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GWCast EXOne SPrint
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GW Casting
Removed from the clean-room of the ExOne SPrint 3D Printer, the pouring of molten metals looks much the same as it has for hundreds of years.3 of 3
GWCast Milling
Subtractive processes still have a central role in the production of final parts.Grainger and Worrall Ltd are experts in casting, especially complex and high-strength castings. This is why the company makes engine blocks for some of the most prestigious automotive brands in the world including Bentley, Aston Martin and — believe it or not —engine blocks for the all-American high-octane speed-fest that is NASCAR. One of the latest tools in the company’s formidable arsenal is a 3D sand printer; not as a design aid or a development tool, but as part of a true manufacturing production line.
Traditionally the beating heart of British manufacturing, the UK’s West Midlands has been amongst the hardest hit by offshoring, recession and — some would say — unrelenting government apathy. But as Charles Darwin deduced, these life-or-death challenges have killed off the weak and left behind only the strong. In this case Grainger and Worrall has not only survived but grown and prospered and has a global client base that would leave most companies green with envy.
Founded in 1946 and still owned by the Grainger family, Grainger and Worrall runs two sites in the UK totalling 17,500 m2 with further representation in the US, Germany, Italy and China. This global footprint combined with customers in the aerospace, automotive, defence, marine, motorsport and power generation industries are the keys to the longevity of the company. A spread of clients with different lead-times, contract lengths and phases of activity helps to balance the books across otherwise lean times.
Truly a full-service partner, Grainger and Worrall has in-house capability from design support and engineering to production including tooling, rapid prototyping, casting and machining for development, pre-series and small series production.
Sand printing is not a new venture for Grainger and Worrall; they have used sand printing from bureaux for over 8 years. Over this time, they evaluated various sand printing systems looking for a system which offers best performance, speed and flexibility. 18 months ago, they began testing with the HHS system from ExOne. Over the course of the following year, they helped refine the process and after repeatedly seeing the additional benefits the system offered made the decision to bring the system in house. Teamed with dedicated 3D printing and casting experts, Grainger and Worrall are already helping to develop the process and capabilities of the machine. The system integrates with the existing depth of knowledge and resource offering the company’s client’s real leadership and choice, be it conventional tooling, printed or a pragmatic hybrid solution .
Housed in a new purpose built production room, the S-Print is fed by two huge sand silos in an adjacent room. The size of the build volume (800 mm x 500 mm x 400 mm) and the speed of operation (9-10 hours per full job box) means that the S-Print swallows up a lot of sand, which takes up a lot of room — quite how much may not be apparent until seeing the machine in operation. In addition to this, the company runs three ‘job boxes’ (removable build chambers), meaning the printer can effectively produce parts 24 hours per day with minimal downtime.
The company uses a special low-expansion sand blend, mixed in precisely controlled proportions. Mixing of the sand occurs at the point of use so the ratio of ingredients can be controlled on a build-by-build basis. The low-expansion sand maintains geometric stability throughout the casting process — which by its nature includes high temperatures that would cause standard printed sand parts to expand and crack. The sand mix can be combined in different proportions with different additive depending on the work being undertaken. The system also has little waste as unbound sand can be recycled and used again in the system. After casting, the sand can be reclaimed and used once more in the conventional foundries sand supply.
The low-expansion sand mix is paired with a high heat strength (HHS) binder to form the cores and moulds directly from the CAD data. The HHS binder and low-expansion sand means the company can create highly accurate intricate structures (such as thin walls) that would be difficult to achieve otherwise. The other major advantage with the HHS binder is the ability to cast iron and steel parts, something which is normally unachievable with standard furan sand printing. Furthermore, the cores and moulds are available for casting work straight away.
The cores and moulds are destined for use in the six foundries Grainger and Worrall operate in Bridgnorth: an Aluminium foundry, Iron foundry, short-run foundry, large mould foundry, motorsport foundry and a foundry dedicated to a single client. Combined with the company's finishing technologies and extensive validation equipment this set up allows delivery of production-ready parts from one-off to runs of up to 10,000 scheduled parts.
The final stage in the production cycle is the validation of the cast parts. Here the company employs an impressive array of technology to ensure that each part is free from defects. Externally a GOM scanning system and five co-ordinate measuring machines (CMMs) are employed to ensure dimensional accuracy but these are of limited use for examining and validating internal structures (which engine manufacturers are reportedly quite keen on).
A pair of industrial grade 450kV X-ray computed tomography machines are used on site for validation of complete parts including checking internal structures and voids within the cast. The CT scanner can also be used to in reverse engineering work taking a solid part and recreating a faithful replica of all internal and external features. Real-time x-ray, digital endoscopes and more are available too.
In 2012, Grainger and Worrall added two awards, the Queen’s Award for Innovation and an R&D100 award for ceramic sand inserts. They continuously push new material development with real world application and operate with a culture to enable and innovate in the toughest sectors of their market. This is shown with their global presence in the most demanding fields of automotive engineering which includes Formula 1 and NASCAR.
