Laser cutting of metallic coated sheet steels - World Lasers, Inc.

Abstract
Journal of Materials Processing Technology 74 (1998) 234–242
Laser cutting of metallic coated sheet steels
G.V.S. Prasad, E. Siores, W.C.K. Wong *
School of Mechanical and Manufacturing Engineering, Queensland Uni�ersity of Technology, G.P.O. Box 2434, Brisbane,
Qld. 4001, Australia
Received 1 June 1996
This paper discusses the laser-beam machining of metallic coated sheet steels such as ZINCALUME, ZINCANNEAL and
GALVABOND of 1 mm thickness. These materials are essentially zinc and aluminium coatings of varying skin thickness on steel.
The experimental work explores some methods for reducing thermal damage of the coatings vis-a-vis the parent/base metal which
impose severe machining restrictions by virtue of their high reflectivity and thermal conductivity. A 500 W continuous-wave, 10.6
�m CO 2 CNC laser centre was used to improve the cut quality in terms of good surface finish, reduced kerf width and dross. An
analytical model was developed to establish the finite-element characteristic of the cutting process and it has been clarified that
an efficient choice of the process parameters is a pre-requisite for minimum thermal damage of the coatings. The topographical
characteristics of the uncut-through kerf and surface roughness are discussed. Some visualisational experiments were also
performed for further understanding of the micro- and macro-mechanics of the cutting process. It is proven that the cutting speed
is a function of the input power and that the laser processing of these materials is a commercially viable option. © 1998 Published
by Elsevier Science S.A.
Keywords: Laser centre; Metallic coated sheet steels; Process parameters
1. Introduction
Lasers are used in many industrial machining operations,
especially for processing the ‘difficult-to-machine’
materials. Laser machining has several advantages over
conventional methods. First, it is a non-contact process
that eliminates such effects as tool wear, machine vibration
and mechanically induced thermal damage. Second,
laser machining is a thermal process and materials
with favourable thermal properties can be successfully
processed regardless of their mechanical properties.
Third, laser machining is a flexible process.
Metallic coated sheet steels have been machined successfully
using conventional equipment such as presses
and guillotines for quite some time now but these
methods have brought with them problems like low
productivity and rapid tool wear although they too are
chipless machining methods. This paper examines the
application of a high energy laser beam as a potential
tool for processing these materials.
* Corresponding author. Fax: +61 7 38641529.
0924-0136/99/$19.00 © 1998 Pubished by Elsevier Science S.A. All rights reserved.
PII S0924-0136(97)00276-8
The basic cutting mechanism is dependent upon the
formation of the radiation trap giving rise to a molten
pool at a localised spot that is then ejected through the
root of the workpiece using a suitable assist gas jet.
Previous studies on the laser–material interactions at
the cutting zone for metals indicate that properties such
as reflectivity and thermal conductivity dictate the efficiency
of the cutting process, as most metals are highly
reflective at the laser wave lengths. Due to this, the
coupling of the beam and the workpiece is often inefficient
and very low.
However, the absorption coefficient of the material is
a function of temperature, which changes during the
transient phase of the process. The initial weak absorption
at the surface of the workpiece begins to increase
the workpiece temperature directly under the optical
beam and thus decreases the reflectivity quite rapidly.
Temperature and absorption increase until melting and
evaporation temperatures are reached that permit a
keyhole or radiation trap to form at the localised spot.
The laser beam acts as an energetic line heat source
within the material and initialises the cutting process.

G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242 235
Thus, it is evident that for this keyhole-cutting process
to be initiated, it is essential that the power density be
high enough to overcome the reflection barrier. Once
this is achieved, the process can be controlled using the
melting and evaporation relationships.
The goal in any laser machining process is to maximise
the material removal rate whilst minimising the
heat affected zone (HAZ). The objectives of this experimental
study are: (i) to identify the parameters that
have detrimental influence on the outcome of the cutting
process; (ii) to establish a relationship between
traverse speed and input power; (iii) to examine the
surface quality aspect through an analysis of the HAZ
formed during the laser–material interaction by virtue
of the oxidation of the coatings directly under the
optical beam; and (iv) to analyse the trade-off between
the material removal rate and the HAZ.
