Toolpath Optim5 axis machine turbine ion for a Turgo Turbine Runner

8/16/2019 Toolpath Optim5 axis machine turbine ion for a Turgo Turbine Runner

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5-Axis Toolpath Optimization for a Turgo Turbine Runner

by

May Thant Sin

A thesis submitted in partial fulfillment of the requirements for the

degree of Master of Engineering in

Industrial and Manufacturing Engineering

Examination Committee: Assoc. Prof. Erik L. J. Bohez (Chairperson)

Dr. Mongkol Ekpanyapong

Dr. Than Lin

Dr. Ketsaya Vacharanukul (External Expert)

Nationality: Myanmar

Previous Degree: Bachelor of Engineering in

Electronic and Communication EngineeringYangon Technological University

Myanmar

Scholarship Donor: Ministry of Foreign Affairs, Norway

Asian Institute of TechnologySchool of Engineering and Technology

Thailand

December 2014


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ACKNOWLEDGEMENTS

First of all, I would like to express my gratitude to all those who have helped me in all

aspects during the past couple of years. Especially to my advisor Assoc. Prof. Erik L. J.

Bohez for the fruitful comments, remarks, engagement, teaching and thorough guidance

in the pursuit of this master thesis. Also to other committee members: Dr. MongkolEkpanyapong and Dr. Than Lin for their helpful comments, guidance and pointing out

what I should emphasize more and the external expert, Dr. Ketsaya Vacharanukul for the

great assistance throughout the manufacturing periods of the prototype in National

Institute of Metrology and also for the useful evaluation for my thesis. To Mr. Somchai

Taopanich who has contributed so much to my accomplishment of the whole process by

sharing his experience as a machine expert and lab specialist and giving helpful advice to

me whenever I needed. To Mr. Choosak Ngaongam for his hearty assistance to me from

the beginning to the end: from the installation of software to the application of them and

the advice to find the alternative way to solve problems whenever I have requested. To

Mr. Kiattisak Sakulphan for giving a hand to me while I asked for the reference documents

and also the advice from him. Furthermore I would like to thank to the responsible personnel from the National Institute of Metrology who have allowed me to utilize their

machine and helped me accomplish my work flawlessly.

In addition, I would like to show my special thanks to Ministry of Foreign Affairs Norway

for giving me the chance to pursue further study in AIT so that I can contribute much more

not only to the betterment of my life but also the welfare of the society.

Finally, I give praise to my parents for their endless support and my lovely friends. Without

the encouragement of those peoples, I cannot stand all the way long to see the beautiful

end. As one embraced me with words, life is a climb but the view is great. I will be grateful

forever for all your love and never forget such a lovely support.


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ABSTRACT

The Turgo turbine model is developed based on the parametric dimensions from the one-

dimensional calculation using Solidworks. It is then imported into MasterCam to generate

tool path conducting ruled surface milling. After that, it is post-processed in Mathamatica

based on Inverse Kinematic. Using the NC file with G-code, the verification isimplemented in Vericut. When tool path is optimized, the prototype is produced with Haas

5-Axis machine with flank milling.

The e-Design concept is applied during the optimization process. The integrated e-design

phase and manufacturing phase is working in parallel. The designed model is revised

several time according to the optimization of tool path generation based on the verified

results using the virtual 5-Axis machine in Vericut with good surface finish, less

manufacturing time, the avoidance of tool break, tool wear, and less scallop. The optimized

machining sequence includes roughing of the extra materials first, then finishing the 20

blades using flank milling 10 mm bull-end tool. The total manufacturing time for

implementing the optimized too path is 4 hours and 45 minutes. With this tool path, thesurface finish, the manufacturing time and the collision avoidance with less tool travel are

optimized. Still, there is one scallop in the bottom as the big tool effect. However it is not

the critical since it has no affect the flow mechanism and can be developed later.

Keyword: Turgo turbine, 5-axis machining, Optimization, e-Design, Runner blade


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TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

ACKNOWLEDGEMENTS iiABSTRACT iii

TABLE OF CONTENTS iv

LIST OF FIGURES vi

LIST OF TABLES

LIST OF ABBREVIATIONS

LIST OF SYMBOLS

viii

ix

x

1 INRODUCTION 1

1.1

Background 1

1.2 Statement of the problems 2

1.3

Objectives of the study1.4 Scope and limitations

22

2 LITERATURE REVIEW 3

2.1 Turgo turbine

2.1.1 Parametric modelling of Turgo turbine

2.2 Flank milling with 5-axis machining

2.2.1 5-axis machine

2.2.2 Flank milling

2.3 e-Design process

3

4

7

7

8

11

3 APPROACH TO THE OPTIMIZATION PROCESS 133.1 Work flow of the whole optimization process 13

3.2 Application of e-Design 14

4 OPTIMIZATION PROCESS 16

4.1 Parametric modelling: One-dimensional calculation for

the turbine design

4.2 CAD/ CAM Iteration (1)

4.2.1 Mechanical design

4.2.2 Toolpath generation


4.3.1 Redesigned process

4.3.2 Toolpath regeneration

4.3.3 Post-processing

4.3.4 Verification of tool path for Turgo turbine revision


4.4.1 Design and experiments


4.5.1 5-axis machining

4.5.2 Comparison of machining time, scallop, undercut

and overcut

4.5.3 Optimized setup

16

21

21

24

26

27

28

30

36

41

41

45

46

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5 CONCLUSION AND RECOMMENDATION5.1 Conclusion

5.2 Recommendation

54

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55

REFERENCES

APPENDIXES

56

58


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LIST OF FIGURES

FIGURE TITLE PAGE

Figure 1.1 The torque generation mechanism for: (a) Pelton turbine and

(b) Turgo turbine

2

Figure 2.1 Drawing of the 1920 Crewdson Turgo design showing the inlet

plane and cut section with jet trace on the inlet wheel plane

shaded

3

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 2.7Figure 2.8

Figure 2.9

Figure 2.10

Figure 2.11

Figure 2.12

Figure 2.13

Figure 2.14

Figure 3.1

Figure 3.2

Figure 4.1

Figure 4.2Figure 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Figure 4.10

Figure 4.11

Figure 4.12

Figure 4.13

Figure 4.14

Figure 4.15

Figure 4.16

Figure 4.17

Figure 4.18

Figure 4.19

(a) Earliest design of Giovanni Branca (b) Sketch of the Turgo

turbine design

Turgo runner configuration:(a)Meridian plane

(b)Velocity triangles

Free body diagram of Turgo shaft

Diagram of blade curve

Water jet and blade curve

5-axis machine with linear and rotation axis(a) Vertical machining and (b) Horizontal machining

Kinematic change diagram

Undercut and overcut

Tool movement and cutter location

Tool orientation and undercut

Tool cross-section

Reduction of undercut

Methodology of tool path optimization of Turgo turbine runner

Flow chart for the optimization process

Cross-section of Turgo runner

The inlet angle, outlet angle, and the velocity diagramOne-dimensional calculation in Excel

Design process of Turgo turbine

Tool selection (a) 6 mm bull-end tool and

(b) 10 mm bull-end tool

Tool path generation using the Turgo turbine

Design process of Turgo turbine revision model

Tool path generation for Turgo turbine revision model

Tool path generation for 20 blades

Step-by-step formatting of CL file

Haas 5-axis machine and the coordinate systems

Positive B rotation along Z-axis

Positive A rotation along X-axis

Machine setting (a) Travel limits and (b) Tooling offset

(c) 6mm milling tool parameter (d) 10mm milling tool parameter

(a) Blank part and (b) the fixture

Toolpath verification for combination of B1B3A3 rotation angle

translation

Toolpath verification for combination of B4B1A1 rotation angle

translation

Rotation of tool path in 19.5 degree

Design process of creating the blade with concave and convexsurfaces

4

5

5

6

6

78

8

9

9

10

10

11

13

14

16

1720

23

25

26

28

29

30

33

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35

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Figure 4.20

Figure 4.21

Figure 4.22

Figure 4.23

Figure 4.24

Figure 4.25

Figure 4.26

Figure 4.27

Figure 4.28

Figure 4.29

Figure 4.30

Tool path verification for blade with 7 concave layers in 1.5

degree


degree


degree(a) HAAS machine (b) The assembly of blank part and fixture on

the machine

Modification of post-processor

Vibration effect

Combination of 4 roughing cuts and 1 finishing cut

Demonstration of scallop and surface finish of different setup

Demonstration of overcut (a) 0.5 mm overcut on convex surface

(6 mm ø cutter) (b) 0.8 mm overcut on convex surface (10 mm ø

cutter)

