Influence of Cutting Tool Wear on the Quality of Poplars Veneers
INFLUENCE OF CUTTING TOOL WEAR ON THE QUALITY
OF POPLAR VENEERS
IRSAN ALIPRAJA
GRADUATE SCHOOL
BOGOR AGRICULTURE UNIVERSITY
BOGOR
2012
ii
DECLARATION
I declare that this thesis titled Influence of Cutting Tool Wear on the
Quality of Poplar Veneers is my own work with the direction of the supervising
committee and has not been submitted in any form for any college except in
ENGREF, France (required by Double Degree Program). Information and quotes
from journals and books have been acknowledge and mentioned in the thesis
where they appear. All complete references are given at the end of the paper.
I understand that my thesis will become part of the collection of Bogor
Agriculture University. My signature below give the copyright of my thesis to
Bogor Agriculture University.
Bogor, October 2012
Irsan Alipraja
NIM E251100081
ABSTRACT
IRSAN ALIPRAJA. Influence of Cutting Tool Wear on the Quality of Poplar
Veneers. Under direction of WAYAN DARMAWAN and REMY MARCHAL.
Poplar wood is well known as a potential raw material for veneer industry.
However, its proportion of tension wood often cause problems on the veneer
quality. Therefore, optimization of machining process is required to improve the
quality of veneer. This study aims to examine the role of machining factors,
especially cutting tool wear on the quality of poplar veneer. The plan of
experiments was done by using the Taguchi method with six machining
parameter. Peeling process was performed by using the micro lathe. The results
showed that cutting tool wear, pressure bar, and temperature of wood give
significance influence on surface roughness while pressure bar and cutting speed
were important factors on lathe check formation.
Keywords: peeling process, cutting tool wear, cutting force, surface roughness,
lathe check
iv
SUMMARY
IRSAN ALIPRAJA. Influence of Cutting Tool Wear on the Quality of Poplar
Veneers. Guide by WAYAN DARMAWAN and REMY MARCHAL.
As a fast growing species, poplar wood (Populus spp) has become potential
raw material for veneer industry, especially in temperate regions such as in
Europe. In France, a total of 1,422,523 m3 timber was harvested in 2008 and
64.3% were used for rotary-cut veneer (lightweight packaging, plywood and
export). Currently, there are more than 140 clone cultivable poplar in Europe that
can make industry has more choice for its raw material. However, due to its
proportion of tension wood, this species often produces poor surface quality. One
way to improve the quality of veneer is by optimization of cutting parameter. The
rate of cutting tool wear is also a factor that must be considered in order to obtain
the best quality of surface. The purpose of this study is to examine the role of
machining factors, especially cutting tool wear, on the quality of veneer product.
Experimental design was conducted using Taguchi method to make the
research more efficient in time and material. Factors control that used in this study
were cutting tool wear, cutting speed, pressure bar, type of bar, cultivar and
temperature of wood. Peeling process was conducted by using microlathe
machine to obtain veneer with thickness of 3 mm. Evaluation of veneer consisted
of cutting force, surface roughness and lathe check. Surface roughness has been
evaluated by using Surfascan SOMICRONIC S-M3 device while lathe checks
have been measured by using SMOF device and its software.
The result from this study showed that cutting tool wear is the factor that
most affect the quality of veneer. In this study, the lowest force on the knife is
obtained at the level of 0 µm cutting tool wear, 0% of pressure bar, cultivar I214
and at room temperature, while 0% of pressure bar, cultivar I214 and with angular
bar sharpened tends to generate optimum force on the bar. The best surface
quality (Ra) is found when peeling wood with 0 µm wear level of the knife, 10%
of pressure bar, cultivar lambro and at room temperature, whereas the optimum of
lathe check was produced by using cutting speed 0.1 m/s with 10% of pressure
bar.
Keywords: poplar, peeling process, cutting tool wear, veneer quality, cutting
force, surface roughness, lathe check
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vi
INFLUENCE OF CUTTING TOOL WEAR ON THE QUALITY
OF POPLAR VENEERS
IRSAN ALIPRAJA
E251100081
Thesis
In partial fulfillment of the requirements for the degree of
Master of Science
At Bogor Agriculture University
GRADUATE SCHOOL
BOGOR AGRICULTURE UNIVERSITY
BOGOR
2012
SHEET APPROVAL
Title
Name
NIM
: Influence of Cutting Tool Wear on the Quality of Poplars Veneers
: Irsan Alipraja
: E251100081
Approved,
Co-Major Professors,
Prof. Dr. Ir. I Wayan Darmawan, M.Sc.
NIP. 19660212 199103 1 002
Prof. Rémy Marchal
Head of the Department of Forest
Product Technology
Dean of the Graduate School
Prof. Dr. Ir. I Wayan Darmawan, M.Sc.
NIP. 19660212 199103 1 002
Dr. Ir. Dahrul Syah, M.Sc.Agr
NIP. 19621026 198803 1 001
Presented : 31 Octobre 2012
Date of graduation : 13 Decembre 2012
viii
FOREWORD
All praise and gratitude to Allah SWT so that the author could finish this
scientific work entitled Influence of Cutting Tool Wear on the Quality of Poplars
Veneers. The results of this study hopefully can contribute and give useful
information in the development of science and technology of wood processing in
particular in veneer manufacturing.
First of all, I would like to convey my gratitude to Ministry of National
Education (DIKNAS) that give the opportunity to continue my study in master
program through the program of double degree Indonesia-France. I would like
also to thank Prof. Dr. Ir. Wayan Darmawan M. Sc. and Prof. Rémy Marchal as
the supervisors who have given a lot of suggestions during the research. High
appreciation for all the teachers, staff and technician LaboBois ENSAM for
excellent reception, warm atmosphere and also for their support during the
research. Thanks also to my father, my mother, my brothers and the whole family,
for all the prayers and love. Finally, I would like to thank all master student of
Forest Product Technology especially to Rentry Augusti Nurbaity, Vera Junita
Sitanggang, Novitri Hastuti, Sonia Somadona and Meylida Nurrachmania for their
desires to share both difficulty and happiness when we lived in France.
The author recognizes that this research is still far from perfect. Therefore,
suggestions and constructive criticism are expected to improve this work.
Bogor, October 2012
Irsan Alipraja
i
TABLE OF CONTENTS
Page
TABLE OF CONTENTS .................................................................................... i
LIST OF TABLES .............................................................................................. ii
LIST OF FIGURES ........................................................................................... iii
LIST OF ANNEXE ............................................................................................. iv
1. INTRODUCTION ........................................................................................... 1
Background ............................................................................................... 1
Formulation ............................................................................................... 2
Objectives .................................................................................................. 2
Benefit ....................................................................................................... 3
Hypotheses ................................................................................................ 3
2. STUDY LITERATURE .................................................................................. 4
Poplar Wood.............................................................................................. 4
Transformation by Peeling Process ........................................................... 5
Quality of Veneer ...................................................................................... 7
3. MATERIALS AND METHODS ................................................................... 9
Taguchi Method ....................................................................................... 9
Cultivar Selection and Preparation of Disk ............................................... 11
Experiments on Microlathe ....................................................................... 12
Evaluation of Veneer................................................................................. 13
Evaluation of Cutting Force.......... .................................................... 13
Evaluation of Veneer Quality.......... .................................................. 14
Lathe Check Measurement ....................................................... 14
Surface Roughness Measurement ............................................. 15
4. RESULTS AND DISCUSSION ..................................................................... 16
Analysis of S/N Ratio (SNR)……………….………………. .................. 16
Cutting Force ……………………………….………. .............................. 17
Surface Roughness .................................................................................... 19
Lathe Check (Depth) ................................................................................. 22
5. CONCLUSION ................................................................................................ 25
REFERENCE ...................................................................................................... 26
APPENDIX .......................................................................................................... 30
ii
LIST OF TABLE
No.
Page
1. Determination levels of control factors ............................................................. 10
2. Experiment matrix ............................................................................................. 11
3. Experimental results for surface roughness, lathe check, and cutting force
with their corresponding SNR .......................................................................... 16
iii
LIST OF FIGURES
No.
Page
1. Poplars and their implementation.........................................................................4
2. Mechanical properties of poplar wood .................................................................5
3. Principe of peeling process ..................................................................................5
4. Cracking formation during the production of veneer with different
pressure level of the bar.......................................................................................8
5. Discs for micro lathe from three types of poplar cultivar .................................11
6. Microlathe ..........................................................................................................12
7. Decompositions of the resulting cutting force Fc ..............................................13
8. Filtering process using Labview software..........................................................14
9. Evaluation of lathe check ...................................................................................14
10. Surfacescan device ...........................................................................................15
11. Surface roughness profile .................................................................................15
12. Chart S/N for cutting force...............................................................................17
13. Cutting force in peeling wood with knots ........................................................19
14. The optimum is minimum S / N graph for surface roughness .........................20
15. Influence cutting tool wear on surface roughness ............................................21
16. The optimum is a minimum S / N graph for cracks .........................................22
17. Lathe check at different level of pressure ........................................................23
iv
LIST OF APPENDIX
No.
Page
1 Matrix experimental L27 ................................................................................. 30
2
Response table for average S/N Ratio for cutting force factors ...................... 31
3
Results of analysis of variance for the efforts ................................................. 32
4
Response table for average S/N Ratio for surface roughness factors .............. 33
5
Results of analysis of variance for roughness ................................................. 34
6
Response table for average S/N Ratio for lathe check factors ........................ 35
7
Results of analysis of variance for cracks ....................................................... 36
8 Average results of cutting force, lathe check, and surface roughness .............. 37
1
INTRODUCTION
Background
Plywood, laminated veneer lumber (LVL) and laminated veneer panels
(LVP) are structural wood products that using veneer as its raw material. The
quality of those products are then could determined from the quality of veneer and
production process. Parameters commonly used to assess the quality of veneer i.e.
lathe check, surface roughness and thickness variation. Research on the effect of
these parameters on the quality of product (such as plywood and LVL) has been
widely done (Neese JL, 1997; DeVallance, 2003; Daoui A et al., 2011; Piirlaid et
al., 2012). Similarly, factors that affect the quality of veneer (Corder SE and
Atherton GH, 1963; Lutz JF et al., 1967; Bakar ES, 2004; Aydin et al., 2006;
Tanritanir E et al. 2006; Dundar et al., 2008a) and methods used to evaluate the
veneer has been widely known (Blomme et al., 2010; Palubicki et al. 2010;
Denaud et al., 2012). However, because of the natures of wood are complex that
often give different responses, performing research on veneer quality is still
interesting to do.
