A Macro - and Micro - Structural Study of Laser Welds in ... · mined. It was found that weld...

Abstract

A 1.7kW CO2 laser was used for the study of bead-on-plate welds in

D36 ship steel. The effect of welding heat input and focal point posi-

tion on weld geometrical features and microstructure was deter-

mined. It was found that weld penetration as well as the width of

weld pool and heat-affected-zone (HAZ) increase with heat input.

Microstructure and hardness in the weld pool, Partial fusion zone

and HAZ are also influenced by heat input. As the heat input is

increased, the associated cooling rate is decreased, resulting in the

formation of softer microstructures. Simple analytical models

describing heat flow during welding were used to calculate the

above mentioned geometrical features. The agreement between the

calculated and experimentally determined weld penetration, as well

as weld pool width, is sufficiently good and depends on weld heat

input. The optimum experimental conditions defined from the bend-

on-plate study were applied to Laser welding of butt joints in 4mm

D36 steel.

1. INTRODUCTION

Laser welding has evolved in the past 15 years as a major

welding process for numerous applications, from small spot

welds to continuous single pass deep penetration welds.

Reported advantages over welding with more conventional

techniques, include among others, the small size of the weld

pool and heat-affected zone (HAZ) combined with full pene-

tration.

In the welding of thin steel plates, e.g. in the shipbuilding

industry, distortion associated with the high heat input of the

conventional welding processes is often a serious problem. In

this case, laser welding, with the associated size reduction of

weld pool and HAZ, is considered as a promising alternative.

It is, therefore, of great importance to characterize quanti-

tatively the effect of laser welding parameters on the pene-

tration, weld pool size, HAZ size and the associated

microstructure of thin plate laser welds. To that end several

efforts have been undertaken in the past.

Breinan and Banas [1] determined that in HY-130 steel as

well as grade B ship steel, laser welding is characterized by a

high depth to width ratio, while penetration depended mainly

on focused power density and travel speed. Masumoto et al.

[2] determined that laser welding of thin steel plates pro-

duced lower distortion than the conventional TIG welding.

Moon [3] determined the effect of focal point on penetration

in A36 steel laser welds. Metzbower et al. [4] as well as

Strychor et al. [5] studied the effect of laser welding parame-

ters on the microstructure and properties of A36 ship steel.

More recently, Ducharme et al. [6] developed a mathe-

matical model for laser welding of thin steel plates in order to

predict the effect of welding parameters on weld pool dimen-

sions and shape.

The aim of the present work was to determine the effect

of welding conditions (laser power, travel speed, focal point)

on penetration, weld pool size, HAZ size and microstructure

in bead-on-plate laser welds of D36 ship steel. The experi-

mental results were compared with simple model predictions

of heat flow during laser welding. The optimum experimental

conditions were then applied to the welding of butt joints.

2. SYMBOLS

T (z,t) is the temperature at depth z below the surface derived

from applying a laser power for time t.

q is the laser power.

ë is the thermal conductivity of the steel.

a is the thermal diffusivity of the steel.

To is the initial temperature of specimens.

A is the absorptivity of the surface.

u is the travel speed of the moving specimen.

The constant to represents the time for heat to diffuse over a

distance of beam radius rb.

The length zo measures the distance over which heat can dif-

fuse during the beam interaction time rb/u.

V* is the volume which melts per second.

zm is the depth below the surface up to which melting has

occurred.

63Tå÷í. ×ñïí. Åðéóô. ¸êä. ÔÅÅ, V, ôåý÷. 1-2 1998 Tech. Chron. Sci. J. TCG, V, No 1-2

A Macro - and Micro - Structural Study of Laser Welds

in D36 Ship Steel

M. A. VLACHOGIANNIS

Dipl. Ing. Mechanical

and Industrial Engineer

A. D. ZERVAKI

Dipl. Ing. Metallurgist

G. N. HAIDEMENOPOULOS

Associate Professor of

University of Thessaly

Submitted: Aug. 14, 1997 Accepted: June 5, 1998

q* is the energy that is available to raise the temperature of

the remaining solid.

L is the latent heat of fusion per unit volume of the material.

x, y, z are the Cartesian co-ordinates.

3. EXPERIMENTAL PROCEDURE

The material used in the present study was the controlled-

rolled fully-killed D36 (per ASTM) ship steel with chemical

composition Fe - 1.7Mn - 0.15Si - 0.018 Al - 0.18C (mass

contents in %). Plates of D36 steel were received with thick-

ness 4mm. Specimens for the experimental study were cut

with dimensions 500 x 200mm. The hardness of the as-

received material was 180 -190HV.

For the laser welding experiments, a 1.7KW CO2 laser

was used. A focusing lens of 27mm focal length was

employed in order to increase the power density on the plate

surface. Helium shielding gas was supplied co-axially to the

laser beam through a nozzle of 4mm diameter. The range of

the laser welding parameters was the following: laser power

1140-1680W, travel speed 200-600mm/min and focal point

position +1, 0, -1 and -2mm from the plate surface. The beam

diameter was between 0.9 and 1.5mm, depending on the

focal point position. In all cases single pass bead-on-plate

welds were performed. A total of 38 beads were produced.

The laser welding parameters are summarized in Table 1. In

order to determine the geometrical characteristics of the laser

welds, macrostructural examination was performed in all

laser weld beads. The examination involved the usual metal-

lographic specimen preparation (mounting, grinding, poli-

shing and etching in 10% Nital for 8sec). The geometrical

parameters determined were the penetration depth, the width of

the weld pool as well as the width of the HAZ (see Figure 1).

Microstructural analysis was performed only on weld

beads which exhibited full penetration. For this purpose the

usual metallographic specimen preparation was employed,

involving mounting, grinding, polishing and etching in 2%

Nital for 10-20sec. Microhardness measurements were per-

formed on the cross section of all full penetration welds

using a microhardness tester with load 300gr.

4. RESULTS AND DISCUSSION

4.1. Geometrical characteristics

The typical appearance of laser weld beads is depicted in

Figure 2a (partial penetration) and Figure 2b (full pene-

tration). Weld penetration was determined as a function of

laser travel speed and focal point position relative to the plate

surface. The results are shown in Figure 3 for laser power

1500W. Weld penetration generally decreases with laser tra-

vel speed. Regarding full penetration conditions, it can be

64 Tå÷í. ×ñïí. Åðéóô. ¸êä. ÔÅÅ, V, ôåý÷. 1-2 1998 Tech. Chron. Sci. J. TCG, V, No 1-2

Table 1: Summary of Laser welding parameters used in the bead-

on-plate experiments.

