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TECHNICAL PAPERS

Surface Modification of Powder Metallurgy Components With a Direct Diode Laser

[+] Author and Article Information
Stuart Barnes, Michael J. Nash, Y. K. Kwok

Warwick Manufacturing Group, School of Engineering, University of Warwick, Coventry, England

J. Eng. Mater. Technol. 125(4), 372-377 (Sep 22, 2003) (6 pages) doi:10.1115/1.1605111 History: Received January 10, 2003; Revised June 17, 2003; Online September 22, 2003
Copyright © 2003 by ASME
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References

Figures

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Component selected for laser processing; a 100 mm diameter ferrous sprocket wheel used in automotive engine applications. Sprocket teeth are induction hardened.
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Laser processing set-up with the laser head positioned above the component which is held in a chuck attached to a CNC controlled X-Y table
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Typical laser processed track produced at 1000 W, sectioned at 90 deg to the track, polished and etched in a 2 percent Nital solution
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Hardness profiles produced at a laser power of 1000 W and indicated processing speeds. It can be seen that the hardness and hardening depth decrease with increasing processing speed and that the induction hardened sample is harder than all laser hardened samples.
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Variation in hardened depth (550 HV) with processing speed at 1200 W showing a consistent decrease in depth of hardening with increasing processing speed
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Variation of maximum surface hardness with processing speed at 1000 W. Hardness is reduced at speeds in excess of 3000 mm/min, but below this speed the trend is a less consistent than that shown in Fig. 5.
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Martensitic microstructure within the laser processed track (top), and parent material (bottom), etched in 2 percent Nital
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SEM images of the surface of (a) untreated material and (b) a laser processed track produced at 1000 W and 1000 mm/min, showing the absence of any melting on the surface; see Figs. 11 and 12 for characteristics of a melted surface.
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Hardness profiles produced at a laser power of 1200 W and the indicated processing speeds. Surface hardness of all profiles is comparable with induction hardening although hardening depth decreases with increasing processing speed.
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Variation in hardened depth (550 HV) with processing speed at 1200 W showing a consistent decrease in hardness depth with increasing processing speed
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SEM images of the surface a laser processed track produced at 1200 W and 1000 mm/min, showing a smooth surface resulting from limited melting, bottom right compared to the un-melted, as-received PM surface top left
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SEM images of the surface a laser processed track produced at 1200 W and 600 mm/min, showing a “weld-like” surface resulting from significant melting, top right and an as-received PM surface bottom left

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