Design & Construction of a Universal Coupling

A project report submitted to the department of Mechanical Engineering, Khulna university

of Engineering & Technology in partial fulfillment of the requirements for the

“Course of ME-3118”

Supervised by Submitted by

Md. Rasedul Islam Antu Datta

Lecturer, Roll No: 1205001

Department of Mechanical Engineering Zulfikar Habib Khan

Khulna University of Engineering & Technology Roll No: 1205003

Md. Shariful Islam

Roll No: 1205004

Sudip Saha

Roll No: 1205005

June 2015

Department of Mechanical Engineering

Khulna University of Engineering & Technology

Khulna-9203, Bangladesh

i

Acknowledgements

All the praises to the almighty who makes authors capable to complete this project work

successfully. The authors are very much indebted to their course teachers Md.Golam Kader ,

professor of department of Mechanical Engineering, Khulna University of engineering &

technology, Bangladesh, and Md. Rasedul Islam ,Lecturer of department of Mechanical

Engineering, Khulna University of engineering & technology, Bangladesh, for their wise

inspiration to do such extraordinary project work. The authors express the heart- felt respect to

them for their proper guidance and all kind of support to perform and complete this special work.

The authors are extremely grateful to Prof. Dr. Nawsher Ali Moral ,Head of the department

of mechanical engineering Khulna University of engineering & technology, Bangladesh, to

provide such a good opportunity to do the experimental work and for providing all other

supports.

May ALLAH bless both of the course teachers.

“Authors”

ii

Abstract

A coupling is a device used to connect two shafts together at their ends for the purpose of

transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment

while permitting some degree of misalignment or end movement or both.

A Universal coupling is a special type of coupling in which misalignment of shafts is allowed.

Shafts are free to move any direction in order to transmit torque or power from one shaft to

another.

In this project work a Universal coupling was designed, in which safe torque on shafts and pin

size of cross determined.

Finally the Universal coupling made by Mild Steel, which is low cost and available in every

workshop.

iii

CONTENTS

Page

Acknowledgement………………………………………………………………….…………i

Abstract…………………………………………………………………………….….………ii

List of Figures…………………………………………………………………………………v

List of Tables………………………………………………………………………………….vi

Nomenclature…………………………...………………………………………….…………vii

CHAPTER-І: INTRODUCTION

1.1 Introduction………………………………………………………………………………..2

1.2 Objectives……………………………………………………….…………………………3

CHAPTER-ІІ: LITERATURE REVIEW

2.1 Historical Background…………………………………………….…………………..........5

2.2 Coupling…………..…………………………………….……………….…….……………5

2.3 Types of coupling…………….………………………………………….………………….5

2.4 Rigid Couplings …………………………………………………………….………....……6

2.5 Flexible couplings …………………………………………………………………….…….6

2.6 Miscellaneous Couplings ………………………………………………………………..….7

2.7 Universal Coupling or Hooke’s coupling …………………………….…………………..…8

2.8 A simple brief about U joint……………………………………………………..................9

2.9 Types of Universal coupling…………………………………………….……………….…..9

2.9.1 Single joints Universal coupling…………………………………….……………..10

2.9.2 Double joints Universal coupling………………………………….………………10

2.9.3 Assembled joints Universal coupling…………………………………...…………10

2.10 Field of Applications of Universal Coupling………………………………………………11

iv

CHAPTER-ІІІ:

3.1 Introduction ………………………………………………...………….…………………12

3.2 Problem………………………………………..………….………….……………………12

3.3 Solution……………………………………………….………….………….…………….14

3.4 Our Designed dimension………………………………………………..…………………16

3.5 CAD design and Rendered view…………………………………..………….…………..17

3.6 Material………………………………………………..………..………………………….18

3.7 Selection Guide………………………………………………..………….………………..18

CHAPTER-ІV:

