Post on 05-Apr-2018
8/2/2019 Sd Article Earh
1/7
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j m a t p r o t e c
Effects of feed speed ratio and laser power on engraved
depth and color difference of Moso bamboo lamina
Cheng-Jung Lin a, Yi-Chung Wang b, Lang-Dong Lin c,Chyi-Rong Chiou d, Ya-Nan Wang d, Ming-Jer Tsai d,
a Division of Forest Utilization, Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei 100, Taiwanb Department of Forestry, Chinese Culture University, 55 Hwa-Kang Road, Yang-Ming-Shan, Taipei 11114, Taiwanc Department of Forest Products Science, National Chiayi University, Chiayi, Taiwand
School of Forestry and Resource Conservation, College of Bio-Resource and Agriculture, National Taiwan University,No.1, Sec. 4, Roosevelt Road, Taipei 10608, Taiwan
a r t i c l e i n f o
Article history:
Received 3 April 2007
Received in revised form
15 May 2007
Accepted 15 July 2007
Keywords:Laser engraving
Engraved depth
Color difference
Moso bamboo
a b s t r a c t
In this study, Moso bamboo (Phyllosachys edulis) lamina was engraved using various laser
output power levels in conjunction with various feed speed ratios in order to understand
the effects of feed speed ratio and laser output power on engraved depth and color differ-
ence. The bamboo culm was sliced into strips and then the strips were planed for obtaining
smooth surfaces. Two kinds of Moso bamboo laminae, including without and with steam
treatment were investigated. The results showed that the engraved depth became deeper
for either higher laser power or a lower feed speed ratio. Moreover, the color difference
values increased under a lower feed speed ratio and higher power, and resulted in a brown-ish color in the engraved zone. The average engraved depth and color difference values
were 0.690.86mm and 46.951.9pixels by different engraving parameters, respectively. The
engraved depth and color difference values could be predicted and estimated by regression
analyses. Because of various desired engraving depths and color differences of product, we
suggested that the fitting both lasers speed and power is important for valuable engraving
and cost effective.
2007 Elsevier B.V. All rights reserved.
1. Introduction
In addition to plantation wood, bamboo is also an impor-
tant material due to its fast growth and a shortage of
wood supplies in Taiwan. Moso bamboo (Phyllostachys edulis)
is a multipurpose species grown in Taiwan for fuel wood,
food (bamboo shoot), construction materials, handicrafts,
mat boards, pressboards, and several other uses. In order to
develop an innovative processing system which significantly
increase the value of the utilization of bamboo, manufactur-
ers have engaged in sequential studies on Moso bamboo, in an
Corresponding author. Tel.: +886 2 33664641; fax: +886 2 23686335.E-mail addresses: d88625002@yahoo.com.tw (C.-J. Lin), tmj@ntu.edu.tw (M.-J. Tsai).
attempt to utilize it as stock for quality products or valuable
handcrafts. For example, laser engraving has gained increas-
ing interest in the bamboo handcraft industry and is well
suited for high-volume automated manufacturing owing to
the high processing speed, low waste, precision of operation,
and high quality of engraved products.
Barnekov et al. (1986, 1989) and Yilbas (2001) indicated
that in the laser cutting process, the process parameters can
be adjusted and tuned to achieve the quality of cut desired.
However, if a different workpiece material is used for cut-
ting,all of theseparameters may require re-adjustment, which
0924-0136/$ see front matter 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2007.07.020
mailto:d88625002@yahoo.com.twmailto:tmj@ntu.edu.twhttp://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020mailto:tmj@ntu.edu.twmailto:d88625002@yahoo.com.tw8/2/2019 Sd Article Earh
2/7
420 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425
consumes a considerable amount of time and effort. These
parameters include the laser power, energy coupling factor,
andcuttingspeed. Black(1998) reported thatthe laser machin-
ing of any material is a complex process involving many
different parameters, all of which need to work is concerned
to produce a qualitymachiningoperation.Straight-line testing
was used to evaluate the laser parameters for acceptable full-
through cutting. This test combines the examination of twoseparate parameters in one test. Laser beam power (W) and
cuttingspeed (mm/min) are the most important laser parame-
ters, as they dictatethe amount of energy input perunit length
of cut. Therefore, they were paired for the test runs.
