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05. January 2018

UK - Recasting additive manufacturing in the foundry

UK - Recasting additive manufacturing in the foundry

Lestercast foundry in the UK.

Metal casting foundries as we know them have been around since the 1800s. It’s a proven process; liquid metal is poured into a mould which is then removed once cooled to leave a cast solid metal shape from the mould cavity. The principle remains the same today but modern casting techniques have come in to make the process more efficient, cleaner and better quality.

Additive manufacturing (AM) was briefly heralded as a modern replacement to casting. As the hype has calmed and businesses have come to understand more about the benefits and current limitations of AM, there’s certainly no necessary urgency for foundries to close their doors. On the contrary, in a resilient twist, some facilities have embraced the benefit of those 3D technologies that are playing a pivotal role in this well-established industry.

A casting challenge

Minneapolis-based Prospect Foundry has been dealing with iron castings in low to medium volumes for over 80 years, supplying primarily to OEMs in agriculture, mining and construction industries. Three years ago the foundry came across a particularly challenging project from a customer, Sunstrand, who required around 1,000 hydraulic valve cores for a piece of machinery. This particular part had been sent around to several foundries who were unable to accept the challenging job before it landed on Prospect’s desk. Having struggled with unsuccessful cores for two months, going back and forth trying different types of sand, binder, coatings and temperatures, in a last ditch attempt, they sought a solution that was less conventional.

Traditionally assembled core

Back in 2012, the company had spotted a possible technology investment that could help them in accepting more complex parts. Greg Colosimo, Metallurgical Engineer at Prospect Foundry explained how sand printing technology from ExOne looked cool but figured it would never become that useful. Fast forward to 2014 when this particular challenge arose, the team took the plunge and gave ExOne a call.

“I asked them about being able to print this core up,” Greg explained. “We use CAD models when we’re making the pattern boxes so we sent the CAD file for the core and they produced them for us. We had stupendous results, we were getting 75% scrap or worse and I think the first time we ran them we had over 90% good castings.”

Rather than investing in its own machine, the team outsourced the job to ExOne’s on demand 3D printing service which produced the cores using its S-Max Binder Jetting technology at a facility in Houston. A more economical solution due to the size of the cores, ExOne’s process offers design freedoms not possible in traditional cores and machining approaches using industrial grade materials. Since implementing, Greg estimates that these cores have been used for around 4,000 parts, with Sunstrand continuing to order 500 at a time.

Though right now 3D printing only impacts a small part of Prospect’s business, Greg believes that “there is a huge opportunity for 3D printing in the foundry,” depending on the use case. For example, that particular valve core is just one that the foundry produces for Sunstrand, the rest are made via more traditional methods. However, Greg notes that in the past when the team had to turn down certain jobs where the cores proved impossible to make, had they known about the idea of 3D printing them, those cores might not have been so trying.

ExOne printed core

“I thought it was something that was way out there and it would never become a critical part of the foundry,” Greg commented. “Now I can see that it could very easily become a huge part of the foundry business and eventually pay off to have several printers, or at least one in every foundry. Right now it’s a big cost. I think that foundry owners are going to still go with conventional methods of making cores because they’re proven over such a long period of time.”

The wider casting business has progressed from very simple parts that required excess machining to creating more complex near-net shape parts that have holes and passageway built in. Greg suggests that features such as small and intricate parts, like valves, which would normally be cast heavy and then machined to finish, could be cast to shape in future with 3D printed cores, significantly saving on time and costs.

“If we can cast those parts with the holes and passageways already in, you wouldn’t have to drill them, you wouldn’t have to machine, which could have huge savings in the end. In the future I believe it will find a huge spot in the foundry but I think it’s a part of the whole industry moving forward, it’ll take small places like us to take the first steps and the bigger foundries will move forward with it. Once they get a big foundry to move forward with printed cores, that will be it.”

Threefold benefits

portraitcollective/Sam Bowles

Rapid prototyping tooling at Lestercast

A more common form of 3D printing used in the casting industry is resin-based stereolithography. Popularised by the jewellery industry, the range of casting-specific resins on the market, optimised to deliver better burnout performance, allow designers and manufacturers to capture the finest details on tiny parts.

But industrial users are also benefitting from SLA in a bid to reduce the need for costly tooling in the casting process. By no means a new methodology, UK-based Lestercast has been using 3D printing for over a decade. The foundry works with Digital Echo, the UK’s largest 3D printing bureau dedicated to foundry and jewellery investment casting, to produce wax moulds for prototyping. Using 3D printed wax patterns brings lead times down from anything up to nine weeks to a matter of days.

“The time scale aspect is obviously the main thing but also expense as well because if you’ve got a low quantity of parts then tooling can be reasonably expensive,” Marc Healey, Sales Manager at Lestercast explained. “It can also be used as a very good technical tool because it can create shapes that tooling would find it very difficult to make.”

Cast automotive parts from Lestercast

After starting out with 3D Systems’ Thermojet technology, the team now uses the service provider’s 3D Systems ProJet machines to create complex castable shapes primarily for the automotive industry. Having a 3D printing service to hand, Lestercast has been able to deliver parts to customers who have been let down by other suppliers and in need of a quick turnaround solution. Working closely with the motorsport sector, having the ability to prototype new designs and make quick changes is imperative and using 3D printing in the tooling process is a major asset.

In addition to making wax castings, Lestercast has found other novel ways of incorporating 3D printing into the business. The team has its own in-house Stratasys Objet30 3D printer which was initially brought in to produce plastic tools overnight instead of waiting several weeks for aluminium. Moreover, it’s been useful in providing proof of concept models for machinists working on the shop floor.

“It saves time because we can print out a model, give it to the machinist and they can work out the fixtures using a tangible model. Then we’re ready to go when our castings arrive so it also saves time at the front end.”

Contrary to the short-lived belief that additive posed a significant threat to the casting business, these foundries are showing where, if used effectively, it can be an asset. Though additive is certainly a tool, there’s a strong belief from the industry that the flexibility, history and cost benefits of investment casting show it will be a long while before AM, particularly in terms of metals, commandeers the market. But to remain competitive you’ve got to take those leaps of faith and keep your finger on the pulse.

As Greg commented, “You can’t stay backwards forever, you have to move forward.”

Source: tctmagazine.com

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