Mechanical Engineering Journal

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J-STAGE Advance Publication date: 18 February, 2016 Paper No.15-00590

Mechanical Engineering Journal

Laser cutting conditions for steel plates having a thickness of more than 100 mm using a 30 kW fiber laser for nuclear

decommissioning

Abstract

Laser cutting conditions for steel plates having a thickness of more than 100 mm using a 30kW fiber laser were studied for the application to the nuclear decommissioning. Specimens of carbon steel and stainless steel plates were irradiated by laser beam and assist gas. The observed kerf widths at the rear face of the plates were considerably enlarged compared with those at the front face with the increase of the plate thickness for both specimens, when the stand-off distance between nozzle tip of the laser head and the specimen surface was kept 5 mm. Both kerf widths became comparable when specimens were cut at a relatively larger stand-off distance, where the incident laser beam size at the front face of the specimen was enlarged because of the defocusing of the beam. The results were applicable to the thick plate cutting, and specimens of stainless steel and carbon steel having a thickness of more than 100 mm were successfully cut based on this setup. The results show that for a very thick plate, sufficiently large kerf width was required for the cutting which was used as a duct for a successful melt flow process. The results are informative for the development of the laser cutting technology, and show that the laser cutting technology is promising for the dismantlement of thick steel components for the nuclear decommissioning.

Key words : Laser cutting, Fiber laser, Decommissioning, Stainless steel, Carbon steel, Stand-off distance, Kerf width

1. Introduction

Laser cutting technology has several advantages such as high efficiency, low-maintenance, and remote controllability, as compared with the conventional technologies such as mechanical cutting, plasma arc cutting (Yanagihara et al., 1988), or abrasive water jet (AWJ) cutting (Tezuka et al., 2014). Recent improvements in the performance of the fiber laser including output power, quality, and reliability make the laser cutting one of the candidates for nuclear decommissioning (Daido, 2013; Hilton and Khan, 2013).

Although the laser cutting technology and cutting processes have been studied from various aspects, the plate thickness examined in most of the previous studies was less than several tens of millimeters. Therefore, considering its applications to the dismantlement of the nuclear power plants which have more than 100 mm thick steel components, development of cutting technology for thicker steel plates was needed. Introduction of a laser source with increased power based on the recent advances in fiber laser technology would be an effective solution for the very thick plate cutting.

In this study, the laser cutting technology of the steel plates having a thickness of more than 100 mm was studied by using a 30 kW fiber laser, and the successful cutting conditions for carbon steel and stainless steel specimens were examined.

Koji TAMURA*^,** and Ryuichiro YAMAGISHI*

* Department of Research and Development, The Wakasa Wan Energy Research Center, 64-52-1 Nagatani, Tsuruga city, Fukui prefecture, 914-0192, Japan.

** Quantum Beam Science Center, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.

E-mail: [email protected]

Received 26 October 2015

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2. Experimental

Figure 1 shows the experimental setup for the laser cutting YLS-30000) was

available. The central laser wavelength was 1070 product at the entrance and the exit of

beam profile

fiber 20 m long, collimated wi The workpiece specimen

the specimens was 100 mm×50 mm×

tested specimens was 120 mm for diameter of 10

linear translator at a constant speed while the laser beam was irradiated. Assist gas

metal was collinearly injected to the workpiece through a nozzle at the tip of the laser head. In as the assist gas. The gas flow rate was about 320 l/min in this

particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be effectively re

a duct. The c

3. Results and discussion

3.1 Examination of kerf width

Cutting conditions required for the front (a, c) and the rear

thickness t was 60 mm and the stand was kept 5 mm, which was typical distance desirable, the observed rear kerf width

Figure 3 summarized the maximum kerf width of the plates face as a function of the plate thickness

mm. Although the kerf wi

considerably with the increase of the plate thickness Fig. 1 Experimental setup

fiber surface.

camera.

Experimental

Figure 1 shows the experimental setup for the laser cutting 30000) was used as a

available. The central laser wavelength was 1070 the entrance and the exit of

beam profile and was operated fiber 20 m long, collimated wi

orkpiece specimen

the specimens was 100 mm×50 mm×

d specimens was 120 mm for diameter of 10 mm, and the

particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be effectively reduced the serious

The cuttings were monitored with a video camera (JVC, GZ

Results and discussion

Examination of kerf width

Cutting conditions required for the and the rear (b, d

was 60 mm and the stand was kept 5 mm, which was typical distance desirable, the observed rear kerf width

3 summarized the maximum kerf width of the plates face as a function of the plate thickness

. Although the kerf wi

considerably with the increase of the plate thickness Experimental setup

fiber, collimated in surface. The workpiece was camera.