As a fast growing species, poplars has become potential raw material for
veneer industry, especially in temperate regions such as in Europe. In Europe,
total production of poplar wood is approximately 8 million m 3 per year and about
40% of this volume is intended for veneer and plywood industry while 31% is
used for sawmill industry (Nervo et al., 2011). In France, a total of 1,422,523 m3
timber was harvested in 2008 and 64.3% used for rotary-cut veneer (lightweight
packaging, plywood, and export).
Poplar wood have an abundant amount of cultivar. The results of research
conducted by Huda et al (2011) showed that the site and clone have had a
significant influence on all the anatomical, physical and mechanical properties of
poplar wood. This characteristics difference is certainly expected able to expand
the potential of poplar wood as raw material for veneer and plywood industry.
However, due to high proportion of tension wood, this species often produces
poor surface quality (fuzzy grain), thus causing problems in gluing process and
finishing treatment. One of the efforts that often do to overcome these problems is
2
by perform the optimization of machining process. Optimization process in
peeling of wood can be done by changing the cutting parameters such as cutting
speed, bar pressure, cutting temperature or clearance angle.
Knife has an important role in peeling process. Its maintenance costs are
relatively high. The high rate of knife wear can also affect the level of
productivity of veneer. On the other hand, research on the effect of cutting tool
wear in peeling process is very little published. Based on this problem, it takes a
study that observe the contribution of cutting tool wear on the quality of veneer,
especially on poplar wood.
Formulation
Poplar is a fast growing species that has long been used as raw material for
plywood and veneer industry. The main constraint that are frequently encountered
in machining process of poplar wood is the presence of tension wood with various
proportions. The presence of tension wood often causes problems in wood
machining processes primarily related to the quality of resulting veneer surface.
One way to solve these problems is by optimize the conditions or cutting
parameters. Another parameter that also important in this process is the knife.
Knife in peeling process should be as sharp as possible to avoid the adhesion of
tension wood fibers on the surface of the knife. Knife wear can also be an obstacle
to produce high quality of veneer and to reduce energy consumption. Problems to
be addressed in this research is how cutting tool wear influence on the cutting
force that occurs and the quality of veneer surface? and how large the contribution
of cutting tool wear compared with other peeling parameters?
Objectives
The objectives of this research were to examine the role of machining
factors, especially cutting tool wear, on the quality of poplar veneers.
3
Benefit
The study is expected to provide scientific information on the role of
cutting tool wear on cutting force, surface quality and lathe check of veneer as
well as on the characteristics of poplar wood in peeling process.
Hypotheses
Knife wear will increase the cutting force that occurs during peeling
process. In addition, knife wear can reduce the quality of the veneer surface
produced from peeling process and plays an important role in the occurrence of
lathe check.
4
STUDY LITERATURE
Poplar Wood
Poplar, also known as the scientific name Populus spp., is an angiosperms plant
that comes from family Salicaceae. It comes from temperate zones and the northern
hemisphere. This species is classified as a fast-growing species, has homogeneous wood
with a high level of productivity (up to 35-40 m3/ha per year) (O Pichard et al., 1997).
The volumetric composition of poplar wood is compiled by high proportion of fibers
(53-60%), followed by vascular elements (28-34%), medullary ray (11-14%), and a
significant proportion of axial parenchyma (0.1-0.3%) (Panshin and de Zeeuw, 1980 in
Balatinecz DD and DE Kretschmann, 2001). The chemical composition of poplar wood
is dominated by high proportion of polysaccharides (up to 80% holocellulose, which
varies among clones and stations) and low proportion in lignin (about 20%).
Figure 1 Poplars and their implementation (source : http://www.science.gouv.fr)
The hybrid poplar have already produced many species. There are currently at
least 145 registered cultivars and cultivable poplar in Europe. The process of vegetative
propagation is usually very easy, by cuttings and plants capable of producing the same
quality. Poplar wood is generally white, sometimes reddish or pink, easy to be worked
(Figure 1) and can be nailed without splitting (Pichard O et al., 1997).
Poplar wood has an average density of 0,45 (at the level of moisture content
12%) with the shrinking value in tangential section 8,3%, and in the radial 4,8%.
Mechanical properties and durability of poplar wood are generally low and it has good
aptitude for peeling and slicing process (Figure 2). Poplar wood can be used for interior
plywood, packing, match, current furniture, lightweight frame, pulp, fiberboard and
particle board.
5
Poplar is one of three main hardwoods in France after oak and beech. Although
his crops tend to decline (after reaching the maximum yield in 1990), its role in the
timber industry, particularly in peeling process, remains high.
Figure 2 Mechanical properties of poplar wood (source: CIRAD, 2011)
Transformation by Peeling Process
Peeling process (Figure 3) is a primary method of wood processing that
transforms the log into veneer sheets. About 90% production of veneer in the world is
obtained by this process. The principle of this process is the rotation of the logs against
the knife, with the veneer being peeled in a continuous sheet; the length of the knife is
equal to the length of the log.
Horizontal opening
Vertical opening
Cutting direction
B
Pressure
bar
Chuck
Cutting angle
Knife
Figure 3 A. Principe of peeling process (source : Tsoumis, 1991); B. Rotary
machine semi-industry at laboratory ENSAM
6
Veneer peeling lathe (veneer rotary lathe) is equipped with a pressure bar (or
often named nosebar) which is placed ahead of the knife and has equal length. Its role is
to prevent or minimize the appearance of cracks on veneer and also to control the
thickness and smoothness of veneer. The nosebar and knife carriage will then move
slowly towards the log, give the pressure in accordance with a veneer thick. As veneer
comes from the lathe, it is received by a conveyor, reel or table. Nosebar adjustment
must be done every turn of the new knife, knife sharpening, changes thick of veneer
peeled or when peeling different wood species. In addition, it requires a fairly high
accuracy in determining the position and pressure levels of the bar to produce high
quality of veneer. If the pressure bar is too big, it will crush the wood while if it is too
low it will produce a lot of crack on the veneer surface (Forest Product Laboratory,
1962; Tsoumis, 1991; Bakar ES and Marchal R, 2001).
There are mainly two types of pressure bars i.e. fixed pressure bar and roller
pressure bar. The fixed bar is the simplest, cheap and most commonly used. It is
normally used on veneer slicers and also for cutting hardwood on a rotary-lathe. The
fixed bar has generally a bevel angle between 74-78°. Other than fixed bars, roller bar is
one of the bars that often used. Compared to fixed bar, utilization roller bar could
reduce cutting force that occurs. However this type of bar cannot cut veneer of any
thickness like fixed bar. Lutz (1978) states that roller bar with diameter 15.9 mm cannot
be used to cut veneer which is thinner than 1.6 mm.
Knife represents the largest maintenance cost in veneer industry thus required
good knowledge in the use of the knife (grinding and setting) to keep the knife remains
in good conditions. The knife is generally low alloy steel with a low sharpness angle,
between 18 and 23 °. Normally, the smaller the angle, the less the veneer is bent when it
is cut thus produce tighter veneer. Otherwise, the larger the sharpness angle, the stiffer
the knife thus the better the knife edge withstand impact. Grinding process for a small
angle knife must be done more carefully than the knife with larger angle. Veneer knife
should has Rockwell hardness of 56-58 on the C scale for rotary-lathe and 58-60 for
veneer slicers. A Rockwell hardness 60-62 may even be used when cutting low density
wood.
The most common knife thickness is 16 mm (for rotary lathe) and 19 mm (for
slicer). In general, to peel thicker veneer, it should be used the thicker knife while when
7
cutting thin veneer, thinner knife can be used as long as it properly supported (Lutz JF,
1978). The knife working in the manner of penetration, cuts wood and often cause
cracks on veneer product.
Quality of Veneer
Veneer quality is an important parameter that determines the success rate of
plywood or LVL production. It is depend on the quality of raw materials used, skill of
the operator, condition of the lathe and cutting parameters used (FPL, 1962; Bakar ES,
1996). The quality of veneer is generally evaluated based on the variation of thickness,
surface roughness and lathe check (frequency and depth). In addition, radius curl of
veneer is also sometimes used as an indicator to assess veneer quality since the curved
veneer is difficult to be worked than flat veneer. For some uses such as face veneer,
color is also one of parameters that need to be considered (Lutz, 1971; Bakar ES, 1996;
Marchal R, 1996; Wang J et al., 2001; Daoui et al., 2011). A good quality of veneer will
certainly be a uniform in thickness, flat, smooth and slightly cracking.
Roughness can be defined as an irregularity on a periodic basis (other than
defects) on the surface of a material generated by the production process. Surface
roughness plays an important role, especially on bonding quality and finishing
treatments. Control of surface roughness in veneer production is substantial to maintain
adhesive quality between veneer on the plywood/LVL or between veneer and other
wood based panel. The surface quality of veneer which is not good (rough) will
produce a weak bonding and reduces the mechanical properties of composite panels
produced (DeVallance 2003; Unsal et al., 2005; Korkut S M and Akgul, 2007; Dundar
et al., 2008b). Rough surface of veneer can also causes excessive resin use and may lead
resin-bleed through the face veneer. On the face veneer, roughness can be reduced by
sanding process. Nevertheless, the veneer which is too rough requires much more
sanding process than "smooth" veneer, resulting in reduced material thickness.
In general, roughness can be caused by two main factors, which are
characteristics of wood anatomy and the machining process. Roughness caused by
wood anatomy is influenced by several factors, including ring width, difference between
juvenile wood and mature wood, the proportion between earlywood and latewood, knots
and reaction wood while machining factors that affecting surface roughness are knife
angle, pressure bar, temperature of cutting, cutting speed and thickness of veneer
8
(Ayrilmis et al. 2006). Furthermore, Sandak J and Martino (2005) added that wood
porosity and moisture content also gives effect to the formation of surface quality.
Similar with roughness, cracking (lathe check) is also an important criteria and
has long time been used as an indicator of veneer quality (Figure 4). In almost all veneer
manufacturing process, lathe checks are present at different level. These cracks occur
during machining process. Lathe check in veneer showed weak zone and cause
excessive penetration of adhesive.
Figure 4 Cracking formation during the production of veneer with different
pressure level of the bar.
Source: Photo by U.S. Forest Products Laboratory
Typically, lathe check is strongly influenced by the level of pressure and also by
cutting speed and geometry of the knife. Lathe checks frequent but shallow are
preferable to less frequent but deep, especially when the appearance of plywood or LVL
is required as in face veneer.
9
MATERIALS AND METHODS
Location and Period of Research
This research was carried out at Laboratory of Wood (Laboratoire
Bourguignon des Matériaux et Procédés), Ecole Nationale Supérieur d’Arts et
Métiers (ENSAM), Cluny, France. The study lasted for six months, starting from
February 2012 to July 2012.
