Mechanisms for Improvement of Weld Appearance in Autogenous Fiber Laser Welding of Thick Stainless Steels

High-power fiber laser welding is an efficient and effective way to produce heavy section structures. However, there is a significant challenge in producing the welds with free of imperfections such as nail-head-shaped welds, spatters, and root sagging. This is partially due to a lack of understanding of the welding mechanism of high-power fiber laser. In this paper, we were especially interested in the mechanism to improve the appearance of welds, and we focused on the autogenous laser welding on thick stainless steel plates by a 10 kW fiber laser. To look into the relations of process parameters and the quality of welds, a high-speed imaging system was applied to observe the molten pool flow and vapor plume during the welding process. The appearances of welds subjected to different welding conditions were analyzed. The results showed that (1) nail-head-shaped welds were suppressed by using a gas jet during laser welding process. (2) In the forward welding, a gentle upwelling molten metal flow on the rear keyhole wall, a deeper weld pool and a weaker vapor plume resulted in no spatter. (3) The gravity affected the formation of underfills and root sagging significantly during autogenous laser welding of thick plates. (4) When the workpiece was placed vertically in the transverse position, the welding process was stable without an aggregation of molten melt at the back surface. Moreover, the mechanisms of forming root sagging and humps were different at the top surface

Improving hole quality of thick CFRP laminates through a laser-mechanical compound drilling process

Conventional mechanical drilling of thick carbon fiber reinforced plastic (CFRP) composite laminates is prone to machining-induced defects such as burrs, delamination, and severe tool wear. However, pulsed laser drilling as an improved strategy results in hole taper and the formation of a heat-affected zone (HAZ). Herein, a new laser-mechanical composite drilling process is proposed, which combines the advantages of pulsed laser drilling for avoiding tool wear and twist drilling for achieving high dimensional accuracy, significantly improving the drilling quality of thick CFRP laminates. The evolution mechanism of the hole taper and HAZ with processing conditions in pulsed laser drilling is investigated. Furthermore, a theoretical model is established to reveal the material removal mechanism during the reaming process. The thrust force variation, drilling quality and tool wear are analyzed and verified by comparative experiments. The results show that due to the shielding effect from the surface materials, the maximum hole taper and HAZ at the hole exit reach up to 37.5° and 650 μm, respectively, which can be removed effectively by subsequent reaming operations. Due to its small amount of material removal, the peak thrust force and the average thrust force in laser-mechanical drilling are only 53.8 % and 37.6 % of the critical thrust force of delamination, respectively, which can effectively inhibit delamination. Compared with direct twist drilling, the average wear of the main cutting edge in laser-mechanical drilling is decreased by 60.87 %, which greatly reduces the size of the delamination by 55 %

Optimization of laser sharpening parameters for diamond grinding wheel based on CNN

To optimize laser sharpening parameters for bronze diamond grinding wheels, the laser sharpening test was carried out on the bronze diamond grinding wheel using the orthogonal test method.The convolutional neural network (CNN) is used to identify the diamond abrasive grains at the pixel level. The protruding height of abrasive grains is obtained by extracting the area information of abrasive grains. Two laser sharpening quality evaluation indicators, the protruding height score and the optimal interval ratio, are obtained by using the statistical distribution law. The quality of the grinding wheel laser sharpening effect obtained by the test is evaluated by the evaluation index proposed and the range method is performed. The results show that the average power is the biggest factor affecting the quality of trimming. The optimal trimming process parameters are as follows: the average power is 35 W; the repetition frequency is 100 kHz; the rotational speed is 300 r/min; the scanning speed is 1.0 mm/min

Local atomic structure studies of Zr55Cu35Al10 alloy around T g

Abstract As a result of examining the structure of Zr55Cu35Al10 alloy around the glass transition temperature (T g ) using the classical molecular dynamics simulations, it was proven that the atomic bonds in the interconnecting zones (i-zones) became loose with the small amount of energy absorption, and it became free volumes easily when the temperature approached T g . Instead of i-zones, when clusters were largely separated by free volume networks, the solid amorphous structure was converted into supercooled liquid state, resulting in a sharp strength reduce and the great plasticity change from a limited plastic deformation to superplasticity

Effect of Additives on the Performance of Monolithic Catalyst for Tar Cracking

Five cordierite-supported monolithic catalysts with different additives were prepared by vacuum wetness impregnation. All catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), temperature-programmed reduction (TPR), and Raman spectroscopy. These catalysts were also tested by the raw gas from biomass pyrolysis to contrast them in terms of catalytic performance and stability. Characterization results show the formation of Mo-Ni alloy in the reduced catalyst with Mo additive; however, the other additives in the reduced catalyst remain in oxidation state. TPR revealed a strong interaction between the active component and the additives, resulting in a decrease of reduction ability. The catalysts with additives were shown to perform more efficiently compared with the catalysts without additives. The catalyst with Mo additive exhibited the best performance, with its tar conversion and gas yield reaching 96.6% and 1.22 N m(3)/kg, respectively, at a weight hourly space velocity of 706 kg/(h.m(3)). The 1Mo3Ni1Co/Cor catalyst exhibited higher stability compared with 1Sm3Ni1Co/Cor because the tar conversion of the former remained higher than 90%, whereas that of the latter decreased to 73.1% after a 4 h catalysis. Coke deposits were formed on the surface of the 1Sm3Ni1Co/Cor catalyst, which mostly exhibited a graphite structure, as observed by Raman spectroscopy

Media 1: Direct observation of keyhole characteristics in deep penetration laser welding with a 10 kW fiber laser

Originally published in Optics Express on 26 August 2013 (oe-21-17-19997

Media 3: Direct observation of keyhole characteristics in deep penetration laser welding with a 10 kW fiber laser

Originally published in Optics Express on 26 August 2013 (oe-21-17-19997

Media 4: Direct observation of keyhole characteristics in deep penetration laser welding with a 10 kW fiber laser

Originally published in Optics Express on 26 August 2013 (oe-21-17-19997