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On cutting and penetration welding processes with high power lasers
Optics and Lasers in Engineering 6 (1985) 1-9
On Cutting aud Penetration Welding Processes with High Power Lasers* C. Esposito, Centro
Laser, Via F. De Blasio,
G. Daurelio 1, Zona. Industriale,
70123 Bari, Italy
and A. Cingolani Dipartimento
di Fisica, Universita (Received:
di Bari, Italy
18 June 1984)
ABSTRACT In this paper cutting and continuous welding laser processes are examined. Experiments with CO, and YAG lasers were cam’ed out on carbon and stainless steels. Two distinct regimes were identified in the gas jet assisted cutting process and in both cases predictions of working parameters can be made. Penetration welding results, when represented on a mathematical model, were seen to be similar to those of cutting ones. Finally, there is a great difference between the above processes and the conduction welding one.
INTRODUCTION This paper is concerned with those processes resented, in a two-dimensional approximation, source with a constant speed U. Laser cutting
which can be repby a moving heat and continuous butt
welding are examples of such processes. The heat source may be a CW or pulsed laser beam, but in this latter case a high degree of overlapping between spots is required. First, gas jet laser cutting will be considered. In the past it was not * Research carried out under the Italian National 81.02018.98 contract.
Research
Council/Centro
Laser no.
1
Optics and Lasers in Engineering 0143-8166/85/$03~30 @ Elsevier Publishers
Ltd, England,
1985. Printed
in Northern
Ireland
Applied
Science
C. Esposito.
7
clear
whether
mochemical
this process reaction
G. Daurelio. A. Cinpdatzi
was strongly
or not.‘.’
However,
aided
by the
instances the oxygen did not act as an energy source; predictions, based solely upon knowledge of laser possible.
In this work
with
aid of oxygen
the
it will be seen (two
energy
oxygen
ther-
it was shown-’ that in some
that
laser
sources)
thus, accurate energy, were
cutting and
occurs
without
both
it (one
energy source), and that the boundary between the two regimes can be calculated a priori for a given laser. Furthermore, predictions of working parameters can be extended to the ‘two energy sources’ regime thus giving a comprehensive method for dealing with laser cutting. The penetration welding process will then be considered and the results will show that it can be theoretically described in a manner which is similar to cutting. However, this result cannot at present be used to calculate problems such as the welding capabilities of a given laser or the most suitable focusing lens for that laser. Finally, a comparison will be made between these two processes and the conduction welding4 one.
BASIC
MODEL
In the following pages we shall refer mainly to what we have called the line source mode1 (LSM).5-’ Briefly, by starting from the steadystate equation of heat diffusion from a stationary heat source in a moving medium,
(K = thermal conductivity, T = temperature, p = density, c’ = specific heat, u = speed) the LSM gives the dependence of the product vb (b = weld or cut width) on the ratio W/a ( W = total laser power, a = slab thickness) if the heat source is assumed to be a line. Non-dimensional coordinates are obtained by making X = WJas and Y = t&/D (where s = KT and D = thermal diffusivity). Average values of the relevant thermal constants of various materials can be found in ref. 5. A list of the LSM Y values for 1 =ZX < 19 is given in ref. 4 and in Figs 1 and 2 (discussed below) a plot of Y versus X is shown which is marked by 100% energy transfer efficiency (ETE). The ETE parameter is discussed in refs 4 and 5 ; briefly, ETE is that proportion of the beam power which is actually transferred to the
On cutting and penetration welding processes with high power lasers
10% ETE
W/as 10
._ 100
Fig. 1. Oxygen jet assisted CW laser cutting, (I) 200 W on low carbon steel; (A) 400 W on low carbon steel; (A) 400 W on 304 stainless steel; (0) 2 KW on low carbon steel; (0) 2 KW on 304 stainless steel.
material. If energy losses are present the curve is shifted towards the right, as can be seen in the xy plots where efficiencies down to 10% have been drawn. In this way, once X= W/as and Y = vb/D are calculated for a given experiment the point position on the plot automatically gives the percentage of absorbed laser power. If a quantity, H, is defined as
C. Esposito.
3
G.
