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Engineering Design and Technology

Product design specifications

Dr Ashraf Afifi
BSc, MSc, PhD, FHEA

Senior Lecturer
of Engineering Management
Outline
• The product design specifications activity
• The process of establishing the target specification
– The needs-metrics matrix
– Quality function deployment (House of quality)

• The process of setting the final specification

– When to set the final specifications

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The product design specifications activity
• Customer needs:
– Expressed in the “language of
the customer”
– Provide little guidance on how
to design and engineer the
product Voice of the Customer Product
customer needs specifications
• Product design specifications:
– Provide precise description of
Sub-system Sub-system Sub-system
specifications specifications specifications

what the product has to do

• Sub-system specifications:
– Product specifications
decomposed into sub-system
specifications

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The product design specifications activity
• Target specifications:
– Based on customer
needs and
benchmarking Development
Identify Establish Generate Select Test Set Plan Plan
Customer Target Product Product Product Final Downstream

– Represent the hopes Needs Specifications Concepts Concept(s) Concept(s) Specifications Development

and aspirations of the Perform Economic Analysis

team Benchmark Competitive Products

Build and Test Models and Prototypes

• Final specifications:
Product design specifications activity in relation to other
concept development activities (Ulrich and Eppinger, 2016)
– Based on selected
concept, feasibility,
models, testing, and
trade-off
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The process of establishing the target specification
• Main steps:
– Prepare the list of
Spec = Metric + Value(s) + Units metrics
– Collect competitive
Example:
benchmarking
metric value units
information
• Time to assemble <75 seconds
• Total mass 8.5-10 kg – Set ideal and marginally
• Cycles to failure >500k cycles acceptable target values
• Unit production cost <110 $
– Reflect on the results
and the process

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Step 1: Prepare the list of metrics
• Metrics are precise,
measurable characteristic of
the product, reflecting the
degree to which the product
satisfies the customer needs
– In the ideal case, there is
one metric for each need
– In practice, this is
frequently not possible

Customer needs for the suspension fork and their

Mountain bike suspension fork relative importance (Ulrich and Eppinger, 2016)
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Step 1: Prepare the list of metrics

List of metrics for the suspension fork

with the relative importance of each
metric and the units for the metric
(Ulrich and Eppinger, 2016)
Note: The abbreviations “Subj.”, “List”, and
“Binary” indicate that a metric is “subjective”,
requires a “list of models”, and involves a
“pass/fail” value, respectively

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The needs-metrics matrix
• Represent the relationship
between needs and metrics
– Rows correspond to
customer needs, and
columns correspond to
metrics
– A mark in a cell means that
the need and the metric
associated with the cell are
related
– Quite useful for
representing complex
mapping from needs to
metrics The needs-metric matrix for the suspension fork
27 September 2023 Engineering Design and Technology (Ulrich and Eppinger, 2016) 8
Quality function deployment (House of quality)
9
3
1

A QFD example for a detergent bottle

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Step 2: Collect competitive benchmarking information
• Information on competing
products support the
positioning of a new product
relative to existing products
• Two ways to benchmark
competitive products:
– Based on the metrics
established: The metrics’
values are gathered from
the competitors’ catalogues
and supporting literature
and sometimes they are
not accurate Competitive benchmarking chart based on metrics
27 September 2023 Engineering Design and Technology (Ulrich and Eppinger, 2016) 10
Step 2: Collect competitive benchmarking information
– Based on the
perceived
satisfaction of
customer needs:
The competitive
values are the
customers’
perceptions of the
relative degree to
which the products
satisfy their needs
• Customer
perception data
can be very
expensive and Competitive benchmarking chart based on perceived satisfaction
time consuming of customer needs (Ulrich and Eppinger, 2016)
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Step 3: Set ideal and marginally acceptable target values
• Two types of target value:
– Ideal value: The best result the
team could hope for
– Marginally acceptable value: The
value of the metric that would just
barely make the product
commercially viable
• Both values are useful in guiding
the subsequent design stages
• To set the values, the design team
considers many factors, including
information on competing products,
the product’s mission statement,
and target market segment Marginal and ideal values for the suspension
27 September 2023 Engineering Design and Technology fork (Ulrich and Eppinger, 2016) 12
Step 4: Reflect on the results and the process
• Reflection helps to ensure that the results are consistent with the goals of
the project
• Questions to consider include:
– Is the design team able to set precise metric values reflecting customer
needs?
– Should the team consider offering multiple products or at least multiple
options for the product to best match the particular needs of more than one
market segment, or will one “average” product suffice?
– Are any specifications missing?
– Do the specifications reflect the characteristics that will dictate commercial
success?
• Target specifications help the design team generate solution concepts,
and select a commercially viable concept
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The process of setting the final specification
• Target specifications • Main steps:
change for several reasons:
– Develop technical models
– Customers change of the product

