Enhancing productivity by elimination of hole offset rejection of an obj socke

International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –

6979(Print), ISSN 0976 – 6987(Online) Volume 4, Issue 2, May - August (2013), © IAEME

10

ENHANCING PRODUCTIVITY BY ELIMINATION OF HOLE OFFSET

REJECTION OF AN OBJ SOCKET BY DESIGN OF A FIXTURE IN

VERTICAL MACHINING CELL

Martin L1, Ashok Kumar V

2, Prakash S

3, Thiyagarajan K

4*

1, 2, 3

Assistant Professors, Department of Mechanical Engineering,

Sri ManakulaVinayagar Engineering College, Puducherry, India. 4Department of Mechanical Engineering, Mailam Engineering College, Mailam

ABSTRACT

Improving and Increasing productivity to cater the needs of customer in shortest

possible time is an ever challenging task in any mass production Industry. The scope for

further improvement production always exists and hence ways and means for design and

fixtures are constantly explored by the engineers. This work focuses on the area of socket

machining cell where sockets are machined in VMC cell and assembled with the Outer Ball

Joints. The problem facing here is that due to component(socket) tilting observed during

machining in the VMC cell there were more number of hole offset rejections in sockets. The

rejections of the sockets were relatively reported for customer dissatisfaction. The main

theme of our project is to reduce high number of rejections in socket production, for

achieving this we proposed a new design for the V-Block in the VMC cell which fits the

socket accurately. The components were designed in Three Dimensional CAD and Solid

Modelling were generated in Pro-E Wildfire Version 5.0.

Keywords: Socket, VMC Cell, Hole Offset, CAD, Pro-E Software, V-Block.

1. INTRODUCTION

In an automobile, ball joints are spherical bearings that connect the control arms to the

steering knuckles. They are used on virtually every automobile made and work similar to the

ball and socket design of the human hip joint.A ball joint consists of a bearing stud and

socket enclosed in a casing; all these parts are made of steel. The bearing stud is tapered and

threaded, and fits into a tapered hole in the steering knuckle. A protective encasing prevents

dirt from getting into the joint assembly. Usually, this is a rubber-like boot that allows

INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING

RESEARCH AND DEVELOPMENT (IJIERD)

ISSN 0976 – 6979 (Print) ISSN 0976 – 6987 (Online)

Volume 4, Issue 2, May - August (2013), pp. 10-18

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movement and expansion of lubricant. Motion control ball joints tend to be retained with an

internal spring, which helps to prevent vibration problems in the linkage. A ball joint is used

for allowing free movement in two planes at the same time, including rotating in those

planes.Combining two such joints with control arms enables motion in all three planes,

allowing the front end of an automobile to be steered and a spring and shock (damper)

suspension to make the ride comfortable. The problem undertaken for the study is the identify

and rectify the hole offset rejections.

1.1 SOCKETS

A mechanical device consisting of a spherical knob at the end of a shaft that fits

securely into a socket. Ball-and-socket joints are used to connect parts of a machine that

require rotary movement in nearly all directions.Ball-and-socket joints allow the front wheels

of a car to be turned by the steering mechanism.At first the socket is loaded in the set where it

is fitted with the V block and a torque is given in order to fit it perfectly with the block.

Fig. 1 Outer Ball Joint Socket (Model H-79)

2. RESEARCH METHODOLOGY

2.1 PROBLEM IDENTIFICATION

V- Block is one of the components in the VMC Cell. It acts as a fixture for holding

the socket for undergoing all the operations under the VMC. From loading to unloading, the

socket is being held in the V-block, tightening plays a vital role. In some kinds of the sockets

like L90 hole offset rejections are more because misalignment in the V-block. Reason for

this misalignment is

• Due to forging problem in the socket.

• Misalignment of the job in fixture by the operator.

• Stem diameter Variation

• Unequal torque applied by the operator.

• Dimensions variations in the socket.

The figure shown is the existing model of V block made of mild steel. This fixture is

designed for various sockets. It is been designed in such a way that the socket butt is being

held in the middle portion of the fixture and then it is fixed for undergoing the operations

under the VMC.

International Journal of Industrial Engineerin

6979(Print), ISSN 0976 – 6987(Online) Volume 4, Issue

Fig. 2

2.2 UNDERSTANDING THE CURRENT SITUATIONIn the OBJ Sockets wall thickness values 1.6 to 2.6 mm, components are reject

Due to these rejections, its impact contributes a lot to the company as given in the diagram

below.

Fig. 3Paretto Diagram of Socket Rejection Category

From the above diagram shown, S

Rejection in ppm. This problem is taken under consideration to be resolved. We planned to

eliminate hole offset rejection through by implementing a model.

current process based upon data analysis using techniques such as design of experiments,

poka yoke or mistake proofing, and standard work to create a new, future state process

Analyze the data to investigate and verify cause

relationships are and attempt to ensure that all factors have been considered.

cause of the defect under investigation.