Ðßíáêáò 1: Óýíïøç ôùí ðáñáìÝôñùí ôçò óõãêüëëçóçò Laser ðïõ

÷ñçóéìïðïéÞèçêáí êáôÜ ôçí ðåéñáìáôéêÞ äéáäéêáóßá.

Figure 1: Geometrical characteristic sizes of laser weld beads

determined by the microstructural analysis (1. Width of HAZ.

2. Width of Weld Pool. 3. Partial Fusion Zone. 4. Penetration 5.

Plate Thickness).

Ó÷Þìá 1: ÃåùìåôñéêÜ ÷áñáêôçñéóôéêÜ ôçò äçìéïõñãïýìåíçò óõãêüë-

ëçóçò Laser, õðïëïãéóìÝíá áðü ôçí áíÜëõóç ôçò ìéêñïäïìÞò (1.

ÐëÜôïò ôçò ÈÅÆ. 2. ÐëÜôïò ôçò ëßìíçò óõãêüëëçóçò. 3. Æþíç ÔÞîçò.

4. Äéåßóäõóç. 5. ÐÜ÷ïò åëÜóìáôïò).

seen that these depend on a combination of focal point posi-

tion and travel speed. For example, when the focal point is

set at -1mm (below the surface), full penetration is obtained

for travel speeds of 200-400mm/min. When the F.P. position

is set at -2mm, a travel speed of 200mm/min causes weld

drop-out.

In order to present the results in a more comprehensible

form, the laser power Q and travel speed u, were combined

in a single parameter, the heat input h, defined as h = Q/u (in

J/mm). The variation of weld penetration with focal point

position and heat input is given in Figure 4. Weld penetration

is not affected substantially when the focal point position is

below the plate surface, while it drops significantly when the

focal point is above the plate surface. Therefore, in order to

determine the effect of heat input on penetration the average

penetration for focal point positions below the surface (0, -1,

-2mm) was determined. The results are depicted in Figure 5.

Initially the average weld penetration increases with heat

input up to 250 J/mm, where it stabilizes to a value corre-

sponding to full penetration between 250 and 400 J/mm. For

higher values of heat input, undercutting and drop-out phe-

nomena were observed.

The variation of the width of the weld pool with focal

point position and heat input is depicted in Figure 6. As in

the previous case, the weld pool width is virtually unaffected

when the focal point is below the plate surface. The average

weld pool width as a function of heat input is given in Figure 7.

A linear dependence on heat input is observed. The depen-

dence of the width of the HAZ on focal point position and


heat input is given in Figure 8. The width of the HAZ varies

between 0.3 and 1.5mm. The average width of the HAZ is

given as a function of heat input in Figure 9.

4.2. Microstructural analysis

The microstructure of the laser weld beads was examined

on cross sections of beads which exhibited full penetration.

Since plate thickness and weld geometry were constant

during the investigation, the resulting microstructure

depended strongly on cooling rate, which in turn depends on

the heat input employed. For each weld area (HAZ, Partial

fusion zone and weld pool) the following microstructures

were observed:

Weld pool: For high heat input (350-450 Joule/mm) the

microstructure consisted mainly at the grain boundary of

Widmanstatten ferrite and Primary Ferrite (PF(G)) and in the

grain interior of acicular ferrite, Primary Ferrite (PF(I)) and

pearlite (figure 10a) according to a nomenclature proposed

by Lancaster [9]. This result is consistent with the lower

cooling rate associated with the high heat input. For lower

heat input values (250-350 Joule/mm) the formation of Wid-

manstatten and acicular ferrite was suppressed in favour of

bainite. The structure therefore consisted of primary ferrite

and bainite, consistent with the high cooling rates associated

with lower heat input (Figure 10b).

Partial Fusion zone: The microstructure in the Partial

fusion zone was martensitic for the entire heat input range

investigated (figure 11). This behavior is consistent with the

highest cooling rates exhibited in the Partial fusion zone, as

it is the boundary between the weld pool and HAZ.

Heat Affected Zone: For high heat input, the microstruc-

ture in the HAZ consisted mainly of a fine equiaxed fer-

rite/pearlite mixture in contrast to the banded ferrite/pearlite

structure of the base plate. The breakdown of the banded

structure in the HAZ is probably the result of the phase trans-

formations occurring during the thermal cycle of the welding

(Figure 12). This is consistent with the lower heating and

cooling rate and, therefore, longer interaction time in the

HAZ. For low heat input, the above behavior was not

observed.

Microhardness was determined on a cross section - in

2mm depth - of the laser weld beads. A characteristic micro-

hardness profile is shown in Figure 13. It can be observed

that maximum hardness appeared in the Partial fusion zone

and is associated with the martensitic structure of this region.

The average hardness of the weld pool, as well as the hard-

ness of the Partial fusion zone, were determined as a function

of heat input. The results are depicted in Figure 14. As the

heat input increases, the hardness of both the weld pool and

Partial fusion zone decrease. This is due to the corresponding

decrease of the cooling rate, thus producing softer structures.

Figure 2: Microstructure of laser weld beads (a) Partial pene-

tration, specimen B12: 1140W, 400mm/min, FP at 0 (b) Full pene-

tration, Specimen B28, 1680W, 600mm/min, FP at -2mm.

Ó÷Þìá 2: ÌéêñïäïìÞ ôçò óõãêüëëçóçò Laser (a) Ìç ðëÞñçò äéåßó-

äõóç, äïêßìéï B12: 1140W, 400mm/min, óçìåßï åóôßáóçò ðÜíù óôçí

åðéöÜíåéá (b) ÐëÞñçò äéåßóäõóç, äïêßìéï B28, 1680W, 600mm/min,

Ó.Å: -2mm.

(a)

(b)


Figure 3: Weld penetration as a function of laser travel speed for

different focal point positions of the laser beam at a laser power of

1.5KW.

Ó÷Þìá 3: Äéåßóäõóç óõãêüëëçóçò ùò óõíÜñôçóç ôçò ôá÷ýôçôáò ôçò

äÝóìçò ãéá äéáöïñåôéêÜ óçìåßá åóôßáóçò ôçò äÝóìçò ôïõ Laser. Ç

éó÷ýò ôçò äÝóìçò Þôáí ßóç ìå 1.5KW.

Figure 5: Average weld penetration as a function of heat input

(focal point positions 0, -1, -2mm).

Ó÷Þìá 5: ÌÝóç ôéìÞ ôçò äéåßóäõóçò óõãêüëëçóçò ùò óõíÜñôçóç ôçò

åéóñïÞò èåñìüôçôáò (Ó.Å.: 0, -1, -2mm).

Figure 6: Width of the weld pool as a function of focal point posi-

tion and heat input.

