Castings Technology International (Cti) based in Sheffield, is a member-based, not-for-profit, ISO 9001-accredited organisation with a budget of approximately £5M. Employing 100 multi-disciplinary personnel, the company provides R&D, consultancy and technical services to casting producers and users around the world. It is one of the largest organisations dedicated exclusively to enhancing both the performance of metal castings and the competency of the casting supply chain.
With 5,000m2 of workshop space and production-scale, state-of-the-art facilities, the organisation is well-equipped to carry out market-led design and development activity and has achieved widespread acceptance as a third-party technical intermediary.
Its skills, experience, knowledge and information in casting design, materials, specifications, manufacturing technologies, applications, structural integrity and performance have proved to be a strategic resource of value to many companies in a broad range of sectors, but none more so than in the valve sector. Castings are pervasive commodities in much of manufacturing and engineering, but valve manufacture is particularly sensitive to the performance of the castings supply chain, if for no other reason than the cost of the cast ‘raw material’ represents a high cost of a finished valve (30-60% or higher).
In the past, improvements in terms of cost, quality and delivery performance have been achieved by enhancing traditional valve casting production techniques. However, globalisation and restructuring in the valve sector has precipitated a demand for new approaches to satisfy the emerging world order.
Valve Market Needs
In general terms, valve manufacturers seek casting suppliers that can:
- achieve short lead time to market of high volume parts and exceptionally fast delivery of one-off or small batches of ‘specials’,
- provide a range of alloys, especially for ‘specials’, embracing super duplex stainless steels and high nickel alloys (Hastelloys, Monels, Inconels and Incoloys),
- attain high integrity, i.e. defect-free castings,
- achieve consistent and accurate dimensions, i.e. minimum machining stock and consistency of form,
- ensure minimum and consistently accurate wall thickness,
- provide castings with good surface finish and lettering definition,
- facilitate achievement of low end-product manufacturing cost and low life-cycle cost.
Quality and cost
Many valve manufacturers have ensured cost competitiveness by sourcing castings in low labour cost countries, with quality and other issues being addressed by procuring cast products in the proof-machined or fully-machined condition.
Failure analyses carried out in Cti’s laboratories testify all too often that this is not necessarily a fail-safe strategy from the end-user’s perspective. Furthermore, if a predominance of valve manufacturers follow the same strategy, no competitive advantage is gained (and hidden costs can mitigate the benefits that low prices in such areas of the world might first imply).
However, technologies developed at Cti specifically to address the market needs listed above provide the opportunity to achieve additional benefits. They can maximise cost reductions, they are intrinsically capable of achieving high levels of quality and dimensional accuracy and they facilitate the attainment of exceptionally short lead times, even for products which are customised with respect to design, material, etc.
Optimisation of such benefits is more dependent on the competency of application of the technologies rather than where in the world they are applied, although it goes without saying that advanced technologies coupled with low labour costs present a very attractive solution to competitiveness issues.
Cti is well aware of legislative and regulatory agendas. For example, the newly developed technology more readily enables compliance with the EU Pressure Equipment Directive and, in addressing sustainability issues, energy consumption per unit of output has been reduced, as have waste streams, the working environment has been improved significantly and external impacts minimised, and so on. These attributes are highly relevant to those companies for which ethical sourcing is a key component of procurement strategy.
Technology options
Medium to high-volume production
The investment (lost wax) process produces near-net shape castings with the highest quality, best surface finish and greatest precision. It is, however, a costly process and is limited to small components.
The Repliwax Process increases the weight range of the lost wax process. The technology embedded in the process achieves manufacturing cost reductions by:
- reducing material consumption and hence waste by as much as 50%,
- increasing effective production capacity by as much as 35%,
- reducing labour content and increasing productivity, i.e. lowering operating costs,improving operational logistics, allowing faster and more flexible production.
The process has been proved to be a technically, environmentally and commercially sustainable, near-net shape technology, capable of reducing the cost of downstream processing of castings of a size greater than otherwise possible with the lost wax process.
A major feature of Repliwax is that, as a ceramic moulding process, the inclusions, gas, hot-tears and other casting defects associated with sand moulding are avoided.
This is also a key feature of Replicast, a companion process which similarly eliminates or minimises the defects commonly encountered on machining sand castings. It differs from the Repliwax process mainly in that it substitutes polystyrene for wax patterns. This enables even larger, near-net shape products to be made cost-competitively with sand castings.