Tools and Materials
Materials used in this study were three 15-20 year old clones of poplar
wood (I214, Lambro and Lena) in a form of disk with a thickness of 30 mm. Tool
used to produce samples of veneer were Microlathe ENSAM, wood peeling
knives, and nosebar. Peeling knives used were three pieces with different levels of
wear (0 μm, 250 μm, and 500 μm) but has the same sharpness angle (20°). The
knives are low alloy steel with a composition of 0.6% C, 1.8% Si, 0.7% Mn, 0.3%
Cr, 0.5% Mo, 0.2% V with hardness value of 55-56 HRC. Evaluation of veneer
quality was performed by using piezoelectric system installed on the microlathe
and its software developed by ENSAM Lab to scan cutting force; System
Measurement Opening of Fissure (SMOF) devices and its software to measure
lathe check; and Surfascan SOMICRONIC S-M3 with its stylus with a tip radius
of 2 μm to evaluate surface quality.
Some of the other tools that used to support this research including
"storage tubs", infrared gun, ruler, calipers (caliper), grinding machine, planer
machine, band saw and drilling machine. Data processing is performed by using
LABVIEW 2011 software and STATISTICA 2011.
Taguchi Method
In general, the plan of experiments was done by using Taguchi method.
Taguchi method allows to examine many factors with a relatively small number of
experiments. This method is based on a matrix experiment that can easily fix most
problems in terms of industrial design experiments.
10
In Taguchi method, it is necessary to select control factors (Main factors
that will be evaluated on their effects on the results of the experiment) and
variation levels to minimize the sensitivity of the response on the experimental
noise. These factors are cutting tool wear, cutting speed, pressure bar, cultivar,
temperature of the wood, and type of bar (Table 1).
Table 1. Determination levels of control factors
Factor
1
A. Cutting tool wear
0µm
B. Cutting speed
0.1 m/s
C. Pressure bar
0%
D. Cultivar
Lena
E.Temperature of
10°C
wood
F. Type of bar
Angular bar
sharpened
Level
2
250µm
1 m/s
5%
Lambro
20°C
3
500µm
2 m/s
10%
I 214
30°C
Angular bar
sharpened both
sides
Angular round
bar
The experimental matrix chosen is type L27 with 27 rows and 7 columns.
The parameters to be studied are placed in columns. Thus, a total of 27 tests were
performed (Table 2).
Taguchi method approach introduces “signal-to-noise” ratio (S/N ratio) to
study the influence of noise on the variations that occur. Generally, there are three
performance categories in the analysis of the S / N ratio, i.e. optimum is nominal,
optimum is a minimum and optimum is maximum. In this study, to obtain
optimum machining performance, conditions optimum is minimum for surface
roughness, lathe check and cutting force should be taken to achieve the highest
quality veneer. The formula used to calculate SNR in the case where the optimum
is a minimum are:
∑
,
where i is the number of the experiment, j the number of the replicate, n
the number of repetition, and yj is the response value.
11
Table 2. Experiment matrix
Cutting
No
tool wear Pressure
(µm)
bar (%)
1
0
0
2
0
0
3
0
0
4
0
5
5
0
5
6
0
5
7
0
10
8
0
10
9
0
10
10
250
0
11
250
0
12
250
0
13
250
5
14
250
5
15
250
5
16
250
10
17
250
10
18
250
10
19
500
0
20
500
0
21
500
0
22
500
5
23
500
5
24
500
5
25
500
10
26
500
10
27
500
10
Cutting
speed
(m/s)
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
Cultivar
Lena
Lambro
I 214
Lambro
I 214
Lena
I 214
Lena
Lambro
Lambro
I 214
Lena
I 214
Lena
Lambro
Lena
Lambro
I 214
I 214
Lena
Lambro
Lena
Lambro
I 214
Lambro
I 214
Lena
Temperature
of wood (°C)
10
20
30
20
30
10
30
10
20
30
10
20
10
20
30
20
30
10
20
30
10
30
10
20
10
20
30
Type of
bar
1
2
3
3
1
2
2
3
1
2
3
1
1
2
3
3
1
2
3
1
2
2
3
1
1
2
3
Cultivar Selection and Preparation of Disk
Selection of cultivars were performed by considering the quality of veneer
produced by another studies (Master of FAGE, Rentry Nurbaity Augusti).
Eighteen discs were prepared for nine tests from a total 27 tests.
Figure 5 Discs for micro lathe from three types of poplar cultivar
12
Three cultivars selected were I214, Lambro and Lena (Figure 5). Veneer
of good quality is represented by the discs I214 with a diameter of ± 360 mm
while the average quality is represented by Lambro with a diameter of 280 mm
and the poor quality represented by Lena with a diameter of 300 mm.
The preparation of discs was done by bandsaw to get constant disc
thickness of 30 mm. They were then stored in water to prevent fungal attack.
Before peeling process, each sample was placed in three different temperatures for
24 hours depending on research model. Storage temperature used were 6 ° C, 20 °
C (room temperature) and 40 ° C.
Experiments on micro-lathe
The micro-lathe was developed by JeanClaude BUTAUD (Butaud et al. 1995). This
machine is specially developed for research
Nosebar
purpose and it can be used to study the
mechanism complete of peeling process from
Knife
disks samples. Knife and nosebar lies in two
different rings that are connected and form a
System piezoelectric
piezoelectric system and can be moved through
the main "computer".
Figure 6 Microlathe
Micro-lathe ENSAM can peel wood with cutting speeds up to 3m/s, and
clearance angle up to 40°. Sample should be in the form of disks with a thickness
5-30 mm and diameter between 25-500 mm. This machine can produce peeled
veneer with a thickness of 0.1-5 mm.
In this study, each sample was peeled five rounds for each modality and
repeated several times. Peeling process was performed with 3 mm thick veneer
and various machining conditions contained in the experimental design.
The veneer samples obtained were then divided into several parts: the
length of the samples taken for measurements of the roughness (SR) and lathe
check (SMOF) are respectively 5 cm and 45 cm.
13
Evaluation of Veneer
In general, the quality assessment of a peeling process is done by two
approaches: evaluation of cutting forces and evaluation of veneer quality. Cutting
force is closely related to the electrical consumption and cutting tool lifetime,
while veneer quality will affect the quality of product (plywood or LVL). The
higher the cutting force generated, the higher the energy consumption and the
shorter the life of the knife.
Evaluation of Cutting Force
Xc . cos Yc . sin
sin( 2 )
Xc . cos( ) Yc . sin( )
Fd
sin( 2 )
Fc
Fa
X
Xc
Xd
Fd
Y
Barre de pression : Xb, Yb
Yd
O
u
t
i
l
Fa
Xa
Yc
Ya
Placage
Xc,
Yc
Figure 7 Decompositions of the resulting cutting force Fc
( = sharpness angle ; = friction angle of wood/metal)
Cutting force measurement is carried out by using piezoelectric system
on the micro lathe. This system allows to measure the forces received by the knife
(Xc, Yc) and nosebar (Xb, Yb) during peeling process (Figure 7). The profiles of
the efforts are then presented on the screen using software developed by ENSAM
laboratory and filtered by labview software before treated statistically. Filtering
process is performed to obtain the average force from stable zone of cutting force
(Figure 8).
14
Figure 8 Filtering process using Labview software
Evaluation of veneer quality
Lathe check measurement
Veneer lathe check was measured by a specific measurement device and
its associated software (SMOF): this set can measure the frequency and the depth
of the cracking of veneer. The measurement technique is based on the opening of
cracks occurring at the time of passage of veneer through the pulley (Figure 9a).
Concerning the nature of veneer which is very fragile, then the success of
measurement is strongly influenced by the choice of pulley diameter. When
diameter of the pulley is too small, the measurement process will lead to cracking
and increase the depth of fissure thus the measure is not reliable. Otherwise, if
diameter of pulley is too large, veneer cracks can not be opened so it is difficult to
be detected by the camera.
LVDT sensor
a
b
c
Veneer place
Bending pulley
Figure 9 Evaluation of lathe check; (a) Devices of SMOF (b) determining the depth
of lathe check, (c) Recommendations of pulley diameter by Palubicki (2010)
Determination pulley diameter is generally done on an experimental basis.
In this study, the observed thick veneer is 3 mm, so that the diameter of pulley
that used is equal to 65 mm or in accordance with the recommendations of the
research performed by Palubicki et al. (2010) (Figure 9c). Measurement process
15
begins when veneer through LVDT sensor. This sensor will measure the thickness
of veneer. Then the moment veneer passed pulley, lathe check formed on the
loose side will be opened and at the same time the camera which is placed on the
back of device will start scanning the side (thickness) of the veneer. The images
obtained are then analyzed its depth (percentage) manually using software of
SMOF.
Surface Roughness Measurement
Surface roughness of veneer were
measured using conventional method by stylus
(Surfascan SOMICRONIC S-M3). The stylus
sensor used in this study has a tip angle of 90 °
with a tip radius of 2 microns. The selection of
this stylus geometry is designed to minimize
Figure 10 Surfascan device
errors in the profiling of the surface. The length of the test performed (tracing
lenght) is 12.5 mm and stylus speed 1.5 mm/s. The roughness parameters
measured were average roughness (Ra), mean peak-to-valley height (Rz), and
maximum roughness (Rmax). The profile of the surface roughness was filtered
using a cutoff value of 2.5 mm.
