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Prototyping
Prototyping has been described by
Tom Kelley of IDEO design consultants as 'the shorthand of
innovation'. Effective prototyping is arguably one of the most
critical skills in product design.
Prototypes serve three main
purposes:
Types
of prototype
Prototypes can take many forms, from very simple mock-ups or
visualisations to demonstrate a principle, through to
sophisticated pre-production products and detailed analytical
simulations. Different types of prototypes can be utilised for
different purposes, as outlined in the table below.
| Type of prototype |
Typical uses |
| Simple sketch |
Great for testing
numerous ideas early on. The simplest, cheapest and
quickest way of evaluating many ideas for form, technical
arrangement and usability but highly under-utilised. |
| Block model |
Primarily for early
testing of usability, ergonomics and form. Also useful to
quickly evaluate a product's physical arrangement. Models
can be made out of paper, card, foam, wood or other easy
to work and cheap materials. |
| Visual (physical)
model |
To enable evaluation of
visual and form aspects. Produced to look as realistic as
possible. Good for testing product feel and form. Need to
be treated carefully as some people may think that the
product is finished and want it now! |
| 3D CAD model |
Evaluation of overall
form, assembly sequence and production issues. Can be
photo realistic. Excellent to gain support and buy in
from senior management but again there is a danger of
thinking that the product is 'finished'. |
| Functional
(technical) model |
To test specific
performance aspects. Not necessarily representative of
production processes. Good for evaluating reliability,
durability, performance, failure etc. Models can evaluate
sub-system or system level performance. |
| Production
prototype |
Evaluation of
performance, function, form, use and producibility. Made
with processes representative of the final production
method. Fully functional. |
| Analytical
(virtual) model) |
Mathematical models to
support component and assembly optimisation, including
stress, thermal properties, weight, strength, vibration
etc. Can be a cheap way of identifying issues, but can
also be very costly. Answers are always approximations. |
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fidelity vs cost
The fidelity of a prototype can be defined as how accurately the
prototype represents either functionality (or performance),
appearance, producibility or usability. A model with high
fidelity will closely mimic the characteristics of the final
production item. There is clearly a trade off between fidelity
and cost. Typically, the greater the fidelity, the higher the
cost. For example, a simple card model of a casting may have low
fidelity compared with a full FEA model but it is also
significantly quicker and cheaper to produce. Examples of
fidelity vs cost are illustrated in the table below.
| Type
of prototype |
Function
/
performance |
Appearance
|
Producibility
|
Usability |
Cost |
| Simple
sketch |
Low |
Medium |
Low |
Low |
Low |
| Block
model |
Medium |
Medium |
Low |
Med-High |
Low |
| Visual
(physical) model |
Low |
High |
Low |
Medium |
Medium |
| 3D
CAD model |
Low |
High |
Medium |
Low |
Med-High |
| Functional
(technical) model |
High |
Low |
Medium |
Medium |
High |
| Production
prototype |
High |
High |
High |
High |
High |
| Analytical
(virtual) model) |
High |
Low |
Low |
Low |
Varies |
Rapid
Prototyping (RP)
Since the introduction of Stereo-lithography in the late 1980s,
RP has come of age. Representative parts and tools can be
produced almost instantly directly from CAD data. RP provides
speed, accuracy, and the ability to produce components with
complex geometry which would otherwise require expensive tooling.
This has provided new opportunities for designers to test ideas
and concepts increasingly quickly. There are three core
techniques:
Stereolithography
The original and most popular RP process. The model is
built up in layers in a bath of photo-curable epoxy
resin, which is solidified by laser. Produces accurate,
strong and translucent parts.
3D Plotting
Utilises a print head to either fuse a powder or deposit
molten material (wax, ABS) in layers to build up a
component, section by section. The process can be viewed
as similar to ink jet printing with the ability to build
in the vertical direction. Especially suitable for small
intricate parts.
Laminated object modelling (or
Adhesive RP)
Layers of either ceramic, paper or plastic sheet are
bonded together, with each layer being cut to the
required sectional profile with a laser. Completed models
have a wood like feel and can be used as either tooling
or concept models.
Further
information
- Baxter M, (1999), Product
design: practical methods for the systematic development
of new products, Stanley Thornes, UK
- Kelley T, (2001), The art of
innovation, Harper Collins Business, London
- Thackara J, (1997), Winners:
how today's successful companies innovate by design,
Gower Publishing, UK
- Ulrich & Eppinger,
(2000), Product design and development, McGraw Hill, USA
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