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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: [email protected] (C.-J. Lin), [email protected] (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:[email protected]:[email protected]://dx.doi.org/10.1016/j.jmatprotec.2007.07.020http://dx.doi.org/10.1016/j.jmatprotec.2007.07.020mailto:[email protected]:[email protected]


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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.2007.07.020


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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.


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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.


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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


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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.


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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.

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