Modulation of the laser power to prevent hot cracking during laser welding of tempered steel

Schaefer, Marcel; Keßler, Steffen; Scheible, Philipp; Graf, Thomas

doi:10.2351/1.4989766

Cited by 15 publications

(3 citation statements)

References 6 publications

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“…1b) [9]. In different fields of laser manufacturing, greater control over the power temporal emission profiles allowed to solve defect formation issues such as hot cracks or porosity [10,11].…”

Section: Introductionmentioning

confidence: 99%

Development of Single Point Exposure Strategy to Suppress Vapour Formation During the Laser Powder Bed Fusion of Zinc and Its Alloys

Caprio

Guaglione

Demir

2021

Lecture Notes in Mechanical Engineering

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The conventional scanning strategies based on linear trajectories in Laser Powder Bed Fusion (LPBF) are highly limited for processing novel materials. In order to manage the energy input and exploit a higher feature resolution, novel scan strategies are required, capable of exploiting the flexibility enabled by the fast modulation capabilities of contemporary fiber laser sources. Zinc and its alloys are among these challenging materials for LPBF aimed to be used in customized biodegradable implants. LPBF of Zn is notoriously difficult to process due to excessive vaporisation which generates high porosity. Accordingly, in this study an innovative LPBF processing strategy based on Single Point Exposure (SPE) was developed. The control over the energy input via single spot exposure allowed to suppress excessive vapour and spark formation typical to Zn alloys. The dynamics of the novel process and its parameters were investigated employing open LPBF platforms and highspeed imaging. Fully dense struts with diameters lower than 300 μm were achieved to produce Zn alloy lattice structures, confirming the effectiveness of the innovative SPE strategy for high precision deposition of challenging materials.

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Section: Introductionmentioning

confidence: 99%

Development of Single Point Exposure Strategy to Suppress Vapour Formation During the Laser Powder Bed Fusion of Zinc and Its Alloys

Caprio

Guaglione

Demir

2021

Lecture Notes in Mechanical Engineering

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“…The authors noticed enhanced removal of material in the kHz regime and suggested that oscillation modes can play a role in ejection but did not provide any detailed explanations. Melt pool surface waves effects were studied in welding for common metals and have been shown to reduce metal porosity 22 , prevent hot cracking 23 and increase keyhole stabilities 24 . While evidence was presented in some of these studies to support the positive effects of periodic modulation, the underlying physics and broader impact on other observables, most notably molten liquid ejection, is far from complete.…”

Section: Introductionmentioning

confidence: 99%

Resonance excitation of surface capillary waves to enhance material removal for laser material processing

Guss

Rubenchik

et al. 2019

Sci Rep

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The results of detailed experiments and high fidelity modeling of melt pool dynamics, droplet ejections and hole drilling produced by periodic modulation of laser intensity are presented. Ultra-high speed imaging revealed that melt pool oscillations can drive large removal of material when excited at the natural oscillation frequency. The physics of capillary surface wave excitation is discussed and simulation is provided to elucidate the experimental results. The removal rates and drill through times as a function of driving frequency is investigated. The resonant removal mechanism is driven by both recoil momentum and thermocapillary force but the key observation is the latter effect does not require evaporation of material, which can significantly enhance the efficiency for laser drilling process. We compared the drilling of holes through a 2 mm-thick Al plate at modulation frequencies up to 20 kHz. At the optimal frequency of 8 kHz, near the resonant response of the melt pool, the drilling efficiency is greater than 10x with aspect ratio of 12:1, and without the collateral damage that is observed in unmodulated CW drilling.

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“…Schaefer et al [15] reduced the hot cracks formation in steel by modulation with laser power. However, additional investigation is still needed to clarify the interaction between the weld pool geometry, the thermally induced tensile stresses, and the strain in the weld zone.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation on the Origin of Solidification Cracking in Laser Welded Thick-Walled Structures

Bakir

Artinov

Gumenyuk

et al. 2018

Metals

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Abstract:One of the main factors affecting the use of lasers in the industry for welding thick structures is the process accompanying solidification cracks. These cracks mostly occurring along the welding direction in the welding center, and strongly affect the safety of the welded components. In the present study, to obtain a better understanding of the relation between the weld pool geometry, the stress distribution and the solidification cracking, a three-dimensional computational fluid dynamic (CFD) model was combined with a thermo-mechanical model. The CFD model was employed to analyze the flow of the molten metal in the weld pool during the laser beam welding process. The weld pool geometry estimated from the CFD model was used as a heat source in the thermal model to calculate the temperature field and the stress development and distributions. The CFD results showed a bulging region in the middle depth of the weld and two narrowing areas separating the bulging region from the top and bottom surface. The thermo-mechanical simulations showed a concentration of tension stresses, transversally and vertically, directly after the solidification during cooling in the region of the solidification cracking.

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Modulation of the laser power to prevent hot cracking during laser welding of tempered steel

Cited by 15 publications

References 6 publications

Development of Single Point Exposure Strategy to Suppress Vapour Formation During the Laser Powder Bed Fusion of Zinc and Its Alloys

Development of Single Point Exposure Strategy to Suppress Vapour Formation During the Laser Powder Bed Fusion of Zinc and Its Alloys

Resonance excitation of surface capillary waves to enhance material removal for laser material processing

Numerical Simulation on the Origin of Solidification Cracking in Laser Welded Thick-Walled Structures

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