Cut off lenght
Average roughness height
Profile height
Profile direction
Devices of stylus
Sampling lenght
Figure 11 Surface roughness profile
16
RESULTS AND DISCUSSION
Analysis of S/N Ratio (SNR)
Table 3 Experimental results for surface roughness, lathe check, and cutting force
with their corresponding SNR
Average
S/N Ratio
Surface
No Roughness
Lathe
Force Yb
Surface
Lathe Check Force Yb
Exp
Check (%)
(daN/m)
Roughness
(%)
(daN/m)
Ra
-35,714
-24,679
1
23,512
61,048
-17,109
-27,446
-35,835
-23,949
2
19,685
61,871
-15,754
-25,929
-35,479
-25,845
3
21,963
59,402
-19,214
-26,834
-27,408
-64,867
4
16,422
23,157
-1745,702
-24,323
-30,429
-58,925
5
21,215
33,223
-875,737
-26,540
-32,360
-61,375
6
18,501
41,495
-1171,410
-25,354
-25,723
-62,594
7
20,346
19,247
-1347,199
-26,180
-28,206
-65,586
8
18,583
25,710
-1886,572
-25,389
-30,997
-64,376
9
13,865
35,270
-1654,943
-22,843
-35,274
-23,918
10
34,712
58,031
-15,687
-30,823
-35,225
-25,274
11
39,891
57,703
-18,347
-32,088
-34,899
-25,129
12
32,492
55,585
-17,946
-30,239
-29,252
-58,903
13
32,710
29,005
-881,130
-30,294
-29,943
-61,162
14
32,350
31,407
-1142,555
-30,199
-32,209
-63,032
15
32,870
40,761
-1408,812
-30,475
-26,804
-64,750
16
24,500
24,648
-1726,829
-27,783
-28,684
-64,508
17
28,253
27,025
-1673,848
-29,023
-29,133
-64,865
18
28,781
28,616
-1750,548
-29,213
-35,125
-24,927
19
55,105
57,476
-17,625
-34,830
-34,985
-24,613
20
56,260
57,641
-16,935
-35,005
-35,862
-25,916
21
58,346
64,396
-19,728
-35,320
-30,881
-60,541
22
51,605
36,889
-1063,035
-34,260
-31,338
-63,821
23
53,774
36,410
-1552,559
-34,612
-31,346
-60,348
24
50,724
37,791
-1040,868
-34,113
-28,806
-65,666
25
50,000
27,176
-1916,361
-33,980
-28,629
-64,070
26
51,345
28,109
-1596,280
-34,212
-30,431
-66,130
27
50,075
32,569
-2025,172
-34,022
Table 3 shows the average experimental results for surface roughness,
lathe check, force (Yb) with its computed S/N ratio value. Since Taguchi
experimental design is orthogonal, it is then possible to separate the effect of each
parameter cutting condition at different level. For example, the mean S/N ratio for
cutting tool wear at levels 1, 2, and 3 can be calculated by averaging the S/N ratio
17
for experiment 1-9, 10-18, 19-27, respectively. The mean S/N ratio for each level
of cutting condition is then summarized in tabular form called the mean S/N ratio
response table or a chart that can be used to predict the influence of parameter
observed, as in the further discussion.
Cutting force
Cutting force plays an important role in wood machining processes,
especially related to energy consumption and cutting tool life. Figure 12 shows
that cutting tool wear has a huge influence on the force exerted on the knife (Xc
and Yc), while the pressure of the bar has a significant influence on the force bar
(Xb and Yb ).
The results in figure 12 correspond to the previous research which states
that tool wear has a parallel relationship with the cutting force (Aknouche et al.
2009). Mankova (2002) states that cutting force is generally used as an indirect
method to identify the level of tool wear. In general, the average signal force
increases as the level of wear increases.
Xc
Yc
Xb
Yb
Figure 12 Chart S/N for cutting force (from left to right: cutting tool wear, cutting
speed, pressure bar, cultivar, temperature, type of bar)
Generally, the cutting force increases with increasing cutting speeds.
Results of research conducted by Darmawan and Tanaka (2004) showed a linear
18
relationship between the cutting force and cutting speed on turning test. However
in this study, the same trend is only can be observed from cutting force on the
horizontal bar (Yb) where the optimum force is obtained at the cutting speed 2
m/s. The opposite result also found on the research conducted by Quentin B and
Marchal R (2007) who reported cutting force fluctuations in peeling process with
cutting speed between 0.5-4 m/s. This phenomenon can be caused due to the
cutting speeds used in peeling process is still relatively low when compared to
cutting speed of other wood machining process, thus causing the different
between cutting force is not very significant.
Based on Figure 12, it can be also seen that type of cultivar had significant
influence on the knife cutting force. Lambro cultivar tends to generate greater
force, while cultivar of I214 tend to produces smaller force. These differences can
be attributed to differences in density between cultivars. The result of research
conducted by Eyma et al. (2004) showed linear correlation between wood density
and cutting force on fourteen species of tropical wood. It appears that cutting
force increases with increasing density. Wood with a higher density will be more
difficult to be cut due to have fewer cell cavities and thicker cell wall.
The cutting force tends to decrease with increasing storage temperature.
These results are similar with the results obtained by Marchal R (1996) which
showed that increased storage temperature of oak from 45 ° C to 80 ° C tended to
reduce cutting force that occurs. Similarly, Daoui et al. (2007) reported that
increasing storage temperature could decreased all cutting force on the knife and
nosebar. It is logic since given the wet heating causes the wood tends to be softer,
make it more plastic and pliable so it can more easily deformed before defect is
present. Increasing storage temperature before logging can also reduce the
resistance of wood so that the peeling process can be carried out under conditions
of lower stress wood. Fronczak FJ and Patzer RA (1982) state that heated wood
generate less force on the pressure bar due to decreased friction at the pressure
bar.
In addition, based on the results of research in the field is also obtained
that wood defects, such as knots, has an important influence on the cutting force.
Figure 13 shows that the knots could increase cutting force 2-3 times greater than
19
normal cutting force. A report on cutting force by Lutz JF and Patzer RA (1976)
also showed that when cut the knots, cutting force increased 1-3 times the force
needed to cut clear wood. Knot in wood represents changes in density and cells
orientation from wood surrounding it. Knots generally more dense than other
wood parts and cell orientation is perpendicular to the knife so it takes a greater
force when cutting the knots.
One turn
of peeling
process
Figure 13 Cutting force in peeling wood with knots and its illustration (up)
Surface Roughness
In almost machining process including peeling process, roughness is one
of the most important parameters that can describe the success rate of cutting
performance. The average of S/N ratio for the roughness Ra, Rz, and Rmax is
shown in Figure 14. Figure 14 shows that cutting tool wear, pressure bar and
temperature of wood are the most important factors. The highest pressure of the
bar with better honed knife seems to be the best choice to get the optimum value
for roughness. In general, in the peeling process of poplar, it is important to keep
the knife sharp. This is due to the percentage of tension wood in poplar which is
20
quite significant. Consequently, the wood tends to bend and cling to the knife
rather than being sheared cleanly.
Rz
Ra
Rmax
Figure 14 The optimum is minimum S / N graph for surface roughness (from
left to right edge of the tool, cutting speed, pressure bar, cultivar, temperature,
type of bar)
Bakar (1996) states that knife sharpness have a significant influence on the
quality of resulting veneer. Research conducted by Darmawan et al. (2009)
reported that the level of surface roughness increases with increasing cutting
length. Surface roughness of veneer (Ra) in peeling process using knife M2
conventional increased to 24-25 μm after a cutting length of 2 km from the range
of 15-16μm at the beginning of cutting process. The same phenomenon was also
obtained in the peeling process using knives M2 melted and M2 clad. Further
explained that the increase in roughness is due to the amount of clearance wear
that occurs and edge fracture on the knife. Cutting edge of knife M2 conventional
has roughness about 5µm at the beginning of cutting process, while after peeling 2
km, its roughness increased to approximately 30µm. The sharper the knife the
easier the knife to cut wood cell to produce smoother surface. Conversely when
using dull knife, knife can no longer cut wood cell, but destroying wood cells and
21
separate them from surrounding cells. It is then resulted in rough veneer and tends
to fuzz.
According to Lutz JF (1974) cutting speed does not seem to be a critical
controlling factor for the production of veneer. However, he recommends using a
moderately slow speed if the tightness of veneer and quality of surface are
important. Another study performed by Dundar et al. (2008) showed that
increasing cutting speed decreased significantly the average roughness. Cutting
speed should be as fast as possible to obtain smooth veneer. In this study,
increasing cutting speed from 0.1 m/s to 1 m/s increased the value of roughness,
whereas when cutting speed was increased to 2 m/s tend to decreased the value of
roughness. This phenomenon may be caused by the knife and bar setting process
that is not always exactly the same or can be caused by the presence of knots. The
presence of the knots in cutting process by using slow to moderate cutting speed
allows the vibration which can lead to poor quality of surface. These vibration
may caused by variation in wood density between the knots and wood
surrounding it. By increasing cutting speed, the vibration that occurs can be
reduced because the knife has enough force to cut the knots.
Figure 15 Influence cutting tool wear on surface roughness (up: cutting with
sharp knife; bottom : cutting with dull knife)
Based on Figure 14, it can be seen that the provision of pressure bar could
reduce surface roughness value of veneer. Dundar et al. (2008) state that in rotarycut veneer manufacturing, wood tends to split along the grain during cutting
process. This splitting causes the formation of vertical cracks (lathe checks) and
produce rough veneer. Utilization pressure bar could keep cutting process remains
on track and avoid wood to split. However, proper adjustment process is required
to obtain the smoothness veneer. The excessive compression of bar may lead
22
rough surface and cause high cost of energy due to extreme friction during cutting
process. In this study the best results for surface roughness were obtain from
pressure bar 10%.
In contrast to the results obtained on the cutting forces, cultivar Lambro
produced the best surface quality while I214 tends to produce the worst. Bakar
(1996) states that a good cutting process occurs when knife success to cut wood
cells on its cutting track. In general, at the same cutting conditions, wood with
higher density will result in better quality of cuts. This is due to wood with high
density have thicker cell walls so that it strong enough to withstand pressure
during cutting process. This allows the knife to split the cell so that it can be
produced either a uniform thickness and better surface quality because there is no
cell or wood fibers is torn. Increasing and lowering temperatures tend to degrade
the quality of the surface while the type of bar does not significantly affect the
surface finish since the measurement is made on the loose side.
Lathe Check (Depth)
The main effects for each level of parameter on lathe check are shown in
Figure 16. Based on S/N ratio, the best choice for lathe check depth is obtained at
condition as followed; at 0µm tool wear, low cutting speed, high pressure bar,
cultivar I214, room temperature, and with angular round bar.
Figure 16 The optimum is a minimum S / N graph for cracks (from left to right
edge of the tool, cutting speed, pressure bar, cultivar, temperature, type of bar)
Based on Figure 16, it can be seen that the value of S/N ratio for pressure
bar increase dramatically from PB0 (-35,378) into PB5 (-30,574), and then follow
to PB10 (-28,602). These value means that pressure bar changes effect
23
significantly on the lathe check depth, and the same trend (with reverse value) can
also be observed on the cutting speed parameter for each level.
Generally lathe check may be caused during peeling process by a tensile
stress field at the front of the cutting edge. It was explained by Corder SE and
Atherton GH (1963) that pressure bar in peeling process creates a field of
antagonist compression that tend to counteract the tensile bending stress on the
tight side of veneer. The greatest pressure of the bar is given, the shallowest crack
that appears on the veneer and vice versa. These compressive force also plays a
role in reducing or limiting splitting wood ahead of the knife edge. However, it
should be noted that giving too much pressure will lead to wood failure and
increase roughness on the veneer tight side. In this study, giving a pressure of
10% generate the most optimal result for lathe check depth (Figure 16, 17).
