JLA Vol:8 Iss:3 (Laser Hardened Materials Evaluation Laboratory (LHMEL))

Authors:
R. J. Hull
M. L. Lander

Since 1976, the Laser Hardened Materials Evaluation Laboratory (LHMEL) has been characterizing material responses to laser energy in support of national defense programs and the aerospace industry. Now that capability is available to commercial industry as well. LHMEL's power levels, beam uniformity, and diagnostics capabilities make it an ideal facility for proof‐of‐concept testing or process development. Located at Wright‐Patterson Air Force Base, Ohio, LHMEL is managed by the Wright Laboratory Materials Directorate and operated by Lawrence Associates, Incorporated. The facility's advanced hardware is centered aroun...

JLA Vol:8 Iss:3 (High‐power, high‐beam‐quality solid‐state lasers for materials processing applications)

Authors:
Lloyd A. Hackel
C. Brent Dane
Mark R. Hermann
John Honig
Luis E. Zapata
Mary A. Norton
Lawrence Livermore National Laboratory, P.O. Box 808, L‐487, Livermore, CA 94550, U.S.A.

The Laser Science and Technology Department at Lawrence Livermore National Laboratory is developing solid‐state lasers with high average power and high beam quality. Specific systems include a laser to generate 1.0–1.4 nm X‐rays for proximity print lithography, a 400‐mJ, 500‐Hz laser for 13.0 nm projection lithography and unique systems for speckle imaging, laser radars, and medical treatments.

JLA Vol:8 Iss:4 (On the relation between fluid dynamic pressure and the formation of pores in laser keyhole welding)

Authors:
John Dowden
Phiroze Kapadia
Andy Clucas
R. Ducharme
W. M. Steen

In the laser welding of metals with a continuous CO₂ laser, a hole containing a partially ionized metal vapor is formed throughout the depth of the material. A full description of flow conditions inside this hole is needed for a complete understanding of the process, but much can be learned from a simpler analysis of this aspect of the problem. The balance of forces that keeps the keyhole open can be investigated in this way. Such a model shows that over most of the keyhole's length, the dominant force keeping the keyhole open against surface tension...

JLA Vol:8 Iss:4 (The role of oxygen pressure in laser cutting mild steels)

Authors:
A. Ivarson
J. Powell
C. Magnusson

This paper presents the results of an experimental program investigating the effects of using high pressure oxygen as assist gas in combination with a pulsed laser while cutting medium thick mild steel plates. It was discovered that if the pulse conditions are optimized, the maximum cutting speed for a set average laser power could be increased by up to 10% compared to low oxygen pressure continuous wave (CW) laser cutting. The assist gas was found to have two optimum pressure ranges between which the material suffered from burning on the cut edge. The paper presents a phenomenological model to explain the ch...

JLA Vol:8 Iss:4 (Some aspects of laser heating of engineering materials)

Authors:
B. S. Yilbas
A. Z. Al‐Garni
Mechanical Eng. Dept., KFUPM, P.O. Box 1913, Dhahran, Saudi Arabia

Laser induced heating processes are important when a laser is used as a machine tool in industry, since the quality of the machining process strongly depends on the heating mechanism. The present study examines a heat transfer model that provides useful information on the laser induced interaction mechanism. Steady state and time dependent heating models are introduced and temperature profiles inside the materials are predicted. Using appropriate assumptions, the time for the surface temperature to reach 90% of its steady state value is estimated. To valid...

JLA Vol:8 Iss:4 (Acoustic emission from modulated laser beam welding of materials)

Authors:
Hongping Gu
W. W. Duley
Guelph‐Waterloo Program for Graduate Work in Physics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Acoustic emission during the laser welding of metals with a modulated CO₂ laser beam has been investigated. Sharp resonances at many frequencies in the acoustic emission spectra have been observed. This was most noticeable when the average laser power was high enough to produce full penetration welds whose acoustic emission at high harmonics with frequencies that overlap with bands of vibrational frequencies corresponding to eigenmodes of the keyhole are greatly enhanced. Lower harmonics were not clearly observe...

JLA Vol:8 Iss:4 (Laser hazard evaluation method for middle infrared laser systems)

Authors:
Wesley J. Marshall
Robert C. Aldrich
Sheldon A. Zimmerman

Hazard evaluation methods for lasers, with wavelengths greater than 1.4 μm (mostly in the middle infrared), have changed significantly in the current version of the American National Standard for the Safe Use of Lasers, ANSI Z136.1‐1993. A correct evaluation involves comparing the hazard potential based on two evaluation models; one based on individual pulses and the other based on an equivalent continuous‐wave exposure. An example of the hazard evaluation method within this spectral region is provided.

JLA Vol:8 Iss:4 (Integrated instruction: Lasers across the curriculum in an associate's degree program)

Authors:
R. Allen Shotwell
Ivy Tech State College, 7999 U.S. Highway 41, Terre Haute, IN 47802, U.S.A.

JLA Vol:8 Iss:5 (Diode‐pumped Nd:YAG laser for precision laser machining)

Authors:
Jason Machan
Marcy Valley
Gerry Holleman
Marc Mitchell
Dave Burchman
Jim Zamel
George Harpole
Hagop Injeyan
Len Marabella
TRW R1/1184, One Space Park, Redondo Beach, CA 90278, U.S.A.

Results are presented on a high power, diode‐pumped, pulsed Nd:YAG laser for precision laser machining. The laser is an unstable resonator with a graded reflectivity outcoupler, generating a beam with excellent beam quality. The gain medium is a single zig‐zag slab, pumped symmetrically by diode arrays. The use of diode arrays minimizes the thermal loading on the slab, and the zig...

JLA Vol:8 Iss:5 (Laser drilling of advanced materials: Effects of peak power, pulse format, and wavelength)

Authors:
X. Chen
W. T. Lotshaw
A. L. Ortiz
P. R. Staver
C. E. Erikson
M. H. McLaughlin
T. J. Rockstroh

The quality of laser‐drilled holes is significantly influenced by the laser peak power, pulse format, and wavelength. Three advanced materials are used to demonstrate the importance of choosing the correct laser parameters for a specific material. The materials are: (1) intermetallic single crystal nickel aluminide (NiAl) alloy; (2) N5, a single crystal nickel‐based superalloy; and (3) a silicon carbide (SiC) ceramic matrix composite (CMC). The laser peak power is varied in terms of the pulse...