Printing possibilities: emerging additive manufacturing technology for sand molds and cores removes design constraints and accelerates speed to market.
"[With additive manufacturing] we are able to manufacture that which we haven't been able to make before," said Steve Murray, an independent sales/marketing liaison for Hoosier Pattern, Decatur, Ind., which uses an in-house printer to make sand molds and cores. "If that doesn't get you excited, then get out of the business."
While direct printing of products like an acoustic guitar, stylized clock, nylon bike or smartphone case makes headlines, secondary processes such as metalcasting could have the most to gain from additive manufacturing.
"The conversation in the media is focused on the production application of saleable goods, but honestly, it's not likely an option for the average company," said Todd Grimm, a 23-year veteran of additive manufacturing and industry advisor to the Additive Manufacturing Users Group. "I see a lack of attention in the media on the product development side, but making models and prototypes is a strong area. Plus, we are seeing some new ingenuity and creativity in applications we haven't seen before."
The investment casting industry has been using 3D printing since the '90s to generate patterns for low run or prototype parts. Sand printing brings similar advantages to sand cast production parts. Engineers can procure prototype parts they are assured accurately reflect how the parts will perform in full-scale production. In some cases, the printed mold or core is used to manufacture castings beyond the trial period because of the complexity of design that is achievable or when it is a low volume order. "Time compression is just one advantage of additive manufacturing," said Jerry Theil, director of University of Northern Iowa's Metal Casting Center, which recently installed a 3D sand printer at its facility in Cedar Falls, Iowa. "Flexibility also comes to play because we don't have to obey conventional molding rules such as draft."
Reducing Tooling, Time to Launch
John Deere has been utilizing) additive manufacturing for sand molds and cores since 2011 as part of an effort to decrease spending on prototype tooling in product development. Enterprise-wide, the company spends about $100 million annually on feasibility and prototype castings. The ability to test several design iterations without investing money in hard tooling, coupled with the ability to achieve desired intricacies with fewer cores, makes the rapid casting process an attractive option.
"We have found different paths to choosing additive manufacturing for a part," said Sheila Dickey, manager of technology integration at the Casting Center of Excellence for John Deere Foundry Waterloo. "To determine if the process is applicable, we consider whether it requires a short lead time or if the casting design itself is so complex that we could print a single core on the printer as opposed to building five different coreboxes as in traditional prototype tooling builds." Dickey said some projects can he completed where no tooling is built, and instead make the prototype castings with the printed molds and/or cores.
One such part was a transmission housing for one of John Deere's iT4 tractors. The part was originally slated to be produced via the traditional route. But an aggressive launch plan drove the team to utilize additive manufacturing. John Deere has found that conventional CNC-cut tooling for prototypes can take between four and eight weeks, depending on part size and complexity. More coreboxes means more time and more cost. With the conventional approach, the transmission housing would have required nine coreboxes and assembly. Using additive manufacturing, John Deere Technology Integration Personnel determined only six cores were needed, four of which were assemblies. The conventional prototype approach would have required a 20.5-week lead time for tooling, castings and machining. Using additive manufacturing cut the total lead time to just 15 weeks and saved close to S44,000 in total spend.
"Reducing the number of cores led to cost savings and time savings, which permitted us to prevent delaying a tractor build," Dickey said. "That was the key driver, that we would not delay a build. And we would have had to with a conventional prototype tooling approach."
John Deere's foundry in Waterloo, Iowa, does not yet have its own 3D printer, so it works with third-party facilitators to produce its molds and cores and ship them to Waterloo. According to Dickey, the company has used additive manufacturing on close to a dozen projects a year since 2011 and is considering investing in its own 3-D printing equipment in the future.
"I see our use growing," Dickey said. "You can use it in casting design for cost reduction in testing. Instead of changing the tooling or making a new corebox, you can make a new prototype core. We have completed projects at John Deere Foundry for large tractor castings and for our sister factories and global operations for entire mold packages, as well."
Is It a Right Fit?
The possibilities of design using 3D sand printing seems limitless in shape, if not in size, but the cost will be high enough in many cases to be a deterrent. Right now, the equipment needed to print the molds and cores is a considerable investment and the resin and sand used to build the molds are not inexpensive. Domestic sources are scarce, and the sand has to be specially processed to achieve a unique screen distribution. So, the decision to use a printed sand mold or core is not made lightly.
Murray has seen his customers arrive at additive manufacturing for a number of reasons and at different points of a product's lifecycle, but the most obvious reasons are for samples and prototypes, he said.
