Tóm tắt luận án tiến sĩ research on dynamic parameters of circular saw in bamboo crosscutting process

The survey results of bamboo processing plants show that the bamboo cutting equipment is mainly used a circular saw, there are still many problems in the cutting process, which is a larg

VIETNAM NATIONAL UNIVERSITY OF FORESTRY

HOANG HA

RESEARCH ON DYNAMIC PARAMETERS OF CIRCULAR SAW IN

BAMBOO CROSSCUTTING PROCESS

DOCTORAL DISSERTATION SUMMARY

HA NOI, 2021

The dissertation is conducted at Vietnam National University of Forestry

The dissertation is defended in front of the scientific committee at the Vietnam

National University of Forestry

Date of doctoral dissertation defence:

The dissertation can be found at the National Library and the Library of Vietnam

National University of Forestry

Ha Noi, 2021

1 The problem statement

According to a report by the Department of Agro-Forestry Processing and Markets under the Ministry of Agriculture and Rural Development, Vietnam has about 1,000 bamboo processing enterprises and thousands of households producing handicrafts from bamboo Export turnover of bamboo products in 2020 will reach about 500 million USD, thereby creating a significant source of income for businesses and households

Currently, processing bamboo products has been mechanized, since then productivity and product quality have been increased, meeting export requirements However, the equipment used in bamboo processing technology still has some shortcomings that need to be overcome to create higher-quality products, thereby enhancing the added value of the products

The survey results of bamboo processing plants show that the bamboo cutting equipment is mainly used a circular saw, there are still many problems in the cutting process, which is a large cutting surface roughness, when cutting parts The pointed end is often scratched and unsmooth, in order to create a smooth surface, it must go through a grinding device

Besides, The circular saw used in bamboo processing is the one used in woodworking, because the structure of bamboo has different characteristics compared to another types of wood, requiring more appropriate cutting equipment This is the aim of research

Currently, the research works on the equipment in bamboo processing are still limited, there is not alot of deeper studies on the dynamics of the bamboo cross-cutting circular saw In order to have a theoretical basis for perfecting the bamboo circular saw, it is necessary to study the dynamics in order to determine the optimal parameters of the bamboo circular saw when cutting

With the reasons stated above, the thesis finds that it is very necessary to study the process of cutting and cutting bamboo with a circular saw Eventually, I chose and conducted the research topic: "Study on some dynamic parameters of circular saws during bamboo cross cutting"

2 Research objectives of the dissertation

Building a model, setting up a system of dynamic equations of the circular saw cutting bamboo, solving the dynamic equations, from which to calculate and determine some reasonable kinetic and dynamic parameters of the circular saw to improve productivity and cutting surface quality

3 New findings of the dissertation

1 The dynamic model has been built, the system of differential equations for the motion of the saw blade in the process of cutting bamboo has been established, the stiffness of the saw blade has been calculated, and the results of the investigation of the system of differential equations have been established The motion of the saw

blade shows that at the rotational speed of the saw blade varying in the range of 3500-4500 rpm, with the angular momentum of the saw blade is the largest

2 The vibration calculation model of the saw blade has been built, the system's vibration differential equation has been established along with its solution, and the horizontal vibration amplitude of the saw blade has been investigated in the time domain Using Matlab-simulink software, a solution has been proposed to reduce the vibration of the saw blade

3 A model of experimental study of the dynamics of a circular saw blade has been built, and some dynamic parameters of the circular saw have been determined to solve problems and verify the computational models Theoretical approach, and experimental model also can be used to study on cutting bamboo

The experimental formula has been developed to determine the specific shear resistance and the surface roughness of the cutting section, and the reasonable parameters of the bamboo cross-section saw have been determined including; cutting angle δ = 48.50; grinding angle of main cutting edge β = 29.50; Rotating speed of saw blade v = 4150.8 rpm, pushing speed U=0.12m/s and motor power N=1.854 kw with the above reasonable parameters for minimum cutting resistance, quality cutting surface is improved