A
B
C
Figure 17 Lathe check at different level of pressure (A: without bar; B: pressure
5%; C: pressure 10%)
At the level of cutting tool wear, a sharp knife has a small edge radius so
that the blade can cut well, but in the case of a dull knife, the edge radius of the
knife
OF POPLAR VENEERS
IRSAN ALIPRAJA
GRADUATE SCHOOL
BOGOR AGRICULTURE UNIVERSITY
BOGOR
2012
ii
DECLARATION
I declare that this thesis titled Influence of Cutting Tool Wear on the
Quality of Poplar Veneers is my own work with the direction of the supervising
committee and has not been submitted in any form for any college except in
ENGREF, France (required by Double Degree Program). Information and quotes
from journals and books have been acknowledge and mentioned in the thesis
where they appear. All complete references are given at the end of the paper.
I understand that my thesis will become part of the collection of Bogor
Agriculture University. My signature below give the copyright of my thesis to
Bogor Agriculture University.
Bogor, October 2012
Irsan Alipraja
NIM E251100081
ABSTRACT
IRSAN ALIPRAJA. Influence of Cutting Tool Wear on the Quality of Poplar
Veneers. Under direction of WAYAN DARMAWAN and REMY MARCHAL.
Poplar wood is well known as a potential raw material for veneer industry.
However, its proportion of tension wood often cause problems on the veneer
quality. Therefore, optimization of machining process is required to improve the
quality of veneer. This study aims to examine the role of machining factors,
especially cutting tool wear on the quality of poplar veneer. The plan of
experiments was done by using the Taguchi method with six machining
parameter. Peeling process was performed by using the micro lathe. The results
showed that cutting tool wear, pressure bar, and temperature of wood give
significance influence on surface roughness while pressure bar and cutting speed
were important factors on lathe check formation.
Keywords: peeling process, cutting tool wear, cutting force, surface roughness,
lathe check
iv
SUMMARY
IRSAN ALIPRAJA. Influence of Cutting Tool Wear on the Quality of Poplar
Veneers. Guide by WAYAN DARMAWAN and REMY MARCHAL.
As a fast growing species, poplar wood (Populus spp) has become potential
raw material for veneer industry, especially in temperate regions such as in
Europe. In France, a total of 1,422,523 m3 timber was harvested in 2008 and
64.3% were used for rotary-cut veneer (lightweight packaging, plywood and
export). Currently, there are more than 140 clone cultivable poplar in Europe that
can make industry has more choice for its raw material. However, due to its
proportion of tension wood, this species often produces poor surface quality. One
way to improve the quality of veneer is by optimization of cutting parameter. The
rate of cutting tool wear is also a factor that must be considered in order to obtain
the best quality of surface. The purpose of this study is to examine the role of
machining factors, especially cutting tool wear, on the quality of veneer product.
Experimental design was conducted using Taguchi method to make the
research more efficient in time and material. Factors control that used in this study
were cutting tool wear, cutting speed, pressure bar, type of bar, cultivar and
temperature of wood. Peeling process was conducted by using microlathe
machine to obtain veneer with thickness of 3 mm. Evaluation of veneer consisted
of cutting force, surface roughness and lathe check. Surface roughness has been
evaluated by using Surfascan SOMICRONIC S-M3 device while lathe checks
have been measured by using SMOF device and its software.
The result from this study showed that cutting tool wear is the factor that
most affect the quality of veneer. In this study, the lowest force on the knife is
obtained at the level of 0 µm cutting tool wear, 0% of pressure bar, cultivar I214
and at room temperature, while 0% of pressure bar, cultivar I214 and with angular
bar sharpened tends to generate optimum force on the bar. The best surface
quality (Ra) is found when peeling wood with 0 µm wear level of the knife, 10%
of pressure bar, cultivar lambro and at room temperature, whereas the optimum of
lathe check was produced by using cutting speed 0.1 m/s with 10% of pressure
bar.
Keywords: poplar, peeling process, cutting tool wear, veneer quality, cutting
force, surface roughness, lathe check
© Copyright IPB, 2012
Copyright Reserved by Law
Prohibited quoting part or all of this paper without mentioning or citing the sources.
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permission
vi
INFLUENCE OF CUTTING TOOL WEAR ON THE QUALITY
OF POPLAR VENEERS
IRSAN ALIPRAJA
E251100081
Thesis
In partial fulfillment of the requirements for the degree of
Master of Science
At Bogor Agriculture University
GRADUATE SCHOOL
BOGOR AGRICULTURE UNIVERSITY
BOGOR
2012
SHEET APPROVAL
Title
Name
NIM
: Influence of Cutting Tool Wear on the Quality of Poplars Veneers
: Irsan Alipraja
: E251100081
Approved,
Co-Major Professors,
Prof. Dr. Ir. I Wayan Darmawan, M.Sc.
NIP. 19660212 199103 1 002
Prof. Rémy Marchal
Head of the Department of Forest
Product Technology
Dean of the Graduate School
Prof. Dr. Ir. I Wayan Darmawan, M.Sc.
NIP. 19660212 199103 1 002
Dr. Ir. Dahrul Syah, M.Sc.Agr
NIP. 19621026 198803 1 001
Presented : 31 Octobre 2012
Date of graduation : 13 Decembre 2012
viii
FOREWORD
All praise and gratitude to Allah SWT so that the author could finish this
scientific work entitled Influence of Cutting Tool Wear on the Quality of Poplars
Veneers. The results of this study hopefully can contribute and give useful
information in the development of science and technology of wood processing in
particular in veneer manufacturing.
First of all, I would like to convey my gratitude to Ministry of National
Education (DIKNAS) that give the opportunity to continue my study in master
program through the program of double degree Indonesia-France. I would like
also to thank Prof. Dr. Ir. Wayan Darmawan M. Sc. and Prof. Rémy Marchal as
the supervisors who have given a lot of suggestions during the research. High
appreciation for all the teachers, staff and technician LaboBois ENSAM for
excellent reception, warm atmosphere and also for their support during the
research. Thanks also to my father, my mother, my brothers and the whole family,
for all the prayers and love. Finally, I would like to thank all master student of
Forest Product Technology especially to Rentry Augusti Nurbaity, Vera Junita
Sitanggang, Novitri Hastuti, Sonia Somadona and Meylida Nurrachmania for their
desires to share both difficulty and happiness when we lived in France.
The author recognizes that this research is still far from perfect. Therefore,
suggestions and constructive criticism are expected to improve this work.
Bogor, October 2012
Irsan Alipraja
i
TABLE OF CONTENTS
Page
TABLE OF CONTENTS .................................................................................... i
LIST OF TABLES .............................................................................................. ii
LIST OF FIGURES ........................................................................................... iii
LIST OF ANNEXE ............................................................................................. iv
1. INTRODUCTION ........................................................................................... 1
Background ............................................................................................... 1
Formulation ............................................................................................... 2
Objectives .................................................................................................. 2
Benefit ....................................................................................................... 3
Hypotheses ................................................................................................ 3
2. STUDY LITERATURE .................................................................................. 4
Poplar Wood.............................................................................................. 4
Transformation by Peeling Process ........................................................... 5
Quality of Veneer ...................................................................................... 7
3. MATERIALS AND METHODS ................................................................... 9
Taguchi Method ....................................................................................... 9
Cultivar Selection and Preparation of Disk ............................................... 11
Experiments on Microlathe ....................................................................... 12
Evaluation of Veneer................................................................................. 13
Evaluation of Cutting Force.......... .................................................... 13
Evaluation of Veneer Quality.......... .................................................. 14
Lathe Check Measurement ....................................................... 14
Surface Roughness Measurement ............................................. 15
4. RESULTS AND DISCUSSION ..................................................................... 16
Analysis of S/N Ratio (SNR)……………….………………. .................. 16
Cutting Force ……………………………….………. .............................. 17
Surface Roughness .................................................................................... 19
Lathe Check (Depth) ................................................................................. 22
5. CONCLUSION ................................................................................................ 25
REFERENCE ...................................................................................................... 26
APPENDIX .......................................................................................................... 30
ii
LIST OF TABLE
No.
Page
1. Determination levels of control factors ............................................................. 10
2. Experiment matrix ............................................................................................. 11
3. Experimental results for surface roughness, lathe check, and cutting force
with their corresponding SNR .......................................................................... 16
iii
LIST OF FIGURES
No.
Page
1. Poplars and their implementation.........................................................................4
2. Mechanical properties of poplar wood .................................................................5
3. Principe of peeling process ..................................................................................5
4. Cracking formation during the production of veneer with different
pressure level of the bar.......................................................................................8
5. Discs for micro lathe from three types of poplar cultivar .................................11
6. Microlathe ..........................................................................................................12
7. Decompositions of the resulting cutting force Fc ..............................................13
8. Filtering process using Labview software..........................................................14
9. Evaluation of lathe check ...................................................................................14
10. Surfacescan device ...........................................................................................15
11. Surface roughness profile .................................................................................15
12. Chart S/N for cutting force...............................................................................17
13. Cutting force in peeling wood with knots ........................................................19
14. The optimum is minimum S / N graph for surface roughness .........................20
15. Influence cutting tool wear on surface roughness ............................................21
16. The optimum is a minimum S / N graph for cracks .........................................22
17. Lathe check at different level of pressure ........................................................23
iv
LIST OF APPENDIX
No.
Page
1 Matrix experimental L27 ................................................................................. 30
2
Response table for average S/N Ratio for cutting force factors ...................... 31
3
Results of analysis of variance for the efforts ................................................. 32
4
Response table for average S/N Ratio for surface roughness factors .............. 33
5
Results of analysis of variance for roughness ................................................. 34
6
Response table for average S/N Ratio for lathe check factors ........................ 35
7
Results of analysis of variance for cracks ....................................................... 36
8 Average results of cutting force, lathe check, and surface roughness .............. 37
1
INTRODUCTION
Background
Plywood, laminated veneer lumber (LVL) and laminated veneer panels
(LVP) are structural wood products that using veneer as its raw material. The
quality of those products are then could determined from the quality of veneer and
production process. Parameters commonly used to assess the quality of veneer i.e.
lathe check, surface roughness and thickness variation. Research on the effect of
these parameters on the quality of product (such as plywood and LVL) has been
widely done (Neese JL, 1997; DeVallance, 2003; Daoui A et al., 2011; Piirlaid et
al., 2012). Similarly, factors that affect the quality of veneer (Corder SE and
Atherton GH, 1963; Lutz JF et al., 1967; Bakar ES, 2004; Aydin et al., 2006;
Tanritanir E et al. 2006; Dundar et al., 2008a) and methods used to evaluate the
veneer has been widely known (Blomme et al., 2010; Palubicki et al. 2010;
Denaud et al., 2012). However, because of the natures of wood are complex that
often give different responses, performing research on veneer quality is still
interesting to do.
