productivity improvement by designing a fixture

i

ACKNOWLEDGEMENT

We remain immensely obliged to Prof. Basavaraj Talikoti for providing us with the

knowledge of this topic, and for his invaluable support in garnering resources for us either by

the way of information or computers; also his guidance and supervision which made this

happen.

We would also like to thank our colleges Automobile department professors; H.O.D.

M. D. Nadar, Prof. Amey Marathe and Prof. Onkar Sahastrabuddhe for their valuable

guidance on the concepts of fixtures and the principle operation of the welding fixture.

We thank Mr. P. M. Chitte (Production Head) for providing us a chance to visit

Mahindra Ugine Steel Company Limited (MUSCO, Stamping Division). We got to learn

many things about press shop, production and working of the company. We also thank Mr.

Vijay Gunjekar (Assembly Shop Manager) for helping us and providing us with the

knowledge about the sub-assembly line.

We thank our Assembly Fixture Maintenance Departments Engineers Mr. Anil

Pingale and Mr. Prashant Borole and everyone from Quality Department for their guidance

on the practical concepts of the Fixtures and their working.

We would like to say that it has been indeed a gratifying and learning experience while

working on this Project.

ii

ABSTRACT

Body panels of vehicles are manufactured and fabricated with help of Welding process.

Welding process (Resistance Arc Welding and Metal Inert Gas (MIG) welding) requires

specially designed fixtures.

In the sub-assembly of Rear Bumper Bracket of Mahindra Verito car, four parts are

spot welded to form assembly. Parts include two panels and two brackets. This was done on

three different fixtures requiring two operators and at least two spot welding guns.

Out of the three fixtures used, one was modified in such a way that the whole Sub-

Assembly could be done on a single fixture.

Thus achieving optimization of workspace, manpower, time and increase in

productivity of the sub-assembly of Rear Bumper Bracket (010BBA0080N) of Mahindra

Verito.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENT ........................................................................................................ i

ABSTRACT .............................................................................................................................. ii

TABLE OF CONTENTS ...................................................................................................... iii

LIST OF FIGURES ................................................................................................................ vi

LIST OF TABLES ............................................................................................................... viii

1 INTRODUCTION................................................................................................................ 1

1.1 COMPANY INTRODUCTION .................................................................................... 1

1.2 WORKSHOP LAYOUT ................................................................................................ 2

1.3 OBJECTIVE .................................................................................................................. 4

2 SUB-ASSEMBLY SHOP FLOOR ..................................................................................... 5

2.1 SUB-ASSEMBLY SHOP LAYOUT ............................................................................. 5

2.2 EQUIPMENT USED ..................................................................................................... 6

2.2.1 WELDING FIXTURES ......................................................................................... 6

2.2.2 TYPES OF WELDING FIXTURES ..................................................................... 6

2.2.3 SPOT WELDING ................................................................................................ 10

3 PRODUCT DETAILS ....................................................................................................... 14

3.1 BRACKET AND PANELS USED IN SUB-ASSEMBLY .......................................... 14

3.2 FINAL PRODUCT 010BBA0080N ............................................................................ 16

3.3 DESCRIPTION ABOUT LOCATION OF PANELS ON FIXTURES ....................... 17

4 LIST OF PROCESS .......................................................................................................... 18

4.1 EXISTING SUB-ASSEMBLY PROCEDURE ........................................................... 18

4.1.1 STAGE 1 .............................................................................................................. 18

4.1.2 STAGE 2 .............................................................................................................. 19

4.1.3 STAGE 3 .............................................................................................................. 20

5 EXISTING SYSTEM......................................................................................................... 21

5.1 FIXTURE 1 .................................................................................................................. 21

5.2 FIXTURE 2 .................................................................................................................. 22

5.3 FIXTURE 3 .................................................................................................................. 23

iv

6 PROBLEM DEFINITION ................................................................................................ 24

6.1 TIME MANAGEMENT .............................................................................................. 24

6.2 SPACE MANAGEMENT ........................................................................................... 25

6.3 COST EFFECTIVENESS ............................................................................................ 26

6.4 MAINTENANCE ........................................................................................................ 26

6.5 REQUIRED MANPOWER ......................................................................................... 26

7 LITERATURE REVIEW ................................................................................................. 27

7.1 FIXTURE ..................................................................................................................... 27

7.2 PURPOSE .................................................................................................................... 28

7.3 3-2-1PRINCIPLE OF LOCATION ............................................................................. 29

7.4 ELEMENTS OF FIXTURES ....................................................................................... 30

7.5 TYPES OF FIXTURES ............................................................................................... 32

7.6 FACTORS TO BE CONSIDERED FOR DESIGN OF FIXTURES............................ 32

7.6.1 COMPONENT ..................................................................................................... 32

7.6.2 LOCATION ......................................................................................................... 32

7.6.3 CLEARANCE...................................................................................................... 33

7.6.4 BURR GROOVES ............................................................................................... 33

7.6.5 CLAMPING ARRANGEMENTS ....................................................................... 33

7.6.6 SAFETY .............................................................................................................. 33

7.6.7 COST ................................................................................................................... 33

8 MODIFICATION OF FIXTURE ..................................................................................... 34

8.1 PROCEDURE FOLLOWED FOR MODIFICATION: ............................................... 34

8.2 PNEUMATIC CIRCUIT: ............................................................................................ 36

8.3 NEW OPERATING PROCEDURE ............................................................................ 38

8.3.1 STEP 1 ................................................................................................................. 38

8.3.2 STEP 2 ................................................................................................................. 39

