Papers by Keyword: Laser Welding

Abstract: The strengthening effect due to high-temperature tempering (HTT) at 700 °C on the microstructure and mechanical properties of welded joints between medium-Mn stainless steel (MMnSS) and high-strength carbon steel (CS) was studied. The microstructure of the weldments was investigated using Laser and scanning electron microscopes. An Electron probe microanalyzer (EPMA) was used to assess quantitatively the elemental distribution profiles of alloying elements within the weld zone. The strengthening precipitates induced during welding and HTT were characterized by transmission electron microscopy (TEM). Uniaxial tensile tests and microindentation hardness (H_IT) measurements of the weld joints were conducted to evaluate the strengthening effect. Fully fresh-martensite and fine-tempered martensitic structures were promoted in the as-weld and HTT processes, respectively. The HTT structure exhibited a remarkable improvement in mechanical properties (a better combination of yield and tensile strength together with moderate ductility) compared to its weld counterpart. TEM investigation revealed that various types of precipitates have been promoted in the structures of the weld and HTT, e.g., nanosized vanadium and chromium carbides. It is apparent that the proposed HTT of the joints is an effective treatment for improving the mechanical properties due to inducing the formation of fine interphase precipitates, resulting in enhanced mechanical strength of the joints.

Abstract: This paper investigates residual stresses of the laser welded abrasion resistant steel butt joints. X-ray diffraction (XRD) was used to measure the residual stresses of the laser welded joints. The geometry and mechanical properties of the joints were also investigated. The weld metal hardness of the weld made with the lowest welding energy corresponded to the hardness of the base material. The welding energy had a significant effect on the hardness profiles of the welds. With the lowest welding energy, the tensile strength reached a strength corresponding to the yield strength of the base material. The residual stress results perpendicular to the weld corresponded well to the hardness profiles of the joints. The residual stresses were mainly tensile stress. The measured maximum residual stresses were 480 MPa.

Abstract: An important problem for plastic injection moulding companies is the deterioration of mould nests due to several factors such as wear and tear caused by heavy use, corrosion, misuse, etc. These defects, even small ones, can affect the injection moulded product. To reduce the cost of making a new mould, damaged areas are repaired. TIG welding or laser welding is commonly used. For areas with small defects, laser welding is preferred due to its advantages. The paper presents research on the choice of wire when reconditioning a mould using laser welding.

Abstract: The present work aims to design an artificial neural network (ANN) for controlling the geometry of the fusion zone in different welding conditions. AA5754 aluminium plates with 6 mm thickness were welded in butt configuration by using an Yb-doped fiber laser in continuous wave regime. Laser power, travel speed, beam diameter and shielding gas were considered as process-related factors, while the weld geometry was evaluated in terms of penetration depth and bead width. The accuracy of the model was endorsed by using untrained test data. Results showed a good agreement between the ANN output and the experimental values.

Abstract: The aim of the work is a comparative analysis of structural features and mechanical characteristics of spot welded joints of thin-sheet stainless steels 03Х11Н10М2T and 12Х18Н10Т, produced by laser welding in different welding positions. The change in the welding position from vertical to flat allowed extend the ranges of variation of welding modes from about ±5% to about ±10%, at which it is possible to produce a welded joint with satisfactory shape and mechanical characteristics. Higher strength is typical for welded joints obtained in a flat position. It also concerns the maximum value of the shear stress, which for the flat position is higher by approximately 10%, and the average value, which is higher by approximately 24%. In addition, the results of mechanical shear tests of these joints have a significantly lower dispersion.

Abstract: Additive manufactured (AM) 316L and Inconel 718 (IN718) parts using laser powder bedfusion technique and the weldability of the mixed pair by laser welding was investigated in this paper.The effect of prior heat treatment of the materials was also taken in to consideration. The motivationbehind this work was to investigate if hybrid products could be manufactured from these materials formore cost­efficient production of AM products. The results showed good reliability of the welds asthe tensile results were on par with the 316L base material. The hardness of the weld fusion zone was50 HV lower compared to the 316L base material hardness at 225 HV. In general, the results showedlaser welding is a very promising method for joining these printed materials and can be utilized asanother tool when integrating these materials into a design.