Design process of the optimized model

Demonstration of machining process

43

44

45

46

47

47

48

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51

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LIST OF TABLES

TABLE TITLE PAGE

Table 4.1

Table 4.2Table 4.3

Important parameters for CAD modelling

Inter-distance between bladesComparison table of manufacturing time

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2449


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LIST OF ABBREVIATIONS

AIT Asian Institute of Technology

CAD Computer Aided Design

CAM Computer Aided Manufacturing

CL Cutter Location NIMT National Institute of Metrology

NURB Non-Uniform Rational B-Spline


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LIST OF SYMBOLS

Ds

d

dh

dt

b1 B

β1a

Β2a

Β1t

Β2t

Β1h

Β2h

R a

R t

R h

cH

Qkn

u1

Diameter of the runner

Diameter of the jet

Diameter of the hub

Diameter of the tip

Inlet WidthRunner Width

Inlet Angle (Average)

Outlet Angle (Average)

Inlet Angle (tip)

Outlet Angle (tip)

Inlet Angle (hub)

Outlet Angle (hub)

Arc Radius (Average)

Arc Radius (tip)

Arc Radius (hub)

Mean Velocity of JetHeight of Water

Nominal Flow Rate

Runner Speed

Nozzle Efficiency

Circumferential Runner Speed

(mm)

(mm)

(mm)

(mm)

(mm)(mm)

(degree)

(degree)

(degree)

(degree)

(degree)

(degree)

(mm)

(mm)

(mm)

( ⁄ ) (m)

(3 ⁄ ) (rpm)

(3 ⁄ )


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CHAPTER 1

INTRODUCTION

1.1 Background

Nowadays the world is growing with a tremendous rate and the developments in every aspectof the world, especially in the physical world, was amazing. However, thanks to this, the

need for energy especially the needs for electricity has become most demanding factors. As

regards this case, in order to fulfill the world electricity requirement, there are four way to

produce electricity from the wind (wind power), the water (hydro power), the sun (solar

power) and the fossil fuel.

Out of these electricity production method, hydro power is the free and renewable energy

source which can be utilized effectively to generate electricity from the falling water or

running water using Turbine. It stands as a clean source for the production of electricity since

it never lead to the air pollution like power plants that burn fossil fuels, such as coal or natural

gas. It uses the Earth’s water cycle to generate electricity because movement of water as itflows downstream creates kinetic energy that can then be converted into electricity. It’s a

clean source for the production of electricity. It doesn’t pollute the air like power plants that

burn fossil fuels, such as coal or natural gas.

Water turbine extracts electricity from the fluid flow by converting the kinetic energy of

water into the potential energy which is converted into electrical energy by the attached

generator. Depending on the type of energy at the inlet of the turbine, they can be classified

into two categories: Impulse turbines which convert the kinetic energy of a jet of water to

mechanical energy and Reaction turbine which convert potential energy in pressurized water

to mechanical energy.

In this respect, the Turgo turbine which will further be investigated for the toolpath

optimization in this paper is one of the Impulse turbines. A Turgo runner looks like a Pelton

runner split in half. For the same power, the Turgo runner is one half the diameter of the

Pelton runner, and so twice the specific speed. The Turgo can handle a greater water flow

than the Pelton because exiting water doesn't interfere with adjacent buckets. The specific

speed of Turgo runners is between the Francis and Pelton. Single or multiple nozzles can be

used. Increasing the number of jets increases the specific speed of the runner by the square

root of the number of jets (four jets yield twice the specific speed of one jet on the same

turbine).

Both Pelton and Turgo turbines generate their torque through the change in momentum of

an incoming jet of water. Turgo turbines differ from Pelton turbines by the angle of the

incoming water jet. In Turgo turbines the jet enters and exits the wheel plane at an acute

angle whereas in Pelton turbines the jet remains in the same wheel plane. Therefore, the

water in a Turgo turbine exits from the bottom of the wheel and does not interfere with the

incoming jet. This allows the diameter of the wheel to be smaller for a given jet diameter,

increasing the rotational speed. (Williamson, Stark, & Booker, 2013)


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Figure 1.1 The torque generation mechanism for: (a) Pelton turbine and

(b) Turgo turbine (Williamson, Stark, & Booker, 2013)

1.2 Statement of the problems

At present, the manufacturing of the Turgo turbine had been started under the interestingtopic in the commercial field. However owing to the complex geometry of the turbine, there

are less manufacturers in the global market. In fact, there is no local manufacturer for the

Turgo turbine in the Thailand yet. What is more, although the turbines are manufactured

with the application of the particular technologies, no optimal tool path is performed for

cutting the runners in the five-axis machine yet. As a matter of fact, if the tool path is

optimized, it would breed great benefit to the manufacturers since it will increment the

productivity reducing cost and time and also improve the quality of the runner with the better

surface finish. In this regard, since the tool path is optimized from the manufacturing aspect,

to reduce the long implementation period for the optimization, the concurrent engineering or

E-design concept is applied. By then, the whole optimization is carried out effectively by

executing all CAD/ CAM process: CAD modelling, tool path generation, post-processingand verification and finally 5-axis machining in parallel.

1.3 Objectives of the study

The main objective of the study is to optimize the 5-axis tool path of the runner of the Turgo

turbine for the better accuracy, minimum cutting time with shortest tool path along with no

collision, less scallop on the hub surface and minimal undercut/overcut on the blade.

1.4 Scope and limitations

The parametric modelling of the Turgo turbine is based on the one-dimensionalcalculation from the literature review.

Only the optimization of the 5-axis tool path for a Turgo turbine runner from the

manufacturing point of view will be emphasized in this study.

The prototyping of small runner using wood resin as a material for the blank part is

aimed at due to the objective of the study is to find optimal tool path only and not to

use it in the field and also thanks to some machine constraints such as machine range,

maximum power, tool size, etc.

The whole optimization process will be implemented by using four softwares mainly

as follows: The modelling of the turbines by using Solidworks, the tool path

generation and optimization by MasterCam, the post-processing by Mathematica, theverification by Vericut.


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CHAPTER 2

LITERATURE REVIEW

Nowadays, as the requirements of the electricity for the population have been increased, the

demand for the hydropower plants became higher and higher all over the world. In this

respect, the improvement to effective manufacturing technology for the water turbinecontribute not only to the manufacturers but also to the consumers in a positive way. Thanks

to this, the tool path optimization of a Turgo turbine runner is executed using 5-axis

machining technology. Therefore, in this chapter, the mechanical design and manufacturing

method will be discussed.

2.1 Turgo turbine

As regards Turgo turbines which will be emphasized in this study, it is the impulse turbine

type. The Turgo wheel is basically an improved version of the Pelton. It was designed by

Eric Crewdson in 1920. The maximum efficiency of an impulse wheel is achieved when the

velocity of the runners at the center line of the nozzle is half the velocity of the incomingwater. To achieve the highest velocities the ratio of the diameter of the wheel and the

diameter to the center of the nozzle should be as small as possible. A Turgo runner looks like

a Pelton runner split in half. For getting the same power, a Turgo runner being one half the

diameter of a Pelton runner, it can twice the specific speed of Pelton’s. This makes the unit

cheaper and reduces the amount of gearing necessary. Turgo can handle a greater water flow

than the Pelton because exiting water doesn't interfere with adjacent buckets. The Turgo has

an efficiency of over 80% and runs on head of 18.3 meter or more.