Ó÷Þìá 6: ÐëÜôïò ôçò ëßìíçò óõãêüëëçóçò ùò óõíÜñôçóç ôïõ óçìåßïõ

åóôßáóçò êáé ôçò åéóñïÞò èåñìüôçôáò.

Figure 4: Weld penetration as a function of focal point position and

heat input.

Ó÷Þìá 4: Äéåßóäõóç óõãêüëëçóçò ùò óõíÜñôçóç ôïõ óçìåßïõ åóôßá-

óçò êáé ôçò åéóñïÞò èåñìüôçôáò.

In summarizing the above discussion the following com-

ments can be made: Regarding the effect of heat input on the

geometrical characteristics of the weld beads, it was shown

that weld penetration, weld pool width and HAZ width

increase with heat input. This is obviously associated with

the higher thermal effect, i.e. higher temperature and longer

interaction time, associated with high values of heat input.

On the other hand, microstructure is mainly influenced by

cooling rate. As the heat input is increased the cooling rate is

decreased, resulting in softer structures in the weld pool and

Partial fusion zone. Therefore, selection of heat input is very

important as it determines the structure and properties of the

welds. In the case of welding a 4mm thick plate for example,

a heat input of the order of 250J/mm would result in full pe-

netration without undercutting or drop-out defects. At the

same time the weld pool width would be only 3.5mm and the

HAZ would be limited to below 1mm. In contrast, conven-

tional MIG welding of the same plate results in a weld pool

width of 8-9mm and HAZ width of 2-3mm.


Figure 7: Average width of weld pool as a function of heat input

(focal point positions 0, -1, -2mm).

Ó÷Þìá 7: Ôï ìÝóï ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò ùò óõíÜñôçóç ôçò

åéóñïÞò èåñìüôçôáò (Ó.Å.: 0, -1, -2mm).

Figure 9: Average width of HAZ as a function of heat input (focal

point positions 0, -1, -2mm).

Ó÷Þìá 9: Ôï ìÝóï ðëÜôïò ôçò È.Å.Æ. ùò óõíÜñôçóç ôçò åéóñïÞò èåñ-

ìüôçôáò (Ó.Å.: 0, -1, -2mm).

Figure. 8: Width of HAZ as a function of focal point position and

heat input.

Ó÷Þìá 8: Ôï ðëÜôïò ôçò È.Å.Æ. ùò óõíÜñôçóç ôïõ óçìåßïõ åóôßáóçò

êáé ôçò åéóñïÞò èåñìüôçôáò.

4.3. Prediction of geometrical features from heat flow

modeling

Heat flow modeling during laser welding was employed

in order to predict the weld penetration and the weld pool

width. The geometry of heat flow depends on weld pene-

tration. When the penetration is partial, the heat flow is three-

dimensional (3-D), while in full penetration heat flow

approaches a two dimensional (2-D) geometry (see Figure 15).

In order to bracket the behavior, two extreme cases were con-

sidered, corresponding to the implementation of 1-D and

3-D models respectively. The 1-D heat flow model was

developed by Ashby and Easterling [7] and incorporates a

moving finite heat source on a semi-infinite plate. According

to this model, the temperature distribution T(z,t) in the plane

perpendicular to the surface through the centerline of the

beam can be expressed as:

(4.1)

In Eq. (4.1), T(z,t) is the temperature at depth z below the

surface derived from applying a laser power q for time t. The

terms ë (48.7 W/m 0C) and á (13.9X10-6 m2/sec) are the

thermal conductivity and diffusivity of the steel, respective-

ly; To is the initial temperature of specimens, 150C; A is the

absorti-vity of the surface, 0.9; and u is the travel speed of the

moving specimen. The constant to represents the time for

heat to diffuse over a distance of beam radius rb (0.9-1.5mm).

The length zo measures the distance over which heat can dif-

fuse during the beam interaction time rb/u.

The model also takes into account the possibility of sur-

face melting during the process. When the surface reaches

the liquidus temperature, a portion of the laser energy is

absorbed as latent heat of fusion. Although this amount of

energy is released later, during solidification, it is temporari-

ly removed from the input energy and is not available to melt

more material. The volume which melts, per second, is equal

to:

V* = 2 rb zm u (4.2)

where zm is the depth below the surface up to which melting

has occurred. So, the energy that is available to raise the tem-

perature of the remaining solid is given by:

q* = q - 2 rb zm u L (4.3)

where L is the latent heat of fusion per unit volume of the

material. The temperature field, in such a case, is calculated

from equation (4.1) by replacing q with q*.

( )[ ]( )

T z t TA q

u t t

z z

to

o

o( , ) exp

/= +

⋅

⋅ ⋅ ⋅ +⋅

+⋅ ⋅

2 41 2

2

π λ α

The 3-D heat flow model was developed by Masubuchi

[8] and incorporates a moving point source on a semi-infinite

plate. According to this model, the temperature distribution

can be expressed as:

T (x,y,z,t) = To + (4.4)

where (4.5)

and w = x - ut (4.6)

The meaning and the value of the various symbols of

equations (4.1) through (4.6) are given in Section 2. Weld

penetration was calculated as the depth z at which the tem-

perature exceeded the liquidus temperature of the steel. The

results are depicted as a function of heat input in Figure 16

and are compared with experimentally determined weld pene-

tration.

For low weld heat input, weld penetration is short and the

heat flow is three-dimensional. Therefore, the calculated

weld penetration according to the 3-D model (solid line) is in

good agreement with the experimental results. As the heat

input is increased, the weld penetration increases and heat

flow approaches a two dimensional condition. The 3-D

model fails to predict the weld penetration in this case. In

contrast, the 1-D model, which incorporates a finite heat

source, is in better agreement with the experimental results

through-out the entire range of heat input.

Weld pool width was calculated, as a function of heat

input, with the 3-D model and the results are compared with

R w y z= + +2 2 2

q

R

u

aw

u

aR

e e2

2

2

⋅ ⋅⋅ ⋅

−⋅

⋅−

⋅⋅

π λ( )

( )


Figure 12: Microstructure of the HAZ of the weld. (Specimen

No.B5, 1500W, 400mm/min, focal point -1).

Ó÷Þìá 12: ÌéêñïäïìÞ ôçò È.Å.Æ. ôçò óõãêüëëçóçò. (Äïêßìéï Íï.Â5,

1500W, 400mm/min, focal point -1).

Figure 10: Microstructure of weld pool at (a) high (450 Joule/mm)

and (b) low heat input (125 Joule/mm).

Ó÷Þìá 10: ÌéêñïäïìÞ ôçò ëßìíçò óõãêüëëçóçò óå (a) ÕøçëÞ

(450 Joule/mm) êáé (b) ×áìçëÞ åéóñïÞ èåñìüôçôáò (125 Joule/mm).

