shipbuilding industry is unusual in that almost every customer wants a
purpose-built design. As a result the manufacturers of ship-related pumps
and valves generally require very small quantities of cast-metal components,
while the propellers themselves are often one-off designs. Thanks to a
recent CRAFT project involving 14 partners from across Europe, a new technique
has been developed that can produce the sand mould for casting directly
at a very high speed and with low running costs. Eliminating the need
for patterns has reduced product lead times from weeks to days. The process
is also more accurate; one SME involved recently used the machine to manufacture
the most accurate propeller casting in the company's 97-year history.
are three stages in the traditional method of casting metal :
1. A pattern is made based on drawings of the product's outline
and cross-sections. The accuracy of the final product is dependent
on the skill of the patternmaker who will 'blend in' any undefined
2. The pattern is used to create a mould from a compacted sand
3. The sand mould is filled with molten metal to produce the end
method is both expensive and time-consuming.
Back in 1996, the UK company Furniss and White proposed an alternative
process which would eliminate the need for a pattern. The moulds
would be machined using computer numerical control (CNC) directly
from blocks of bonded sand. The plan was to use computer-aided manufacturing
(CAD/CAM) software to control a high-speed multi-axis spindle on
an automated milling machine. The use of CAD/CAM ensures that all
surfaces are defined and precise dimensions are established prior
to cutting the mould.
award under the BRITE-EURAM
programme allowed the company to prove the feasibility of the idea.
a working machine
next phase was to develop a working machine. As a member of the
UK-based Castings Development Centre (CDC), an international organisation
providing a wide range of research-related services exclusively
for its members, Furniss and White had ample assistance in putting
together a two-year CRAFT
project to carry out the development under the BRITE-EURAM programme.
The 13 project partners hailed from Italy, the Netherlands, Norway,
Spain, Sweden and the UK, with CDC acting as the project co-ordinator.
The project had 13 defined tasks, with the first year being dedicated
to defining the specifications for the machine and the CAD/CAM hardware
machine itself was built by Italian company CMS,
which had not worked in the casting industry before. The success
of the project has therefore opened up a new market for it. The
machine is programmed using commercially available software, for
which another partner, Grenville Consulting, developed an operator-friendly
interface that allows rapid program storage and retrieval. CDC also
designed and built a manipulator to ease the movement of the sand
blocks in and out of the machine.
Peter Haigh of CDC is keen to emphasise the contribution of all
the partners: "The success of the project definitely had its
foundation in the combined skills of the consortium which represented
a complete cross-section of the industry from end users through
to equipment manufacturers and suppliers."
SMEs played a significant part in putting the machine through its
paces. In one trial, a controllable-pitch propeller was made from
aluminium bronze for partners Kamewa
and Oshaug Metall. The test indicated that it would be possible
to manufacture a castable mould within an eight-hour shift. This
compares extremely favourably with the conventional production timescale
of at least three weeks.
were produced with and without mould coatings, and on visual examination
the surfaces of the uncoated moulds appeared superior. Moulds were
also made from reclaimed sand, and radiographic inspection has shown
all the castings to be sound and free of non-metallic inclusions.
In a second set of trials, fixed-pitch propellers weighing over
a tonne were manufactured for F Bamford, with extremely accurate
results. F Bamford produces high-speed, highly loaded propellers
for naval applications. The propellers have very large, thin blades
with a required surface accuracy of ±0.2 mm. They are rarely
manufactured in large quantities as each class of naval boat requires
a different design.
patterns cannot be used for these propellers because the design
involves stresses that wood is not strong enough to withstand. Consequently,
expensive aluminium patterns are used, but even these must be handled
with care. The patternless process offers a number of advantages,
among them significant cost savings: there is no need to store patterns,
and design data can be transmitted electronically.
world leader in submersible pumps and mixers, ITT
Flygt Products of Sweden, also tested the machine by manufacturing
a prototype of a 150-kg pump casing required for a new product.
being made available
new technology is now being made available to industry. Interested
parties should approach CDC who can advise on the optimum way of
implementing the technique, taking into account individual product
specifications and the existing mode of manufacture. CDC is acting
as a technical intermediary between the equipment and software manufacturers,
interested casting users and their existing casting suppliers.
least two of the consortium partners are expected to take up the
technology and other companies are already showing interest in the
benefits. CDC intends to make a machine available to its members
and also to extend use to non-members on a commercial basis. They
should be on a winner: users of the new technology will be able
to improve productivity, reduce delivery times, become more competitive
and safeguard jobs.