2. Laser–metal interactions
Although the CO 2 laser cutting of metals has become
a well established manufacturing process, the processing
of metallic coated sheet steels is considered as
‘difficult’. These materials are cut at lower speeds and
at thinner maximum sections than for most other
metals. The reasons behind this reduction in the cutting
efficiency as compared with, for example steels, can be
accounted for by examining the physical properties of
these materials: (i) their reflectivity to the 10.6 �m CO 2
laser radiation is very high, up to 99% at room temperature;
and (ii) their thermal conductivity is approximately
thrice that of other metals such as mild steels.
The principles of laser processing of metals suggest
that the cutting process depends upon the establishment
of a localised area of melting and/or evaporation
throughout the depth of the workpiece. The melt thus
generated by the focused beam is removed from the cut
zone by the incident gas jet, which is also chemically
reactive with the melt. The chemical reaction most
often employed is the exothermic oxidation of the
metallic surface under the heat of the laser radiation.
The melt is chemically degraded and the reaction forms
a secondary heat input to the cut zone.
The high reflectivity and thermal conductivity makes
it very difficult to establish a localised molten zone. At
ambient temperatures, all metals have high reflectivity
(�99%) to the incident laser beam. The small proportion
of the absorbed light has the effect of heating the
area under the beam and the subsequent rise in temperature
is accompanied by a reduction in reflectivity. This
reduction in reflectivity results in further heating until a
highly absorptive molten pool is established.
The small percentage of heat that is absorbed by the
material is converted into heat but is quickly dissipated
across the surface of the sheet by virtue of its high
thermal conductivity. As a result of the low thermal
input and the rapid dissipation of the heat, a highly
absorptive, localised hot spot is established less readily
that in the case of other metals. Continuing the comparison
with steels, the aluminium exothermic reaction:
(4)Al+(3)O2=(2)AL2O3+1670 kJ/mol (1)
1is far less effective as a heat source in the cut zone than
the similar reaction employed when cutting steels:
(4)Fe+(3)O2=(2)Fe2O3+822 kJ/mol (2)
The aluminium oxidation reaction is capable of generating
more energy than the iron reaction but the
oxide generated forms an impermeable seal on the
surface of the underlying aluminium and thereby suppresses
any further reaction with oxygen. During laser
cutting, this seal is continuously fractured due to the
turbulent nature of the melt flow out of the cut zone.
Consequent to this turbulence, the oxidation reaction
can act as a substantial thermal input to the cutting
process although its contribution is not of the same
order of magnitude as that of the oxidation of iron
during the cutting of steels.
The foregoing theoretical aspects were considered in
the experimental investigations conducted on the specimens.
The work was carried out using a Cincinnati
CL-5 CNC Laser Centre with the combination of high
power modulation and good mode, attaining extremely
high energy densities, so that the problems of high
reflectivity and thermal conductivity could be overcome.
3. Experimental methodology
These series of experiments were carried out using
the Cincinnati CL-5 CNC Laser Centre at different
power inputs with a view to optimise the cut quality.
The machine produces a beam with a wave length in
the range of 3×10 −7 –3×10 −3 �m. The beam was
focused using a 127 mm focal length lens and a simple
conical cutting nozzle that had a exit diameter of 1.7
mm with the nozzle–workpiece standoff distance being
1 mm.
The cutting head assembly of the machine is designed
such that turning the materials follower changes the
distance from the lens to the workpiece. Adjusting the
material follower thus moves the beam focal point
above or below the material surface. The material
follower rotates (relative to the lens assembly) on
threads that move it vertically 0.05 in. (1.27 mm) per
revolution, over a total range of 0.4 in. or eight full
turns.
1 Enthalpies of formation at 293 K (for comparison only).

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Oxygen was employed as the assist gas which is also
the primary assist gas specified for the machine, whilst
up to eight different gases can be incorporated into the
experimental design. The flow rates and the operating
pressures of the assist gas generally depend on each
specific application. Three process parameters were
identified as important in the cutting of the specimens
under study viz., input power, cutting velocity and the
assist gas pressure.