However, the applicability of laser engraving for creating
valuable and quality wood materials has been investigated
(Su et al., 2005; Wang et al., 2005). No report has been pub-
lished that details the effects of feed speed ratio (%) and laser
power (W)on the engraving depth andcolor difference of Moso
bamboo engraved by laser machining. Therefore, it is impor-
tant to develop such information to understand the effect of
the two parameters on the engraved results of bamboo when
estimating engraving performance using lasers.In the light of the above reasons, the present study
was carried out to investigate the effect of engraving
speed ratio and laser power (two important parameters)
on the engraved depth and color difference. Furthermore,
mathematical models based on the two parameters were
employed to formulate relationships between the engraved
depth and color difference. Thus, the process parameters
(feed speed ratio and laser power) can be adjusted and
tuned to achieve the quality (engraved depth and color
difference) of engraving desired. The results can provide infor-
mation for estimating utilization of Moso bamboo in laser
engraving.
2. Materials and methods
2.1. Preparation of test samples
Moso bamboo culm was sliced into strips and then the
strips were planed for obtaining smooth surfaces. Two dif-
ferent bamboo laminae, including internode material without
steam treatment (laminae N) and internode material with
steam treatment (laminae S) were selected. The bamboo
laminae were boiled in a solution (H2O2, 100 C, 68h) to
reduce the starch and sugar contents that would otherwise
attract termites or beetles, and then half the laminae (lam-inae S) were steamed (carbonized) under heat and pressure
(3.5kg/cm2, 145 C, 90 min) to darken the color. Twenty lami-
nae were prepared from each type of material for each set of
experiments.
2.2. Experimental materials
Two kinds of bamboo laminae, including laminae N and
laminae S were investigated. The size of each specimen
of bamboo lamina was 200 (longitudinal) 25 (tangen-
tial) 7.5 mm (radial). Specimens were conditioned in a
controlled-environment room at 20 C and 65% relative
humidity (moisture content of 12%).
The density value of lamina was calculated from the fol-
lowing formula:
=W
V(1)
where (g/cm3
) is the density, V (cm3
) the volume, and W (g)is the weight of lamina at moisture content of 12%.
2.3. Laser engraving method
A nominal 100-W EPILOG, a commercially designed carbon-
dioxide laser coupled to a precision computer-controlled XY
table, was used in the study. The laser engraving tests were
conducted for two kinds of bamboo specimens, using a laser
machine (Epilog Radius Model 4000, Denver, CO, USA). The
standardof thelaser focusinglens was 2 in.(5.1 cm). The scan-
ning model factor was used to set the laser engraving (in the
raster mode). The scanning resolution of the operation soft-
ware was 600 dpi (dots per inch).Image to engraving in following processes: (1) start by con-
necting laser system to computer, (2) import the engraving
image into CorelDRAW software, (3) convert the image to
grayscale, (4) configure the lasers speed and power, and then
(5) send the print job to the laser system for engraving. Two
factors (speed and power) were considered in this practical
experiment: (1) nominal engraving speed ratios (S) (set 10%
[780mm/min], 20% [1560mm/min], 30% [2340 mm/min], 40%
[3120mm/min], 50% [3900mm/min], 60% [4680mm/min], 70%
[5460mm/min], 80% [6240mm/min], 90% [7020mm/min], and
100 %, with the fastest feed speed at 7800 mm/min); (2) laser
output power (P) (set10,20,30, 40, 50, 60, 70, 80, 90, and 100 W).
Otherlaser-engraving factors were held constant at the default
settings.
The XY table was computer-programmed to engrave an
8-mm2 area on the surface of the specimens. The engrav-
ing positions and sequences on the surface of the specimens
are shown in Fig. 1. The engraving feed speed ratio and laser
power (S P) were paired for the test runs. The same S P
treatments were repeated 20 times. Therefore, the data set
consisted of 20 replicates 10 feed speed ratios 10 laser
power levels 2 kinds of bamboo specimens. In total, 4000
engraved areas were investigated for engraved depth and color
difference.
