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Improved AM Processes Shorten Lead Times, Boost Quality

By Karen Haywood Queen Contributing Editor, SME Media
This investment casting pattern was 3D-printed using QuickCast technology, saving the manufacturer significant amounts of time and increasing design flexibility. (Provided by Samjeong Turbine Co., Ltd.)

Improved additive manufacturing (AM) processes used for tooling and sandcasting molds and cores are shortening design and manufacturing lead times from months to weeks.

Other benefits include lowering weight, reducing potential failure points, shortening supply chains, enabling the production of legacy parts, cutting scrap, allowing for more complex parts, and establishing tighter quality control. Vastly improved software, better hardware processing, and faster 3D printing are fueling these improvements.

“When it comes down to it, it’s about saving time,” said Kirk Keithly of Burlington, Mass.-based Desktop Metal Inc., which acquired The ExOne Co. and its eponymous industrial binder jet 3D-printing systems in November 2021. ExOne, which now operates as a subsidiary of Desktop Metal in North Huntingdon, Pa., has created molds for Lockheed Martin Corp.’s Sikorsky Aircraft unit and others.

“Post-COVID, there’s a lot of onshoring. There’s a frantic surge in the foundries trying to keep up with the orders coming in,” Keithly noted. “It changes the dynamic. With traditional molding technology, you go to a pattern shop, have a pattern made, and—depending on the complexity—wait two weeks to two months to pour your first casting.

“Ninety-nine percent of the time, that first casting is not good, and you may need two or three of those iterations.” he continued. “With 3D printing, if they can print molds and cores, they’re able to cast without traditional tooling.

They’re not waiting on patterns and molds; you design your mold, print it that day, and pour the next. It’s continuous production: print, clean, assemble, and pour. You have a finished casting off to your customer in two to three days.”

One of the main drivers pushing the adoption of additive in the investment casting industry is the ability to drastically reduce manufacturing lead times while reducing costs, added Evan Kuester, platform manager for stereolithography and Figure 4 at 3D Systems Inc, Rock Hill, S.C.

“Additive manufacturing has given foundries the ability to quickly produce castable patterns in-house without the slow and costly step of manufacturing injection molding tools for each part,” Kuester explained. “Various aerospace customers have seen lead times drop from months, or even a year, to days by using 3D Systems’ QuickCast technology while at the same time saving hundreds of thousands of dollars in injection molding tooling.”

SLA-Quickcast manifold printed pattern (Provided by 3D Systems)

Custom Applications

Applications include gearcase housings, valves, and struts on helicopters. An early win for the ExOne printer in aerospace and defense was a helicopter transmission mold for Sikorsky. ExOne created molds for eight transmission assembles, each one a slightly different design, Keithly said. ExOne designed the first one, printed it, delivered it, and Sikorsky asked for a small change.

No problem.

“If a customer is 3D-enabled, you’re taking the pattern shop out of the equation,” Keithly said. “Design changes are simple. They’re electronic. You make a design change today. You can print and pour tomorrow.”

The potential savings can be huge.

“In some cases, we’ve seen lead times drop 20 to 50 percent,” said Mark Douglass, business development manager for additive solutions at Cleveland-based Lincoln Electric Holdings Inc., which focuses on wire-arc AM, also called wire directed energy deposition (DED). “We’ve seen a reduction in costs of 10 to 30 percent and material savings of 20- to 30 percent.”

Wire DED was born about a decade ago, evolving from the long-established process of weld metal buildup, Douglass explained. Weld metal buildup involves stacking welds on top of each other to build a crude block of material to make a billet and then create a part, he said. But the process requires an experienced welder.

With DED, a robot or other automation combined with laser or arc welding deposits the weld metal into the layers of melted layers of beads of melted wire, Douglass said. Although the addition of robots has been helpful, what makes the difference are software improvements.

Finished manifold casting. (Provided by 3D Systems)

Additive Advancements

“Robots are great; automation is great,” Douglass enthused. “But what has really enabled additive in the last decade is the improvements in software and processing power of the hardware to run the software.”