3.1. Input power
The drastic fluctuation in the melting and evaporation
temperatures of the coatings and the parent/base
metal renders the input power one of the crucial factors
in achieving optimum machining quality. The initial set
of experiments conducted for varying power input in
the range 450–700 W produced deteriorating quality of
cuts in all of the specimens. It was decided to modulate
the power at 500 W and vary the cutting velocity and
the assist gas pressure.
3.2. Cutting �elocity
Most laser systems are based on a low pressure
cutting head that means that the maximum cutting
pressure is limited by the optical system in the cutting
head. Lenses normally made of GaAs or ZnSe are
specified to withstand a maximum pressure of about 5
bar. It is generally known that the cutting velocity
increases with increasing gas pressure. There is a particular
area in which high quality cuts appear. The maximum
velocity is found at pressures of around 5 bar.
Investigations indicate that there is a gap between the
theoretically calculated and the experimentally obtainable
cutting velocities, which indicate more scope for
improvements.
3.3. Assist gas pressure
The oxygen pressure was increased in the range 5–20
bar. At levels of 20 bar, the material begins to act like
a mirror and there is no interaction between the material
and the incident beam. This implies that for a
specific laser power, there is a particular pressure range
within which the material can be processed. The gas
pressure variation was thus limited to a maximum of 14
bar. The cutting rate as a function of input power was
investigated.
The cuts were evaluated in terms of fine, good,
acceptable and poor quality. The qualities were optimised
by optimising the focal point position of the
focusing optics of the laser system.
4. Results and discussion
The basic philosophy behind the discussion is that
the wasted energy, which does not contribute to the
cutting process, should not be viewed as an aspect of
the laser–material interaction. Ignoring the reflected
energy which is not, by definition, an input to the
cutting process, the losses by conduction, convection
and radiation can be treated solely as a function of the
melt on its surroundings.
A simple analytical model of the above can be interpreted
with the help of the following energy balance
equation:
Input energy=(energy used in cutting)+
(losses by conduction, convection and radiation)
As an initial approximation, assume that the specific
cutting energy used to remove a unit volume of cut
material is independent of the material thickness. The
energy used in cutting is, therefore, a function of this
specific cutting energy multiplied by the volume of the
material removed during the cutting. The losses by
conduction, convection and radiation are a function of
the temperature of the cutting front and its surface area
in contact with its surroundings. Under these conditions,
the energy balance equation can be written as
follows.If a laser power P can cut a line L in time t,
then:
(P−b)t(x/100)=E cutldk+tBdk/2(A+B+C) (3)
where b is the laser power transmitted to the cut zone;
x is the absorptivity of the cut zone; E cut is the specific
energy needed to melt and remove a unit volume of
material from the cut zone; d is the material thickness
and A, B and C are the conductive, radiative and
convective loss functions.
Theory suggests that during cutting, it is often the
case that the trailing edge of the cut front does not
extend to the full diameter of the incident beam. A
proportion of the light therefore passes straight through
the kerf without interacting with the cut front. Consequently,
the absorptivity will partially be much higher
than the theoretical values at ambient room temperature.
This is because the cut zone has its absorptivity
increased as a result of the high temperature, the presence
of oxides, the shallow angle of incidence of the
laser beam, the roughness and the absorptive layer of
vapour.
The specific cutting energy can be assumed constant
for any given material as all cuts appear similar and
thus can be thought of as being produced by similar
mechanisms. Based on this assumption, the average
cutting temperature can also be assumed to remain
constant for a given material. Considering the losses

G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242 237
indicated in the above equation, the conductive losses
per unit area of cutting front can again be assumed to
be constant for a given material, so that while the
conductive heat loss is generally determined by the
temperature of the heat sink and the heat source, this
factor will not interfere with the central idea of this
discussion.