4 Scientific significance of the research results of the thesis topic

The research results of the thesis project have built a model, established the equation to calculate the force acting on the elements of the cutting teeth, the system of differential equations of motion of the saw blade, the system of vibration equations of the saw clade to investigate the influence of some parameters of cutting teeth, the rotational speed of the saw blade on dynamics functions of the circular saw when cutting bamboo Theoretical survey results and experimental research have identified a number of reasonable parameters of the bamboo cross-section saw, which can be the scientific basis for the calculation, design and manufacture of cross-sectional circular saws used for cutting some bamboo species

in Vietnam

5 The practical significance of the thesis

The research results of the thesis can be used for the design and manufacture of bamboo circular saws, in addition, they can also be used as references for establishments of and other facilities related to bamboo processing in Vietnam

Chapter 1 STATE OF THE ART 1.1 Overview of researches on bamboo crosscutting saws

1.1.1 Overview of research works on circular saws in the world

In the world, there are many research works on circular saws, but only focusing

on the vibration of the saw blade, the cutting speed of the saw blade, there only are

circular saw for cutting bamboo

1.1.2 Overview of research works on circular saws in Vietnam

Wood cutting has been studied by many scientists for a long time that has been relatively completed, but research on cutting bamboo is still limited, in which research on cutting bamboo with a circular saw has not yet been published But bamboo has a vascular structure like in wood, so the principle of cutting bamboo can be based on the principle of cutting wood

1.2 Research contents

In order to achieve the research objectives stated above, and based on the limitations and scope of the study, the research content is set out as follows:

1.2.1 Theoretical research

The content of theoretical research addresses the following issues:

– Building a model to calculate the force acting on the elements of the blade in the process of cutting bamboo;

– Formulate the calculation equations for the force acting on the cutting tooth elements in the process of cutting bamboo;

– Determine the specific shear resistance, investigate the parameters affecting the cutting force ratio, working as a basis for calculating and designing the elements of the cutting teeth;

– Building a dynamical model of the saw blade's motion, setting up the differential equations of motion of the saw blade, examining the set of dynamic differential equations to draw the necessary conclusions;

– Build a model, set up the vibration equation of the saw blade, investigate the set of equations to propose solutions for anti-vibration of the saw disc to improve the quality of the cutting surface

1.2.2 Experimental study

Experimental results have been calculated according to the theory and determine the shear force, the specific shear force in the process of cutting bamboo From the experimental results, some optimal parameters of cutting teeth have been determined, so the content of the experimental research includes the following issues:

– Measure the force acting on the cutting teeth when cutting the bamboo to test the results that had already been calculated based on the theory approach;

– Measure the vibration of the saw blade when cutting horizontally to verify the theoretical calculation model;

– Determine the specific cutting resistance as a basis for calculation to determine the optimal parameters of the cutting edge;

– Determine the reasonable pushing speed, cutting speed and motor power for the bamboo cutting cicular saw

Chapter 2 Kinematics and dynamics of the bamboo crosscutting process

2.1 Determination of the forces acting on the cutting teeth during crosscutting bamboo

2.1.1 Modeling the force acting on the cutting elements of the saw tooth

The diagram of the force acting on the elements of the cutting teeth is shown in Figure 2.1

Figure 2.1: General diagram of the total forces acting on the elements of the cutting

teeth of the saw disc The sum of the forces acting on the cutting elements is determined by the following formula:

)2

2 2 2 1

1 1

2 2 2 1

1 1

h s t m s

t m

h s t m b s t m

Q Q Q Q Q Q Q

P P P P P P P P

Where : Pm1; Qm1 - Cutting force and thrust acting on the cutting tooth tip;;

Pt1; Qt1 - Cutting force and thrust acting on the front face of the cutting tooth;

Ps1; Qs1 - Cutting force and thrust acting on the back face of the cutting tooth;

Pb - Cutting force acting on saw blade;

 - Main cutting edge , - rear angle of the main cutting edge,

 - Grinding angle of the main cutting edge,

γ - front angle of the main cutting edge,

2.1.2 Diagram of the total forces acting on the cutting tooth

The diagram of the total forces acting on the cutting teeth, chipless cutting is shown in Figure 2.2