Those improvements in software and hardware also made the difference at 3D Systems, resulting in drastically reduced build times, Kuester said. “Parts that at one point took weeks to print can now be printed in a matter of hours,” he noted.

Today’s software, with a library of the process setting necessary to melt the wire for a particular process, can automatically take a CAD model, slice it into layers to be stacked in the additive process, send it to a robot, and program the robot—all within minutes or hours instead of days, according to Douglass.

Lincoln Electric developed its own software, SculptPrintOS, to focus solely on wire-arc AM. “We have full control, which for us is important,” Douglass said. “We can make updates at any time. Our welding people are informing the software people.

“If our engineers run across a new part that the software might be challenged to create,” he continued, “we work with our software engineers and can get things turned around, sometimes on the same day. We can adapt and improve the software based on ground conditions.”

Lincoln Electric has printed a 3D prototype mold for a Boeing aircraft component used in vertical takeoff and landing. The company also used AM to print a mold for a UAV for General Atomics. “Both cases went through a battery of tests and passed with flying colors,” Douglass said.

Implementation for these emerging AM techniques is being driven by OEMs demanding greater speed from supplier foundries. At the same time, foundries concerned about scrap are dictating the use of the new technologies—or demanding higher prices. OEMs are asking for castings in two weeks instead of two months, which is now possible with AM.

For OEMs, shorter lead times are critical—even more important than cost savings—and can make the difference between winning or losing a bid.

“That’s now rolled into their tier ones, into their supply chains,” Keithly said. “It’s becoming more and more accepted. The OEMs are not hesitant. They understand what the capabilities are.”

Faster print speeds play a role. ExOne’s S-Max Pro platform, released in 2018, increased print speeds for its 3D sand printers by 25 percent, according to Keithly. And OEMs are starting to take notice.

“If a foundry tells an OEM, ‘I can have the first casting back to you in eight weeks,’ the OEMs won’t tolerate that,” Keithly asserted. “They’ll tell the foundry, ‘I’m going to go to your competitor who can have this back to me in a week or less.’”

ExOne has first-hand experience with the practice. “We have multi-machine customers that do nothing but quick turn castings,” Keithly said. “They’re advertising that they can have a complete, machine-tested casting in their customers’ hands in five days or fewer. It’s a huge game changer.”

Meantime, the foundries can reduce scrap by 10-60 percent. “If it’s a legacy type program that’s been running for a while, a complex core with 10 or 12 pieces that has been around for a lot of years with a lot of assembly problems—that can cause a lot of rework and scrap,” Keithly said. “If they’re struggling with a legacy casting or having high scrap issues, we’ve seen them go back to the OEMs and say, ‘We can’t handle this anymore. We want to make the change in 3D,’” he continued. “Foundries are getting more sensitive to what their total costs are: How much am I putting into casting and rework? And when do I say, ‘Stop and pour a new casting?’ They are going back to OEMs with price increases and those don’t go over very well.”

Application of the technology is evolving from low-run prototypes to medium-run prototypes to high-rate production, Keithly added.

The Nature of Things

AM also shines when it comes to printing complex organic shapes, and reducing weight. “One pound (less weight) over the life of a flight platform is many millions of dollars (saved) in extra fuel,” Keithly said.

“Aerospace guys are seeing a big push toward organically designed parts,” he continued. “When you look at nature, trees are designed to be lightweight with strong branches and strong leaves. Organic castings look a lot like what you see in nature. We emulate that. There’s a lot of stress analysis to ensure that the part can handle the expected stress or torque.”

Improved technology has enabled the design of more complex, optimized objects that weigh less and have far fewer components. Keithly added.

Finished machine surface of 3D metal Invar lay-up tool. (Provided by Lincoln Electric)

Fewer Constraints, Simplified Solutions

“Normally, designers and engineers are limited not by their imaginations but by the limitations of the tools used to manufacture the objects,” Kuester said. “Sometimes details are simply too small or too deep for a cutting head to reach, or too complex to be removed from an injection molding tool. In many cases, parts end up weighing significantly more than desired because it’s too expensive to remove the extra material,” he noted.