4.1 Machine & Apparatus Required………………………..………………..………………..20

4.2 Machining Processes…………………………………..………………..…………………20

4.2.1 Drafting…………………..………………..………………..…………….……20

4.2.2 Gas Cutting……………………………………………………………………20

4.2.3 Facing…………………………..………………..…………………………….21

4.2.4 Turning………………………………..………………..………………………21

4.2.5 Grinding…………………………………………..………………..…………21

4.2.6 Drilling………………………..………………..………………..…………….22

4.3 FINAL PROJECT……………………………………………………………………….23

CHAPTER-V

5.1 Discussion……………………………………………………………………….……..25

5.2 Conclusion…………….……………………………………………………………….25

References………………………………………………………………………….…….26

v

LIST OF FIGURES

Figure Title Page

Figure-1.1 Different types of alignment……………………………...2

Figure-2.1 Flanged Coupling…………………………………………6

Figure-2.2 Muff coupling …………………………………………….6

Figure-2.3 Flanged Pin Bush Couplings ……………………………..7

Figure-2.4 Gear Tooth Coupling ……………………………………..7

Figure-2.5 Oldham’s Coupling …………………………….………....7

Figure-2.6 Universal Coupling ……………………………….………7

Figure-2.7 Jaw type coupling …………………………………………8

Figure-2.8 Sleeve type coupling………………………………….……8

Figure-2.9 Universal Coupling ………………………………………..8

Figure-2.10 A simple brief about U joint………………………………9

Figure-2.11 Single Joint……………………………………………….10

Figure-2.12 Double joint ………………………………………………10

Figure-2.13 Telescopic Joint ……………………………………….….10

Figure-3.1 Problem fig………………………………………………..13

Figure-3.2 Solution fig………………………………………….….…14

Figure-3.3 Dimensions of the cross………………………….……….16

Figure-3.4 Dimensions of the shaft…………………………….…….16

Figure-3.5 CAD design………………………………………..…..…17

Figure-3.6 Rendered view of CAD design……………………...…...17

Figure-4.1 A typical draft ………………………………….………..20

vi

Figure-4.2 Gas Cutting………………………………………………20

Figure-4.3 facing operation on Lathe machine………………...….…21

Figure-4.4 Turning operation on Lathe machine……………………21

Figure-4.5 Grinding operation………………………………………21

Figure-4.6 Drilling operation………………………………….……21

Figure-4.7 Designed product……………………………..…………23

LIST OF TABLES

Table Title Page

Table-3.7 Selection Guide………………………………..…18

vii

NOMENCLATURE

Symbol Description

Ns2 …………………………………………………. Angular velocity of the driven shaft

Ns1 ………………………………………………… Angular velocity of the driver shaft

Θ…………………………………………………….Angle between axes of the shafts

α………………………………………………….... Angle of the driving shaft from the position

where the pins of the drive shaft yoke are

F…………………………………………………….Force

M……………………………………………………Torque applied to shaft

Sb………………………..………………………….Bearing stress

Ss…………………………………………………..Transverse shear stress

Sc……………………………………………….….Compressive stress

A…………………………………………………...Cross-sectional area of pin

d………………………………………………...…Diameter of pin

I……………………………………….……….….Mass moment of inertia

1

Chapter One:

Introduction

Objectives

2

1.1 Introduction:

Couplings are mechanical elements that ‘couples’ two drive elements which enables motion to be transferred from one element to another. The drive elements are normally shafts. We tend to see lot of applications of the couplings mainly in the automobiles, for example the drive shaft which connects the engine and the rear axle in a bus or any automobile is connected by means of a universal joint.[1]

The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime. There are various types of coupling based on area of application and misalignment or degree of freedom to move in any direction. Such as the universal coupling allows the shafts to move in any directions. The different types of alignments are:[2]

Fig.1.1: Different types of alignment

Details about different types of coupling will be discussed latter.

3

1.2 objectives:

The main objectivesof this project work are-

I. To solve a problem related to Universal coupling

II. To design that problem

III. To calculate the safe torque on shaft.

IV. To know about its application.

4

Chapter Two:

Historical Background

Coupling

Types of coupling

Rigid Couplings

Flexible or Compensating Couplings

Miscellaneous Couplings

Universal Coupling or Hooke’s Coupling

A simple brief about Universal Coupling

Types of Universal coupling

Field of Applications of Universal Coupling

5

2.1: Historical Background:

The main concept of the universal joint is based on the design of gimbals, which have been in

use since antiquity. The first person known to have suggested its use for transmitting motive

power was GerolamoCardano, an Italian mathematician, in 1545, although it is unclear whether

he produced a working model. In Europe, the device is often called the Cardan joint or Cardan

shaft. Christopher Polhem of Sweden later reinvented it, giving rise to the name Polhemsknut in

Swedish.

Gaspar Schott ((1664), who called it the paradoxum, but mistakenly claimed that it was

a constant-velocity joint. Shortly afterwards, between 1667 and 1675, Robert Hooke analysed the

joint and found that its speed of rotation was nonuniform, but that this property could be used to

track the motion of the shadow on the face of a sundial. The first recorded use of the

term universal joint for this device was by Hooke in 1676, in his book Helioscopes. He

published a description in 1678, resulting in the use of the term Hooke's joint in the English-

speaking world. In 1683, Hooke proposed a solution to the non-uniform rotary speed of the

universal joint: a pair of Hooke's joints 90° out of phase at either end of an intermediate shaft, an

arrangement that is now known as a type of constant-velocity joint.

