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Research Paper

International Journal of Informative & Futuristic Research ISSN (Online): 2347-1697

Volume 2 Issue 11 July 2015

Pavan Tejasvi 1 Assistant Professor , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

Dr. K. M. Purushothama 2 Associate Professor , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

Dr. S. Satish 3 Assistant Professor , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

F. M. Lewis 4 B.E. Student , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

A. Narahari 5 B.E. Student , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

S. K. Chattopadhyay 6 B.E. Student , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

C. R. Sujir B.E. Student , Department of Mechanical Engineering, Dr. Ambedkar Institute of Technology, Bengaluru

Design of Clamping Fixture for

Manufacturing of Long Turbine

Blades on 5 Axis Machinery Paper ID IJIFR/ V2/ E11/ 031 Page No. 4149-4157 Subject Area

Mechanical

Engineering

Key Words Warping, Bending, Cutting Force Analysis, Clamping System, Material

Properties

Received On 11-07-2015 Accepted On 22-07-2015 Published On 25-07-2015

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ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)

Volume - 2, Issue - 11, July 2015 23rdEdition, Page No: 4149-4157

Pavan Tejasvi , Dr. K. M. Purushothama , Dr. S. Satish , F. M. Lewis , A. Narahari , S. K. Chattopadhyay, C. R. Sujir:: Design of Clamping Fixture for Manufacturing of Long Turbine Blades on 5 Axis Machinery

Abstract

This paper deals with novel ideas for improvement in the manufacturing process of long twisted and tapered turbine blades by means of addition of a simple and adaptable clamping fixture. The attached external fixture as discussed is a possible method of preventing warping and bending while machining long twisted and tapered blades. Applying compression springs and power screws, the fixture serves the purpose of securing the blade near the machining area, in 5 axis machines without such a suitable clamping device. The fixture is so designed such that it is able to accommodate the changes in blade length and size. This fixture can be used for the cases where the turbine blade, while machining may deform or bend during subsequent stages of the machining process, the result of machining away 80% of the original rolled or annealed raw material and the residual stresses thus created. This is particularly possible for large blades, 400–600 mm long, which may bend by as much as 1.5 mm. The fixture is capable of synchronizing itself with the x,y,z,a,b axes of machine movement. A profound study of machining cell configuration is conducted, the key features and designs of the clamping fixture are devised and general analyses are performed on the designs.

1. Introduction When a steel part is machined using certain methods, residual stresses are induced due to the

difference in thermal dilatation between steel and enamel. Those stresses can give rise to buckling

and warping. Slender designs, such as baking trays and architectural panels, are especially prone to

these defects.[1] Warp is an inherent problem with heating and working steel. Everything around

the blade may affect the warp. A cold counter with a warm blade set on it may make the blade

warp. Uneven cooling in quench, or uneven heating in temper, etc. Stresses placed on the blade by

the way it is held or suspended, etc.[11] Countermeasures affected at the granular level, such as

normalizing multiple times, grain refinement, implementation of different forging techniques might

be effected. A simple slotted board clamped in a vise can straighten 99% of most warped blades in

two seconds as shown in figure (1) further. [10]

Reworking the fixturing elements during the machining process, so that the position of

the work piece in the machining centers is modified to account for the deformation, can counteract

this phenomenon.

2. Experimental Details

2.1 Machining Fixture

2.1.1 Description of Clamping Systems

Machining fixture are additional parts added to the original processes which require a systematic

design to clamp, hold and guide the tool during machining process. The obvious place for Fixtures is in

mass production, where large quantity of output offers ample opportunity for recovery of the necessary

investment. It is a special tool used for locating and firmly holding a workspace in the proper position

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during a manufacturing operation. As a general rule it is provided with devices for supporting and

clamping the work piece. It is fixed to the machine bed by clamping in such a position that the work in

the correct relationship to the machine tool elements.[8]

The main purpose of the fixture is to locate the work quickly and accurately, Support it properly

and hold it securely, thereby ensuring that all parts produced in the fixture will come out alike within

the specified limits. In this way accuracy and interchangeability of the parts are provided. [9]

Figure 2: Shows A 3D Representation of the Concept of the Clamp and its Skeletal Structure

2.1.2 Description of the Concept and the Basic Fixture Drawings

During the machining of cuboidal blocks to obtain a blade, it undergoes transitional errors due to

vibration & heavy machining forces. This leads to loss in time & resources, in the form of correctional

measures. In economical 5- axis machines, these problems are very prominent. On the other hand, the

higher end ones are provided with in-built clamping systems, which reduce the aforementioned errors to

a great extent. Hence the addition of a clamping system can make economical 5-axis machines much

more efficient. Addition of a clamping system is done, in the form of an external fixture. There is no

availability of the aforementioned function & hence can be categorized as a novel design. This design is

intended for industries involved in turbine machining production, operating on economical 5- axis

machines. The body is made of SAE 5 Chromium steel, & the ball bearings within the body, aiding the

free movement of clamping unit is made of ANSI 52100.

