Effect of Solid-State Laser Parameters on the Surface’s Topography Formation During Texturization of Hard Metal Cutting Tools

W2014084724 · 수집 2026-10-04 18:12:19

T10732 Laser Material Processing Techniques

CoT 라벨링

라벨링 전

PDF 파일

자동 다운로드한 PDF PDF 보기

기본 정보

DOI 제목 발행년도 저널 URL 페이지 열기 PDF URL PDF 열기 발행기관 피인용수 라이선스

추가 정보 초록 본문

doi: 10.5028/jatm.v7i1.411

Effect of Solid-State Laser Parameters on the Surface’s Topography Formation during Texturization of Hard Metal Cutting Tools

# Effect of Solid-State Laser Parameters on the Surface’s Topography Formation During Texturization of Hard Metal Cutting Tools

Patrícia Helena de Oliveira Teixeira 1,2, Adriano Gonçalves dos Reis 1,2, Andreas Janssen 3

ABSTRACT: The objective of this paper is to analyze
the influence of specific laser system parameters on the
microstructure of the ring formation process on the hard
metal tool’s surface. The parameters analyzed were: working
distance, incident beam power and tool surface treatment,
flank and rake. The microstructures were analyzed with
regard to its diameter and depth by an optical 3-D surface
metrology instrument. The analyses were made by comparing
the ring’s process formation with the dimples’ process
formation, a well-known process called ablation. The results
show that the ring’s diameter is increased by increasing
incident beam power or the distance of the laser beam’s
focus for both surfaces. In addition, increasing the working
distance decreases the ring’s depth for both surfaces.

KEYWORDS: Surface finishing, Pulsed lasers, Ablation,
Microstructure.

INTRODUCTION

One of the biggest concerns of industry is the improvement
of manufacturing efficiency in order to obtain minimization of
production costs, maximization of production rate and maximization
of production accuracy, etc.. In aeronautic industry, these are main
concerns as well, especially with the prediction that the number of
new airplanes will grow by more than 27.000 until 2025 compared
to 2005 (Klocke _et al_ ., 2012). This prediction leads to an economic
pressure on the aviation industry manufacturers, and the search for
optimization in the manufacturing processes becomes necessary.

For the aircraft components construction, several
manufacturing processes are used, and machining stands between
the most applied ones. According to Aurich _et al_ . (2011), during
machining process, high mechanical and thermal loads occur at
the cutting tool, causing tool failure. Due to this, optimization
at the cutting tool represents an advantageous possibility. Cutting
tools have been optimized by improvements of cutting tool
material, coating system and tool macrogeometry. however,
cutting tools with higher qualities regarding material removal
rates, chip removal of hard-to-machine materials and tool life
are each day more requested.

1. Faculdade de Tecnologia de São José dos Campos – São José dos Campos/SP – Brazil 2. Instituto Tecnológico de Aeronáutica – São José dos Campos/SP – Brazil
3. Fraunhofer Institute for Production Technology – Aachen – Germany.

Author for correspondence: Patrícia Helena de Oliveira Teixeira | Faculdade de Tecnologia de São José dos Campos | Avenida Cesare Mansueto Giulio Lattes, s/n, Eugênio
de Melo | CEP: 12.247-014 – São José dos Campos/SP – Brazil | Email: patriciahelena.oliveira@yahoo.com.br

Received: 09/01/2014 | Accepted: 01/07/2015

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

64 Effect of Solid-State Laser Parameters on the Surface’s Topography Formation during Texturization of Hard Metal Cutting Tools

LASER-BASED CUTTING TOOL
PRODUCTION

Looking on technical and mechanical assemblies, contact
surfaces mainly determine the performance of systems in
terms of being the interfaces where energy is transferred,
converted and dissipated. The preparation of cutting tools
using laser radiation is a useful improvement compared to
the use of conventional techniques for optimization of these
surfaces. Laser processing is a very powerful technique for
manufacturing modification of defined cutting tool geometries.
It is a non-contacting, wear free technique and not only offers
highest flexibility due to the fact that the beam can be moved
very fast by optical devices, but also provides excellent control
of shape and size of microstructures, and, furthermore, a
process relatively clean to the environment (Etsion, 2004).