Abstract: The paper is focused on the effects of air gap size to mechanical properties of laser welded lap joints. Structural steel plates of 3 mm thickness were used in the laser welding experiments. The laser welding experiments were conducted at two very different energy inputs (EI) of 60 and 320 J/mm. The weld geometries were investigated using optical microscopy. The shear strength of the lap joints was evaluated by uniaxial tensile tests. Results showed that with low EI of 60 J/mm the size of air gap had significant effect on the width of the interface as the larger air gap size increased the width of the interface. At high EI of 320 J/mm, the width of the weld at the interface did not change significantly as the air gap increased. The hardness of the weld metal was greater than the hardness of the base material at both EIs. The shear strength of the joint increased significantly with low EI of 60 J/mm, as air gap size increased. The size of the air gap did not have a large effect on the shear strength of the joint with higher EI of 320 J/mm.

Abstract: The article presents the results of the impact of laser welding parameters on defect occurrence in the welded seam of the Ni-based heat-resistant alloy Kh45VMTYuBR applied for the manufacture of gas-turbine engines. On the basis of the research the authors conduct the analysis of dimensions as well as the number of pores and micro-cracks in the welded seam. The paper provides the recommendations on the selection of the laser welding mode for the heat-resistant alloy to reduce defect occurrence in a welding seam.

Abstract: The solidification temperature range was numerically analyzed to optimize nonequilibrium solidification behavior during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification with variation of laser welding conditions (either heat input or welding configuration). The distribution of solidification temperature range along the fusion boundary is beneficially symmetrical about the weld pool centerline in the (001)/[100] welding configuration. The distribution of solidification temperature range along the fusion boundary is detrimentally asymmetrical about the weld pool centerline in the (001)/[110] welding configuration. The stray grain formation and solidification cracking are preferentially confined to [100] dendrite growth region. [001] epitaxial growth region with columnar dendrite morphology is favored at the expense of undesirable [100] growth region with equiaxed dendrite morphology to facilitate essential single-crystal solidification with considerable reduction of heat input. The smaller heat input is used, the narrower solidification temperature range is thermodynamically promoted to reduce nucleation and growth of stray grain formation with decrease of constitutional undercooling ahead of dendrite tip and mitigate thermo-metallurgical factors for morphology instability and microstructure anomalies. Potential low heat input(both decreasing laser power and increasing welding speed) with (001)/[100] welding configuration decreases solidification temperature range to significantly minimize columnar/equiaxed transition (CET) and stray grain formation, and improve resistance to solidification cracking through microstructure control. On both sides of weld pool are imposed by the same heat input, while the solidification temperature range along the fusion boundary inside of [100] dendrite growth region on the right part of the weld pool is spontaneously wider than that of [010] dendrite growth region on the left part to increase solidification cracking susceptibility in the (001)/[110] welding configuration. Furthermore, another mechanism of solidification cracking as consequence of severe solidification behavior and anomalous microstructure with asymmetrical crystallographic orientation is therefore proposed. The theoretical predictions are well verified by experiment results. The useful and satisfactory numerical modeling is also available for other single-crystal superalloys during successful laser repair process without stray grain formation.

Abstract: Multicomponent dendrite growth is theoretically predicted to optimize solidification cracking susceptibility during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification. The distribution of dendrite trunk spacing along the weld pool solidification interface is clearly symmetrical about the weld pool centerline in beneficial (001)/[100] welding configuration. The distribution of dendrite trunk spacing along the weld pool solidification interface is crystallography-dependent asymmetrical from bottom to top surface of the weld pool in detrimental (001)/[110] welding configuration. The smaller heat input is used, the finer dendrite trunk spacing is kinetically promoted by less solute enrichment and narrower constitutional undercooling ahead of solid/liquid interface with mitigation of metallurgical contributing factors for solidification cracking and vice versa. Vulnerable [100] dendrite growth region is predominantly suppressed and epitaxial [001] dendrite growth region is favored to spontaneously facilitate single-crystal columnar dendrite growth and reduce microstructure anomalies with further reduction of heat input. Optimum low heat input (both lower laser power and higher welding speed) with (001)/[100] welding configuration is the most favorable one to avoid nucleation and growth of stray grain formation, minimize both dendrite trunk spacing and solidification cracking susceptibility potential, improve resistance to solidification cracking, and ameliorate weldability and weld integrity through microstructure modification instead of inappropriate high heat input (both higher laser power and slower welding speed) with (001)/[110] welding configuration. The dendrite trunk spacing in the [100] dendrite growth region on the right side of the weld pool is considerably coarser and grows faster than that within the [010] dendrite growth region of the left side in the (001)/[110] welding configuration to deteriorate weldability, although the welding conditions are the same on the either side. Furthermore, the alternative mechanism of crystallography-dependent solidification cracking as consequence of asymmetrical microstructure development and diffusion-controlled dendrite growth of γ phase is therefore proposed. The theoretical predictions are comparable with experiment results. The reliable model is also useful for welding conditions optimization for crack-free laser processing.