Duurelio.
A. Cingolani
10
1
W/as 0.1
100
10
1
Fig. 2. Laser penetration welding. (A) 275 W (average) pulsed YAG duration) on low carbon steel: (A) 300 W (average) pulsed YAG on steel: (U) 400 W (average) pulsed CO, (200 pps, 0.9 ms duration) on steel; (0) 2 KW CW CO, on low carbon steel; (0) 2 KW CW CO, on steel; ( x ) conduction welding.’
then the melting
ratio
(MR),
which is defined
(SO pps. 3 ms 304 stainless 304 stainless 430 stainless
as
MR = Hvabl W, represents the amount of heat needed to melt the volume of metal in the fusion zone compared with the beam power.5 Since D = Klpc and ‘I s=
KdT
On cutting and penetration
welding processes with high power lasers
5
the MR can be rewritten, if an average value is assumed for thermal conductivity, as MR = YIX On the LSM plot constant MR curves are represented lines of unit slope. EXPERIMENT
by straight
AND RESULTS
In the experiment two carbon dioxide lasers and one YAG laser were used. The first one was a Valfivre LIS 500 slow axial flow COz laser, with 500 W CW rated output power. However, pulsed mode operation could also be achieved by electrical pumping modulation. This mode was used in penetration welding experiments,6 where aspect ratios of about 2.5 : 3 were obtained on 1.5 mm thick 304 steel using 200 s-l, 0.9 ms, 2 J pulses. The experimental cutting procedure was carried out according to ref. 3. The second laser was a control laser fast axial flow machine, which was capable of emitting a 2 kW CW beam with a TEMoo predominant structure. Both welding and oxygen assisted cutting experiments were carried out by this laser. Welding tests were also done with a JK 300 W pulsed Nd-YAG laser. Some typical results are shown in Figs 1 (cutting) and 2 (welding), on an LSM plot. In both figures it can be seen that the experimental points have a tendency to group around straight lines which are parallel to the MR lines. Hence, when the thickness is varied while keeping the laser power constant and the corresponding maximum cutting (or welding) speed is then measured, the results from both cutting and penetration welding experiments fall on an MR line. An initial conclusion can thus be drawn: when thickness is increased (i.e. X decreased), the cutting points approach and go beyond the 100% ETE curve, which clearly shows that an additional energy source, the oxygen thermochemical reaction, is now at work. In contrast, the welding lines cannot go beyond that curve, which seems to be related to the maximum penetration capability of a given laser machine. However, it must be said that difficulties were sometimes involved when analysing the results of cutting experiments because of the destructive action of oxygen which occurred when great thicknesses were considered. Such problems were reduced to a minimum by
6
C. Esposito,
G. Daurelio,
A. Cingolani
properly designing the gas jet nozzles and by choosing gas flow rate. Notwithstanding this, the effect of oxygen in unpredictable (and uncontrollable) demonstrates that the thermochemical beam-shaped
but probably
has a more
an adequate often results
cut width values, a fact which energy source is not precisely diffused
shape.
