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Additive Manufacturing

Printing with purpose

By Gretchen Salois

Above: MX3D linked a 6-axis robot and welding machine through proprietary software. Photo: Oliver de Gruijter/MX3D

Pioneers rethink additive manufacturing to tackle complex geometries with stunning results

May 2019 - Industry innovators are pushing additive manufacturing beyond producing highly precise, lightweight, small metal parts in low volume and lot sizes. In Amsterdam, MX3D is in the final months of completing its full-scale, metal-printed bridge to go across one of the channels of the 17th century Amsterdam Canal Ring.

Meanwhile at ETH Zurich, researchers have tackled the challenges of fabricating large volumes of larger metal parts needed quickly. For its complex, large-scale architectural projects, powder-bed metal printing would not be the most efficient method. So they rethought the process. Casting metal in 3D printed molds—using binder jetting technology with sand prints layer by layer—“has enormous advantages when high-volume custom parts or parts with larger dimensions are needed,” says Mania Aghaei Meibodi, co-founder of meonia HB and senior researcher at ETH Zurich.

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MX3D began printing its bridge using ”dotted” printing, which later evolved into “continuous” and “solid” printing methods. Photo: Joris Laarman Lab (below)

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Intersecting waterways

In order to 3D print an entire canal bridge, MX3D used an industrial-grade 6-axis robot and welding machine and proprietary software to link the two machines together. “We currently use ABB robots and Oerlion welding machines,” says Casey Hemingway, production manager.

Using a range of metals, including grade 308 stainless steel, duplex steel, HSS and carbon steel, aluminum and bronze alloys, MX3D’s method includes splitting geometries into smaller pieces to accommodate the robot’s reach. “One of our midsized robots (ABB IRB-2600ID) can produce an object of roughly 500 mm by 1,000 by 1,000 mm [19.7 in. by 39.4 in. by 39.4 in.], depending on the complexity of the shape,” Hemingway says.

MX3D began its bridge printing process in 2015 with “dotted” printing, “essentially creating mesh/lattice geometries with printed rods measuring roughly 4 mm in diameter (see Dragon Bench image),” says Hemingway. “After which, we developed ‘continuous’ printing to create sheet structures (see Butterfly Screen image).”

Since then, MX3D has worked to develop “solid” printing to create non-hollow objects, combining all the previous printing strategies used before. “The designs we began with were all mostly oriented vertically on the print-bed but, since then, we have developed the technology to be able to print at almost all angles of geometrical overhang,” Hemingway says.

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MX3D estimates it has used 20 metric tons of materials to build the bridge. Photo: Adriaan de Groot

The entire bridge comprises more than 100 unique printed parts—“all of which had to be assembled by TIG welding,” Hemingway explains. “Whilst our initial vision was to place two robots on site in the Red Light District, there were numerous health and safety restrictions which prevented us from doing so. We adjusted our approach to instead print pieces separately across four robots in our factory.” MX3D also had to combat corrosion, leading the company to test various coating options.

Throughout the company’s printing projects, MX3D estimates total metal consumption of up to 20 metric tons. Challenges include designing and building certifiable welding cells. “The pieces our robots print are different every single time in regards to shape, size and material. Our welding cells require a level of modular adaptability that doesn’t lend itself to the certification process,” says Hemingway. MX3D is in the planning stages of building certified welding cells as it remodels its workshop.

“Additive manufacturing robots can be adapted to perform other related processes such as grinding, cutting and welding for assembly with relative ease,” Hemingway says. “This is a result of the versatility of the industrial robots.”

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Binder jetting technology with sand prints uses a liquid agent selectively dropped between each layer to bind the sand. Photo: Jetana “Jet” Ruangjun

Rethinking casting molds

Proving cost-effective and fast turnaround solutions with additive includes using the technology to evolve old methods of metalworking to adapt to today’s quick project delivery expectations. Led by Mania Aghaei Meibodi, the team at ETH Zurich used binder jetting technology with sand prints. A liquid agent is selectively dropped in between each layer to bind the sand. “Binder jetting is attractive because it offers a unique combination of geometric freedom, resolution of parts, print-bed dimension and faster printing time,” says Aghaei Meibodi. “We have used both voxeljet’s and ExOne’s binder jetting technologies for additive sand casting.”

ETH Zurich researchers connected with Christenguss AG. “With our printer, we print sand molds in which we can cast aluminum and copper alloys,” says Florian Christen, CEO at Christenguss AG.

3D printing is not ideal for high-volume, large piece production so Christenguss applies the technology as the in-between step. “We reintegrate our 3D printed sand molds into conventional large-scale production,” Christen says.

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Algorithms automatically generate molds for each individual joint. Photos: Demetris Shammas/Digital Metal, ETH Zurich

Printing complex geometries is not the challenge, says Aghaei Meibodi. The challenge is finding more efficient ways to use materials and produce sustainable products. “Casting is a well-established process—there is nothing new to learn there,” she says. “Most of the new knowledge is in the digital design of the parts, design of the mold in a digital environment, development of software that enables automatic generation of sand molds for any desired geometry, and simulation of liquid metal flow in the molds.”

Beyond convention

In the space frame structure project “Liquid Pavilion,” 182 geometrically different joints were produced in only two and a half weeks. Printing the molds took less than 50 hours total. The “Deep Façade” project required production of 28 large aluminum panels, which were completed in less than a week. “That included sand printing, casting and post processing,” Aghaei Meibodi says.

Post processing was not needed for façade elements because they used an open mold system. Fabricators cut off the gating system, which served as the channels that allows molten metal to enter into the mold cavity. “From the final cast joints, the parts were not riveted or welded together,” she adds. “They were connected to one another using screws and bolts.”

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MX3D developed “continuous” printing to create sheet structures like the Butterfly Screen. Photo: MX3D

The ability to produce the variety and volume of parts would not be possible if each part were 3D printed in metal, “nor by a conventional mold making process,” Aghaei Meibodi says.

Aluminum is ideal for many projects, in part because of its durability. “When aluminum parts are in open air, a thin oxide layer forms on its surface, which prevents further corrosion,” explains Aghaei Meibodi. “Aluminum is a very commonly used material for cladding in contemporary architecture.”

Sand printing castings isn’t limited to aluminum. “You can cast other alloys—another benefit of 3D printing sand molds and casting the metal over using direct metal printing,” Aghaei Meibodi says.

The significance of ETH Zurich’s projects is shown both in the fabrication methods behind the pieces and in the parametric mold design used.

“Custom algorithms are developed to automatically generate molds for each individual joint, integrating the relevant casting details of the gating system,” Aghaei Meibodi says. “This fast design-to-fabrication pipeline allows us to optimize the digital model by casting and testing multiple physical prototypes.”

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MX3D used printed rods measuring roughly 4 mm in diameter for the Dragon Bench. Photo: MX3D

In the future, Aghaei Meibodi is excited that there will be “a plethora of approaches,” she says. “Many of them are developing at a fast pace. It really depends on the application and required properties of the result.”

The result of MX3D’s efforts goes beyond outfitting Amsterdam’s waterway system with a new canal bridge. “We’ve known for some time now that 3D printing has the ability to disrupt entire industries the world over,” Hemingway says. “When it comes to metal fabrication, the types of industries that we are poised to disrupt rely upon sometimes century-old manufacturing techniques and relatively entrenched methods of operation.”

Industries like mining and oil are some of the largest potential areas of opportunity and “we’re of the opinion that working in partnership with companies such as these will create more of a win-win scenario in the long run.” FFJ

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