A collaboration between GE Aviation and GE Additive is striving to prove that metal Additive Manufacturing can be comparable to conventional castings on price, with GE Aviation’s switch from casting to AM for production of bleed air parts from a land/marine turbine. The engineering team expects these additively manufactured parts will reduce cost by up to 35% – which is said to be enough to justify retiring the old casting moulds permanently.
The conversion process took only ten months, from identifying target parts to additively manufacturing the final prototypes. Ordinarily, producing aerospace and land/marine turbine parts using a casting process can take twelve to eighteen months or longer.
“This is a game-changer,” stated Eric Gatlin, GE Aviation Additive Manufacturing Leader. “This is the first time we did a part-for-part replacement, and it was cheaper doing it with additive than casting. 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 identified scores of other parts on a variety of engines that could be converted to AM and save cost. Already, the additively manufactured fuel nozzle tip for GE Aviation’s LEAP engine, for example, consolidates twenty different parts – and the steps needed to machine and assemble them – into a single structure. The company’s new turboprop engine took that to another level by combining 855 parts into just ten AM components. In both cases (and others), GE Aviation took advantage of parts consolidation to utilise cost savings from assembling these parts.
As the number of demanding applications grows, equipment makers seek to improve the productivity of their metal laser AM machines. An example of this is GE Additive’s Concept Laser M2 Series 5 machine, with dual lasers that melt and fuse metal layers faster than a single laser alone, producing more consistent results for complex builds. The M2’s lasers are also powerful, either 400 watts or 1 kilowatt, and produce 50-micron-thick layers. It also has a large, 21,000-cubic-centimeter build chamber in which to make parts.
“We said right up front that we were going to pick a material that we had already qualified,” Gatlin added. “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 enabled the project team to develop final prototypes between April and September 2020. All four parts were slated for the LM9000, a land/marine turbine derived from the GE90 turbojet, which GE Aviation is building for Baker Hughes, but, as aviation companies supply replacement parts for the lifetime of their products, the group also considered dozens of parts for older engines and products.
“We need to figure out how to come up with replacements, before we run out of parts,” stated Joseph Moore, a senior project manager and project lead from GE Aviation. “We need to move quickly through the development cycle and create a part we can actually ship. To prove we could do it, we were put under a deadline and told to do the part as quickly and cost efficiently as possible.”
“Our goal was always to look at ways to disrupt production,” Moore continued. “There are only a few suppliers that make investment castings for the aviation industry, so we need to have options to ensure we’re not impacted by obsolescence and reliant on the cost models of specific suppliers. If we can make an additive part for less, we can save money now and avoid any increase in the future.”
The path to choosing those four additively manufactured bleed air parts started in early 2020 with GE Aviation’s annual audit of castings.
“We are always looking to pull costs out of existing products, so, we cast a wide net that includes hundreds of castings we buy,” stated Gatlin. “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 took into consideration a variety of factors, such as the capabilities of GE Aviation’s AM machines and part size, shape and features. The engineers asked whether the parts used well-characterised 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.
By February 2020, the GE Aviation team had already identified 180 cast parts for which they thought Additive Manufacturing could potentially save money. To ensure this, a team of GE Aviation and GE Additive engineers, each using their own organisation’s production and financial models, split into small groups to calculate the ROI on producing each part.
Then, COVID-19 upended production worldwide. At GE Aviation’s additive production facility in Auburn, Alabama, where parts for other GE Aviation engines are made, the pandemic presented an opportunity for the team to focus on other projects. Unexpectedly, the team had machine and post-processing time available to start making parts. The project was born to take advantage of those machines.
“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,” commented 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.”
Dozens of parts had passed the initial screening; additional analysis down-selected nine parts from them, including parts on other marine-industrial gas turbine engines, regional jet turbofans, and some military programs. The parts were all made of either CoCr, an alloy of cobalt and chrome widely used for hot-turbine parts, or Ti-64. They looked only at parts that could fit inside a Concept Laser M2 machine.
The team then narrowed it down further, prioritising parts-based engineering resources and the importance of cost savings to the engine program. The team settled on the four adapter caps for the LM9000’s bleed air system, which became the focus of the programme at Auburn.
All four were about 8.9 cm in diameter and a height of about 15.2 cm, made of CoCr to handle the hot compressed air from the turbine’s compressor section. From a manufacturing standpoint, they shared a base geometry and similar features. The team assumed the M2 could manufacture three parts at a time, but engineers soon redesigned the layout to increase it to four, which immediately boosted productivity, since it takes about the same amount of time to manufacture four as it does three.
Steve Slusher, a GE Additive Manufacturing Engineer on the project, added that using simulation and analysis, the team showed that the parts performed the same as the cast parts they replaced. The team also built test bars with each build, 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 was said to be a major success. Gatlin reported that it 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 economic – and it was done quickly.
“The thing that stuck out to me,” stated Eschenbach, “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, added, “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.”