Figure 1 shows the experimental setup for the laser cutting a laser source.

available. The central laser wavelength was 1070 the entrance and the exit of the

and was operated at a continuous wave mode. The fiber 20 m long, collimated with a pair of lens, and irradiated to

orkpiece specimens of stainless stee the specimens was 100 mm×50 mm× t

d specimens was 120 mm for stainless steel and 160 mm for the cutting started

particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be serious thermal load to the

uttings were monitored with a video camera (JVC, GZ

Results and discussion

Examination of kerf width

Cutting conditions required for the , d) views of the

was 60 mm and the stand-off distance betwe was kept 5 mm, which was typical distance

desirable, the observed rear kerf widths

3 summarized the maximum kerf width of the plates face as a function of the plate thickness

. Although the kerf width on the front face was kept small (about 1 mm), the kerf width on the rear face increased considerably with the increase of the plate thickness

Experimental setup for the laser cutting of thick , collimated in a laser head, and irradi

The workpiece was moved with a translator during Figure 1 shows the experimental setup for the laser cutting

laser source. By combining outputs from modules, available. The central laser wavelength was 1070-1080 nm with

the fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser h at a continuous wave mode. The

th a pair of lens, and irradiated to of stainless steel (SUS304)

mm, where t

inless steel and 160 mm for started from the edge of the hole.

particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be thermal load to the wall

uttings were monitored with a video camera (JVC, GZ

Cutting conditions required for the thick steel plates were examined views of the carbon steel

off distance betwe

was kept 5 mm, which was typical distance used in laser cutting. Although the front kerf width were considerably enlarged.

3 summarized the maximum kerf width of the plates face as a function of the plate thickness t for carbon steel

dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased considerably with the increase of the plate thickness

the laser cutting of thick laser head, and irradiated to

moved with a translator during Figure 1 shows the experimental setup for the laser cutting of

By combining outputs from modules, 1080 nm with

fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser h at a continuous wave mode. The laser

th a pair of lens, and irradiated to the (SUS304) and carbon steel

t is the thickness of the specimens. The maximum thickness of the inless steel and 160 mm for carbon ste

the edge of the hole.

particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be wall surface. Generated fume was gathered from uttings were monitored with a video camera (JVC, GZ

steel plates were examined

carbon steel (a, b) and stainless steel (c, d)

off distance between nozzle tip and the plate surface during the cutting process laser cutting. Although the front kerf width

considerably enlarged.

3 summarized the maximum kerf width of the plates

carbon steel (a) and stainless steel

dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased considerably with the increase of the plate thickness t for both materials within th

the laser cutting of thick steel plates.

ated to a workpiece.

moved with a translator during

of thick steel specimens By combining outputs from modules, a

1080 nm with a typical line width of 3

fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser h laser output was delivered to

the surface of workpiece and carbon steel (SM490A)

the thickness of the specimens. The maximum thickness of the carbon steel. Each specimen has a through

the edge of the hole. The specimens linear translator at a constant speed while the laser beam was irradiated. Assist gas

metal was collinearly injected to the workpiece through a nozzle at the tip of the laser head. In

as the assist gas. The gas flow rate was about 320 l/min in this study. The penetrated laser and the sputtered metal particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be

enerated fume was gathered from uttings were monitored with a video camera (JVC, GZ-E565) through infra

steel plates were examined in this section. Figure 2 (a, b) and stainless steel (c, d)

en nozzle tip and the plate surface during the cutting process laser cutting. Although the front kerf width

considerably enlarged.

observed after cutting on the front face and the rear stainless steel

dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased for both materials within th

plates. Laser from a fiber laser was delivered with a pro workpiece. Assist gas was also ejected to the

moved with a translator during the cutting. The cuttings were monitored with a video steel specimens. A high

a maximum output power of 30 kW was typical line width of 3

fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser h output was delivered to

workpieces.

(SM490A) were set in a holder. The size of the thickness of the specimens. The maximum thickness of the

el. Each specimen has a through cimens in the holder

linear translator at a constant speed while the laser beam was irradiated. Assist gas used to blow off metal was collinearly injected to the workpiece through a nozzle at the tip of the laser head. In

. The penetrated laser and the sputtered metal particles were blocked using a wall of refractory bricks, where grazing incidence of the laser be

enerated fume was gathered from E565) through infra-red cut

this section. Figure 2 (a, b) and stainless steel (c, d) specimen

en nozzle tip and the plate surface during the cutting process laser cutting. Although the front kerf width

after cutting on the front face and the rear (b) measured

dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased for both materials within the experimental condition

Laser from a fiber laser was delivered with a pro Assist gas was also ejected to the

The cuttings were monitored with a video A high power fiber laser (IPG, maximum output power of 30 kW was typical line width of 3 nm. The beam

fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser h

output was delivered to a laser head by a process

were set in a holder. The size of the thickness of the specimens. The maximum thickness of the

el. Each specimen has a through

in the holder were moved with a to blow off generated metal was collinearly injected to the workpiece through a nozzle at the tip of the laser head. In this study, air was used