According to Aurich _et al_ . (2011), certain morphology
modifications of contacted surfaces on cutting tools can
improve tool performance. The so called laser-manufactured
“micro-dimples” are microstructures already analyzed in
recent research (Scaraggi _et al._, 2013; Kim _et al._, 2012). The
fundamental formation process is the well-known process
of laser ablation, which forms single ablation cavities by
single laser pulses or complex superposition of many pulses.

According to Meijer _et al._ (2002), the term “ablation”
relates to the effect of vaporizing irradiated material by
incident laser beam. According to Poprawe (2004), laser
radiation is used as a working tool to structure matter by
ablation, defining the lateral precision. For this reason, laser
radiation is projected by objectives onto the surface, thereby
being formed to a specific spatial intensity distribution.
Ablation is a process strongly dependent of pulse duration
and wavelength, and it can occur by two main principles:
short pulse and ultra-short pulse laser ablation. The type of
ablation process determines the finishing quality of the ring
(Poprawe, 2004). The characteristic of the ablation process

- short or ultra-short laser ablation — is determined by
the pulse duration, as shown in Fig. 1.

When the pulse duration is longer than 1 nanosecond
(1 ns = 10 -9 s), the process is called short pulse laser ablation
and its major characteristic is the significant amount of material
being removed from the irradiated area in liquid phase. At
this process, there is a high absorption of laser energy in the
vaporized material along the duration of one pulse. When
the pulse duration is smaller than 1 ns, the heating mostly takes

place after the period of time of pulse duration and the process
is called ultra-short pulsed laser. In opposite to pure ablation
process, the formation process of rings is still not widely studied.
During the rings’ formation, there is just a slightly melting of
surface material and very few of it is evaporated. According
to Cabeza _et al._ (2012), the morphology at the surface can be
characterized as solidified melted zone combining fine grain
appearance and waves in the radial direction.

Janssen (2012) introduced the possible benefits of
such microstructures manufactured by laser ablation on
highly stressed parts. Based on this, in the present context,
the functionalizing aims of three technological benefits
for the cutting process are:

• An optimized surface topography enables the reduction
of friction and cutting forces in the regime of direct
tool-work piece contact.

• The lubrication shall be improved, leading then, to a
reduction of tool’s wear and hence to increased tool’s
life time. Alternatively higher cutting velocities can be
applied without decreased life time.

• For several applications, it can be assumed that the
current laser process allows supplying a higher surface
quality on the treated work piece and thus increases
an qualitative process output.
These benefits can be achieved optimizing tool surface by
the combination of two phenomena: formation of a beneficial
topography and formation of a new material microstructure
in a surface near a layer of several hundred nanometers. The
target surfaces are the flank and rake surface of cutting tools.

The target surface’s texture in the present work is called
“rings structure”. Figure 2 shows an example of both structures,

Melt
ejection

SP laser
ablation

USP laser
ablation

Absorption

Laser beam

Absorption

Laser beam

Heat
conduction Melting Evaporation

2 3 4 5

Isothermal

lines Melt Melt Melt

Vapor Vapor Vapor

Work piece lines

Super fast heating

Evaporation

Vapor

1 2

Work piece

Figure 1. Physical mechanisms in SP and USP laser ablation
(Janssen, 2012).

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

100 μm

50 μm

(a) (b)

Figure 2. (a) regular dimples, distributed on the surface, and
(b) textured composed of overlapping dimples, completely
covering the surface (Klocke and Schmitt, 2012).

dimples and rings. The difference between both microstructure
is that, unlike dimples, which allow some parts of the original
tool material to be in contact with the workpiece, in the ring’s
microstructure, the tool surface in contact with the workpiece
is completely modified by laser texturing. The present work
aimed analyzing the formation process of ring’s microstructure
subjected to the main process parameters.

Due to positive results considering tool life, high material
removal rates etc., obtained in previous works, the laser
texturing process becomes an important tool in the cutting
tool preparation field. Research about the laser functions and
operation methods is necessary in order to define a behavior
profile of laser parameters in obtaining textured surfaces,
especially when these textured surfaces are now starting to be
used, as for the case of ring’s structures.