Afterengraving, the averageengraved depthof the different
treatments (S P) was measured in specimens with a caliper
(with an accuracy of 0.001 mm). The engraved color difference
(grayscale intensity differences) was calculated using Eq. (2):
Colordifference = (pixelsbefore engraving)
(pixels after engraving) (2)
Specimens were scanned (using a MICROTEK scanner,
China), and the average number of pixels (ranging from 0
[black] to 255 [white]) was measured using Adobe Photoshop
software (version 7.0.1).
http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.0208/2/2019 Sd Article Earh
3/7
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425 421
2.4. Analysis
An analysis of variance (multifactor ANOVA by the SPSS soft-
ware) was used to determine if the feed speed ratio (%) and
laser power (W) levels significantly affected the engraved
depth and color difference. F values were computed to test
for the significance of different treatments. A stepwise mul-
tiple regression was applied to deduce the most appropriate
Fig. 1 Diagram of Moso bamboo specimen with different laser feed speed ratios and output power levels using laser
engraving machining.
8/2/2019 Sd Article Earh
4/7
422 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425
Table 1 Average engraved depth and color difference of Moso bamboo
Specimen Density (g/cm3) Engraved depth (mm) Color difference (no. of pixels)
With steam treatment 0.710 0.855 46.89
Without treatment 0.832 0.689 51.88
Means within each column significantly differ at p < 0.05.
regression equations for engraved depth and color difference
to provide a better understanding of their interrelationships.
3. Results and discussion
3.1. Density
The mean densities () of the internode material with steam
treatment (laminae S) and internode material without steam
treatment (laminae N) are summarized in Table 1.
A statistical t-test indicated that the mean values of spec-
imens S and N significantly differed (p < 0.05). It was found thatthe average values of in the bamboo laminae obtained from
specimens without steam treatment were significantly higher
than those from specimens with steam treatment.
It is speculated that heating the bamboo strips during the
carbonization process may have altered the chemical compo-
nents (heat and pressure). This treatment reduces the starch
and sugar contents of bamboos so that have less mass or den-
sity than those without treatment. Lin et al. (2006) indicated
that the density of bamboo was reduced after carbonizing
treatment.
3.2. Engraved depth
The average engraved depths of specimens S and N were 0.855
and 0.689mm (Table 1) which significantly differed (p < 0.05).
The specimen S had a deeper engraved depth than specimen
N. Wang et al. (2005) and Arai et al. (1976) indicated that there
is a negative relationship between wood densityand engraved
depth. Therefore, our result showed that a deeper engraved
depth in specimens S occurred with engraving owing to the
decrease in bamboo density.
The effects of feed speed ratio, laser power, and feed
speed ratio plus laser power interaction regimens on the
engraved depth were significant by ANOVA. A comparison of
Fig. 2 Average engraved depth with various feed speed
ratios.
Fig. 3 Average engraved depth with various laser power
levels.
the engraved depth for various feed speed ratio and laser
power regimens are plotted in Figs. 2 and 3. As shown in
Fig. 2, the engraved depth values decreased with an increase
in the feed speed ratio. However, the engraved depth values
increased with an increase in laser power (Fig. 3).
The engraved depth under various feed speed ratio plus
laser output power interaction regimens for the two kinds of
Moso bamboo specimens are shown in Figs. 4 and 5. Results
indicated that a lower feed speed ratio and higher laser powerproduced deeperengraved depths than dida higherfeed speed
ratio and lower laser power. Li and Mazumder (1991) and Su et
al. (2005) reported that the engraved depth became deeper for
either higher laser power or lower feed speed ratio. The total
work per unit length was found to have increased either with
an increase in laser output power or with a decrease in feed
Fig. 4 Engraved depth under various feed speed ratios
and laser output power levels for Moso bamboo with steam
treatment.
8/2/2019 Sd Article Earh
5/7
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425 423
Fig. 5 Engraved depth under various feed speed ratios
and laser output power levels for Moso bamboo without
steam treatment.
speed ratio. Therefore, the engraved depth increased with anincrease in the total power, with but a decrease in the feed
speed.