Figure 2.1 Drawing of the 1920 Crewdson Turgo design showing the inlet plane and

cut section with jet trace on the inlet wheel plane shaded

(Anagnostopoulos & Papantonis, 2008)

It doesn't need an airtight housing like the Francis higher specific speed and can handle a

greater flow than the same diameter Pelton wheel operate in a head range where the Francis

and Pelton overlap. It possesses higher angular velocity due to smaller runner diameter. It

can avoid the turn multiplier in the coupling with electrical generator. Moreover, it can

decrease cost and increase mechanical reliability of the system.


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Figure 2.2 (a) Earliest design of Giovanni Branca (b) Sketch of the Turgo turbine

design (Anagnostopoulos & Papantonis, 2008)

By using Turgo turbine, all initial potential energy can be converted to kinetic energy with a

nozzle. High speed water jet is directed on turbine blades which deflect and reverse the flow

resulting the impulse that spins the runner and imparting energy to the shaft. The moving

fluid forces on the blade rotate the rotor of the generator and convert the mechanical energy

of the shaft to electrical energy by the attached motor.

2.1.1 Parametric modelling of the Turgo turbine

In order to achieve the parametric model of the turgo runner, the dimensions of the runner

are calculated based on the nominal flow rate (Q), net head (H) and shaft rotation speed (n).

The jet diameter (d) can be obtained from the nominal flow rate (QK ) and mean velocity of

the jet (c).

Where is the efficiency of the nozzle and taken as 0.97.

Then the runner diameter can be calculated from circumferential speed (u 1) of the runner

which is related to jet velocity (c).

After getting the jet diameter and runner diameter, the diameter of the hub (dh) and tip (dt)

can be obtained.

dh = Ds – d

dt = Ds + d


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Moreover the inlet width (b1) can also be obtained since it is larger than jet diameter (d) (b 1

= 1.2 d ) to make sure water jet entrance for highest flow rate. In addition the runner width

(B) in the axial direction is taken as 1.45 d. Then the blade inlet and outlet angles, β1 and β2

can be computed form the corresponding velocity triangles (Fig 2.3 b).

Figure 2.3 Turgo runner configuration: (a) Meridian plane (b) Velocity triangles


Figure 2.4 Free body diagram of Turgo shaft

(Kiattisak, Bohez, Choosak, & Somchai)

For Inlet Angle β1 ,

ø = 90 – α


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β1 = 180 – ø – 65

For Outlet Angle β2,

β2

Then to get the center points of the curves: hub, average and tip, that represent the blade, the

calculation is implemented based on the runner width (B). The curve of the runner is circle

since its derivative is linear function which matched with the requirement of the linear

variation of the tangent. There the radius of each circle also needed to find out. The following

are the formulae used to calculate the radius and center point location of each circle.

Figure 2.5 Diagram of blade curve

Z = R cos β1

X = R sin β1

After that, in order to find the number of blades to equip in the whole assembly, the concept

that the water coming from the water jet hit the three blades was applied.

Figure 2.6 Water jet and blade curve


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Finally the CAD model of the Turgo Turbine can be designed based on the calculated result

of the above-mentioned one-dimension calculation. (Anagnostopoulos, J. S., & Papantonis,

D. E., 2008)

2.2 Flank milling with 5-axis machining

The utilization of 5-axis machining for the production of a Turgo turbine runner is

advantageous not only to increase the productivity of the product since it can implement all

the machining operation in single setup but also it can optimize the product with theenhancement of the part quality and the tool by setting the cutting speed and depth of cut

conditionally. What is more, it is very useful for the mass production for having the

automotive tool change (ATC) system. Today machines with a tool exchange time below 1

s are available. (Bohez, E. L., 2002). Due to this, this technology has already applied

successfully in the manufacturing of complex parts such as turbine blades or impellers (Lin,

T., Lee, J. W., & Bohez, E. L., 2009). In this respect, the term that 5-axis machining

comprises of all the processes from the selection of tool, the material, the generation of tool

path, the simulation of virtual machining. Only after the simulation, the possible problems

such as the collision of tool against part or jigs and fixtures and the undercut and overcut can

be inspected and avoided.

2.2.1 5-axis machine

The five degrees of freedom in 5-axis machining bring about more independency in

controlling the motion on the machine slides. Standard machines are ability to perform three

linear motions along X and Y axis of the working table and the tool axis along Z-axis, and

three rotational movement in A rotation around X-axis, B rotation around Y axis and C

rotation around Z axis. (Fig 2.7) Depending on the tool orientation, the machine can be

identified into two types: the vertical machine when the tool is in the vertical position (Figure

2.8 a) and the horizontal machine when the tool is in the horizontal position (Figure 2.8 b).

Figure 2.7 5-axis machine with linear and rotation axis (Bohez, E. L., 2002)


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(a) (b)

Figure 2.8 (a) Vertical machining and (b) Horizontal machining(Bohez, E. L., 2002)

The nature of working mechanism of a 5-axis machine can be represented with the kinematic

diagram of that machine since it is similar to two cooperating robots, one robot carrying the

work piece and one robot carrying the tool. The kinematic diagram which is also called the

chain diagram distinguish two groups of axes exclusively: the work piece carrying axes and

the tool carrying axes. The example of the kinematic diagram of the five-axis machine can

be observed in Fig. 2.9.

Figure 2.9 Kinematic change diagram (Bohez, E .L., 2002)

2.2.2

Flank milling

As regards Turgo turbine, the runner blades are created with ruled surface with three

reference curves: the hub, the average and the tip and a straight line sliding over the reference

curve. Therefore the application of flank milling is the most appropriate method since the

machining can be performed over ruled surface which is obtained by the motion of the rule


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on the guiding rail. In this case, the machining is implemented using the cylindrical cutters

with a large depth of cut but still using the minimum shortest tool, reducing the machining

and improving surface finish. According the previous record, the flank milling have

successfully applied for the machining of complex products such as aircraft structural parts,

turbine blades and other mechanical parts.

However, with the utilization of the flank milling through 5-axis machining, some problems

such as the interference owing the usage of the complex tool, the geometry errors likewise

overcut and undercut due the tool strength can be experienced too. Therefore the careful

selection of the milling tool for the machining and several solutions for the overcut and

undercut problem have been observed by many researchers.

In fact, the overcut is the over-identification of tool in the surface. (Harik, Gong, & Bernard,

2013) To make it clearer, some materials which should not be removed have been taken out

while cutting by the tool. On the contrary, the term undercut stand for the excessive material

which have not been removed and have to remove again. The illustration of undercut and

overcut is shown in figure 2.10.

Figure 2.10 Undercut and overcut (Harik et al., 2013)

Figure 2.11 Tool movement and cutter location (Bohez et al., 1997)


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Due to the linearization of the tool movement, the generation of curved real tool path being

out of tolerance creating the over and undercut is resulted when the real translation of tool

path is deviated from the actual tool end path. (Figure 2.11)

In 1997, Bohez suggested the smaller diameter of the cutter or the reduction of the angle θ

between the surface normal and isoperimetric line. Under this study, the isoperimetric lineis considered to be on a blade surface to be machine where the surface normal of each point

is not parallel forming the twisted ruled surface. (Figure 2.12). It can be seen that the

undercut occur because the tool cannot touch exactly to the twisted line AB since the tool

axis is straight.

Figure 2.12 Tool orientation and undercut (Bohez et al., 1997)

In this case, the maximum undercut is determined by R(1-cos θ) created by the tool tangent

at point B and the tool axis is parallel to the point AB where R is the radius of the tool.

(Figure 2.13) Therefore, it is observed further that changing the orientation of the tool can

reduce the maximum undercut into R(1-cos θ /2) however which in turn can create the smallovercut. To be more precise, in this method, the tool axis is located in parallel to the drive

surface while the tool is tangent to the ruled surface at point P on the respective isoperimetric

line. (Figure 2.14)

Figure 2.13 Tool cross-section (Bohez et al., 1997)


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Figure 2.14 Reduction of undercut (Bohez et al., 1997)

Concerning the avoidance of the collision, the right selection of the tool depending of the

tool geometry and the best combination of tool motion have to be applied. In addition, it isnoted that the machine motion have to be within the limit of the machine that it can travel

and the maximum movement limit of the axes in relation to one another. Acceleration must

be control to prevent backlash when an axis moves too fast due to the fact that linear motion

is always faster and more accurate than rotary motion. Moreover care must be taken while

machining since the cutting on the concave side have less tension on the runner rather than

cutting from the convex side.