METHODOLOGY – STUDY ON RING’S
FORMATION

The work was performed at the Fraunhofer Institute for
Production Technology (IPT), a research laboratory, localized
in the city of Aachen, Germany. For texturing experiments, a
custom-designed laser structuring machine has been utilized,
which was installed within former research projects.

EXPERIMENTAL SETUP

Based on industrial as well as research demands, the machine
has been designed based on a 5-axis milling machine, which
was adapted by implementation of an entire nanosecond laser
ablation system including laser source, transportation fiber and

Teixeira, P.H.O., Reis, A.G. and Janssen, A.
65

laser scanner. With this machine, a real 3-D laser structuring process
is possible by means of using 8 axes (5 machine, 3 optical, 1 virtual).

The laser source used was the Ytterbium pulsed fiber
laser YLPM-1-A4-20-20, from IPG Laser. Regarding to its
configurations, the laser presents an extended pulse repetition
rate from 1.6 to 1,000 kHz, selectable pulse durations (4, 8, 14,
20, 30, 50, 100 and 200 ns) and maximum peak power of 15 kW.
The tool material used was cemented carbide from the group
K (red), a conventional tungsten carbide grade. The material
was chosen by the fact that the cemented carbide is one of the
most utilized cutting tool materials today and the group derived
from tungsten carbide is most readily employed.

The tool utilized was manufactured by SECO, from the model
TNMA160404F, 410, 5µ. It was specially developed for specific
applications in Fraunhofer IPT. It presents the flank surface specially
treated but the rake surface is free of any surface treatment, which
means the laser hits a hard metal WC-Co surface.

EXPERIMENTAL APPROACH

It has to be considered that the formation of the desired rings
is based on a reduced ablation process. The process parameters
are selected for causing a slight melt formation on the surface
and subsequent evaporation of a very small amount of heated
material. In regular laser ablation, this amount is decreased
to the achievable maximum, since it enables high material
removal and thus ablation rate. Here, the evaporation is only
utilized to evolve a back pressure on the molten material. The
molten layer, however, is only several hundred nanometers in
thickness, thus the re-solidification takes place very fast, leading
to the formation of rings in terms of “frozen liquid structures”.
For a better understanding, it can be imagined a stone being
thrown in the water, and then it immediately solidifies in the
first ring’s formation.

Among the existing process parameters, which define
a laser process, this work focused on the influence of two
main process parameters: laser power and working distance.
These process parameters control the process. However, they
are no real process quantities. In the following, the meaning
of these two parameters is described.

The laser power PL describes the average laser radiation energy
emitted by the laser source per time. Pulsed laser emits pulses
with single durations much smaller than 1 s. In this case, the size
of average output power of the laser is sometimes misleading,
since it includes the time between the pulses. In the process of
SP and USP laser processing, the pulse pause, which separates

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

66 Effect of Solid-State Laser Parameters on the Surface’s Topography Formation during Texturization of Hard Metal Cutting Tools

each pulse from the following one is commonly several thousand
times higher than the pulse duration. Thus, the average power PL
can be several ten Watts only, while the pulse peak power PLM,
which is the absolute power within the pulse duration, can reach
many thousand Watts.

Øf

_ZW_

To meet this fact, it is common in the field of SP and USP
laser ablation processing to give not the laser output power
but the intensity I or the fluency F, while the intensity gives the
energy coupled into a unit area per time (Eq. 1):

_I_ =

_Ep_

_A . tL_

(1)

where _EP_ is the pulse energy; A is the focal spot area and
_tL_ is the pulse duration.

The fluency gives the energy coupled into a unit area without
time information, according to Eq. 2.

_F_ =

_Ep_

_A_

(2)

This is more common in USP laser processing, where effects
can be interpreted independently from the pulse duration. In
the project around this work, a laser has been utilized not only
in the SP regime but it is additionally capable of emitting pulses
of variable pulse duration. The pulses can be selected between
4 and 200 ns. Based on preliminary investigations, the pulse
duration was kept constant at 100 ns.

In the present work’s evaluations, the parameter PL is given. So,
the variables _A_ and _EP_ could be varied independently.