The term universal joint was used in the 18th centuryand was in common use in the 19th century.

19th century uses of universal joints spanned a wide range of applications. Numerous universal

joints were used to link the control shafts of the Northumberland telescope at Cambridge

University in 1843. The term Cardan joint appears to be a latecomer to the English language.[3]

2.2 Coupling:

Couplings are mechanical elements that ‘couples’ two drive elements which enables motion to

be transferred from one element to another. The drive elements are normally shafts.Couplings

are used to connect two shafts for torque transmission in varied applications. It may be to

connect two units such as a motor and a generator or it may be to form a long line shaft by

connecting shafts of standard lengths say 6-8m by couplings.

2.3 Types of coupling:

Based on the area of applications there are various types of coupling available. But they are

generally categorized in the following varieties-[1]

6

i. Rigid Couplings

ii .Flexible or Compensating Couplings

iii. Miscellaneous Couplings

2.4 Rigid Couplings:

Rigid Couplings are mainly used in areas where the two shafts are coaxial to each other. There

are many types of couplings that fall under the rigid couplings category. They are

i. Flanged Coupling

ii. Muff coupling

Fig 2.1: Flanged Coupling Fig 2.2 : Muff coupling

2.5 Flexible or Compensating Couplings :

Flexible couplings are normally used in areas where the coaxiallity between the connecting

shafts is not always assured and in areas where there is a possibility of occurrence of shocks in

the transmission is applicable. They are also called as Elastic Couplings. By construction these

couplings tend to have an elastic member in between the two connecting entities. The different

types of flexible couplings are

i.Flanged Pin Bush Couplings

ii. Bibbly Coupling

iii. Gear Tooth Coupling

iv. Tyre couplings

7

v. Elastomeric Couplings

vi. Oldhams Coupling

vii. Universal Coupling or Hooke’s Coupling (OUR CONCERN)

2.6 Miscellaneous Couplings:

This group of couplings incorporate design features which are frequently unique,approximations

or combiations of universal,Oldham and flexible shaft couplings.such as- Jaw type coupling

and Sleeve type coupling.

8

2.7 Universal Coupling or Hooke’s coupling:

A universal joint, (universal coupling, U-joint, Cardan joint, Hardy-Spicer joint, or Hooke's

joint) is a joint or coupling that allows the shafts to 'bend' in any direction, and is commonly

used in shafts that transmit rotary motion. It consists of a pair of hinges located close together,

oriented at 90° to each other, connected by a cross shaft. The universal joint is not a constant

velocity joint.

Fig 2.9: Universal Coupling

9

2.8 A simple brief about Universal Coupling:

A universal joint is like a ball and socket joint that constrains an extra degree of rotational

freedom. Given axis 1 on body 1, and axis 2 on body 2 that is perpendicular to axis 1, it keeps

them perpendicular. In other words, rotation of the two bodies about the direction perpendicular

to the two axes will be equal.

In the picture, the two bodies are joined together by a cross. Axis 1 is attached to body 1, and

axis 2 is attached to body 2. The cross keeps these axes at 90 degrees, so if you grab body 1 and

twist it, body 2 will twist as well.

A Universal joint is equivalent to a hinge-2 joint where the hinge-2's axes are perpendicular to

each other, and with a perfectly rigid connection in place of the suspension.

Universal joints show up in cars, where the engine causes a shaft, the drive shaft, to rotate along

its own axis. At some point you'd like to change the direction of the shaft. The problem is, if you

just bend the shaft, then the part after the bend won't rotate about its own axis. So if you cut it at

the bend location and insert a universal joint, you can use the constraint to force the second shaft

to rotate about the same angle as the first shaft.[4]

Fig 2.10: A simple brief about U joint

2.9 Types of Universal coupling:

The universal couplings are categorized as-[5]

i. Single joints

10

ii. Double joints

iii.Telescopic or assembled joints

2.9.1 Single joints Universal coupling:

Precision single joints suit angles up to 45° and speeds to 4000 r/min. Shaft sizes 6 to 50 mm,

dimensions to DIN 808.

Fig 2.11: Single Joint Fig 2.12: Double joint

2.9.2 Double joints Universal coupling:

Precision double joints suit angles up to 90° and give constant velocity output. Shaft sizes 6 to 50

mm, dimensions to DIN 808.