3.3. Color difference
The average color differences of specimens S and N were 46.89
and 51.88pixels (Table 1). Specimen S had a lower color differ-
ence than specimen N. According to the statistical analysis,
significant differences (p < 0.05) existed for the color difference
between specimens S and N. Specimen S was steamed (car-
bonized) under heat and pressure which caused a darkening
of the color. Therefore, our result showed that a lower color
difference in specimen S occurred after engraving owing tothe already darkened color.
The effects of feed speed ratio, laser power, and feed speed
ratio plus laser power interaction regimens on the color dif-
ference were significant by ANOVA. A comparison of the color
difference with various feed speed ratio and laser power regi-
mens are plotted in Figs. 6 and 7. As shown in Fig. 6, the color
difference values decreased with an increase in the feed speed
ratio. However, the color difference values increased with an
increase in laser power (Fig. 7).
Fig. 6 Average color difference with various feed speed
ratios.
Fig. 7 Average color difference with various laser power
levels.
Fig. 8 Color difference under various feed speed ratios
and laser output power levels for Moso bamboo with steam
treatment.
The color difference under various feed speed ratio plus
laser output power interaction regimens for the two kinds of
Moso bamboo specimens are shown in Figs. 8 and 9. Results
indicated that a lower feed speed ratio and higher laser power
produced larger color differences than did a higher feed speed
ratio and lower laser power. Su et al. (2005) reported that color
difference values increased under higher power and a lower
feed rate in wood materials. Li and Mazumder (1991) indicatedthat the process of cutting wood with a laser is always accom-
panied by an exothermic reaction of distillation of the wood
material. Therefore, the color difference values increase with
an increase in the laser output power.
3.4. Relationship between density and engraved depth
The values of engraved depth under different feed speed
ratio plus laser power interaction regimens increased with a
decreasein thebamboodensity, andthe relationships could be
represented by negative linear regression formulas. Relation-
ships between engraved depth and density under feed speed
ratio of 10% plus laser power of 10100W interaction regimens
8/2/2019 Sd Article Earh
6/7
424 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425
Fig. 9 Color difference under various feed speed ratios
and laser output power levels for Moso bamboo without
steam treatment.
had R2 values of 0.440.70; the coefficients of determination
obtained under the other conditions in this study were lower
(R2 = 0.010.50).
Su et al. (2005) indicated that the engraved depth was shal-
lower for higher-specific-gravity materials, because of the high
ratio of wood substance and the accompanying greater ther-
mal conductivity.
3.5. Relationship between engraved depth and color
difference
Values of color difference for all bamboo specimens increased
with an increase in engraved depth under different feed speedratio plus laser power interaction regimens, and the rela-
tionship could be represented by the following second-order
polynomial regression formula:
engraved depth = 0.001colordifference2
0.006 colordifference + 0.12, R2 = 0.75,
F = 6061
3.6. Engraved depth and color difference estimation by
regression analysis
Values of engraved depth increased with an increase in laser
power; however, there was a decrease in the feed speed ratio.
Their relationships could be represented by the following lin-
ear and polynomial regression formulas:
engraved depth = 0.015laser power 0.037, R2 = 0.15,
F = 679.6 and engraveddepth
= 0.208 speedratio + 0.003 speedratio2
1.549 speedratio3 + 4.72, R2 = 0.58,
F = 1846
Moreover, values of color difference increased with an
increase in laser power, but with a decrease in the feed speed
ratio. Their relationships couldbe represented by the following
linear and polynomial regression formulas:
colordifference = 0.59 laserpower + 17.0, R2 = 0.54,
F = 1664
and color difference
= 0.21 speed ratio + 0.012 speed ratio2
+ 114.5, R2 = 0.50, F = 2030.
This suggests that engraved depth and color difference
were greatly affected by the two engraving treatments of
feed speed ratio and laser output power. There were pos-
itive relationships for engraved depth and color difference
with laser power, but negative ones with the feed speed
ratio.