The clamping unit is present on the inner ring of the body, of the system & consists of 6 clamping

fingers with a point contact surface attached to its tip. . It is arranged in an equiangular fashion,

powered by a power screws. The power screws are accompanied by a spring to absorb unwanted

vibrations. The clamping unit is capable of moving along the contours of the material & also clamps the

material firmly during its machining. The fixture is placed between the head & the tail stock. It also has

the freedom to move along the y-axis, over the guide rails.

3. Cutter Force Calculations and Blade Analysis

The clamping force applied to this generic blade of dimensions 550mmx60mmx50mm made

from a block of material x20 Cr13 should be equal or more than the cutting force. Hence cutting force

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and torque acting at various points due to various width and depth of cuts and other are calculated

keeping parameters like speed and feed constant. And selecting the ones generally used for longer

blades. The following formulae are utilized for cutter force calculations during the process of roughing.

3.1 Pre-process Calculations

Rough machining blade profile Available Data:

Material: - X20Cr13

Tool: - Φ50mm Face Mill Cutter

Cutting speed: - 2480rpm (n)

Cutter diameter: - 50mm

Number of teeth: - 4 (z)

Feed at the table: - 6000 ⁄

Maximum power of machine: - 20KW

1) Speed Calculation

V=

⁄

2) Feed per tooth

=

⁄ ( = 5)

3) Feed at spindle per minute

= (mm)

4) Material removal rate

Q =

⁄

5) Power at spindle (N)

N = UKn KrQ (KW)

Unit Power = 32 × 10-3

(Table 4.6 HMT Production design)

Radial rake angle = -5 degree for 50mm diameter cutter

Correlation coefficient (Kn) = 1.07

For radial rake angle

Flank wear = 0.8mm/0.6mm/1.0mm

Correction factor = 1.20/1.13/1.25

6) Tangential cutting force:

Pz = 6120 ×

(N)

7) Torque of spindle

T = 975 ×

(Nm)

8) Clamping force

C= FOS × Pz (N)

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4. Experimental Setup

4.1 Assumptions

1) At any given point of time, during machining, the blade used is assumed to be a simply

supported beam.

2) The material of the blade is perfectly homogeneous i.e., has the same material throughout.

3) The material of the blade is isotropic i.e., equal elastic properties in all directions.

4) The cross section has an axis of symmetry in a plane along the length of the blade.

5) The material of the blade obeys Hooke’s law.

6) The transverse sections which are plane before bending remain plane even after bending.

7) Each layer of the blade is free to expand or contract, independent of the layer above or

below it.

8) The Young’s modulus is same in both tension and compression.

4.2 Cutting Force Analyses

In case of long and slender turbine blade, during machining, these are subjected to cutting forces

thereby causing it to bend irreversibly. It was observed that the long and slender turbine bend and warp

during the rough cut operations. In order to avoid the bending or restrict it within the acceptable limits,

there is a need to have clamping system to provide the necessary support to the turbine blade while the

machining operation.

Hence, in order to prove that the clamping system can turn out to be a fruitful solution, there will be

two cases of FEA be performed on a generic turbine blade of dimensions, firstly, when loaded under

the Cutting forces and the deflection is observed; secondly, turbine being well supported under the

loading conditions using a conceptual clamping system.

4.3 Case 1 – Without Clamping System

Figure 3. shows the considered blade without a clamp

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4.4 Case 2: With Clamping System

1) Material Properties

Table 1:Material Properties of the Blade and Fixture

Properties

Name: X20 Cr13 or AISI420

Model type: Linear Elastic Isotope

Default Failure Criterion: Max Von Mises Stress

Yield Strength: 3.5e+008 N/m2

Tensile Strength: 6.5e+008 N/m2

Elastic Modulus: 2e+011 N/m2

Poisson’s Ratio: 0.27

Mass Density: 7700 Kg/m3

Name: SS-Alloy Steel

Model type: Linear Elastic Isotope

Default Failure Criterion: Max Von Mises Stress

Yield Strength: 6.2e+008 N/m2

Tensile Strength: 7.2e+008 N/m2

Elastic Modulus: 2e+011 N/m2

Poisson’s Ratio: 0.27

Mass Density: 7700 Kg/m3

2) Mesh Details

Table 2: Mesh Details of the Blade and Clamp Assembly

Figure 4: Shows a Warping and Bending Phenomenon Figure 5. Shows the Meshed Assembly

Mesh type Mixed Mesh

Mesher Used: Curvature based mesh

Jacobian points 4 Points

Jacobian check for shell On

Maximum element size 5 mm

Minimum element size 1 mm

Mesh Quality High

Re mesh failed parts with incompatible mesh On

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5. Analysis & Results

5.1 Cutter Force

5.1.1 Results of Analyses of Blade without Clamp

I. Von Mises Stress: This analysis is done considering a maximum of 400 N of force being

applied while machining under safe conditions. The point of application selected for the force is

the midpoint of the blade. It is observed that there is a concentration of stress in the region in

the inset. The maximum stress induced is 98.6 MPa, but this magnitude is well within the yield

limit of the material, hence it is safe and the blade doesn’t undergo any sort of failure.

