JLA Vol:9 Iss:4 (Are we ready for the future?)

Authors:
R. James Rockwell
Rockwell Laser Industries, 77454 Camargo Rd., Cincinnati, OH 45243, U.S.A.

JLA Vol:9 Iss:3 (Effective laser ablation of enamel and dentine without thermal side effects)

Authors:
Peter Kohns
Ping Zhou
Reinhard Sto¨rmann
Optikzentrum NRW, Universita¨tsstraß 142, D‐44799 Bochum, Germany

We present a feasibility study into laser treating dental materials by using femtosecond pulses generated by a titanium:sapphire laser system which consisted of an oscillator and a regenerative amplifier. The pulse duration was varied between 200 fs and 2 ps. The observed energy thresholds for the ablation process of dentine and enamel were clearly smaller than those observed when longer pulse durations were used. The consequence of this observation is a lower thermal load within the vicinity of the radiated area. Thus no th...

JLA Vol:9 Iss:3 (A power distribution model of industrial CO₂ lasers for system diagnosis)

Authors:
James G. Katter
Jay F. Tu
Mark Gartner

Industrial lasers are high power pieces of equipment that occasionally function under undesirable operating conditions. For example, the performance of a transverse‐flow d.c.‐excited gas laser can be adversely affected by many factors such as electrode arcing, poor lens and mirror cleanliness, focusing problems, improper gas mixture composition, poor gas quality, poor beam stability, poor beam path cleanliness, operator error, poor maintenance, poor chiller water temperature and flow rate stability, and improper laser beam ramp‐in/ramp‐out rates. Many of these factors which occur in ...

JLA Vol:9 Iss:3 (In‐process monitoring of laser welding by the analysis of ripples in the plasma emission)

Authors:
Kiyokazu Mori
Isamu Miyamoto

A novel in‐process monitoring system employing two detectors set above the workpiece at different aiming angles of 5° and 75° has been developed to detect whether or not CO₂ laser welding fully penetrates through to the back surface of steel sheets. The acquired signal contained a.c. components of the emission of the laser‐induced plasma in the plume and in the keyhole with frequencies up to approximately 10 kHz. The mean square value of the a.c. signal obtained by using the 75° sensor during full penetration welding was much larger than that of the partial penetration welding, showing that full p...

JLA Vol:9 Iss:3 (Diode laser scribing of non‐oriented 3 wt% Si‐steel for core loss reduction)

Authors:
Ravisankar Gurusamy
P. A. Molian
Mechanical Engineering Department, Iowa State University, Ames, IA 50011, U.S.A.

The electrical power industries are experiencing a considerable energy loss in transformers and motors because of inefficiencies caused by core loss. The objective of our research is to investigate any effect of laser scribing on the reduction of the core loss in the low cost, non‐oriented steels used in numerous utility applications. A 15 W diode laser transmitted through fiber optics was used to scribe 0.35 mm thick, non‐oriented 3 wt% Si steel. The magnetic properties including the core loss and permeability were evaluated both...

JLA Vol:9 Iss:3 (Experimental study of cutting thick aluminum and steel with a chemical oxygen–iodine laser using an N₂ or O₂ gas assist)

Authors:
David L. Carroll
James A. Rothenflue

A chemical oxygen–iodine laser (COIL) was used to cut aluminum and carbon steel. Cut depths of 20 mm in aluminum and 41 mm in carbon steel were obtained using an N₂ gas assist and 5–6 kW of power on target. The same laser at the same power level produced a cut depth of 65 mm in carbon steel with an O₂ gas assist; a low quality cut to a depth of nearly 100 mm in carbon steel was also demonstrated. These data are compared with existing COIL and CO₂ laser cutting data. COIL cuts carbon steel and stainless steel at approximately the same rate. For a given cut depth, power and spot size...

JLA Vol:9 Iss:2 (Relationship between airborne acoustic and optical emissions during laser welding)

Authors:
D. Farson
Y. Sang
A. Ali
Department of Industrial, Welding and Systems Engineering, Ohio State University, Columbus, OH, 43210 U.S.A.

This paper describes experimental work directed at understanding the relationship between acoustic and optical emissions from the laser welding process. Laser welds were performed and the emissions were measured with a microphone and photodiode and recorded with a data acquisition system. A time‐domain correlation analysis of the acoustic and optical signals revealed them to be highly related at a phase shift corresponding to the delay time for sound to propagate from the weld area to the microphone. A moving av...

JLA Vol:9 Iss:2 (Integration of real time quality control systems in a welding process)

Authors:
E. Nava‐Ru¨diger
M. Houlot
Ecole Nationale Supe´rieure d'Arts et Me´tiers, Laboratoire Proce´de´s et Techniques de Production Me´canique, Paris, France

The automation of laser welding processes requires the control of the various process components as well as the control of the laser—material interaction. These systems are essential for ensuring the quality of the weld seam as they are able to react to dynamic fluctuations during the process. During the process various phenomena occur which are potential sources of diagnostic signals: these include thermal, electrical, optical, mechanical and acoustic events. This pa...

JLA Vol:9 Iss:4 (In the beginning there was ANSI Z136.1)

Authors:
Sidney S. Charschan
Charschan Associates, 7351 Kinghurst Drive, Delray Beach, Florida, U.S.A.

In the early 1960s concerns about eye safety were concentrated in a handful of research laboratories and the military. Memoranda and guidelines were circulated internally with their own set of priorities and recommended practices. Then, in 1968, the First International Laser Safety Conference (the brainchild of Dr Leon Goldman), was held in Cincinnati with one of its avowed purposes, the development of a consensus among the most prominent investigators as to what exposure criteria should be adopted. They saw the (laser) light. By 1969 it had become clear that, because of widespread d...

JLA Vol:9 Iss:3 (High power laser welding in hyperbaric gas and water environments)

Authors:
G. J. Shannon
W. McNaught
W. F. Deans
J. Watson

A hyperbaric laser welding facility has been constructed and the feasibility of high power CO₂ and Nd:YAG laser welding in both high pressure gas and water environments, to simulated water depths of 500 m, has been established. From initial trials on welding through water at atmospheric pressure, it was found that the different absorption characteristics of water to 10.6 μm (CO₂ laser) and 1.06 μm (Nd:YAG laser) radiation proved crucial. The Nd:YAG laser was totally unsuitable as the beam was largely diffused in the water, whereas the CO₂ beam was rea...