As a fast growing species, poplars has become potential raw material for
veneer industry, especially in temperate regions such as in Europe. In Europe,
total production of poplar wood is approximately 8 million m 3 per year and about
40% of this volume is intended for veneer and plywood industry while 31% is
used for sawmill industry (Nervo et al., 2011). In France, a total of 1,422,523 m3
timber was harvested in 2008 and 64.3% used for rotary-cut veneer (lightweight
packaging, plywood, and export).
Poplar wood have an abundant amount of cultivar. The results of research
conducted by Huda et al (2011) showed that the site and clone have had a
significant influence on all the anatomical, physical and mechanical properties of
poplar wood. This characteristics difference is certainly expected able to expand
the potential of poplar wood as raw material for veneer and plywood industry.
However, due to high proportion of tension wood, this species often produces
poor surface quality (fuzzy grain), thus causing problems in gluing process and
finishing treatment. One of the efforts that often do to overcome these problems is
2
by perform the optimization of machining process. Optimization process in
peeling of wood can be done by changing the cutting parameters such as cutting
speed, bar pressure, cutting temperature or clearance angle.
Knife has an important role in peeling process. Its maintenance costs are
relatively high. The high rate of knife wear can also affect the level of
productivity of veneer. On the other hand, research on the effect of cutting tool
wear in peeling process is very little published. Based on this problem, it takes a
study that observe the contribution of cutting tool wear on the quality of veneer,
especially on poplar wood.
Formulation
Poplar is a fast growing species that has long been used as raw material for
plywood and veneer industry. The main constraint that are frequently encountered
in machining process of poplar wood is the presence of tension wood with various
proportions. The presence of tension wood often causes problems in wood
machining processes primarily related to the quality of resulting veneer surface.
One way to solve these problems is by optimize the conditions or cutting
parameters. Another parameter that also important in this process is the knife.
Knife in peeling process should be as sharp as possible to avoid the adhesion of
tension wood fibers on the surface of the knife. Knife wear can also be an obstacle
to produce high quality of veneer and to reduce energy consumption. Problems to
be addressed in this research is how cutting tool wear influence on the cutting
force that occurs and the quality of veneer surface? and how large the contribution
of cutting tool wear compared with other peeling parameters?
Objectives
The objectives of this research were to examine the role of machining
factors, especially cutting tool wear, on the quality of poplar veneers.
3
Benefit
The study is expected to provide scientific information on the role of
cutting tool wear on cutting force, surface quality and lathe check of veneer as
well as on the characteristics of poplar wood in peeling process.
Hypotheses
Knife wear will increase the cutting force that occurs during peeling
process. In addition, knife wear can reduce the quality of the veneer surface
produced from peeling process and plays an important role in the occurrence of
lathe check.
4
STUDY LITERATURE
Poplar Wood
Poplar, also known as the scientific name Populus spp., is an angiosperms plant
that comes from family Salicaceae. It comes from temperate zones and the northern
hemisphere. This species is classified as a fast-growing species, has homogeneous wood
with a high level of productivity (up to 35-40 m3/ha per year) (O Pichard et al., 1997).
The volumetric composition of poplar wood is compiled by high proportion of fibers
(53-60%), followed by vascular elements (28-34%), medullary ray (11-14%), and a
significant proportion of axial parenchyma (0.1-0.3%) (Panshin and de Zeeuw, 1980 in
Balatinecz DD and DE Kretschmann, 2001). The chemical composition of poplar wood
is dominated by high proportion of polysaccharides (up to 80% holocellulose, which
varies among clones and stations) and low proportion in lignin (about 20%).
Figure 1 Poplars and their implementation (source : http://www.science.gouv.fr)
The hybrid poplar have already produced many species. There are currently at
least 145 registered cultivars and cultivable poplar in Europe. The process of vegetative
propagation is usually very easy, by cuttings and plants capable of producing the same
quality. Poplar wood is generally white, sometimes reddish or pink, easy to be worked
(Figure 1) and can be nailed without splitting (Pichard O et al., 1997).
Poplar wood has an average density of 0,45 (at the level of moisture content
12%) with the shrinking value in tangential section 8,3%, and in the radial 4,8%.
Mechanical properties and durability of poplar wood are generally low and it has good
aptitude for peeling and slicing process (Figure 2). Poplar wood can be used for interior
plywood, packing, match, current furniture, lightweight frame, pulp, fiberboard and
particle board.
5
Poplar is one of three main hardwoods in France after oak and beech. Although
his crops tend to decline (after reaching the maximum yield in 1990), its role in the
timber industry, particularly in peeling process, remains high.
Figure 2 Mechanical properties of poplar wood (source: CIRAD, 2011)
Transformation by Peeling Process
Peeling process (Figure 3) is a primary method of wood processing that
transforms the log into veneer sheets. About 90% production of veneer in the world is
obtained by this process. The principle of this process is the rotation of the logs against
the knife, with the veneer being peeled in a continuous sheet; the length of the knife is
equal to the length of the log.
Horizontal opening
Vertical opening
Cutting direction
B
Pressure
bar
Chuck
Cutting angle
Knife
Figure 3 A. Principe of peeling process (source : Tsoumis, 1991); B. Rotary
machine semi-industry at laboratory ENSAM
6
Veneer peeling lathe (veneer rotary lathe) is equipped with a pressure bar (or
often named nosebar) which is placed ahead of the knife and has equal length. Its role is
to prevent or minimize the appearance of cracks on veneer and also to control the
thickness and smoothness of veneer. The nosebar and knife carriage will then move
slowly towards the log, give the pressure in accordance with a veneer thick. As veneer
comes from the lathe, it is received by a conveyor, reel or table. Nosebar adjustment
must be done every turn of the new knife, knife sharpening, changes thick of veneer
peeled or when peeling different wood species. In addition, it requires a fairly high
accuracy in determining the position and pressure levels of the bar to produce high
quality of veneer. If the pressure bar is too big, it will crush the wood while if it is too
low it will produce a lot of crack on the veneer surface (Forest Product Laboratory,
1962; Tsoumis, 1991; Bakar ES and Marchal R, 2001).
There are mainly two types of pressure bars i.e. fixed pressure bar and roller
pressure bar. The fixed bar is the simplest, cheap and most commonly used. It is
normally used on veneer slicers and also for cutting hardwood on a rotary-lathe. The
fixed bar has generally a bevel angle between 74-78°. Other than fixed bars, roller bar is
one of the bars that often used. Compared to fixed bar, utilization roller bar could
reduce cutting force that occurs. However this type of bar cannot cut veneer of any
thickness like fixed bar. Lutz (1978) states that roller bar with diameter 15.9 mm cannot
be used to cut veneer which is thinner than 1.6 mm.
Knife represents the largest maintenance cost in veneer industry thus required
good knowledge in the use of the knife (grinding and setting) to keep the knife remains
in good conditions. The knife is generally low alloy steel with a low sharpness angle,
between 18 and 23 °. Normally, the smaller the angle, the less the veneer is bent when it
is cut thus produce tighter veneer. Otherwise, the larger the sharpness angle, the stiffer
the knife thus the better the knife edge withstand impact. Grinding process for a small
angle knife must be done more carefully than the knife with larger angle. Veneer knife
should has Rockwell hardness of 56-58 on the C scale for rotary-lathe and 58-60 for
veneer slicers. A Rockwell hardness 60-62 may even be used when cutting low density
wood.
The most common knife thickness is 16 mm (for rotary lathe) and 19 mm (for
slicer). In general, to peel thicker veneer, it should be used the thicker knife while when
7
cutting thin veneer, thinner knife can be used as long as it properly supported (Lutz JF,
1978). The knife working in the manner of penetration, cuts wood and often cause
cracks on veneer product.
Quality of Veneer
Veneer quality is an important parameter that determines the success rate of
plywood or LVL production. It is depend on the quality of raw materials used, skill of
the operator, condition of the lathe and cutting parameters used (FPL, 1962; Bakar ES,
1996). The quality of veneer is generally evaluated based on the variation of thickness,
surface roughness and lathe check (frequency and depth). In addition, radius curl of
veneer is also sometimes used as an indicator to assess veneer quality since the curved
veneer is difficult to be worked than flat veneer. For some uses such as face veneer,
color is also one of parameters that need to be considered (Lutz, 1971; Bakar ES, 1996;
Marchal R, 1996; Wang J et al., 2001; Daoui et al., 2011). A good quality of veneer will
certainly be a uniform in thickness, flat, smooth and slightly cracking.
Roughness can be defined as an irregularity on a periodic basis (other than
defects) on the surface of a material generated by the production process. Surface
roughness plays an important role, especially on bonding quality and finishing
treatments. Control of surface roughness in veneer production is substantial to maintain
adhesive quality between veneer on the plywood/LVL or between veneer and other
wood based panel. The surface quality of veneer which is not good (rough) will
produce a weak bonding and reduces the mechanical properties of composite panels
produced (DeVallance 2003; Unsal et al., 2005; Korkut S M and Akgul, 2007; Dundar
et al., 2008b). Rough surface of veneer can also causes excessive resin use and may lead
resin-bleed through the face veneer. On the face veneer, roughness can be reduced by
sanding process. Nevertheless, the veneer which is too rough requires much more
sanding process than "smooth" veneer, resulting in reduced material thickness.
In general, roughness can be caused by two main factors, which are
characteristics of wood anatomy and the machining process. Roughness caused by
wood anatomy is influenced by several factors, including ring width, difference between
juvenile wood and mature wood, the proportion between earlywood and latewood, knots
and reaction wood while machining factors that affecting surface roughness are knife
angle, pressure bar, temperature of cutting, cutting speed and thickness of veneer
8
(Ayrilmis et al. 2006). Furthermore, Sandak J and Martino (2005) added that wood
porosity and moisture content also gives effect to the formation of surface quality.
Similar with roughness, cracking (lathe check) is also an important criteria and
has long time been used as an indicator of veneer quality (Figure 4). In almost all veneer
manufacturing process, lathe checks are present at different level. These cracks occur
during machining process. Lathe check in veneer showed weak zone and cause
excessive penetration of adhesive.
Figure 4 Cracking formation during the production of veneer with different
pressure level of the bar.
Source: Photo by U.S. Forest Products Laboratory
Typically, lathe check is strongly influenced by the level of pressure and also by
cutting speed and geometry of the knife. Lathe checks frequent but shallow are
preferable to less frequent but deep, especially when the appearance of plywood or LVL
is required as in face veneer.
9
MATERIALS AND METHODS
Location and Period of Research
This research was carried out at Laboratory of Wood (Laboratoire
Bourguignon des Matériaux et Procédés), Ecole Nationale Supérieur d’Arts et
Métiers (ENSAM), Cluny, France. The study lasted for six months, starting from
February 2012 to July 2012.