. The penetrated laser and the sputtered metal particles were blocked using a wall of refractory bricks, where grazing incidence of the laser beam to the bricks

enerated fume was gathered from atmosphere through red cut-off filters.

this section. Figure 2 show example specimens after cutting. The plate en nozzle tip and the plate surface during the cutting process laser cutting. Although the front kerf widths were very narrow and

after cutting on the front face and the rear asured at a stand-off distance of 5 dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased

experimental condition Laser from a fiber laser was delivered with a pro

Assist gas was also ejected to the

The cuttings were monitored with a video power fiber laser (IPG, maximum output power of 30 kW was nm. The beam-parameter fiber coupler was 4.0 and 10.0 mm*mrad, respectively. The laser had top-hat laser head by a process

were set in a holder. The size of the thickness of the specimens. The maximum thickness of the el. Each specimen has a through hole with a were moved with a generated molten this study, air was used . The penetrated laser and the sputtered metal am to the bricks atmosphere through off filters.

examples of the after cutting. The plate en nozzle tip and the plate surface during the cutting process very narrow and

after cutting on the front face and the rear off distance of 5 dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased experimental conditions. Since the Laser from a fiber laser was delivered with a process

Assist gas was also ejected to the workpiece The cuttings were monitored with a video

power fiber laser (IPG, maximum output power of 30 kW was parameter hat laser head by a process

were set in a holder. The size of the thickness of the specimens. The maximum thickness of the hole with a were moved with a molten this study, air was used . The penetrated laser and the sputtered metal am to the bricks atmosphere through

of the after cutting. The plate en nozzle tip and the plate surface during the cutting process very narrow and

after cutting on the front face and the rear off distance of 5 dth on the front face was kept small (about 1 mm), the kerf width on the rear face increased . Since the

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severe increase of the kerf width deterior

conditions were not appropriate for the thick plate cutting.

Figure 4 shows an example of the side view of mm and the stand

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting position started from th

the front face (F) to the point

face (R) of the specimen. The behavior explains the increase of the shown in Fig. 3. Although in

by assist gas pressure, figure 4 suggests that the successful removal process from the front f Fig. 2 Observation

(c, d) were

Fig.3 Front and rear kerf width thickness.

Figure 4 shows an example of the side view of mm and the stand-off distance

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting osition started from the t

the front face (F) to the point

face (R) of the specimen. The behavior explains the increase of the shown in Fig. 3. Although in

by assist gas pressure, figure 4 suggests that the successful removal process from the front f Observation of example

(c, d) specimens after cutting enlarged.

ront and rear kerf width thickness.

Figure 4 shows an example of the side view of off distance during the

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting through hole side face in the specim

the front face (F) to the point (P) shown in this figure was small, the width expanded from th face (R) of the specimen. The behavior explains the increase of the

shown in Fig. 3. Although in a successful cutting process,

by assist gas pressure, figure 4 suggests that the successful removal process from the front f of examples of the front

after cutting (t=60 mm)

ront and rear kerf widths of (a) carbon steel and (b) stainless steel specimens as a function of severe increase of the kerf width deteriorates the cutting quality and will lead to

Figure 4 shows an example of the side view of a

the cutting was 5 mm.

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting le side face in the specim

shown in this figure was small, the width expanded from th face (R) of the specimen. The behavior explains the increase of the

successful cutting process,

by assist gas pressure, figure 4 suggests that the successful removal process from the front f front (a, c) and

=60 mm). Although

of (a) carbon steel and (b) stainless steel specimens as a function of ates the cutting quality and will lead to

a stainless steel specimen after cutting. The plate thickness was 100 was 5 mm. For

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting le side face in the specimens. The figure shows that although the kerf width from shown in this figure was small, the width expanded from th

face (R) of the specimen. The behavior explains the increase of the

successful cutting process, the molten metal produced by laser irradiation was removed by assist gas pressure, figure 4 suggests that the successful removal process from the front f

and the rear (b, d

. Although the front kerf width

of (a) carbon steel and (b) stainless steel specimens as a function of ates the cutting quality and will lead to

stainless steel specimen after cutting. The plate thickness was 100 this measurement, the cutting position was

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting . The figure shows that although the kerf width from shown in this figure was small, the width expanded from th

face (R) of the specimen. The behavior explains the increase of the rear kerf width as compared with

molten metal produced by laser irradiation was removed by assist gas pressure, figure 4 suggests that the successful removal process from the front f