– Competitors respond – Develop a cost model of

the product
– Technical capabilities improve – Refine the specifications,
making tradeoffs where
– Designs evolve as details necessary
develop
– Flow down the
– Tradeoffs and conflicts specifications as
become apparent appropriate
• Specifications must be – Reflect on the results and
revisited and refined the process
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Steps 1&2: Develop technical and cost models of the product
• Technical models: • Cost models:

– May be analytical, computer – Used to develop early

simulation, or a prototype of estimates of the product
cost, including the cost of
the product
components, assembly and
– Used to assess the manufacturing, and other
costs (e.g., overhead)
technical feasibility of a
particular product concept – Ensure that the product can
be produced at the target
– Prevent the design team cost
from setting a combination
of specifications that cannot – Facilitate realistic tradeoffs
be achieved in the product specifications
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Step 3: Refine the specifications, making tradeoffs where necessary
• Specifications are refined
and made more precise 120

Rox Tahx Ti 21

Estimated Manufacturing Cost ($)

after concept selection 110

Maniray 2 Tradeoff Curves

•
for Three Concepts
Finalising specifications 100 Gunhill Head Shox

is difficult because of 90
Rox Tahx Quadra
tradeoffs between 80
marginal
values
Tonka Pro

different technical 70
performance metrics ideal
ST Tritrack
60
values

• Technical and cost 50

models of the product 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0

and competitive maps Score on Monster (Gs)

are important tools for A competitive map for the suspension fork
(Ulrich and Eppinger, 2016)
resolving tradeoffs
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When to set the final specifications
• Early freeze: Preferred when
competing on cost and
performance
– Allows downstream tasks to get
started with firm input information
– Facilitates downstream
optimisation (cost, performance,
etc.)
• Late freeze: Preferred when
competing on market match
– Allows better match with changing
market (customers, competition) The final specification for the suspension fork
(Ulrich and Eppinger, 2016)
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Step 4: Flow down the specifications as appropriate
• System-level specs determine System
whether we can meet the specifications
customer needs
• Sub-system specs determine Sub-system Sub-system Sub-system
how to meet the system specs specifications specifications specifications

• Component specs determine

Component Component Component
how to meet the sub-system specifications specifications specifications
specs
• Manufacturing specs determine Manufacturing Manufacturing Manufacturing
how to meet the component specifications specifications specifications
specs
• Process specs determine how Process
specifications
Process
specifications
Process
specifications
to meet the component specs
The flow-down process of specifications
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Step 5: Reflect on the results and the process
• Questions to consider include:
– Is the product a winner?
– How much uncertainty is there in the technical and cost
models?
– Is the concept chosen by the team best suited to the
target market?
– Should the firm initiate a formal effort to develop better
technical models of some aspect of the product’s
performance for future use?

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Summary
• Specifications provide specific guidance about how to design and engineer a
product
• Specifications are typically established at least twice
– Immediately after identifying the customer needs (target specifications)
– After concept selection and testing (final specifications)
• Target specifications are established before knowing the constraints the product
technology will place on what can be achieved
• Final specifications are developed by assessing the actual technological
constraints and expected production costs using analytical and physical models,
and by making tradeoffs among various desirable characteristics of the product
• The specifications process is facilitated by several tools such as the needs-
metrics matrix, the competitive benchmarking charts, and the competitive maps
• The specifications process requires active participation from the marketing,
design, and manufacturing functions of the enterprise
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 Thank You

Comments and questions to:

Teams, discussion forum, or
Ashraf.Afifi@bristol.ac.uk

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