Papers by Keyword: YAG Laser

Abstract: Laser welding are well reported to be excellent in precision parts joining with high reputations in external finishing. However, the process in obtaining the best processing parameters is not an easy task. In the case of pulse wave laser, the parameter setting constrained by the laser generator specification. Each laser parameters such as pulse width t_p, pulse repetition rate f_p and average laser power P_avg has relation which others. Increasing one parameter will directly decreases the maximum value of other parameters. The limited applicable combination and rage of processing parameters make it difficult to obtain the optimized processing parameters. This study is conducted to investigate the influence of each lasing parameters on the welding penetration capability. The range of applicable parameters for titanium alloy sheet metal has been successfully clarified

Abstract: Laser transmission welding (LTW) is a new technology for joining plastic components, involves a laser beam passing through a laser-transmitting part being absorbed by a laser-absorbing part at the weld interface. To form a strong bond, it is important that the weld interface be exposed to sufficient heat to melt the polymer without degrading it. This paper investigates the quality of PMMA (Polymethyl Methacrylate) laser transmission welding by using YAG (1.06um) laser. Using the orthogonal experiment method, the specimens under different parameters have been studied. In order to evaluate the mechanical resistance of the welded joint, surface profilometry and metallographic microscopy were employed. It was shown that welding quality was significantly influenced by speed, power, and welding spot size. We summarized the influence of various factors, and eventually obtained the experimental results under different experimental parameters.

Abstract: Laser transmission welding of plastics is a joining technique which permits the welding of plastic parts with low process inherent thermal and small welding heat response area. It has high demand of process parameters and material characteristic. In order to study thermoplastic materials properties and ir-absorbing agent in laser transmission welding, experiments were taken under the same process parameters. The YAG laser Output power 200W, working distance 25mm, movement speed 10mm / s. Through the experimental results, we concluded that the different welding quality of different materials and absorbing agent, and analyzed its material characteristic reasons.

Abstract: This paper indicates the experiments of YAG laser cutting soda-lime glass with controlled fracture. The qualities of glass obtained by laser cutting and mechanical cutting are compared. The impact of laser power, scanning speed and spot size on the cutting quality is studied and the optimum laser parameters are given. Finally the experiments of laser cutting two-layer glasses, glass tube and laser cutting in curve paths are carried out. The results show that good cutting quality of glass can be acquired by YAG laser cutting.

Abstract: In laser cutting of glass with controlled fracture, thermal stress induces a fracture and the material is cleaved along the cutting path by fracture propagation. Compared with CO2 laser, YAG laser has many advantages in cutting glass with controlled fracture. As a volumetric heat source, YAG laser can penetrate through the glass. Therefore, the temperature distribution is uniform across the thickness of the glass and the fracture propagates from the top and bottom surface to the middle so that better cutting quality can be acquired and multi-layer glasses can be cut simultaneously. In this paper, a 1064nm YAG laser is applied to cut two-layer and four-layer glasses. Fracture propagation mechanism is studied by examining the temperature and stress fields using finite element software ANSYS11.0. Good cutting qualities of fracture surfaces for all the layer glasses are acquired and the cutting efficiency is greatly improved by this technique as well. Additionally, due to smaller laser spot size the glasses that are closer to the focal point have higher laser power density inside glass, which may lead to ablation and evaporation phenomenon. But lower laser power density is not enough for fracture initiation and expansion. Therefore, it’s important to find a proper laser power for all the layer glasses. Small tensile stresses on the top and bottom surfaces will make the material separate from up and down to middle, whereas the compressive stresses in the middle ensure stable fracture propagation. Moreover, the stable fracture propagation always lags behind the laser beam spot. High tensile stresses are distributed throughout the thickness of the glass in the leading and trailing edges, which leads to unstable fracture extension in the leading and trailing edges.

Abstract: A new welding technique called hybrid FSW was developed to decrease the tool load and the defects during the FSW of high melting point materials. This method consists of FSW and a laser for preheating ahead of the tool. The hybrid FSW enables the proper welding conditions to be significantly expanded, and the joint characteristics are similar to those obtained by the normal FSW at the same welding speeds.