9 DATA COLLECTION AND ANALYSIS ....................................................................... 40

9.1 DATA COLLECTION................................................................................................. 40

9.1.1 TIME MANAGEMENT ...................................................................................... 40

9.1.2 COST EFFECTIVENESS ................................................................................... 41

9.1.3 REQUIRED MANPOWER ................................................................................. 42

9.1.4 SPACE MANAGEMENT ................................................................................... 42

v

9.2 ANALYSIS OF BOTH SUB-ASSEMBLY PROCEDURES ........................................ 43

10 CONCLUSION AND FUTURE SCOPE ........................................................................ 44

10.1 EFFECTS OF OPTIMIZATION ................................................................................. 44

10.2 CONCLUSION ............................................................................................................ 45

10.3 FUTURE SCOPE: ........................................................................................................ 45

REFERENCES ....................................................................................................................... 46

BIBLIOGRAPHY ................................................................................................................ 46

WEBSITES .......................................................................................................................... 46

PAPERS ............................................................................................................................... 46

vi

LIST OF FIGURES

Fig. 1.1 Company Layout ........................................................................................................ 3

Fig. 2.1 Sub Assembly Shop Floor Layout ............................................................................. 5

Fig. 2.2 Classification of Welding Fixtures ............................................................................ 6

Fig. 2.3 Manual Fixture ........................................................................................................... 7

Fig. 2.4 Pneumatic Fixture ...................................................................................................... 8

Fig. 2.5 Handy Fixture ............................................................................................................. 9

Fig. 2.6 Principle of Spot Welding ........................................................................................ 10

Fig. 2.7 Spot Welding Gun .................................................................................................... 11

Fig. 2.8 Pedestal Spot Welding Machine .............................................................................. 12

Fig. 2.9 Spot Welding Robot.................................................................................................. 13

Fig. 3.1 Panel No. PMRL8200297206 ................................................................................... 14

Fig. 3.2 Panel No. PMRL 8200709438 .................................................................................. 14

Fig. 3.3 Bracket No. PMRL8200212827 ............................................................................... 15

Fig. 3.4 C-Bracket .................................................................................................................. 15

Fig. 3.5 Final Product 010BBA0080N .................................................................................. 16

Fig. 4.1 Sub-Assembly Stage 1 .............................................................................................. 18



Fig. 5.1 Fixture 1..................................................................................................................... 21

Fig. 5.2 Fixture 2..................................................................................................................... 22

Fig. 5.3 Fixture 3..................................................................................................................... 23

Fig. 6.1 Space Required for Existing Sub Assembly ........................................................... 25

Fig. 7.1 A Typical Fixture ...................................................................................................... 27

Fig. 7.2 Possible degrees of freedom of a solid body ........................................................... 29

Fig. 7.3 Arresting all degrees of freedom of a blank in a fixture ....................................... 30

Fig. 8.1 Locator Pin Unit ....................................................................................................... 34

Fig. 8.2 Modified fixture ........................................................................................................ 35

Fig. 8.3 Pneumatic Circuit for Modified Fixture when de-clamped.................................. 36

Fig. 8.4 Pneumatic Circuit for Modified Fixture when clamped ....................................... 37

Fig. 8.5 New Sub-Assembly step 1 ........................................................................................ 38

Fig. 8.6 New Sub-Assembly step 2 ........................................................................................ 39

Fig. 9.1 Optimization parameters ......................................................................................... 40

vii

Fig. 9.2 Space Required for New Fixture ............................................................................. 42

Fig. 9.3 Comparison between Optimization Parameters of Old and New Procedure ..... 43

viii

LIST OF TABLES

Table 7.1 Difference between Jigs and Fixtures ................................................................ 28

Table 10.1 Effect of Optimization ......................................................................................... 44

1

Chapter 1

INTRODUCTION

Mahindra Ugine Steel Co Ltd (MUSCO), incorporated on 19th December 1962, is a

premier Steel Manufacturer. It is a part of Mahindra rise. It is the most trusted brand in alloy

steel.

1.1 Company Introduction

Mahindra Ugine Steel Company Limited (MUSCO) Stampings creates a value chain

between steel and automobiles by efficiently and economically converting sheet metal into

automotive components and systems.

They offer sheet metal stamping and welding based solutions to their customers from

four modern plants at Kanhe, Nashik, Rudrapur and Pantnagar. These plants are equipped with

modern equipment and tool rooms for providing cutting edge sheet metal solutions.

In addition to this, there is a matured tool and die design facility for co-creation of

lighter and more durable automotive components for OEMs.

MUSCOs stamping division is present in Nasik. Its manufacturing area is about 8700

sq. meters. Body panels of following cars are produced in this plant:

Mahindra Bolero

Mahindra Scorpio

Mahindra Xylo and

Mahindra Verito

Out of the above mentioned, this plant produces about 146 panels of Bolero, 50 of

Scorpio, 41 of Xylo and 19 of Verito. Not only body panels but sub-assembly is also done and

then sent to various plants. Some of the body panels are exported. The major product produced

in this plant are the panels of Mahindra Bolero followed by Scorpio and Xylo.

2

1.2 Workshop Layout

The layout of the company can be divided into following categories:

1. Press Shop:

Company has a large press shop having both Mechanical and Hydraulic presses.

Most of the presses are imported from Germany. There are total 18 presses available in

main press shop and 8 machines available in small press shop. These press machines

have around 500 dies used for stamping around 300 various panels. Machines in main

press shop were ranging from 500T to 1200T and in the small press shop from 50T to

300T.

In press shop, tool room is also present for maintenance and repair of dies used.

2. Sub-Assembly Shop:

In the sub-assembly shop two or panels were spot welded together and then sent

for the main assembly. Most of the body panels assembled was made in the main and

small press shop but some were ordered from other companies too.