Figure 2.2: Diagram of the total forces acting on the cutting edge during cutting

process

2.1.3 Components of the force acting on the cutting tooth

According to the principle of wood cutting [21], there are 3 basic force components acting on the cutting teeth:

a) Force acting on the tip of the blade

At point B, the deformation is the largest, so the maximum stress causes the bamboo fiber cells to be destroyed At the point N and M, the deformation is smaller, so the stress is smaller, so the pressure distributed on the cutting edge

is zero Thus, to facilitate the calculation process, the thesis divides pressure into two parts:

+ The part is evenly distributed in arcs AB and BC with pressure P1 and P2

in figure (2.3);

+ The part is distributed according to the law of cosine in arcs NI and IM, with pressures (Po - P1) and (Po - P2)

b) Force acting on the cutting edge front surface

According to the principle of wood cutting, the force acting on the front face is distributed according to the polygonal shape AGHN, to facilitate the calculation is divided into two parts:

- The distribution follows the parallelogram AGZN with pressure , (Figure 2.3);

- The distribution follows the triangle NZH

c) Force acting on the back of the blade

According to the principle of wood cutting, the force acting on the back of the blade is distributed in a triangle CC1d with the largest pressure at C being P2 2.1.4 Determination of the total force acting on the cutting tooth

d

C 1

After determining the impact forces on the nose, front, back, and side of the cutting edge, replace the formulas (into formula (2.6), after calculating the reduced transformation, we get the total force formula cutting P and pushing force Q acting on the cutting teeth when cutting bamboo is as follows:

2 1

1 cot

cos 4

2

sin

4

) 2 cos(

)(

2 ( ) 2 ( ) 2

sin(

) 2 ( 4

) 2 )(

(

2

1

2 2

2 1 2

2 2

2 0

B h f

B g

l

F

f

f g B

C g

EB l

L

hE

f

P P

B

Q

t cd

From the formula (2.32), (2.33), there are the following conclusions:

In the process of cross-cutting bamboo, the blade performs a complex cutting process, many cutting angles and cutting edges simultaneously join to form the cutting chip The formula for total forces acting on the cutting edge (2.32) is established by taking into account most of the factors involved in the cutting process In the formula of total force acting on the cutting teeth (2.32), there are many influencing factors, these factors affect the cutting force differently The law

of influence of factors on the shear force is shown in formula (2.32), to find the law

of influence of the parameters on the shear force, it is necessary to investigate the formula (2.32), the results are basis to calculate the optimal parameters of the blade and cutting power

2.2 Kinematics of a circular saw for cutting bamboo

2.2.1 Kinetic relationship between saw blade cutting speed and bamboo push speed a) Calculation model of the circular saw when cutting

Calculation model of the kinematic relationship between shear speed and thrust speed is shown in Figure 2.3

(2.32)

(2.33)

Figure 2.3: Calculation model of a circular saw when cutting bamboo b) Kinetic relationship between the cutting speed of the saw blade and the pushing

speed of the bamboo

Assuming that the shear rate vector V has the same direction as the line connecting

the tooth vertices, the vector →𝒖 forms an angle . with the vector V

During the cutting process with time interval t0, point A moves to B with a travel

distance t (tooth step), and at the same time B also moves to point D, the displacement

distance is BD=C called is the displacement of a tooth or the amount of chip intake of a

The chip thickness is the distance between the two orbits of the two saw teeth In

Figure 2.9, that distance is MB = h (chip thickness) h=C.sin1 In which:

1- Angle formed by the orbit of the tooth tip with the direction of the vector →𝑢

Since u is much smaller than v, then 1= Therefore:

ℎ = 𝐶 𝑠𝑖𝑛 𝜑 = 𝑡𝑢⋅𝑠𝑖𝑛 𝜑𝑉

Relation of thrust speed and pitch: 𝑢 = 𝑡⋅𝑠𝑖𝑛 𝜑𝑉⋅ℎ (2.35)

From the kinematic relationship of the bamboo cross-section, the following

observations are made:

