Mechanical design engineering handbook

Mechanical Design Engineering

Handbook

Mechanical Design

Engineering Handbook

Peter RN Childs

Second edition

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Preface to the second edition

This edition of the Mechanical Design Engineering Handbook has been extensively

updated. Each chapter has been reviewed and developed. Chapters 1 and 2 dealing

with the design process and specification have been updated with a development of

the total design process and an introduction to project management. Chapter 3 has

been revised substantially incorporating developments in creativity and ideation pro￾cesses relevant to engineering. Chapter 4 has been further developed to illustrate the

scope and context of machine elements.

Chapters 5 and 6 introducing the first of the machine elements to be considered in

detail, bearings, have been expanded to include flow charts illustrating the design of

boundary lubricated, hydrodynamic and ball bearings. The introductory and extended

worked examples have been retained throughout the chapters on machine elements in

the book to enable the reader to follow the detailed analysis and associated design

decisions. Chapter 7 addressing shaft design has been expanded to include consider￾ation of a factor of safety according to the DE Goodman, DE Gerber, DE ASME ellip￾tic and DE Soderberg criteria. Chapters 8–11 introducing gears have been expanded to

include flow charts for the selection of spur gears, and the calculation of bending and

contact stresses, and the design of gear sets using the AGMA equations. Similarly

Chapter 13 introducing belt and chain drives has been extended with flow charts

for the selection and design of wedge and synchronous belts, and roller chain drives.

Chapter 14 on seals has been updated to include additional examples. Chapter 15

has been extended to include selection and design flow charts for helical compression

spring and helical extension spring design. Chapters 16–18 have been extended with

additional examples of various fastener, wire rope, and pneumatic and hydraulic tech￾nologies, respectively. Three short case studies have been included in Chapter 19 illus￾trating the importance of a detailed consideration of tolerancing in precision

engineering. Chapter 20 is a new chapter providing an overview of a diverse range

of machine elements as building blocks for mechanism design.

Throughout the text an additional 100 or so images have been included in order to

aid the reader in becoming familiar with the technology being considered.

Mechanical engineering design is an engaging subject area with many applications

and this major revision has been a pleasurable undertaking enabling implementation

of many updates from my engineering and design practice and associated interactions.

I hope this text is able to aid the reader in the development of understanding of the

principles and associated technology and in its implementation in worthwhile innova￾tions and applications.

Acknowledgements

I have the delight of having developed and practised my design and engineering

skills and their application with so many impressive individuals and organisations.

I would like to thank my colleagues at Imperial College London and Q-Bot Ltd,

and former colleagues from the University of Sussex for their extensive support

and patience through the years. Without the chance to practise engineering and design

on exciting and ambitious commercial applications and research projects, the oppor￾tunity to develop knowledge is limited. I have had the privilege of working with

diverse companies and organisations including Rolls-Royce plc, Alstom, Snecma,

DaimlerChrysler, BMW, MTU, Volvo, Johnson Matthey, Siemens, Industriales

Turbinas Propulsores, Fiat Avio, Airbus, Ricardo Consulting Engineers, Ford, Rio

Tinto, McLaren, Dyson, Naked Energy and Q-Bot Ltd, Innovate UK, the EPSRC

and Horizon 2020. I would like to thank the engineers, designers and managers from

these companies and organisations for the opportunity to engage in such exciting

technologies.

Several colleagues in particular have been very helpful in the implementation of

this edition including Shayan Sharifi and Andy Brand who assisted with proof reading,

Ben Cobley and Ruth Carter who assisted with several of the images. Many collab￾orators and companies have kindly given permission to include key images to aid in

the effective presentation of this book and this is gratefully acknowledged. Finally,

I would like to thank my wife Caroline for her patience over the last year when I have

expended a significant number of hours working on this project.

