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TECHNICAL PAPERS

An Analysis of the Effect of Laser Beam Geometry on Laser Transformation Hardening

[+] Author and Article Information
Shakeel Safdar1

Laser Processing Centre, Department of Mechanical, Aerospace and Civil engineering, University of Manchester, Manchester M60 1QD, UKs.safdar@postgrad.manchester.ac.uk

Lin Li, M. A. Sheikh

Laser Processing Centre, Department of Mechanical, Aerospace and Civil engineering, University of Manchester, Manchester M60 1QD, UK

Zhu Liu

Corrosion and Protection Centre, School of Material, University of Manchester, M60 1QD, UK

1

To whom correspondence should be addressed.

J. Manuf. Sci. Eng 128(3), 659-667 (Dec 06, 2005) (9 pages) doi:10.1115/1.2193547 History: Received May 13, 2005; Revised December 06, 2005

The effect of transformation hardening depends upon both heating and cooling rates. It is desirable to have a slow heating rate and a rapid cooling rate to achieve full transformation. To date laser transformation hardening has been carried out using circular or rectangular beams which result in rapid heating and cooling. Although the use of different beam intensity distributions within the circular or rectangular laser beams has been studied to improve the process, no other beam geometries have been investigated so far for transformation hardening. This paper presents an investigation into the effects of different laser beam geometries in transformation hardening. Finite element modeling technique has been used to simulate the steady state and transient effects of moving beams in transformation hardening of EN 43A steel. The results are compared with experimental data. The work shows that neither of the two commonly used beams, circular and rectangular, are optimum beam shapes for transformation hardening. The homogenization temperature exceeds the melting point for these beam shapes for the usual laser scanning speeds and power density. Triangular beam geometry has been shown to produce the best thermal history to achieve better transformation and highest hardness due to slower heating without sacrificing the processing rate and hardening depths.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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dT∕dt versus time

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Figure 5

Temperature time in lateral direction

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Temperature versus depth

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Figure 9

dT∕dt (heating rate) versus depth

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Figure 13

Isotherms in y-z plane

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Figure 14

HAZ for (a) circular beam and (b) Rec L beam

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Figure 15

Microstructure as seen from top for (a) circle and (b) Tri F beam

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Figure 1

Sinulation of moving laser beam

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Figure 2

Schematic representation of the experimental set up

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Figure 3

Temperature versus time

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Figure 6

dT∕dt (heating rate) versus distance in lateral direction

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Figure 7

dT∕dt (cooling rate) versus distance in lateral direction

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Figure 10

dT∕dt (cooling rate) versus depth

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Figure 11

Experimentally measured hardness (HV) versus depth

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Figure 12

Hardness (HV) versus% martensite (for 0.50% carbon, derived from (32))

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