The working distance is the distance between focusing lens
and work piece. To understand the meaning, Fig. 3 shows the
beam propagation of a laser beam. By varying the working
distance _zW_, the spot diameter can be adjusted, offering the
possibility to control the focal spot size. This is limited due
to the laser beam’s propagation profile, which is the intensity
distribution within a fixed z-plane.

Having these two control parameters, laser power and
working distance, one is able to influence the ring formation in
terms of varying the irradiated and the impinged energy per area.
The main characteristics which are evaluated concerning the
ring’s formation are their diameter and depth. The arrangement
of rings in a pattern can be easily done by adapting the program
which controls the tool path for the laser scanner mirrors and
thus is not investigated in this work.

Resulting ring diameter Øf
f: focal d istance.

Figure 3. Beam propagation and spot size variation
(Janssen, 2012).

Because the rake and the flank surfaces passed by different
treatments, each surface has, therefore, different properties. For
this reason, both were laser-treated and the laser parameters’
influence was also investigated under the circumstances of the
two material differences.

The surface measurements — diameter and depth — of the
structured tool were made by the surface measurement device
Alicona Infinite Focus Real 3-D — an optical 3-D surface metrology
instrument. It automatically measures the complete structure of
a surface (form, roughness and contour, for example).

For the tests, 20 different laser parameter combinations
were defined, as shown in Table 1, in order to achieve different
diameters and depth in the rings’ structure.

RESULTS AND DISCUSSION
DIAMETER ANALYSIS

The first results were obtained by varying the power
percentage. The working distance was kept in -0.8 mm. The
graph from Fig. 4 shows the diameter’s behavior through
the variation of the power percentage. The increment in
diameter presents a tendency of growth when the incident
beam power is increased. In the flank surface, which
received the special surface treatment, the increment in the
diameter is constant and it occurs in a smoother behavior.
On the other hand, for the rake surface, where there is no
treatment, the increasing in the diameter occurs through
an irregular manner.

In the second analysis, the power was kept constant at
100%, while the working distance was varied. The graph from
Fig. 5 shows a comparison of the diameter’s behavior between
the two surfaces tested.

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

Table 1. Laser parameter variation.

Working distance
Parameter Power (%) Tool surface

(mm)

1 -0.4 100 Rake
2 -0.7 60 Rake
3 -0.7 80 Rake
4 -0.7 100 Rake
5 -0.8 70 Rake
6 -0.8 80 Rake
7 -0.8 90 Rake
8 -0.8 100 Rake
9 -0.8 50 Rake
10 -0.8 60 Rake
11 -0.4 100 Flank
12 -0.7 60 Flank
13 -0.7 80 Flank
14 -0.7 100 Flank
15 -0.8 70 Flank
16 -0.8 80 Flank
17 -0.8 90 Flank
18 -0.8 100 Flank
19 -0.8 50 Flank
20 -0.8 60 Flank

Teixeira, P.H.O., Reis, A.G. and Janssen, A.
67

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

Working distance (mm)
Flank surface Rake surface

(a)

20
-0.9 -0.8 -0.7 -0.6 -0.5 -0.4

Distance of the focus beam (mm)

Flank surface Rake surface

(b)

Figure 5. Diameter’s behavior through working distance variation.

50 60 70 80 90 100

Power (%)

Flank surface Rake surface

60%

90%

70%

100%

50%

80%

Figure 4. Diameter’s behavior through power percentage variation.

50μm

Figure 6. Images of ring’s texture for different power
Focus position is one of the most critical process parameters percentage values on flank tool surface.
and directly affects the remaining geometry after material
removal (Bordatchev and Nikumb, 2006). in the diameter’s shape. In both surfaces, it is possible to

On both tool surfaces, the decrease in laser focus distance
caused an increase in the spot’s diameter, which was the
result expected according to the situation presented in Fig. 3.

Figures 6 and 7 show the result of the laser surface treatment
on both tool surfaces.

Althought increasing the power increases the diameter’s
values, it also causes other effects on the rings, as it can be
seen in Figs. 6 and 7. The images show that the tests where
the power percentage was higher presented less precision

in the diameter’s shape. In both surfaces, it is possible to
notice that the laser ring’s edges become less defined as the
power grows.

