DFX
Design for Manufacture, etc.
• Standardization
• DFX
• Group Technology
• Concurrent Engineering
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Innovation, KV Patri
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The best design
is the simplest one
that works.
- Albert Einstein
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Innovation, KV Patri
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Cost
Precision Vs Cost
Precision
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Cost of design
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Innovation, KV Patri
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Client + User + Designer + Maker
Client
+
User
Designer
+ Maker
Client
User
Client
+
User
Designer
Maker
Designer
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Innovation, KV Patri
Maker
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Standard v. One-off Design (Time Comparison)
Set-up
Set-up
Production
Production
Standard
One-off
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Innovation, KV Patri
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Standard v. One-off Design (Cost Comparison)
Labor
Factory
Overhead
Design
Tech. OH
Labor
Development
Factory OH
Material
Testing
Development
Material
Special Tests
Standard
One-off
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Standardization
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Development costs eliminated.
Training costs reduced.
Fewer mistakes.
Start-up costs reduced due to familiarity.
Less debugging. Therefore, higher quality, lower lead time,
and higher productivity.
• Tooling costs reduced since tools are already available.
• Production quantities higher because same parts are
reused. Hence economies of scale and easier just-in-time
(JIT) arrangements.
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What can be standardized
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Engineering drawing formats, conventions and units.
Design features (e.g. hole sizes, bend radii, snap-fit tabs)
Parts: do not design new part if an existing part suffices.
Fasteners: Have list of preferred but limited variety.
Materials: It is enough to have a satisfactory material - not
necessarily the optimum.
Commercial parts (from catalogues).
Linear materials (e.g. wire)should be standardized by
diameter and material but not by length.
Modules: easy installation and substitution.
Processes and tooling.
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Group Technology (1)
• As the demand for product variety is increasing, there is a
need to find ways of making batch manufacture
economical. GT enables this.
• GT concentrates on components or parts rather than end
products. Products may vary, but they usually have many
similar parts. If these parts are grouped together, one can
obtain economies of scale at the part level although the
batch sizes for the end products continue to be small.
• Without GT, different product sections may process similar
parts differently. Effort is duplicated leading to loss of
overall efficiency.
• A separate production cell manufactures each family or
group of parts.
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Innovation, KV Patri
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Group Technology (2)
• Classification: assignment of parts into groups or families.
• Coding: Allocation of identities (numeric codes with each
code digit having a certain predetermined meaning) to
these groups. Several popular coding schemes are
available. A factory may adopt one of these or develop its
own. Commercial software are available to facilitate
manual or semi-automated coding (e.g. MICLASS).
• A product designer must be aware of the groups and utilize
them. Do not unnecessarily create parts which fall outside
existing families.
• Standardization is a benefit of GT.
• Modularization is an extension of GT
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The Need for DFM
% o f L ifetim e co st
C o m m itted
C o ncep t V alid atio n
S p ent
C o ncep t
F o rm ulatio n
F ull S cale
D evelo p m ent
P ro d uctio n
U se
P ro d uct L ifetim e
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What is ‘X’ in DFX?
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Design for Manufacture
Design for Assembly
Design for Quality
Design for Reliability
Design for Serviceability/Maintainability
Design for Safety
Design for the Environment
Design for User-Friendliness
Design for Shorter Time-to-Market
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Design for User-Friendliness
• Human Factors Engineering: designing products that are
easy to understand, safe, and in proper scale to the human
form.
• Ergonomics: attempts to provide harmony between people
and the products they use, to make products fit people
well.
• User-friendly: ease of operation, reliability of results in
the initial use and repeatedly afterwards, user satisfaction
with operation.
• The above should be considered at the concept design
stage.
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Design for User-friendliness Principles (1)
• Fit the product to the users: Fit to user’s knowledge of the world and
habits. Higher readings on dials should be clockwise. Knobs must
tighten when rotated clockwise. Activating forces required should be
compatible with human strength.
• Simplify tasks: Control operations should be designed to minimize
planning, problem solving and decision making on the user’s part. In
personal computers, macros combine a complex series of key strokes
into a single stroke.
• Make things obvious: Controls must simulate the arrangement of the
mechanism. In a refrigerator/freezer, if a single thermostat controls the
flow of air into the two chambers, then do not give two thermostat
control knobs.
• Place controls for a function adjacent to the device to be controlled.
E.g. place knobs for tape-player adjacent to the tape cartridge
mechanism in a tape player. Centralizing controls in neat rows may be
aesthetic but is not user-friendly.
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Design for User-friendliness Principles (2)
• Use mapping: Controls must reflect or map the mechanism. Pushing
the car seat positioning lever up should raise (not lower) the seat.
• Utilize constraints: Make the system fool-proof by incorporating
constraints: an automobile that will not go into reverse when the car is
moving forward; a car door will not lock unless the door handle is
depressed.
• Provide feedback: The effect of each action should be immediate,
obvious and clear to the user: periodic clicking sound and dashboard
flashing light when a turn signal is activated in a car; a push button
switch is confusing because one does not know whether it will turn the
motor on or off - a sliding or lever will not have this problem.
• Provide clear displays: clear, visible, interpretable, distinctive,
legible, intelligible, easily readable, etc.; analogue displays are more
user friendly whereas digital displays are more precise.
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Innovation, KV Patri
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Design for User-friendliness Principles (3)
• Anticipate user errors: alarm sounds when a wrong
control is actuated.
• Avoid awkward and extreme motions for the user: keep
wrists straight; keep elbows in lower position; minimize
bending and twisting; provide adjustments (adjustable seat)
to eliminate awkwardness; controls should provide the
force or power needed internally rather than using user’s
force or power; handles should have rounded corners and
have high friction for gripping; etc.