Sub-assembly shop has spot welding guns, pedal step spot welding machines,

mechanical and pneumatic types of fixtures for holding the panels during the sub-

assembly, CO2 and MIG welding machines too. Also a robotic spot welding cell was

present.

Sub-Assembly shop has around 200 types of sub-assemblies on different types

of fixtures.

3. Inventory:

This plant has a large area for inventory storage which provides sufficient buffer

time. But as SAP system is integrated in the company, all the inventory is ordered just

before the need. Thus requiring less investment and optimum space.

4. Tool Room:

In tool room, maintenance of die takes place. As a large number of dies are

required, their maintenance and repairing also plays an important role.

3

A rough layout of the company is as below:

Dispatch Area

Dispatch Area

Inventory Shop

Tool Room

Main Press

Shop

Pallet

Storage

Rework

Sub-Assembly Shop

Dispatch

Scrap Yard

Parking and Garden

Fig. 1.1 Company Layout

4

1.3 Objective

The project is about optimizing the productivity in the Sub-Assembly procedure of Rear

Bumper Bracket of Mahindra Verito by modification of fixture. The existing process is more

time consuming, so we have to develop a new fixture which will increase the productivity.

Chapter two is about the sub assembly shop layout, welding fixtures and types of

welding fixtures, spot welding and types of spot welding guns used in MUSCO. The product

details are explained in the third chapter along with Description about how panels are located

on fixtures. Existing sub-assembly procedure is done in the fourth chapter. Chapter five has the

detailed description about the procedure followed for existing welding procedure. Chapter six

defines the various problems encountered with the existing system. Literature review is done

in seventh chapter in which definition of fixture, its purpose, 3-2-1 principle of location of a

fixture are explained. This chapter also covers elements of fixture, its types and the factors to

be considered for the design of fixture. The eighth chapter deals with the new procedure

followed for the welding. The pneumatic circuit is also explained in the same chapter. Data

collection and the analysis for the two operating procedures of spot welding procedures in in

the ninth chapter. And the last chapter, chapter number tenth, is about the conclusion and the

future scope of the project.

5

Chapter 2

SUB-ASSEMBLY SHOP FLOOR

2.1 Sub-Assembly Shop Layout

The layout of Sub-Assembly shop is as follows:

1. Mahindra Scorpio and Bolero sub-assembly section

2. Mahindra Verito and Xylo sub-assembly section

3. Storage and Rework area

4. Quality check

5. Dispatch area

6. Robotic spot welding cell

7. Pedal step spot welding section

8. Storage area

2

1

3

4

5

6

7

8

Fig. 2.1 Sub Assembly Shop Floor Layout

6

2.2 Equipment Used

Sub-Assembly shop consists of the following equipment:

2.2.1 Welding Fixtures

Welding fixture is use to hold the sheet metal workpiece during the welding

operation, clamp different types of workpieces.

2.2.2 Types of Welding Fixtures

Depending on the mode of operation they are classified as follows:

(a). Manual Welding Fixture:

In this type of fixture, the clamps used have to be operated manually

with the help of hands. Manual clamping can be the best alternative when some

or all of the following apply:

Low cost justification. Manual clamping fixtures can reduce the upfront cost of

a Pneumatic fixture up to 20%-60% in many cases.

Large and heavy work-pieces. When machining larger parts that provide much

of the rigidity necessary for absorbing machining and clamping forces due to its

weight and size, manual clamping may be an effective solution.

Attentive and experienced operators. Manual clamping can provide similar

clamping capabilities as Pneumatic clamping, as long as the operator is careful

to ensure its proper usage.

Welding Fixtures

Manual Pneumatic Handy

Fig. 2.2 Classification of Welding Fixtures

7

Manual clamping devices can vary in the force they apply to parts during

a production run. Many factors account for the variation, including clamp

position on the workpiece, but operator fatigue is the most-common fault. The

simplest and often-best way to control clamping force is to replace manual

clamps with power clamps.

(b). Pneumatic Welding Fixture:

This type of fixture uses compressed air for operating of clamps. Various

types of switches and valves are used for clamping and de-clamping operation,

limiting switches, flow control valve and sometime sensors are also used for

sequencing of the cylinders.

Pneumatic welding clamps relieve operator fatigue of clamping movements.

A number of clamps can be used simultaneously.

A number of clamps with different sequences can be simultaneously operated.

One or more clamps can be controlled from machine panel.

One or more clamps can be operated from different positions.

Fig. 2.3 Manual Fixture

8

Clamps stay locked in the event of air-failure.

Low air consumption with maximum leverage.

Large opening angle ensures easy component removal.

Assurance of maximum power to movement ratio.

Production time is reduced.

Fig. 2.4 Pneumatic Fixture

9

(c). Handy Fixtures:

This type of fixtures is mostly used on Pedestal spot welding machines.

The operator locates the fixture on workpiece then holds in hand and takes the

spots on the machine. These are small and light weight fixtures. These are made

in the company for reducing the number of manual and pneumatic fixtures. They

are mostly used when the size of brackets to be spot welded is considerably

small.

Fig. 2.5 Handy Fixture

10

2.2.3 Spot Welding

Resistance welding is one of the oldest of the electric welding processes in use

by industry today. The weld is made by a combination of heat, pressure, and time. As

the name resistance welding implies, it is the resistance of the material to be welded to

current flow that causes a localized heating in the part. The pressure exerted by the

tongs and electrode tips, through which the current flows, holds the parts to be welded

in intimate contact before, during, and after the welding current time cycle. The

required amount of time current flows in the joint is determined by material thickness

and type, the amount of current flowing, and the cross-sectional area of the welding tip

contact surfaces.

