Design process

Basic module in design process-scientific method and
design method-Need identification, importance of
definition of problem-structured problem, real life
problem- gathering information-customer
requirements- Quality Function Deployment (QFD)-
product design specifications-generation of
alternative solutions- Analysis and selection-Detail
design and drawings-Prototype, modeling,
simulation, testing and evaluation (Basics only)
UNIT
2

Importance of the Engineering Design Process
Product cost commitment during phases of the
design process

Basic module in the design process
Design operation are,
(1) Exploring the alternative concepts that could satisfy the specified need,
(2) Formulating a mathematical model of the best system concept,
(3) Specifying specific parts to construct a subsystem, and
(4) Selecting a material from which to manufacture a part
Specific information are,
(1) Manufacturer’s catalog on miniature bearings,
(2) Handbook data on the properties of polymer composites, or
(3) Personal experience gained from a trip to observe a new manufacturing process

Basic module in design process-scientific method
and design method-Need identification, importance
of definition of problem-structured problem, real
life problem- gathering information-customer
requirements- Quality Function Deployment (QFD)-
product design specifications-generation of
alternative solutions- Analysis and selection-Detail
design and drawings-Prototype, modeling,
simulation, testing and evaluation (Basics only)
UNIT
2

Design Method Vs Scientific Method

Need identification
• Needs usually arise from dissatisfaction with the existing
situation
• Needs are identified at many points in a business or
organization
• Most organizations have R&D whose job it is to create ideas
that are relevant to the goals of the organization
• Managing this input is usually the job of the marketing
organization of the company
• Needs are generated by government agencies, trade
associations, or the attitudes or decisions of the general public.
• The need drivers may be to reduce cost, increase reliability or
performance, or just change because the public has become
bored with the product

• The formulation of the problem should start by writing down a
problem statement.
• This document should express as specifically as possible what the
problem is.
• It should include,
Objectives and Goals
The current state of affairs and the desired state
Any constraints placed on solution of the problem
• The definition of any special technical terms.
• While it is important to identify the needs clearly at the beginning
of a design process.
• Design is problem solving only when all needs and potential issues
with alternatives are known.
• Experience is one of the best remedies for this aspect of
designing.
PROBLEM DEFINITION / NEEDS ANALYSIS

and design method-Need identification,
importance of definition of problem-structured
problem, real life problem- gathering information-
customer requirements- Quality Function
Deployment (QFD)- product design specifications-
generation of alternative solutions- Analysis and
selection-Detail design and drawings-Prototype,
modeling, simulation, testing and evaluation (Basics
only)
UNIT
2

Gathering Information
• Information needed in design is different from that
usually associated with an academic course.
• Textbooks, Technical Journals,
• Technical reports published as a result of government-
sponsored R&D,
• Company reports, trade journals, patents, catalogs,
and handbooks and
• Literature published by vendors and suppliers of
material and equipment are important sources of
information.
• Internet search, or by a telephone call or an e-mail to
a key supplier

• What do I need to find out?
• Where can I find it and how can I get it?
• How credible and accurate is the information?
• How should the information be interpreted for
my specific need?
• When do I have enough information?
• What decisions result from the information?
Generation of Alternative Solutions
• The ability to generate high-quality alternative
solutions is vital to a successful design.
• Of course, experience helps greatly in this task.

Evaluation of Alternatives and Decision Making
• The evaluation of alternatives involves systematic
methods for selecting the best among several concepts,
often in the face of incomplete information.
 Engineering analysis
 Design for manufacturing analyses
 Cost estimation
 Simulation of performance
 Testing of full sized prototypes
 Mathematical checks
 Optimization technique

Communication of the Results
• Surveys typically show that design engineers spend 60 percent
of their time in discussing designs and preparing written
documentation of designs, while only 40 percent of the time is
spent in analyzing and testing designs and doing the designing.
• Purpose of the design is to satisfy the needs of a customer or
client
• The communication is usually by oral presentation to the
sponsor as well as by a written design report
• Detailed engineering drawings, computer programs, 3-D
computer models, and working models are frequently among
the “deliverables” to the customer.

