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Dynamic laser piercing of thick section metals
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0001-6261-2019
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-3569-6795
2018 (engelsk)Inngår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 100, s. 82-89Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2018. Vol. 100, s. 82-89
Emneord [en]
Laser cutting, laser piercing, reliability, efficiency, fibre laser, high speed imaging
HSV kategori
Forskningsprogram
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-63492DOI: 10.1016/j.optlaseng.2017.07.012ISI: 000414108700010Scopus ID: 2-s2.0-85026484330OAI: oai:DiVA.org:ltu-63492DiVA, id: diva2:1097825
Merknad

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

Tilgjengelig fra: 2017-05-23 Laget: 2017-05-23 Sist oppdatert: 2019-02-18bibliografisk kontrollert
Inngår i avhandling
1. Laser cutting and piercing: Experimental and theoretical investigation
Åpne denne publikasjonen i ny fane eller vindu >>Laser cutting and piercing: Experimental and theoretical investigation
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis concerns experimental investigations of laser cutting and piercing, with theoretical and practical discussions of the results. The thesis is made up of an introduction to laser cutting and six scientific Papers. These Papers are linked in such a way that each of them studies a different aspect of laser cutting: process efficiency in Paper I, morphology and melt flow on the laser cut front in Papers II, III and IV and laser piercing in Papers V and VI.

Paper I 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 CO2 and fibre laser cutting machines. Here the cutting efficiency is defined in its most fundamental terms: as the area of cut edge created per Joule of laser energy.

In Paper II a new experimental technique is presented which has been developed to enable high speed imaging of laser cut fronts produced using standard, commercial parameters. The results presented here suggest that the cut front produced when cutting 10 mm thick medium section stainless steel with a fibre laser and a nitrogen assist gas is covered in humps which themselves are covered in a thin layer of liquid. Paper III presents numerical simulations of the melt flow on a fibre laser ablation-driven processing front during remote fusion cutting, RFC. The simulations were validated with high speed imaging observations of the processing front. The simulation results provide explanations of the main liquid transport mechanisms on the processing front, based on information on the temperature, velocity and pressure fields involved. The results are of fundamental relevance for any process governed by a laser ablation induced front. In Paper IV 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. The resulting three-dimensional shapes have been curve fitted as ninth order polynomials. 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. In this paper, mathematical descriptions of the cutting fronts are obtained, which can be used as input parameters by any researcher in the field of laser cutting simulations.

Paper V investigates the subject of laser piercing. Before any cut is started the laser needs to pierce the material. In this paper the laser piercing process is investigated using a wide range of laser pulse parameters, for stainless steel using a fibre laser. The results reveal the influence of pulse parameters on pierce time and pierced hole diameter. A high speed imaging camera was used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. In Paper VI a ‘dynamic’ or ‘moving beam’, laser piercing technique is introduced for processing 15 mm thick stainless steel. 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 a comparison was made between a stationary laser and a laser which moves along a circular trajectory with varying processing speeds. High speed imaging was employed during the piercing process to understand melt behavior inside the pierce hole.

Throughout this work experimental techniques, including advanced high speed imaging, have been used in conjunction with simulations and theoretical analysis, to provide new knowledge for understanding and improving laser beam cutting and its associated piercing process.

sted, utgiver, år, opplag, sider
Luleå: Luleå tekniska universitet, 2017
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Emneord
Laser cutting, laser piercing, efficiency, fibre laser, CO2 laser, high speed imaging
HSV kategori
Forskningsprogram
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-63498 (URN)978-91-7583-916-5 (ISBN)978-91-7583-917-2 (ISBN)
Disputas
2017-09-29, E 231, Luleå tekniska universitet/ 971 87 Luleå , Luleå, 09:30 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2017-05-24 Laget: 2017-05-23 Sist oppdatert: 2017-11-24bibliografisk kontrollert

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