Peter Childs

Professor and Head of School, Dyson School of Design Engineering,

Imperial College London, United Kingdom

1 Design

Chapter Outline

1.1 Introduction 2

1.2 The design process 4

1.2.1 Case Study 7

1.3 Total design 10

1.3.1 Need/Opportunity Analysis 12

1.3.2 Specification 12

1.3.3 Conceptual Design 12

1.3.4 Detailed Design 13

1.3.5 Manufacturing And Production 13

1.3.6 Sustainable Enterprise 14

1.3.7 Total Design Information Flows And Activities 15

1.4 Systematic design 16

1.5 Double diamond 19

1.6 Conceive, design, implement, operate 19

1.7 Design for six sigma 20

1.8 Design optimisation 21

1.9 Project management 23

1.9.1 The Traditional Approach 25

1.9.2 PRINCE and PRINCE2 32

1.9.3 Waterfall 33

1.9.4 Das V Modell 36

1.9.5 Stage-Gate 36

1.9.6 Agile 39

1.10 Design reviews 41

1.11 The technology base 41

1.12 Conclusions 44

References 44

Standards 46

Websites 46

Further reading 47

Abbreviations

BS British Standard

CDIO conceive, design, implement, operate

CDR critical design review

CTP critical to process

Mechanical Design Engineering Handbook. https://doi.org/10.1016/B978-0-08-102367-9.00001-9

© 2019 Elsevier Ltd. All rights reserved.

CTQ critical to quality

DFA design for assembly

DFM design for manufacture

DFSS design for six sigma

DMADV design, measure, analyse, design, verify

DoE design of experiments

ERP Enterprise resource planning

FMEA failure mode and effects analysis

ID Identifier

IDOV identify, design, optimise, verify

ISO International Organisation for Standardisation

KPI key point indicator

MDO multiobjective design optimisation

PDS product design specification

PID project initiation document

QFD quality function deployment

PDR preliminary design review

PLR Postlaunch review

PRINCE Projects IN Controlled Environments

R&D research and development

SDR system design review

SMART specific, measurable, achievable, relevant, time-bound

XP extreme programming

1.1 Introduction

The aims ofthis book are to present an overview ofthe design process andtointroducethe

technology and selection of a number of specific machine elements that are fundamental

to a wide range of mechanical engineering design applications. This chapter introduces

the design process from an inventor’s perspective and double diamond to more formal

models such as ‘total design’ and systematic approachesto design. The chapterintroduces

a series of approachesto project management and concludes with an overview ofthetech￾nology base serving as building blocks for machinery and mechanical design.

The term designis popularly usedto referto an object’s aesthetic appearance with spe￾cific reference to its form or outward appearance as well as its function. For example we

often referto designer clothes, designicons and beautiful cars, and examples of some clas￾sically acclaimed vehicles are given in Figs 1.1 and 1.2. Inthese examples itis both visual

impact, appealing to our visual perception, and the concept of function, that the product

will fulfil a range of requirements, which are important in defining so-called good design.

The word ‘design’ is used as both a noun and a verb and carries a wide range of

context-sensitive meanings and associations. George Cox (2005) stated “Design is

what links creativity and innovation. It shapes ideas to become practical and attractive

propositions for users or customers. Design may be described as creativity deployed to

a specific end.” The word design has its roots in the Latin word ‘designare’, which

means to designate or mark out. Design can be taken to mean all the processes of con￾ception, invention, visualisation, calculation, refinement and specification of details

2 Mechanical Design Engineering Handbook

that determine the form of a product. Design generally begins with either a need or

requirement or, alternatively, an idea. It can end with a set of drawings or computer

representations and other information that enables a product to be manufactured, a

service or system realised and utilised. While recognising that there are no widely

accepted single definitions, to clarify what the term design means the following state￾ment can provide a basis.

Design is the process of conceiving, developing and realising products, artefacts,

processes, systems, services, platforms and experiences with the aim of fulfilling iden￾tified or perceived needs or desires typically working within defined or negotiated

constraints.

This process may draw upon and synthesise principles, knowledge, methods skills

and tools from a broad spectrum of disciplines depending on the nature of the design

initiative and activity. Design can also be regarded as ‘the total activity necessary to

Fig. 1.1 Piaggio’s Vespa launched in 1946. The Vespa was an early example of monocoque

construction where the skin and frame are combined as a single construction to provide

appropriate rigidity and mounting for the vehicle’s components and riders.

Design 3

provide a product or process to meet a market need’. This definition comes from the

SEED (Sharing Experience in Engineering Design, now DESIG the Design Education

Special Interest Group of the Design Society) model, see Pugh (1990).

According to a Royal Academy of Engineering document, engineering can be

defined as

The discipline, art and profession of acquiring and applying scientific, mathematical,

economic, social and practical knowledge to design and build structures, machines,

devices, systems, materials and processes that safely realise solutions to the needs of

society.