1866 1740

75%

0

4000

Socket

Hole

Offset

Boot

Grooving

Not OK

Re

ject

ion

AV

G P

PM

International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976

6987(Online) Volume 4, Issue 2, May - August (2013), © IAEME

12

Fig. 2Existing Model of V – Block

2.2 UNDERSTANDING THE CURRENT SITUATION In the OBJ Sockets wall thickness values 1.6 to 2.6 mm, components are reject


Paretto Diagram of Socket Rejection Category

From the above diagram shown, Socket Drill Offset Contributes 75% Total Socket

This problem is taken under consideration to be resolved. We planned to

eliminate hole offset rejection through by implementing a model.Improve or optimize the


yoke or mistake proofing, and standard work to create a new, future state process

the data to investigate and verify cause-and-effect relationships. Determine what the

relationships are and attempt to ensure that all factors have been considered. Seek out root

cause of the defect under investigation.

1740 1168 778 733 226 111

101%

119%131%

142% 145% 147%

0%

20%

40%

60%

80%

100%

120%

140%

160%

Boot

Grooving

Not OK

Socket

Rust

Painting

Not Ok

Socket

Damage

Socket

Thread

Damage

Plating

Not Ok

Socket Rejection category

g Research and Development (IJIERD), ISSN 0976 –

(2013), © IAEME

In the OBJ Sockets wall thickness values 1.6 to 2.6 mm, components are rejected.


% Total Socket

This problem is taken under consideration to be resolved. We planned to

or optimize the


yoke or mistake proofing, and standard work to create a new, future state process.

effect relationships. Determine what the

Seek out root

100%

120%

140%

160%



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3. ANALYSIS

OBJ sockets is being prepared in various number of operations in various units as

shown in the above process flow diagram. In the sequence milling, drilling, tapping and

chamfering are done in the VMC cell. From the analysis its been clearly noted that number

of hole offset rejections is more in the VMC cell. The VMC Cell operation is as follows :

• Loading - Manual Process

• Facing

• Chamfering - Automatic Process

• Drilling

• Tapping

During the Automatic process, the socket is misplaced to the V-block due to which

there is some problem in V-block and also in the socket. Problem due to

• V- block design

• Forging

Fig. 4 Hole Offset and Rejected Socket Component

4. DATA COLLECTION

This is the Final stage of our analysis, here we have collected the data of number of

rejections which took place with shift wise due to the existing V-block design and the

clamping which is done manually. Here the rejection is high which is indicated in ppm. We

have calculated for more than 5000 components, in which nearly 45 components undergoing

hole offset rejections in which ppm will be around 6500, which shows that sigma level will

be very less due to this customer dissatisfaction and economic loss is quite high.So we want

to eliminate this problem by designing a V-Block with a new fixture to exactly fix the socket

accurately for machining in the VMC.

From the below table, the data collected is for the existing V-block design in the

fixture and for the Manually Clamping Process. As stated above the data is collected shift

wise. The production details of the sockets are given, while skimming over the shift wise

details the number of products produced in the shift 3 is comparatively less when compared

to the shift 1. This reduction in the quantities produced is due to the human fatigue.

The hole offset rejection quantity is been mentioned in each date with the shift wise

data collection. Here we come to know that nearly 30 components are being rejected as far

sockets are concerned, there will be a economic loss for the organization undergoing these

operations.



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DATE SHIFT

1

SHIFT

2

SHIFT

3

TOTAL

PRODUCTION

HOLE OFFSET REJ.

QTY

25.01.2013 222 168 0 390 2

26.01.2013 312 0 0 312 2

27.01.2013 0 0 0 0 0

28.01.2013 0 0 0 0 0

29.01.2013 0 0 624 624 6

30.01.2013 390 180 0 570 2

31.01.2013 450 330 0 780 2

02.02.2013 180 378 30 588 6

03.02.2013 0 0 0 0 0

04.02.2013 0 0 144 144 2

05.02.2013 90 408 0 498 4

06.02.2013 510 360 0 870 4

Production Quantity Jan 25 – Feb 6 4776

Hole Offset Rej. Qty. Jan 25 – Feb 6 30

Hole Offset Rejection PPM 6281

Table. 1 Hole Offset Rejection Detail in VMC (Existing V-Block Model)

5. COUNTER MEASURE

Forging is the main reason for hole offset in the VMC, so we are undergoing a

modification in the existing V-Block near the butt position. Due to this, hole offset will be

terminated to an extent even though the forging is misaligned. Burr accumulation in the V

block is been reduced by the modified design. The design is done in Autocad software in

Version 10 and generated in solid model for fixture using PTC Wildfire 5.0. This counter

measure is then implemented in the VMC for further socket machining of components.

