Offshore supply chain snarls, national-security concerns and the pandemic have all heightened the focus on domestic manufacturing capabilities. A new concept that is currently under development — metamorphic manufacturing — may usher in the capacity for local, flexible production that is especially suited for rapid and economical fabrication of small batch, complex, customized parts with tailored material properties.
Metamorphic manufacturing (MM) combines the incremental thermo-mechanical deformation techniques of a metalsmith with the precision of computer controlled robotic systems. It’s often referred to as robotic blacksmithing. In essence, MM is well-controlled open-die forging where machine accuracy and repeatability replace a worker’s limited precision.
It relies on closed-loop, digitally controlled, incremental forming to fashion intricate parts with specific engineering properties and locally defined microstructures. Proponents envision it as a new, powerful, agile way to make components that attempts to optimize shape and properties using well-understood metal-processing methods.
Glenn Daehn, professor of materials science and engineering at The Ohio State University, sees it as a key part of a broader concept called hybrid autonomous manufacturing. “There are really only six fundamental things that you do in manufacturing: remove, deposit, deform, transform, position and inspect. When you’re doing the deformation, metallurgists know very well how to use thermo-mechanical processing to change material properties. That’s the big idea behind trying to make hybrid autonomous systems, to put the skills of an artisan into reproducible digital systems,” he said.
Parts are shaped by repeatedly and incrementally forming a piece of metal which is precisely positioned into a press. By automating the process of shaping a part, but using the basic approach of a blacksmith, a machine can treat larger parts and be more efficient and reproducible than a human ever could, said Daehn.
Tech building blocks
The five basic elements needed for MM, to certain degrees, already exist: sensors, thermal control, actuators and forming tools, robotic manipulation systems and computational power. Fully developing MM requires a synthesis of these underlying technologies, said Daehn. The system must be able to sense and understand the shape, temperature and condition of the material at each location of the part being formed. Simultaneously it must control the temperature to produce the right structure and properties. The actuator must contact the component where needed with robotic control, deforming the part bit by bit. And a computer must make decisions on how to move and strike the part in order to optimize shape and properties, often learning from how previous parts were made.
The suite of sensors might range from vision systems for geometric measurements to thermal cameras, hardness testers and ultrasonic devices to measure internal stresses. Local thermal control could be via induction, plasma or flame heat treating, as well as gas or liquid cooling sprays. Advanced robots driven by CAD/CAM software would precisely manipulate tools and actuators and could run non-stop.
The actuators and associated tools are essential because they provide the plastic deformation needed to move from raw material to final product. High-speed mechanical peening hammers or rollers are possibilities, but hydraulic actuators are ideally suited for the task. They’re generally proven, off-the-shelf components that stand up to the rigors of industrial environments.
“Closed-loop, servohydraulic actuators would be the gold standard, where you could run in displacement control,” said Daehn. “At forming temperatures, most materials have a flow strength of around 50,000 psi, so relatively small tooling sets can take bites of about one square inch at a time.” But engineers can readily tailor pressure levels and actuator size to generate the requisite forces to suit the task at hand.
Advanced computers, software and AI capabilities lie at the heart of successful MM integration. They would handle tasks like specifying tool paths and sequencing operations, but would also collect and process sensor data and adapt operations in response to changing component shape or properties. The system might also tap into the latest materials engineering software models to better control properties and microstructures, and even encompass predictive simulations.
Incorporating all of these elements into a seamless work cell is no simple task. But the idea of integrating robots and tools with sensors and software, the essence of IoT, is increasingly being embraced across the manufacturing landscape. All of the base technologies needed for MM are progressing rapidly, and there is no reason they cannot be quickly melded together as a useful and practical manufacturing technology, said Daehn.
Some experts consider MM the third wave of digital manufacturing, following CNC machining and additive manufacturing. And ongoing advances in software and manufacturing technologies associated with CNC and 3D printing will help spur development of MM.
This will bring numerous advantages. CNC machining and additive manufacturing typically don’t produce parts with the highest levels of strength or toughness, and they lack the ability to tailor material properties, as in thermomechanical deformation. A part might need corrosion resistance in one area and high toughness in another. MM can do that by both modifying the chemistry through locally-controlled deposition in additive manufacturing and then deforming the material into the best possible structure, said Daehn.