This definition is not attributed to a single individual and ABET (2011), the Insti￾tution of Mechanical Engineers and the National Academy of Engineering (2004) all

have similar definitions for engineering involving the application of scientific and

mathematic principles to design. The following statement provides an indication of

the scope of engineering.

Engineering is the application of scientific and mathematic principles in combination

with professional and domain knowledge, to design, develop and deliver artefacts,

products and systems to realise a societal, commercial or organisation requirement

or opportunity.

The terms ‘engineering design’ and ‘design engineering’ are often used inter￾changeably. The inclusion of the word engineering in both suggests that they involve

the application of scientific and mathematical knowledge and principles. It may be

useful to think of ‘engineering design’ sitting alongside ‘engineering science’ as

the strand of engineering that is concerned with application, designing, manufacture

and building. Design engineering suggests a process in which engineering (scientific

and mathematical) approaches are applied in the realisation of activities that began

with a design concept or proposal (Childs and Pennington, 2015). However such dis￾tinctions remain subtle and subject to context.

1.2 The design process

Design processes abound and have been widely documented, with many design

schools, consultancies and engineering corporations developing their own brand of

approaches (see, e.g. Clarkson and Eckert 2005). Commonly cited methods include

the educational approach CDIO (conceive, develop, implement, operate), total design,

double diamond, concurrent engineering, six sigma, MDO (multiobjective design

optimisation) and gated reviews. Design processes can be broadly categorised as

activity-based, involving generation, analysis and evaluation, and stage-based,

involving distinct phases of, for example, task clarification and conceptual design.

It is also widely recognised that experienced practitioners approach design in a differ￾ent manner to novice designers (see, e.g. Bj€orklund 2013).

4 Mechanical Design Engineering Handbook

Probably from your own experience you will know that design can consist of exam￾ining a need or opportunity and working on the problem by means of sketches, models,

brain storming, calculations as necessary, development of styling as appropriate, mak￾ing sure the product fits together and can be manufactured, and calculation of the

costs. The process of design can be represented schematically to levels of increasing

formality and complexity. Fig. 1.3 represents the traditional approach associated with

lone inventors. This model comprises the generation of the ‘bright idea’, drawings and

calculations giving form or shape to the idea, judgement of the design and reevaluation

if necessary, resulting in the generation of the end product. The process of evaluation

and reworking an idea is common in design and is represented in the model by the

iteration arrow taking the design activity back a step so that the design can be

improved. Fig. 1.4 illustrates the possible results from this process for a helmet pro￾viding peripheral and reverse vision.

Fig. 1.5 shows a more prescribed description of a design process that might be asso￾ciated with engineers operating within a formal company management structure. The

various terms used in Fig. 1.5 are described in Table 1.1.

Although Figs 1.3 and 1.5 at first sight show design occurring in a sequential fash￾ion, with one task following another, the design process may actually occur in a step

forward, step back fashion. For instance you may propose a solution to the design need

and then perform some calculations or judgements, which indicate that the proposal is

inappropriate. A new solution will need to be put forward and further assessments

made. This is known as the iterative process of design and forms an essential part

Fig. 1.2 The Audi TT, originally launched in 1998, and a contender for the most attractive

sports car of the 20th century.

Courtesy of Audi.

Design 5

of refining and improving the product proposal. The nonlinear nature of design is con￾sidered by Hall and Childs (2009).

Note that the flow charts shown in Figs 1.3 and 1.5 do not represent a method of

design, but rather a description of what actually occurs within the process of design.

The method of design used is often unique to the engineering or design team. Design

methodology is not an exact science and there are indeed no guaranteed methods of

design. Some designers work in a progressive fashion, while others work on several

Idea

Sketches and

calculations

Evaluation

Final

solution

Influencing

factors

Iteration

Fig. 1.3 The traditional and

familiar ‘inventor’s’ approach to

design.

Fig. 1.4 Panoramic helmet. (A) The need: to be able to view around you. (B) The idea: Use of a

VR visor and camera feeds to enable forward as well as peripheral vision. (C) Practical sketches

showing the concept.

Sketches courtesy of Ruth Carter.

6 Mechanical Design Engineering Handbook

aspects simultaneously. An example of design following the process identified in

Fig. 1.5 is given in the following example (Section 1.2.1).