Fig. 5 Existing V- Block Design in VMC, Fixture Diagram in AutoCAD Ver10



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Fig. 6 Proposed V- Block Design in VMC, Fixture Diagram in AutoCAD Ver10

Fig. 7 Generated Solid Model of V-Block Design from AutoCAD to Pro-E Wildfire Ver5



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In this counter measure, the existing model of the V –Block design is modified in

order to reduce the rejection rate by altering the butt placing position and to hold the

component firmly. The existing model view drawn out from the company profile and we

made a new design for the V-Block to reduce the rejection due to offset. The contact ratio

between the job and the V-Block was increased by this altered V-Block.In order to reduce the

hole offset rejection in OBJ Socket, the V-Block design is altered on basis of the socket

which is to be machined. The contact ratio between the V-Block and the job is increased by

this proposed V-Block design. Then a solid model was generated from AutoCad to Pro-E to

make a fixture from the design.

Fig. 8 V-Block Fixture for the VMC

6. CHECK RESULTS AND DISCUSSION

DATE

SHIFT

1

SHIFT

2

SHIFT

3

TOTAL

PRODUCTION

HOLE OFFSET

REJ. QTY

21.02.2013 36 180 0 216 1

22.02.2013 192 0 0 192 1

23.02.2013 228 0 0 228 2

24.02.2013 252 162 0 414 0

25.02.2013 198 222 0 420 1

26.02.2013 138 180 0 318 0

27.02.2013 318 120 0 438 0

28.02.2013 306 402 420 1128 0

01.03.2013 168 276 0 444 0

02.03.2013 0 242 0 242 0

03.03.2013 204 510 294 1008 0

04.03.2013 420 510 246 1176 0

Production Quantity Feb 21 – Mar 4 6224

Hole Offset Rej. Qty. Feb 21 – Mar 4 5

Hole Offset Rejection PPM 803.35

Table.2 Hole Offset Rejection Detail in VMC (Implemented V-Block Model)



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Fig. 9 Implemented V-Block Fixture in VMC For Socket Machining

Now that by implementing the fixture in the VMC Cell the data is again collected for

the check of the number of rejections that occurs during the drilling operation in the V-block

placed for holding the socket. And we find that the rejection rates compared with the old

model was really less and the prodution quantity without rejections were high. The Average

PPM of the rejection rate with previous was less by implementing this fixture to the V-Block.

And thus during maching in the VMC Cell the rejection rates were les and hole offset

problem was eradicated to an extent so that the production of sockets increased and purpose

was achieved.

7. CONCLUSION

Manufacturing plays vital role in any industry for producing the product. With

stiffcompetition and challenges in the present-day market, manufacturers are compelled to be

more responsive to the customer’s demands regarding not only quality, but scheduled

delivery. Enhancing productivity is a key concern for almost all the mass manufacturing

industries. The achievements in productivity for this following Machining Cell can be noticed

as :

• By designing a new model for the V-Block fixture in the Vertical Machining Cell the

hole offset problem is completely reduced.

• As an attempt to overcome the Hole Offset Rejection problem and to improve the

productivity of machining this work focuses upon the design of V-Block Model to

machine Sockets simultaneously in a single pass.

• The cycle time of the operation is consumed so that the productivity is reduced.

• The need of this study is to reduce the customers dissatisfaction.



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8. ACKNOWLEDGEMENT

We would like to thank Dr. S. Senthil B.E., M.Tech IIT Madras, Ph.D, Our

Respected Principal, Mailam Engineering College for guiding and supporting us

throughout this project. We express our deep sense of gratitude to Dr. R. Rajappan, M.E.,

Ph.D, Dean/Head – Department of Mechanical Engineering, Mailam Engineering College

for his encouragement and guidance. We also thank Mr. AbilAnandan, Senior Engineer,

MED DepartmentRANE MADRAS LIMITED for facilitating us to undergo this project in

Research and Development Department.

9. REFERENCES

[1] Machine Design, D. K. Agarwal, 10th edn., S. K. Kataria& Sons, Delhi.

[2] Mechanical Engineering Design, Shigley, 8th edn., McGraw-Hill.

[3] Venugopal K and Prahu Raja V, “Basic Mechanical Engineering”, AnuradhaPublishers,

Kumbakonam, (2000).

[4] Shantha Kumar S R J., “Basic Mechanical Engineering”, Hi-tech Publications,

Mayiladuthurai, (2000).

[5] SeropeKalpajian, Steven R.Schmid, Manufacturing Engineering and Technology,

Pearson Education, Inc. 2002(Second Indian Reprint).

[6] Beddoes.J and Bibby M.J, ‘Principles of Metal Manufacturing Processes’, Elsevier,

2006.

[7] Rajput R.K, ‘A text book of Manufacturing Technology’, Lakshmi Publications, 2007.

[8] Boby K George and Dr. Shouri P.V, “Maintenance Optimization in Manufacturing

System”, International Journal of Production Technology and Management (IJPTM),

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0976 – 6391.