3D printing has eliminated much of the tedium of the 3,000-year-old sand casting process
Excerpt from the September 2020 The Additive Report article by Kip Hanson.
Humans began pouring the first sand castings approximately three millennia ago. And until recently, that technology has remained virtually unchanged:
• A replica, or "pattern," of the desired object is placed in an open-ended, steel molding box.
• A special type of sand is poured around the pattern, which is pounded firmly into place and then removed.
• A sprue is cut to allow molten metal to flow into the mold, along with a gate that joins the sprue to the mold cavity.
• A core is used to replicate parts having internal features.
• Molten metal is poured into the mold; when the metal cools, the completed part is removed.
That's sand casting in a nutshell, although journeyman pattern maker Dave Rittmeyer will tell you there's far more to it than that. Rittmeyer, the customer care and additive manufacturing manager at Hoosier Pattern Inc., Decatur, Ind., also will tell you the industry has undergone a dramatic shift over the past decade or so, thanks in part to AM.
It's eliminated much of the tedium of the sand casting process while making the process faster, more flexible, and significantly more cost-competitive than other casting methods.
"Lead times with traditional pattern-making processes are best measured in weeks and months," Rittmeyer said. "3D printing has drastically shortened that, sometimes to just a day or two. In one example, we tooled up for a crane case in three weeks. That normally would have taken us 14 weeks. We’re also able to print very complex molds and cores that would otherwise have been impractical to manufacture."
In 1993, researchers at MIT invented a 3D printing process called binder jet. Three years after that the company now known as ExOne Inc. took the binder jet ball and ran with it, changing the sand casting industry forever.
It developed a cold-hardening binder system that deposits sand in layers 0.26 to 0.38 mm thick, then binds selective areas with a liquid polymer that solidifies the sand.
Hoosier was founded in 1997 by three journeyman pattern makers who operated a couple of CNC machines. They bought their first sand printer—an ExOne S-Max—in 2013.
"Today we have more than 25 machining centers and four S-Max sand printers, and roughly half of our business is 3D-printed sand cores and molds," said Rittmeyer. "I don't have an exact figure, but we literally print thousands and thousands of each annually."
The Indiana company also operates a Stratasys Fortus 450mc FDM machine and a 3ntr A2 for building prototypes, low-volume patterns, and various tooling for around the shop.
3D printing has transformed the company from a regional pattern shop to a global one. Hoosier Pattern now ships 3D-printed sand products "all over the world," said Rittmeyer.
Higher volumes and relatively simple tooling are still produced using traditional manufacturing methods—milling, turning, and EDM—while everything else is sent to one of the company's 3D printers. But the balance is steadily shifting to printing.
Said Rittmeyer, "For one piece, or even a hundred pieces, the [printer] usually is the way to go—although we do have one print job that calls for 2,200 parts a year, and just this morning the customer called to see if we can double that."
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