This is because the technology, on a like-for-like basis, uses less than 50% of the same high quality ceramic as the lost wax process. Ceramic material costs are just 8pence/kg of finished casting, less than the material costs of a sand mould. Furthermore, Replicast valve castings are typically 25% lighter than a sand cast equivalent, which not only enables savings to be made in their manufacture, but also leads to machining cost savings of 45% or more.
Repliwax and Replicast are complementary processes which use common equipment and lend themselves to high levels of automation. The trend now is for valve casting producers to adopt both processes to provide flexibility and opportunity of choice to their customers.
Low-volume production and ‘specials’
Two approaches provide innovative solutions to market needs for small batch manufacture. The first exploits high-speed machining systems to produce:
- polystyrene patterns to manufacture small and medium size castings by ceramic moulding,
- precision patterns and core boxes for sand castings, large and small,
- sand moulds and cores directly, i.e. without the need for patterns or core boxes.
Machining of polystyrene patterns for one-off or small batches of castings (up to 20 say) has been refined over the years at Cti. It is now well-established as a fast, cost-effective way of producing ‘specials’ or prototypes. Many castings have been produced using this approach, especially in super-duplex alloys, Monel, etc. It combines the attributes of Replicast, with the capability of producing a casting in as little as five days.
Modern, high-speed machining systems can also reduce lead times for conventional pattern equipment, while simultaneously achieving an accuracy and precision of form impossible by manual techniques. A large-scale machining system at Cti (working envelope 4×2.5x1m) has been used to meet otherwise impossible lead times on numerous occasions. For example, patterns and core boxes for 3-tonne and 6.5-tonne, 600mm Flowserve valve bodies have been manufactured in half the time quoted by traditional pattern shops. Pattern costs were reduced by 20% and subsequent projects on similar valve components have been executed in just ten days with only 65 man-hours of labour.
Even these gains have been eclipsed by a relatively new technology — the Patternless process — emerging from Cti’s R&D programme. Elimination of patterns and core boxes by directly machining precision moulds and cores from blocks of sand provides unprecedented opportunities for one-off or small production quantities.
For example, rather than fabricating two large valve bodies, Severn Glocon of Gloucester, took advantage of the facilities at Cti (a purpose-designed sand-mould milling machine with a working envelope 2.6×2.6×1.2m) to produce the castings in a record time to high standards of integrity and dimensional accuracy. Surface finish and lettering definition exceeded all expectations, after assembly and painting, the cast surfaces were indistinguishable from fabricated parts.
Severn Glocon’s business is ‘specials’ and storing digital machining data rather than patterns is commercially attractive. Geometry and lettering changes can be readily accommodated, especially for different cast materials and storage and repair costs associated with conventional patterns are eliminated.
The second approach Cti is pursuing for one-off or small batch production is that of Rapid Prototyping, a generic term used to describe a range of technologies which can quickly convert a digital, computer-based definition of the 3D geometry of an object into a ‘hard copy’ physical model.
It is not the intention here to describe the range of Rapid Prototyping techniques, suffice it to say that a replica of the required casting can be manufactured quickly in materials which lend themselves to conversion to a casting, notably from ceramic shell moulds, within five days. For example, wax or resin patterns within a maximum envelope of 500mm3 can be generated in a day or so.
Beyond this size, the machining techniques described earlier are more appropriate — and more competitive — but Rapid Prototyping unquestionably offers a complementary approach for smaller valve castings.
A case in point is a current project involving the conversion of a 65mm cryogenic gate valve body for industrial gas manufacture. Previously machined from solid, the component is now to be produced by the Repliwax process. The potential for ‘end product’ cost savings have been demonstrated using wax patterns grown directly and automatically from a 3D CAD geometry in just 17 hours.
Cti has embarked on a major initiative to develop the ‘enabling’ technologies to exploit Rapid Prototyping, not only for fast manufacture of ‘specials’ but also to accelerate ‘time-to-market’ of new, high-volume product ranges. This entails significant investment in facilities to demonstrate the capability of Rapid Prototyping on ‘real world’ products and to benchmark its performance against alternative techniques — such as machining of polystyrene or wax.
Design Optimisation
The benefits of these techniques, especially those for small batch or one-off production, can be maximised when a 3D CAD file exists. This saves time and ensures the valve manufacturer receives the precise geometry specified.
