: The basic principle of the X-ray diffraction analysis is based on the determination of components of residual stresses. They are determined on the basis of the change in the distance between atomic planes. The method is limited by a relatively small depth in which the X-ray beam penetrates into the analysed materials. For determination of residual stresses in the surface layer the X-ray diffraction and electrolytic polishing has to be combined. The article is deals with the determination of residual stress and real material structure of a laser-welded steel sample with an oxide surface layer. This surface layer is created during the rolling and it prevents the material from its corrosion. Before the X-ray diffraction analysis can be performed, this surface layer has to be removed. This surface layer cannot be removed with the help of electrolytic polishing and, therefore, it has to be removed mechanically. This mechanical procedure creates “technological” residual stress in the surface layer. This additional residual stress is removed by the electrolytic polishing in the depth between 20 and 80 μm. Finally, the real structure and residual stresses can be determined by using the X-ray diffraction techniques.

Abstract: 2205 duplex (austenitic-ferritic) stainless steel has a good weldability and an excellent corrosion resistance. The good weldability is achieved when in close to 50-50 ferrite-austenite ratio. In this study, the welding process and properties were investigated by pulsed Nd:YAG laser welding. Tensile test, surface microhardness test, surface topography and microstructures of 2205 duplex stainless steel welds were performed under different welding speeds, input currents, pulse widths, frequencies and defocus distance. The relationship among them was revealed and the optimal welding parameters were obtained. The results showed in the condition of I = 160 A, T = 5 ms, f = 25 Hz, V = 500 mm/min and Z =-1 mm, the amount of ferrite and austenite in welds was roughly same, overlap rate of solder joints was above 78% and the weldability was good.