Measurement of Beam Energy Absorption in CO, Laser Beam Welding

0 downloads 0 Views 5MB Size Report
Key words : CO, laser beam welding, mild steel plate, absorption efficiency, water calorimetric ..... welding. The general layout of the CO2 laser machine and the.
[Quarterly Journal of Japan Welding Society, Vol. 17, No. 4, pp. 493-500 (1999)]

Measurement

of Beam Energy

by Tomohiko

SHIDA,

Taisuke

Absorption

WAKASA,

Susumu

in CO, Laser Beam Welding (2nd Report)

TSUKAMOTO

and

Kazuo

HIRAOKA

Abstract

Water-calorimetric measurements of absorption efficiencies in CO, laser beam welding of mild steel plates were made. In this study, the same measurement method was used to measure absorption efficiencies of heat in TIG-DCEN arc welding, electron beam welding in a high vacuum and CO2 laser beam welding. Improvements were applied to the welding jig and the measurement system used in the previous report No. 1. The absorption efficiencies for TIG arc welding and EB welding agreed with reported values in the literature. The values of absorption efficiency for CO, laser beam welding of mild steel specimen in bead-on-plate welding are changeable with welding conditions but generally in the range of 72-87%. Key words : CO, laser beam welding, mild steel plate, absorption efficiency, water calorimetric measurement

authors 1.

used the same measuring

considerable

Introduction

described Industrial various

applications

fields

spreading. applied

of

Metal in

is required

reason

Nd-YAG

as a welding

In the present absorption

mild

steel plates

ing

would

the

known,

or CO, laser

beams

are

a certain

amount

has been

study

measured

of

industrial

(Shida) subject.

widely

tried

efficiencies of heat in TIG arc welding and

using the same measuring

the accuracy 2.

selected

to measure

in CO, laser beam

in the belief

that

to better

improvements

method

to verify

of our measurements.

Measuring

method

of absorption

efficiency

using

the results

the

of

One of the co-authors also published to this report,

2.1

Measuring

system

using

water-calorimetry

of present

understanding of

the

welding

of weld-

processes

and

applications.

and Terauchi According

method)

efficiency again.

For this

There have been several reports on the topic published in the past.

the absorption

calorimetry

the authors

contribute

(water-calorimetric

is

Absorption

surface

applications.

method

electron beam (EB) welding in a high vacuum were also

beam

and

but made

in

steadily

laser

welding

in the welding

efficiency

phenomena,

wider

laser

in the report

principle

to the measuring

and measured

heat source.

heat

study

by

drilling,

As it is well

energy

power

fabrication

fabrication

cutting,

modification.

of high

material

improvements

of this report a report on this the absorption

The general

layout of the measuring

system is illus-

trated in Fig. 1. The measuring principle is the same as the previous system5~, but several important improvements are added to the previous the tank 1 is pumped

one. Cooling water

out by a constant

into the cooling channel of the welding jig. head in the tank is kept constant

in

volume pump The water

all the time. The outlet

efficiency of the CO, laser beam during bead-on-plate

water from the welding jig passes through

welding of a mild steel plate was in the range of 30-50%.

for reference.

However

is decided by dividing the exact mass of the total cooling

there were several problems

remaining

in this

report : namely accuracy of the laser power settings, the

water

method

the heat of welding from the backside

of applying

He side-shielding

gas and plume

control during welding, and the time constant speed)

of the sheathed

*Received

thermocouples.

(response

The present

by measuring

welding specimen.

: 1998 . 11. 19

of Ibaraki Institute

University for Metals

, Presently

time.

The cooling water

Each temperature

absorbs

of the T-shaped of the inlet water

to or the outlet water from the welding jig is separately

**Member

, Ibaraki University ***Formerly Graduate Student ****Member , National Research

a flow meter

The exact flow rate of the cooling water

Mitsutoyo

Corp.