Spot welding (RSW) is a process in which contacting metal surfaces are joined

by the heat obtained from resistance to electric current. Work-pieces are held together

under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020

to 0.12 in) thickness range. The process uses two shaped copper alloy electrodes to

concentrate welding current into a small "spot" and to simultaneously clamp the sheets

together. Forcing a large current through the spot will melt the metal and form the weld.

The attractive feature of spot welding is that a lot of energy can be delivered to the spot

in a very short time (approximately ten-one hundred milliseconds). That permits the

welding to occur without excessive heating of the remainder of the sheet.

The amount of heat (energy) delivered to the spot is determined by the resistance

between the electrodes and the magnitude and duration of the current. The amount of

Fig. 2.6 Principle of Spot Welding

11

energy is chosen to match the sheet's material properties, its thickness, and type of

electrodes. Applying too little energy won't melt the metal or will make a poor weld.

Applying too much energy will melt too much metal, eject molten material, and make

a hole rather than a weld.

(a). Spot Welding Gun

Spot welding guns are normally designed to fit the assembly when

mounted on a fixture. Many basic types of guns are available, the two most

used being the direct acting type, generally known as a C type gun, where

the operating cylinder is connected directly to the moving electrode, and the

X type (also known as "Scissors" or "Pinch") where the operating cylinder is

remote from the moving electrode, the force being applied to it by means of a

lever arm. C guns are generally the cheapest and are used more. There are many

variations available in each basic type with regard to the shape and style of the

frame and arms, and also the duty for which the gun is designed with reference

to welding pressure and current. Depending upon the requirement, this guns

are chosen for the spot welding operation.

Fig. 2.7 Spot Welding Gun

12

(b). Pedestal Spot Welding Machine:

This type of machine is similar to spot welding gun except for the fact

that it is not movable and is fixed at a spot. Operator presses a foot pedal to

operate this machine. Advantage of this machine is that it can weld thick sheet

of metal because it has big cylinder which produces large amount of pressure

for the welding. It is also used to weld nuts and bolts on brackets. Handy fixture

can be used to hold different types of bracket and panels to be spot welded.

Disadvantage of this type of machine is that it is not flexible and operator has

to hold the bracket or panel in hand during spot welding.

Fig. 2.8 Pedestal Spot Welding

Machine

13

(c). Spot Welding Robot:

A robot can repeatedly move the welding gun to each weld location and

position it perpendicular to the weld spot. It can also replay programmed

welding schedules. A manual welding operator is less likely to perform as well

because of the weight of the gun and monotony of the task. Spot welding robots

should have six or more axes of motion and be capable of approaching points

in the work envelope from any angle. This permits the robot to be flexible in

positioning a welding gun to weld an assembly. Some movements that are

awkward for an operator, such as positioning the welding gun upside down,

are easily performed by a robot. By using a spot welding robot more accuracy

can be achieved and also the production time of an assembly is reduced.

Fig. 2.9 Spot Welding Robot

14

Chapter 3

PRODUCT DETAILS

3.1 Bracket and Panels used in Sub-Assembly

The product which we are concern about is the Rear Bumper Bracket of

Mahindra Verito consist of following brackets and panels as named by Mahindra rise

Company:

1. PMRL8200297206

2. PMRL8200709438

Fig. 3.1 Panel No. PMRL8200297206

Fig. 3.2 Panel No. PMRL 8200709438

15

3. PMRL8200212827

4. C-Bracket

The material used for this panels and brackets is High Strength Low Alloy Steel. This

material is used because it is light weight, low cost, safe and crashworthy. Also it gets easy

recycled and has a better life. Thickness is different for panels and bracket. Thickness of panel

is 1.2mm and that of bracket is 2mm.

Fig. 3.3 Bracket No. PMRL8200212827

Fig. 3.4 C-Bracket

16

3.2 Final Product 010BBA0080N

This final product is made on three fixtures. Total number of spots taken is 27. The

daily requirement of this product is 50.

Fig. 3.5 Final Product 010BBA0080N

17

3.3 Description about location of panels on fixtures

The description of the location of panels is as follows:

1. PMRL8200297206:

This panel is the base panel upon which other brackets and panels are spot welded.

This panel is located on fixture by two locating pin and a slot.

2. PMRL820070943:

This panel is spot welded in the end with the help of 21 spots. Two locating pin

locates the holes of this panel. This pannel is spot welded at 21 positions. Four

pneumatic cylinder clamps hold this panel in position.

3. PMRL8200212827:

This bracket is located by a locating pin mounted on a pneumatic cylinder and

a slot. This bracket is spot welded at two places. A pneumatic cylinder clamp hold

this bracket in position.

4. C-bracket:

This bracket is located by one pin and stopping block. A magnet and a manual

clamp hold this bracket in position. Four number of spots are taken for welding.

18

Chapter 4

LIST OF PROCESS

4.1 Existing Sub-Assembly Procedure

This assembly is performed in three stages.

4.1.1 Stage 1

This fixture has a total of six cylinders and three locating pins. Five

cylinders are used for clamping and one for locating pin. Firstly, operator takes

panel PMRL8200297206 (fig. 3.1) from a pallet and locates it on the fixture,

then takes the bracket PMRL8200212827 (fig. 3.2) from a crate and locates it

with location pin and a slot on the panel and spot weld on two places. Then

removes it and keep it in another pallet. This procedure takes about 30 seconds

counted from picking up the panel from the pallet to again keeping it into

another pallet.

Fig. 4.1 Sub-Assembly Stage 1

19

4.1.2 Stage 2

Second fixture consists of four cylinder, and one manual clamp. It has

three locating pins. An operator locates the panel finished from 1st fixture in 2nd

fixture and then locates the C-bracket (fig. 3.4) and spot welds it with 4 spots

and again keep it in pallet. This procedure takes about 45 seconds. It takes more

time than the previous step because number of spot welds are more.