2.9.3 Assembled joints Universal coupling:

Telescopic universal joint with plain bearings either to standard lengths or customised to your

requirements. Angles up to 45° per joint and speeds to 1000 r/min, Type HA offers higher

speeds.

11

Fig 2.13: Telescopic Joint

2.10 Field of Applications of Universal Coupling:

Typical applications of universal joints include-

AUTOMOBILE

Aircraft

Appliances

Control mechanisms

Electronics instruments

Medical & optical devices

Ordinance radio

Sewing machines

Textile machineries etc.

12

Chapter Three:

Introduction

Problem

Solution

Our Designed dimension

CAD design and Rendered view

Material

Selection Guide

3.1 Introduction:

To design is either to formulate a plan for the satisfaction of a specified need or to solve a

problem. If the plan results in the creation of something having a physical reality, then the

product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.

Design is an innovative and highly iterative process. It is also a decision-making process.

Decisions sometimes have to be made with too little information, occasion-ally with just the

right amount of information, or with an excess of partially contradictory information. Decisions

are sometimes made tentatively, with the right reserved to adjust as more becomes known. The

point is that the engineering designer has to be personally comfortable with a decision-making,

problem-solving role.[6]

3.2 Problem:[7]

A universal coupling (universal joint, or Hooke’s joint) is used to connect two shafts which

intersect but which are not necessarily in the same straight line, as shown in Fig below. The

angular velocity of the output shaft is not equal to the angular velocity of the input shaft, unless

the input and output shafts are in line. The ratio of speeds is given by

Ns2

Ns1 =

cosθ

1 − Cos2αSin2θ

Where

Ns2 = angular velocity of the driven shaft

13

Ns1 = angular velocity of the driver shaft

θ=angle between axes of the shafts

α= angle of the driving shaft from the position where the pins of the drive shaft yoke are in the

plane of the two shafts.

A torque of 40N m is applied to shaft S1 of a universal joint in which S1 and the output shaft S2

are in the same horizontal plane.

Fig 3.1: Problem fig

a. Determine the torque on shaft S2 for the position shown in Fig.

b. Determine the size of the pins of the connecting cross for an allowable bearing stress of

14 MPa (per projected area), an allowable bending stress of 140 MPa, and an allowable

shear stress of 70 MPa.

c. Calculate the maximum shear stress on section E-E, which is 50 m from axis Y-Y.

14

3.3 Solution:

(a)

The components of F, acting on the shaft S1, are

F cos200 and F sin200.

The troque acting on the shaft S1 due to the action of the cross is

Mt= ( F cos200)(0.05)

or, 40 = ( F cos200)(0.05)

or, F = 851N

The torque on the shaft S2 is

0.05 =(851)(0.05) = 42.6 Nm. (Ans.)

Fig 3.2: Solution fig

15

(b)

(1) The size of the pins will depend on the maximum load, which occurs for the position

shown.

The maximum pin load is 851N.

Diameter of pin based on bearing:

sb = �

�

or, 140 * 106 =���

�.����

or, d = 10 mm

(2) Diameter of pin bending on based:

s = ��

�

or, 140 * 106 = ���∗�,���(

�

��)

��

�����

or, d = 7.2 mm

(3) Diameter of pin based on transverse shear:

Ss = 4 3� * � ��

or, 70 * 106 = (4 3� )(851�

���2� )

or, d = 4.6 mm

Therefore bearing dictates the minimum size of pin; a 10mm diameter pin should be

satisfactory.

(c)Maximum compressive stress at section E-E is

Sc = ��

� +

�

� =

���∗�,��∗�.����

�.���∗(�.���)�/�� +

���

�.���∗�.���= 65.9 MPa

Maximum shear = �

� * (65.9) = 33 Mpa (Ans.)

16

3.4 Our Designed dimension:

Fig 3.3: Dimension of the cross

Fig 3.4: Dimensions of the shaft

17

3.5 CAD design and Rendered view:

Fig 3.5: Cad design of universal coupling

Fig 3.6: Rendered view of the cad design

18

3.6 Material:

Considering cost, strength, ease of access taken into account the selected material for this design

is MILD STEEL.

3.7 Selection Guide:[5]

19

Chapter Four:

Machine & Apparatus Required

Machining Process

Methodology

Final Project

20

4.1 Machine & Apparatus Required:

Lathe

Drilling

Grinding machine

Welding apparatus

4.2 Machining Processes:

4.2.1 Drafting:It’s a pre-manufacturing process in which a replica of the designed

prototype is made.

Fig.4.1: A typical draft Fig 4.2: Gas Cutting

4.2.2 Gas Cutting: Oxy-fuel welding (commonly called oxyacetylene welding, oxy

welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and

oxygen to weld and cut metals, respectively.