2.3 e-Design process

The application of concurrent manufacturing method which is introduced by US department

of defense (DoD) in 1989 is found to be the best solution for the optimization process. Underthis method, the design phase and Manufacturing phase are working in parallel so that it

reduce the cost and time during the whole design and manufacturing process effectively.

(Siti Mahfuzah Mohamad, Ahmad Razlan Yusoff, 2013)

To be added, based on the concurrent engineering, the integration of the e-design and virtual

manufacturing was conducted for the development of the rotorcraft design. (Vu, N. A., Lin,

T., Azamatov, A., Lwin, T., & Lee, J. W., 2011)The concept is absolutely robust and efficient

that it fill the gap between theoretical design and practical aspects.

As regards the optimization of the Turgo turbine production, it begins with parametric one-

dimensional calculation then proceeding to the design phase, the post-processing process,

the virtual manufacturing and the production of prototype model with optimized tool path.

The blades are designed based on calculation, the tool path is generated with ruled surface

using swarf milling, and finally machining with flank milling. Several factors are considered

from the design to the manufacturing since it is designated to optimization. For example, to

cut the runner blade, it would be better to cut from the concave side first rather than cutting

from the convex side so that the force to the convex surface was reduced and it solve the risk

of breaking of the blade due to tool vibration. (Bohez, E., 1997)

Using concurrent concept as a fundamental, the design phase, the tool path generation phase

and the post-processing and verification phase are linked together. If there found to be globalor local collision with the machine or the tool defect, the problem of the undercut and


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overcut, the long production time and any other possible error in the process, steps can be

taken back to rewind the process up to the first design phase which will bring the prompt

effect to the virtual manufacturing step. Thanks to this, the whole process can be run together

continuously saving time and since the optimization can be done without the waste of time,

it also save the money to be spent.


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CHAPTER 3

APPROACH TO THE OPTIMIZATION PROCESS

3.1 Work flow of the whole optimization process

As aforementioned the objective behind carrying out this study is to optimize the tool pathto manufacture the runner of the turgo turbine. This chapter will present the approach to

achieve this objective.

The following figure (3.1) mentions methodology that will be implemented.

Figure 3.1 Methodology of tool path optimization of Turgo turbine runner

As showed in the Figure 3.1, the first step is to conduct the one dimensional calculation

required for the modelling of the Turgo runner. In this regards, the Microsoft Excel software

is utilized for the calculations using the formulae that has mentioned in section 2.1.1 of

Chapter 2. The turbine model is then created with Solidworks software based on the resulted

parameter from the calculation. After that, it is retrieved into MasterCam software as an

IGES model with NERB surface to be able to generate which is further be optimized for the

tool motion. The NCI (Numerical Control Intermediate) output file of MasterCam software

is converted into the delimited text file format to be post-processed with the utilization of

Mathematica software. Inverse Kinematic concept using the real machine offset is adapted

during the post-processing process. The output NC (Numerical Control) file of Mathematica

which include G-code is imported into the Vericut software where the tool path optimization

can be conducted with the utilization of virtual 5-axis machine with the exact specification

of the Hass 5-axis that the prototype of the turbine will be machining. Finally, the prototype

is manufactured using the HAAS VF-2TR 5-axis milling machine with shorter cutting timewith shortest toolpath and with no collision and less scallop.


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3.2 Application of e-Design

Figure 3.2 Flow chart for the optimization process


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In the endeavor to achieve the effective time management, the E-design or concurrent

engineering concept is applied to implement the optimization process as shown in Fig 3.2.

With this concept, after the parametric modelling using one-dimensional calculation is

finished, all the steps from the design of the turbine to the verification of the optimized tool

path have been conducted in parallel.

At first, as explained in the section 3.1, based on the data that is resulted from the parametric

calculation, the modelling of the Turgo turbine is done with Solidworks. In addition, the

reference model is created using the Solidworks software to be utilized in comparing the

blade model in the verification step. Moreover the fixture to clamp the work piece with the

working table of the 5-axis machine is also designed with that software. After that, the tool

path generation is implemented using MasterCam software using the IGES file version of

the turbine model with NURB surface. In this stage, the design is checked if there is any

global or local collision while cutting the blade using the specific milling tool. If the collision

occurred, the blade is redesigned. One revision of the turbine model is done at that check

point. As a matter of fact, a plenty of revision is done in this stage until the optimal tool path

is achieved. The optimization of tool have also conducted in the tool path generation process.The tool path from MasterCam is then exported as the NCI file format which is required to

convert into delimited text format with the cutter location data for X,Y, Z and the unit vector

i, j, k under code 11 so that it can further be post-processed using Mathematica software. In

the post-processing process, the cutter location file is retrieved into the NC (Numerical

Control) file including G-code by means of Inverse Kinematic. The G-code comprises of the

axial translation of X, Y and Z coordinate and A, B rotation of the 5-axis machine. It is then

used as the input to Vericut software in order to simulate the tool path verification process

with the usage of the virtual 5-axis machine which occupied the exactly the same geometry

as HAAS VF-2TR 5-axis milling machine that is used of the manufacturing of the prototype

of the turbine with optimal tool path using that G-code. Therefore, the NC file from the post-

processor is checked in this verification stage and if it is not optimized, the whole process islooped into either the tool path generation stage or even the modelling stage. Finally only

when the tool path is verified to be optimized though Vericut, the prototyping of the whole

turgo runner will be cut with the 5-axis machine. The 5-axis that is used for machining is

Hass VF-2TR 5-axis milling machine from National Institute of Metrology (NIMT).


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CHAPTER 4

OPTIMIZATION PROCESS

4.1 Parametric modelling: One-dimensional calculation for the turbine design

The parametric modelling is calculated using the one-dimensional formulae base on theliterature review of the previous researcher. For this, the fundamental parameter to be known

are net head (H), nominal flow rate (QK ), the efficiency of the nozzle (ϕ) and the speed of

the runner (n). In this case, since the emphasis of the study is to optimize the tool path, only

small turbine is created using net head of 50 m with runner speed 1500 rpm and nominal

flow rate of 0.03 cubic meter per second to provide 0.97 nozzle efficiency.

The turbine is designed based on the important dimension: the jet diameter (d), the runner

diameter (Ds), the inlet width (b1), the runner width (B).

Figure 4.1 Cross-section of Turgo runner (Anagnostopoulos & Papantonis, 2008)

At first the mean velocity of the jet (c) is computed to get the jet diameter (d) which is

based on that value.

Then the runner diameter is determined based on the inlet velocity which is approximate

half-time smaller than jet velocity.

In fact, the runner diameter stand for the diameter of the average arc to design the turbine

blade. Therefore the diameter of the hub arc can be determined with the subtraction of jet


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diameter from the runner diameter whereas that of tip arc with the addition of diameter of

the jet to runner diameter as follows.

Moreover the calculation for both inlet width (b1) and runner width (B) can also be

determined based on the runner diameter.

Then to find the dimensions of the three arcs: the hub, the average and the tip which will be

surfaced to get the ruled surface that can be machined later, the inlet angle β1 and outlet

angle β2 . In addition, The curve of the runner is circle since its derivative is linear function

and we want linear variation of the tangent. So it is alos required to determine the radius of

the circles(R) and the center points of each circle in X and Z coordinates.

Figure 4.2 The inlet angle, outlet angle, and the velocity diagram


For average arc,


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Then for determination of the radius of the arc and the center of the arc,

Simliarly

For tip arc which will be the furthest arc with the largest diameter which in turn will

determine the diameter for the blank park to be cut,


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Finally fo the hub arc,

However although it is important to find the dimensions which matter the most to determine

the blade geometry and mechanical design, to know the efficiency of the turbine and the power that can be generated by the turbine is still an interesting factors.

