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Powell, John
Publications (10 of 128) Show all publications
Pocorni, J., Powell, J., Frostevarg, J. & Kaplan, A. F. H. (2018). Dynamic laser piercing of thick section metals. Optics and lasers in engineering, 100, 82-89
Open this publication in new window or tab >>Dynamic laser piercing of thick section metals
2018 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 100, p. 82-89Article in journal (Refereed) Published
Abstract [en]

Before a contour can be laser cut the laser first needs to pierce the material. The time taken to achieve piercing should be minimised to optimise productivity. One important aspect of laser piercing is the reliability of the process because industrial laser cutting machines are programmed for the minimum reliable pierce time. In this work piercing experiments were carried out in 15 mm thick stainless steel sheets comparing a stationary laser and a laser which moves along a circular trajectory with varying processing speeds. Results show that circular piercing can decrease the pierce duration by almost half compared to stationary piercing. High speed imaging (HSI) was employed during the piercing process to understand melt behaviour inside the pierce hole. HSI videos show that circular rotation of the laser beam forces melt to eject in opposite direction of the beam movement, while in stationary piercing the melt ejects less efficiently in random directions out of the hole.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Laser cutting, laser piercing, reliability, efficiency, fibre laser, high speed imaging
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-63492 (URN)10.1016/j.optlaseng.2017.07.012 (DOI)000414108700010 ()2-s2.0-85026484330 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-08-15 (andbra)

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-11-24Bibliographically approved
Atiyah, H., Powell, J., Petring, D., Stoyanov, S. & Voisey, T. (2018). Fiber laser cutting: The use of carbon-filled acrylic as a qualitative and quantitative analysis tool. Journal of laser applications, 30, Article ID 032009.
Open this publication in new window or tab >>Fiber laser cutting: The use of carbon-filled acrylic as a qualitative and quantitative analysis tool
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2018 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, article id 032009Article in journal (Refereed) Published
Abstract [en]

The use of carbon-filled black acrylic (CFBA) as a quantitative and qualitative analytical tool for fiber laser cutting is investigated. In the qualitative work, CFBA targets placed below the laser cutting zone when cutting stainless steel showed a distinctive “leaf” shaped evaporation crater which can provide information about the nature of the reflections taking place in the cut zone. Quantitative measurements have revealed a specific evaporation energy of 3.4 J/mm3 for CFBA. However, this figure is only applicable when considering intense beams when the CFBA target is stationary with respect to the laser beam.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-70243 (URN)10.2351/1.5045349 (DOI)2-s2.0-85051221820 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-07 (andbra)

Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2018-08-17Bibliographically approved
Haglund, P., Frostevarg, J., Powell, J., Eriksson, I. & Kaplan, A. (2018). Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses. Optics and Laser Technology, 100, 1-6
Open this publication in new window or tab >>Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses
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2018 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 100, p. 1-6Article in journal (Refereed) Published
Abstract [en]

Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-66009 (URN)10.1016/j.optlastec.2017.09.053 (DOI)000417669700001 ()2-s2.0-85030758159 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-10 -09 (andbra)

Available from: 2017-10-09 Created: 2017-10-09 Last updated: 2017-12-28Bibliographically approved
Pocorni, J., Powell, J., Frostevarg, J. & Kaplan, A. F. .. (2018). The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions. Optics and Laser Technology, 103, 318-326
Open this publication in new window or tab >>The geometry of the cutting front created by Fibre and CO2 lasers when profiling stainless steel under standard commercial conditions
2018 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 103, p. 318-326Article in journal (Refereed) Published
Abstract [en]

Cutting fronts created by CO2 and fibre lasers in stainless steel at thicknesses between 2 mm and 10 mm have been ‘frozen’ and their geometry has been measured. Standard commercial cutting parameters were used to generate the cuts for both types of laser. The resulting three-dimensional cutting front shapes have been curve fitted as polynomials and semicircles. Various features of the cutting front geometry are discussed including the lack of correlation of the cut front inclination with either the relevant Brewster angle or the inclination of the striations on the cut edge.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-67687 (URN)10.1016/j.optlastec.2018.01.055 (DOI)000427339000041 ()2-s2.0-85041470309 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-19 (andbra)

Available from: 2018-02-19 Created: 2018-02-19 Last updated: 2018-06-11Bibliographically approved
Pocorni, J., Powell, J., Deichsel, E., Frostevarg, J. & Kaplan, A. (2017). Fibre laser cutting stainless steel: Fluid dynamics and cut front morphology (ed.). Optics and Laser Technology, 87, 87-93
Open this publication in new window or tab >>Fibre laser cutting stainless steel: Fluid dynamics and cut front morphology
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2017 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 87, p. 87-93Article in journal (Refereed) Published
Abstract [en]