This phenomenon can be explained by the texturing laser
mechanism. Since the utilzed laser pulses where set to 100 ns
in duration, the laser matter interaction time is long enough to
enable a large amount of material being melted whithin the pulse
duration. Evaporating material evolves a huge back pressure on
the underlying material, which, in this case, is in melted state and
thus can be expelled to the outer region of the irradiation zone.

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

68 Effect of Solid-State Laser Parameters on the Surface’s Topography Formation during Texturization of Hard Metal Cutting Tools

3.5

3.0

40 50 60 70 80 90 100

Power (%)
Flank surface Rake surface

50%

80%

60%

90%

70%

100%

2.5

2.0

1.5

50μm

Figure 7. Images of ring’s texture for different power
percentage values on rank tool surface.

DEPTH ANALYSIS

The second microstructure parameter analyzed was the
depth of the rings. For this analysis, the same variation of laser
parameters used for diameter’s analysis was used.

Figure 8 shows the dependency of the resulting ring’s depth
on laser’s power. The working distance was kept constant at
0.8 mm. Figure 8 also shows that, for the flank surface, there
is a slight decrease in depth when the power increases. It is
also possible to see, for the rake surface, that the depth slightly
increases as well, when the power percentage increases.

In previous researches, Dumitru _et al._ (2004) presented a
study where one could observe that higher incident fluencies
generated larger ablation rate. In other words, it means that with/
when increasing the laser power, the depth will also increase.

However, the same behavior is not seen in either the studied
cases. Changing the power in the rings’ formation does not
present the same correlation as in the pure ablation process,
when analyzing the depth of the microstructure.

Caused by the formation principle, described before, the
resulting surface after the meltiwng is not flat, but with peaks
and valleys, created by the solidification of the thermally driven
motion of molten material. This surface characteristic makes it
difficult to define a right spot to measure the depth. In addition,
the depth profile of the rings is just slightly above the order
of the original surface’s roughness, which also complicates the
depth’s determination.

For the second analysis of the microstructure’s depth, the
power was kept constant at 100%, while the working distance was
varied. The graph from Fig. 9 shows a comparison of the depth
behavior between the two tested surfaces. In the rake surface,
it is seen that when increasing the working distance, the depth

Figure 8. Graph of depth’s behavior through power variation
on the flank and rake tool surfaces.

3.5

3.0

2.5

2.0

1.5
-0.9 -0.7 -0.5 -0.3
Working distance (mm)
Flank surface Rake surface

Figure 9. Ablated depth for different fluencies.

also decreases. In the flank surface, however, this behavior is
not constant, although, in general, there is the decrease of the
depth with the increase of the working distance.

It is known that, when the laser beam operates in its exact
focus, the incident intensity (and also fluency) in the irradiated
surface’s area is maximal. For a pure ablation processes, the
bigger the incident intensity, the bigger is the ablation rate
during the process, which leads to a bigger depth. However,
the intensity hitting the surface is decreased when the laser
beam works out of its focus. Thus, the manufacturing of the
ring’s texture needs to be conducted in a defocused range in
order to find the optimum intensity. The latter is found when
the amount of evaporated material is just sufficient to force the
molten material to form a ring exhibiting the desired shape.

CONCLUSION

Based on this investigation, the following conclusions
could be drawn:

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

• Increasing the laser power or the distance of the laser
beam focus from the surface led to an increase in the
rings’ diameter on the flank and rake surface due to
enhanced thermal affection of the surface’s material.
These results are in agreement with the results for the
laser ablation process.

• The variation in the incident power beam generated
different results in the microstructure’s depth of each
tested surface. This difference was explained by the
process of ring formation and by the superficial melting
in the surface’s material caused by the laser. The behavior
of the ring’s structural formation is not the same as the
phenomenon of ablation.