(a)

(b)

Figure 11: Microstructure of the Partial fusion zone of the weld.

(Specimen No.B28, 1680W, 600mm/min, focal point -2).

Ó÷Þìá 11: ÌéêñïäïìÞ ôçò Æþíçò ÔÞîçò ôçò óõãêüëëçóçò. (Äïêßìéï

Íï.Â28, 1680W, 600mm/min, focal point -2).


Figure 13: Microhardness profile of laser weld bead. (Specimen

No.B14, 1500W, 200mm/min, focal point 0).

Ó÷Þìá 13: Ðñïößë ìéêñïóêëçñüôçôáò ôçò óõãêüëëçóçò Laser. (Äïêß-

ìéï Íï.Â14, 1500W, 200mm/min, focal point 0).

Figure 14: Microhardness of weld pool and Partial fusion zone as

a function of heat input.

Ó÷Þìá 14: Ìéêñïóêëçñüôçôá ôçò ëßìíçò óõãêüëëçóçò êáé ôçò æþíçò

ôÞîçò ùò óõíÜñôçóç ôçò åéóñïÞò èåñìüôçôáò áíÜ ìïíÜäá ìÞêïõò.

the experimentally determined width of the weld pool in

Fig. 17. The agreement between calculated and experimental

results is good for heat input above 200 J/mm, while at lower

values of heat input the discrepancy increases. This can be

explained by considering that the 3-D model incorporates a

point heat source, meaning that the temperature distribution

is substantially affected only in the region adjacent to the

source. Therefore while the temperature can be predicted

with accuracy away from the source, the inaccuracy is

increased substantially close to the source.

5. LASER WELDING OF BUTT JOINTS

Laser welding of butt joints was carried out for type D-36

steel plates using a 1.7 kW CO2 laser facility. The welds

were evaluated by both destructive and non-destructive tests.

Figure 15: Geometry of heat flow: a) 3-D, partial penetration b) 2-D,

full penetration.

Ó÷Þìá 15: Ãåùìåôñßá ôçò ñïÞò èåñìüôçôáò: a) 3-D, ìç ðëÞñçò

äéåßóäõóç b) 2-D, ðëÞñçò äéåßóäõóç.

Plates of D-36 steel with dimensions 300x150x4mm,

were welded in butt joint geometry by applying the experi-

mental conditions depicted in table 2. These conditions were

determined from the previously presented bead-on-plate

experiments.

The welds were subjected to non-destructive quality con-

trol (radiography, liquid penetrants, magnetic particles), as

well as to destructive testing (tensile and bend testing, macro-

examination)

The non-destructive testing revealed that specimens 1, 3

and 4 (see table 2) exhibited imperfections such as pores,

incomplete penetration and misalignment, while specimen 2

showed almost complete penetration.

The macrostructure of specimen No. 2 is shown in Figure 18.

The tensile tests for specimens No2 and No3 were performed

according to DIN 50120 specification and the results are pre-

sented in table 3. In the same table, the tensile properties of

D36 steel, as well as tensile test results for conventional

M.I.G. welds are presented for comparison. Compared to the

conventional M.I.G. welding method, laser welding for the

case of specimen No 2 shows an increase in both yield and

tensile strength, indicating the superiority of the laser welding

method.

The high quality of laser butt welds is also indicated by

bend test results. For example, specimen No 2, after being

subjected to bend test, according to DIN 50121 specification,

showed no microcracks in the face position.

6. CONCLUSIONS

According to the proceeding discussion, the following

conclusions can be made:


Figure 17: Weld pool width as a function of heat input. Comparison

of experimental results with prediction of 3-D heat flow model.

Ó÷Þìá 17: Ôï ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò ùò óõíÜñôçóç ôçò åéó-

ñïÞò èåñìüôçôáò. Óýãêñéóç ôùí ðåéñáìáôéêþí áðïôåëåóìÜôùí ìå

ôçí ðñüâëåøç ôïõ ôñéäéÜóôáôïõ ìïíôÝëïõ ñïÞò èåñìüôçôáò.

Table 2: Experimental conditions for butt joint welding.

Ðßíáêáò 2: ÐåéñáìáôéêÝò óõíèÞêåò óõãêïëëÞóåùí óõìâïëÞò.

Table 3: Tensile test results and comparison between M.I.G. and

Laser Welding.

Ðßíáêáò 3: ÁðïôåëÝóìáôá ôïõ ôåóô åöåëêõóìïý êáé óýãêñéóç ôùí

ìåèüäùí óõãêüëëçóçò M.I.G. êáé Laser.

Figure 18: Macrostructure of laser welded butt joint.

Ó÷Þìá 18: ÌáêñïäïìÞ óõãêüëëçóçò laser.

(A) Weld penetration, width of weld pool as well as width

of the heat affected zone, depend strongly on laser welding

heat input. All the above geometrical characteristics increase

with heat input. At the same time they are not affected sub-

stantially by the focal point position when the focal point of

the laser beam is below the surface.

(B) The resulting microstructures depend also on heat

input. Measured microhardness decreases with increasing

heat input due to the lower cooling rates involved.

(C) Heat flow modeling can predict with sufficient

accuracy the weld penetration when the heat input is low. For

high heat input the 3-D model fails, while the 1-D model is

in better agreement with the experimental results. The weld

pool width can be predicted with sufficient accuracy with the

3-D model at high values of heat input. At low heat input the

inaccuracy is increased due to the point heat source assumption

incorporated in the model.

(D) Successful laser welds of butt joints can be performed

Figure 16: Weld penetration as a function of heat input. Compa-

rison between experimental and calculated results with 1-D

(dashed curve) and 3-D (solid curve) modeling.

Ó÷Þìá 16: Äéåßóäõóç óõãêüëëçóçò ùò óõíÜñôçóç ôçò åéóñïÞò èåñ-

ìüôçôáò. Óýãêñéóç ìåôáîý ðåéñáìáôéêþí êáé èåùñçôéêþí áðïôåëå-

óìÜôùí ôïõ ìïíïäéÜóôáôïõ êáé ôïõ ôñéäéÜóôáôïõ ìïíôÝëïõ.

by using the proper set-up and experimental conditions. The

quality of these laser welds is superior to the conventional

M.I.G. welding of the same material.

ACKNOWLEDGEMENT

This work has been partially supported by the Greek Sec-

retariat of Research and Technology through the EPET II-170

project. The material used in this study was kindly offered by

Hellenic Shipyards (Skaramanga Yard).

REFERENCES

1. Breinan E.M., Banas C.M., �Welding with High-Power Lasers�,

Proc. Conf. on Advances in Metal Processing, 25th Sagamore Army

Materials Research Conference, Lake George, N.Y., 1981, pp. 111/131.

