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Quantification of Melt Ejection Phenomena During Laser Drilling

Published online by Cambridge University Press:  10 February 2011

K.T. Voisey,
C.F. Cheng and
T.W. Clyne
K.T. Voisey
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, England, Tel: +44 (0)1223 334332, Fax: +44 (0)1223 334567
C.F. Cheng
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, England, Tel: +44 (0)1223 334332, Fax: +44 (0)1223 334567
T.W. Clyne
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, England, Tel: +44 (0)1223 334332, Fax: +44 (0)1223 334567, Email: twc10@cam.ac.uk
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Abstract

During laser drilling, material removal in general occurs both by vaporisation and by the expulsion of molten material. The latter commonly arises as a result of the rapid build-up of gas pressure within the growing cavity as evaporation takes place, but the precise mechanisms responsible for the phenomenon are still unclear. The current work is aimed at gaining an insight into these mechanisms via measurements of the amount of material ejected from cavities during laser drilling under different conditions. Attention is first devoted to the issues which need to be considered when making experimental measurements of the fraction of material removed by melt ejection. These include the collection efficiency and the possibility of chemical changes occurring during the process. Results are then presented from work with a range of metallic substrates (mild steel, tungsten, copper, titanium, aluminium and nickel), drilled with a JK701 Nd-YAG laser under different conditions. Observed variations in the melt ejection levels have been studied for mild steel and aluminium and these are briefly considered in terms of the expected effects of certain material property values and the mechanisms of melt ejection. Results from an existing finite difference heat flow model are used to investigate the significance of melt ejection.

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