DISCUSSION In the previous section it was seen that the results of both cutting and penetration welding experiments fall on MR lines. In the case of cutting, at a certain point, this tendency becomes so strong that the process is driven well beyond the 100% ETE curve. As can be seen, more is now known of the laser cutting process for not only can we say that it occurs both with and without the aid of oxygen, but also that a precise boundary can be established between the two regimes. The two source regime corresponds to low X values, while at high X values cutting is carried out by the laser alone. In this latter case, the experimental lines lie, on average, near the 70-80% ETE curves, which is typical of oxygen assisted laser cutting.’ Hence, at high X values oxygen play; no part in the cutting process (i.e. energy balance) though it does ensure a high absorption of the laser light itself. Esposito and Daurelio3 noted that with high laser power on thin steel sheets, cutting is accomplished in the cp = 0 condition-in other words the process proceeds as if the laser is the sole energy source. This observation has made possible accurate predictions about the cutting parameters for the high X regime.’ They were not able to make predictions for the cp> 0 field, however (we now say ‘low X’ or ‘two source’ regime), since the boundary itself, or the second source switch-on point, was not known. It can now be said that this boundary is known and that it can easily be calculated, as can be seen in Fig. 1; this helps in deciding the most suitable laser to be used in each gas-assisted cutting application. If, for example, a 10 mm thick steel slab were to be cut with a 500 W laser the X value would immediately indicate a strongly two source regime which ought to be avoided since it is characterized by difficulties in controlling the cut edge quality. An interesting fact is that low X predictions for the cutting parameters might also be made but the above-mentioned lack
On cutting and penetration
welding
processeswith high power lasers
7
of thermochemical heat source cutting sharpness prevents us from being accurate because the cut width b is somewhat uncontrollable. In this case the only thing which can be said is that b ‘in the order of’ the focused spot diameter d. Normally, one can often succeed in carrying out predictions about n which are based upon this nominal value of the cut width, even if b is really larger because of the oxygen destructive action. Hence, low X predictions are still possible for cutting speeds, v (which is more important), but this is no longer true for b. This can be underlined by saying that it is not possible to develop an exact, low X laser cutting mathematical model; thus we must conclude that only estimates should be sought if a priori knowledge of low X cutting parameters is required. Also, the penetration welding results form straight lines (Fig. 2). While in cutting melting ratios of only 30-40% are allowed (which are consistent with a high X ETE of about 70-80%), in penetration welding a wider MR range is allowed. The exact position of each experimental line seems to depend on various parameters such as the total laser power, the power density, the beam mode, its wavelength, the type of pulse (if the laser is pulsed), the machined material, etc. What must be noted, however, is the rectilinear behaviour. Penetration welding is, in fact, a one source process, hence its typical MR line cannot exceed the 100% ETE. A first limit to the maximum weld penetration achievable with a given laser machine is thus established. It is worth noting that this limit can, in practice, be calculated once a single welding datum of that laser machine on a much thinner steel slab is known. It is also worthwhile noting that once the penetration ‘saturation’ point is reached the experimental data leave the straight line and group around a maximum constant ETE curve. From then on the weld depth increases according to normal heat conduction laws. For all practical purposes such a regime ought to be considered of no interest. It can be seen in Fig. 2 that the 300 W pulsed Nd-YAG laser gives a better MR value than the 400 W pulsed CO, one. Such a value corresponds to similar welding speed performances but to a greater weld width for the YAG laser, despite the substantial difference in power. So, it is evident that the Nd-YAG wavelength interacts more effectively with steels and metals than that for CO,.7 It now seems of interest to compare the penetration welding data with those for conduction welding,4 both of which are given in Fig. 2. The data for conduction welding follow an ETE rather than an MR
C. Esposito,
8
A. Cingolani
G. Daurelio,
curve, and while in penetration welding many positions are possible, in conduction welding only the 15% ETE curve is allowed. The peculiarity
of
the
conduction
welding
process
is thus
effectively
demonstrated; being based simply upon the metal emissivity, this process must naturally follow a fixed, constant ETE curve. This fact is extensively discussed in refs 4 and 8, though the ETE derived is characteristic seems metals
of
CO,
laser
logical to expect or different lasers
conduction
a different (e.g. YAG)
welding
on
steels
transfer efficiency are considered.
only.