2. Masumoto I., Shinoda T., Ishiyama H., �Application of Laser Beam

Welding to Thin Steel Sheet�, Trans. Jpn. Weld. Soc., 1989, Vol. 20,

pp. 50/55.

3. Moon D.W., �Some Factors Affecting Penetration in Laser Welding�,

Materials Processing, 1985, Vol. 44, pp. 53/59.

4. Metzbower E.A., Hella R.A., Theodorski G., �Laser Beam Welding

at NIROP�, A Navy Manufacturing Technology Program in Lasers in

Material Processing, Los Angeles, California, ASM, 1983, pp. 266/272.

5. Strychor R., Moon D.W., Metzbower E.A., �Microstructure of ASTM

A-36 Steel Laser Beam Weldments�, J. Metals, 1984, Vol. 36, pp. 59/61.

6. Ducharme R., Williams K., Kapadia P., Dowden J., Steen W.,

Glowacki M., �The Laser Welding of Thin Metal Sheets: An Integrated

Keyhole and Weld Pool Model with Supporting Experiments�, J. Phys. D,

Appl. Phys., 1994, Vol. 27, pp. 1619/1627.

7. Ashby M.F., Easterling K.E., �The Transformation Hardening of

Steel Surfaces by Laser Beams-I. Hypo-Eutectoid Steels�, Acta Metall.,

1984, Vol. 32, pp. 1935/48.

8. K. Masubuchi, Analysis of welded structures, Pergamon Press,

1980.

9. J. F. Lancaster, Metallurgy of Welding, Charman & Hall, 1993.


Michael A. Vlachogiannis,

Dipl. ing. mech. and industrial engineering, University of Thessaly, Pedion Areos, 383 34 Volos.

Anna D. Zervaki,

Dipl. ing., Metallurgical Industrial Research and Technology Center, 1st Industrial Area of Volos, 385 00 Volos.

Gregory N. Haidemenopoulos,

Associate professor, Dept. of Mech. and Industrial Engineering, University of Thessaly, Pedion Areos, 383 34 Volos.

Ðåñßëçøç

Ãéá ôç ìåëÝôç ôùí óõãêïëëÞóåùí ôïõ íáõðçãéêïý ÷Üëõâá D36 ÷ñçóé-

ìïðïéÞèçêå laser äéïîåéäßïõ ôïõ Üíèñáêá éó÷ýïò 1.7kW. Õðïëïãß-

óôçêå ç åðßäñáóç ôïõ óçìåßïõ åóôßáóçò êáé ôçò éó÷ýïò ôçò äÝóìçò óôá

ãåùìåôñéêÜ ÷áñáêôçñéóôéêÜ êáé ôç ìéêñïäïìÞ ôçò äçìéïõñãïýìåíçò

óõãêüëëçóçò. ÂñÝèçêå üôé ç äéåßóäõóç ôçò ëßìíçò óõãêüëëçóçò, ôï

ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò êáé ôï ìÝãåèïò ôçò ìåñéêÞò æþíçò

ôÞîçò áõîÜíïíôáé ìå ôçí áýîçóç ôçò éó÷ýïò ôçò äÝóìçò. Ç ìéêñïäïìÞ

êáé ç óêëçñüôçôá ôçò ëßìíçò óõãêüëëçóçò, ôçò ìåñéêÞò æþíçò ôÞîçò

êáé ôçò È.Å.Æ. åðçñåÜæïíôáé áðü ôçí éó÷ý ôçò äÝóìçò. Êáèþò ç éó÷ýò

ôçò äÝóìçò (êáé êáôÜ óõíÝðåéá ç åéóñïÞ èåñìüôçôáò) áõîÜíïíôáé, ï

ñõèìüò øýîçò ìåéþíåôáé, ìå áðïôÝëåóìá íá äçìéïõñãïýíôáé äéáöïñå-

ôéêÝò ìéêñïäïìÝò. ×ñçóéìïðïéÞèçêáí áðëÜ áíáëõôéêÜ ìïíôÝëá ðïõ

ðåñéãñÜöïõí ôç ñïÞ èåñìüôçôáò êáôÜ ôç äéÜñêåéá ìéáò óõãêüëëçóçò,

ãéá ôïí õðïëïãéóìü ôùí ðñïáíáöåñèÝíôùí ãåùìåôñéêþí ÷áñáêôçñé-

óôéêþí. Ç óõìöùíßá ìåôáîý ôùí èåùñçôéêþí êáé ôùí ðåéñáìáôéêþí

áðïôåëåóìÜôùí åßíáé áñêåôÜ êáëÞ, åîáñôþìåíç áðü ôï ìÝãåèïò ôçò

éó÷ýïò ôçò äÝóìçò. Ïé âÝëôéóôåò ðåéñáìáôéêÝò óõíèÞêåò ÷ñçóéìïðïé-

Þèçêáí ãéá ôç óõãêüëëçóç óõìâïëÞò åëáóìÜôùí ðÜ÷ïõò 4mm, áðü ôï

ßäéï õëéêü.

1. ÐÅÉÑÁÌÁÔÉÊÇ ÄÉÁÄÉÊÁÓÉÁ

Ôï õëéêü ðïõ ÷ñçóéìïðïéÞèçêå óôç ðáñïýóá åñãáóßá

Þôáí ï íáõðçãéêüò ÷Üëõâáò D36, ìå óêëçñüôçôá ìåôáîý

180-190HV êáé ìå ÷çìéêÞ óýíèåóç: Fe - 1.7Mn - 0.15Si -

0.018 Al - 0.18C (ê.â.%). ×ñçóéìïðïéÞèçêáí åëÜóìáôá

ðÜ÷ïõò 4mm, ìå äéáóôÜóåéò 500×200mm.