The foregoing will also conveniently imply that the
convective and radiative heat losses per unit area can be
approximated to be proportional to the surface area of
the front. It follows that in the equation, the energy
used in cutting is independent of the cutting time. The
losses will then be proportional to the cutting time, so
Fig. 1. Graphs of input power (W) vs. cutting rate (mm min 1 ): (a)
GALVABOND; (b) ZINCANNEAL; (c) ZINCALUME.
that the proportion of the useful and the wasted energy
will change if the cutting speed is changed in order to
cut materials of different thickness.
4.1. Effect of material thickness on cutting speeds
In the equation, suppose that d is halved at the same
laser power input:
(P−b)(t/2)(x/100)=E cutlk(d/2)+tBdk/4(A+B+C)
(4)
For the sake of comparison, let everything be doubled
in Eq. (4):
(P−b)t(x/100)=E cutldk+(t/2)Bdk(A+B+C) (5)
It is clear that the imbalance in the equation with
respect to Eq. (3) is that the losses have been halved.
Thus, the equation can be balanced by simply manipulating
t.
The foregoing clearly implies that there is a specific
limit to the material thickness beyond which the cutting
mechanism breaks down and cannot be re-established
at any cutting speed. The reason for this is the relative
increase in thermal losses from the cut zone as the
cutting speed is decreased. In the case of the machining
of the materials under study, the thermal conductivity
of the coatings dictates the cutting speed although the
material thickness is not the primary concern.
The effects of the rapid oxidation reactions have to
be considered in determining the optimum selection of
the input power and the proportional increase in the
cutting speeds. In this case, it follows that with an
increase in the material thickness, there is a proportional
increase in the energy wasted, but this is more
gradual, due mainly to the dissipation of the energy
across the material surface by virtue of high thermal
conductivity. In other words, there is less concentration
of energy absorbed in any particular region across the
material surface.
4.2. Impact of the incident beam on the surface of the
material
Fig. 1 shows graphs plotted for input power versus
cutting rates. It can be inferred that GALVABOND
specimens are cut faster than the ZINCALUME and
ZINCANNEAL specimens. This is due to the aluminium
coating being highly absorptive at the laser
wavelength of 10.6 �m. The oxides thus formed are
firmly bonded to the substrate and are not vaporised by
the incident beam, owing to their high melting and
boiling points. This highly absorptive and refractory
surface replaces the original aluminium surface and so
the problems associated with reflection are minimised.

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G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242
Fig. 2. Comparison of kerf widths: (a) GALVABOND; (b) ZINCALUME; (c) ZINCANNEAL.
4.3. Influence of the assist gas on cutting
The photographs in Fig. 4 show the effect of the
cutting gas on the surface of the various specimens.
There is greater/pronounced surface disintegration in
the case of GALVABOND specimens as compared
with the others. This is indicated by the distinct oxide
formation along the length of the cut. The cut edge
surfaces represent the extreme edge of the molten cut
zone which is then left behind by the cutting process. In
this region, the melt is in contact with the parent/base
metal, where the temperature is not greatly in excess of
the melting point of the base metal.
This low temperature melt has a higher surface tension
than the much hotter top surface of the coating at
the centre of the laser–material interaction zone. This
surface tension gradient acts to draw the molten material
towards the sides of the cut whilst it is at the same
time being propelled vertically downwards by the impinging
gas jet. In this way, the molten materials can
accumulate on the bottom of the cut edge and will
thereafter solidify as dross. Further, the melt zone is
covered with the oxide coating, which tends to increase
the overall melt surface tension. Also, experience from
brazing has shown that a hotter surface tends to attract
the melt more efficiently hence the hotter, the lower the
surface tension.
High surface tension forces tend to restrict the surface
geometry of fluid to large radii. This reduction in
the melt surface tension might have been expected to
accelerate the cutting process. The gas moving through
the cut zone acts primarily as a mechanical propellant
of the liquid metal out of the cut zone. Chemically, it
can possibly also act as a source of energy if oxygen is
input to the cutting process but it must be borne in
mind that the gas also serves to refrigerate the cutting
zone by forced convective cooling. Using this interpretation,
it can be predicted that the higher specific heat
and thermal conductivity of some other assist gas such
as nitrogen or helium should render it more effective as
a means of cooling the laser melt zone.