It
if different
CONCLUSIONS Laser cutting and penetration welding have been compared. It is found that both processes occur on constant MR lines. Two distinct regimes have thus been identified in oxygen jet assisted laser cutting. Predictions are satisfactory for the single source case and succeed in estimating the cutting speed in the two source case. Moreover, the boundary can always be calculated. Laser penetration welding is only a one source process; hence, a limit to the penetration depth achievable with a given laser machine is imposed. At present the limit can roughly be calculated once the welding parameters of a thinner slab are known. Finally, a large difference between the above processes and conduction welding has been demonstrated. ACKNOWLEDGEMENTS The authors are grateful to the University of Bari and encouragement. Thanks are discussions. Thanks are also their metallurgical support valuable help.
Professor Luigi Ambrosi, chancellor of President of the Centro Laser, for his due to Dr M. Dell’Erba for valuable due to the Istituto Ricerche Breda for and to Miss 0. De Pascale for her
REFERENCES 1. V. P. Babenko and V. P. Tychinskii, Gas jet Quantum Electron., 2 (1973), 399-410. 2. W. W. Duley, CO2 lasers: effects and applications, York, 1976, pp. 248-63.
laser cutting, Academic
Sov. J.
Press. New
On cutting and penetration welding processes with high power lasers
9
3. C. Esposito and G. Daurelio, Tuning of a parametric model for the laser cutting of steels, Optics and Lasers in Engineering, 2 (1981), 161-72. 4. C. Esposito, G. Daurelio and A. Cingolani, On the conduction welding process of steels with the CO2 laser, Optics and Lasers in Engineering, 3 (1982), 139-51. 5. D. T. Swift-Hook and A. E. F. Gick, Penetration welding with lasers, Welding Research Supplement (1973), 492-9. 6. C. Esposito and G. Daurelio, Perfectioning of a 500 W CO2 laser in order to carry out penetration welds on steels and other metals. CNR Pat. No. 2110/A82 (1982). 7. R. N. Burbeck et al., Versatile High-Average-Power Pulsed Nd-YAG Welder, J.K. Lasers Ltd. 8. C. Esposito, A. Cingolani and G. Daurelio, Mechanical applications of lasers (Inv. paper), Proc. 3rd Quantum Electr. CNR Conference, Como, Italy, 27-29 May 1982.
On Cutting aud Penetration Welding Processes with High Power Lasers* C. Esposito, Centro
Laser, Via F. De Blasio,
G. Daurelio 1, Zona. Industriale,
70123 Bari, Italy
and A. Cingolani Dipartimento
di Fisica, Universita (Received:
di Bari, Italy
18 June 1984)
ABSTRACT In this paper cutting and continuous welding laser processes are examined. Experiments with CO, and YAG lasers were cam’ed out on carbon and stainless steels. Two distinct regimes were identified in the gas jet assisted cutting process and in both cases predictions of working parameters can be made. Penetration welding results, when represented on a mathematical model, were seen to be similar to those of cutting ones. Finally, there is a great difference between the above processes and the conduction welding one.
INTRODUCTION This paper is concerned with those processes resented, in a two-dimensional approximation, source with a constant speed U. Laser cutting
which can be repby a moving heat and continuous butt
welding are examples of such processes. The heat source may be a CW or pulsed laser beam, but in this latter case a high degree of overlapping between spots is required. First, gas jet laser cutting will be considered. In the past it was not * Research carried out under the Italian National 81.02018.98 contract.
Research
Council/Centro
Laser no.
1
Optics and Lasers in Engineering 0143-8166/85/$03~30 @ Elsevier Publishers
Ltd, England,
1985. Printed
in Northern
Ireland
Applied
Science
C. Esposito.
7
clear
whether
mochemical
this process reaction
G. Daurelio. A. Cinpdatzi
was strongly
or not.‘.’
However,
aided
by the
instances the oxygen did not act as an energy source; predictions, based solely upon knowledge of laser possible.
