Control of the power density on the machined surface is most important in laser material removing processes like Nd:YAG laser micro machining or in CO2 laser caving. It has been found that secondary emissions from the plume which is formed above the surface contain valuable control information. In case of pulsed processes the time required to form a plume can be measured easily. This time depends on the power density, the spot radius and the thermal erosion resistance E of the specific material.

For a given configuration (e.g. laser, optics) also the focal position, relative to the material surface, can be expressed as a function of the plume formation time. In a control strategy this measurement is used to control the focal position real time.

A measuring device has been built and evaluated in combination with Nd:YAG and CO2 lasers. When using clean materials the results correspond very well with the mathematical model. In most applications, however, debris is formed on the surface causing some scatter in the results. In that case a digital filtering technique or a fuzzy control strategy is advised.

The paper describes the theoretical background, the measuring device and the experimental results.

Topics
Surface collisions, Digital filter, Laser materials processing, Micro-machining, Mathematical modeling, Fuzzy control
1.
Carslaw
,
H.S.
 and
J.C.
Jaeger
, (
1959
).
Conduction of heat in solids
.
Oxford University Press
.
Google Scholar
 
2.
Gelb
,
A.
 (
1974
).
Applied optimal estimation
.
MIT Press
Massachusetts
.
Google Scholar
 
3.
Ooie
,
T.
,
I.
Miyamoto
,
H.
Maruo
,
Y.
Hirota
,
T.
Matsuyoshi
 and
Y.
Orii
, (1992).
Ablation characteristics of material by excimer laser under different gas pressure and species. Proc. of Laser Materials Processing, ICALEO
1992
.
Google Scholar
 
4.
Tangelder
,
R.J.
,
L.H.J.F.
Beckmann
 and
J.
Meijer
, (
1992
).
Influence of the temperature gradient on the performance of ZnSe lenses
.
Lens and optical systems design. SPIE
1780
–
20
.
Google Scholar
 
5.
Wisselink
,
F.W.A.
,
R.R.
van Kessel
 and
J.
Meijer
, (
1995
). Laser safety by control of power density in pulsed laser machining.
Proceedings of the Industrial Laser Safety Forum
,
Copenhagen
,
Denmark
.
Google Scholar
 
6.
Wisselink
,
F.W.A.
,
R.R.
van Kessel
,
L.H.J.F.
Beckmann
,
C.J.
Heuvelman
 and
J.
Meijer
, (
1995
).
Using a PLIM for focal point determination
.
Laser und Optoelektronik
27
(
4
), p
61
–
64
.
Google Scholar
 
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© 1995 Laser Institute of America.
1995
Laser Institute of America
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