Tools and Materials
Materials used in this study were three 15-20 year old clones of poplar
wood (I214, Lambro and Lena) in a form of disk with a thickness of 30 mm. Tool
used to produce samples of veneer were Microlathe ENSAM, wood peeling
knives, and nosebar. Peeling knives used were three pieces with different levels of
wear (0 μm, 250 μm, and 500 μm) but has the same sharpness angle (20°). The
knives are low alloy steel with a composition of 0.6% C, 1.8% Si, 0.7% Mn, 0.3%
Cr, 0.5% Mo, 0.2% V with hardness value of 55-56 HRC. Evaluation of veneer
quality was performed by using piezoelectric system installed on the microlathe
and its software developed by ENSAM Lab to scan cutting force; System
Measurement Opening of Fissure (SMOF) devices and its software to measure
lathe check; and Surfascan SOMICRONIC S-M3 with its stylus with a tip radius
of 2 μm to evaluate surface quality.
Some of the other tools that used to support this research including
"storage tubs", infrared gun, ruler, calipers (caliper), grinding machine, planer
machine, band saw and drilling machine. Data processing is performed by using
LABVIEW 2011 software and STATISTICA 2011.
Taguchi Method
In general, the plan of experiments was done by using Taguchi method.
Taguchi method allows to examine many factors with a relatively small number of
experiments. This method is based on a matrix experiment that can easily fix most
problems in terms of industrial design experiments.
10
In Taguchi method, it is necessary to select control factors (Main factors
that will be evaluated on their effects on the results of the experiment) and
variation levels to minimize the sensitivity of the response on the experimental
noise. These factors are cutting tool wear, cutting speed, pressure bar, cultivar,
temperature of the wood, and type of bar (Table 1).
Table 1. Determination levels of control factors
Factor
1
A. Cutting tool wear
0µm
B. Cutting speed
0.1 m/s
C. Pressure bar
0%
D. Cultivar
Lena
E.Temperature of
10°C
wood
F. Type of bar
Angular bar
sharpened
Level
2
250µm
1 m/s
5%
Lambro
20°C
3
500µm
2 m/s
10%
I 214
30°C
Angular bar
sharpened both
sides
Angular round
bar
The experimental matrix chosen is type L27 with 27 rows and 7 columns.
The parameters to be studied are placed in columns. Thus, a total of 27 tests were
performed (Table 2).
Taguchi method approach introduces “signal-to-noise” ratio (S/N ratio) to
study the influence of noise on the variations that occur. Generally, there are three
performance categories in the analysis of the S / N ratio, i.e. optimum is nominal,
optimum is a minimum and optimum is maximum. In this study, to obtain
optimum machining performance, conditions optimum is minimum for surface
roughness, lathe check and cutting force should be taken to achieve the highest
quality veneer. The formula used to calculate SNR in the case where the optimum
is a minimum are:
∑
,
where i is the number of the experiment, j the number of the replicate, n
the number of repetition, and yj is the response value.
11
Table 2. Experiment matrix
Cutting
No
tool wear Pressure
(µm)
bar (%)
1
0
0
2
0
0
3
0
0
4
0
5
5
0
5
6
0
5
7
0
10
8
0
10
9
0
10
10
250
0
11
250
0
12
250
0
13
250
5
14
250
5
15
250
5
16
250
10
17
250
10
18
250
10
19
500
0
20
500
0
21
500
0
22
500
5
23
500
5
24
500
5
25
500
10
26
500
10
27
500
10
Cutting
speed
(m/s)
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
0.1
1
2
Cultivar
Lena
Lambro
I 214
Lambro
I 214
Lena
I 214
Lena
Lambro
Lambro
I 214
Lena
I 214
Lena
Lambro
Lena
Lambro
I 214
I 214
Lena
Lambro
Lena
Lambro
I 214
Lambro
I 214
Lena
Temperature
of wood (°C)
10
20
30
20
30
10
30
10
20
30
10
20
10
20
30
20
30
10
20
30
10
30
10
20
10
20
30
Type of
bar
1
2
3
3
1
2
2
3
1
2
3
1
1
2
3
3
1
2
3
1
2
2
3
1
1
2
3
Cultivar Selection and Preparation of Disk
Selection of cultivars were performed by considering the quality of veneer
produced by another studies (Master of FAGE, Rentry Nurbaity Augusti).
Eighteen discs were prepared for nine tests from a total 27 tests.
Figure 5 Discs for micro lathe from three types of poplar cultivar
12
Three cultivars selected were I214, Lambro and Lena (Figure 5). Veneer
of good quality is represented by the discs I214 with a diameter of ± 360 mm
while the average quality is represented by Lambro with a diameter of 280 mm
and the poor quality represented by Lena with a diameter of 300 mm.
The preparation of discs was done by bandsaw to get constant disc
thickness of 30 mm. They were then stored in water to prevent fungal attack.
Before peeling process, each sample was placed in three different temperatures for
24 hours depending on research model. Storage temperature used were 6 ° C, 20 °
C (room temperature) and 40 ° C.
Experiments on micro-lathe
The micro-lathe was developed by JeanClaude BUTAUD (Butaud et al. 1995). This
machine is specially developed for research
Nosebar
purpose and it can be used to study the
mechanism complete of peeling process from
Knife
disks samples. Knife and nosebar lies in two
different rings that are connected and form a
System piezoelectric
piezoelectric system and can be moved through
the main "computer".
Figure 6 Microlathe
Micro-lathe ENSAM can peel wood with cutting speeds up to 3m/s, and
clearance angle up to 40°. Sample should be in the form of disks with a thickness
5-30 mm and diameter between 25-500 mm. This machine can produce peeled
veneer with a thickness of 0.1-5 mm.
In this study, each sample was peeled five rounds for each modality and
repeated several times. Peeling process was performed with 3 mm thick veneer
and various machining conditions contained in the experimental design.
The veneer samples obtained were then divided into several parts: the
length of the samples taken for measurements of the roughness (SR) and lathe
check (SMOF) are respectively 5 cm and 45 cm.
13
Evaluation of Veneer
In general, the quality assessment of a peeling process is done by two
approaches: evaluation of cutting forces and evaluation of veneer quality. Cutting
force is closely related to the electrical consumption and cutting tool lifetime,
while veneer quality will affect the quality of product (plywood or LVL). The
higher the cutting force generated, the higher the energy consumption and the
shorter the life of the knife.
Evaluation of Cutting Force
Xc . cos Yc . sin
sin( 2 )
Xc . cos( ) Yc . sin( )
Fd
sin( 2 )
Fc
Fa
X
Xc
Xd
Fd
Y
Barre de pression : Xb, Yb
Yd
O
u
t
i
l
Fa
Xa
Yc
Ya
Placage
Xc,
Yc
Figure 7 Decompositions of the resulting cutting force Fc
( = sharpness angle ; = friction angle of wood/metal)
Cutting force measurement is carried out by using piezoelectric system
on the micro lathe. This system allows to measure the forces received by the knife
(Xc, Yc) and nosebar (Xb, Yb) during peeling process (Figure 7). The profiles of
the efforts are then presented on the screen using software developed by ENSAM
laboratory and filtered by labview software before treated statistically. Filtering
process is performed to obtain the average force from stable zone of cutting force
(Figure 8).
14
Figure 8 Filtering process using Labview software
Evaluation of veneer quality
Lathe check measurement
Veneer lathe check was measured by a specific measurement device and
its associated software (SMOF): this set can measure the frequency and the depth
of the cracking of veneer. The measurement technique is based on the opening of
cracks occurring at the time of passage of veneer through the pulley (Figure 9a).
Concerning the nature of veneer which is very fragile, then the success of
measurement is strongly influenced by the choice of pulley diameter. When
diameter of the pulley is too small, the measurement process will lead to cracking
and increase the depth of fissure thus the measure is not reliable. Otherwise, if
diameter of pulley is too large, veneer cracks can not be opened so it is difficult to
be detected by the camera.
LVDT sensor
a
b
c
Veneer place
Bending pulley
Figure 9 Evaluation of lathe check; (a) Devices of SMOF (b) determining the depth
of lathe check, (c) Recommendations of pulley diameter by Palubicki (2010)
Determination pulley diameter is generally done on an experimental basis.
In this study, the observed thick veneer is 3 mm, so that the diameter of pulley
that used is equal to 65 mm or in accordance with the recommendations of the
research performed by Palubicki et al. (2010) (Figure 9c). Measurement process
15
begins when veneer through LVDT sensor. This sensor will measure the thickness
of veneer. Then the moment veneer passed pulley, lathe check formed on the
loose side will be opened and at the same time the camera which is placed on the
back of device will start scanning the side (thickness) of the veneer. The images
obtained are then analyzed its depth (percentage) manually using software of
SMOF.
Surface Roughness Measurement
Surface roughness of veneer were
measured using conventional method by stylus
(Surfascan SOMICRONIC S-M3). The stylus
sensor used in this study has a tip angle of 90 °
with a tip radius of 2 microns. The selection of
this stylus geometry is designed to minimize
Figure 10 Surfascan device
errors in the profiling of the surface. The length of the test performed (tracing
lenght) is 12.5 mm and stylus speed 1.5 mm/s. The roughness parameters
measured were average roughness (Ra), mean peak-to-valley height (Rz), and
maximum roughness (Rmax). The profile of the surface roughness was filtered
using a cutoff value of 2.5 mm.
