JLA Vol:14 Iss:1 (Melt instabilities during laser surface alloying)

Authors:
M. H. McCay
J. A. Hopkins
T. D. McCay
The University of Tennessee Space Institute, Center for Laser Applications, Tullahoma, Tennessee 37388

The depth of the melt layer during laser surface alloying plays a significant role in the shape of the melt pool. There appear to be critical depths at which the molten layer becomes unstable and alters its shape in response to convective flow patterns. The Marangoni number provides an understanding of the influence of the material properties on convection and subsequently the melt shape, being inversely proportional to depth squared, viscosity, and thermal diffusivity, and directly proportional to the surface t...

JLA Vol:14 Iss:1 (Multiple reflection and its influence on keyhole evolution)

Authors:
Hyungson Ki
Pravansu S. Mohanty
Jyotirmoy Mazumder
Center for Laser Aided Intelligent Manufacturing, Department of Mechanical Engineering and Applied Mechanics, The University of Michigan, Ann Arbor, Michigan 48109-2125

In laser drilling and keyhole welding, multiple reflection phenomena determine how the energy is transferred from the laser beam to the workpiece, and, most importantly, all other physics such as fluid flow, heat transfer, and the cavity shape itself depend on these phenomena. In this study, a multiple reflection model inside a self-consistent (or self-evolving) cavity has been developed based on the level set method and ray tracing t...

JLA Vol:14 Iss:1 (Particle size analysis of material removed during CO₂ laser scabbling of concrete for filtration design)

Authors:
L. M. Lobo
K. Williams
Optical Engineering Group, Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom

E. P. Johnson
Laser Group, Department of Mechanical Engineering, Liverpool University, Liverpool, Merseyside L69 3BX, United Kingdom

J. T. Spencer
BNFL, Rutherford House, Risley, Warrington, Cheshire WA3 6AS, United Kingdom

This article examines the particles formed during optimized laser scabbling of concrete in order to help determine an effective filtration strategy for the process. The laser scabbling technique has been developed ...

JLA Vol:14 Iss:1 (Phosphoric acid activated surface modification of tooth dentine by 9.45 μm transversely excited atmosphere CO₂ laser)

Authors:
Kunio Awazu
Mikio Tanaka
Institute of Free Electron Laser, Osaka University, 2-9-5, Tsudayamate, Hirakata, Osaka 573-0128, Japan

Junji Kato
Department of Pediatric Dentistry, Faculty of Dentistry, Tokyo Medical and Dental-University, Japan

Tuning a laser wavelength to the stretching vibration of specific biomolecules has some advantages in ablating hard tissue and for surface modification induced by the photothermal or the photomechanical interaction. A tunable pulsed transversely excited atmosphere CO₂ laser was tuned to 9.45 μm, which is the stretching vibration of phosphoric acid in hydroxyapatite. Dried cow dentine was irra...

JLA Vol:14 Iss:1 (Physical–computational model to describe the interaction between a laser beam and a powder jet in laser surface processing)

Authors:
O. O. Diniz Neto
Array

R. Vilar
Departamento de Engenharia de Materiais, Instituto Superior Te´cnico, 1049-001 Lisboa, Portugal

Frequently laser surface treatments use a powder jet in conjunction with the laser beam. In this study we present a physical–computational model to describe the interaction between a laser beam and a powder jet. The model can be used to calculate the spatial distribution of particle temperature and laser beam attenuation at any moment and all over the region where the laser and particle beams interact. In calculating particle temperature, the attenuation of the laser beam by the particles themselves is taken into acc...

JLA Vol:14 Iss:2 (An investigation of rapid prototyping of sand casting molds by selective laser sintering)

Authors:
G. Casalino
L. A. C. De Filippis
A. D. Ludovico
L. Tricarico
Dipartimento di Ingegneria Meccanica e Gestionale, Politecnico di Bari, 70126 Bari, Italy

Among the layer fabrication techniques, selective laser sintering (SLS), is widely used for manufacturing various products made of different materials (i.e., polycarbonates, nylons, polyamides, sand casting, metal powders, and others). The SLS of precoated foundry sands allows the aggregation of adjacent particles, which are then cemented by furnace heat treatment. Moreover, geometrically complex molds and cores not obtainable with conventional methods can be realized by this method. In th...

JLA Vol:14 Iss:2 (Application of 7 kW class high power yttrium–aluminum–garnet laser welding to stainless steel tanks)

Authors:
Yoshiaki Shimokusu
Kobe Shipyard & Machinery Works, Mitsubishi Heavy Industries Ltd., 1-1-1 Wadasaki-cho, Hyogo-ku, Kobe Hyogo 652-8585, Japan

Seiji Fukumoto
Kobe Shipyard & Machinery Works, Mitsubishi Heavy Industries Ltd., 1-1-1 Wadasaki-cho, Hyogo-ku, Kobe Hyogo 652-8585, Japan

Michisuke Nayama
Technology Planning Department, Technical Headquarters, Mitsubishi Heavy Industries Ltd., 3-3-1 Minatomirai, Nishi-ku, Yokohama Kanagawa 220-8401, Japan

Takashi Ishide
Takasago R&D Center, Mitsubishi Heavy Industries Ltd., 2-2-1 Shinhama, Arai-cho, Takasago Hyogo 676-8686, Japan

Shuho Tsubota
Takasago...

JLA Vol:14 Iss:2 (Deformation behavior and microstructural changes of a hardened high carbon alloy steel in laser bending)

Authors:
K. C. Chan
J. Liang
Department of Manufacturing Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong

In this article, the deformation behavior and microstructure of a hardened high carbon steel in laser bending were examined. A CO₂ laser unit (TEM₀₀) was used to bend the samples at different laser powers, scanning velocities, and number of scans. A relatively linear relationship between bending angle and number of scans was obtained at laser powers of 150 and 200 W and at a scanning velocity of 30 mm/s. A threshold heat input of about 3.25 J/mm was observed, below which bending was unlikely to occur. The bending angle was al...

JLA Vol:14 Iss:2 (Development of simulated pigmented lesions in an optical skin-tissue phantom: Experimental measurements in the visible and near infrared)

Authors:
Manuela Lualdi
Ambrogio Colombo
Alberto Mari
Stefano Tomatis
Renato Marchesini
Medical Physics Unit, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy

Realistic, pigmented skin simulants (“phantoms”) can be useful in optimizing dermal laser procedures and for laser surgical training. Diffuse reflectance of skin pigmented lesions depends on the amount and distribution of the absorbing/diffusing chromophores, mainly hemoglobin and melanin, embedded in the skin layers. The reason why diffuse reflectance of benign melanocytic lesions is different from that of melanoma is still unclear. In an attempt...

JLA Vol:14 Iss:2 (Energy redistribution during CO₂ laser cladding)

Authors:
H. Gedda
Luleå University of Technology, Division of System and Manufacturing Engineering, S-971 87 Luleå, Sweden

J. Powell
Laser Expertise Ltd., Acorn Park Industrial Estate, Harrimans Lane, Nottingham NG7 2TR, United Kingdom

G. Wahlstro¨m
Duroc AB, Industriva¨gen 8, S-90130 Umeå, Sweden

W.-B. Li
H. Engstro¨m
C. Magnusson
Luleå University of Technology, Division of System and Manufacturing Engineering, S-971 87 Luleå, Sweden

This article examines the factors that effect the efficiency of the CO₂-laser powder cladding process. By the...