, d) face of a carbon steel front kerf widths

of (a) carbon steel and (b) stainless steel specimens as a function of

ates the cutting quality and will lead to the specimen damage, the applied

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting . The figure shows that although the kerf width from shown in this figure was small, the width expanded from th

kerf width as compared with

molten metal produced by laser irradiation was removed by assist gas pressure, figure 4 suggests that the successful removal process from the front f

carbon steel (a, b) and stainless steel were narrow,

of (a) carbon steel and (b) stainless steel specimens as a function of

specimen damage, the applied

side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting . The figure shows that although the kerf width from shown in this figure was small, the width expanded from the point (P)

kerf width as compared with the front molten metal produced by laser irradiation was removed by assist gas pressure, figure 4 suggests that the successful removal process from the front face (F)

(a, b) and stainless steel narrow, the rear kerf width

of (a) carbon steel and (b) stainless steel specimens as a function of the

specimen damage, the applied

stainless steel specimen after cutting. The plate thickness was 100 this measurement, the cutting position was from the side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting . The figure shows that although the kerf width from (P) until the rear the front width molten metal produced by laser irradiation was removed

) has become (a, b) and stainless steel

rear kerf widths

the specimen specimen damage, the applied

stainless steel specimen after cutting. The plate thickness was 100 the side face of the specimen to observe the cutting part appearance, and was different from other tests where the cutting . The figure shows that although the kerf width from until the rear width molten metal produced by laser irradiation was removed me

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unsuccessful at the point

Assuming that the kerf is a duct assumed to depend

same. Therefore, for

and keep sufficient gas pressure to blow off molten metal until the rear end of the plate, incident to the front face were the same. When the factor

by the pressure loss to residual metal accumulate and finally enlarge local heating by the expansion o

It was possible to Figure 5 shows the

stand-off distances. Since the increased with the increase of the diameter

applied until the rear end of the specimen even when the

Fig.4 Observation of the side face of (R) of the specimen are shown.

Fig. 5 Laser beam diameter at the front fa unsuccessful at the point (P)

Assuming that the kerf is a duct depend on the factor . Therefore, for a thick

by the pressure loss to completely residual metal accumulate

and finally enlarged the kerf width. Since incident laser power was very high in this study so as to cut very thick plate, local heating by focused laser was very serious when the energy penetration was obstructed

the expansion of the kerf width from the point It was possible to increase

Figure 5 shows the laser beam diameters at the off distances. Since the

increased with the increase of d as a parameter of

until the rear end of the specimen even when the

Observation of the side face of (R) of the specimen are shown.

Laser beam diameter at the front fa (P).

Assuming that the kerf is a duct for on the factor t/d, where

thick specimen with large

completely remove the molten metal residual metal accumulated in the kerf region. The energy

the kerf width. Since incident laser power was very high in this study so as to cut very thick plate, focused laser was very serious when the energy penetration was obstructed

f the kerf width from the point increase the duct

beam diameters at the off distances. Since the focal point increased with the increase of the stand

as a parameter of the stand

until the rear end of the specimen even when the

Observation of the side face of a (R) of the specimen are shown. The k

Laser beam diameter at the front fa

for assist gas flow in , where t is the length and ecimen with large t, the diameter

remove the molten metal in the kerf region. The energy

f the kerf width from the point (P) observed

duct diameter d by increasing the stand beam diameters at the plate

point of the laser beam

stand-off distance due to the extended defocusing of the laser beam.

stand-off distance in this setup, until the rear end of the specimen even when the

a stainless steel specimen The kerf width

Laser beam diameter at the front face of the specimen measured at

assist gas flow in a laser cutting process is the length and d is the diameter of the duc

, the diameter d

and keep sufficient gas pressure to blow off molten metal until the rear end of the plate, incident to the front face were the same. When the factor t/d was

remove the molten metal in the kerf in the kerf region. The energy heated

observed in Fig. 4 by increasing the stand

plate surface estimated by measuring the size of burn marks at various er beam was set 12 mm outside of the nozzle tip, the beam diameter off distance due to the extended defocusing of the laser beam.

off distance in this setup, until the rear end of the specimen even when the plate thickness

stainless steel specimen (t=

(d) expanded from

ce of the specimen measured at

laser cutting process is the diameter of the duc

d need to be increased to compensate the pressure loss and keep sufficient gas pressure to blow off molten metal until the rear end of the plate,

was large enough, the gas pressure

in the kerf. Then, part of the laser energy irradiated to the ed the region, melt

in Fig. 4 and the increase of the rear by increasing the stand-off distance

surface estimated by measuring the size of burn marks at various was set 12 mm outside of the nozzle tip, the beam diameter off distance due to the extended defocusing of the laser beam.

off distance in this setup, it was expected that the sufficient thickness t was considerably large.