20

4.1.3 Stage 3

In last stage, fixture has four cylinders which holds the panels with the

help of clamps. Operator locates the above panel in 3rd fixture and locates the

panel PMRL8200709438 (fig 3.2) and takes 21 spots. This is the final step so

the panel 010BBA0080N is kept in pallet and sent to the dispatch area. This

stage requires 90 seconds. This stage takes maximum amount of time because

more number of spots are taken.


21

Chapter 5

EXISTING SYSTEM

The existing sub assembly procedure includes three fixtures. The details of those

fixtures are as follows:

5.1 Fixture 1

Operator first takes Panel No. PMRL8200297206 and locates onto first fixture. Using

a locating pin, Bracket No. PMRL8200212827 is placed on the panel. For proper positioning

while spot welding, a nut is fastened to this bracket and two spots are welded. The total number

of accessories used in fixture 1 are as follows:

Pneumatic cylinders : 6

Locating pins : 3

Clamps : 5

Fig. 5.1 Fixture 1

22

5.2 Fixture 2

Operator then takes this assembly from fixture 1 and mounts it to fixture 2. C-Bracket

is then housed on this assembly with the help of a locating pin. A stopping block is provided

for proper location of this bracket. A magnet is used to hold tis bracket to its position so that

the bracket is located and positioned completely. The total number of accessories used in

fixture 2 are as follows:


Locating pins : 5

Clamps : 6

Fig. 5.2 Fixture 2

23

5.3 Fixture 3

Operator then takes this assembly from fixture 2 and mounts it to fixture 3. Panel no.

PMRL 8200709438 is then housed on this assembly with the help of total of four locating

pin. A stopping block is provided for proper location of this panel so that the panel is located

and positioned completely. The total number of accessories used in fixture 3 are as follows:


Locating pins : 4

Clamps : 4

Fig. 5.3 Fixture 3

24

Chapter 6

PROBLEM DEFINITION

The Existing sub assembly procedure was relying on three fixtures and therefore

required three stages for its job completion. The problems faced during the Existing sub

assembly procedure are as follows:

6.1 Time Management

The sequence opted in the previous procedure lead the company to the following

segregation of time (per fixture).

Stage 1 = 30 seconds



Time required / job = 30 + 45 + 90 seconds

= 165 seconds

Thus the total time required for the job to get completed by all the three fixtures was

roughly about 165 seconds. Thus for the target of 50 jobs per day,

Time required for 50 jobs = 165 * 50

= 8250 seconds

So the Existing procedure would require about 8250 seconds. Some amount of time

was required for transport of pallets from one fixture to other in the Existing procedure. In

Existing procedure this time was considered as 15 min. Thus the time required for Existing

procedure for 50 jobs,

Total time for 50 jobs = 8250 / 60 + 15 min

= 152.5 min

= 2.5 hours

25

Therefore number of jobs/ hour = 50 / 2.5

= 20 jobs / hour

Thus according to the conventional way of subassembly, it could produce 20 jobs per

hour.

6.2 Space Management

The conventional way consisted of three fixtures, each being used at three stages of

sub assembly. The space occupied by each fixture can be used for new modified fixture and

also to setup new sub assembly line. This will increase the production rate by thrice as

compared to Existing sub assembly procedure.

Fig. 6.1 Space Required for Existing Sub Assembly

26

6.3 Cost Effectiveness

The purchase cost for each fixture in the Existing procedure is about ` 4 lakhs per

fixture, which sums up to ` 12 lakhs for the entire sub assembly. The pneumatic energy

consumed by the three fixture is also one of the parameter, the new optimized sub assembly

procedure will require lesser amount of compressed air as compared to Existing sub assembly

procedure.

The Existing sub assembly procedure requires three spot welding guns. This increases

the operation cost, handling cost for these three spot welding guns.

6.4 Maintenance

The existing sub assembly procedure is required to have three fixtures and three

separate spot welding guns for the completion of the job. Hence, the maintenance required for

these fixtures and the spot welding guns increases trivially, which is a major headache for the

operator as well as the company.

Currently, total number of locating pins on fixture are 12 and total number of cylinders

are 15. Therefore their maintenance has to be carried out once in three weeks. It increases the

maintenance cost due to more number of locating pins required.

6.5 Required Manpower

The conventional way of sub assembly was in need of minimum of two operators

working simultaneously whereas in case of new improved and optimized way of sub assembly,

it will require only one skilled operator for its operation, thus operator cost is saved in new

improved and optimized way of sub assembly.

27

Chapter 7

LITERATURE REVIEW

Production devices are generally workholders with/without tool guiding/setting

arrangement. This are called Jigs and Fixtures.

7.1 Fixture

A fixture is a work-holding or support device used in the manufacturing industry.

Fixtures are used to securely locate (position in a specific location or orientation) and support

the work, ensuring that all parts produced using the fixture will maintain conformity and

interchangeability. Using a fixture improves the economy of production by allowing smooth

operation and quick transition from part to part, reducing the requirement for skilled operator

by simplifying how workpieces are mounted, and increasing conformity across a production

run.

A fixture differs from a jig in that when a fixture is used, the tool must move relative to

the workpiece, a jig moves the piece while the tool remains stationary.

