JLA Vol:7 Iss:3 (Study of liquid and vapor ejection processes during laser drilling of metals)

Authors:
Bekir S. Yilbas¸
Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

In an experimental investigation of laser–metal interaction, one of the important parameters is the propagation velocity of the liquid–vapor interface. The quantity appears as a direct result of the theoretical examination of the interaction and may be used to test the accuracy of the theory. Consequently, in the present study, the nature of the interaction mechanism between a pulsed laser beam and metals is examined using streak photographs of the ejecta from four metals: titanium, tantalum, nickel, and EN58B stainless steel. It...

JLA Vol:7 Iss:3 (Characterization of chromium bearing surface alloys produced by laser alloying on low carbon steel substrates)

Authors:
G. L. Goswami
Dilip Kumar
A. L. Pappachan
A. K. Grover
K. Sridhar
Array

High‐chromium ferritic alloys were produced on mild steel substrates by laser surface alloying. For this, chromium‐plated mild steel samples were treated with a pulsed Nd:YAG laser (300 W maximum power) by varying the average power level from 21.6 W to 30.0 W. The chromium content of the surface alloys was in the range of 3.0–27.0 wt%, with fairly uniform depth of alloying. Microscopy showed very fine austenite needles within elongated/equiaxed ferrite grains in the laser‐alloyed zone (LAZ). X‐ray diffraction indi...

JLA Vol:7 Iss:3 (Determination of energy absorption during laser welding by an iterative conduction method)

Authors:
Junji Mimatsu
Jeannine A. Bos
Elijah Kannatey‐Asibu
Michael M. Chen
Department of Mechanical Engineering and Applied Mechanics, The University of Michigan, 2146 G. G. Brown, Ann Arbor, MI 48109‐2125, U.S.A.

Energy absorption is a key process in laser welding. While there is now good qualitative empirical knowledge of the dependence of the effective absorptivity on laser power level, detailed quantitative understanding is poor. In recent years there has been considerable interest in computational modeling of the heat transfer and fluid flow phenomena during laser welding, in order to have a better understanding of the physic...

JLA Vol:7 Iss:3 (Impact resistance of adhesive joints using laser‐induced shock waves)

Authors:
I. Gilath
R. Englman
Z. Jaeger
A. Buchman
H. Dodiuk

The impact resistance of aluminum–aluminum joint bonded with FM‐73 (American Cyanamid) structural adhesive was studied using laser‐induced shock waves. The adhesive joint failed in a ductile mode, showing shock absorbtion ability through plastic deformation. All stages of the impact damage were identified from threshold damage through complete sample perforation. In the theoretical study, the damage induced in the target is obtained as follows. The shock wave is modeled by an expanding stress front, which creates a void population in the laser‐im...

JLA Vol:7 Iss:3 (Laser operator training and competency assessment in the community hospital setting)

Authors:
Michael A. Connor
Allan F. Cook
Marymount Hospital, Cleveland, Ohio, U.S.A.

At the 279 bed Marymount community hospital, Cleveland, Ohio, the importance of providing a safe laser environment for patients as well as staff was identified. The decision was made to cross‐train all full‐time RNs, LPNs, and SAs to allow flexibility in staffing all laser procedures with a qualified operator. A competency based training program was implemented, utilizing a combination of techniques to assist the adult learner. Selected video tapes were used to teach laser physics and applications. Comprehension was assessed through written and oral quizzing. Individual time...

JLA Vol:7 Iss:3 (Laser beam surveying, refractive index measurements and the making of a 360° reflection hologram)

Authors:
David Foster
Notre Dame High School, 596 South Second St., San Jose, California 95112, U.S.A.

Triangulation measurements, using a laser to find the height of a room and of buildings, will be described first. This will be followed by triangulation and laser beam divergence measurements for range finding. The use of a hollow prism to hold liquids, whose refractive indicies are to be found, will then be described. The final topic will describe how a 360° reflection hologram was made at Notre Dame High School, utilizing three lasers and beam spreaders and four lasers and beam spreaders. The 360° hologram, made by a student, will be available for viewing.

JLA Vol:7 Iss:4 (Laser cutting of thick sectioned steels using gas flow impingement on the erosion front)

Authors:
P. M. Ilavarasan
P. A. Molian
Department of Mechanical Engineering, Iowa State University, Ames, IA 50011, U.S.A.

An off‐axial gas jet has been developed that has the potential to extend the laser's effectiveness by improving the rate at which parts can be machined, producing high‐quality surfaces, enhancing the cutting thickness, and adding to the range of materials that can be machined. In laser cutting, an erosion front (liquid–gas region) forms at the momentary end of the cut. Laser heating, exothermic reactions and shear force between the gas flow and the molten layer dictate the material removal rates. The principle of the off‐axi...

JLA Vol:7 Iss:4 (Laser machining of ablating materials — overlapped grooves and entrance/exit effects)

Authors:
Michael F. Modest
Sriram Ramanathan
Armin Raiber
Birgit Angstenberger

A three‐dimensional conduction model has been developed to predict the transient temperature distribution inside a thick solid that is irradiated by a moving laser source, and the changing shape of single or overlapping grooves carved into it by evaporation of material. The laser may operate in CW or in pulsed mode (with arbitrary temporal intensity distribution) and may have an arbitrary spatial intensity profile. The governing equations are solved, for both constant and variable thermophysical properties, using a finite‐difference method on a boundary&...

JLA Vol:7 Iss:4 (Production of Fe–noble metal surface alloys using laser beams)

Authors:
M. Manohar
C. E. Albright
B. E. Wilde

A new method to produce iron‐noble metal surface alloys is described. Quenched‐and‐tempered AISI 4135 steel was electroplated with Pd, Pt and Au and laser surface melting was carried out to produce the respective surface alloys. CW CO₂ laser power levels of 50, 100 and 200 W were employed. Auger depth profiling showed that alloying was achieved with Pt and Pd at all three power levels, but only at 200 W with Au.

JLA Vol:7 Iss:4 (Overview of laser technology at Los Alamos National Laboratory)

Authors:
Gary K. Lewis
David A. Cremers