100 mm) after cutting. Front face (F) and rear face from the point

ce of the specimen measured at various stand

laser cutting process, the pressure loss in the duct is the diameter of the duct

need to be increased to compensate the pressure loss and keep sufficient gas pressure to blow off molten metal until the rear end of the plate, when

large enough, the gas pressure

. Then, part of the laser energy irradiated to the the region, melted the composite metal in the the kerf width. Since incident laser power was very high in this study so as to cut very thick plate, focused laser was very serious when the energy penetration was obstructed．

and the increase of the rear off distance and defocusing

surface estimated by measuring the size of burn marks at various was set 12 mm outside of the nozzle tip, the beam diameter off distance due to the extended defocusing of the laser beam.

it was expected that the sufficient was considerably large.

after cutting. Front face (F) and rear face the point (P).

various stand-off distance

the pressure loss in the duct when other factors are the need to be increased to compensate the pressure loss

when the gas flo large enough, the gas pressure would be

. Then, part of the laser energy irradiated to the composite metal in the the kerf width. Since incident laser power was very high in this study so as to cut very thick plate,

．The process well explains and the increase of the rear kerf width

and defocusing the laser beam surface estimated by measuring the size of burn marks at various

was set 12 mm outside of the nozzle tip, the beam diameter off distance due to the extended defocusing of the laser beam. B

it was expected that the sufficient gas was considerably large.

after cutting. Front face (F) and rear face

off distances.

the pressure loss in the duct is when other factors are the need to be increased to compensate the pressure loss the gas flow conditions would be insufficient . Then, part of the laser energy irradiated to the composite metal in the wall, the kerf width. Since incident laser power was very high in this study so as to cut very thick plate,

The process well explains widths in Fig. 3.

the laser beam.

surface estimated by measuring the size of burn marks at various was set 12 mm outside of the nozzle tip, the beam diameter By increasing gas pressure was

after cutting. Front face (F) and rear face is when other factors are the need to be increased to compensate the pressure loss w conditions insufficient . Then, part of the laser energy irradiated to the wall, the kerf width. Since incident laser power was very high in this study so as to cut very thick plate, The process well explains . surface estimated by measuring the size of burn marks at various was set 12 mm outside of the nozzle tip, the beam diameter y increasing pressure was

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3.2 Determination of cutting conditions

Figure 6 summarizes the maximum kerf width at the front and the rear face steel plates at

considerably larger than that of the front

larger than about 30 mm, both kerf widths became comparable. Although the kerf widths distances were about

acceptable and applicable to th

The applicability of the cutting conditions was examined

50 mm thick carbon steel plate was set and irradiated at the side part of the plate the cutting appearance

the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a duct at the side part

duct was generated. The result shows that this plate, and suggests that it is applicable to width as observed

Fig. 6 Summary of the front and steel specimen

Determination of cutting conditions

Figure 6 summarizes the maximum kerf width at the front and the rear face steel plates at different stand

larger than about 30 mm, both kerf widths became comparable. Although the kerf widths were about 4 m

acceptable and applicable to th

50 mm thick carbon steel plate was set and irradiated at the side part of the plate appearance shown in Fig. 4. The stand

the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a at the side part in the plate. Figure 7(c) shows the appearance of the plate after cutting where

duct was generated. The result shows that this suggests that it is applicable to observed in Fig. 4.

Summary of the front and steel specimens

Figure 6 summarizes the maximum kerf width at the front and the rear face stand-off distances. When

larger than about 30 mm, both kerf widths became comparable. Although the kerf widths mm and were larger than

acceptable and applicable to the thick plate cutting.

50 mm thick carbon steel plate was set and irradiated at the side part of the plate shown in Fig. 4. The stand

the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a in the plate. Figure 7(c) shows the appearance of the plate after cutting where

duct was generated. The result shows that this suggests that it is applicable to

in Fig. 4.

Summary of the front and the s (t= 40 mm).

Figure 6 summarizes the maximum kerf width at the front and the rear face off distances. When the

considerably larger than that of the front face. On the other hand, when the stand larger than about 30 mm, both kerf widths became comparable. Although the kerf widths

m and were larger than th thick plate cutting.

50 mm thick carbon steel plate was set and irradiated at the side part of the plate shown in Fig. 4. The stand-off distance

duct was generated. The result shows that this setup

suggests that it is applicable to the very thick steel plate

the rear kerf width

Figure 6 summarizes the maximum kerf width at the front and the rear face

the stand-off distance was small (5 mm), the rear k . On the other hand, when the stand

larger than about 30 mm, both kerf widths became comparable. Although the kerf widths those observed with smaller stand