4.4. Kerf width analysis
The kerf width of all the cuts carried out for this
experimental programme varied only slightly about an

G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242 239
Fig. 3. Microphotographs of the transverse edge: (a) GALVABOND; (b) ZINCANNEAL; (c) ZINCALUME.
average value of 250 �m with the ZINCANNEAL and
ZINCALUME specimens occupying the range 220–250
�m and the GALVABOND specimens in the 250–270
�m range (see Fig. 2). This is in close conformity with
the studies undertaken by other researchers for similar
metals and most of the results reported thus far exhibit
this tendency towards uniformity of the kerf width.
This almost independence of the kerf width with respect
to cutting speed, material thickness or the type of assist
gas used, is reminiscent of mechanical cutting methods
and it can be postulated that for a particular combination
of laser–lens–metal, the focused laser assumed an
effective width which is not necessarily changed by
altering the process parameters. The metal itself determines
this width as a result of its high thermal conductivity,
which effectively cools all the material not
directly irradiated by the beam and thereby prevents
lateral expansion of the kerf width.
4.5. Influence of assist gas pressure on the cutting
At pressure of around 5 bar, good quality cuts were
obtained for ZINCALUME nad ZINCANNEAL, (see
Fig. 3) with insignificant burr and heat-affected zone
(HAZ) while GALVABOND exhibited a little wider
HAZ. The cutting velocity increased with increasing gas
pressure by about 60% as the gas pressure moved from
5 to 20 bar. Repeat experiments for GALVABOND
revealed that the parameter area in which good quality
cuts are obtained narrowed compared to low gas pressure
parameters. At low cutting velocities, the high O 2
pressure resulted in a strong burring effect that was
uncontrollable and produced a wide irregular kerf.
It can be inferred that this is due to the high pressure
of pure oxygen that reacts with zinc and steel, forming
zinc and chromium oxides along the edges of the cuts.
End results indicated that at higher O 2 pressures, the
cutting velocities increased in the range of 40–70%,
proving machining profitable for these specimens using
the high energy laser.
4.6. Metallographic in�estigation
The micrographs in Fig. 5 show the front views of
the specimens. While the HAZ is very narrow in ZIN-
CALUME and ZINCANNEAL specimens, it is more
pronounced in the case of GALVABOND. This is also
true for the case of oxide deposition across the length

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G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242
of cut. The figure covers the area towards the bottom of
the cut edge, and clearly shows the adhesive dross and
the porous nature of the resolidified molten zone. The
angularity of most of the pores implies that they are the
result of the entrapment of the gas from the top to the
bottom of the cut. Also, a kind of folding mechanism is
revealed in the lines parallel to the cut edge. During the
fluid flow from the central hot spot to the side of the
cut zone, it could be possible that the two adjacent,
oxidised surfaces can come into contact and become
trapped as a linear inclusion of the type shown in the
figure.
Fig. 4. Microphotographs of the top surface: (a) ZINCALUME; (b)
ZINCANNEAL; (c) GALVABOND.
4.7. Control of dross
While the deposition of dross on the lower edge of
the cut is an undesirable effect, it is rather easy to
remove mechanically in the case of these specimens by
either scraping or abrasion. To minimise the dross,
there are numerous techniques available. One option
could be the use of a pulsed laser beam rather than a
CW mode. This is because the peak energy of a pulsed
laser beam is much higher than the CW output but the
average output is generally lower.
The high peak powers of each pulse should act to
rapidly melt and vaporise these metallic coatings. A cut
can be carried out in this way with minimum surplus
melting by conduction effects. This reduction in the
surplus melting could further inhibit the generation of
dross although the cutting speeds tend to be lower than
for the higher power CW mode.
5. Conclusions
The metallic coated sheet steels under study, i.e.
ZINCALUME, ZINCANNEAL and GALVABOND,
can be cut at commercially acceptable rates in the
observed thickness range of 0.5–1.0 mm at high laser
powers. While the cutting speed is same in the case of
ZINCALUME and ZINCANNEAL, it is slightly
higher (about 20%) in the case of GALVABOND. The
input power, cutting velocity and the assist gas pressure
dictate the quality of cuts obtainable in the machining
of these materials.
