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Green Sand Metalcasting Foundry News

Casting Goes Digital with Sand 3D Printing, Nondestructive Testing

Posted by Hill and Griffith Company on Jan 12, 2021 5:04:14 PM

Tooling & Equipment International (TEI) used to make tooling for castings. Now, it casts prototype parts in a digital workflow using 3D printed sand molds in combination with simulation software, CT scanning and X-ray technology.

Excerpt from the January 2019 Additive Manufacturing article by Stephanie Hendrixson.

"In the early days, before numerically controlled machines, casting tools were made by highly skilled pattern makers carving mahogany into patterns and packing sand around them," says Oliver Johnson, president of Tooling & Equipment International (TEI). "You'd be talking six or nine months to make all the tooling for a part that we could do today with a 3D printed mold in two days."

Engine Block Prototype Sand Casting

Founded in 1918 as Automotive Pattern, TEI has witnessed the major changes in casting technology alongside its own transformation. For most of its history the Livonia, Michigan, company has focused on providing tooling to production casting facilities, first using hand tools and later CNC machines to make patterns, cores and cavities. Its own small foundry was used only to test the tools that would be passed on to these customers — but this focus has recently changed.

"Now, we don’t make tooling other than the tooling we need for our own processes," Johnson says. Over the last 10 years, TEI has converted its test foundry into a full-fledged manufacturing facility for prototype and low-volume production castings. Sand 3D printing now provides the majority of the molds for this work, designed with the help of simulation software. Casts are computer-controlled for consistency, and the company’s CT and X-ray scanning capability helps to ensure quality. This is casting gone digital, and it’s these advances that have helped TEI condense the timeline for a cast part from months down to just days.

3D Printing Sand Castings

Sand Printing for Prototype Cast Parts

TEI's specialty today is cast metal parts, primarily aluminum, in quantities ranging from 1 to 5,000, Johnson says. Its capabilities include in-house heat treatment, a machine shop and an inspection lab in addition to the foundry. The company serves the automotive industry, centralized around nearby Detroit, but also the aerospace, defense, energy and telecommunications sectors. Most of the parts it makes are test parts, like a component for a car subframe needed for crash testing before the automaker invests in a mold for full-scale production.

The company has been utilizing sand 3D printing since 2004, but has come to rely on this capability in transitioning to a production facility. Rather than build a form and pack sand around it by hand to form a mold, sand printing enables TEI to simply print the mold directly. The process uses a print head to deposit droplets of binding agent across a bed of sand, fusing the material together. 3D printing enables more complex geometries than hand-built molds and also makes it possible to condense and consolidate mold assemblies. In one example, TEI was able to redesign the tooling for a helicopter gearbox, reducing the number of sand cores from 78 to just five printed pieces, eliminating many joints and reducing assembly for the mold.

TEI today has the largest sand 3D printer in the United States, a Voxeljet VX4000 with a build envelope that measures 2 meters wide and 4 meters long. The printer head sits on a gantry that can travel up and down this build volume, depositing binding agent wherever needed. This flexible printer allows TEI to build large molds when necessary, or many small molds at once; the job box can be created along with the print, allowing it to be as large as it needs to be. For smaller jobs, the company also has an ExOne binder jetting system with a 1 by 1.8 meter build volume. Finished sand molds are unpacked by TEI's expert pattern makers, cleaned of loose sand, and ready to use.

To design and simulate these molds, TEI uses EKKcapcast, software specialized for the metal casting process. The software allows the company to iterate mold designs quickly and test them before ever building a physical tool, a necessity for the kind of small-batch and quick-turnaround work it does today. 

"Sand printing in the early days was very expensive, and so the traditional way of developing prototypes, where you'd have a foundry doing trial and error, was just too expensive," Johnson says. "But we put that printing technology together with simulation. We can simulate the whole process of filling the mold with aluminum and then see how the material solidifies. Instead of doing all the iterations of testing with expensive 3D printed molds, you do it on the screen. You can do 10 iterations in a few hours and then you finalize your design and 3D print the entire mold." If there are needed design changes, TEI can easily reprint the mold.

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