The applicability of the cutting conditions was examined using

50 mm thick carbon steel plate was set and irradiated at the side part of the plate off distance used

is applicable to thick steel plate

rear kerf width observed as a function of the stand Figure 6 summarizes the maximum kerf width at the front and the rear face

off distance was small (5 mm), the rear k . On the other hand, when the stand

larger than about 30 mm, both kerf widths became comparable. Although the kerf widths observed with smaller stand

using the experimental setup shown in Fig. 7(a), where a 50 mm thick carbon steel plate was set and irradiated at the side part of the plate

used in this measurem

is applicable to generate relatively thick steel plate cutting without

as a function of the stand

Figure 6 summarizes the maximum kerf width at the front and the rear face measured by using off distance was small (5 mm), the rear k . On the other hand, when the stand-off distance larger than about 30 mm, both kerf widths became comparable. Although the kerf widths observed

observed with smaller stand-off distances, the results were

the experimental setup shown in Fig. 7(a), where a 50 mm thick carbon steel plate was set and irradiated at the side part of the plate. The setup

in this measurement was 60 mm. Figure 7(b) shows the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a

in the plate. Figure 7(c) shows the appearance of the plate after cutting where relatively larger diameter of without the serious expansion of

as a function of the stand-off distance

measured by using 40 mm thick carbon off distance was small (5 mm), the rear kerf width was

off distance was increased and observed at larger stand off distances, the results were

the experimental setup shown in Fig. 7(a), where a . The setup was also used to

ent was 60 mm. Figure 7(b) shows the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a in the plate. Figure 7(c) shows the appearance of the plate after cutting where an almost parallel

larger diameter of serious expansion of

off distances for the carbon 40 mm thick carbon

erf width was increased and set larger stand-off off distances, the results were

the experimental setup shown in Fig. 7(a), where a was also used to observe ent was 60 mm. Figure 7(b) shows the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a an almost parallel larger diameter of a duct in the serious expansion of the rear kerf

for the carbon 40 mm thick carbon

erf width was set off off distances, the results were

the experimental setup shown in Fig. 7(a), where a observe ent was 60 mm. Figure 7(b) shows the cutting process. By the laser irradiation and the assist gas ejection, glowing molten metal was blasted out, making a an almost parallel duct in the the rear kerf

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3.3 Stainless steel

Thick stainless steel plate cutting was examined based on the above cutting process

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful cutting of the

Fig. 7 Observation of

assist gas were ejected from the nozzle tip to the workpiece surface set in cutting process,

Stainless steel

Thick stainless steel plate cutting was examined based on the above process of a stainless steel

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful the stainless steel specimens

Observation of the

assist gas were ejected from the nozzle tip to the workpiece surface set in cutting process, and

Thick stainless steel plate cutting was examined based on the above stainless steel plate

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful stainless steel specimens up to 120 mm thickness was

the cutting process of

assist gas were ejected from the nozzle tip to the workpiece surface set in and (c) specimen after cutting. A duct of molten metal flow was

Table 1 Cutting conditions for

Thick stainless steel plate cutting was examined based on the above (t=120 mm). The cutting condition

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful up to 120 mm thickness was

cutting process of a carbon steel specimen

assist gas were ejected from the nozzle tip to the workpiece surface set in (c) specimen after cutting. A duct of molten metal flow was

Cutting conditions for

Thick stainless steel plate cutting was examined based on the above . The cutting condition

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful up to 120 mm thickness was

carbon steel specimen

assist gas were ejected from the nozzle tip to the workpiece surface set in (c) specimen after cutting. A duct of molten metal flow was

Cutting conditions for the stainless steel specimen Thick stainless steel plate cutting was examined based on the above setup

. The cutting conditions are

8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful up to 120 mm thickness was observed based on th

carbon steel specimen (t= 50 mm assist gas were ejected from the nozzle tip to the workpiece surface set in

(c) specimen after cutting. A duct of molten metal flow was

stainless steel specimen

setup. Figure 8(a) shows the side view of the summarized in table 1. Figures 8(b) and 8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful

based on these 50 mm). (a) Experimental assist gas were ejected from the nozzle tip to the workpiece surface set in the holder. (b)

(c) specimen after cutting. A duct of molten metal flow was produced

stainless steel specimen

. Figure 8(a) shows the side view of the summarized in table 1. Figures 8(b) and 8(c) show the front and the rear face of the plate after cutting, respectively. The kerf width was about 6 mm. Successful

conditions.

xperimental setup. Laser and holder. (b) Observation of

produced.

setup. Laser and bservation of the

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3.4 Carbon steel

Thick carbon steel plate cutting was also studied based on the similar condition process of 160 mm thick plate with the cutting cond

the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting steel specimens

Fig. 8 (a) observation of the cutting process for and (c) rear face after cutting.

