Transport Phenomena and the Associated Humping Formation in Laser Welding

2005 ◽  
Author(s):  
J. Zhou ◽  
H. L. Tsai ◽  
P. C. Wang
Keyword(s):  
Heat Transfer ◽  
Liquid Metal ◽  
Laser Welding ◽  
High Speed ◽  
Solidification Rate ◽  
Transport Phenomena ◽  
Metal Flow ◽  
Welding Process ◽  
Solidification Process ◽  
Melt Flow

Humping is a frequently observed welding defect in laser welding which is caused when the welding speed exceeds a certain limit while the other welding conditions remain unchanged. Humping is characterized by the appearance of unsmooth and discontinuity of humps at the surface of the weld. The formation of humping is generally understood to be caused by the complex heat transfer and melt flow in a high speed welding process. However, so far the fundamental mechanisms causing humping are not fully understood, and research on determining the onset of humping has been based on the “trial-and-error” procedure. In this paper, mathematical models previously developed by the authors for the transport phenomena in laser welding have been extended to investigate the formation of the humping defect. In this study, the transient heat transfer and melt flow in the weld pool during the keyhole formation and collapse, and melt solidification are calculated for a 3-D moving laser welding. Different humping patterns have been predicted by the present study in different laser power levels and welding speeds. From the present study, it was found that the formation of humping in laser welding is caused by the interplay between two important factors: a) the strong liquid metal flow in the real part of the keyhole induced mainly by the laser recoil pressure and b) the rapid solidification rate of the liquid metal. The humping pattern can be well explained by the calculated melt flow and the solidification process.

Investigation of Fluid Flow and Heat Transfer in 3D Dual-Beam Laser Keyhole Welding

2010 ◽  
Author(s):  
Jun Zhou ◽  
Hai-Lung Tsai
Keyword(s):  
Heat Transfer ◽  
Laser Welding ◽  
Welding Process ◽  
Solidification Process ◽  
Melt Flow ◽  
Single Beam ◽  
Keyhole Welding ◽  
Beam Laser ◽  
Dual Beam ◽  
Laser Keyhole Welding

Dual-beam laser welding has become an emerging joining technique. Studies have demonstrated that it can provide benefits over conventional single-beam laser welding, such as increasing keyhole stability, slowing down cooling rate and delaying the humping onset to a higher welding speed. It is also reported to be able to improve weld quality significantly. However, due to its complexity the development of this promising technique has been limited to the trial-and-error procedure. In this study, mathematical models are developed to investigate the heat transfer, melt flow, and solidification process in three-dimensional dual-beam laser keyhole welding. Effects of key parameters, such as laser-beam configuration on melt flow, weld shape, and keyhole dynamics are studied. Some experimentally observed phenomena, such as the changes of the weld pool shape from oval to circle and from circle to oval during the welding process are analyzed in current study.

Effect of Welding Speed on Melt Flow Behavior in High Speed Laser Welding Process

2013 ◽  
Vol 40 (5) ◽  
pp. 0503001
Author(s):  
裴莹蕾 Pei Yinglei ◽  
单际国 Shan Jiguo ◽  
任家烈 Ren Jialie
Keyword(s):  
Laser Welding ◽  
Welding Speed ◽  
High Speed ◽  
Flow Behavior ◽  
Welding Process ◽  
Melt Flow ◽  
Laser Welding Process

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

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 625 ◽  
Author(s):  
Mingjun Zhang ◽  
Shun Chen ◽  
Yingzhe Zhang ◽  
Genyu Chen ◽  
Zhuming Bi
Keyword(s):  
Laser Welding ◽  
Fiber Laser ◽  
High Power ◽  
High Speed ◽  
Imaging System ◽  
Metal Flow ◽  
Welding Process ◽  
Back Surface ◽  
Fiber Laser Welding ◽  
Vapor Plume

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.

Modelling of Thermal Quantities for Quick Process Assessment and Process Capability Space Refinement at an Early Design Phase During Laser Welding

2021 ◽  
Author(s):  
Anand Mohan ◽  
Dariusz Ceglarek ◽  
Michael Auinger
Keyword(s):  
Heat Transfer ◽  
Laser Welding ◽  
Cooling Rate ◽  
Process Parameters ◽  
Thermal Cycle ◽  
Welding Process ◽  
Process Capability ◽  
Peak Temperature ◽  
Transfer Model ◽  
Process Assessment

Abstract This research aims at understanding the impact of welding process parameters and beam oscillation on the weld thermal cycle during laser welding. A three-dimensional heat transfer model is developed to simulate the welding process, based on the finite element (FE) method. The calculated thermal cycle and weld morphology are in good agreement with experimental results from literature. By utilizing the developed heat transfer model, the effect of welding process parameters such as heat source power, welding speed, radius of oscillation, and frequency of oscillation on the intermediate performance indicators (IPIs) such as peak temperature, heat-affected zone volume (HAZ), and cooling rate is quantified. Parametric contour maps for peak temperature, HAZ volume, and cooling rate are developed for the estimation of the process capability space. An integrated approach for rapid process assessment, process capability space refinement, based on IPIs is proposed. The process capability space will guide the identification of the initial welding process parameters window and help in reducing the number of experiments required by refining the feasible region of process parameters based on the interactions with the IPIs. Here, the peak temperature indicates the mode of welding performed while the HAZ volume and cooling rate are weld quality indicators. The regression relationship between the welding process parameters and the IPIs is established for quick estimation of IPIs to replace time-consuming numerical simulations. The proposed approach provides a unique ability to simulate the laser welding process and provides a robust range of process parameters.

scholarly journals Liquid Metal Flow Under Traveling Magnetic Field—Solidification Simulation and Pulsating Flow Analysis

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 532
Author(s):  
Evgeniy Shvydkiy ◽  
Egbert Baake ◽  
Diana Köppen
Keyword(s):  
Magnetic Field ◽  
Liquid Metal ◽  
Neutron Radiography ◽  
Metal Flow ◽  
Flow Analysis ◽  
Solidification Process ◽  
Electromagnetic Stirring ◽  
Pulsation Frequency ◽  
Conductive Liquid ◽  
Traveling Magnetic Field

Non steady applied magnetic field impact on a liquid metal has good prospects for industry. For a better understanding of heat and mass transfer processes under these circumstances, numerical simulations are needed. A combination of finite elements and volumes methods was used to calculate the flow and solidification of liquid metal under electromagnetic influence. Validation of numerical results was carried out by means of measuring with ultrasound Doppler velocimetry technique, as well as with neutron radiography snapshots of the position and shape of the solid/liquid interface. As a result of the first part of the work, a numerical model of electromagnetic stirring and solidification was developed and validated. This model could be an effective tool for analyzing the electromagnetic stirring during the solidification process. In the second part, the dependences of the velocity pulsation amplitude and the melt velocity maximum value on the magnetic field pulsation frequency are obtained. The ability of the pulsating force to develop higher values of the liquid metal velocity at a frequency close to the MHD resonance was found numerically. The obtained characteristics give a more detailed description of the electrically conductive liquid behaviour under action of pulsating traveling magnetic field.

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