| 1. |
- Kaplan, Alexander, et al.
(författare)
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Imaging in cooperation with modeling of selected defect mechanisms during fiber laser welding of stainless steel
- 2008
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Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035123 ; , s. 789-798
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Konferensbidrag (refereegranskat)abstract
- Fiber laser welding of stainless steel was studied for different joint configurations and gaps. The higher focusing capability of fiber lasers compared to traditional Nd:YAG and CO2 lasers creates different, usually smaller, keyhole and melt pool geometries. These geometrical aspects, accompanied by a different laser energy redistribution, are essential for the weld pool dynamics and the resulting joint, with or without defects. Typical defects identified during fiber laser welding were spatter, humping, or lack of material at the top or root. High-speed imaging enables observation of the geometry and motions of the melt pool surface and keyhole during welding. This is illuminated by an additional diode laser permitting spectral filtering and also the metal vapor dynamics can be visualized. Mathematical modeling provides the possibility to estimate and study additional phenomena that are difficult to measure, such as effects inside the melt volume or the impact of surface tension forces on dynamic melt motion. For recorded melt surface motion images, in particular, the corresponding surface tension forces and other mechanisms can be estimated by cooperative complementary modeling, enabling to draw conclusions. This advanced method was carried out for the different joint and defect cases studied, resulting in an illustrated theoretical description of the observed physical phenomena.
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| 2. |
- Norman, Peter, et al.
(författare)
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Correlation between photodiode monitoring and high speed imaging of the dynamics causing laser welding defects
- 2008
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Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035123 ; , s. 829-837
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Konferensbidrag (refereegranskat)abstract
- Today merely a few monitoring systems for in-process detection of laser welding defects are commercially available. Despite a trend towards cameras, industrially more robust is still a photodiode, measuring in an optically filtered spectral window either the thermal emissions from the melt and vapour or the laser beam reflections. The monitoring rule for each application is identified empirically through correlations between the signal dynamics and welding defects, as the linking mechanism is non-trivial and therefore hardly understood. Thus the method does not provide a systematic guideline to detect a certain welding defect.The here presented approach studies the context between the photodiode signal, the welding defects and the vapour, melt pool, keyhole and temperature dynamics. Simultaneous laser-illuminated high speed imaging is compared to photodiode monitoring at three spectral windows in order to identify through simultaneous timing any linking dynamics in a qualitative manner. Supportive methods are emission modelling and thermal imaging. Several cases of joints, materials and defects were studied to develop an illustrated theoretical description of the defect-signal correlations.
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| 3. |
- Powell, John, et al.
(författare)
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The energy generated by the oxidation reaction during laser-oxygen cutting of mild steel
- 2008
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Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 9780912035123 ; , s. 628-636
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Konferensbidrag (refereegranskat)abstract
- This paper presents an in-depth analysis of the Iron to FeO oxidation reaction in the context of laser-oxygen cutting of mild steel. The paper concludes by presenting a number of guidelines for future theoretical models of laser-oxygen cutting.
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