The common methods used in cutting metal are oxygas flame cutting, air carbon-arc cutting, and

plasma-arc cutting. The method used depends on the type of metal to be cut and the availability

of equipment. As a Steelworker, oxygas or air carbon-arc equipment is the most common type of

equipment available for your use.

21

4.2.3 Facing:Facing is the process of removing metal from the end of a work-piece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

Fig 4.3: facing operation on Lathe machine Fig 4.4: Turning operation on Lathe

machine

4.2.4 Turning:Turning is the removal of metal from the outer diameter of a rotating cylindrical work-piece. Turning is used to reduce the diameter of the workpiece, usually to a specified dimension, and to produce a smooth finish on the metal. Often the workpiece will be turned so that adjacent sections have different diameters.

4.2.5 Grinding:Grinding is a finishing process used to improve surface finish, abrade hard materials, and tighten the tolerance on flat and cylindrical surfaces by removing a small amount of material. Information in this section is organized according to the subcategory links in the menu bar to the left.

Fig.4.5:Grinding operation Fig 4.6:Drilling operation

22

4.2.6 Drilling:Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit is pressed against the workpiece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the work-piece, cutting off chips (swarf) from the hole as it is drilled.

4.3 Methodology:

Various Machines were used for several machining processes:-

I. Lathe machine was used for facing, turning.

II. Drilling machine was used for drilling & boring.

III. Grinding machine was used for surface finishing.

IV. Welding apparatus was used to connect different parts at the time of setting up.

23

4.4 FINAL PROJECT:

Fig 4.7: Designed product

24

Chapter Five:

Discussion

Conclusion

25

5.1 Discussion:

Mechanical couplings have a principal use in the connection of rotating shafts for the transfer of

rotary motion and torque. As with all mechanical devices, a coupling must match its’ intended

purpose and application parameters, including many different performance, environmental, use

and service factors. There are various reasons for which a coupling fails, such as-improper

installation, excessive vibration, abnormal noise and chattering etc. The failure of coupling can

be minimized by proper maintenance, such as-checking and changing lubricant regularly,

performing visual inspection, checking signs of wear and fatigue and cleaning coupling

regularly etc.

5.2 Conclusion:

Mechanical design is a complex undertaking, requiring many skills. Design and fabrication of a

Universal coupling was done in this project work. In designing problem safe torque on shaft was

determined. The cross pin size (diameter) was determined considering bearing stress, shearing

stress and bending stress taken into account. The application of a universal coupling also studied

in this project work.

26

References:

[1]: http://www.brighthubengineering.com/machine-design/43237-shaft-couplings-

types/#imgn_1

[2]:https://www.google.com.bd/search?q=types+of+misalignment&espv=2&biw=1093&bih=53

4&tbm=isch&imgil=NT3Hya-

mp4X71M%253A%253BWa1ZBFnm6w2zQM%253Bhttp%25253A%25252F%25252Fsdp-

si.com%25252FD757%25252Fcouplings1.htm&source=iu&pf=m&fir=NT3Hya-

mp4X71M%253A%252CWa1ZBFnm6w2zQM%252C_&usg=__Ctk4urH8tWcUMRt3asG7xLg

nZ1E%3D&ved=0CDoQyjc&ei=LQaFVfKnHY28uATA5YMg#imgrc=NT3Hya-

mp4X71M%253A%3BWa1ZBFnm6w2zQM%3Bhttp%253A%252F%252Fsdp-

si.com%252FD757%252FImages%252Ffig1.gif%3Bhttp%253A%252F%252Fsdp-

si.com%252FD757%252Fcouplings1.htm%3B550%3B250&usg=__Ctk4urH8tWcUMRt3asG7x

LgnZ1E%3D

[3]: Mills, Allan, "Robert Hooke's 'universal joint' and its application to sundials and the sundial-

clock", Notes & Records of the Royal Society, 2007, accessed online 2010-06-16

[4]: http://ode-wiki.org/wiki/index.php?title=Manual:_Joint_Types_and_Functions

[5]: http://www.techdrives.co.uk/Multimedia/Shaft%20Couplings/shaft-couplings-universal-

joints-feb13.pdf

[6]: Budynas−Nisbett,” Shigley’s Mechanical Engineering Design”, Eighth Edition, McGraw-

Hill, ISBN: 0−390−76487−6

[7]: Hall, Holowenko,Laughlin,”Theory and problems of Machine Design” ,SI metric edition,

Schaum’s outline series.