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Research Papers

The Effect of Laser Type and Power on the Efficiency of Industrial Cutting of Mild and Stainless Steels

[+] Author and Article Information
Jetro Pocorni

Department of Engineering
Sciences and Mathematics,
Luleå University of Technology,
Luleå 971 87, Sweden
e-mail: Jetro.Pocorni@ltu.se

Dirk Petring

Fraunhofer ILT,
Steinbachstr. 15,
Aachen 52074, Germany
e-mail: Dirk.Petring@ilt.fraunhofer.de

John Powell

Department of Engineering
Sciences and Mathematics,
Luleå University of Technology,
Luleå 971 87, Sweden
e-mail: John.Powell@laserexp.co.uk

Eckard Deichsel

Bystronic Laser AG,
Industriestr. 21,
Niederönz CH-3362, Switzerland
e-mail: Eckard.Deichsel@bystronic.com

Alexander F. H. Kaplan

Department of Engineering
Sciences and Mathematics,
Luleå University of Technology,
Luleå 971 87, Sweden
e-mail: Alexander.Kaplan@ltu.se

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received May 6, 2015; final manuscript received July 27, 2015; published online October 1, 2015. Assoc. Editor: Y. B. Guo.

J. Manuf. Sci. Eng 138(3), 031012 (Oct 01, 2015) (6 pages) Paper No: MANU-15-1212; doi: 10.1115/1.4031190 History: Received May 06, 2015; Revised July 27, 2015

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 the material thickness increases. 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.

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Figures

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Fig. 1

Relative cutting efficiency results for stainless steel (nitrogen cutting gas)

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Fig. 2

Relative cutting efficiency results for mild steel cut with nitrogen assist gas

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Fig. 3

Relative cutting efficiency results for mild steel cut with oxygen assist gas. (Note: the 3 mm sample cut with the 2 kW fiber laser and oxygen assist gas had the highest efficiency ofthe whole experimental set and is thus normalized to a value of 1.)

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Fig. 4

Relative average kerf width measurements for samples cut by (a) fiber laser and (b) CO2 laser

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Fig. 5

Relative cutting volume efficiency for stainless steel

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Fig. 6

Relative cutting volume efficiency for mild steel

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Fig. 7

During laser cutting the laser beam interacts with the cut front at a glancing angle [14]

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Fig. 8

(a) Left: if the material is 1 mm thick and the beam is 200 μm wide then the cut front angle needs to be 11 deg if all the cutting front is to interact with the beam. (b) Right: if the cut front angle is changed, for example, to the 3 deg (the Brewster angle for CO2 lasers) then the absorptivity is high but most of the beam misses the cut front. (The beam and cut front geometry have, of course, been greatly simplified in this figure.)

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Fig. 9

Absorptivity as a function of cut front/laser beam glancing angle (glancing angle = (90 deg − angle of incidence), see Fig. 7)

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Fig. 10

Multiple reflections in a fiber laser cut kerf

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