In this work
with
aid of oxygen
the
it will be seen (two
energy
oxygen
ther-
it was shown-’ that in some
that
laser
sources)
thus, accurate energy, were
cutting and
occurs
without
both
it (one
energy source), and that the boundary between the two regimes can be calculated a priori for a given laser. Furthermore, predictions of working parameters can be extended to the ‘two energy sources’ regime thus giving a comprehensive method for dealing with laser cutting. The penetration welding process will then be considered and the results will show that it can be theoretically described in a manner which is similar to cutting. However, this result cannot at present be used to calculate problems such as the welding capabilities of a given laser or the most suitable focusing lens for that laser. Finally, a comparison will be made between these two processes and the conduction welding4 one.
BASIC
MODEL
In the following pages we shall refer mainly to what we have called the line source mode1 (LSM).5-’ Briefly, by starting from the steadystate equation of heat diffusion from a stationary heat source in a moving medium,
(K = thermal conductivity, T = temperature, p = density, c’ = specific heat, u = speed) the LSM gives the dependence of the product vb (b = weld or cut width) on the ratio W/a ( W = total laser power, a = slab thickness) if the heat source is assumed to be a line. Non-dimensional coordinates are obtained by making X = WJas and Y = t&/D (where s = KT and D = thermal diffusivity). Average values of the relevant thermal constants of various materials can be found in ref. 5. A list of the LSM Y values for 1 =ZX < 19 is given in ref. 4 and in Figs 1 and 2 (discussed below) a plot of Y versus X is shown which is marked by 100% energy transfer efficiency (ETE). The ETE parameter is discussed in refs 4 and 5 ; briefly, ETE is that proportion of the beam power which is actually transferred to the
On cutting and penetration welding processes with high power lasers
10% ETE
W/as 10
._ 100
Fig. 1. Oxygen jet assisted CW laser cutting, (I) 200 W on low carbon steel; (A) 400 W on low carbon steel; (A) 400 W on 304 stainless steel; (0) 2 KW on low carbon steel; (0) 2 KW on 304 stainless steel.
material. If energy losses are present the curve is shifted towards the right, as can be seen in the xy plots where efficiencies down to 10% have been drawn. In this way, once X= W/as and Y = vb/D are calculated for a given experiment the point position on the plot automatically gives the percentage of absorbed laser power. If a quantity, H, is defined as
C. Esposito.
3
G.
Duurelio.
A. Cingolani
10
1
W/as 0.1
100
10
1
Fig. 2. Laser penetration welding. (A) 275 W (average) pulsed YAG duration) on low carbon steel: (A) 300 W (average) pulsed YAG on steel: (U) 400 W (average) pulsed CO, (200 pps, 0.9 ms duration) on steel; (0) 2 KW CW CO, on low carbon steel; (0) 2 KW CW CO, on steel; ( x ) conduction welding.’
then the melting
ratio
(MR),
which is defined
(SO pps. 3 ms 304 stainless 304 stainless 430 stainless
as
MR = Hvabl W, represents the amount of heat needed to melt the volume of metal in the fusion zone compared with the beam power.5 Since D = Klpc and ‘I s=
KdT
On cutting and penetration
welding processes with high power lasers
5
the MR can be rewritten, if an average value is assumed for thermal conductivity, as MR = YIX On the LSM plot constant MR curves are represented lines of unit slope. EXPERIMENT
by straight
AND RESULTS
In the experiment two carbon dioxide lasers and one YAG laser were used. The first one was a Valfivre LIS 500 slow axial flow COz laser, with 500 W CW rated output power. However, pulsed mode operation could also be achieved by electrical pumping modulation. This mode was used in penetration welding experiments,6 where aspect ratios of about 2.5 : 3 were obtained on 1.5 mm thick 304 steel using 200 s-l, 0.9 ms, 2 J pulses. The experimental cutting procedure was carried out according to ref. 3. The second laser was a control laser fast axial flow machine, which was capable of emitting a 2 kW CW beam with a TEMoo predominant structure. Both welding and oxygen assisted cutting experiments were carried out by this laser. Welding tests were also done with a JK 300 W pulsed Nd-YAG laser. Some typical results are shown in Figs 1 (cutting) and 2 (welding), on an LSM plot. In both figures it can be seen that the experimental points have a tendency to group