研究論文

494

Tomohiko

SHIDA

et al.:

Measurement

of Beam Energy Absorption

Fig.3

Fig.1

General system.

layout

of the water-calorimetric

measured

Appearance

type temperature

The output signals from the thermistors computer

and necessary

are connected calculations

The appearthe welding

assembled

welding

jig and

Fig.5

Position

maximum

60°C. The electrical

acrylic

water temperature

by considering

thermal

and

The dimension of the jig is shown in Fig.

3 and the cross-section

at the mid-length is shown in Fig.

4. Acrylic pieces marked the cross-sectional Bead-on-plate

as A and B are used to adjust

area for cooling water flow. welding

through the slit opening.

in the flat position

sensor

is made

The water inlet and the outlet

holes of the jig are 10 mm in diameter thermistor

insulation

is placed,

respectively.

of the thermistor

temperature

specimen is shown in Fig. 2. The welding jig is made of transparency'.

welding

jig at the

sensor

and orifices.

are

ance

plastics

of the acrylic

sensor.

made as described in the following section. of the

Cross-section mid-length.

of the assembled welding jig.

using a thermistor

to a personal

Shape and dimension of the acrylic welding jig.

measuring

Fig.4

Fig.2

in CO, Laser Beam Welding (2nd Report)

The

as shown in Fig. 5, in the

high precision absorption

range of each thermistor

resistance

of the thermistor

was calibrated

thermometer.

by comparing

is 10 to at each with a

In the following study, the

efficiency of EB welding in a high vacuum,

which is the most typical high energy density welding, is going to be measured also for comparison. For that reason the welding jig is so designed and made that the jig can be used in a high vacuum modification. 2.2

Welding

chamber

without

specimen

middle of the hole where two orifices are placed to mix the outlet supplied

(warm)

water

by Shibaura

flow.

Electronic,

The thermistors and

were

the guaranteed

The welding specimens steel

were made of SM400A mild

(C: 0.15, Si : 0.14, Mn : 0.94 mass%)

and capital

溶接学 会論 文 集

第17巻(1999)第4号

Fig.7 Fig.6

Shape

and dimension

letter T-shapes necessary

of the welding

Change pattern of water temperature-rise (Defined as outlet temperature minus inlet temperature).

specimen .

were adopted as shown in Fig. 6. It is

that the welding heat which is absorbed

the welding specimen during welding is carried

into

away by

Then

bead-on-plate

started.

The

welding

several

welding specimen should be small and the water-cooled

the temperature

area should be large.

ture

And also the deformation

of the

length.

The

minus

will be no water leakage between

MT,

and the rubber packings The

cross

section

of the

becomes a T-shape.

and welding conditions demagnetized

welding

Thickness

was 10 mm but it is changed water temperature

the specimen surface

in a high vacuum.

with the welding

so that a desirable EB welding

laser beam welding

received

inlet

value

thus

FR and WT as shown

The principle the same

method

pattern

Measurement

is shown

of

tempera-

in Fig . 7.

The

DT, and values

of

e is absorption

efficiency,

treat-

DT is average

temperature

of each experiment,

report;

where

To

some of

by TIG arc welding at the

are

/ V(V)•~I(A)•~WT(s)•~0.238846(cal/J)

for

surface

for the calculation

duration

I is arc current, by

replaced

beam

WT

water,

water,

V•~I

is

of cooling

for measurement,

of cooling

V is arc voltage,

laser

and some were stud-welded

is time

rise

LP

(laser

power

W)

in

case

of

welding,

is welding

time.

of the EB welding specimen.

and

calculation

of

absorption

3.

Measurement

of absorption

efficiency

in TIG arc

welding

The welding

specimen

were assembled

and the acrylic

using rubber

packings

welding

jig

and 18-8 type

Absorption measured Okada.

the two thermistors

and reported

were connected

to an A/D con-

and the digitized output signals were processed computer.

efficiency in TIG-DCEN

and

stainless steel bolts. The cooling water hoses were connected to the welding jig. The voltage signals from

by a personal

One example as outlet

in our previous

are

efficiency

verter

in

increases

in Fig. 7 are used for calcula-

All specimens

men to fix the specimen to the acrylic cover plate.