Ç ðñáãìáôïðïßçóç ôùí «ñáöþí» (bead-on-plate) Ýãéíå

ìå ôç âïÞèåéá ìéá äÝóìçò laser CO2 1.7kW êáé äéáìÝôñïõ

ìåôáîý 0.9 êáé 1.5mm (åîáñôþìåíç áðü ôï óçìåßï åóôßáóÞò

ôçò). Ïé óõíèÞêåò êáé ïé ðáñÜìåôñïé ôçò óõãêüëëçóçò áðåé-

êïíßæïíôáé óôïí ðßíáêá 1. Ãéá ôç ìÝôñçóç ôùí ãåùìåôñéêþí

÷áñáêôçñéóôéêþí ôçò óõãêüëëçóçò (ó÷Þìá 1), Ýãéíå óôá

äïêßìéá ç áðáñáßôçôç ìåôáëëïãñáöéêÞ ðñïåôïéìáóßá (åãêé-

âùôéóìüò, ëåßáíóç, óôßëâùóç êáé ÷çìéêÞ ðñïóâïëÞ ìå 10%

Nital ãéá 8 sec) êáé ìå ôç âïÞèåéá ôçò áíÜëõóçò ôçò ìáêñï-

äïìÞò õðïëïãßóôçêáí ïé ãåùìåôñéêÝò ðáñÜìåôñïé ðïõ Þôáí:

ôï âÜèïò äéåßóäõóçò êáé ôï ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò

êáèþò êáé ôï ðëÜôïò ôçò ìåñéêÞò æþíçò ôÞîçò. Ç ðñïáíá-

öåñèåßóá ìåôáëëïãñáöéêÞ ðñïåôïéìáóßá ÷ñçóéìïðïéÞèçêå

êáé ãéá ôçí áíÜëõóç ôçò ìéêñïäïìÞò ôùí äïêéìßùí ðëÞñïõò

äéåßóäõóçò.

2. ÁÐÏÔÅËÅÓÌÁÔÁ-ÓÕÌÐÅÑÁÓÌÁÔÁ

2.1. ÁíÜëõóç ìéêñïäïìÞò - ÐáñáìåôñéêÞ áíÜëõóç

Óôá ó÷Þìáôá 2a êáé 2b áðåéêïíßæïíôáé äýï ÷áñáêôçñéóôé-

êÝò ìïñöÝò ôçò ìáêñïäïìÞò ôçò óõãêüëëçóçò laser ãéá

ðëÞñç êáé ìç ðëÞñç äéåßóäõóç.

Óôï ó÷Þìá 3 öáßíåôáé ç åîÜñôçóç ôçò äéåßóäõóçò ôçò

ëßìíçò óõãêüëëçóçò áðü ôçí ôá÷ýôçôá êáé ôï óçìåßï åóôßá-

óçò ôçò äÝóìçò. Ç äéåßóäõóç ôçò ëßìíçò óõãêüëëçóçò ìåéþ-

íåôáé, êáèþò áõîÜíåôáé ç ôá÷ýôçôá ôçò äÝóìçò laser. Ç áðáß-

ôçóç ðëÞñïõò äéåßóäõóçò ùò ðáñÜãïíôá åðéôõ÷ïýò óõãêüë-

ëçóçò áðïôåëåß ôï êñéôÞñéï åðéëïãÞò ôùí âÝëôéóôùí óõíèç-

êþí óõãêüëëçóçò. ¼ðùò öáßíåôáé áðü ôï ó÷Þìá 3, õðÜñ÷ïõí

óõãêåêñéìÝíïé óõíäõáóìïß óõíèçêþí ðïõ åðéöÝñïõí ôï åðé-

èõìçôü áðïôÝëåóìá. Ãéá ðáñÜäåéãìá, üôáí ôï óçìåßï åóôßá-

óçò åßíáé 1mm êÜôù áðü ôçí åðéöÜíåéá ôïõ åëÜóìáôïò, ðëÞ-

ñçò äéåßóäõóç åðéôõã÷Üíåôáé, üôáí ç ôá÷ýôçôá âñßóêåôáé

ìåôáîý 200-400mm/min.

ÐïëëÝò öïñÝò êáôÜ ôç óõãêüëëçóç ÷ñçóéìïðïéåßôáé ç

ðáñÜìåôñïò h=Q/u (J/mm), ãéá íá åêöñáóôïýí ôáõôü÷ñïíá

ç éó÷ýò êáé ç ôá÷ýôçôá ôçò äÝóìçò. Óôï ó÷Þìá 4 ðáñïõóéÜ-

æåôáé ç åðßäñáóç ôçò åéóñïÞò èåñìüôçôáò h êáé ôïõ óçìåßïõ

åóôßáóçò óôï ìÝãåèïò ôçò äéåßóäõóçò. Ç äéåßóäõóç äåí åðç-

ñåÜæåôáé óçìáíôéêÜ áðü ôï óçìåßï åóôßáóçò, áñêåß áõôü íá

åßíáé êÜôù áðü ôçí åðéöÜíåéá. Ç åðéññïÞ ôçò åéóñïÞò èåñ-

ìüôçôáò óõíïøßæåôáé óôï ó÷Þìá 5, üðïõ öáßíïíôáé ôá üñéá

åðéôõ÷ßáò ðëÞñïõò äéåßóäõóçò óå Ýëáóìá 4mm.

Óôï ó÷Þìá 6 áðåéêïíßæåôáé ç åîÜñôçóç ôïõ ðëÜôïõò ôçò

ëßìíçò óõãêüëëçóçò áðü ôï Óçìåßï Åóôßáóçò (Ó.Å.) êáé ôçí


ÅêôåôáìÝíç ðåñßëçøç

ÌåëÝôç ÌéêñïäïìÞò ÓõãêïëëÞóåùí Laser

Íáõðçãéêïý ×Üëõâá D36

Ì. Á. Âëá÷ïãéÜííçò

Ìç÷/ãïò Ìç÷/êüò Âéïìç÷áíßáò

Á. Ä. ÆåñâÜêç

Ìåôáë/ãïò Ìç÷/êüò

Ãñ. Í. ×áúäåìåíüðïõëïò

Áíáðë. ÊáèçãçôÞò Ðáíåð. Èåóóáëßáò

ÕðïâëÞèçêå: 14.8.1997 ¸ãéíå äåêôÞ: 5.6.1998

åéóñïÞ èåñìüôçôáò. Êáé ðÜëé üôáí ôï óçìåßï åóôßáóçò åßíáé

åíôüò ôïõ õëéêïý, ôï ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò ðáñá-

ìÝíåé áìåôÜâëçôï (ãéá óôáèåñü h). Ç ìÝóç ôéìÞ ôïõ ðëÜôïõò

ôçò ëßìíçò óõãêüëëçóçò, ãéá ôá äéÜöïñá óçìåßá åóôßáóçò,

åßíáé ãñáììéêÞ åîÜñôçóç ôçò åéóñïÞò èåñìüôçôáò h (ó÷Þìá 7).

ÁíÜëïãá áðïôåëÝóìáôá ðáñáôçñïýíôáé êáé ãéá ôï ðëÜôïò

ôçò ìåñéêÞò æþíçò ôÞîçò. Óôá ó÷Þìáôá 8 êáé 9 öáßíïíôáé ç

åîÜñôçóç ôïõ ðëÜôïõò ôçò ìåñéêÞò æþíçò ôÞîçò áðü ôï

óçìåßï åóôßáóçò êáèþò êáé ç ãñáììéêÞ åîÜñôçóç ôçò ìÝóçò

ôéìÞò ôïõ ðëÜôïõò áðü ôçí åéóñïÞ èåñìüôçôáò. Ðáñáôçñåß-

ôáé ìåãéóôïðïßçóç ôïõ ðëÜôïõò ôçò ìåñéêÞò æþíçò ôÞîçò,

üôáí ôï óçìåßï åóôßáóçò åßíáé -1mm.