Carbon steel

Thick carbon steel plate cutting was also studied based on the similar condition of 160 mm thick plate with the cutting cond

the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting steel specimens up to 160 mm thickness was shown based on th

(a) observation of the cutting process for and (c) rear face after cutting.

the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting up to 160 mm thickness was shown based on th

(a) observation of the cutting process for and (c) rear face after cutting.

the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting up to 160 mm thickness was shown based on th

(a) observation of the cutting process for a stainless steel specimen with

Thick carbon steel plate cutting was also studied based on the similar condition

of 160 mm thick plate with the cutting conditions shown in table 2. Figure 9(b) and 9(c) shows the front and the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting

up to 160 mm thickness was shown based on these

stainless steel specimen with

Thick carbon steel plate cutting was also studied based on the similar condition

shown in table 2. Figure 9(b) and 9(c) shows the front and the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting

ese conditions.

stainless steel specimen with

Thick carbon steel plate cutting was also studied based on the similar conditions. Figure 9(a) shows the cutting shown in table 2. Figure 9(b) and 9(c) shows the front and the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting

stainless steel specimen with a thickness of 120 mm

. Figure 9(a) shows the cutting shown in table 2. Figure 9(b) and 9(c) shows the front and the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting

thickness of 120 mm. (b)

. Figure 9(a) shows the cutting shown in table 2. Figure 9(b) and 9(c) shows the front and the rear face of the plate after cutting, respectively. The kerf width was about 7 mm. Successful cutting of the carbon

(b) Front face,

. Figure 9(a) shows the cutting shown in table 2. Figure 9(b) and 9(c) shows the front and carbon

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By using

more than 100 mm was shown. It was found that for to keep sufficient

the experiment the generated

cutting. The amount of generated molten metal increase and it would cause

minimum kerf width gas flow rate

The method is

sufficiently reduced by laser heating so that the melt the introduced assist gas

Since the thickness of most of

(Matsumoto, 1992), the results show that the high power laser steel components

4. Conclusions

Laser cutting conditions Although the kerf width at the increase of the

stand-off distance

were shown by using this setup. The results metal removal

for the thick plate cutting

Acknowledgement

The Authors are grateful to Dr. R. Ishigami, Dr. E. J. Minehara, T. Shigeta, Y. Shinoda and Dr. S.

Wakasa Wan Energy Research Center for their supports in this study.

References

Daido, H., Prospects of optical and Engineering

Fig. 9 (a)

and (c) rear face after cutting.

using the 30 kW fiber laser, laser cutting of stainless steel and carbon steel more than 100 mm was shown. It was found that for

sufficient pressure experimental conditions

generated wider kerf.

The amount of generated molten metal increase would cause unwanted dross formation. The minimum kerf width d sufficient

flow rate, and also the

The method is also expected to be applicable to various sufficiently reduced by laser heating so that the melt

the introduced assist gas flow Since the thickness of most of

(Matsumoto, 1992), the results show that the high power laser components in the nuclear

Conclusions

Laser cutting conditions Although the kerf width at the increase of the specimen

off distances. Cutting

shown by using this setup. The results metal removal until the rear face of the specimen for the thick plate cutting applied

Acknowledgement

References

Daido, H., Prospects of optical and Engineering, Vol. 41, (2013), pp.

(a) Observation of the cutting process of and (c) rear face after cutting.

30 kW fiber laser, laser cutting of stainless steel and carbon steel more than 100 mm was shown. It was found that for

pressure until the rear end of the plate so as to blow off al conditions including the

. The requirement for The amount of generated molten metal increase

unwanted dross formation. The sufficient to remove

the optimal laser irradiation density suff expected to be applicable to various sufficiently reduced by laser heating so that the melt

flow even at the rear end of the specimen.

Since the thickness of most of steel

(Matsumoto, 1992), the results show that the high power laser the nuclear power plant.

Laser cutting conditions for stainless steel and carbon steel Although the kerf width at the rear face of the

specimen thickness, both widths became compara . Cuttings of the stainless and the carbon steel shown by using this setup. The results

until the rear face of the specimen

applied to the nuclear decommissioning.

Daido, H., Prospects of optical and laser technology for decommissioning nuclear power plants, Rev , Vol. 41, (2013), pp.906

Table

bservation of the cutting process of and (c) rear face after cutting.

30 kW fiber laser, laser cutting of stainless steel and carbon steel more than 100 mm was shown. It was found that for

the rear end of the plate so as to blow off including the assist gas flow

e requirement for the The amount of generated molten metal increase

unwanted dross formation. The

to remove the melt until the rear end of the specimen optimal laser irradiation density suff

expected to be applicable to various sufficiently reduced by laser heating so that the melt

even at the rear end of the specimen.

steel components

(Matsumoto, 1992), the results show that the high power laser plant.

stainless steel and carbon steel rear face of the specimens

thickness, both widths became compara of the stainless and the carbon steel shown by using this setup. The results indicated

until the rear face of the specimen was

to the nuclear decommissioning.

laser technology for decommissioning nuclear power plants, Rev 906-910 (in Japanese).

Table 2 Cutting conditions for carbon steel specimen bservation of the cutting process of a

and (c) rear face after cutting.