2.3

is each

ƒÃ= DT(•Ž)•~MT(s)•~FR(m3/s)•~1000(kg/m3)•~0.001(cal/kg•Ž)

FR is flow rate

directly on the surface

is started.

and the equation

as described

of

There are bolt-holes in the welding speci-

of the specimen

water

is defined

temperature,

MT

backside

welding

in

120 to 200 mm

outlet

of the temperature-rise

8 ,um Rmax.

the bolts were tack-welded

of

and specimens

shot-blast

the slit-opening somewhat

it is from

rise, which

ment before welding to achieve the surface roughness of

comply with the objective

but

after

through varies

tion of F.

specimen

t in the original design

rise is obtained.

before

length

temperature

seconds

average

welding

bead

experiment,

the cooling water flow quickly and almost completely . To achieve this objective, the heat capacity of the

specimen during welding should be small so that there

495

the absorption authors DCEN

reported

previously

In their study, Hiraoka

arc welding was by

Hiraoka

and

and Okada measured

efficiency in stationary

TIG arc welding

that it was in the range of 85-90% . The measured the absorption efficiency in TIG-

arc

welding

using

the

above-mentioned

new

研究論文

496

Tomohiko

SHIDA

et al.:

Measurement

of Beam Energy Absorption

Fig.9 Fig.8

Appearance

measuring

system.

of setup

except

to

the improved

Absorption

efficiency

in TIG-DCEN

arc welding.

of TIG arc welding.

The welding

Fig. 8 is identical

in CO,. Laser Beam Welding (2nd Report)

that

of

measuring

setup

which

is shown

Hiraoka's

Cooling water

in

Four values

experiment

four

system.

flow rate : approx. 50 L/hour.

of absorption

experiments

efficiency

: namely

86.5,

were obtained 83.0,

89.3

from

and

86.9%

respectively. 3.1

Stationary

TIG arc

on a water-cooled

copper

plate 3.3

Stationary tungsten

TIG-DCEN

electrode

(3.2 mm in diameter)

cooled copper plate welding jig. Arc

current

Arc voltage Arc

length

Tip

angle

arc was ignited between

(1.5 mm in thickness)

The welding conditions

Moving

TIG arc

and a water-

Bead-on-plate

placed in the

steel specimen

are as follows :

in the experiments.

: 10 V,

obtained

tungsten

electrode

ted by Hiraoka

50 or 100 L/hour.

When the arc is ignited, the temperature increases

and sometime

moment,

measurement

efficiency

The values of absorption

Results of experiments

: 45deg,

Cooling water flow rate : approx.

this

jig.

in section 3.2 was also used

from five experiments

summarized

during

in the welding

efficiency

were 92.2, 94.1, 93.8, 89.

1 and 99.1% respectively.

: 3 mm,

between

steel plate

welding was made on a SM400A mild

Welding condition described

Shielding gas flow rate : Ar 10 L/min,

difference

on a mild

(t=10 mm) placed

: 100 A,

of the

welding

the

later

is started.

The

inlet and outlet

stationary

condition

is calculated.

Three

efficiency were obtained

of outlet water

is stabilized.

At this

temperature

water

is recorded

and

values

from three experiments

: name-

3.1, 3.2 and 3.3 are

in Fig. 9. The absorption

efficiencies repor-

et al.') are in the range of 85-90%.

The

values obtained in our experiments are in the range of 83 -94% except 99.1% which is apparently a result of unclarified

measurement

independent surement

error,

experiments

As a conclusion,

absorption of absorption

in sections

and agreement

of two

is almost good.

it is clear that the developed

mea-

method and the welding jig has passed the first

step of check and evaluation.

ly 92.4 (at 101.6 L/h), 86.9 (at 54.45 L/h) and 84.5% (at 4.