In this respect, the efficieny is determind by ratio of the intial velociy of the blade and the

final velocity of the blade.

Initial velocity of the blade = c = v1 = 30.37 m/sec

Final velocity of the blade = v2 = w2 sin β2a = 16.68 * sin 79.58 = 16.4 m/sec

Efficiency =

The power generated by the turbine will be determined as the multiplication of specific

weight of the liquid γ , the head H and the flow rate Q .

In this regard, to make the calculation more convinient and ediable, all one-diemensional

calculation are developed in Microsoft Excel. (Figure 4.3)


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Figure 4.3 One-dimensional calculation in Excel


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With the usage of the parameter that is obtained from the one-dimensional calculation, the

turbine model is designed in Solidworks. The critical dimensions for modeling turbine are

shown in Table 4.1. As mentioned in section 3.2, owing to the iteration steps to attain the

optimal tool path, several revision models are redesigned in this stage. Therefore the firstiteration process is carried out to check the tool collision in the tool path generation.

Table 4.1 Important parameters for CAD modelling

4.2.1 Mechanical design

The first revision model of Turgo turbine is created step by step as follows. In order to createthe concave surface, three arcs are the drawn on the three planes: Hub, Average and Tip

which are created from three circles with diameters 146.3 mm, 181.8 mm and 217.3 mm

respectively from center points 31.1 mm (Z axis) and 24.9 mm (X axis) for Hub arc, 31.1

mm (Z axis) and 24.9 mm (X axis) for Average arc and 48.4 mm (Z axis) and 59.4 mm (X

axis) for Tip Arc. (Figure 4.4 a) Then, by connecting these three arcs using the boundary

surface feature, the concave surface was created. (Figure 4.4 b) After that, the convex surface

is create by thickening the boundary surface with 4mm thickness. (Figure 4.4 c) For the

smooth flow of water from the inlet, the blade was fillet to some extent. (Figure 4.4 d) Three

blade model is finally made using the curve driven feature to be observed in the MasterCam

software for tool path generation and also to check the collision possibility. (Figure 4.4 e)


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(a) Creating the hub, average and tip arcs in three planes respectively

(b) Creating boundary surface by connecting three arcs


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(c)

Creating blade by thickening the resulted surface

(d) Making three blades to get the check surface for simulation

Figure 4.4 Design process of Turgo turbine


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4.2.2 Toolpath generation

After the modelling is done in Solidworks, the model file is saved in the IGES format since

the flank milling will be conducted on the NURB surfaces and trimmed surfaces of the

turbine with the utilization of MasterCam software. The selection of the cutting tool relies

on the minimum distance between the blades since the maximum diameter of the cutter must be less than that distance and the cutter needs to avoid the occurrence of collision to other

blades. Therefore the observation of the distance between blades is done as shown in Table

4.2.

Table 4.2 Inter-distance between blades

Bottom Distance Middle Distance Top Distance

Hub Arc 17.82 17.85 17.88

Average Arc 23.67 23.21 22.96

Tip Arc 29.25 28.98 28.48

In this respect, while the tool is select from the available tooling from the market, care must

be taken to check the flute length of the tool. As a matter of fact, the cutting height rely on

the flute length. It is a necessity for the cutter to have the flute length is long enough to cut

the designed surface of the blade. Owing these critical factors, the 6 mm bull-end milling

tool with flute length 50 mm (Figure 4.5 a) and corner radius 1mm and 10 mm tool with flute

length 50 mm and corner radius 1 mm (Figure 4.5 b) are chosen as the minimum and

maximum tool for the machining.

(a)


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(b)

Figure 4.5 Tool selection (a) 6 mm bull-end tool and (b) 10 mm bull-end tool

In these collision check test, the 6 mm bull end tool is used for cutting the blade in the tool

path generation process. The problem that was first encountered is that both concave and

convex sides cannot be cut simultaneously since they are isolated surfaces created by

thickening. At worst, the collision happened while cutting the convex side although the

generation of tool path in the concave side and the fillet have no interference. Therefore, the

tool path can be generated only in concave surface. The step-by-step simulation process is

shown in figure 4.6.

(a)

Turgo Runner Revision model (1) (green) which is imported as IGES files with NERB surface together with the blank part (pink)


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(b) The cutting on the concave surface

(c) The cutting on the convex surface (Fail)

Figure 4.6 Tool path generation using the Turgo turbine


Owing to this, the final revision model is designed using the same parameters from the

calculation but designed with the usage of the different method and then simulated in the

MasterCam to be further processed in post-processor and verified the generated tool path.


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4.3.1 Redesigned process

In this model, the surface was not thickened. Instead the six arcs were sketched with 4mm

distance in circular position (Figure 4.7 a), the whole surface including both convex and

concave surfaces was lofted to be one continuous surface. (Figure 4.7 b) Finally, the Turgo

runner with three blades is created with the curve pattern feature. (Figure 4.7 c)

(a) Creating 6 arcs to get the close loop path for surface lofting

(b) Creating the single surface blade model with surface loft feature


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(c)

Making three blades model for machining

Figure 4.7 Design process of Turgo turbine revision model

4.3.2 Toolpath regeneration

The second revised turbine model is then imported with IGES file format including NERB

surfaces for flank milling in MasterCam. Since the model is now the single surface one, the

tool can then be cut the whole surface simultaneously using one tool path. (Figure 4.8)

(a) Turgo Runner Revision Model


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(b) The continuous cutting on both concave and convex sides of the runner

Figure 4.8 Tool path generation for Turgo turbine revision model

Furthermore, under the observation for the collision of the tool, the whole turbine with 20

blades was cut. The cutting was done successfully without any collision in MasterCam

simulation as described in the figure. (Figure 4.9 a) However, more step is needed to be done

to clear the extra material and the scallop which is still needed to be cleared was found after

the cutting. (Figure 4.9 b)


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Figure 4.9 Tool path generation for 20 blades

4.3.3 Post-processing

The output file of MasterCam software is NCI (Numerical Control Intermediate) file type

which represent the non-ISO standard cutter location file that include un-necessary

information besides the motions of the tool with code 11. In this regards, the post-processerneeds only text file that is including the location of the cutter in the X, Y and Z coordinates

and the unit vector of that vector i, j and k coordinates. Therefore, the exported NCI files is

converted into the text file that includes only necessary information using Microsoft Excel

software.

In fact, the necessity of post-processing step happens because the cutter location data that is

attained from MasterCam represent only the tool motions and the real-time machining

requires G-code which refer to both movements of the machine and the tool in X, Y and Z

direction, including the rotation of the working table with the rotation angles A (tilt axis)

rotated around the X axis and B (rotation axis) rotated around the Z axis while cutting the

runner blade. The step-by-step formatting of NCI file into CL file is listed in Figure 4.10.


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Step 1: save NCI files including CL data (MasterCam Output)


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Step 2: Striping of un-necessary information (Excel) and saving only X,Y,Z and unit vector

i, j, k under code 11


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Step 3: Importing cutter location file to Postprocessor (Mathematica)

Figure 4.10 Step-by-step formatting of CL file

After retrieving the CL data with code 11 via Excel, the next step is to process it using the

specific post-processor. In this case, Mathematica software was utilized with the application

of the Inverse Kinematics. Under that concept, the work piece coordinate system is translated

into the machine coordinate system. For this necessity, four coordinate systems: O1, O2 , O3

and O4 are assigned to the machine whereas the origin 1 (O1) refer to work piece origin, theorigin 2 (O2) for the trunnion table coordinate system on A table centerline and on centerline

of B rotation, the origin 3 (O3) for B table coordinate system on A table centerline but 0.003

mm further in the machine and the origin 4 (O4) for the machine coordinate system on the

same location as o2. (Figure 4.12)


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Figure 4.11 Haas 5-axis machine and the coordinate systems

As a result, the inverse kinematics starts off at the work piece side where the coordinate

system O1 is transformed to O2 on the A-table. However the work piece is placed over the

customized fixture which is 75 mm height. (Figure 4.11) And the origin 2 (O2) is 3.307 mm

over the B table surface. Since origin of work piece is right at the center of the bottom

surface, the translation Zo1o2 became (75-3.307 = 71.693 mm). Then the first translation

happens as follows.