Because AM parts aren’t constrained by the limitations of traditional manufacturing, designers and engineers have more freedom when it comes to problem solving.

“In many cases, this results in designs where the overall complexity is significantly simpler while the complexity of any one individual part may become more complex,” Kuester said. “This is because those parts may now be playing several roles in the design due to the use of part consolidation.

This normally results in an overall simplification that is both easier to manufacture and easier to install than its traditionally manufactured predecessor.”

Employing Design for Additive Manufacturing (DfAM) techniques can have a huge impact. In fact, Kuester said, through the proper use of DfAM, designers and engineers can create shapes “so perfectly optimized for their application that traditionally manufactured parts look clunky and old in comparison.”

The technology also makes it easier to replace legacy parts, a welcome benefit since patternmaking is becoming a lost art and, even when a pattern shop can do the work, the process takes months, Keithly said.

“We just helped an aerospace customer on one of the old airframes,” he explained. “They didn’t have spare parts. Luckily, they had a casting. If there’s a casting, you can scan it and reverse engineer it. We were able to send their casting out, get a. model, get molds designed.”

While a lot of foundries are still in the 2D, non-digital world—basically paper and pencil—a growing number of services convert a 2-D drawing to a 3-D model, according to Keithly.

In many cases, Kuester added, AM makes it possible to create a component that once had several hundred individual parts and reduce it to “one elegant part that is both cheaper to manufacture and also more reliable than its traditionally manufactured counterpart.”

Such consolidation also eliminates the need for nuts, bolts, gaskets, and other fasteners to hold everything together, Kuester said. This saves weight, time, and money by drastically reducing the time spent sourcing, tracking, and assembling hundreds of different parts throughout the manufacturing process.

“One of the main drivers of part consolidation is the desire to reduce the number of potential failure points inside any given component,” Kuester said.

For example, manifolds are often created by assembling many different parts into a large assembly, sometimes containing hundreds of individual elements. Each time parts are mated together, they need to be manufactured, assembled, sealed, and leak-checked before being put into service.

“Not only do these assemblies represent a significant amount of time and money when it comes to manufacturing the individual elements, but they will have to continue to be checked throughout the product’s entire lifespan,” Kuester explained. “Part consolidated components are not only easier to manufacture, but due to the lack of joints, welds, gaskets, and seals, they have far fewer places where the component could fail. You can’t crack a weld if there are no welds,” he continued. “This not only increases the speed at which complex components can be manufactured but also increases the ruggedness of the individual components as they have far fewer failure points.”

3D metal printed Invar lay-up tool with as-printed sub structure. (Provided by Lincoln Electric)

Getting Started

Early AM adopters learned from the feedback of their first customers.

3D Systems was one of the first organizations beyond a few universities to leverage additively manufactured patterns in the investment casting process, according to Kuester. The company started with investment casting solid plastic patterns that were printed on its first-generation machines.

But the solid patterns expanded during the burnout phases and cracked the ceramic molds. Company engineers eventually learned that hollowing the patterns resolved many of these issues, Kuester said. That led to many years of r&d to discover the best way to hollow the patterns, a process that has resulted in the recent development of QuickCast Diamond.

The improvements in the investment casting process also led to advances in material science, as industries demanded specific qualities in the materials used to create the patterns, Kuester said.

“Various industries required specific elements in the material formulations to increase the pattern’s durability or reduce impurities in the final castings,” Kuester noted. “This drove us to make many material innovations over the last 30 years in support of the investment casting industry.”

ExOne, meanwhile, released its first sand binder jetting machine, the S-15, in 2002 to automotive customers. Feedback was positive overall, Keithly said, but customers wanted more speed. The S-Max, released in 2014, is twice as fast.

Increasing speed remains a priority. “We need to be faster,” Keithly said. “We need to be volumetric. We need to take the labor out.”

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