53.72 L/h) respectively. 3.2

Moving

TIG arc

on the water-cooled

copper

TIG arc was moved on the same water-cooled plate placed in the welding jig. are as follows :

Measurement

of absorption

ing in a high

vacuum

copper

The welding conditions

Electron typical

: 100 A, : 10 V,

reported

Shielding

tungsten

aluminum

gas flow rate

electrode

: Ar 10 L/min,

Welding speed : 100, 150 mm/min, Bead

length : 120 mm,

: 45deg,

density

into a base metal

voltage

: 3 mm,

energy

in a high vacuum

with

current

of the

welding

compared

Arc

angle

beam

high

Arc

Tip

in EB weld-

plate

absorption

Arc length

efficiency

tion

tem

beam

to be in the range alloy".

efficiency

measured

laser

to verify

welding.

is often

Electron

beam

in the past and

of 80-95%"

or 92-97%

welding

experiment,

in a high

the above-mentioned

the system

which

was studied

In the following

of EB

using

welding

is the most

performance.

vacuum

measurement

for

absorpwas sys-

溶 接 学 会 論 文 集

4.1

Preparation

第17巻(1999)第4号

of measurement

in EB welding

in a 5.

high vacuum A

high

Mitsubishi

The

confirmed setting to

experiments,

bolts

problem.

and

The at

cooling

avoid

the

of

cooling jig

to

of

rate water

in the

setup

in

the

measuring

Experimental

Accelerating

voltage

Beam

conditions

L/hour jig.

vacuum

Fig.

Pressure

position in

: Df =320 the

chamber

mm,

:

ments.

He shielding gas is supplied through

The

These

identical to the values reported able with another

report"

racy of measurement

Fig.10

The welding chamber.

100 L/hour were 95.

are almost

twice

power

setting

which

accuracy

in reference

and agree-

by comparing

with the accu-

in TIG arc welding.

jig setup

in the high vacuum

the

(1)

4 kW

is

The focus

a

was

welding

as shown later in Fig. 17.

the

power

laser

machine

settings

hand-hold

and type

within •}5%).

were

made

at

was

used

for

Deviation

Experiment

Fig.11

from

using

CO, laser

The

welding

at

value

average

5.2

and reported"

power

brated

efficiency.

values

the nozzle

direction of the focusing beam.

output

average

efficiency obtained

trans-

position of the laser beam and relation between the focus position and the depth of penetration were sepa-

measurements

: 200 mm,

The values of absorption

was used in the

This laser machine is of a 3-axial

to the coaxial

down-slope

ab=1.03,

flow rate : approx.

Electric

(PURE: Phase Unified REsonator, trade name). A ZnSe lens of 254 mm focal length is used in all experi-

: 2•~10-2Pa,

4 and 97.9% respectively.

system is shown in Fig. 11. A 6 kW CO2 laser

verse flow type and emits the PURE mode laser beam

Bead

Cooling water

beam

layout of the CO2 laser machine and the

made by Mitsubishi

Welding speed : 1000 mm/min, length

in CO2 laser

10

welding

were not used), Focus

measure-

experiments.

are as follows

and

a good

by using the developed

of measurement

rately measured

(up-slope

to make

welding

to

: 69.5 kV,

current : 50.2 mA

Preparation

machine

plate and measuring

possible

experi-

system.

measuring

was

result of EB welding on a mild steel

The welding

it is quite

The general

chamber.

4.2

from the above-mentioned

for CO2 laser beam

5.1

welding,

100

clear

welding

specimen

welding high

beam

leakage

during at

in CO, laser

with

water

fixed

that

ment

cup

specimens

welding

was

ments

(70 focus

Faraday

minimize

the

kW

the

efficiency

welding

It has become

Throughout

melting-through

flow

welding

the

power.

welding

used

35 beam

and

using

T-shaped

avoid

water

boiling

shows

to

the

of absorption

by The

is

of

method,

EB

made

experiment.

machine

test

exact

thickness

13 mm

the

the

measured

were

machine

position

ab

the

the

stud-welded

fixed

the

was

know

in

of

exact

by

method

welding

used

power

mA).

