Client + User + Designer + Maker
Standard v. One-off Design (Time Comparison)
Standard v. One-off Design (Cost Comparison)
• 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)
What can be standardized
• 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.
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
• A separate production cell manufactures each family or
group of parts.
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
• Standardization is a benefit of GT.
• Modularization is an extension of GT
What is ‘X’ in DFX?
• 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
Design for User-Friendliness
• Human Factors Engineering: designing products that are
easy to understand, safe, and in proper scale to the human
• 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
• The above should be considered at the concept design stage.
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
• 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
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
• 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.
Design for User-friendliness Principles (3)
• Anticipate user errors: alarm sounds when a wrong control
• 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!
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 micro-chip 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.
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
• 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
• Minimize unnecessary variety: Different hole sizes require drill
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.
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.
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.
Design for Assembly (3)
• 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
• 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.
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:
Concurrent Engineering (2)
1. Concurrence: Product and process design take place at the
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
4. Consensus: (A Confucian value!) The full concurrent
engineering team participates and agrees with major
product design decisions.
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