around straight lines which are parallel to the MR lines. Hence, when the thickness is varied while keeping the laser power constant and the corresponding maximum cutting (or welding) speed is then measured, the results from both cutting and penetration welding experiments fall on an MR line. An initial conclusion can thus be drawn: when thickness is increased (i.e. X decreased), the cutting points approach and go beyond the 100% ETE curve, which clearly shows that an additional energy source, the oxygen thermochemical reaction, is now at work. In contrast, the welding lines cannot go beyond that curve, which seems to be related to the maximum penetration capability of a given laser machine. However, it must be said that difficulties were sometimes involved when analysing the results of cutting experiments because of the destructive action of oxygen which occurred when great thicknesses were considered. Such problems were reduced to a minimum by
6
C. Esposito,
G. Daurelio,
A. Cingolani
properly designing the gas jet nozzles and by choosing gas flow rate. Notwithstanding this, the effect of oxygen in unpredictable (and uncontrollable) demonstrates that the thermochemical beam-shaped
but probably
has a more
an adequate often results
cut width values, a fact which energy source is not precisely diffused
shape.
DISCUSSION In the previous section it was seen that the results of both cutting and penetration welding experiments fall on MR lines. In the case of cutting, at a certain point, this tendency becomes so strong that the process is driven well beyond the 100% ETE curve. As can be seen, more is now known of the laser cutting process for not only can we say that it occurs both with and without the aid of oxygen, but also that a precise boundary can be established between the two regimes. The two source regime corresponds to low X values, while at high X values cutting is carried out by the laser alone. In this latter case, the experimental lines lie, on average, near the 70-80% ETE curves, which is typical of oxygen assisted laser cutting.’ Hence, at high X values oxygen play; no part in the cutting process (i.e. energy balance) though it does ensure a high absorption of the laser light itself. Esposito and Daurelio3 noted that with high laser power on thin steel sheets, cutting is accomplished in the cp = 0 condition-in other words the process proceeds as if the laser is the sole energy source. This observation has made possible accurate predictions about the cutting parameters for the high X regime.’ They were not able to make predictions for the cp> 0 field, however (we now say ‘low X’ or ‘two source’ regime), since the boundary itself, or the second source switch-on point, was not known. It can now be said that this boundary is known and that it can easily be calculated, as can be seen in Fig. 1; this helps in deciding the most suitable laser to be used in each gas-assisted cutting application. If, for example, a 10 mm thick steel slab were to be cut with a 500 W laser the X value would immediately indicate a strongly two source regime which ought to be avoided since it is characterized by difficulties in controlling the cut edge quality. An interesting fact is that low X predictions for the cutting parameters might also be made but the above-mentioned lack
On cutting and penetration
welding
processeswith high power lasers
7
of thermochemical heat source cutting sharpness prevents us from being accurate because the cut width b is somewhat uncontrollable. In this case the only thing which can be said is that b ‘in the order of’ the focused spot diameter d. Normally, one can often succeed in carrying out predictions about n which are based upon this nominal value of the cut width, even if b is really larger because of the oxygen destructive action. Hence, low X predictions are still possible for cutting speeds, v (which is more important), but this is no longer true for b. This can be underlined by saying that it is not possible to develop an exact, low X laser cutting mathematical model; thus we must conclude that only estimates should be sought if a priori knowledge of low X cutting parameters is required. Also, the penetration welding results form straight lines (Fig. 2). While in cutting melting ratios of only 30-40% are allowed (which are consistent with a high X ETE of about 70-80%), in penetration welding a wider MR range is allowed. The exact