current

EB

was

output

kV•~500 was

type

Electric

maximum

Measurement beam

vacuum

497

of less

each

than

beam

once

power Three

each

power

cali-

at

5 kW

probe

(of

independent setting

calculation measured

was

of power

and

the

absorption level

from

1%.

welding

on a mild

steel plate

conditions

in this experi-

No. 1 and measuring

General layout of the COz laser measuring system.

machine

and the

研 究論文

498

ment

are

as

Tomohiko

follows

SHIDA et al.: Measurement of Beam Energy Absorption in CO, Laser Beam Welding (2nd Report)

:

Laser power : 4 kW nominal

(calibrated

Focus

position

the surface,

Laser

nozzle

: 2 mm below distance

: 5 mm

above

3923 W),

the surface,

Shielding gas : He 15 L/min, Welding speed : 500 mm/min, Cooling

water

flow rate

The experimental of absorption

: variable

result is shown in Fig. 12. The values

efficiency

stay in the range

above the flow rate of 20 g/s flow rate

is below

15 g/s

(72 L/hour).

(54 L/hour),

efficiencies fluctuate widely.

of 80-87% When the

the absorption

The phenomenon

is attrib-

utable to boiling of water in the cooling channel

Fig.12

Absorption efficiency in CO, laser beam welding (Effect of cooling water flow rate).

Fig.13

Absorption efficiency in CO, laser beam welding (Effect of shielding gas flow rate and welding speed).

of the

welding jig. (2)

Experiment

No. 2

In the experiment

No. 2, effects

of the shape

of slit

opening of the welding jig, flow rate of He shielding gas and welding measuring Laser

speed were evaluated.

conditions power

: 4 kW

Focus

position

Laser

nozzle

The welding

in this experiment

and

are as follows :

nominal,

: 2 mm

below

distance

the

surface,

: 5 mm above

the surface,

Shielding gas : He 15, 30, 45 L/min, Welding

speed : 500, 1000 mm/min,

Thickness

of the

Cooling water

specimen

: 10 mm,

flow rate : approx.

welding

20 L/hour

mm acrylic block in the water

with 10

channel

It was found that the shape of the slit opening had little effect on absorption

efficiency.

The experimental

is shown in Fig. 13. The values of absorption

result

efficiency

are in the range of 72-81% and not affected by the flow

Focus

position

: 2 mm

below

Laser

(3)

Shielding gas : He 15, 30 L/min,

No. 3

In the experiment water

Nos. 1 and 2, boiling

in the cooling

channel

was

of cooling

observed.

When

boiling occurs, water flow is blocked for a moment and fluctuates. cooling increase

It is effective

water

to reduce

causes decrease

to increase

the flow rate

the boiling.

However

of the maximum

of that

of tempera-

ture rise at the same time and thus reduces sensitivity measurement.

of

For this reason the flow rate of cooling

water is fixed at 100 L/hour in the following experiment No. 3. Thickness

t of the welding specimen was adjust-

with welding speed , and depth of the cooling channel in the welding jig was also adjusted to

1 mm

above

the

surface,

rate of He shielding gas. EXperiment

and

nozzle

distance

: 5 mm above

the surface,

Welding speed : 500, 1000 mm/min, Thickness

of the specimen : 17 mm (500 mm/min),

10

mm (100 mm/min), Cooling

water

flow rate : approx.

acrylic block in the water The

experimental

result

100 L/hour

with

channel is shown

in Figs.

14 and

15.

The values of absorption efficiency are in the range of 74 -78% for the focus position of -2 mm below the surface (Fig. 14). When the focus position is at +1 mm above the surface, absorption efficiency is somewhat lower

ed in accordance

than this value and in the range of 65-71%

become

(4) Experiment No. 4 In the experiment No. 4, the effect of focus position on

The ment

7.5 to 8.0 mm. welding

and measuring

are as follows

conditions

in this experi-

:

Laser power : 4 kW nominal

the absorption

efficiency was investigated.