Ç áíÜëõóç ôçò ìéêñïäïìÞò åóôéÜóôçêå óôá äïêßìéá ðëÞ-

ñïõò äéåßóäõóçò. Ç äçìéïõñãïýìåíç ìéêñïäïìÞ åîáñôÜôáé

áðü ôï ñõèìü øýîçò êáé êáôÜ óõíÝðåéá áðü ôï ðïóü åéóñïÞò

èåñìüôçôáò. Ãéá êáèåìßá áðü ôéò ðñïáíáöåñèåßóåò ðåñéï÷Ýò

ðáñáôçñÞèçêáí ïé áêüëïõèåò ìéêñïäïìÝò:

Óôç ëßìíç óõãêüëëçóçò, ç ìéêñïäïìÞ áðïôåëåßôáé áðü

«Widmanstatten» öåññßôç, âåëïíïåéäÞ öåññßôç êáé ðåñëßôç,

üôáí ôï ðïóü åéóñïÞò èåñìüôçôáò åßíáé ìåôáîý 350-450

Joule/mm (ó÷Þìá 10a). Ç ðáñïõóßá ôùí ðáñáðÜíù ìéêñïäï-

ìþí ïöåßëåôáé óôïõò ÷áìçëïýò ñõèìïýò øýîçò, ïé ïðïßïé ìå

ôç óåéñÜ ôïõò ïöåßëïíôáé óôï õøçëü ðïóü åéóñïÞò èåñìüôç-

ôáò h. ¼ôáí ç ôéìÞ ôïõ h êõìáßíåôáé ìåôáîý 250-350

Joule/mm (÷áìçëüôåñïé ñõèìïß øýîçò), ç äçìéïõñãßá ìðáé-

íßôç åßíáé åìöáíÞò (ó÷Þìá 10b).

Óôç ìåñéêÞ æþíç ôÞîçò, ïé õøçëïß ñõèìïß øýîçò åßíáé ç

êýñéá áéôßá äçìéïõñãßáò ðëÞñïõò ìáñôåíóéôéêÞò äïìÞò

(ó÷Þìá 11). Óôç ÈåñìéêÜ Åðçñåáæüìåíç Æþíç (È.Å.Æ.) ç

ìéêñïäïìÞ áðïôåëåßôáé áðü éóïáîïíéêü öåññßôç êáé ðåñëßôç

(equiaxed ferrite/perlite) óå áíôßèåóç ìå ôç äéáóôñùìáôùìÝíç

(banded) öåññéôïðåñëéôéêÞ äïìÞ ôïõ ìåôÜëëïõ âÜóçò

(ó÷Þìá 12).

¸íá ôõðéêü ðñïößë ìéêñïóêëçñüôçôáò áðåéêïíßæåôáé óôï

ó÷Þìá 13, üðïõ äéá÷ùñßæïíôáé ïé ðñïáíáöåñèåßóåò ðåñéï÷Ýò.

Ãéá ðáñÜäåéãìá, ç õøçëÞ óêëçñüôçôá ôçò ìåñéêÞò æþíçò

ôÞîçò ïöåßëåôáé óôç äçìéïõñãßá ìáñôåíóéôéêÞò äïìÞò, ç

ïðïßá ìå ôç óåéñÜ ôçò åßíáé áðïôÝëåóìá ôùí õøçëþí ñõèìþí

øýîçò. Ç åðßäñáóç ôïõ ñõèìïý øýîçò (ïõóéáóôéêÜ ôïõ

ðïóïý åéóñïÞò èåñìüôçôáò h) óôç ìÝóç ôéìÞ ôçò óêëçñüôç-

ôáò ôçò ëßìíçò óõãêüëëçóçò êáé ôçò ìåñéêÞò æþíçò ôÞîçò

öáßíåôáé óôï ó÷Þìá 14.

Óõíïøßæïíôáò ôá óõìðåñÜóìáôá ôçò ðáñáìåôñéêÞò êáé

ìéêñïóêïðéêÞò áíÜëõóçò, ðáñáôçñåßôáé áýîçóç ôçò äéåßóäõ-

óçò, ôïõ ðëÜôïõò ôçò ëßìíçò óõãêüëëçóçò êáé ôçò ìåñéêÞò

æþíçò ôÞîçò, êáèþò ôï ðïóü åéóñïÞò èåñìüôçôáò áõîÜíåôáé.

Áðü ôçí Üëëç ìåñéÜ, ç äçìéïõñãïýìåíç ìéêñïäïìÞ åîáñôÜ-

ôáé áðïêëåéóôéêÜ áðü ôïõò ñõèìïýò øýîçò. ¼ôáí áõîÜíåôáé

ï ñõèìüò øýîçò, ç ìéêñïäïìÞ ôçò ìåñéêÞò æþíçò ôÞîçò êáé

ôçò È.Å.Æ. áðïôåëåßôáé áðü ëåðôüêïêêï ìáñôåíóßôç êáé éóï-

áîïíéêü öåññßôç. Ìå ìåßùóç ôïõ ñõèìïý øýîçò ï ìáñôåíóß-

ôçò ãßíåôáé ÷ïíäñüêïêêïò êáé ãåíéêüôåñá äçìéïõñãïýíôáé ðéï

ìáëáêÝò äïìÝò. Ãéá ÷áëýâäéíï Ýëáóìá 4mm ç áðáßôçóç ðëÞ-

ñïõò äéåßóäõóçò éêáíïðïéåßôáé, ìüíï üôáí ôï ðïóü åéóñïÞò

èåñìüôçôáò åßíáé ôïõëÜ÷éóôïí 250 Joule/mm. Ãé� áõôü ôï

ðïóü èåñìüôçôáò, ôï ðëÜôïò ôçò ëßìíçò óõãêüëëçóçò åßíáé

3.5mm êáé ôçò È.Å.Æ. ðåñéïñßæåôáé êÜôù áðü 1mm, óå áíôß-

èåóç ìå ôç ìÝèïäï M.I.G., üðïõ ôá áíôßóôïé÷á ìåãÝèç åßíáé

8,5mm êáé 2,5mm.

