Laser Applications Newsletter

27 November 1997
Laser Kinetics Inc.
Mtn. View, CA 94041
Issue 3, Vol. 1
Notes on ICALEO '97




INTRODUCTION

I just got back from the Laser Institute of America's 16th International Congress on Applications of Lasers and Electro-Optics, more commonly referred to as ICALEO '97. This year, the organizers had the good sense to hold it in San Diego, CA, where the surf was up and the sun was shining like it always does.

To draw us away from the beach, a record number (176) of papers were presented, making it necessary to hold as many as 4 simultaneous sessions. I had to go through the abstracts to decide which paper to listen to at a particular instant and did a lot of running up and down stairs to get to the right conference room. Only 20 minutes were allowed for each paper. I guess these are the consequences of success: All the papers, at least from the abstracts, seemed relevant to the conference, and it would be impractical to run ICALEO for more than a week.

Of the many presentations I heard, there were several that seemed noteworthy to me. Here are brief descriptions of them:


CUTTING

Thick Plate Cutting with Spinning Laser Beam
Arai, T. and Riches, S.

One limitation on laser cutting thick steel plate is that a wide kerf is needed to allow the molten material to leave the cutting region. Just defocusing the beam reduces irradiance and makes the process inefficient; this is why very large lasers are needed to cut 25 mm steel. Arai and Riches rotated a 2 kW beam at several hundred RPM and were able to increase kerf widths in thick steel. They were able to cut 25 mm stainless steel at 250 mm per minute and 12 mm stainless at 700 mm per minute. This approach looks quite practical and allows lasers of moderate power to cut much thicker steel than was otherwise possible.

Cutting of Composites by Pulsed Green Laser Beams
Maher, W.

Many of us have seen TRW's photo of a section of graphite-epoxy composite cut by their frequency-doubled Nd:YAG laser. In this paper, Maher describes what it took to do that (among other things, taking 6 passes to get through), and why such lasers are not immediate panaceas for composite cutting. In general, cuts made with 532 nm lasers suffer from the same problems as cuts made by more common lasers: uneven absorption, matrix degradation, large heat-affected zones and rough surfaces. Most of the materials examined by Maher could not be laser-cut with acceptable surface quality on the cut edges.


WELDING

Successful 3-Dimensional Laserwelding of Al2O3 Ceramics
Nagel, A.M. and Exner, H.

Good sound welds were produced in Al2O3 up to 3.5 mm thick by using laser preheating. Control of the thermal cycle eliminates cracking and allows the manufacture of built-up articles as long as the parts can be heated to 1600 C or so without damaging anything.

Laser Welding of Aluminum Alloys 5754 and 6061 Using CO2 and Nd:YAG Lasers
Gassmann, R. et al

While it is possible to weld aluminum with a CO2 laser, the process window is narrow. The assist gas is very critical, with a 50/50 mixture of argon and helium working much better than either gas alone. Nd:YAG welding is less affected by shield gas and, at speeds of 10 meters per minute or higher, can be done without shielding. The 6061 welds had solidification cracking at speeds over 4 meters per minute. Filler wire additions were needed to eliminate this problem.


WELD MONITORING

Capabilities of Infrared Weld Monitor
Leong, K. and Sanders, P.

A device developed by Argonne Laboratories looks at the temperature of the weld keyhole and the surrounding metal. The signal shows some correlation to weld penetration and, more interestingly, drops off sharply when full penetration is reached. The device, marketed by Spawr, may be effective in monitoring full-penetration welds in production.

A Technique for Melt Pool Oscillation Monitoring During Laser Spot Welding
Semak, V. et al

Very simple and robust: The molten metal in a spot weld is driven into oscillation by evaporation forces when the beam is on. After the pulse stops, the oscillation frequency is a function of the melt volume. Semak illuminated the weld with a probe laser and looked at the frequency of the intensity variations of the reflected light. This correlated well with the observed fusion zone size and quality.


ENDNOTE
The above selection reflects my interests in laser processing; there was a wide range of topics discussed during the conference, and I had to miss most of them. The areas of micromachining, fabrication of medical devices, rapid prototyping and diode laser applications were significant this year. As always, the results of experimental work done at Osaka University, the Fraunhofer Institute and elsewhere provided us with a better understanding of what actually happens during laser processing. There is a lot of work being done on aluminum welding, mostly for automotive applications.

Proceedings of ICALEO '97 will be available from the LIA. Look them up at http://www.lia.org/ for more information.

Next year, ICALEO will be in Orlando, Florida. Plan to attend if you want to keep up with laser applications.

Call 650 575-4919 or e-mail us for more information.