(Fig. 15).

In this exper-

iment the laser power is fixed at 5 kW (nominal value) (calibrated

3801 W) ,

so that the result is directly compared

with the result of

溶接 学会 論 文集

our

Fig.14

Absorption efficiency in CO, laser beam welding (Effect of shielding gas flow rate, focus : -2 mm).

Fig.15

Absorption efficiency in CO, laser beam welding (Effect of shielding gas flow rate, focus: +1 mm).

previous

machine.

experiment

The welding

experiment

using

Laser

nozzle

CO,

conditions

laser in this

Fig.16

Absorption efficiency in CO, laser beam welding (Effect of focus position).

Fig.17

Penetration

(calibrated

5572 W),

the surface,

: 5 mm above

and dimension

compared.

lowered below the surface

of the specimen.

This trend

to the data on pene-

depths in the published reference

on mild steel plates All welding

was

(Fig. 17). The

experiments,

the

obtained

efficiency for TIG-DCEN

values

reported

values in the references.

the developed measurement

He shielding gas are changeable

Discussions

a new

As the results of of

absorption

well with previously This means that

The values of absorption efficiency obtained by abovementioned experiments for CO, laser beam welding in conditions.

above,

and

by bead-on-plate

method is reliable and appli-

6.

described

Using the new

arc welding and EB welding in

a high vacuum agreed considerably

cable to CO, laser beam welding.

of experiments

to over-

were measured

made

difference of absorption efficiencies between Ar shielding gas and He shielding gas is not appreciable.

In this series

as well as the

efficiency for TIG-DCEN

welding on a SM400 mild steel plate.

as the focus position is

and the data in Fig. 16 correspond tration

100 L/hour

result is shown in Fig. 16. The values

efficiency decrease

The shape

arc welding, EB welding in a high vacuum and CO, laser beam welding

of absorption

and used.

were also re-examined

method, values of absorption

the surface,

focus position.

come problems in the previous report".

Welding speed : 1000 mm/min, The experimental

of various

of the welding specimen system

Shielding gas : He 30 L/min, Ar 30 L/min, Cooling water flow rate : approx.

depth

acrylic welding jig was developed measurement

6, 2, 0 mm below distance

same

:

Laser power : 5 kW nominal position:

the

and measuring

are as follows

Focus

499

第17巻(1999)第4号

The absorption

depending

on welding

efficiency is in the range of

72-87% within our experimental

conditions

of 4-5 kW

laser

Tomohiko

研究論文

500

power,

0.5-1.0 m/min

SHIDA et al.: Measurement of Beam Energy Absorption in CO2 Laser Beam Welding (2nd Report)

welding

speed,

bead-on-plate

the focus

position at 2-0 mm below the surface, He shielding gas 15-45 L/min. and bead-on-plate welding on a SM400

(3)

The

From

data

maximum

ciable

of Figs. 16 and

17 it is understood

depth of the moving

absorption

difference

He shielding

mild steel plate. follows ; when the depth of penetration of beam

energy

on a SM400

of absorption

mild steel plate.

efficiencies

gas and Ar shielding

in our experiments.

ACKNOWLEDGEMENT:

is increased,

is also increased.

This

The authors

would like to express

sincere thanks to

phenomena is probably attributable to multi-reflections and increased absorption of the beam energy in the

the following persons for their contributions

key-hole.

the National

The above-mentioned

values

of absorption

for CO, laser are by approximately those for TIG-DCEN than those

0-10% lower than

in a high vacuum.

difference of approximately mainly

to formation

10-20% maybe

above the keyhole and partly

to reflection

of the laser

is always larger for gas.

efficiencies between

in Fig. 16. This means that

an amount

energy, which is once absorbed

7.

DCEN

newly

values arc

welding,

and CO2 laser were

developed

welding

does not

ably

previously

well

with

references',".