- The push speed of bamboo into the saw is proportional to the cutting speed,

inversely proportional to the tooth pitch, when the cutting speed is large, the

pushing speed is high, thereby increasing the cutting productivity, when the tooth

pitch is large, making the thickness of cutting chip larger, and pushing speed

smaller

2.2.2 Building a kinematic model to calculate the arc length and cutting area

at a bamboo cross-section

First formula problem: Given two circles with centers O and O1 with radius

R and d, respectively (R > d) Let L be the OO1 distance (Figure 2.4) Let's calculate the length L:

Figure 2.4: Diagram of calculating the arc length of the saw blade with bamboo

So in this case we get S = α.R 2 + β.d 2 - R.L.sinα (2.44)

Second problem: The saw blade is a circle with center O and radius R The donut shape is limited by two circles of bamboo with the same center O1 with radius d1 and d2 (with d2 < d1 < R) The donut moves on a straight line with a distance of h from O, with constant speed v, it is necessary to calculate the length of the circumference of the circle with center O inside the donut shape and the area of the donut inside the circle with center O by time t

Figure 2.5: Diagram to calculate the contact area of the saw blade with bamboo

We consider only the time during which the donut shape is at the starting position (a) of the cutting process and at the end (b) Thus, the donut shape travels the distance:   2 2   2 2

 

2.3 Dynamics of circular saws for crosscutting bamboo

2.3.1 Building a dynamic model of the circular saw during crosscutting

The system has 3 links, including 2 rotating joints and one translational, the dynamic model of the bamboo cross-section saw is shown in Figure 2.6

Figure 2.6: Dynamic model of a circular saw for cutting Symbols on figure 2.6:

M1- Active torque of shaft I (motor shaft);

M2- Active torque of shaft II

M2 M1 , in which -belt drive efficiency

M c- The shear resistance moment caused by the bamboo cutting force

M c F R c where, R is the radius of the saw blade

F d - Pushing force of bamboo in to saw blade;

Fms - The friction force of the table pushing the bamboo into the saw

); (F ms m gf3 3);

f3- Coefficient of friction of the table pushing force of the bamboo into the saw blade

F c- Shear resistance of bamboo (value depends on the type of bamboo)

2.3.2 The differential equation of motion of the saw blade

The motor drives the saw disc with a power of W0 and transmits it through the belt to create a rotational torque M for the saw disc and the maximum angular speed for the blade

Figure 2.7: Calculation diagram of motion kinematics of saw discs cutting through

bamboo a) Kinetic energy of the saw blade

Kinetic energy of volume element dm at coordinate (x,y,z) can be calculated:

where J2 moment of inertia about the center of a disc of uniform thickness, radius

R2, mass density  (kg/m2), with 1

2

R R

Figure 2.8: The calculation diagram potential energy of the circular disc

The force component perpendicular to the disc surface of centrifugal force vector dN is dN with dN dN.sin dN. , the force component causes a moment

with: dM LT  ( r R ).dN 1  (2.55)

From (2.54) and (2.55), Integrate both sides of the equation (2.55) on on the

part of volume V satisfying R 1 ≤ r ≤ R 2 Since the saw disc has the same thickness

in about R 1 ≤ r ≤ R 2 so dm .r.dr.d

The component perpendicular to the blade surface of the centrifugal force dN is

dN,with dN dN.sin dN. , this force component causes a moment:

LT 1

Substitute (2.54) into (2.55) and integrate both sides (2.55) over the part of volume

V according to R1 ≤ r ≤ R2 Since the saw blade has the same thickness in the

range R1 ≤ r ≤ R2, so Result is investigated:

c LT C 2 C LT 2

       (2.59)

c) Work of the external force

- Work generated by the bamboo cutting resistance and the friction force

between the saw blade and the bamboo: Ac

If the ratio of the bamboo cross-sectional force is K (N/mm2), the bamboo

shear force will now be: F c K.h h n c cua rc , (N)

(2.61)

With : h cưa - saw circuit thickness, (mm)

Force F c and momentum M c

With R 2 - Radius of saw blade, (m)