"They can try out a design and actually have a casting, machine it and put it out there to see if it works," Murray said. "They don't have to build foundry tooling or wait weeks to get something cast."
So what makes for a good additive manufacturing candidate? Grimm offered four elements:
* Low volume.
* High complexity
* Efficiency gains in the process.
* Flexibility for design changes.
"When a new part or a redesigned part feels like a risk or could be problematic, that is your alarm bell," he said. "When you are not sure about the design, trying something new or missed a date and in a time crunch, you could be a good candidate for additive manufacturing. In the designer's realm, it is an insurance policy."
The additive manufacturing process works similarly to that of an inkjet printer. Finely powdered sand and binder are repeatedly layered to build a sand mold or core based on a CAD file. Production-wise, sand printed cores and molds are available in a variety of molding materials and binders, including organic and inorganic, and can be used with most metals, including aluminum, magnesium, copper-base, iron and steel. Suppliers of sand printing technology continue to research new materials and binders to use. Build volumes range from 2.6 x 1.6 x 1.3 ft. to 13.1 x 3.3 x 2.3 ft.
Letting Imagination Loose
What makes Murray giddy about additive manufacturing goes beyond prototyping, into a Walt Disney, "If you can dream it, you can do it," realm of manufacturing. Designers are not limited to working within the constraints of manufacturability. Because you are not removing cores from a corebox, certain conventional molding rules, such as draft, do not apply. Designing core assemblies as single cores removes the need for a fin where cores might have been glued together. In some instances, the core can be printed as part of the sand mold, providing closer tolerances because cores don't have to be set into the mold separately. For highly specialized, lower volume jobs, this design freedom is a strong case to utilize additive manufacturing for production runs.
"The young engineers are going to start designing stuff that can only be made this way," Murray said. "Before, an engineer would design a casting, and the foundry would have to tell him why it can't be made and why it won't work. That doesn't fly anymore." In markets such as military, aircraft and automotive, where designing weight out of a component is a huge driver, Murray sees additive manufacturing playing the hero's role.
"If you can make a casting without draft and take a pound out of an aircraft part, you are a god," he said.
Ingenuity abounds even in shipping. Hoosier Pattern can ship cores printed within a thin-walled printed sand box that is then filled with loose sand.
"You could print a box in a box in a box, making it all at once," Murray said. "You are limited only by your imagination."
In production scenarios, core printing is emerging as a valuable tool for intricate parts requiring extensive core assemblies. Hoosier Pattern often ships cores that will be placed in traditional green sand or nobake molds in metalcasting facilities.
"You can make the mold your way and have a core inside that is made with a 3D printer. You can have a green sand cope with a printed drag, if that is what it takes to get the design you want," Murray said. "Right now, we are doing some production runs of over 2,000 pieces a year. In the realm of aircraft, marine and heavy equipment, this is very doable."
OEMs are also using the technology to serve as gap fillers when a few parts are needed right away while tooling is made for full production, or when a legacy part needs to be replaced and the tooling no longer exists.
"It's not going to be the answer every time," Murray said. "It is going to serve a niche to solve a technical
Because the technology and investment in equipmenr required is expensive and so few domestic businesses have 3D printing capabilities, additive manufacturing in sand has only been adopted by a few, but that is changing.
"It's interesting that work in sand printing technology has been ignored until recently," Grimm said. "But now it has been a growth area and one of interest to people."
Organizations such as the Additive Manufacturing Users Group have been collaborating with additive manufacturing equipment suppliers and colleges such as UNI to find ways to reduce cost and help industry gain fill value of the process.
"The cost is relatively high, but the cost benefits are relatively high," Thiel said. "The industry has to determine problem. And when it does that, everyone feels like a champion." the sweet spot for cost effectiveness."
Through its Metal Casting Center, UNI hopes to build a portfolio of successful additive manufacturing case studies in sand to help develop the market for potential users or providers of the technology.
"We think improving the accessibility and availability of the technology to companies in the Midwest is a hurdle,"Thiel said. "We want to show companies--not just foundries, but also equipment manufacturers and entrepreneurs--that this is a viable process and has flexibility in design not available in conventional coremaking."
SHANNON WETZEL, SENIOR EDITOR
Using the Actable App, scan this page to see a video of additive manufacturing in action at Hoosier Pattern. To watch online, go to www.metalcastingtv.com.
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|Date:||Dec 1, 2013|
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