1.2.1 Case study

Following some initial market assessments, the Board of a plant machinery company

has decided to proceed with the design of a new product for transporting pallets around

factories. The Board have in mind a forklift truck but do not wish to constrain the

design team to this concept alone. The process of the design can be viewed in terms

of the labels used in Fig. 1.5.

Analysis and

optimisation

Influencing

factors

Synthesis

Definition

of problem

Evaluation

Market

Recognition

of need

Iteration

Fig. 1.5 The design process illustrating some of the iterative steps associated with the process.

Design 7

Recognition of need (or market brief )

The company has identified a potential market for a new pallet-moving device.

Definition of problem

A full specification of the product desired by the company should be written. This

allows the design team to identify whether their design proposals meet the original

request. Here a long list of information needs to be developed and clarified before

Table 1.1 Design phases

Phase Description

Recognition of

need

Often design begins when an individual or company recognises a need,

or identifies a potential market, for a product, device or process.

Alternatively ‘need’ can be defined as when a company decides to

reengineer one of its existing products (e.g. producing a new car

model). The statement of need is sometimes referred to as the brief or

market brief.

Definition of

problem

This involves all the specification of the product or process to be

designed. For example this could include inputs and outputs,

characteristics, dimensions and limitations on quantities.

Synthesis This is the process of combining the ideas developed into a form or

concept, which offers a potential solution to the design requirement.

The term synthesis may be familiar from its use in chemistry where it is

used to describe the process of producing a compound by a series of

reactions of other substances.

Analysis This involves the application of engineering science; subjects explored

extensively in traditional engineering courses such as statics and

dynamics, mechanics of materials, fluid flow and heat transfer. These

engineering ‘tools’ and techniques can be used to examine the design to

give quantitative information such as whether it is strong enough or will

operate at an acceptable temperature. Analysis and synthesis invariably

go together. Synthesis means putting something together and analysis

means resolving something into its constituent parts or taking it to

pieces. Designers have to synthesise something before it can be

analysed. The famous chicken and the egg scenario! When a product is

analysed some kind of deficiency or inadequacy may be identified

requiring the synthesis of a new solution prior to reanalysis and

repetition of the process until an adequate solution is obtained.

Optimisation This is the process of repetitively refining a set of often-conflicting

criteria to achieve the best compromise.

Evaluation This is the process of identifying whether the design satisfies the

original requirements. It may involve assessment of the analysis,

prototype testing and market research.

8 Mechanical Design Engineering Handbook

design can proceed. For example for the pallet-moving device being explored here this

would likely include aspects for consideration such as:

What sizes of pallet are to be moved?

What is the maximum mass on the pallet?

What is the maximum size of the load on the pallet?

What range of materials are to be moved and are they packaged?

What maximum height must the pallet be lifted?

What terrain must the pallet-moving device operate on?

What range is required for the pallet-moving device?

Is a particular energy source/fuel to be used?

What lifetime is required?

Are there manufacturing constraints to be considered?

What is the target sales price?

How many units can the market sustain?

Is the device to be automatic or manned?

What legal constraints need to be considered?

This list is not exhaustive and would require further consideration. The next step is

to quantify each of the criteria. For instance the specification may yield information

such as that standard size pallets (see Fig. 1.6) are to be used, the maximum load to be

moved is 1000 kg, the maximum volume of load is 2m3

, the reach must be up to 3m,

and use is principally on factory floor and asphalt surfaces. The pallet-moving device

must be capable of moving a single pallet 100 m and must be able to repeat this task at

least 300 times before refuelling if necessary, electricity, gas or diesel fuel, 7 year life￾time, production in an European country, target selling price 20,000 Euros,

12,000 units per year, manned use, design to ISO (International Organisation for

Standardisation) and target country national standards (see, e.g. BS ISO 509, BS

ISO 6780, BS EN ISO 445, BS EN 1726-1, BS EN 13545, 99/705213 DC, ISO

18334, 99/712554 DC, BS 3726, BS 5639-1 and BS ISO 2330). The task of specifi￾cation is an involved activity and is considered more fully in Chapter 2.

Length

Width

Notch

Stringer

Bottom deckboards

Opening height

Overall height

Hand pallet truck opening

End board

Top deckboard

Chamfer

Fig. 1.6 Pallet dimensions and terminology (see BS ISO 509, 99/712554 DC and

99/712555 DC).

Design 9