Figure 6: Shows the Stresses Developed In an Unclamped Blade

II. Deflection: This Analysis is also done considering a maximum of 400 N of force being applied

while machining under safe conditions. For the given cutting forces, it is observed that the

deflection observed in the Blade is 0.47mm (almost approx. 0.5mm).

Figure 7: Shows the Deflection of the Blade before Clamping

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5.1.2 Results of Analyses of Blade with Clamping

Von Mises Stress: This Analysis is done considering a maximum of 400 N of force being

applied while machining under safe conditions. The point of application selected for the force is

close to the midpoint of the blade. The clamping forces counteract the applied forces at a safe

distance from tool operation point, i.e. application of cutter force. It is observed that there is a

concentration of stress in the region in the inset. The maximum stress induced in the system is

288.9 MPa on the clamping fingers, but this magnitude is well within the yield limit of the material,

hence it is safe. The stress experienced by the blade is now reduced to the region of around 24.1

MPa to 48.1 MPa which is well within the accepted limits of the material and is much lesser than

the stress experienced in Case1.

Figure 8: Shows the Stresses Developed In the Blade after Clamping

Deflection: This Analysis is also done considering a maximum of 400 N of force being

applied while machining under safe conditions. The clamping forces counteract the applied forces

at a safe distance from tool operation point, i.e. application of cutter force. For the given cutting

forces the deflection observed in the Blade is 0.0705 mm variable with different iterations upto

about 0.08 mm. For the given cutting forces, it is observed that the deflection observed in the Blade

is 0.08 mm while the deflection in the first case was nearly 0.5mm. We observe that a difference of

0.42 mm is noted in deflection and hence there is a difference of nearly 84% while deflection is

brought under acceptable limits.

Figure 9: Shows the Deflection Of The Blade After Clamping

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6. Conclusion

Viewing from overall experimental results, the following conclusion have been drawn,

i.) These results have been confined from the numerical analysis by using Ansys software.

ii.) This novel fixture is designed and proposed for application has been suggested to the

concerned industry.

iii.) The main purpose of fixture is to locate the work accurately, support it properly and hold it

securely, thereby ensuring the all parts produced in same fixture will come within specified

limits.

iv.) Theoretically bending is reduced by 85%. Operator conformability has prime consideration in

fixture design. In this fixture design ergonomic aspects have studied carefully reducing

operator fatigue to minimum.

References

[1] S. Cooreman, P. Gousselot, M. Leveaux, P. Pol and J. Antonissen. "Understanding thermal warping

and sagging in enamelled steel parts through an integrated FE simulation." International Heat

Treatment and Surface Engineering 2013; 8(2), 55-60.

[2] Kurokawa, Eiki. Flexible Conformable Clamps for a Machining Cell with Applications to Turbine

Blade Machining, 1986.

[3] BAUSCH John J “Turbine Blade Fixture Design using Kinematic Methods and Genetic

Algorithms”, SPIE Publisher, 2000-11 -06, USA.

[4] A Al-Habaibeh Proceeding of the Institution of Mechanical Engineers, Part B: Journal of

Engineering Manufacture, Sage Publications, volume 217,Number 12/2003.

[5] Kailing Li Ran Liu Guiheng Bai, “Development of an Intelligent Jig and Fixture Design System”,

Computer-Aided Industrial Design and Conceptual Design, 2006. CAIDCD'06.pp 1 -5.

[6] Y. Zheng, Y. Rong and Z. Hou, “The Study of Fixture Stiffness Part I: A Finite Element Analysis

for Stiffness of Fixture Units”, The International Journal of Advanced Manufacturing Technology,

Volume 36, Numbers 9-10, 865-876, DOI: 10.1007/s00170-006-0908-5

[7] Yan Zhuang Goldberg, K. “Design Rule for Tolerance Insensitive and Multi-purpose Fixtures”,

Advanced Robotics,1997.ICAR’97.pp. 681 – 686

[8] Frank W.Wilson, Hand Book of Fixture design, Society of Manufacturing Engineers, Tata McGraw

Hill, 1997

[9] Hiram E. Grant, Jigs and Fixtures, Tata McGraw Hill, 1967, New York.

[10] Apelt, Stacey E., “Blade Warp”, 2012 .

[11] http://www.bladeforums.com/forums/showthread.php/945231-Blade-Warp

[12] Tester, John T.,“Reducing Distortion in Simulated Injection Moulded Wind Turbine Blades”

01/2004; DOI: 10.2514/6.2004-171

[13] Shigley, Joseph E., Mischke, Charles R., & Brown, Thomas Hunter, Standard Handbook of Machine

Design, 3E, Tata McGraw-Hill Education, 1996.

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Design of Clamping Fixture for Manufacturing of Long ... · Design of Clamping Fixture for Manufacturing of Long Turbine ... Fixture for Manufacturing of Long Turbine Blades on 5