In this paper the morphology of the laser cut front generated by fibre lasers was investigated by observation of the ‘frozen’ cut front, additionally high speed imaging (HSI) was employed to study the fluid dynamics on the cut front while cutting. During laser cutting the morphology and flow properties of the melt film on the cut front affect cut quality parameters such as cut edge roughness and dross (residual melt attached to the bottom of the cut edge). HSI observation of melt flow down a laser cutting front using standard cutting parameters is experimentally problematic because the cut front is narrow and surrounded by the kerf walls. To compensate for this, artificial parameters are usually chosen to obtain wide cut fronts which are unrepresentative of the actual industrial process. This paper presents a new experimental cutting geometry which permits HSI of the laser cut front using standard, commercial parameters. These results suggest that the cut front produced when cutting medium section (10 mm thick) stainless steel with a fibre laser and a nitrogen assist gas is covered in humps which themselves are covered by a thin layer of liquid. HSI observation and theoretical analysis reveal that under these conditions the humps move down the cut front at an average speed of approximately 0.4 m/s while the covering liquid flows at an average speed of approximately 1.1 m/s, with an average melt depth at the bottom of the cut zone of approximately 0.17 mm.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-9223 (URN)10.1016/j.optlastec.2016.08.002 (DOI)000384867900012 ()2-s2.0-84982085472 (Scopus ID)7c9617db-b7dc-4cd4-bfde-993e46efa21a (Local ID)7c9617db-b7dc-4cd4-bfde-993e46efa21a (Archive number)7c9617db-b7dc-4cd4-bfde-993e46efa21a (OAI)
Note

Validerad; 2016; Nivå 2; 20160817 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-09-13Bibliographically approved
Powell, J. (2017). Hail to the new, popular, units [Letter to the editor]. Physics world, 30(4), 52
Open this publication in new window or tab >>Hail to the new, popular, units
2017 (English)In: Physics world, ISSN 0953-8585, Vol. 30, no 4, p. 52-Article in journal, Letter (Other (popular science, discussion, etc.)) Published
National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-62967 (URN)10.1088/2058-7058/30/4/45 (DOI)000399018100026 ()
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-11-24Bibliographically approved
Pocorni, J., Powell, J., Frostevarg, J. & Kaplan, A. (2017). Investigation of the Piercing Process in Laser Cutting of Stainless Steel. Journal of laser applications, 29(2), Article ID 022201.
Open this publication in new window or tab >>Investigation of the Piercing Process in Laser Cutting of Stainless Steel
2017 (English)In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 29, no 2, article id 022201Article in journal (Refereed) Published
Abstract [en]

This paper investigates the laser piercing process which precedes nearly every laser cutting operation. The two most important aspects of the piercing process are: a) How long does it take to pierce the material? And b) How wide is the pierced hole? If the hole is no wider than the cut line, the material can be pierced on the line to be cut. In this paper 10 mm thick stainless steel was pierced by a multikilowatt fibre laser to compare efficiency and quality when piercing with a continuous wave (cw) output and a selected range of power modulation parameters. The different processes were observed by high speed imaging and subsequently examined by visual observation. High speed imaging is used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. The results show that appropriate laser power modulation settings can considerably reduce both the piercing time and the required energy to generate any piercing hole required for the subsequent cutting process. This pulse-pierce technique and the differences between piercing with a continuous and a power modulated laser beam are further explained and discussed. Also the effect on the size of the entrance to the pierced hole depending on power modulation regimes was investigated in this paper.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
Keywords
Laser cutting, laser piercing, efficiency, fibre laser, high speed imaging
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-60387 (URN)10.2351/1.4983260 (DOI)000405475100004 ()2-s2.0-85019497656 (Scopus ID)
Projects
HALO project
Funder
EU, FP7, Seventh Framework Programme, 314410
Note

Validerad; 2017; Nivå 2; 2017-05-17 (andbra)

Available from: 2016-11-14 Created: 2016-11-14 Last updated: 2018-07-10Bibliographically approved
Pocorni, J., Petring, D., Powell, J., Deichsel, E. & Kaplan, A. (2016). The Effect of Laser Type and Power on the Efficiency of Industrial Cutting of Mild and Stainless Steels (ed.). Journal of manufacturing science and engineering, 138(3), Article ID 31012.
Open this publication in new window or tab >>The Effect of Laser Type and Power on the Efficiency of Industrial Cutting of Mild and Stainless Steels
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2016 (English)In: Journal of manufacturing science and engineering, ISSN 1087-1357, E-ISSN 1528-8935, Vol. 138, no 3, article id 31012Article in journal (Refereed) Published
Abstract [en]

