Analytical heat conduction modelling for shaped laser beams

Sundqvist, Jesper; Kaplan, Alexander; Shachaf, L.; Kong, Choon Yen

doi:10.1016/j.jmatprotec.2017.04.011

Cited by 21 publications

(5 citation statements)

References 19 publications

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“…Emission-based measurements are limited to surface temperature measurements, while Abderrazak et al [33] employed computation fluid dynamics to predict volumetric temperature fields. During welding, complex melt pool convections can alter the temperature field, as was observed by Sundqvist et al [31], depending on the driving forces like Marangoni convection accelerated by surface tension gradients or flow initiated by laserinduced ablation pressure. Chemical inhomogeneity of the weld metal arises from base metal diluting into the wire material.…”

Section: Introductionmentioning

confidence: 85%

“…Thermocouples, pyrometers, or thermal imaging can measure the thermal history experienced at a specific position of the welded metal, with limitations as explored by Sundqvist et al [31]. Here, for the Snapshot method, it was preferred to apply a technique known as Dualscope, based on high-speed imaging (HSI) where the camera image is split into two domains, each recording the process in a different spectral window, which enables the unknown emissivity to be cancelled out when deriving the temperature field.…”

Section: Introductionmentioning

confidence: 99%

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Microstructures of high-strength steel welding consumables from directed thermal cycles by shaped laser pulses

Robertson

Frostevarg

Ramasamy³

et al. 2020

Int J Adv Manuf Technol

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Filler wire metallurgy was modified through temporally shaped laser pulses, controlling cooling cycles in a recently developed method. Trends were identified through efficient mapping while maintaining representative thermal cycles of welding processes. A primary pulse melted preplaced filler wires while a secondary, linearly ramped-down pulse elevated the nugget to re-austenization temperatures. Ramped-down pulses resulted in linear cooling rates comparable with and exceeding furnace-based methods, between 50 and 300 • C/s. The linear decay of laser output power guided the temperature through a regime to obtain desired microstructures. For three very high-strength steel filler wire chemistries, quenching resulted in smaller plates with cross-hatched microstructures, accompanied by grain boundary ferrite. Finer bainite microstructures started forming for fast linear temperature decay, about 250 • C/s. Slower decay or a weaker third cycle formed coarser microstructures with coalescent sheaves and less cross-hatching.

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Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Microstructures of high-strength steel welding consumables from directed thermal cycles by shaped laser pulses

Robertson

Frostevarg

Ramasamy³

et al. 2020

Int J Adv Manuf Technol

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“…The calculated and measured data were compared with the width of the melted zone. Using the melting point isotherm, the value of emissivity could be calculated, and the true temperature could be restored [6,24].…”

Section: Introductionmentioning

confidence: 99%

Semi-Analytical Solution for Modelling Moving Heat Sources in a Semi-Infinite Medium with Radiative and Convective Boundary Conditions

Metallo

2023

International Journal of Thermodynamics

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The weld quality is highly related to the thermal history of the weld and there have been many trials to monitor the quality using an infrared (IR) sensor. To obtain the real temperature of a surface based on the brightness temperature values measured by an IR camera, the emissivity value must be derived. For an accurate assessment of the emissivity, one must be aware of the melting point isotherm. The temperature profiles only depend on three factors during laser processing, specified as constants the characteristics of the material: laser beam speed (v), laser beam diameter (d), and power (P). Predicting the width of the melted zone reached during the welding process as the parameters vary is a tool for helping a quality laser processing and for determination of true temperature in laser welding using IR camera. This study describes the semi-analytical (SA) solution of the heat conduction equation for a localized moving Gaussian heat source with constant parameters on a semi-infinite medium. The solution, simple and quick to obtain, provides information on the width of the melted zone with an average error < 5 %. The outcome is assessed numerically and contrasted with FEM solutions for a Gaussian source, the latter having undergone experimental validation. With two distinct defocus values, def0 and def-6, and by varying the speed and power settings, two separate types of experiments were run. Thus, the SA solution was obtained and compared after the FEM solution had been obtained with a good approximation (max err 4.3 %, average err 2.7 %). Only in regard to the 1AL test is an error more than 5 % detected; in the other case, the average error is 3.75 %. Two more tests at the defocus values of def-4 and def-8 were conducted to confirm the model's validity as the parameters varied. Overall, the average error between the semi-analytical and the FEM solution is 4.1%. The SA solution may be used to effectively estimate the isotherms related to the melting point of aluminum (770 K). This allows to obtain a tool which helps restoring the real temperature based on the brightness values measured by the IR camera during laser welding. At the same time, this effective tool allows to investigate the importance of different processing parameters in laser manufacturing.

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“…The thermal cycles experienced by a cell of metal during welding can to a certain extent be measured by employing thermocouples, by pyrometers, or by thermal imaging. 7 Recently, advanced thermal imaging techniques have been developed and more accurate identification of the emissivity was achieved, for calibration. 8 While most of the measurements are limited to surface temperatures, numerical simulation aims to predict the volumetric temperature field, 7 which is altered by convection from complex melt pool flow.…”

Section: Introductionmentioning

confidence: 99%

“…7 Recently, advanced thermal imaging techniques have been developed and more accurate identification of the emissivity was achieved, for calibration. 8 While most of the measurements are limited to surface temperatures, numerical simulation aims to predict the volumetric temperature field, 7 which is altered by convection from complex melt pool flow. Apart from Marangoni-convection, depending on the welding technique additional driving forces can govern the flow, for laser beams particularly ablation pressure in the case of keyhole boiling.…”

Section: Introductionmentioning

confidence: 99%

Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles

Robertson

Frostevarg

Kaplan

et al. 2019

Journal of Laser Applications

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A robust method is introduced to simulate and study the filler wire metallurgy for controlled cooling conditions after melting, enabling efficient mapping with prompt analysis of trends. Proposed is a reduced, though representative, process with more controllable conditions. Short lengths of filler wires are preplaced in a cavity, drilled into a base metal sheet. Irradiation by a pulsed laser beam melts the wire to generate a sample nugget. Pulse shaping influences the cooling rate, granting the ability to tailor weldament microstructures. The method is demonstrated for S1100QL steel and undermatched filler wire, to obtain high toughness for processes like laser-arc hybrid welding, where a representative thermal cycle is needed. For high toughness, a controlled amount of acicular ferrite and, in turn, nonmetallic inclusions is desirable. This "snapshot" method has revealed a characteristic histogram of inclusion sizes, for different pulse shapes. Additional information on the thermal cycle can be acquired by employing thermocouples, a pyrometer, or advanced methods like high speed imaging or modeling. The method offers a wide spectrum of variants and applications.

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Analytical heat conduction modelling for shaped laser beams

Cited by 21 publications

References 19 publications

Microstructures of high-strength steel welding consumables from directed thermal cycles by shaped laser pulses

Microstructures of high-strength steel welding consumables from directed thermal cycles by shaped laser pulses

Semi-Analytical Solution for Modelling Moving Heat Sources in a Semi-Infinite Medium with Radiative and Convective Boundary Conditions

Tailored laser pulse method to manipulate filler wire melt metallurgy from thermal cycles

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