| 1. |
- Kaplan, Alexander, et al.
(författare)
-
Analysis of different methods for the prevention of pore formation in keyhole laser spot welding
- 2002
-
Ingår i: Advanced processes and technologies in welding and allied processes. - Roissy : International Institute of welding. ; , s. 39-50
-
Konferensbidrag (refereegranskat)abstract
- Pore formation in keyhole Nd:YAG-laser spot welding has been investigated experimentally and theoretically. High speed X-ray imaging of the process delivers the shape of the keyhole just before switching off the laser beam. Starting from this shape the keyhole collapse is calculated by the aid of a mathematical model, distinguishing various physical phases of differing time scales, i.e. post-vaporisation, cooling, relaxation flushing of the excess vapour, and surface tension driven collapse of the keyhole along with vapour and melt flow. In case of a bottleneck-shaped keyhole, which is likely to form due to the paradox of flow inversion, necking forms a cavity, thus trapping vapour. According to X-ray observation and numerical simulation a contracting bubble forms that rises and is finally trapped by re-solidification of the melt, thus forming a pore. Different strategies for the prevention of pores are discussed, namely pulse-tail shaping for controlled keyhole contraction, welding under low ambient pressure which rarefies the keyhole vapour, and proper choice of the process parameters like spot size, pulse duration and shielding gas pressure for avoiding a bottleneck-shaped keyhole
|
|
| 2. |
- Kaplan, Alexander, et al.
(författare)
-
Keyhole laser spot welding
- 2002
-
Ingår i: Congress proceedings. - Orlando, Fla : Laser institute of America. - 0912035722
-
Konferensbidrag (refereegranskat)abstract
- Based upon a literature survey, a review is presented highlighting areas of research carried out into keyhole laser spot welding. The survey looks at parametric effects on weld geometry, types and formation of weld defects, the welding thermal cycle, pulse shaping, the use of image processing to investigate the process and modelling and simulation of processes such as the drilling and collapse of the keyhole and porosity formation.
|
|
| 3. |
- Kaplan, Alexander, et al.
(författare)
-
Modelling of keyhole spot welding
- 2003
-
Ingår i: Proceedings of the 16th Meeting on Modelling, Simulation, Virtuality in High Power Laser Technology, M4PL 16.
-
Konferensbidrag (refereegranskat)
|
|
| 4. |
- Kaplan, Alexander, et al.
(författare)
-
On the mechanism of pore formation during keyhole laser spot welding
- 2003
-
Ingår i: First Internaional Symposium on High-Power Laser Macroprocessing. - Bellingham, Wash : SPIE - International Society for Optical Engineering. - 0819446025 ; , s. 186-191
-
Konferensbidrag (refereegranskat)abstract
- An experimental and theoretical study was carried out to investigate the keyhole collapse and pore formation in keyhole laser spot welding; based on this a process theory was developed. Laser spot welding experiments were carried out mainly in liquid zinc (to simplify the investigation); X-ray imaging was used to observe keyhole behaviour i.e. collapse following switching off of the laser beam. A semi analytical mathematical model was used to simulate keyhole collapse taking into account a number of physical processes. The experimental results and mathematical analysis were used to determine the different process phases occurring during keyhole collapse, also indicating the timescales involved: post-vaporisation, excess keyhole vapour relaxation flow, inertia driven collapse, bubble contraction, recondensation, and rising and resolidification.
|
|
