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Graphic element Research > Growth > Research projects > Products & processes projects > New casting technique propels success
Graphic element New casting technique propels success
    09-06-2000
 

The 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.

Breaking the pattern

There 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 areas.
2. The pattern is used to create a mould from a compacted sand block.
3. The sand mould is filled with molten metal to produce the end product.

This 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.

An exploratory award under the BRITE-EURAM programme allowed the company to prove the feasibility of the idea.

Developing a working machine

The 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 and software.

The 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.

Dr 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."

  Producing quality results

End-user 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.

Castings 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.

Wooden 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.

The 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.

  Technology being made available

The 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.

At 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.

   
Breaking the pattern
Developing a working machine
Producing quality results
Technology being made available
   

Key facts

Improving production techniques is an important part of the Innovative products, processes and organisation key action. In typical foundries, wooden patterns are used to produce moulds from blocks of compacted sand, into which molten metal is poured to produce castings. Small batch production and one-off prototypes can make the cost and lead time for this style of manufacture prohibitive. A CRAFT project has developed a faster, more accurate and cheaper alternative.

Project: Short lead-time 'patternless' manufacture of prototypes and small batches of large or small castings (BRST-97-5130)

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