30 kW fiber laser, laser cutting of stainless steel and carbon steel more than 100 mm was shown. It was found that for a very thick plate cutting,

the rear end of the plate so as to blow off

flow, it was achieved by increasing the stand the thick plate limited the narrow kerf

The amount of generated molten metal increased by this method especially with the increase of unwanted dross formation. Therefore to minimize the dross

melt until the rear end of the specimen optimal laser irradiation density sufficient

expected to be applicable to various other

sufficiently reduced by laser heating so that the melted material is completely removed by aerodynamic momentum even at the rear end of the specimen.

components in a commercial nuclear power plant is less than about 100 mm (Matsumoto, 1992), the results show that the high power laser cutting

stainless steel and carbon steel thick plates were studied using the 30 kW fiber laser.

specimens was enlarged compared with that at the front face with the thickness, both widths became compara

of the stainless and the carbon steel

indicated that the generation of the sufficient was required for

to the nuclear decommissioning.

laser technology for decommissioning nuclear power plants, Rev Japanese).

Cutting conditions for carbon steel specimen

a carbon steel specimen with thickness of 160 mm

30 kW fiber laser, laser cutting of stainless steel and carbon steel plate cutting, the the rear end of the plate so as to blow off the generated

, it was achieved by increasing the stand thick plate limited the narrow kerf

by this method especially with the increase of refore to minimize the dross

melt until the rear end of the specimen

icient to process the whole kerf region.

other materials when the viscosity

is completely removed by aerodynamic momentum even at the rear end of the specimen.

commercial nuclear power plant is less than about 100 mm cutting is applicable to

thick plates were studied using the 30 kW fiber laser.

enlarged compared with that at the front face with the thickness, both widths became comparable when specimens were cut at

of the stainless and the carbon steel specimens having a generation of the sufficient for very thick plate cutting to the nuclear decommissioning.

laser technology for decommissioning nuclear power plants, Rev Cutting conditions for carbon steel specimen

carbon steel specimen with thickness of 160 mm

30 kW fiber laser, laser cutting of stainless steel and carbon steel specimens the kerf width need

generated molten metal in the kerf , it was achieved by increasing the stand

thick plate limited the narrow kerf width by this method especially with the increase of refore to minimize the dross amount

melt until the rear end of the specimen for a

to process the whole kerf region.

materials when the viscosity

is completely removed by aerodynamic momentum

commercial nuclear power plant is less than about 100 mm pplicable to the dismantlement

enlarged compared with that at the front face with the ble when specimens were cut at

having a thickness generation of the sufficient

very thick plate cuttings. The

laser technology for decommissioning nuclear power plants, Rev Cutting conditions for carbon steel specimen

carbon steel specimen with thickness of 160 mm

specimens having a

kerf width needed to be large enough molten metal in the kerf

, it was achieved by increasing the stand-off distance and width desirable for the laser by this method especially with the increase of the thickness

amount, it is desirable to select for a specimen thickness to process the whole kerf region.

materials when the viscosity of the material is completely removed by aerodynamic momentum

commercial nuclear power plant is less than about 100 mm dismantlement of

enlarged compared with that at the front face with the ble when specimens were cut at relatively large

ness of more than 100 mm generation of the sufficient kerf width for successful . The information was useful

The Authors are grateful to Dr. R. Ishigami, Dr. E. J. Minehara, T. Shigeta, Y. Shinoda and Dr. S. Toyama of The

laser technology for decommissioning nuclear power plants, Rev carbon steel specimen with thickness of 160 mm. (b)

having a thickness of to be large enough molten metal in the kerf. Within off distance and with desirable for the laser

the thickness t, , it is desirable to select thickness t and a

of the material is is completely removed by aerodynamic momentum of

commercial nuclear power plant is less than about 100 mm of many of the

enlarged compared with that at the front face with the relatively larger more than 100 mm

for successful information was useful

Toyama of The

laser technology for decommissioning nuclear power plants, Review of Laser (b) Front face

of to be large enough Within with desirable for the laser , , it is desirable to select a

is of

commercial nuclear power plant is less than about 100 mm of the

enlarged compared with that at the front face with the r more than 100 mm for successful information was useful

Toyama of The

Laser

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Hilton, P. and Khan, A., The potential of laser cutting and snake arm robots in aspects of nuclear decommissioning, Review of Laser Engineering, Vol. 41, (2013), pp.911-916.

Matsumoto, O., Sugihara M. and Miya K., Underwater cutting of reactor core internals by CO laser using local-dry-zone creating nozzle, Journal of Nuclear Science and Technology, Vol. 29, (1992), pp.1074-1079.

Tezuka, M., Nakamura, Y., Iwai, H., Sano, K. and Fukui, Y., The development of thermal and mechanical cutting technology for the dismantlement of the internal core of Fukushima Daiichi NPS, Journal of Nuclear Science and Technology, Vol. 51, (2014), pp.1054-1058.

Yanagihara, S., Ashida, S. and Usui, H., Dismantling of JPDR internals using underwater plasma arc cutting technique operated by robotic manipulator, Journal of Nuclear Science and Technology, Vol. 25, (1988), pp.891-894.