| 1. |
- Samarjy, Ramiz Saeed Matti, 1965-, et al.
(författare)
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Imaging of the Dynamic Melt Movement Induced by a Pulsed Laser
- 2016
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 83, s. 1308-1318
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Tidskriftsartikel (refereegranskat)abstract
- A special case of an interrupted superheated process was developed, governed by the ablation pressure of a boiling melt, induced by a pulsed Nd:YAG-laser. A kind of cutting process was carried out, but at very low speed to generate a large melt pool that can be well studied. The interaction zone was observed by high speed imaging, with and without illumination. When switching the laser pulse on or off, different dynamic phenomena can be clearly observed, like drilling into a bulk of melt, breaking of a melt bridge, controlled pushing of the melt pool, waves running down, all driven by boiling. After the pulse, the melt smoothens and oscillates and is dragged back upwards by the surface tension forces from the melt shape curvature, ending in a torus-like equilibrium shape. The fundamental understanding that was generated could be applied to improve processes like keyhole laser welding, laser remote fusion cutting or laser drilling
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| 2. |
- Samarjy, Ramiz Saeed Matti, 1965-
(författare)
-
Interaction mechanisms for a laser-induced metallic boiling front
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about fundamental interaction mechanisms of laser remote fusion cutting, RFC, which is based on the formation of a quasi-stationary laser-induced boiling front that causes drop ejection, preferably downwards. Laser cutting of metals, invented in 1967, has developed from a niche to a well established high quality cutting technique in the manufacturing industry. Usually a gas jet is employed concentric to the laser beam, to eject the molten metal. One technique option, interesting though hardly applied yet because of usually low quality and speed, is remote laser cutting. Two techniques are distinguished, remote ablation cutting, grooving down through a sheet, layer-by-layer, and the here addressed remote fusion cutting, by a single pass through the sheet. For the latter, the ablation pressure from laser-induced boiling at the cutting front continuously accelerates and ejects the melt downwards. Advantages of remote laser cutting, facilitated by high brilliance lasers during the last decade, are the possibility of a larger working distance along with the avoidance of cutting gas and of a gas jet nozzle. The review paper of the thesis surveys different laser remote cutting techniques, including their modelling, as well as the transition to keyhole welding, owing to similarities particularly from the boiling front and from root spatter ejection. The six Papers I-VI that compose the thesis address fundamental mechanisms of laser remote fusion cutting, theoretically and experimentally. In Paper I a simplified mathematical model of the RFC cutting front enables to estimate the geometrical and energetic conditions of the process. By evidence and post-modelling from high speed imaging, HSI, the simplified smooth cutting front model is developed further to a wavy topology in Paper III, for more sophisticated absorption analysis. As a systematic support, Paper II categorizes and analyses for the first time the different wavy topologies observed at the front, from HSI. The melt dynamics induced by a pulsed laser beam was studied in Paper IV, again from HSI. Apart from other interesting transient melt phenomena it was demonstrated that the ablation pressure can push the melt to a certain pending position during the laser pulse while the melt retreats by surface tension during the pulse break. To engage remote fusion cutting with additive manufacturing, Paper V introduces a novel technique where the drops ejected from RFC are transferred to a substrate, about a centimetre underneath, on which a continuous track forms. This technique can even be applied as an efficient recycling approach. In Paper VI a variant of the technique is presented, to develop a boiling front along the edge of a metal sheet from which the drop transfer takes place, in a different manner. This enables to systematically machine-off the entire sheet, which can be converted to a new shape and product. Summarizing, the thesis provides a variety of analysis of fundamental mechanisms of a laser-induced boiling front that bear a certain simplicity and in turn controllability, of interest for established as well as for new applications, in manufacturing and in other sectors, including remote fusion cutting.
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| 3. |
- Samarjy, Ramiz Saeed Matti, 1965-, et al.
(författare)
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Laser-induced boiling and melt transfer from a metal edge
- 2017
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197.
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Tidskriftsartikel (refereegranskat)abstract
- A new technique for additive manufacturing was recently presented, by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt even can attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling of a whole sheet of waste metal. By the aid of high speed imaging from two different perspectives, the melt flow behaviour, the drop jet precision as well as process trends with respect to parameters, drop ejection and deposition were studied.
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| 4. |
- Samarjy, Ramiz Saeed Matti, 1965-, et al.
(författare)
-
Using laser cutting as a source of molten droplets for additive manufacturing : A new recycling technique
- 2017
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 125, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- A new variant of additive manufacturing is proposed which involves transferring molten droplets via a laser beam to a substrate. The droplets are generated by laser remote fusion cutting of a supply sheet that could be a waste material, for recycling purposes. The laser-induced ablation pressure at the cutting front continuously drives melt downwards below the supply sheet in the form of a liquid column. Droplets separate from the column and solidify as a track on a substrate below. The droplets, surrounded by vapour, had in this case an average diameter of 500 μm and a speed of 2 m/s, with deviations up to 50%. Sound clad tracks were generated on steel and aluminium substrates. In the case of a copper substrate discontinuous clad tracks were produced as a result of poor wetting. The droplet jet had a small divergence of about 5°, which is suitable for controlled deposition. The transmitted part of the laser beam interacted with the clad track but did not affect the process result. High speed imaging was found to be a suitable tool for qualitative and quantitative analysis of the technique.
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| 5. |
- Sundqvist, Jesper, 1987-, et al.
(författare)
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High-speed imaging of droplet behaviour during the CYCLAM drop-deposition technique
- 2019
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Ingår i: Procedia Manufacturing. - : Elsevier. - 2351-9789. ; 36, s. 208-215
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Tidskriftsartikel (refereegranskat)abstract
- The material in laser additive manufacturing is traditionally supplied in the form of powder or sometimes wire. A technique called CYCLAM was recently presented which is a fast and direct recycling technique which lowers the number of steps that need to be taken in typical recycling, allowing for a more circular economy. The CYCLAM technique proposes that waste metal is directly recycled through laser cutting or laser ablation of one sheet and the molten droplet is directly deposited onto a new product and can be used for additive manufacturing or cladding. The technique also can also use materials that otherwise are not available as powder or wires. Because of the novelty of the technique, it is still scarcely studied, and many aspects still needs to be understood. This paper focusses on high-speed imaging of the technique to understand the droplet behaviour. The material removal of the feeding sheet was done with Remote Fusion Cutting. Different power levels lead to different drop geometry and flight pattern of the drops where the drops at higher power are pushed further forward. The influence of the laser power on the shape of the deposited track can be seen from cross sections of the cladded track where higher power means that more power is transmitted through the feeding sheet and onto the substrate which creates a smoother surface
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