GE Makes Transition from Investment Casting to 3DP

July 13, 2021
Four components of the LM9000 turboprop engine are being laser-printed in CoCr, with production cost and time savings.

GE Aviation, working with its affiliate GE Additive, has converted several components of the LM9000 land/marine turbine engine from investment castings to additive-manufactured parts. GE maintains that the results of prove metal 3DP can compete on a cost basis with conventional cast parts, and in the particular case it will reduce production cost by 35%.

Equally important, GE reported the conversion took just 10 months, rather than the typical 12-18 months, from identifying target parts to 3D printing final prototypes.

“This is the first time we did a part-for-part replacement, and it was cheaper doing it with additive than casting,” explained GE Aviation’s Eric Gatlin, additive manufacturing leader. “To make sure we demonstrated cost competitiveness, we had four outside vendors quote the parts, and we still came in lower with additive manufacturing.”

The project has gone on to identify “scores of other parts on a variety of engines” that could be convert to AM production, with cost savings.

Additive manufacturing has been applied to turbine engine program production for several years, as for example a 3D-printed fuel nozzle tip for GE Aviation’s LEAP engine. That program consolidated 20 different parts—saving production, finish-machining, and assembly cost and time. For the new, LM9000 turboprop engine, 3DP combined 855 parts into just 10 3D-printed components.

The efficacy of AM production is being advanced by improvements in the productivity of metal laser printers. GE Additive’s Concept Laser M2 Series 5 machine has dual lasers to melt and fuse layers of metal powders faster than a single laser -- and produce more consistent results for complex builds. The M2’s 400-W or 1-kW lasers produce 50-micron- thick layers, and it has a 21,000-cubic-centimeter build chamber in which to manufacture parts.

“We said right up front that we were going to pick a material that we had already qualified,” Gatlin said. “In production, we opted for the M2 because we know it well. And we were not going to do any wholesale design changes, just some tweaks so we could print the parts successfully. We simplified as many steps as we could so the team could run fast.”

This allowed the project team to develop final prototypes for four parts slated for the LM9000 land/marine turbine, between April and September 2020. The group considered dozens of parts for older engines and products, too, GE noted.

“We are always looking to pull costs out of existing products,” Gatlin said, “so, we cast a wide net that includes hundreds of castings we buy. Then we ask, ‘Are we getting more competitive?’ ‘Are there things we couldn’t do a year ago that are now technically feasible?’”

The vetting process considered both new and older products, and other factors like the capabilities of GE Aviation’s 3D printers, and part size, shape, and features. The engineers asked whether the parts used well-characterized materials they had worked with on those machines before. They also took into account the ease of post-processing steps, like machining to eliminate surface imperfections and brazing to add fittings to a part.

AM is suited to making complex parts, such as those with internal channels, but it also works well for parts with simple geometries since they are relatively fast and easy to print from existing models, and they eliminate the up-front time and investment in molds or tooling needed for casting.

The audit looked at both low-volume replacement parts and production-volume parts for new programs, like the LM9000 engine.

When production programs were suspended during 2020’s Covid-19 pandemic, GE Aviation’s AM operation in Auburn, AL, had machine and post-processing time available to start making parts for the LM9000 project.

“We’re a production shop and would not see a project like this until after GE Aviation’s Additive Technology Center had developed the process for low-rate production,” said Jeff Eschenbach, a senior project manager and project lead at the Auburn facility. “What was different about this project is that we took this on from the very beginning. It created an opportunity for the engineers here on site to get involved.”

The project team considered dozens of parts, paring the choice to nine parts, including parts of other marine-industrial gas turbine engines, regional jet turbofans, and some military programs. All the parts were all made of either CoCr, an alloy of cobalt and chrome widely used for hot-turbine parts, or Ti-64, a stiff, lightweight titanium-aluminum-vanadium alloy used for structural parts.

They looked only at parts that could fit inside a Concept Laser M2 machine.

Then, they cut the selection further by prioritizing parts-based engineering resources and the importance of cost savings. The four parts selected are all adapter caps for the LM9000’s bleed air system. All four are about 3.5 inches in diameter and about six inches tall, and made of CoCr to handle the hot compressed air from the turbine’s compressor section.

Each of these parts share a base geometry and similar features. The team assumed the M2 could print three parts at a time, but engineers soon redesigned the layout to increase it to four, again boosting productivity.

Using simulation and analysis, the team showed that the parts performed the same as the cast parts they replaced, according to Steve Slusher, a GE Additive manufacturing engineer on the project. The team also built test bars with each print, some in the open cavity of the cap that went down to the build plate, so technicians could measure the integrity of each production run.

The project marked the first time GE Aviation had shifted production from investment casting to additive manufacturing based strictly on cost. The parts were one-to-one replacements, without any redesign or parts consolidation to improve their economics, Gatlin said. And it was done fast.

“The thing that stuck out to me,” Eschenbach said, “was that we could take an existing casting design, replicate it quickly on our printers, and within weeks of starting on the project, the final parts were the same quality as to their cast counterparts. This project serves as a template for future work.”

Kelly Brown, senior technical leader at GE Additive agreed: “From a business perspective, Auburn showed muscle we didn’t have in the past, and now we have a bank of parts that we can go after next. What the team has done is remarkable, and it really showcases their capabilities.”