Furthermore, for a better understanding of the relation-
ships between these engraved parameters (feed speed ratio
and laser power) and two engraved performances (depth and
color difference), the resulting data were fitted to curves by
multivariable models. Then, a stepwise regression procedure
was used to acquire the most-suitable multiple regression to
predict various engraveddepths andcolor differences.The fol-
lowing regression equations were obtained using the F-value
test:
engraved depth = 0.540.005 speed ratio+0.006 speed ratio2
0.001 speed ratio3 + 0.0015 laser power,
R2 = 0.73, = 2648
and
color difference = 7.21 0.712speed ratio+0.012 speed ratio2
+ 0.59 laser power, R2 = 0.80, F = 5258
Some causes for thevariation in resultsmay have been due
to radial variation, anatomic characteristics (vascular bun-
dles), and steam treatment. Lin et al. (2006) indicated that
the bamboo cavity layer-to-bamboo skin radial variation pat-
terns of density (profiled in the radial direction) increase from
the inner bamboo cavity layer outward to the outer bam-
boo skin. Moreover, the tissue structure of bamboo differs
from that of wood. For example, vascular bundles of lepto-
morph rhizome species possess a central vascular strand only.
In addition, the properties of bamboo are affected by var-
ious levels of steam processes (carbonizing). Owing to the
above reasons, the engraved depth and color difference val-
ues may have been influenced by the engraving methods
used.
4. Conclusions
The effects of different feed speed ratios and laser output
power levels on the engraved depth and color difference of
Moso bamboo laminae were investigated, with the following
results.
8/2/2019 Sd Article Earh
7/7
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 419425 425
1. The laser engraved depth became deeper for either higher
laser power or a lower feed speed ratio.
2. Color difference values increased under a lower feed speed
ratio and higher power, and resulted in a brownish color in
the engraved zone.
3. Effects of the feed speed ratio by laser power interaction
regimens on the engraved depth and color difference were
significant. Therefore, values of the engraved depth andcolor difference increased with an increase in laser output
power; however, there was a decrease in the feed speed
ratio.
4. The engraved depth and color difference values of Moso
bamboo could be predicted and estimated by regression
analyses. This prediction of two engraving performances
can help laser engraving achieve varied requests and
applied to the fields of decoration and gift industry. We
suggested that the fitting both lasers speed and power is
important for valuable engraving and cost effective that
desired engraved depth and color difference.
Acknowledgement
The authors wish to thank the financial support of the Taiwan
Forestry Research Institute.
r e f e r e n c e s
Arai, T., Shimakawa, H., Hayashi, D., 1976. Study on lasermachining of woodeffect of laser parameters onmechinability. Wood Ind. 31, 338342.
Barnekov, V.G., McMillin, C.W., Huber, H.A., 1986. Factors
influencing laser cutting of wood. For. Prod. J. 36, 5558.Barnekov, V.G., Huber, H.A., McMillin, C.W., 1989. Laser machiningwood composites. For. Prod. J. 39, 7678.
Black, I., 1998. Laser cutting decorative glass, ceramic tile. Am.Ceram. Soc. Bull., Acad. Res. Library 77, 5357.
Li, L., Mazumder, J., 1991. A study of the mechanism of lasercutting of wood. For. Prod. J. 41, 5359.
Lin, C.J., Tsai, M.J., Wang, S.Y., 2006. Nondestructive evaluationtechniques for assessing dynamic modulus of elasticity ofMoso bamboo (Phyllosachys edulis) lamina. J. Wood Sci. 52,342347.
Su, W.C., Tsai, M.H., Yang, C.M., Wang, Y., 2005. Factors affectingthe characteristics of wood engraved by laser. Taiwan For.Prod. Ind. 24, 4555.
Wang, Y.S., Lin, Y.J., Lee, M.C., 2005. Test of treatments of a
laser-engraving technique on native woods of Taiwan. TaiwanJ. For. Sci. 18, 401408.Yilbas, B.S., 2001. Effect of process parameters on the kerf width
during the laser cutting process. Proceedings of the Institutionof Mechanical Engineers. ProQuest Sci. J. 215, 13571365.