• Standardize: use standardized controls that are familiar to
the user rather than developing your own. In some cars, an
upward motion of the lever starts the wind-shield wipers.
In others, the opposite is true!
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Design for (Ease of) Manufacture (1)
• Minimize the number of parts: this minimizes the amount of
manufacturing work. Electronic devices have been particular succesful
in this regard. Integrated circuits combine thousands of elements into
one component. According to Noyce’s law, the number of circuit
elements (resistors, transistors, etc.) incorporated into a single microchip doubles every year (due to continued innovation). Use ICs as
much as possible and put as many elements into the IC as possible.
• Minimize the number of manufacturing steps: Surface Mount
Technology reduces the number of steps. Pin-in-hole systems need
bending and trimming of leads, inserting in the PCB, and then
crimping of the leads. Hence the speed of assembly currently is only
25 pieces per minute. SMT avoids these problems and is able to enable
assembly at 80 piece per minute.
• Be sensitive to the impact of each design decision on
manufacturability: Heat sinks may prevent overheating of circuit
elements, but they also lead to cold solders.
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Design for (Ease of) Manufacture (2)
• Minimize or eliminate adjustments: Mechanical adjustments of
potentiometers, etc. are labor-intensive. Eliminate them by utilizing
voltage regulators, feedback loops, etc. Positional adjustments of
components are also expensive. Footprint designs of SMT boards
should provide space for a good solder joint even if the part shifts
slightly.
• Be aware that the objective wide spacing of components for
manufacturability conflicts with the objective of ‘fine pitch’ to achieve
miniaturization.
• Standardize: Standardize PCB dimensions so that standard fixtures
can be used during wave soldering, cleaning, etc. Standardize the
location of tooling holes and board thickness. When smaller boards
suffice, design them such that multiple quantities can be cut from a
larger standard board.
• Minimize unnecessary variety: Different hole sizes require drill
changing.
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Innovation, KV Patri
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Importance of DFA
Boothroyd and Redford 1968
Experience shows that it is difficult to make large
savings in cost by introduction of mechanized
assembly in the manufacture of an existing
product. In those cases where large savings are
claimed , examination will show that often the
savings are really due to changes in the design of
the product necessitated by the new process. …
Undoubtedly, the greatest cost savings are to be
made by careful consideration of the design of the
product and its individual component parts.
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Innovation, KV Patri
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Design for Assembly (1)
• The optimum design is different for different methods
of assembly: manual assembly, hard automation with
fixed tooling (for large quantities), flexible assembly
(using robots) for medium batch sizes, etc.
• Minimize the number of parts: This reduces the number
of assembly operations. According to Boothroyd and
Dewhirst:
Design efficiency = (No. of parts) x 3s/ Assembly time (s)
Assembly time = sum of (handling + insertion) times.
Each part should be examined to see if it can be eliminated
or combined with other parts. Two parts need to be
separate only if there is relative motion between them,
need to be of different materials, or it is necessary for
assembly.
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Innovation, KV Patri
Design for Assembly (2)
• Combine parts: Incorporate hinges into plastic - plastic
can bend. Use internal springs - the functional metal part
itself acts as a spring. Eliminate fasteners - use snap fits.
Incorporate elements such as guides, bearings and covers
into plastic parts - remember plastic has low friction. Put
electrical and electronic components in one location and
consolidate them. One PCB is preferable to several in
several locations. A light switch and ventilation switch on
the same mounting plate is preferable.
• Standardize designs and components.
• “Once a part is oriented, never lose that orientation.”:
Assemble it, move it and ship it with its orientation
retained.
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Innovation, KV Patri
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Design for Assembly (3)
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Use subassemblies: Use modules (a PCB is a module).
Avoid too many subassemblies at one time.
Design parts so that they cannot be inserted incorrectly.
Avoid the use of flexible parts. They can get tangled during
handling.
Avoid slippery parts. They are difficult to insert.
Use layered, top-down assembly.
Avoid connecting cables by using direct plug-in boards.
Avoid switches and jumpers by configuring in software.
Use consistent design strategy. Assembling SMT boards
alone is easier than when SMT and PIH are mixed.
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Concurrent Engineering (1)
• The traditional “Over the wall” approach: Designers
and manufacturing engineers do not communicate about
the design. Design documents are transmitted to
manufacturing without a pre-release review by
manufacturing engineers.
• An improvement - The Sign-off Procedure:
Manufacturing engineers approve and accept the design
after it is completed but before it is released to production.
• Concurrent Engineering: Designers and manufacturing
engineers work together on the design at the same time.
• Four Key Elements of Concurrent Engineering:
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Concurrent Engineering (2)
1. Concurrence: Product and process design take place at the
same time.
2. Constraints: The limitations and capabilities of the
available manufacturing processes are considered during
the design phase itself. In recent times, software for
evaluating specific DFX features are available. Hong Kong
hasn’t yet learnt to use any.
3. Co-ordination: Products and process requirements and
other objectives are closely co-ordinated during the design
process (itself).
4. Consensus: (A Confucian value!) The full concurrent
engineering team participates and agrees with major
product design decisions.
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Concurrent Engineering (3)
• I leave it to you to describe the advantages of CE. But what
are the risks associated with CE?
• Teams are more difficult to manage than individuals. Team
meetings can take excessive time. Achieving team work
may require delicate and diplomatic approach.
• Not all good designers are team players.
• Maybe, CE can be achieved without team work. May be
designers can use DFX computer programs to evaluate
their designs.
• There can be much resistance to change to CE (why?).
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