PICASSO represents a collaboration
between a market-leading specialist CAD/CAM software house, one of
its largest customers, and expert technical and academic advisers.
The project developed and tested a prototype system to support the
design of assemblies built primarily from standard components. It
will dramatically improve the speed and accuracy of assembly design,
and provides a simple and reliable means of optimising manufacturing
tolerances. The result will be cheaper manufacture and shorter lead
Refined and extended since the completion of the project, the PICASSO
software promises to revolutionise the assembly design process in
the mould tool industry and in other fields.
Computer aided design (CAD) systems can
dramatically reduce the time and cost of bringing new products to
market. Why then is CAD rarely used for the design of assemblies
built from standard components - one of the areas in which it should
confer the greatest benefits?
Even within industries such as mould tool manufacturing, where extensive
and sophisticated use is made of CAD for more complex tasks, assembly
designs are generally still prepared by hand, on old-fashioned drawing-boards.
To date, CAD systems have simply not offered support tools with
the right mix of flexibility and dedication to a specific assembly
type. Without such support, their benefits have not been great enough
to persuade companies to abandon traditional manual or semi-manual
The PICASSO project has overcome this barrier - 1996 saw the first
release of the resulting new CAD tool, which will assist assembly
designers to select appropriate components and add them to finished
Precision assemblies from standard parts
Every moulded plastic product, from a car dashboard to a milk crate,
needs its own mould tool. This incorporates not only the milled
steel plates forming the cavity into which the plastic is injected,
but also the mechanism for releasing and ejecting the hardened product.
The mould tool industry uses advanced three dimensional CAD technology
(3D-CAD) to define the complex surfaces of the mould plates, passing
these definitions to Computer-Aided Manufacturing (CAM) software,
which controls the milling process.
However, the tools which house these plates are themselves complicated
pieces of equipment. Mounted on pillars, the plates must slide freely
and fit snugly. To facilitate the release of items with undercut
or rebated faces, they may require many sliding sections. Channels
and pockets must be accurately machined.
The specification of correct tolerances is also critical. If they
are too small, manufacturing costs are unnecessarily high; if they
are too large, the tool will not function properly.
Mould tools are built almost exclusively from standard components,
ordered from specialist suppliers whose catalogues contain tens
of thousands of items. Current design methods depend entirely on
the skill of experienced draughtsmen for the selection of the right
parts, which are drawn by hand or, at best, using conventional 2D-CAD.
As they choose each component, draughtsmen must also add its part
number to the list of materials to be ordered, either by referring
to the supplier's catalogue or, as very often happens, relying on
Some component suppliers provide CAD definitions of their parts,
but selection still depends upon the expertise of the individual
designer, and the process remains laborious, requiring extensive
user input and manual positioning of the new part. Most draughtsmen
find it quicker to draw each part from scratch.
The complete design process for a large and complex mould tool may
take as long as a year, and errors are frequent and costly. Each
'misremembered' or mistyped part number means a costly delay while
the correct part is ordered.
Worse, incorrect positioning on the plan of a hole in the mould
plate may not become apparent until the tool has been assembled.
Too expensive to discard, the plate must be removed, welded, redrilled
Cutting design time in half
Delcam International, one of the two world market leaders in specialist
CAD/CAM systems for mechanical parts with complex three-dimensional
shapes, has produced an entirely new design support tool. Developed
in close collaboration with academic and industrial end-user partners,
PICASSO promises to revolutionise the design of assemblies built
from standard components, both in the mould tool industry and in
Following evaluation of a prototype by the leading Spanish mould
tool manufacturer Marés, PICASSO is expected to reduce design
time by 50%. It will also dramatically reduce the incidence of the
costly ordering and manufacturing errors so often generated by traditional
Operating as an add-on to Delcam's established CAD/CAM package,
PICASSO enables the designer to select components from a simple
list. A data library, mirroring suppliers' catalogues, contains
representations of each part. Starting with the required dimensions
for the mould plate, each choice constrains the options available
for the next component. The system only presents parts which are
compatible with the designer's previous choices.
A single mouse-click on a component type, and a second click on
one of the components offered by the system, is all that is needed
to draw and position a part on the plan. The software records each
part number, and can automatically generate an accurate bill of
materials, as well as conventional plan and three-dimensional views
of the assembly.
As a specialist supplier of CAD/CAM software, principally to the
mould tool industry, Delcam knew that its customers were failing
to exploit the full potential of CAD/CAM. The aim of this BRITE-EURAM
project was to help these companies to standardise and streamline
their assembly design processes, and to integrate them with the
design of mould plates.
Marés, an established customer, was already looking for ways
to reduce design times and standardise assembly tolerances around
best-practice models. With support from the Technical University
of Clausthal, the partners have built into PICASSO a functional
tolerancing module based on Marés' expertise. A good example
are the sliding-sealing fits found in mould tool components such
as ejector pins. The pin must slide easily through a plate, without
allowing leakage. With the function and its required tolerances
defined, PICASSO can automatically apply the appropriate tolerances
whenever that particular fit between two parts is called for.
Like all PICASSO's features, the functional tolerancing module
can be overridden. The system is highly configurable, allowing end-users
to define their own non-standard components and assembly rules to
supplement or supersede the supplied defaults.
This flexibility was important to mould tool manufacturers such
as Marés, but Delcam was also keen to generalise the software
so that it could be tailored for use in the design of quite different
types of assembly. Its broader compatibility was checked by experts
in press tool design at the University of Liverpool. In consultation
with a number of manufacturers, the University also built libraries
of press tool components, as Marés did for mould tools.
Now the system can be configured to support the design of mould
tools, press tools, or even bicycles or gearboxes. The application
is determined by the component, layout, and assembly rule definitions
loaded into its databases.
Delcam has continued the development of the project's prototype,
giving it a standard MS-Windows interface and adding to its component
libraries. PICASSO's first commercial release was at the end of
1996. Delcam expects the majority of its existing customers to want
the new system immediately. In the longer term, it will be marketed
outside the mould tool industry, following a further upgrade from
wireframe to solid assembly modelling, planned for 1997.
PICASSO already provides a complete 3D model, containing enough
information to control the machining and assembly process. The next
stage of development, which Delcam is hoping to undertake in a follow-up
project, will be its full integration with CAM systems, making possible
optimised assembly manufacture at the press of a button.