JLA Vol:9 Iss:5 (Characteristics of Nd:YAG laser welded high carbon steels)

Authors:
Eng S. Ng
Ian A. Watson
Laser and Optical System Engineering Centre, Department of Mechanical Engineering, James Watt Building, University of Glasgow, Glasgow G12 8QQ, U.K.

A quantitative study of the relationship between the laser process parameters and the mechanical properties of welded high carbon steels was performed utilizing a Lumonics Nd:YAG pulsed laser, operating at 1.06μm, and a robotically manipulated fiber optic beam delivery system. A gage plate (0.88 mm thick) was butt welded with a constant power of 200 W and a He shielding gas was used at a pressure of 5 × 10⁴ Pa. The welding performance of the Nd:YAG laser was strongly affect...

JLA Vol:9 Iss:5 (Experimental development of a machining database for the CO₂ laser cutting of ceramic tile)

Authors:
S. A. J. Livingstone
K. L. Chua
I. Black
Department of Mechanical and Chemical Engineering, Heriot‐Watt University, Riccarton, Edinburgh EH14 4AS, U.K.

This paper covers the cutting of commercially‐available ceramic tiles using a CO₂ laser cutting machine, with the object of producing a laser beam machining database which contains the essential parameter information for their successful processing. Various laser cutting parameters were investigated that would generate a cut in ceramic tile which required minimal posttreatment. The effects of various shield gases, multipass cutting and underwater cutting were also examined.

JLA Vol:9 Iss:5 (Laser safety analysis of a retinal scanning display system)

Authors:
Erik Viirre
Richard Johnston
Homer Pryor
Satoru Nagata
Thomas A. Furness
Human Interface Technology Laboratory, University of Washington, Box 352142, Seattle, WA 98195–2142, U.S.A.

The Virtual Retinal Display (VRD) is a visual display that scans modulated laser light on to the retina of the viewer's eye to create an image. Maximum permissible exposures (MPE) have been calculated for the VRD in both normal viewing and possible failure modes. The MPE power levels are compared to the measured power that enters the eye while viewing images with the VRD. The power levels indicate that the VRD is safe in both normal operatin...

JLA Vol:9 Iss:5 (Laser‐Induced Damage in Optical Materials at the October 7–9, 1996 Symposium on Optical Materials for High‐Power Lasers (the Boulder Damage Symposium) Boulder, Colorado)

Authors:
Arthur H. Guenther
Sandia National Laboratories, Albuquerque, New Mexico 87106, U.S.A.

The 28th annual symposium on optical materials for high‐power lasers (Boulder damage symposium) was held at the National Institute of Standards and Technology in Boulder, CO, 7–9 October 1996. The symposium was held under the joint sponsorship of Bennett Optical Research, the Center for Research and Education in Optics and Lasers (CREOL) at the Center for Research and Education in Optics and Lasers (CREOL) at the University of Central Florida, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Sandia National Laboratories, and SPIE—The International ...

JLA Vol:9 Iss:5 (Threshold laser beam irradiances for melting and welding)

Authors:
K. H. Leong
H. K. Geyer
K. R. Sabo
P. G. Sanders
Technology Development Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A.

A model based on the conservation of energy for a moving heat source incident on a flat plate is used to predict the threshold laser beam irradiance required to initiate melting on a metal surface. With the use of a non‐dimensional variable and its solution, the threshold irradiance can be predicted with the use of a simple equation. This equation is a function of the absorptivity of the surface, thermal conductivity of the metal, temperature increase for melting, diameter of the laser beam at th...

JLA Vol:9 Iss:6 (… .But is it really safe?)

Authors:
Peter A. Smith
DERA Centre for Human Sciences, Farnborough, Hampshire, U.K.

JLA Vol:9 Iss:6 (Amendments to the Center for Devices and Radiological Health Federal Performance Standard for laser products)

Authors:
Jerome E. Dennis
Center for Devices and Radiological Health, Food and Drug Administration, Rockville, MD, U.S.A.

Federal law requires that all laser products that are imported into or introduced into commerce in the United States comply with the performance standard published in the Code of Federal Regulations (CRF), Title 21, Parts 1040.10 and 1040.11, administered by the Center for Devices and Radiological Health (CDRH), US Food and Drug Administration. Although it contains somewhat different requirements for hazard classification, engineering controls and labeling, the ANSI Z136.1 standard defers to the CDRH standard. The CDRH standard became effective in August, 1976 and ...

JLA Vol:9 Iss:6 (Effect of nozzle orientation on the gas dynamics of inert-gas laser cutting of mild steel)

Authors:
Aaron D. Brandt
Gary S. Settles
Gas Dynamics Laboratory, Mechanical Engineering Department, Penn State University, University Park, PA 16802, U.S.A.

This investigation applies sonic and supersonic coaxial and off‐axis nozzles to the cutting of mild steel sheet of 1–4 mm thickness. A 1.5 kW CW CO₂ laser is used with nitrogen as the assist gas. Sonic coaxial cutting is compared to that of off‐axis nozzles, which vary in orientation from 20–60° behind the laser axis and in exit Mach number from 1 to 2.4. Results show a 50% increase in maximum cutting speed at approximately a 40° off‐axis nozzle angle. In com...

JLA Vol:9 Iss:6 (Evolving issues in laser safety)

Authors:
David H. Sliney
US Army Center for Health Promotion and Preventive Medicine, Laser/Optical Radiation Program, Aberdeen Proving Ground, MD 21010‐5422, U.S.A.

The approach to laser safety has come a long way since the 1960s when the first guidelines were issued by defense research organizations in the US and the UK, and then by the American Conference of Governmental Industrial Hygienists. Although the search for ‘eye‐safe’ numbers continues in a few laboratories, this work is almost exclusively centered on deriving retinal thresholds for ultra‐short (sub‐nanosecond) lasers. Setting limits in this temporal region has been difficult, since...

JLA Vol:9 Iss:6 (Improved hole drilling using a high peak power Nd:YAG laser at the second harmonic wavelength)

Authors:
Xiangli Chen
Angel L. Ortiz
P. Randall Staver
William T. Lotshaw
Todd J. Rockstroh
Michael H. McLaughlin

We have previously described the drilling of advanced materials such as intermetallics, superalloys, and composites using an Nd:YAG laser operating at the fundamental wavelength of 1.064 μm [1]. We have now extended these studies to the second harmonic wavelength of 532 nm of a high peak power Nd:YAG laser. The results show that drilling using the shorter wavelength further reduces undesired thermal effects such as recast layers and heat affected zones. A comparison of these results with those obtained at...