position of each experimental line seems to depend on various parameters such as the total laser power, the power density, the beam mode, its wavelength, the type of pulse (if the laser is pulsed), the machined material, etc. What must be noted, however, is the rectilinear behaviour. Penetration welding is, in fact, a one source process, hence its typical MR line cannot exceed the 100% ETE. A first limit to the maximum weld penetration achievable with a given laser machine is thus established. It is worth noting that this limit can, in practice, be calculated once a single welding datum of that laser machine on a much thinner steel slab is known. It is also worthwhile noting that once the penetration ‘saturation’ point is reached the experimental data leave the straight line and group around a maximum constant ETE curve. From then on the weld depth increases according to normal heat conduction laws. For all practical purposes such a regime ought to be considered of no interest. It can be seen in Fig. 2 that the 300 W pulsed Nd-YAG laser gives a better MR value than the 400 W pulsed CO, one. Such a value corresponds to similar welding speed performances but to a greater weld width for the YAG laser, despite the substantial difference in power. So, it is evident that the Nd-YAG wavelength interacts more effectively with steels and metals than that for CO,.7 It now seems of interest to compare the penetration welding data with those for conduction welding,4 both of which are given in Fig. 2. The data for conduction welding follow an ETE rather than an MR
C. Esposito,
8
A. Cingolani
G. Daurelio,
curve, and while in penetration welding many positions are possible, in conduction welding only the 15% ETE curve is allowed. The peculiarity
of
the
conduction
welding
process
is thus
effectively
demonstrated; being based simply upon the metal emissivity, this process must naturally follow a fixed, constant ETE curve. This fact is extensively discussed in refs 4 and 8, though the ETE derived is characteristic seems metals
of
CO,
laser
logical to expect or different lasers
conduction
a different (e.g. YAG)
welding
on
steels
transfer efficiency are considered.
only.
It
if different
CONCLUSIONS Laser cutting and penetration welding have been compared. It is found that both processes occur on constant MR lines. Two distinct regimes have thus been identified in oxygen jet assisted laser cutting. Predictions are satisfactory for the single source case and succeed in estimating the cutting speed in the two source case. Moreover, the boundary can always be calculated. Laser penetration welding is only a one source process; hence, a limit to the penetration depth achievable with a given laser machine is imposed. At present the limit can roughly be calculated once the welding parameters of a thinner slab are known. Finally, a large difference between the above processes and conduction welding has been demonstrated. ACKNOWLEDGEMENTS The authors are grateful to the University of Bari and encouragement. Thanks are discussions. Thanks are also their metallurgical support valuable help.
Professor Luigi Ambrosi, chancellor of President of the Centro Laser, for his due to Dr M. Dell’Erba for valuable due to the Istituto Ricerche Breda for and to Miss 0. De Pascale for her
REFERENCES 1. V. P. Babenko and V. P. Tychinskii, Gas jet Quantum Electron., 2 (1973), 399-410. 2. W. W. Duley, CO2 lasers: effects and applications, York, 1976, pp. 248-63.
laser cutting, Academic
Sov. J.
Press. New
On cutting and penetration welding processes with high power lasers
9
3. C. Esposito and G. Daurelio, Tuning of a parametric model for the laser cutting of steels, Optics and Lasers in Engineering, 2 (1981), 161-72. 4. C. Esposito, G. Daurelio and A. Cingolani, On the conduction welding process of steels with the CO2 laser, Optics and Lasers in Engineering, 3 (1982), 139-51. 5. D. T. Swift-Hook and A. E. F. Gick, Penetration welding with lasers, Welding Research Supplement (1973), 492-9. 6. C. Esposito and G. Daurelio, Perfectioning of a 500 W CO2 laser in order to carry out penetration welds on steels and other metals. CNR Pat. No. 2110/A82 (1982). 7. R. N. Burbeck et al., Versatile High-Average-Power Pulsed Nd-YAG Welder, J.K. Lasers Ltd. 8. C. Esposito, A. Cingolani and G. Daurelio, Mechanical applications of lasers (Inv. paper), Proc. 3rd Quantum Electr. CNR Conference, Como, Italy, 27-29 May 1982.