Fig. 7.1 A Typical Fixture

28

The basic difference between jigs and fixtures is as follows:

7.2 Purpose

A fixture's primary purpose is to create a secure mounting point for a workpiece,

allowing for support during operation and increased accuracy, precision, reliability, and

interchangeability in the finished parts. It also serves to reduce working time by allowing quick

set-up, and by smoothing the transition from part to part. It frequently reduces the complexity

of a process, allowing for unskilled workers to perform it and effectively transferring the skill

of the tool maker to the unskilled worker. Fixtures also allow for a higher degree of operator

safety by reducing the concentration and effort required to hold a piece steady.

JIGS FIXTURES

1. It is a work holding device that holds,

supports and locates the work-piece and

guides the cutting tool for a specific

operation

1. It is a work holding device that holds,

supports and locates the work-piece for a

specific operation but does not guide the

cutting tool

2. Jigs are not clamped to the drill press

table unless large diameters to be drilled and

there is a necessity to move the jig to bring

one each bush directly under the drill.

2. Fixtures should be securely clamped to

the table of the machine upon which the

work is done.

3. The jigs are special tools particularly in

drilling, reaming, tapping and boring

operation.

3. Fixtures are specific tools used

particularly in milling machine, shapers and

slotting machine.

4. Gauge blocks are not necessary. 4. Gauge blocks may be provided for

effective handling.

5. Lighter in construction. 5. Heavier in construction.

Table 7.1 Difference between Jigs and Fixtures

29

Economically speaking, the most valuable function of a fixture is to reduce operator

costs. For example, without a fixture, operating a machine or process may require two or more

operators; using a fixture can eliminate one of the operators by securing the workpiece.

Fixtures must correctly secure a workpiece in a given orientation with respect to a

welding torch or measuring device, or with respect to another component. Whenever any

component is in space it will have 6 degrees of freedom and for correct location of that

component it is required to restrict those 6 degrees of freedom. These degrees of freedom can

be restricted by 3-2-1 location system. Such location must be invariant in the sense that the

devices must clamp and secure the workpiece in that location for the particular processing

operation.

7.3 3-2-1Principle of location

For accurate machining, the workpiece is to be placed and held in correct position and

orientation in the fixture which is again appropriately located and fixed with respect to the

cutting tool and the machine tool. It has to be assured that the blank, once fixed or clamped,

does not move at all.

Fig. 7.2 Possible degrees of freedom of a solid body

30

Any solid body may have maximum twelve degrees of freedom as indicated in Fig. 2.2.

By properly locating, supporting and clamping the blank its all degrees of freedom are to be

arrested as typically shown in Fig. 2.3

The three adjacent locating surfaces of the blank (workpiece) are resting against 3, 2

and 1 pins respectively, which prevent 9 degrees of freedom. The rest three degrees of freedom

are arrested by three external forces usually provided directly by clamping. Some of such forces

may be attained by friction. Clamping forces workpiece locating and supporting pins locating

and supporting locating pin

Fig. 7.3 Arresting all degrees of freedom of a blank in a fixture

31

7.4 Elements of Fixtures

Most fixtures have a solid component, affixed to the floor or to the body of the machine

and considered immovable relative to the motion of the machining bit, and one or more

movable components known as clamps. These clamps (which may be operated by many

different mechanical means) allow workpieces to be easily placed in the machine or removed,

and yet stay secure during operation. Many are also adjustable, allowing for workpieces of

different sizes to be used for different operations. Each component of a fixture is designed for

one of two purposes:

Location:

Locating components ensure the geometrical stability of the workpiece. They

make sure that the workpiece rests in the correct position and orientation for the

operation by addressing and impeding all the degrees of freedom the workpiece

possesses.

For locating workpieces, fixtures employ pins (or buttons), clamps, and

surfaces. These components ensure that the workpiece is positioned correctly, and

remains in the same position throughout the operation. Surfaces provide support for the

piece, pins allow for precise location at low surface area expense, and clamps allow for

the workpiece to be removed or its position adjusted. Locating pieces tend to be

designed and built to very tight specifications.

Support:

In designing the locating parts of a fixture, only the direction of forces applied

by the operation are considered, and not their magnitude. Locating parts technically

support the workpiece, but do not take into account the strength of forces applied by

the process and so are usually inadequate to actually secure the workpiece during

operation. For this purpose, support components are used.

To secure workpieces and prevent motion during operation, support

components primarily use two techniques: positive stops and friction. A positive stop

is any immovable component (such as a solid surface or pin) that, by its placement,

physically prevents the motion of the workpiece. Support components are more likely

to be adjustable than locating components, and normally do not press tightly on the

32

workpiece or provide absolute location. Support components usually bear the brunt of

the forces delivered during the operation. To reduce the chances of failure, support

components are usually not designed as clamps.

7.5 Types of Fixtures

Fixtures are usually classified according to the machine for which they were

designed. Different types of fixtures are listed below:

(a) Turning fixtures or lathe fixtures

(b) Milling fixtures

(c) Welding fixtures

(d) Fixture for broaching

(e) Fixture for boring/drilling

(f) Tapping fixture

(g) Fixture for grinding

(h) Assembling fixtures

7.6 Factors to be considered for design of Fixtures

7.6.1 Component

Design to be studied carefully

Ensure work is performed in a proper sequence

Maximum operations should be performed on a machine in single setting

7.6.2 Location

Location should ensure equal distribution of forces throughout all sequence of

operation.

Location should be hard resistant, wear resistant and high degree of accuracy.

Movement of workpiece should be restricted.

Should be full proofed to avoid improper locations of the workpiece.

Should facilitate easy and quick loading of workpiece.

33

7.6.3 Clearance

Clearance is provided in the jig or fixture body

To allow for any variation in component sizes specially casting and forging.

To allow for hand movements so that the work piece can easily place in the jig

or fixture and removal after machining.