This paper investigates the effect of material type, material thickness, laser wavelength and laser power on the efficiency of the cutting process for industrial state-of-the-art cutting machines. The cutting efficiency is defined in its most basic terms: as the area of cut edge created per Joule of laser energy. This fundamental measure is useful in producing a direct comparison between the efficiency of fiber and CO2 lasers when cutting any material. It is well known that the efficiency of the laser cutting process generally reduces as the material thickness increases, because conductive losses from the cut zone are higher at the lower speeds associated with thicker section material. However, there is an efficiency dip at the thinnest sections. This paper explains this dip in terms of a change in laser-material interaction at high cutting speeds. Fiber lasers have a higher cutting efficiency at thin sections than their CO2 counterparts, but the efficiency of fiber laser cutting falls faster than that of CO2 lasers as material thickness is increased. This is the result of a number of factors including changes in cut zone absorptivity and kerf width. This paper presents phenomenological explanations for the relative cutting efficiencies of fiber lasers and CO2 lasers, and the mechanisms affecting these efficiencies for stainless steels (cut with nitrogen) and mild steel (cut with oxygen or nitrogen) over a range of thicknesses. The paper involves a discussion of both theoretical and practical engineering issues. Key Words; Laser Cutting, Fiber Laser, CO2 Laser, Efficiency.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-8003 (URN)10.1115/1.4031190 (DOI)000369666000012 ()2-s2.0-84942927258 (Scopus ID)67180056-91cc-4c93-abd0-5dc50bc39299 (Local ID)67180056-91cc-4c93-abd0-5dc50bc39299 (Archive number)67180056-91cc-4c93-abd0-5dc50bc39299 (OAI)
Note

Validerad; 2015; Nivå 2; 20150807 (jetpoc)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Keskitalo, M., Mentyjärvi, K., Sundqvist, J., Powell, J. & Kaplan, A. (2015). Laser Welding Of Duplex Stainless Steel With Nitrogen As Shielding Gas (ed.). Paper presented at . Journal of Materials Processing Technology, 216, 381-384
Open this publication in new window or tab >>Laser Welding Of Duplex Stainless Steel With Nitrogen As Shielding Gas
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2015 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 216, p. 381-384Article in journal (Refereed) Published
Abstract [en]

Nitrogen loss from laser welding melt pools and can have a deleterious effect on weld toughness for duplex stainless steels. This effect can be alleviated by using nitrogen as the shielding gas during laser welding. The use of Nitrogen results in increased austenite levels in the weld metal and improved toughness levels.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-6988 (URN)10.1016/j.jmatprotec.2014.10.004 (DOI)000347020800039 ()2-s2.0-84908377287 (Scopus ID)55223c78-9f7c-4c94-aaaf-b2f3780420f2 (Local ID)55223c78-9f7c-4c94-aaaf-b2f3780420f2 (Archive number)55223c78-9f7c-4c94-aaaf-b2f3780420f2 (OAI)
Note
Validerad; 2014; Nivå 2; 20141017 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Pocorni, J., Petring, D., Powell, J., Deichsel, E. & Kaplan, A. (2015). Measuring the Melt Flow on the Laser Cut Front (ed.). Paper presented at Nordic Laser Materials Processing Conference : 25/08/2015 - 27/08/2015. Physics Procedia, 78, 99-109
Open this publication in new window or tab >>Measuring the Melt Flow on the Laser Cut Front
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2015 (English)In: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 78, p. 99-109Article in journal (Refereed) Published
Abstract [en]

The flow characteristics on the laser cut front for 10 mm stainless steel AISI 304 (EN 1.4301) are studied in this paper using High Speed Imaging (HSI). The laser cut samples were produced with a 6 kW fiber laser with nitrogen gas assist. Previous work in this field has used unusual cutting parameters to make the experimentation easier. This work presents, for the first time, HSI results from standard commercially viable cutting parameters. This was made possible by the development of a new experimental technique. The results presented here suggest that the cut front produced when cutting stainless steel with a fiber laser and a nitrogen assist gas is covered in bumps which themselves are covered in a thin layer of liquid. Under the conditions shown here the bumps move down the cut front at an average speed of approximately 0.4m/s. The liquid flows at an average speed of approximately 1.1m/s. The average melt depth at the bottom of the cut zone under these conditions is approximately 0.17 mm.

National Category
Manufacturing, Surface and Joining Technology
Research subject
Manufacturing Systems Engineering
Identifiers
urn:nbn:se:ltu:diva-30740 (URN)10.1016/j.phpro.2015.11.022 (DOI)000370876600011 ()2-s2.0-84965050315 (Scopus ID)4a83279a-0219-412a-9ca9-5fc4016ce67e (Local ID)4a83279a-0219-412a-9ca9-5fc4016ce67e (Archive number)4a83279a-0219-412a-9ca9-5fc4016ce67e (OAI)
Conference
Nordic Laser Materials Processing Conference : 25/08/2015 - 27/08/2015
Note
Validerad; 2015; Nivå 1; 20151126 (andbra); Konferensartikel i tidskriftAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
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