A breakthrough for parts designers and manufacturers everywhere was quietly playing out among a team of four U.S. engineers late last summer and fall. 

A geometry software firm called nTopology, which serves the aerospace industry and specializes in topology optimization, joined forces with advanced manufacturing leader and AFS Corporate Member Humtown Products (Columbiana, Ohio), as well as casting simulation software company and AFS Corporate Member Flow Science (Sante Fe, New Mexico) and Penn State University, which has developed novel mold design techniques––all for the purpose of demonstrating the full capabilities of American manufacturing in an end-to-end digital casting workflow. They did this by combining cutting-edge design techniques with advanced casting features that can only be manufactured additively. 

The result of the group’s digitally-enabled remote collaboration was the creation of a redesigned robotic arm 1 meter long that went from 204 lbs. to 165 lbs., a weight reduction of 40%. In the process, the team also successfully averted common casting defects, directly 3D printed the entire sand mold, and manufactured the part in less than a week.

In addition to its being a large-sized and low-rate-of-production part, the robotic arm was selected for the project because it presented an opportunity to create weight savings while increasing the payload of the robot, according to Brandon Lamoncha, director of Additive Manufacturing at Humtown.

“We were going after something large, and we definitely wanted to show that this part cannot be direct metal printed,” he said. “There are no metal printers out there right now that would be able to print a part that large. The mold itself was huge—we had almost a 1,000-lb. pour by the time we had all the gating and the rigging. This was to show that you wouldn’t be able to produce this casting any other way; you can’t do it with tooling, and you can’t do it with direct metal printing––it was to show that this technology can be used on very large components.

The part was ideal to showcase nTopology’s software capabilities, too.

“It is well suited to our design space,” said Dr. Ryan O’Hara, director of Aerospace Engineering at nTopology. “This part really speaks to some of our core technologies and how we can put material where it’s needed and remove it where it’s not. Robotic arms are all around us, and they’re also in varying size. One of the key things here is that they have a lot of scalability, so we thought that was a good application.”

Time Is Finally On Your Side

Over the course of half a dozen design iterations, supported with simulation technology at each interval, the team proved that casting design limitations within traditional mold-making can be entirely eliminated; that indeed, risers and gates can be placed anywhere.

“In today’s competitive manufacturing environment, I think it’s really important for designers to be bold in their designs and realize that the design and manufacturing tools that are available to them can allow them to do that,” said O’Hara. “We really wanted to demonstrate through this project that not only can you be bold in design, you can actually be so bold and manufacture those parts the first time with centuries-old manufacturing methods.”

Although substantial dialogue and planning transpired over several weeks, the impressive speed with which the mold printing and casting production actually occurred is proof that the combined technologies are a game-changer for enterprising manufacturers.

“If you can take something that takes three months and you can condense it into three weeks, what does that do to give you the competitive advantage of being first to market?” said Lamoncha. “There are so many incalculable benefits to this.

“That’s one focus of this project,” he added—“to show that we can we can introduce nTopology’s software into the metalcasting realm, and that is going to buy you the one thing that you can’t purchase: time.”

Shining in Their Roles

The initial robotic arm design was covered by nTopology, and O’Hara then participated with the rest of team as the project moved to mold design and simulation stages. 

Involving students in the project was significant, according to Lamoncha, who wanted Penn State as much for its knowledge needs as its knowledge base.

“Without teaching the next generation of engineers and designers how to embody these technologies, we’re going to be stagnant,” he said. “That’s exactly why I brought the university in.”

Dr. Guha Manogharan, assistant professor at Penn State University, a noted expert in mold design, contributed extensive experience in leveraging the additive side of casting.

“In this project,” he told nTopology Product Marketing Manager Alkaios Bournias Varotsis, “we applied all the sand casting knowledge that we have developed in the lab. We were able to incorporate theoretically optimal sprue and riser designs that cannot be manufactured using traditional methods. That was very effective in reducing the overall defects and was further validated using simulations.”

Speaking about Manogharan’s team, Ajit D’Brass, Flow 3D metal casting simulation engineer, said,

“We’ve been working with Guha for years ... they have a lot of interesting research in helical sprues––a helix that feeds into a runner. And they’re getting some really interesting results on how that has an effect on air entrainment, first of all, and then also slowing down the metal coming into the mold. They have, I think, their own of set of calculators and methods that they’re using right now.”

D’Brass supplied simulation information to the Penn State group, who would work on the mold design and return it back to Flow 3D.

“From there, we would do a full spectrum simulation. We were setting up the mold properties. We were getting fill rates from Guha and his team. And then we’d do a full filling simulation and then a full solidification simulation ... we were primarily concerned with air entrainment, as well as velocities through the gate, and trying to keep the turbulence down within the mold. We were also looking at oxide formation––this was an aluminum casting and aluminum has this propensity to form oxides and bond with oxygen really fast. 

“We went through five or six different iterations of this; just small changes on riser placement; they’d change the dimensions of the helical sprue; we changed some of the configurations of the gates and the casting. In this exchange, that was where the team really shined.”

Lamoncha provided insight into what was possible in the printing process, and due to the great size of the part, the sand mold was printed in about six sections. He also helped drive the mold’s unique rigging and design.

“I wanted to push people to use unconventional methods and maximize the technology,” he said. 
Humtown did the printing in a day and Lamoncha was onsite at Trumbull Foundry and Alloy in Niles, Ohio, for the pour, which also was completed in a day.

Ultimately, the digital demonstration delivered the art of the possible for the casting industry, said Lamoncha. “The future is now. It’s happening. What’s next is going be the next generation of castings designed using these types of tools that can only be produced by 3D sand printing.”     

Click here to read the article in the digital edition of July 2021 Modern Casting.