CUSTOMER REQUIREMENTS
 Physiological needs
such as thirst, hunger, sleep, shelter, and
exercise
 Safety and security needs
 Social needs
 Psychological needs
 Self-fulfillment needs

Differing Views of Customer Requirements
– Performance
– time dimension
– Cost
– Quality
Eight basic dimensions of quality
 Performance
 Features
 Reliability
 Durability
 Serviceability
 Conformance
 Aesthetics
 Perceived quality

Classifying Customer Requirements
Kano Diagram
(1) Expecters,
(2) Spokens,
(3) Unspokens
(4) Exciters
http://cozybeehive.blogspot.in/2008/02/kan
o-diagram-applied-to-cycling.html

PDS for Compact Disc Jewel Case

generation of alternative solutions - Analysis and
selection-Detail design and drawings-Prototype,
only)
UNIT
2

• Functional Decomposition and Synthesis
Logical approach for describing the transformation between the initial and
final states of a system or device
• Morphological Analysis
Morphological chart approach to design generates alternatives from an
understanding of the structure of necessary component parts
• Theory of Inventive Problem Solving(TRIZ)
It is a creative problem-solving methodology especially tailored for
scientific and engineering problems
• Axiomatic Design
Methods provide a means to translate a design task into functional
requirements (the engineering equivalent of what the customer wants)
and use those to identify design parameters, the physical components of
the design

• Design Optimization
Many of the strongest and currently recognized design methods are
actually searches of a design space using optimization strategies
• Decision-Based Design
Design differs from past design models that focus on problem solving in
two major ways. The first is the incorporation of the customers’
requirements as the driver of the process. The second is using the design
outcomes (e.g., maximum profit, market share capture, or high-quality
image)

selection- Detail design and drawings-Prototype,
only)
UNIT
2

Detail Design
All of the details are brought together, all
decisions are finalized, and a decision is made
by management to release the design for
production

Make/buy decision
• Even before the design of all components is completed and the
drawings finalized, meetings are held on deciding whether to
make a component in-house or to buy it from an external
supplier.
Complete the selection and
sizing of components
•Some components may not yet have been selected or designed.
•If the product design is at all complex, it most likely will be necessary
to impose a design freeze at some point prior to completion.
•This means that beyond a certain point in time no changes to the
design will be permitted unless they go through a formal review by a
design control board.

Complete engineering drawings
• As each component, subassembly, and assembly
is designed, it is documented completely with
drawings.

Complete the bill of materials
The bill of materials (BOM) or parts list is a list of each individual component in
the product. It is used in planning for manufacture and in determining the best
estimate of product cost.

Revise the product design specification
• In detail design the PDS should be updated to
include all current requirements that the design
must meet.
• The specification contains information on the
technical performance of the part, its
dimensions, test requirements, materials
requirements, reliability requirement, design life,
packaging requirement, and marking for
shipment.

Complete Verification Prototype Testing
• Once the design is finalized, a prototype is built
and verification tested to ensure that the design
meets the PDS and that it is safe and reliable.
• Prototypes are made with the same materials and
manufacturing processes as the product but not
necessarily from the actual production line.
Final Cost Estimate
The detail drawings allow the determination of final
cost estimates, since knowledge of the material, the
dimensions, tolerances, and finish of each part are
needed to determine manufacturing cost.

Prepare Design Project Report
• Design project report usually is written at the
conclusion of a project to describe the tasks
undertaken and to discuss the design in detail.
• A design project report may be an important
document if the product becomes involved in
either product liability or patent litigation.

Final design review
The final design review results in a decision by
management on whether the product design is
ready for production, and the major financial
commitment that this required.
Release design to manufacturing
If the product is being managed by a project manager
in a heavyweight matrix organization. This manager
continues with the project as it passes from design to
manufacturing and on to product launch.

• Prototypes are physical models of the product
that are tested in some way to validate the design
decisions that have been made up to that point in
the design process.