2.2. Ðñüâëåøç ôùí ãåùìåôñéêþí ÷áñáêôçñéóôéêþí

áðü ôá áíáëõôéêÜ ìïíôÝëá ñïÞò èåñìüôçôáò

×ñçóéìïðïéÞèçêáí äýï ìïíôÝëá ñïÞò èåñìüôçôáò ãéá

ôçí ðñüâëåøç ôçò äéåßóäõóçò êáé ôïõ ðëÜôïõò ôçò ëßìíçò

óõãêüëëçóçò. ¼ôáí ç äéåßóäõóç åßíáé ìç ðëÞñçò, ç ñïÞ èåñ-

ìüôçôáò åßíáé ôñéäéÜóôáôç, åíþ, üôáí ç äéåßóäõóç åßíáé ðëÞ-

ñçò, ç ñïÞ èåñìüôçôáò åßíáé äéäéÜóôáôç (ó÷Þìá 15).

Ôï 1ï ìïíôÝëï ñïÞò èåñìüôçôáò èåùñåß ìïíïäéÜóôáôç

ñïÞ óå çìéÜðåéñï óþìá, üðïõ ç êáôáíïìÞ ôçò èåñìïêñáóßáò

ðåñéãñÜöåôáé áðü ôç ó÷. (4.1). Ôï ìïíôÝëï ëáìâÜíåé õðüøç

ôçí ðéèáíüôçôá åðéöáíåéáêÞò ôÞîçò êáôÜ ôç äéÜñêåéá ôçò

óõãêüëëçóçò ìÝóù ôçò ó÷. (4.3). Ôï 2ï ìïíôÝëï ñïÞò èåñìü-

ôçôáò èåùñåß ôñéäéÜóôáôç ñïÞ óå çìéÜðåéñï óþìá êáé ðåñé-

ãñÜöåôáé áðü ôéò ó÷. (4.4)-(4.6).

Ç äéåßóäõóç ïñßæåôáé ùò ôï âÜèïò z, üðïõ ç èåñìïêñáóßá

ðïõ õðïëïãßæåôáé îåðåñíÜ ôç èåñìïêñáóßá ôÞîçò ôïõ õëéêïý.

Ç óýãêñéóç ìåôáîý ôùí èåùñçôéêþí êáé ôùí ðåéñáìáôéêþí

áðïôåëåóìÜôùí áðåéêïíßæåôáé óôï ó÷Þìá 16, üðïõ ðáñéóôÜ-

íåôáé ç äéåßóäõóç ùò óõíÜñôçóç ôçò åéóñïÞò èåñìüôçôáò. Óå

÷áìçëÝò ôéìÝò åéóñïÞò èåñìüôçôáò ç äéåßóäõóç åßíáé ìç ðëÞ-

ñçò êáé ôï ôñéäéÜóôáôï ìïíôÝëï óõìðßðôåé ðåñéóóüôåñï ìå ôá

ðåéñáìáôéêÜ áðïôåëÝóìáôá. Êáèþò áõîÜíåôáé ç åéóñïÞ èåñ-

ìüôçôáò, ðáñáôçñåßôáé áýîçóç ôçò äéåßóäõóçò êáé êáôÜ

óõíÝðåéá ç ñïÞ èåñìüôçôáò åßíáé äéäéÜóôáôç. Óõíåðþò, ôï

ìïíïäéÜóôáôï ìïíôÝëï óõìöùíåß ðåñéóóüôåñï ìå ôá ðåéñá-

ìáôéêÜ áðïôåëÝóìáôá, üôáí áõîÜíåôáé ç åéóñïÞ èåñìüôçôáò.

Ãéá ôï èåùñçôéêü õðïëïãéóìü ôïõ ðëÜôïõò ôçò ëßìíçò

óõãêüëëçóçò ÷ñçóéìïðïéÞèçêå ôï ôñéäéÜóôáôï ìïíôÝëï êáé

ç óýãêñéóç ìå ôéò ðåéñáìáôéêÝò ìåôñÞóåéò öáßíåôáé óôï

ó÷Þìá 17. ¼ôáí ç ôéìÞ ôçò åéóñïÞò èåñìüôçôáò åßíáé ìåãá-

ëýôåñç áðü 200 Joule/mm, ç óõìöùíßá èåùñçôéêþí êáé ðåé-

ñáìáôéêþí áðïôåëåóìÜôùí åßíáé áñêåôÜ êáëÞ. Áõôü ïöåßëå-

ôáé óôçí ðáñáäï÷Þ åðßëõóçò ôùí åîéóþóåùí ñïÞò èåñìüôç-

ôáò (ãéá ôç äçìéïõñãßá ôïõ ôñéäéÜóôáôïõ ìïíôÝëïõ) üôé ç

ðçãÞ èåñìüôçôáò åßíáé óçìåéáêÞ.

ÔÝëïò, ðñáãìáôïðïéÞèçêå óõãêüëëçóç óõìâïëÞò óå äýï

åëÜóìáôá ðÜ÷ïõò 4mm. Ïé óõíèÞêåò óõãêüëëçóçò êáé ôá

áðïôåëÝóìáôá ôçò äïêéìÞò ôïõ ôåóô åöåëêõóìïý áðåéêïíßæï-


íôáé óôïõò ðßíáêåò 2 êáé 3. Óõãêñßíïíôáò ôçí áíôï÷Þ åöåë-

êõóìïý êáé ôï üñéï äéáññïÞò ìåôáîý ôùí ìåèüäùí laser êáé

M.I.G., ðáñáôçñåßôáé ìéá óçìáíôéêÞ áýîçóç ôùí éäéïôÞôùí

óôç óõãêüëëçóç laser. ÅîÜëëïõ, ïé ìç êáôáóôñïöéêïß Ýëåã-

÷ïé Ýäåéîáí ôçí Ýëëåéøç ðüñùí êáé áôåëåéþí óôç äïìÞ ôïõ

åîåôáæüìåíïõ õëéêïý.


Ìé÷Üëçò Á. Âëá÷ïãéÜííçò,

Ìç÷áíïëüãïò ìç÷áíéêüò âéïìç÷áíßáò, ÐáíåðéóôÞìéï Èåóóáëßáò, Ðåäßïí ¢ñåùò, 383 34 Âüëïò.

¢ííá Ä. ÆåñâÜêç,

Ìåôáëëïõñãüò ìç÷áíéêüò, ÅÂÅÔÁÌ Á.Å, 1ç Âéïìç÷áíéêÞ Ðåñéï÷Þ Âüëïõ, 385 00 Âüëïò.

Ãñ. Í. ×áÀäåìåíüðïõëïò,

ÁíáðëçñùôÞò êáèçãçôÞò, ÔìÞìá Ìç÷áíïëüãùí Ìç÷áíéêþí Âéïìç÷áíßáò, ÐáíåðéóôÞìéï Èåóóáëßáò, Ðåäßïí ¢ñåùò, 383 34 Âüëïò.

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