Cut off lenght
Average roughness height
Profile height
Profile direction
Devices of stylus
Sampling lenght
Figure 11 Surface roughness profile
16
RESULTS AND DISCUSSION
Analysis of S/N Ratio (SNR)
Table 3 Experimental results for surface roughness, lathe check, and cutting force
with their corresponding SNR
Average
S/N Ratio
Surface
No Roughness
Lathe
Force Yb
Surface
Lathe Check Force Yb
Exp
Check (%)
(daN/m)
Roughness
(%)
(daN/m)
Ra
-35,714
-24,679
1
23,512
61,048
-17,109
-27,446
-35,835
-23,949
2
19,685
61,871
-15,754
-25,929
-35,479
-25,845
3
21,963
59,402
-19,214
-26,834
-27,408
-64,867
4
16,422
23,157
-1745,702
-24,323
-30,429
-58,925
5
21,215
33,223
-875,737
-26,540
-32,360
-61,375
6
18,501
41,495
-1171,410
-25,354
-25,723
-62,594
7
20,346
19,247
-1347,199
-26,180
-28,206
-65,586
8
18,583
25,710
-1886,572
-25,389
-30,997
-64,376
9
13,865
35,270
-1654,943
-22,843
-35,274
-23,918
10
34,712
58,031
-15,687
-30,823
-35,225
-25,274
11
39,891
57,703
-18,347
-32,088
-34,899
-25,129
12
32,492
55,585
-17,946
-30,239
-29,252
-58,903
13
32,710
29,005
-881,130
-30,294
-29,943
-61,162
14
32,350
31,407
-1142,555
-30,199
-32,209
-63,032
15
32,870
40,761
-1408,812
-30,475
-26,804
-64,750
16
24,500
24,648
-1726,829
-27,783
-28,684
-64,508
17
28,253
27,025
-1673,848
-29,023
-29,133
-64,865
18
28,781
28,616
-1750,548
-29,213
-35,125
-24,927
19
55,105
57,476
-17,625
-34,830
-34,985
-24,613
20
56,260
57,641
-16,935
-35,005
-35,862
-25,916
21
58,346
64,396
-19,728
-35,320
-30,881
-60,541
22
51,605
36,889
-1063,035
-34,260
-31,338
-63,821
23
53,774
36,410
-1552,559
-34,612
-31,346
-60,348
24
50,724
37,791
-1040,868
-34,113
-28,806
-65,666
25
50,000
27,176
-1916,361
-33,980
-28,629
-64,070
26
51,345
28,109
-1596,280
-34,212
-30,431
-66,130
27
50,075
32,569
-2025,172
-34,022
Table 3 shows the average experimental results for surface roughness,
lathe check, force (Yb) with its computed S/N ratio value. Since Taguchi
experimental design is orthogonal, it is then possible to separate the effect of each
parameter cutting condition at different level. For example, the mean S/N ratio for
cutting tool wear at levels 1, 2, and 3 can be calculated by averaging the S/N ratio
17
for experiment 1-9, 10-18, 19-27, respectively. The mean S/N ratio for each level
of cutting condition is then summarized in tabular form called the mean S/N ratio
response table or a chart that can be used to predict the influence of parameter
observed, as in the further discussion.
Cutting force
Cutting force plays an important role in wood machining processes,
especially related to energy consumption and cutting tool life. Figure 12 shows
that cutting tool wear has a huge influence on the force exerted on the knife (Xc
and Yc), while the pressure of the bar has a significant influence on the force bar
(Xb and Yb ).
The results in figure 12 correspond to the previous research which states
that tool wear has a parallel relationship with the cutting force (Aknouche et al.
2009). Mankova (2002) states that cutting force is generally used as an indirect
method to identify the level of tool wear. In general, the average signal force
increases as the level of wear increases.
Xc
Yc
Xb
Yb
Figure 12 Chart S/N for cutting force (from left to right: cutting tool wear, cutting
speed, pressure bar, cultivar, temperature, type of bar)
Generally, the cutting force increases with increasing cutting speeds.
Results of research conducted by Darmawan and Tanaka (2004) showed a linear
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relationship between the cutting force and cutting speed on turning test. However
in this study, the same trend is only can be observed from cutting force on the
horizontal bar (Yb) where the optimum force is obtained at the cutting speed 2
m/s. The opposite result also found on the research conducted by Quentin B and
Marchal R (2007) who reported cutting force fluctuations in peeling process with
cutting speed between 0.5-4 m/s. This phenomenon can be caused due to the
cutting speeds used in peeling process is still relatively low when compared to
cutting speed of other wood machining process, thus causing the different
between cutting force is not very significant.
Based on Figure 12, it can be also seen that type of cultivar had significant
influence on the knife cutting force. Lambro cultivar tends to generate greater
force, while cultivar of I214 tend to produces smaller force. These differences can
be attributed to differences in density between cultivars. The result of research
conducted by Eyma et al. (2004) showed linear correlation between wood density
and cutting force on fourteen species of tropical wood. It appears that cutting
force increases with increasing density. Wood with a higher density will be more
difficult to be cut due to have fewer cell cavities and thicker cell wall.
The cutting force tends to decrease with increasing storage temperature.
These results are similar with the results obtained by Marchal R (1996) which
showed that increased storage temperature of oak from 45 ° C to 80 ° C tended to
reduce cutting force that occurs. Similarly, Daoui et al. (2007) reported that
increasing storage temperature could decreased all cutting force on the knife and
nosebar. It is logic since given the wet heating causes the wood tends to be softer,
make it more plastic and pliable so it can more easily deformed before defect is
present. Increasing storage temperature before logging can also reduce the
resistance of wood so that the peeling process can be carried out under conditions
of lower stress wood. Fronczak FJ and Patzer RA (1982) state that heated wood
generate less force on the pressure bar due to decreased friction at the pressure
bar.
In addition, based on the results of research in the field is also obtained
that wood defects, such as knots, has an important influence on the cutting force.
Figure 13 shows that the knots could increase cutting force 2-3 times greater than
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normal cutting force. A report on cutting force by Lutz JF and Patzer RA (1976)
also showed that when cut the knots, cutting force increased 1-3 times the force
needed to cut clear wood. Knot in wood represents changes in density and cells
orientation from wood surrounding it. Knots generally more dense than other
wood parts and cell orientation is perpendicular to the knife so it takes a greater
force when cutting the knots.
One turn
of peeling
process
Figure 13 Cutting force in peeling wood with knots and its illustration (up)
Surface Roughness
In almost machining process including peeling process, roughness is one
of the most important parameters that can describe the success rate of cutting
performance. The average of S/N ratio for the roughness Ra, Rz, and Rmax is
shown in Figure 14. Figure 14 shows that cutting tool wear, pressure bar and
temperature of wood are the most important factors. The highest pressure of the
bar with better honed knife seems to be the best choice to get the optimum value
for roughness. In general, in the peeling process of poplar, it is important to keep
the knife sharp. This is due to the percentage of tension wood in poplar which is
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quite significant. Consequently, the wood tends to bend and cling to the knife
rather than being sheared cleanly.
Rz
Ra
Rmax
Figure 14 The optimum is minimum S / N graph for surface roughness (from
left to right edge of the tool, cutting speed, pressure bar, cultivar, temperature,
type of bar)
Bakar (1996) states that knife sharpness have a significant influence on the
quality of resulting veneer. Research conducted by Darmawan et al. (2009)
reported that the level of surface roughness increases with increasing cutting
length. Surface roughness of veneer (Ra) in peeling process using knife M2
conventional increased to 24-25 μm after a cutting length of 2 km from the range
of 15-16μm at the beginning of cutting process. The same phenomenon was also
obtained in the peeling process using knives M2 melted and M2 clad. Further
explained that the increase in roughness is due to the amount of clearance wear
that occurs and edge fracture on the knife. Cutting edge of knife M2 conventional
has roughness about 5µm at the beginning of cutting process, while after peeling 2
km, its roughness increased to approximately 30µm. The sharper the knife the
easier the knife to cut wood cell to produce smoother surface. Conversely when
using dull knife, knife can no longer cut wood cell, but destroying wood cells and
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separate them from surrounding cells. It is then resulted in rough veneer and tends
to fuzz.
According to Lutz JF (1974) cutting speed does not seem to be a critical
controlling factor for the production of veneer. However, he recommends using a
moderately slow speed if the tightness of veneer and quality of surface are
important. Another study performed by Dundar et al. (2008) showed that
increasing cutting speed decreased significantly the average roughness. Cutting
speed should be as fast as possible to obtain smooth veneer. In this study,
increasing cutting speed from 0.1 m/s to 1 m/s increased the value of roughness,
whereas when cutting speed was increased to 2 m/s tend to decreased the value of
roughness. This phenomenon may be caused by the knife and bar setting process
that is not always exactly the same or can be caused by the presence of knots. The
presence of the knots in cutting process by using slow to moderate cutting speed
allows the vibration which can lead to poor quality of surface. These vibration
may caused by variation in wood density between the knots and wood
surrounding it. By increasing cutting speed, the vibration that occurs can be
reduced because the knife has enough force to cut the knots.
Figure 15 Influence cutting tool wear on surface roughness (up: cutting with
sharp knife; bottom : cutting with dull knife)
Based on Figure 14, it can be seen that the provision of pressure bar could
reduce surface roughness value of veneer. Dundar et al. (2008) state that in rotarycut veneer manufacturing, wood tends to split along the grain during cutting
process. This splitting causes the formation of vertical cracks (lathe checks) and
produce rough veneer. Utilization pressure bar could keep cutting process remains
on track and avoid wood to split. However, proper adjustment process is required
to obtain the smoothness veneer. The excessive compression of bar may lead
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rough surface and cause high cost of energy due to extreme friction during cutting
process. In this study the best results for surface roughness were obtain from
pressure bar 10%.
In contrast to the results obtained on the cutting forces, cultivar Lambro
produced the best surface quality while I214 tends to produce the worst. Bakar
(1996) states that a good cutting process occurs when knife success to cut wood
cells on its cutting track. In general, at the same cutting conditions, wood with
higher density will result in better quality of cuts. This is due to wood with high
density have thicker cell walls so that it strong enough to withstand pressure
during cutting process. This allows the knife to split the cell so that it can be
produced either a uniform thickness and better surface quality because there is no
cell or wood fibers is torn. Increasing and lowering temperatures tend to degrade
the quality of the surface while the type of bar does not significantly affect the
surface finish since the measurement is made on the loose side.
Lathe Check (Depth)
The main effects for each level of parameter on lathe check are shown in
Figure 16. Based on S/N ratio, the best choice for lathe check depth is obtained at
condition as followed; at 0µm tool wear, low cutting speed, high pressure bar,
cultivar I214, room temperature, and with angular round bar.
Figure 16 The optimum is a minimum S / N graph for cracks (from left to right
edge of the tool, cutting speed, pressure bar, cultivar, temperature, type of bar)
Based on Figure 16, it can be seen that the value of S/N ratio for pressure
bar increase dramatically from PB0 (-35,378) into PB5 (-30,574), and then follow
to PB10 (-28,602). These value means that pressure bar changes effect
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significantly on the lathe check depth, and the same trend (with reverse value) can
also be observed on the cutting speed parameter for each level.
Generally lathe check may be caused during peeling process by a tensile
stress field at the front of the cutting edge. It was explained by Corder SE and
Atherton GH (1963) that pressure bar in peeling process creates a field of
antagonist compression that tend to counteract the tensile bending stress on the
tight side of veneer. The greatest pressure of the bar is given, the shallowest crack
that appears on the veneer and vice versa. These compressive force also plays a
role in reducing or limiting splitting wood ahead of the knife edge. However, it
should be noted that giving too much pressure will lead to wood failure and
increase roughness on the veneer tight side. In this study, giving a pressure of
10% generate the most optimal result for lathe check depth (Figure 16, 17).
A
B
C
Figure 17 Lathe check at different level of pressure (A: without bar; B: pressure
5%; C: pressure 10%)
At the level of cutting tool wear, a sharp knife has a small edge radius so
that the blade can cut well, but in the case of a dull knife, the edge radius of the
knife