7.6.4 Burr Grooves

A burr raised on the work piece at the start of the cut is termed a minor burr and

at the end of a cut is called a major burr. Fixture should be designed so that the

removal of the work piece is not obstructed by these burr for this suitable

clearance grooves or slots should be provided.

7.6.5 Clamping arrangements

Quick acting clamps must be used as far as possible.

The clamping should not cause any deformation to the workpiece

It should always be arranged directly above points supporting the work.

Power driven clamps are favored as they are quick acting controllable, reliable

and operated without causing any fatigue to the operators.

7.6.6 Safety

Fixtures must be safe and convenient in use, following are the some of the

factors for safety of worker working on fixtures:

Sharp corner on the body of jig and fixture should be avoided.

Sighting surfaces should be cleared.

Bolt and nut should be inside the body of jig or fixture and not protrude on the

surface.

7.6.7 Cost

Fixtures should be

Simple in construction.

Give high accuracy.

Sufficiently rigid and lightly weight.

To satisfy these conditions an economical balance has to be made.

34

Chapter 8

MODIFICATION OF FIXTURE

The design of new modified fixture is achieved by fulfilling the above mentioned criteria. The

procedure followed for modification of the fixture is as follows:

8.1 Procedure followed for modification:

1. Locating pin pneumatic unit was removed from 1st fixture. All the bolts were loosen

with Helen key and removed and dowel pins were also removed.

2. Two units were present at the 2nd fixture which was working as receiving and clamping

surface. Both were pneumatic units, removed by removing bolts and place was made to

accommodate the location pin unit of 1st fixture.

3. Fixture was taken to Tool room, marking was done at the places where the unit is to be

fitted. Bed of the fixture was drilled with the help of drilling machine and tapping was

done so that bolts could be fitted.

Fig. 8.1 Locator Pin Unit

35

4. Height of the Locating pin was adjusted so that panel could be kept and bracket could

be located.

5. Locating pin unit was fitted on the fixture and the pneumatic connection was done.

6. Panels and brackets were placed and trial was taken to check for any errors.

This new modified fixture will require less space, only one operator for the whole

sub-assembly, one spot welding gun. Also from the trail taken no errors were found in the

final sub-assembly by the Quality Checking team and this modification was accepted.

Fig. 8.2 Modified fixture

36

8.2 Pneumatic Circuit:

Fixture contains total five cylinders, two valves and four push buttons. Out of five

cylinders four are connected to one valve and the remaining one cylinder to other. Both valves

are 4/2 way valve and push buttons are 3/2 way spring return.

Pneumatic circuit of the new modified fixture when no cylinders are actuated is as

shown below:

1. The green button C1 is pressed to clamp the base panel PMRL8200297206, C1 is

connected to a 4/2 valve which actuates four cylinders which clamps and holds base

panel in position.

2. Then button L1 is pushed which is connected to other 4/2 valve which actuates Locating

pin cylinder. This pin locates bracket PMRL8200212827.

3. Then C-bracket is placed and manually clamped. Then the required amount of spots are

taken.

4. Then button L2 is pushed which de-actuates the Locating pin cylinder and followed by

C2 to de-clamp other four cylinders.

Fig. 8.3 Pneumatic Circuit for Modified Fixture when de-clamped

L1 L2 C1 C2

Locating Pin Cylinder Clamping Cylinders

37

5. Then panel PMRL8200709438 is placed in position and button C1 is pushed to again

clamp the panels in position using four cylinders and takes required spots.

Pneumatic circuit of the new modified fixture when no cylinders are actuated is as

shown below:

In all, this fixture contains four 3/2 way spring return push buttons for operating two

valves, these valves are 4/2 way and has a total of five cylinders.

Locating Pin Cylinder Clamping Cylinders

L1 L2 C1 C2

Fig. 8.4 Pneumatic Circuit for Modified Fixture when clamped

38

8.3 New Operating Procedure

For the modified fixture following procedure can be followed:

8.3.1 Step 1

Operator will first place panel PMRL8200297206 (fig. 3.1) on the fixture, then

will push pneumatic switch for the locating pin cylinder and holding cylinders and

locate bracket PMRL8200212827 (fig. 3.3) and then he will locate the other C-bracket

(fig 3.4) and clamp the manual clamp. He will take two spots on first bracket and four

spots on second as per the given standards. By doing this stage one and stage two is

performed on same fixture there by reducing the loading and un-loading time. Also the

operators fatigue to pick up and then again place the panel in pallet is removed.

Fig. 8.5 New Sub-Assembly step 1

39

8.3.2 Step 2

Then operator will de-clamp all cylinders and place and locate the remaining

panel PMRL8200709438 (fig 3.2) and again clamp the clamping cylinders. He will take

the remaining 21 spots and keep the final assembly product 010BBA0080N in pallet.

Thus stage three is also performed on same fixture.

This new procedure contains two steps and not three stages as it was in old procedure.

Only one operator will be doing this assembly. Only one spot welding gun is required. The

space required for keeping the pallets is also reduced.

Fig. 8.6 New Sub-Assembly step 2

40

Chapter 9

DATA COLLECTION AND ANALYSIS

9.1 Data Collection

The parameters of interest for the optimization of rear bumper bracket of Mahindra

Verito are as follows:

Cost effectiveness

Time management

Space management

Manpower required

The major parameter that was heavily optimized is that of the time management. For

the given target of jobs to be performed, the time required by the system newly designed takes

much less time than the conventional one. Also the number of jobs performed per unit hour

also increased significantly as compared to the conventional way of sub assembly.

9.1.1 Time Management

When the new procedure was implemented, it was observed that the time

required per step for fixture was reduced significantly.