x2w = x1 + xo1o2; xo1o2 = 0;

y2w = y1 + yo1o2; yo1o2 = 0;

z2w = z1 + zo1o2; zo1o2 = 71.693;

Next the B-table will be rotated at an infinitesimal angle ε, which can be viewed from the

XY plane as depicted in Figure 4.13. The z coordinate will still be the same since it did not

change. The equations for a positive 3D rotation along the axis Z axis are expressed as

follows.

x2wb = x2w Cos[B] + y2w Sin[B];y2wb = y2w Cos[B] - z2w Sin[B];

z2wb= z2w

Figure 4.12 Positive B rotation along Z-axis

Y Y


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Then transform coordinate system O2 to O3, the offset value is only valid along the vertical

Y-axis as denoted in the following equations for a 3D translation. In this respect, it is noted

as the origin 2 is at the A table centerline but -0.003 mm further from the machine center in

the Y-axis.

x3w = x2wb + xo2o3; xo2o3 = 0;

y3w = y2wb + yo2o3; yo2o3 = -0.003;

z3w = z2wb + zo2o3; zo2o3 =0;

At O3 coordinate system, the A table will be rotated along the X-axis in YZ plane. A-table

will be rotated at an infinitesimal angle ε, which can be viewed from the XZ plane as depicted

in Figure 4.14. The equations for a positive 3D rotation along the axis X are expressed as

follows.

x3wa = x3w;

y3wa = x3 Cos [A] + z3 Sin [A];

z3bwa= z3 Cos [A] - x3 Sin [A];

Figure 4.13 Positive A rotation along X-axis

The final coordinate transform from O3 to O4 by translation will finally orient the tool and

the work piece in accordance to the designated tool vector. The offset values for this

transform between O3 and O4 is horizontal distance between this two points (ZO3O4) and

the tool offsets is z4T. In addition, the machine slide motions from the handshake (delX,

delY and delZ) have also been taken into account while doing the final transformation.

x4w = x3wa + xo3o4 + delX; xo3o4 = 0;

y4w = y3wa + yo3o4 + delY; yo3o4 = 0;

z 4w= z3wa + zo3o4; zo3o4 = 0;

The tooltip coordinates can be calculated as follows. The tool tip coordinate in Z coordinate

system (z4T) depends on the tool length value. It is the distance from the machine origin to

the Z0 position of the tool tip. Therefore for the 6mm ball nose tool with length 139.465 mm,

the z4T becomes (271.48-3.307-139.46 = 128.708 mm).

x4t = 0;

y4t = 0;

z4t = z4T+ delZ; z4T = 128.708;


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To find the handshake motions, it depends on the workpiece coordinates around A axis and

the translation from O3 to O4 as follows.

delX = -x3wa - xo3o4;

delY = -y3wa - yo3o4;

delZ = z3wa + zo3o4 - z4T;

As regards the rotation angles A and B, they can be determined from the unit vector i, j, k

unit vector of CL points and there are four possible solutions for both A and B.

B1 = -ArcTan[i1/j1];

B2 = 2 Pi + B1;

B3 = Pi + B1;

B4 = -Pi + B1;

A angles for solutions B1 & B2:A1 = -ArcCos[k1];

A2 = -2 Pi + A1;

A angles for solutions B3 & B4

A3 = +ArcCos[k1];

A4 = 2 Pi + A3;

Based on these parameters, the program is implemented to find the best combination of A

rotation angle and B rotation angle. A plenty of experiments is conducted in this post-

processing phase working back and forth between the post-processing phase and verification

phase thanks to the fact that although the G-code file was seemed to be good, it probably

will not be working well while tool path was verified in Vericut. Finally two best solutions

with different combination of rotation angles was achieved. First combination is the

machining keep going with B4 angle and if the angle is larger than 90 percent of Pi, the B

rotation will switch to B1 angle. With this B4 and B1 combination, the best A rotation angle

is A1. The other solution is the rotation with B1 angle comes first until the rotation angle

became lager than 90 percent of Pi. Then it change to B3 angle. The coordination A angle in

this case is A3 rotational angle. After post processing, the resulted NC file representing G-

codes is imported to Vericut for the verification of that fact that these G-codes are optimized

using the virtual 5-axis machine.

4.3.4

Verification of tool path for Turgo turbine revision

In the verification, the X, Y, Z coordinates and the rotation angles A, B inside G-codes are

proved with the virtual machine to make sure that there is no collision with the machine and

to check the undercut and overcut. The virtual machine is built following the exact dimension

and travel limits of HAAS VF-2TR 5-axis machine, the real-time machine used for

manufacturing turbine. As for reference, the travel limits of machine are 762 mm, 406 mm

and 508 mm in X, Y and Z axis respectively and the rotation limits of the angles A and B

are +/- 120 degree and 360 degree each. In addition, during the simulation in the Vericut

software, the tooling offset must be the same as the zTo4 parameter (128.708 mm for 6mm

bull-end nose tool) mentioned in the post-processor. Also the tool and the holder are also

created with the same dimensions as the tooling from MasterCam software with the sametool name as utilized in real-time HAAS machine. (Figure 4.14)


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(a)

(b) (c) (d)

Figure 4.14 Machine setting (a) Travel limits and (b) Tooling offset

(c) 6mm milling tool parameter (d) 10mm milling tool parameter

What is more the blank is created inside the machine based on the largest tip diameter of the

turbine (217.3 mm) and the height (51.4 mm). (Figure 4.15 a)Through check on the clearance

between the blank part and the cutting path of the tool, the geometry of the fixtures to clamp

the work piece to the working table is determined as described in the Figure 4.15 b.


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(a)

(b)

Figure 4.15 (a) Blank part and (b) the fixture

The verification of these two possible solutions are decipted in Figure 4.16 and Figure 4.17.

Out of these two best combinations, the combination of rotation angle B1, B3 and A3 angle

was selected to be processed with the following optimization process. The reason is that

though the application of B4, B1 and A1 angles also brings the same results, it cannot be

observed in the real-time machine (HAAS 5-axis machine) since the angle A1 angle turns

the working table from the eyesight of the observer.


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Figure 4.16 Toolpath verification for combination of B1B3A3 rotation angletranslation


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Figure 4.17 Toolpath verification for combination of B4B1A1 rotation angle

translation


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In the previous CAD/CAMA iteration (2), it have been proved that the toolpath generated to

cut the blade can be simulated without any collision in verification step. Therefore the next

step is to find the optimized toolpath for cutting the whole runner including the blades and

the materials between blades. Towards this end, a plenty of experiments have been conductedto find the best way which will lead to the optimization. Out of this experiments, in this

section, some experiments that matter the most will be discussed.

4.4.1

Design and experiments

As for the modelling of the turbine, the blade is created following the design concept in the

revision model which is confirmed already that it can be machined without collision.

However, in order to clear the extra material, the blade needs to be redesigned to create extra

concave and convex surfaces to be milled.

The first experiment is the rotation of tool path in the MasterCam using the pre-defined

toolpth for cutting the blades. Then it had become the failure since even the rotation of 19.5

degree lead to the breaking of blades in some cuts although the initial cutting is working

well. (Figure 4.18)

Initial cut (20 blades) Rotated toolpath

Figure 4.18 Rotation of tool path in 19.5 degree

Thanks to this, in this CAD/CAM iteration (3), all the experiments were conducted with the

usage of the redesigned runner model. The modelling of the blade follows the same design

method as one used for making the revision model in iteration (2). Then the extra concave

and convex surfaces are created. Then, in order to utilize the several layers of these surfaces

as the reference surface to generate the toolpath in MasterCam, they are copied with 1.5

degree angle distance by using the circular pattern feature in Solidworks. (Figure 19)


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Making extra concave and convex surfaces for the reference surface for tool path

generation

Copying concave surfaces with 1.5 degree

Figure 4.19 Design process of creating the blade with concave and convex surfaces


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Then the tool path is generated in MasterCam with the IGES file of the turbine model with

ruled surface to achieve the cutter location data which is then converted into NC file

including G-codes that is the imported into Vericut software for verification. In the

verification phase, the tool path is rotated to check the tool collision with both machine and

work piece. The 6 mm bull-end milling tool is used for all cutting to get the good surface

finish.

