Dr. Sanna Siddiqui, assistant professor of mechanical engineering at Florida Polytechnic, has received nearly $150,000 from the National Science Foundation to lead the efforts focused on 3D-printed, nickel-based metal super-alloy materials used in jet and rocket engines.
The research is expected to better inform the aerospace manufacturing industry about the durability and best usage of these alloys, according to a Florida Polytechnic press release.
"Many industries including aerospace and automobile manufacturing are shifting towards 3D printing because you can rapidly prepare parts, with flexibility in geometric designs, and hence improved efficiency," Siddiqui said.
"The question is, can these 3D-printed materials perform as effectively as their counterpart materials developed through prior conventional manufacturing methods or not," she added.
Although the current 3D-printed parts are exceptionally strong, Siddiqui said it is important to test how well they perform under expected operational conditions. Torsional fatigue — characterized by cyclic twisting loads — is often the culprit behind failure of the materials being researched.
Siddiqui will work to uncover the main deformation mechanisms at the microstructural level governing this type of fatigue failure, according to the release.
"There is research needed for this information," Siddiqui explained. "We need to understand how the material is going to perform under torsional fatigue. Aside from the multidirectional loading these materials experience, understanding their performance at the high temperatures the engines experience is critical."
Siddiqui's work in Florida Polytechnic's materials characterization lab will consider the combination of high temperatures, cyclic loads, and the effects of additive manufacturing print parameters.
"The lab has over $1.5 million in characterization equipment," Siddiqui said. "We will use those resources to investigate the deformation mechanisms at the microscopic level that impact the torsional fatigue performance of these materials."
The two-year grant was awarded by the NSF's Civil, Mechanical and Manufacturing Innovation Division. Siddiqui said the funds allow for the hiring of two underrepresented minority graduate or undergraduate students each year to help complete the work. Minority students are underrepresented in mechanics, manufacturing material science and engineering, according to the researcher's NSF abstract.
"I'm very excited," she said. "I think this is a great opportunity. One of the broader impacts besides full participation of underrepresented minorities is looking at incorporating our research findings into the teaching curriculum at Florida Poly."
Embry Riddle University's professor of aviation maintenance science Marshall Tetterton said 3D printed parts are starting to be used by manufacturers such as General Electric but the parts still need to gain Federal Aviation Administration approval for air readiness and other tests. These parts include low-hanging fruit, including parts such as burner cans and fuel nozzles, he said.
"There are already FAA parts that are certified for less complicated parts of a jet engine," Tetterton, adding that there could be more complex parts coming soon if they undergo testing to become certified.
He explained some traditionally manufactured parts are difficult to manufacture because they currently require separate layers of metals that are extruded and welded together, in which case a 3D-printed part may be easier to produce because it is the whole part.
The first announced 3D-printed jet engine part came in 2015 in a GE press release.
"The fist-sized piece of silver metal that houses the compressor inlet temperature sensor inside a jet engine is a part that's bit obscure even for many aviation aficionados. Starting now, however, it's becoming a symbol of one of the biggest changes sweeping jet engine design," the GE release stated
"The housing for the sensor, known as T25, recently became the first 3D-printed part certified by the U.S. Federal Aviation Administration ( FAA) to fly inside GE commercial jet engines." The GE website shows several award winning new parts for engines but cautions that mass producing the parts can be a challenge.
Within the industry, 3D printing is often called additive manufacturing because layers of alloys are layered to create the parts.
In contrast, subtractive manufacturing is a process of material removal, which starts with solid blocks, bars, rods of plastic, metal, or other materials that are shaped by removing material through cutting, boring, drilling, and grinding, according to a blog post at formlabs.com.
These processes are either performed manually or more commonly, driven by computer numerical control, the blog said.
According to airline industry consultant Robert Mann, "3D is generally used to rapidly prototype limited production components in 'cheap' materials (plastics) for fit purposes, which often go on to be 3D."
"I am aware of complex geometry components such as jet engine shrouds and combustion chambers being 3D printed, though blades, disks and blisks tend to be CNC or grown as single crystals from exotic alloys for required strength, heat tolerance, and durability.
Many of the jet engine manufacturers are involved in studying how to use 3D printing in the development and production processes.
"Having recently won the Air Force's B-52 re-engineering contract, Rolls Royce is expanding its Indiana facility to do this work over the next 20 years, Mann said. "They may have prototyped components of the F-130 engine they will use on the B-52."
At Pratt & Whitney, additive manufacturing fellow Jesse Boyer said the jet engine manufacturer has been using 3D printed polymer parts for more than 30 years but in the past decade the process of using metals has really taken off.
"Over the last 10 years, we've been doing additive manufacturing in earnest from a metals standpoint and that's what really is important to the challenge from our product side," Boyer said. "Additive manufacturing brings us some flexibility that we didn't have with conventional manufacturing so we can design things that we couldn't design before."
Three-dimensional printing of metal parts would be an improvement to conventional manufacturing techniques, he said. The flexibility with 3D printed parts could ultimately leads to lighter engines. Overall, The process leads to fuel saving, safer aircraft and lower costs for airlines that buy airplanes.
Lower costs are also gained through shorter lead times for prototypes for the jet engine manufacturers. Substituting parts on existing jet engines can also improve fuel economy right away as the super alloys could make the engine lighter. Less carbon emissions come from better designed jet engines, Boyer added, which creates sustainability benefits.
While Pratt & Whitney uses two primary metal alloys — nickel super-alloys and titanium alloys — having material data from the professor's research would help speed up certification of engine parts. Less is known about the physics-based material properties of additively manufactured super-alloys, for example their torsional fatigue levels under harsh, high temperature environments within a jet engine, Boyer explained. More is known about conventional methods such as castings and forgings of the metal parts.
"Physics-based research means that we can do potentially a little material testing," Boyer said. That testing takes a significant amount of money to do; having the professor's research results available could shorten times from testing to certification from years to months, he added.
Once manufactured, jet engines are overhauled at about 6,000 hours of use depending on environmental conditions. More modern jet aircraft digitally track vibrations and temperatures among other readings to more accurately determine when the engine needs to be overhauled.
At least for 3D-printed parts, the amount of time between the replacement of parts could be better known once professor Siddiqui finishes her research.
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