Leading edge: 3D printing is delivering complex castings to the automotive and defence industries
As a family owned business now in its third-generation, Grainger & Worrall
knows all about tradition. Over the years, it has become one of the best-known suppliers of precision sand castings to the automotive industry, providing moulds and cores to hundreds of customers.
Casting, in one form or another, has been around for centuries. But that’s not to say to that it’s a simple foundryman process that anyone can perform. These days, the fundamentals of good casting practice involves engineering and mathematical iterations working in harmony, requiring knowledge of metallurgical and chemical interactions, thermo and fluid dynamics and stresses and strains. And increasingly, companies like Grainger & Worrall are having to invest in the adoption of new manufacturing equipment as customers demand pieces with ever-more intricate features.
That point is illustrated by Grainger & Worrall’s adoption of 3D sand printing, used in the development and prototyping of turbo chargers, complex water jackets within engine blocks and other filigree elements used in the field of precision casting.
Unlike many businesses that have invested in 3D technology only to struggle to find the holy grail of commercial viability, Grainger & Worrall is hitting utilisation rates of more than 80% using this process and has found that its relatively modest initial investment has created a genuine competitive advantage for the casting sector.
“Casting is a traditional industry, but we know that we can’t sit still as technology moves on,” says Edward Grainger, director of Grainger & Worrall. “3D printing is relatively new to us, but it has already proved that it has a genuine business case.
“The technology enables us to provide customers with an additional innovative and highly advanced rapid prototyping service. We’re starting to make moulds that simply couldn’t have been produced using traditional methods alone. And that capability is starting to open up new opportunities for our company across the automotive, motorsport and aerospace sectors, with customer benefit in terms of time, cost and performance.”
Profit maker: The S-Print machine costs about £500,000
The equipment being used is a £500,000 S-Print high heat strength sand printer, housed in a production facility at Grainger & Worrall’s Bridgenorth site in Shropshire, and feeding cores to the company’s various foundries. Grainger & Worrall says it’s the first commercially available installation of its type in Europe that uses a high-heat strength binder paired with low-expansion sand mix to create intricate core structures direct from CAD data. The tool-less casting system provides greater design freedom by enabling the construction of previously unfeasible internal geometry, when compared with conventional processes.
The high heat strength sand print process produces up to 250 per cent stronger cores that are able to maintain even greater geometric stability throughout the casting procedure. Indeed, this makes it suitable for use with both iron and steel. In addition, the use of a phenol-based binder and silica synthetic blended sand offers advantages in the stability of aluminium castings.
At Grainger & Worrall, the 3D printer is being used mainly for prototype production, typically for low-volume numbers of between five and 10. The more complex the mould, the better suited it is to printing. Cost comes into it too. With traditional methods, there’s an inherent upfront expense in laying down tooling, and there’s the cost of material and of manual finishing to get it to the desired standard. That cost is amortised over time, depending on the number of castings. For prototyping purposes involving just a few items, there’s an obvious cost benefit of going straight from a CAD file to printer. And it’s a much quicker process, too.
Grainger & Worrall has offered a 3D sand printing capability before, but through a sub-contract supplier. There were, however, several imitations to the older technology, which restricted its use.
“The older type of sand printing was fine for aluminium and lower temperature melting alloys, but we found that when we started looking at irons and steels, there was a definite degradation of the mould,” says Antony Middleton, a senior product engineer at Grainger & Worrall. “We wanted to start looking at producing a range of parts with passageways and some fairly fragile cores, but the heat of the steel melt was double that of aluminium.
“That higher temperature was having a rapid effect, causing the cores to break down.”
The high heat strength sand system got round these issues – the parts were much better at withstanding higher temperatures, maintaining their shape for longer. The quality of the castings was also improved as there was less gas given off compared to the older type of 3D printing systems.
Grainger & Worrall has started to use the 3D printer more regularly. It now runs 24 hours a day, six days a week. The 3D printing machine at its Bridgenorth site has a job box size of 800mm x 500mm x 400mm – and this size of machine takes just over 10 hours to print a full box.
“For most of the parts we do – such as a three-cylinder head – we can fit a full mould pack into one box,” says Middleton. “We try to orientate parts in such a way that they are tightly packed. That means we produce two or three cylinder heads in a day.
“Alternatively, we use the printer for small turbocharger components. With those, we can actually produce several hundred small cores in a day. For very small parts, we are at the stage where we can produce them faster than we could on a traditional moulding machine. And with the very small parts in low volumes we are talking very low costs – literally pounds and pence.”
The printer is also being used to produce special products such as water jackets for motorsport clients. “Speed is important in this sector,” says Middleton. “We can quickly produce just about any shape. Customers can place an order with us at 5pm in the afternoon, and by 9am the parts requested are ready to go into the foundry.”
While the 3D printer brings many such benefits, there are a few disadvantages too. The surface finish when compacting sand onto a hard tool is very predictable and smooth. When generated additively, with a quarter of a millimetre step surface, the finish isn’t quite as defined. “On certain surfaces the layer step creates what we refer to as ‘artiefacting’ on the surface. That causes a slightly different appearance. It’s not a technical disadvantage, but there is a slightly different finish,” says Middleton.
And the 3D printer at Grainger & Worrall has become a victim of its own success. “We bought it for core making – but it has emerged to be a bit of a do-all, catch-all machine, as we do both cores and moulds on it. The speed at which we can produce parts is currently 10 hours for a full job box at the moment.
“That’s fine for prototyping, but we’re starting to look at using it with production intent. For that kind of process we will need to look at adapting our current machine or look at new machines which have a much higher throughput.”
It seems 3D printing in the casting sector is here to stay.
Source: imeche.org