Abstract: Pulsed Nd;YAG laser was applied to investigate the bond characteristics of Sn- 3.5wt%Ag (hereafter, Sn-3.5Ag) solder ball. The ball diameter is 500µm, and the UBM (Under Bump Metallurgy) on a FR4-PCB consisted of Cu/Ni/Au from bottom to top with thickness of 50µm/25µm/0.05µm, respectively. A RMA (rosin mildly activated) flux for BGA (Ball Grid Array) was applied before laser soldering to set up the solder ball on the UBM. Laser power was 250W, and its beam diameter at the focal point was around 250µm. Experimental results reveal that the solder ball showed a good bonded state when the laser energy was in the range between 0.8 and 1.0 J. Laser energy lower than 0.8J caused non-wetting of the solder ball, and energy higher than 1.2J showed crack along the UBM. Microstructure of the laser soldered Sn-3.5Ag was examined with the number of pulse, when the frequency, pulse width and laser energy were fixed at 5 Hz, 20 ms and 0.8 J, respectively. The IMC (Intermetallic Compound) of Ag3Sn in the solder changed from acicular to rod type with increasing laser pulses. Ni3Sn4 was produced between the solder and the UBM, and its thickness increased from 0.65 to 1.80µm with increasing number of pulse from 2 to 4. These are thinner than those of general air reflow. Shear strength of the laser soldered ball with output energy of 1 J showed 652.3 gf, and it was similar value compared to the result from hot plate soldering, 654.5 gf.

Abstract: This paper reports a new laser conditioning method for micro-wheels with ultra-fine grit diamond, which are used for the micro grinding of micro-aspherical optics. Resinoid-bonded micro-wheels with ultra-fine grit diamonds are used for micro grinding. Such small wheels have the problem of poor ground surface roughness due to their few effective cutting edges and low peripheral speeds. In the present work, new truing and dressing methods are proposed to produce many effective cutting edges. The new method uses the third harmonic of a Nd:YAG laser, which is suitable for processing resinoid bond material. It was found that a SD1500B wheel treated using the new method had a higher cutting edge density than one treated using a conventional method, the cup truer method. A good surface roughness was obtained using the new method.

Abstract: The appearance of buildings and towns is ruined by graffiti drawn on walls made of concrete or brick. Much money and labor are spent in removing graffiti from such rough surface. This paper is a comparative study of the laser irradiation method and the high-pressure water jet method for removing graffiti from the surface of concrete. The former uses a YAG laser beam and the later uses water containing sodium bicarbonate particles. The graffiti were drawn in nine colors on the surface of concrete specimens using oil spray paint and emulsion spray paint. The main results of this study are as follows: Graffiti drawn with oil paint is easier to remove than that with emulsion paint. Yellow and orange colors are harder to remove compared to other colors. In both methods (laser irradiation and water jet) of removal, the surface of concrete is damaged only slightly. Overall, the laser irradiation method appears to be more effective for graffiti removal than the water jet method.

Abstract: With the intention of improving butt or lap joint of dissimilar materials, specially devised weld beads together with lap and butt-joints were produced between A5052 and SPCC, where A5052 butt-joint was melted by heat-conduction of SPCC weld bead in addition to the formation of a limited weld fusion zone at the lap part in A5052 alloy. The thickness of intermetallic compounds at the butt-joint interface was approximately 2 μm and free of cracks. It was also revealed that crack-free lap weld metals were formed between aluminum alloy and steel when the penetration was controlled to be of less than 0.3 mm in depth at small heat input. It was moreover found that the majority of a laser weld fusion zone solidified as alpha(bcc)-iron phase containing small amount of aluminum, and cracks were absent in the case of hard intermetallic (AlxFey type) layer of less than 10μm zone. It was confirmed that a weld with lap and butt joints possessed high strength (leading to the load 3500 N to 4,380 N for 40 mm width specimen). In addition, SPCC and A1100 or A5052 were subjected to lap welding with a cw YAG laser, where one to three passes were performed to produce wider bonded areas. Dissimilar steel and aluminum joints with good mechanical properties were obtained, since the fracture occurred in the aluminum alloy base metal in the tensile test. It is concluded that welded joints of high strength can be produced between aluminum alloy and steel with proper devices.