Because small deformation bites are taken, the component can be much larger than the press and MM can be used to fabricate parts of any size, including very large structural components for aircraft, ships, submarines and locomotives. Or the concept could be scaled down to make small individualized medical implants. “We can imagine this being used in operating rooms, where you could deform a nominal mandibular plate to fit a patient’s specific anatomy and do that very quickly, much more quickly than you could with additive manufacturing and, importantly, with better properties,” he said.
Automation can make these processes more agile and more productive. We can generally turn out parts much faster versus 3D printing or CNC machining, he said. Because it is a shaping technology, there is little material loss, which drastically reduces the amount of waste material compared to CNC machining. And MM uses a lot less energy than does additive manufacturing. “Deformation is inherently a very green process,” said Daehn.
In addition, MM can minimize or eliminate the need for component-specific manufacturing dies which often have long lead times and are expensive to machine and store. This die-less manufacturing technique is ideal for rapid prototyping and small batch production. The ability to make components on demand is often essential, such as to replace a forged aircraft landing gear that is decades old and is no longer in production. And the technology might lower the economic barriers many small- and medium-sized manufacturers face and help expand domestic production capacity.
MM could offer manufacturers a better, faster, more cost-effective way to make complex, 3D components. Much work is still needed to make it a reality, including integrating hardware and software into an actual, autonomous production cell. The same holds for research into areas like computational materials-engineering models that accurately predict material behavior throughout the various stages of the MM process.
A major roadblock is funding. Several affiliated universities around the country are beginning to consider hybrid autonomous manufacturing, but significant government support is only starting to catch up to the concepts. Federal agencies annually provide significant grants to advance science and engineering, but they haven’t been particularly kind to new process developments that focus on problem solving via integration versus new fundamental ideas, said Daehn. European and Asian funding models have a more favorable view of manufacturing R&D because it ultimately benefits their economies, he said.
“We are getting a lot of good traction from the defense world,” he continued. This February, the DoD issued a report, “Securing Defense-Critical Supply Chains,” that detailed forgings and castings as one of the four most critical vulnerabilities to national security, the others being hypersonics, energy storage and batteries, and microelectronics.
Forged and cast components are essential in everything from ships and subs to aircraft, combat vehicles and weapons systems. But due to offshoring and industry consolidation there are relatively few domestic suppliers of many mission-critical components. For instance, China produces four times the tonnage of castings as does the U.S.
“DoD counts on foreign countries, including China, for very large cast and forged products used in the production of some defense systems and many machine tools and manufacturing systems in which the DoD is reliant,” said the report.
“The other thing we don’t recognize enough is these are key processes in making the machines that make the machines. If you’re going to build a big press, you need big forgings and big castings. Our capacity to make those kinds of machines has diminished,” added Daehn.
DoD’s action plan for castings and forgings involves devising a strategy to increase the industry base, expand partnerships and develop domestic production capability. Current plans call for publication of a roadmap no later than the end of the second quarter of FY 2023.
“The center of gravity in metal forming is absolutely outside the U.S.,” said Daehn. “There are a handful of professors here in the United States that do metal forming, a very small handful. And we have a hard time fighting for funds. Whereas the Chinese metal-forming society is very robust. Germany likewise has a very robust metal-forming culture, a number of professors and chairs, and a strong tradition.
“I think we have a fairly unique approach, trying to bring together the machines, the controls, and really putting the material science kind of front and center to it. But there are labs in Germany that are better equipped and staffed than we are. The same holds for China and, to a certain extent, Japan. In many ways the United States did a lot of the great, early machine tool work, but the center of gravity has been absolutely moving away from us,” he said.
We’ve talked to people across the aerospace industry, as well as forgings suppliers, Air Force research labs, logistics experts and equipment makers, said Daehn. “We have a consensus that, yes, this is a good idea. We’ve made a lot of converts and I haven’t had anybody who has maintained skepticism.
“If we are going to reverse this trend, the workforce is also crucial. We need to start getting students involved and encourage a lot more people to be in manufacturing,” he said. To achieve widespread MM adoption, the next-generation will need a broad understanding of materials science and engineering, manufacturing processes and robotics, and software engineering.
The Ohio State University, Dept. of Materials Science and Engineering
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