The first experiment is implemented on the design model with one blade and 7 concave

surfaces. The concave surface offset is used since the cutting on the concave surface bring

less force of the tool. When the tool path is implemented for verification in Vericut, although

the first blade cutting has no collision with the machine and the blank part, the rotation of

tool path with 18 degree to cut the new blade and the extras, the tool path is failed since tool

cut into the first blade. (Figure 4.20)

Figure 4.20 Tool path verification for blade with 7 concave layers in 1.5 degree


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Then the concave surface is reduced to 6 surfaces with the same 1.5 degree rotation of tool

cutting. The whole implementation step from the tool path generation to the verification is

repeated. Nevertheless, the collision of tool is still happen to the first blade. (Figure 4.21)


Finally when the 5 concave surfaces with the 1.5 degree is applied, the collision is found to

be avoided. (Figure 4.22)


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Along with the CAD/CAM iteration (4), the runner model with the reference concave

surfaces which is already confirmed for no collision towards the adjacent blades is utilized

for all the observations conducted using HAAS 5-axis machine to achieve the optimized tool

path with minimum production time with minimal toolpath. In this respect, the minimum

tool (6 mm bull-end milling tool) and the maximum tool (10 mm bull-end milling tool) are

used alternatively.

In this process, the tool path with different roughing steps and the finish tool path are

implemented in MasterCam first. Since the length of blade is 35.5, the depth of cut isdetermined by the equal-distance distribution of that length by the number of roughing cut.


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The different machine sequences are conducted in this iteration. In this step, the machine

offset is certified with the correct offset with the HAAS machine at the very first moment.

With the application of e-Design, the toolpath generation, post-processing, verification and

the machining is implemented in parallel during the experiments.

4.5.1

5-Axis machining

The HAAS VF 2TR 5-Axis machine from the National Institute of Metrology Thailand is

utilized to cut the blades for the Turgo turbine with flank milling process. In the figure 4.23,

the machine itself and the assembly of the blank part and the fixture to the machine is

presented.

(a)

(b)

Figure 4.23 (a) HAAS machine(b) The assembly of blank part and fixture on the machine


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In addition, during the machining process, the post-processor is optimized to attain the

minimum tool travel. With the previous post-processor, when the spindle is activated, the

tool tip have to go to the zero origin of the machine in the initial stage. Also since the

customized fixture is 75 mm high and the clamp with 10 mm high is placed over the blank part with 51.4 mm, the tool needs to be raised to the safest high until the cutting is started.

Then the post-processor is modified to meet these requirements which in turn not only avoid

collision but also reduce the tool motion. The previous post processor and the modified post

processor are shown in Figure 4.24.

(a)

The previous post-processor

(b) The modified post-processor

Figure 4.24 Modification of post-processor

The first direct cutting the whole runner without using any roughing step is executed with

the usage of 6 mm bull-end tool. Meanwhile, that minimum tool experienced with the

instability and vibration effect. (Figure 4.25)

Figure 4.25 Vibration effect


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Therefore, in the next text, to reduce the flank force to the tool, 4 roughing cut with 8.75 mm

in each step and 0.5 mm finishing for the extra material and the blade is performed. The

cutting is then stable and provide the good surface finish as well. (Figure 4.26)

Figure 4.26 Combination of 4 roughing cuts and 1 finishing cut


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4.5.2 Comparison of machining time, scallop, undercut and overcut

However since 4 roughing is performed, the cutting consumed a lot of time over 7 hours and

the usage of small tool leads to the risk of the tool wear when it comes to mass production.

Owing to this, some more experiments using 10 mm diameter tool (the maximum tool) for

the roughing for the extra material clearance first then 6 mm diameter cutter for the finishingwith different set up of the number of roughing cuts with the respective depth of cuts. As the

comparison results can be observed from the table 4.3, the changing of the tools brought

more time because of two switching time.

Table 4.3 Comparison table of manufacturing time

IGES

model

Machining Sequence Machining

TimeRoughing between

blades Roughing and finishing blade

No

of

cuts

Depth

of cut

(mm)

Tool

No

of

cuts

Depth of cut

(mm)Tool Total cutting

time (hours)

Air

cutting

time (%)

1 35.5 6 mm ø

cutter

1 35.5 6 mm ø

cutter

- -

4 8.75 6 mm ø

cutter

4 8.75 (roughing)

1 (finishing)

6 mm ø

cutter

7.57 hours 64

2 17.5 6 mm ø

cutter

4 8.75 (roughing)

1 (finishing)

6 mm ø

cutter

6.25 hours 59

2 17.5 6 mm øcutter

3 11.5 (roughing)0.05 (finishing)

6 mm øcutter

5.5 hours 58

2 17.5 10 mm

ø cutter

2 17.5 (roughing)

0.05 (finishing)

10 mm

ø cutter

4.17 hours 55

2 17.5 10 mm

ø cutter

3 11.5 (roughing)

1 (finishing)

10 mm

ø cutter

4.75 hours 57

In this case, it is noted that the number of the roughing cuts have an effect on the increment

of the manufacturing time, the tool flank and the surface finish. In the cutting of second

blades, 10 mm diameter is cutter is used for the 2 roughing cuts with 17.5 mm depth and the

finishing of the blade is performed with 6 mm diameter tool with 4 roughing cuts with 8.75mm depth of cuts and 0.5 mm depth of cut for 1 finishing cut. Then the estimated

manufacturing time is reduced to 6 hours and 15 minutes. The scallop still happen at the

bottom with 1.2 mm height. Then as for the experiments, the roughing cutting is kept the

same but for the finishing, the cutting step is reduced to 3 roughing cuts with 11.5 mm depth

and 1 finishing cut with 1 mm depth of cut. Then the estimated time is reduced to 5 hours

and 30 minutes. But the scallop is still the same. So in the next cutting, the blade is machined

with 2 roughing cuts with 17.5 mm depth of cut and 0.5 mm depth of cut for the finishing.

Then the manufacturing time is comparatively reduced to 4 hours and 10 minutes but the

surface finish is obviously severe due to two roughing step. Then in the final optimized

cutting, the same 10 mm cutters is applied for all the roughing and finishing steps. Since the

tool is big enough, the extra material clearance is performed with 2 roughing cuts and the


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final cutting for the blade is executed with 3 roughing steps with 17.5 mm depth of cut and

1 mm finishing cut for achieving the good surface finish. (Figure 4.27)

Blade 1 Blade 2


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Figure 4.27 Demonstration of scallop and surface finish of different setup

Since the ruled surface milling is used for the machining, as afore-mentioned in section 2.2.2,

the overcut and undercut occurred while processing the toolpath. The tool axis, which is not

parallel to the twisted surface of the blade although it has to be, lead to that geometry errorson the surface. The bigger tool brings about bigger overcut. Therefore with the usage of 6

mm ø cutter, the maximum overcut is 0.5 mm while the 10 mm ø cutter is applied, it became

0.8 mm as the maximum overcut. (Figure 4.28)

(a) (b)

Figure 4.28 Demonstration of overcut (a) 0.5 mm overcut on convex surface (6 mm øcutter) (b) 0.8 mm overcut on convex surface (10 mm ø cutter)

Blade 4Blade 3


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Furthermore, it have been acknowledged that the initial cutting rail starting from the convex

surface bring too much vibration and the force is inserted to the blade a lot. Due to this, for

all the blade cutting in different machining setup, the initial cutting starts from the concave

surface. As for the cutting speed, care must be taken not to make any breaking to the blades

because the wood dressing is used as a raw material for blank part. In this respect, the

initialization of the program start with very high speed: 1000 rpm meanwhile the spindlestart and the working table start. However the feed rate differ depending on the tool usage.