Oxygen is quite effective as an assist gas for the
cutting process as far as the cutting speeds are concerned.
However, difficulties associated with localised
overheating, particularly in the case of GALVABOND
specimens, may be encountered if detailed work is
required. In the laser cutting of GALVABOND specimens,
the oxidised edges can be totally eliminated by
using some other assist gas such as nitrogen or helium,
which should render totally oxidised-free cut edges.
If two different laser powers are compared, it is
probable that the higher power will have an inferior
mode quality which will not focus to as small spot as
the lower power. This larger focal spot will produce a
wider cut, thus rendering the process less efficient, as
more material will have to be removed to generate the
cut.
The fluid dynamics of the cut zone play a very
important role in determining the material removal
rate. Increase in power input changes the inclination
and the geometry of the cut front, which will in turn,
induce changes in the material removal rates. Thus,
above a limiting cutting speed, the viscosity of the melt
may become the rate determining factor.

G.V.S. Prasad et al. / Journal of Materials Processing Technology 74 (1998) 234–242 241
Fig. 5. Microphotographs of the front view: (a) GALVABOND; (b) ZINCALUME; (c) ZINCANNEAL.
As a result of the reduction in thermal losses to the
workpiece when cutting at higher speeds, the thermal
gradients around the cutting zone become more severe
as the material along the cut line is not preheated by
the moving cut front and therefore requires more energy
to become melted and ejected.
Slag-free cuts are obtainable in the cutting of ZIN-
CALUME and ZINCANNEAL but in the case of
GALVABOND, the oxides formed are concentrated in
the slag. Owing to the high thermal conductivity and
melting point, the slag solidifies before it leaves the
kerf.
It is observed that the slag is partly pressed into the
melt zone in the cut kerf, which could cause problems
when these specimens are subjected to further processing.
Adherent dross is generally formed at the lower edge
of the cut as a result of high surface tension forces and
surface tension gradients within the melt. While dross
can be easily removed, it can also be minimised by
pulsed laser cutting, which is of course, at the expense
of the cutting speed or probably by the use of a dross
jet which directs all the dross onto the waste-material
side of the cut.
5.1. Implication of the arguments
It is evident from the foregoing results and discussion
that the analytical model thus developed exhibits a
finite-element character, when applied to the materials
under consideration. This is due to the presence of
different materials of various thicknesses and their
sandwiching influence. The simplified model precludes
the possibility of studying the laser–material interactions
at the various interfaces, where the real time
interactions continue to remain drastic and intricate, by
virtue of different expansion rates of the metals, viz.
zinc, aluminium and steel, as the beam power travels
down the sandwich, thereby giving rise to different
temperature gradients at the interfaces.
Although it is intended to amplify the model to
investigate the laser cutting of metallic coated sheet

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steels in future work, the situation is rather complex,
considering the composition of these specimens. The
model developed so far thus provide scope for further
modifications in the light of the above-mentioned intricacies
and can be modified to accommodate the interactions
at the interfaces of the sandwich of the specimens
in terms of the temperature gradients and the different
coefficients of linear expansions of the various metals.
Acknowledgements
The authors wish to express their thanks and
appreciation to BHP Steels Ltd., Australia, for
providing the specimens and the Queensland
Manufacturing Institute, Brisbane, Australia, for the
Cincinatti CL-5 CNC laser centre to carry out the
experiments.
Bibliography
[1] Y. Arata, I. Miyamoto, Metal heating by laser beam, Weld.
Constr. 57 (8) (1978) 239.
[2] Y. Arata, I. Miyamoto, Some fundamental properties of highpower
laser beam as a heat source (report 2)—CO 2 laser absorption
characteristics of metals, Trans. Jpn. Weld. Soc. 3 (1) (1972)
152–162.
[3] F.N. Birkett et al., Prevention of dross attachment during laser
cutting, in: F. Kimmit (Ed.), Proc. 2nd Int. Conf. on Lasers in
Manufacturing, 26–28 March 1985, Birmingham, UK, IFS,
Bedford, UK, 1985, pp. 63–66.