This

measurement

The

method beam

absorption

for

TIG-

steel

The obtained

for TIG-DCEN

in a high

vacuum

that

is reliable

plates

1)

2)

4)

6)

consider-

values the

5)

in the

developed

and applicable

to

7) 8)

welding. efficiency

of CO, laser

beam

weld-

ing is in the range of 72-87% within our experimental conditions of 4-5 kW laser power, 0.5-1.0 m/min. welding speed, the focus position at 2-0 mm below the

surface,

He shielding

gas

Mr.

of Ibara-

to Production

of Hitachi, Ltd. (TIG arc specimens)

of Hitachi,

and

Ltd. (Finan-

effort and help from Mr. M. Mr. H. Fuchida

during experiments

and Mr. T. are also quite

References

values

arc welding

agreed

reported

means

(Ph. D. student), (ex-students)

(Technicians

of welding

Laboratory

Dedicated

University),

thanks

of

Mr. Y.

appreciated.

in a high vacuum on mild

and compared. efficiency

and EB welding

CO, laser

Research

cial support).

form

water-calorimetric efficiency

EB welding

Institute

Hitachi

of the specimen.

beam

measured

of absorption

(2)

(which

of absorption

Training

for preparation

3)

the

method,

Also sincere

welding

trans-

Conclusion

(1) Using

Technology

of Ibaraki

and Mr. M. Ohtani

ki University).

for Metals),

of laser beam

in a scattered

heating

mean melting)

Y. Yasuzawa

Hirano

: Mr. G. Asai (Technician Institute

(Chief technician

as shown

is consequently

ferred on the surface of the specimen necessarily

But the

into Ar gas and metal

vapor plume above the keyhole, to general

Miyazaki

Research

and support

He shield-

ing gas and Ar shielding gas is not appreciable

and contributes

plume

to conduct the experiments

Oguma

gas than for Ar shielding

of absorption

vapor

surface.

In Fig. 17, the depth of penetration difference

This

attributable

of gas and metal

beam from the specimen He shielding

efficiency

arc welding and by 10-20% lower

for EB welding

between

gas is not appre-

as

(that means the

key-hole)

welding

15-45 L/min.

and

9)

Tarui, T., Sakamoto, H. and Shibata, K.: Energy coupling between materials and beam in laser welding (2nd report), Preprints of the National Meeting of JWS, No. 55, Oct. 1994, pp. 40-41 (in Japanese). Tarui, T., Sakamoto, H. and Shibata, K.: Energy coupling between materials and beam in laser welding (3rd report), Preprints of the National Meeting of JWS, No. 56, Mar. 1995, pp. 44-45 (in Japanese). Maruo, H., Miyamoto, I., Kawabata, F. and Arata. Y.: Laser welding of metal, Journal of the Japan Welding Soc., Vol. 50 (1981), No. 4, pp. 404-409 (in Japanese). Dausinger, F., Beck, M. et al.: Energy Coupling in Surface Treatment Processes, Journal of Laser Applications, Summer/Fall 1990, pp. 17-21. Shida, T. and Terauchi, T.: Measurement of Beam Energy Absorption in CO, Laser Beam Welding, Quarterly Journal of JWS, Vol. 14, No.3, pp. 477-482 (1996). Hiraoka, K. and Okada, A : Heat input characteristics in TIG arc welding with Ar or Ar-He mixture shielding gas, Report presented to 87th Welding Arc Physics Research Committee of JWS, 23rd July 1987 (in Japanese). AWS ed.: Welding Handbook 8th ed., Vol. 1, p. 69 (1987). Irie, H., Hashimoto, T. et al.: Investigation on factors influencing weld penetration depth in electron beam welding, Transactions of National Research Institute for Metals, Vol. 21, No. 2, pp. 8-18 (1979). Tsukamoto.

S.. Hiraoka.

K. et al.:

Effect of plasma

forma-

tion on penetration depth in C02 laser welding, Preprints of the National Meeting of JWS, No. 61, Sept. 1997, pp. 330-331 (in Japanese).