• The variation in the working distance caused the same
result in depth of both studied surfaces. Increasing the

REFERENCES

Aurich, J.C., Zimmermann, M. and Leitz, L., 2011, “The Preparation
of Cutting Edges Using a Marking Laser”, Production Engineer, Vol. 5,
No.1, pp. 17-24. doi: 10.1007/s11740-010-0275-9

Bordatchev, E. and Nikumb, S.K., 2006, “Effect of Focus Position on
Informational Properties of Acoustic Emission Generated by LaserMaterial Interactions”, Applied Surface Science, Vol. 253, No. 3, pp.
1122-1129. doi: 10.1016/j.apsusc.2006.01.047

Cabeza, M., Castro, G., Merino, P., Pena, G. and Román, M., 2012, “Laser
Surface Melting: a Suitable Technique to Repair Damaged Surfaces Made
in 14 Ni (200 grade) Maraging Steel”, Surface and Coatings Technology,
Vol. 212, pp. 159-168. doi:10.1016/j.surfcoat.2012.09.039

Dumitru, G., Romano, V., Weber, H.P., Gerbig, Y., Haefke, H., Bruneau,
S., Hermann, J. and Sentis, M., 2004, “Femtosecond Laser Ablation
of Cemented Cabides: Properties and Tribological Applications”,
Applied Physics A – Materials Science & Processing, Vol. 79, No. 3,
pp. 629-632. doi: 10.1007/s00339-004-2675-1

Etsion, I., 2004, “Improving Tribological Performance of Mechanical
Components by Laser Surface Texturing”, Tribology Letters, Vol. 17,
No. 4, pp. 733-737. doi: 10.1007/s11249-004-8081-1

Janssen, A., 2012, “Laserstrukturieren senkt Reibung hochbelasteter
Serienteile”, Maschinenmarkt, Vol. 11.

Kim, B.S., Chung, W.Y., Rhee, M. and Lee, S., 2012, “Studies on
the Application of Laser Surface Texturing to Improve the Tribological
Performance of AlCrSiN - Coated Surfaces”, Metals and Materials

Teixeira, P.H.O., Reis, A.G. and Janssen, A.
69

working distance caused the decrease on the ring’s
depth, which corresponds to the results of the laser
ablation process.
Further studies are required to evaluate the tribological
performance of such ring’s textures on the desired application.

ACKNOWLEDGMENTS

This work was supported by the Deutsche Forschungsgemeinschaft (German Research Foundation) and Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES),
within the research project “Surface conditioning and texturing
of cutting tools edges for the optimization of manufacturing
processes - ConTexTool”.

International, Vol. 18, No. 6, pp. 1023-1027. doi: 10.1007/

s12540-012-0483-2

Klocke, F., Gierlings, S., Adams, O., Aerbach, T., Kamps, S., Veselovac,

D., Eckstein, M., Kirchheim, A., Blattner, M., Thiel, R. and Kohler,

D., 2012, “New Concepts of force measurement systems for specific

machining processes in aeronautic industry”, Proceedings of the 5th

Conference on High Performance Cutting.

Klocke, F. and Schmitt, R., 2012, “Surface conditioning and texturing of

cutting tools for the optmization of machining processes”. Proceedings

of the 3rd International Meeting of Brazilian-German Collaborative

Research Initiative on Production (BRAGECRIM), Aachen, Germany.

Meijer, J., Du, K., Gillner, A., Hoffmannc, D., Kovalenkod, V.S., Masuzawae,

T., Ostendorfc, A., Poprawec, R. and Schulzc, W., 2002, “Laser Machining

by Short and Ultrashort Pulses, State of Art and New Opportunities in the

Age of the Photons”, CIRP Annals - Manufacturing Technology, Vol. 51, No.

2, pp. 531-550. doi:10.1016/S0007-8506(07)61699-0

Poprawe, R., 2004, “Lasertechnik für die Fertigung”, Springer,

Heidelberg, Germany, 526p.

Scaraggi, M., Mezzapesa, F.P., Carbone, G., Ancona, A. and Tricarico,

L., 2013, “Friction Properties of Lubricated Laser-Microtextured
Surfaces: An Experimental Study from Boundary- to Hydrodynamic
Lubrication”, Tribology Letters, Vol. 49, No. 1, pp. 117-125. doi:

10.1007/s11249-012-0045-2

J. Aerosp. Technol. Manag., São José dos Campos, Vol.7, N o 1, pp.63-69, Jan.-Mar., 2015

본문 출처 PDF: PDF 보기 · 다른 PDF는 위 [PDF 업로드]로 올릴 수 있습니다.

활용가능성

이력 0건

아직 편집 이력이 없습니다. 저장할 때마다 이전 내용이 여기에 백업됩니다.