For 6 mm ø tool, 200 rpm is used whereas 300 rpm is applied for the 10 mm ø tool.

Nevertheless, during the cutting into blank part, as soon as the tool cut into it, the federate is

adjusted to 50 percent of original amount to reduce the tooling temperature.

4.5.3

Optimized setup

By means of the observations through different set-up, the one that bring the optimal tool

path is the execution of the cutting using the same tool (10 mm bull-end milling tool). The

machining step include the 2 roughing cuts for the clearance of the extra material and the

combination of 3 roughing cuts and 1 finishing cut for the blade which lead to the totalcutting time 4 hours and 45 minutes with good surface finishing on the blade surface. The

machining time is minimum and the toolpath is optimized with the shortest toolpath,

following the practical constraints such the interference of the tool, the tool temperature and

tool wear. The initial modelling for this optimized solution and the record of the machining

are demonstrated in Figure 4.29 and Figure 4.30.

Figure 4.29 Design process of the optimized model


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Figure 4.30 Demonstration of machining process


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CHAPTER 5

CONCLUSION AND RECOMMENDATION

5.1 Conclusion

Under this study, the overall dimension of a Turgo turbine runner is 51.4 mm height, 4 mmthickness and 35.5 mm length. The runner had been optimized using the flank milling along

with the use the vertical 5-axis machine. The trial-machining is executed with the utilization

of 10 mm bull-end milling tool with corner radius 1 mm. The selection of cutter based on

the distance between and also practical constraint such as the availability of tool in the market

with the sufficient flute length for cutting. It is also based on the fact that the shorter tool

provide more stiffness of the tool improving the tool life.

As regards the 5-axis machining of Turgo runner, it is manufactured by use of HAAS VF

2TR 5-axis machine. The CAD modelling is performed in Solidworks 2014 to get the IGES

model to be imported into Mastercam X5 for toolpaths generation. The toolpath generation

in Mastercam can be divided into two main parts: “Roughing between blades” and “Finishingthe blade”. The removal of extra material is done by rotating the roughing cuts and then with

finishing cuts, the removal of the material around the blade is carried out. The CL data from

this toolpaths was post-processed in the Mathematica7 to attain the NC file with the

utilization of the inverse kinematic with the exact offset of the HAAS machine. After that,

the completed NC files including G-code data is verified in the Vericut 7.3 for confirmation

of the machining process.

As regards the optimization of the runner, the machining time of the runner especially

optimized. It took 45 minutes for the roughing of the material between the blades and to

complete the blades and the extra materials which is about 3 mm around the blade, the

combination of the 3 roughing cuts and 1 finishing cut required 4 hours. Therefore the totalmachining time for the whole runner is 4 hours and 45 minutes. There is a scallop in the

bottom surface of the blade which is 1.3 mm height as a result of maximum cutter (10 mm

diameter tool) usage. However, it does not affect to the flow mechanism of the runner. Also

there is some overcut in the middle the blade surface with maximum height 0.8 mm.

In addition, during the optimization process, the consideration of practical constraints such

tool wear, tool life and the interference of tool are taken into account. The post-processing

program is modified to achieve the minimal tool travel. The federate of the tool is 300 rpm

and is reduced to 50 percent while cutting the blank part in this case. Although there are two

possible combination of rotation angle to cut the runner, only the combination of angle B1,

B3 and A3 is used since the machining can be seen and checked during practical machining

period. With the other combination of B1, B4 and A4 angles, the observation cannot be done

because the working table faced to the back side of the machine.

To sum up, with the proposed optimization process, the manufacturing time, the surface

finish of the blade and the tooling aspect are optimized. However further implementation for

the clearance of the scallop at the bottom is still needed to be implemented which will be

discussed in the following recommendation setting.


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5.2 Recommendation

A CAD model of the runner needs to be exported as the IGES file format with NURB

surface from Solidworks CAD software for toolpath generation in Mastercam.

The roughing of the materials between can be done for all 20 blades in single NC

program. However the finishing on the blade should be perform on one blade after

another since the rotation of the toolpath using the G-code file resulted from the post-

processing of CL data lead to the collision of the tool in the verification step.

Blade profile is created with ruled surface over the curves. Therefore due to the tool

motion which cannot match exactly with the requirements to be parallel with the

twisted drive surface, the overcut which is about 0.2 mm in the top of the blade and

the scallop with 1.3 mm height is experienced at the hub surface. Therefore, it is

suggested to fix this problem by two alternative methods: the modification of the CL

vector where the tool is oriented to form the scallop and reduction of the diameter ofthe cutter. However care must be taken when CL vector is modified to make sure that

there is no collision of the tool to the part and jigs.

In addition, it would be advantageous to study the flow simulation of the resulted

blade model to find out to what extent the deviations on the runner have an effect on

the efficiency of the blade. If the study can prove that there is a little bit difference in

efficiency, the proposed modelling can be brought off to the manufacturing because

it is the fastest and cost saving.

Moreover, the metrological analysis of the runner to observe the possible geometrical

errors between the designed model and the machined prototype would be aninteresting study to be conducted. It is suggested as the further study for the proposed

optimization process.


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REFERENCES

1. Anagnostopoulos, J. S., & Papantonis, D. E. (2008). Flow Modeling and Runner Design

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Bohez, L. J. Erik, Ranjith Senadhera, S. D., Pole, K., Duflou, J. R., & Tar, T. (1997). A

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analysis. International Journal of Machine Tools and Manufacture, 42(4), 505-520.

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G. Ardizzon,G.Cavazzini n, G.Pavesi (2014). A new generation of small hydro and

pumped-hydro power plants: Advances and future challenges. Renewable and

Sustainable Energy Reviews 31, 746 – 761

6. Harik, R. F., Gong, H., & Bernard, A. (2013). 5-axis flank milling: A state-of-the-art

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7. Kiattisak, S., Bohez, L. J. Erik, Choosak, N., & Somchai, T. The design and development

of efficient turbine for micro hydro power plant of provincial electricity authority.

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optimal tool based five-axis machining algorithm. Journal of Mechanical Science and

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M. Singh1, Bohez, L. J. Erik, A.C. Munar3, T. Lin 4, S.S. Makhanov5 (1994). 5-Axis

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International Conference on Production Research

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536-541, ISSN 1877-7058.


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13. Williamson, S. J., Stark, B. H., & Booker, J. D. (2013). Performance of a low-head pico-

hydro Turgo turbine. Applied Energy, 102, 1114-1126. doi: 10.1016/j.apenergy.

2012.06.029

14.

Beckman, L. (2012). 5 Advantages of 5-Axis Machining. from

http://www.productionmachining.com/articles/5-advantages-of-5-axis-machining

15.

Multiaxis machining. from http://en.wikipedia.org/wiki/Multiaxis_machining

16. Turgo turbine. from http://en.wikipedia.org/wiki/Turgo_turbine

http://www.productionmachining.com/articles/5-advantages-of-5-axis-machininghttp://www.productionmachining.com/articles/5-advantages-of-5-axis-machininghttp://en.wikipedia.org/wiki/Multiaxis_machininghttp://en.wikipedia.org/wiki/Multiaxis_machininghttp://en.wikipedia.org/wiki/Multiaxis_machininghttp://en.wikipedia.org/wiki/Turgo_turbinehttp://en.wikipedia.org/wiki/Turgo_turbinehttp://en.wikipedia.org/wiki/Turgo_turbinehttp://en.wikipedia.org/wiki/Turgo_turbinehttp://en.wikipedia.org/wiki/Multiaxis_machininghttp://www.productionmachining.com/articles/5-advantages-of-5-axis-machining


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APPENDIXES


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APPENDIX A: Post Processor for Extra Clearance


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APPENDIX B: Post Processor for Cutting Blade


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APPENDIX C: HAAS 5-Axis Machine Offset


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APPENDIX D: Blank Part Drawing


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APPENDIX D: Fixture Drawing

Toolpath Optim5 axis machine turbine ion for a Turgo Turbine Runner

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Transcript of Toolpath Optim5 axis machine turbine ion for a Turgo Turbine Runner