Availability of a 3D CAD file also facilitates optimisation of design with respect to manufacturability as a casting. Neglect of this issue puts at risk ‘right first time’ manufacture which, in the case of one-off or small batch production, especially in ‘difficult’ alloys, destroys any prospect of achieving the cost and lead time benefits associated with the technologies described herein.
It is furthermore essential that, in parallel with assessment of valve performance by the application of finite element analysis (FEA) and computational fluid dynamics (CFD), simulation of the casting process is conducted to ensure the design is optimised with reference to the specific casting manufacturing technique selected.
The value of such concurrent or simultaneous engineering is well-established in other engineering sectors and Cti is engaged in a major project (e-valves) aimed at promoting and facilitating design interaction across the valve casting supply chain interface.
The project will deliver the potential value of concurrent engineering by ensuring the selected casting manufacturing technique is capable of meeting the requirements specified during the design process.
The market failure to recognise this dependency and the commensurate lost opportunities for quality improvement, cost reduction and delivery performance have blighted valve casting supply chain relationships for many years.
These issues are raised here because there is little sense investing in new valve casting manufacturing technologies if no attention is paid to the design of parts to be produced specifically by those technologies. The design must reflect the process capabilities in order to extract maximum benefit, merely reproducing the geometry of a sand-cast part by Replicast, for example, will ‘short-change’ the opportunities for cost and quality improvement to a degree which brings a process with so much potential into disrepute — and sadly, too many examples of consequential failure exist.
Market pull
It is noteworthy that penetration of all these techniques has been greatest in vertically-integrated operations, where the internal supply chain interface is seamless and due recognition is given to the importance of design. Typically the driver for adoption of a new technology has been the development of a new range of valves.
Achieving the same benefits in an environment of independent customer-contractor relationships is a far greater challenge. Cti is well-aware that promoting the benefits of
technology to casting manufacturers will get nowhere. Only by
demonstrating the potential
to casting users can a market pull be developed to
stimulate adoption.
Most success in promoting adoption has been achieved where a strong relationship exists between a valve manufacturer and casting supplier. This applies regardless of where the casting supplier is located (it is a perverse aspect of the digital age that the technologies developed to compete with low-cost sources of supply can readily be exploited by those same sources).
Typically, Cti acts as a technical intermediary, using its facilities and competencies to minimise risk and cost and to provide underpinning and ongoing technical support. Whereas a conventional foundry produces castings by a specific process, Cti has available the entire range of processes and cast materials (air and vacuum melted) and so is in a unique position to determine and demonstrate which process provides the best, integrated solution to a particular need.
A number of market leaders and several small but progressive valve manufacturers have exploited the opportunities this capability presents in partnership with their casting suppliers. The most successful arrangements have been predicated on Cti’s assistance with:
- the development of a ‘wish list’ with respect to procurement and processing of castings in order to identify,
characterise and quantify
key issues,
- a detailed review of machining strategies, jigging and fixturing, etc, and all other casting processing operations to establish opportunities for cost reduction through supply of cast product forms with appropriate attributes,
- an audit of supplier operations to benchmark capability against global best practice criteria held in Cti’s databases,
- definition of mismatch between customer expectations and the prospect of the casting supplier meeting those expectations with existing technology and current casting designs,
- optimisation of existing or new valve casting designs and/or manufacturing technologies to achieve the lowest cost solution to the ‘wish list’ criteria and to achieve
maximum valve functionality and reliability,
- demonstration in Cti’s production-scale operations, at minimum risk, cost and time, the improved match between expectation and the capability of the improved design and/or technology solution to deliver,
- specification of supplier development plans embracing the plant and equipment, materials, skills, etc, necessary to operate to the proven supply standard,
- ongoing technical support to the partnership to ensure best practice is maintained, to troubleshoot any issues which arise and to facilitate continuous improvement, especially in the light of any new developments.
Cti has worked hard to overcome adversity in the casting supply chain. Where constructive and mutually beneficial relationships have been developed, quite massive gains have been realised and Cti has played no small part in bringing such relationships about.
This has been done in enlightened self-interest, because our collective future is inextricably linked. As casting production migrates eastward, valve manufacture will surely follow. Our co-destiny, therefore, should stimulate us all to preserve what we can of our manufacturing base and we are able and willing to help. But we cannot do so without the market pull.
This article was originally published in the proceedings of Valve World 2002 Conference and Expo and is reprinted here by kind permission of KCI Publishing BV.