OPTIMIZATION

PARAMETERS

COST

EFFECTIVENESS

TIME

MANAGEMENT

SPACE

MANAGEMENT

MANPOWER

REQUIRED

Fig. 9.1 Optimization parameters

41

The time segregation for new procedure when opted in the subassembly was as

follows:

Step 1 = 30 seconds

Step 2 = 30 seconds

Step 3 = 75 seconds

Thus the time required per job will be,

Time required / job = 30 + 30 + 75 seconds

= 135 seconds

Thus the total time required for the jobs to get completed by using new

procedure is about 135 seconds. Thus for the target of 50 jobs per day,

Time required for 50 jobs = 135 * 50

= 6750 seconds

= 112.5 min

= 1.875 hours

The new procedure would require about 6750 seconds that is, about 112.5

minutes.

Therefore number of jobs / hour = 50 / 1.875

= 26.66

Hence according to the Optimized way of subassembly, it is expected to produce 26

jobs per hour. Thus an increase of 6 jobs per hour will be achieved.

9.1.2 Cost Effectiveness

The purchase cost for each fixture in the old procedure is about ` 4 lakhs per

fixture, which sums up to ` 12 lakhs for the entire sub assembly. But in the new

improved and optimized way of sub assembly, the purchase cost for the only fixture

used is ` 4 lakhs.

42

Thus when company is to purchase the fixture again in future, then it would

require buying only one fixture than three fixtures. This monotonously suggests that,

instead of spending ` 12 lakhs for the entire sub assembly, the company would require

to spend only ` 4 lakhs, saving ` 8 lakhs per machine.

9.1.3 Required Manpower

The conventional way of sub assembly was in need of minimum of two

operators working simultaneously whereas in case of new improved and optimized way

of sub assembly, it will require only one skilled operator for its operation. Thus operator

cost is saved in new improved and optimized way of sub assembly.

9.1.4 Space Management

The new improved and optimized way of sub assembly includes only one fixture

which saved the space required to house the extra two fixtures on the shop floor. This

saved place was later been used by the company for some more fixtures which were

principled on the new procedure of sub assembly.

Fig. 9.2 Space Required for New Fixture

43

9.2 Analysis of both Sub-Assembly Procedures

The following graph gives the comparison between the parameters

which are improved in the new sub assembly procedure:

120

152.5

20

40

112.5

26

0

20

40

60

80

100

120

140

160

180

Cost in Rs. ( In Ten

Thousand)

Time required per 50 jobs

in mins

Number of jobs per hour

Old procedure New procedure

Fig. 9.3 Comparison between Optimization Parameters of Old and New Procedure

44

Chapter 10

CONCLUSION AND FUTURE SCOPE

10.1 Effects of Optimization

After implementation of the modification made in fixture following changes could be seen:

Old procedure

New procedure

Time required per job in seconds

165

135

Time required for 50 jobs for entire sub

assembly in minutes

152.5

112.5

Total number of jobs per hour

20

26

Cost for complete sub assembly in `

`12,00,000

`4,00,000

Manpower required for complete sub assembly

2

1

Space required for complete sub assembly

More

Less

Table 10.1 Effect of Optimization

45

10.2 Conclusion

So the key features of this project are:

Optimization of workspace. Instead of three fixtures, only one fixture is required.

This available space can be utilized for setting up new sub-assemblies.

Reduction in Operator, now instead of two, only one operator is required.

Reduction in the total time required for the sub-assembly. Earlier 165 seconds were

required for one job to be completed, now only 130 seconds are required. This

resulted in increase in number of jobs per hour from 20 to 26.

Reduction in number of spot welding guns required, which can be used elsewhere

in the sub-assembly shop for other sub-assemblies.

Reduction in the consumption of compressed air, optimizing the consumption of

energy.

Future investment required in the same sub-assembly which as to be

done per two years due to up-gradation in the design will cost only ` 4

lakhs instead of ` 12 lakhs saving ` 8 lakhs.

10.3 Future Scope:

There may be a very little chance for the bracket PMRL8200212827 getting

offset by a small distance. This can be corrected by providing the locating pin with few

threading to it and locking the bracket with a wing nut, so that, the bracket can be

clamped with precision. Such that accuracy to spot weld that bracket can be further

increased.

A PLC circuit can be designed to make the fixture automated such that it can be

used for robotic spot welding.

46

REFERENCES

BIBLIOGRAPHY

P. H. Joshi, Jigs and fixtures Design Manual

McGraw-Hill Publications, Second Edition 2003

WEBSITES

Pneumatic Welding Fixtures

[email protected], 1-oct-13, 20:09

Manual Welding Fixtures

http://www.dmtworkholding.com/manualclampingfixturebenefits, 28-sept-13, 16:09

PAPERS

Design and Manufacturing of Modular Welding Fixture

National Conference on modular welding fixture- B.V.M. Engineering College V.V.

Nagar Gujarat India. (13-14 May 2011)

www.bvmengineering.ac.in/docs/published%20papers/601047.pdf, 01-oct-13, 19:59

Handbook for Resistance Spot Welding (pdf), 2012

ww.millerwelds.com/pdf/Resistance.pdf, 28-sept-13, 16:25

Chapter introduction to jig and fixture (pdf)

www.nitc.ac.in/dept/me, 1-oct-13, 19:58

Jigs (pdf)

www.ignou.ac.in,1-oct-13, 20:00

Spot Welding (pdf)

www.ewf.be/media/documentosDocs/doc_20_spot_welding.pdf, 1-oct-13, 11:47

Materials in Automotive Application, State of the Art and Prospects, Elaheh

Ghassemieh University of Sheffield, UK (pdf)

www.intechopen.com/download/pdf/13343, 4-oct-13, 12:45

productivity improvement by designing a fixture

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