Steps in Rapid Prototyping
• Create a CAD model
• Convert the CAD model to
the STL file format
STL- STereoLithography
OR Standard
Tessellation Language
• Slice the STL file into thin
layers
• Make the prototype
• Post processing

problem, real life problem- gathering
information-customer requirements- Quality
Function Deployment (QFD)- product design
specifications-generation of alternative solutions
- Analysis and selection- Detail design and
drawings-Prototype, modeling, simulation,
testing and evaluation (Basics only)
UNIT
2

Models
 What is Model
 A model of a system is a representation of the construction and working of the
system
 Similar to but simpler than the system it represents
 Close approximation to the real system and incorporate most of its salient features
 Should not be so complex that it is hard to understand or experiment with it
 Physical Model
 A physical object that mimics some properties of a real system
 e.g. During design of buildings, it is common to construct small physical models
with the same shape and appearance as the real buildings to be studied
 Through prototyping process
 Prototyping is the process of quickly putting together a working model (a prototype)
in order to test various aspects of a design, illustrate ideas or features and gather
early user feedback

Models
 Mathematical Model
 A description of a system where the relationship between variables of the system
are expressed in a mathematical form
 e.g. Ohm's law describes the relationship between current and voltage for a resistor;
Hooke's Law gives the relationship between the force applied to an unstretched
spring and the amount the spring is stretched when the force is applied, etc.
 Through virtual prototyping
 Deterministic vs. stochastic models
 In deterministic models, the input and output variables are not subject to random
fluctuations, so that the system is at any time entirely defined by the initial
conditions chosen
 e.g. the return on a 5-year investment with an annual interest rate of 7%,
compounded monthly
 In stochastic models, at least one of the input or output variables is probabilistic or
involves randomness
 e.g. the number of machines that are needed to make certain parts based on the
probability of machine failure

FSpring = -k∙x
Hooke’s Law
x= -FSpring/k
spring constant The amount spring
is stretched
Fspring
Fspring

Simulation
 What is Simulation
 A simulation of a system is the operation of a model of the system, as an
imitation of the real system
 A tool to evaluate the performance of a system, existing or proposed, under
different configurations of interest and over a long period of time
 e.g. a simulation of an industrial process to learn about its behavior under different
operating conditions in order to improve the process
 Reasons for Simulation
 Experiments on real systems are too expensive, too dangerous, or the system to
be investigated does not yet exist
 e.g. Investigating ship durability by building ships and letting them collide is a very
expensive method of gaining information; training nuclear plant operators in
handling dangerous situations by letting the nuclear reactor enter hazardous states is
not advisable

Simulation
 Reasons for Simulation (Cont.)
 The time scale of the dynamics of the system is not compatible with that of the
experimenter
 e.g. It takes millions of years to observe small changes in the development of the
universe, whereas similar changes can be quickly observed in a computer simulation
of the universe
 Easy manipulation of parameters of models (even outside the feasible range of a
particular physical system)
 e.g. The mass of a body in a computer-based simulation model can be increased from
40 to 500 kg at a keystroke, whereas this change might be hard to realize in the
physical system
 Suppression of disturbances
 Allow isolating particular effects and gaining a better understanding of effects of
particular interest as a result
 e.g. simulation of free-fall objects ignores the effect of air resistance
54

selection- Detail design and drawings-Prototype,
modeling, simulation, testing and evaluation
(Basics only)
UNIT
2

• Testing of design prototypes
• Testing for all mechanical and electrical modes of failure.
• Specialized tests on seals, or for thermal shock, vibration, acceleration, or
moisture resistance, as design dictates.
• Accelerated life testing. Evaluating the useful life of the critical-to-quality
components.
• Testing at the environmental limits. Testing at specification extremes of
temperature, pressure, humidity, etc.
• Human engineering and repair test. Evaluate all human interfaces with actual
users.
Check maintenance procedures and support equipment in a user environment.
• Safety and risk test.
• Evaluate the capability and quality of built-in test.
• Manufacturing supplier qualification. Determine the capability of suppliers
with regard to quality, on-time delivery, and cost.
• Packaging. Evaluate the ability of the packaging to protect the product.

Design process

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