[4] G. Buness, S. Weber, New sheet metal cutting using CO 2 lasers,
ZIS Mitt. 19 (1) (1977) 120–129.
[5] J.S. Ekersley, Laser cutting of sheet steel with the revolutionary
turbolase T1000 CO 2 laser, in: ICAEO 1982, Proc. Mater.
Process. Symp. 31 (1982) pp. 20–23, September, 1982, Boston,
MA, Laser Institute of America, Toledo, OH, pp. 131–134.
[6] S.G. Gornyi et al, et al., An investigation of the process of
gas-laser metal cutting, Weld. Eng. 3 (1992) 31–32.
[7] V.G. Gregson, Laser metal cutting, Mach. Tool Blue Book 76
(9) (1981) 72–75.
.
.
[8] A.G. Grigoryants, Basics of Laser Material Processing, Mir
Publishers, Moscow, 1994.
[9] S. Hoshinouchi, M. Kobayashi, et al., Quality improvement in
CO 2 laser cutting of metals, in: Colloq. on Thermal Cutting and
Flame Processes, 7 September, 1982, Ljubljana, Yugoslavia,
International Institute for Welding, London, UK, 1982.
[10] J.N. Kamulu, W.M. Steen, The importance of gas flow parameters
in laser cutting, in: Metall. Soc. AMIE, Paper No. 81-38,
Warrendale, PA.
[11] E.P. Kudrayavstev, A.V. Tikhomirov, Gas laser cutting of materials,
in: Colloq. on Thermal Cutting and Flame Processes, 7
September, 1982, Ljubljana, Yugoslavia, International Institute
for Welding, London, UK, 1982.
[12] C.S. Lee, A. Goel, H. Osada, Parametric studies of pulsed laser
cutting of thin metal plates, in: J. Majumdar (Ed.), ICALEO
1984, Proc. Mater. Process. Symp. 44, 12–15 November 1984,
MA, Laser Institute of America, Toledo, OH, 1985, pp. 86–93.
[13] M. Lepore, et al., A quantative theory for the role of oxygen in
the laser cutting process (Centro Laser, Italy), in: E.A. Metzbower
(Ed.), ICALEO ’83, Proc. Mater. Process. Symp. 38,
November 1983) Los Angeles, CA, Laser Institute of America,
Toledo, OH, 1984, pp. 160–165.
[14] G. Manassero, et al., Laser beam cutting of metallic and structural
components, Commission of the European Communities,
Luxembourg, 1985, p. 27.
[15] J. Mazumdar, W.M. Steen, Heat transfer model for CW laser
material processing, J. Appl. Phys. 51 (2) (1980) 941–947.
[16] M. Mitani, et al., Laser cutting of aluminium thin film with no
damage to under-layers, Ann. CIRP 28 (1) (1979) 113–115.
[17] J. Powell, et al., CO 2 laser cutting of aluminium alloys, in: Proc.
5th Int. Conf. on Lasers in Manufacturing, September 1988,
IFS, pp. 15–24.
[18] J. Powell, The influence of material thickness on the efficiency of
laser cutting, in: Proc. 6th Int. Conf. on Lasers in Manufacturing,
September 1988, IFS, pp. 135–153.
[19] J. Powell, Metallurgical implications of laser cutting of stainless
steels, in: Proc. Int. Conf. on Power Beam Technology (10–12
September 1986), Brighton, UK, Welding Institute.
[20] R. Rothe, et al., Laser cutting of sheet metal ranging in thickness
from 3 to 30 mm, in: Schweissen und Schneiden ’82, 29 September–1
October, 1982, Berlin, Germany, pp. 40–48.
[21] W.M. Steen, J.N. Kamalu, Laser Cutting, Imperial College of
Science and Technology, London, UK, 1985, p. 111.
[22] A.V. Tikhomirov, et al., Technology and equipment for the gas
laser cutting of thin sheet steel, Weld. Prod. 26 (11) (1979)
11–13.