Most manufacturers would never dream of switching from an investment cast part to one made by additive manufacturing (AM), especially if they already had paid for the casting mould.

However, that is exactly what GE Aviation is doing with four bleed air parts from a land/marine turbine — the decision was made based on cost and time to market.

A collaboration between GE Aviation and GE Additive is proving that metal AM can match conventional castings on price. In fact, the engineering team expects its four 3-D printed parts will cut the manufacturing cost by up to 35% — enough to justify retiring the old casting moulds forever.

Equally important, the conversion process took only 10 months to go from identifying target parts to 3-D printing final prototypes. Ordinarily, producing aerospace and land/marine turbine parts using a casting process takes 12 to 18 months or more.

Eric Gatlin, GE Aviation AM leader, said: “This is a game-changer. This is the first time we did a part-for-part replacement, and it was cheaper to produce them with additive manufacturing (AM) than casting.

“To make sure we demonstrated cost competitiveness, we had four outside vendors quote the parts, and we still came in lower with AM.”

This is just the beginning. The project has identified scores of other parts on a variety of engines that they could produce with AM and save signficant costs.

AM has been growing more competitive for a number of years and this is especially true for new aircraft engine programmes.

The 3-D printed fuel nozzle tip for GE Aviation’s LEAP engine, for example, consolidates 20 different parts — and the steps needed to machine and assemble them — into one single structure.

Parts consolidation
Meanwhile, the company’s new turboprop engine took that to another level by combining an astonishing 855 parts into just 10 3-D printed components. In both cases, GE Aviation took advantage of parts consolidation to squeeze major cost savings from the assembly process.

As the number of demanding applications grew, equipment makers have rapidly improved the productivity of their metal laser printers, which build parts from metal powders, one thin layer at a time. One example is GE Additive’s Concept Laser M2 Series 5 machine. Its dual lasers melt and fuse metal layers faster than a single laser alone and produce more consistent results for complex builds.

The M2’s lasers are also powerful, either 400W or 1kW, and produce 50µ thick layers. It also has a large, 21,000cm³ build chamber in which to make parts.

Mr Gratlin said: “We said from the outset that we were going to pick a material that we had already qualified. 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 that the team could run fast.”

This enabled the project team to develop final prototypes between April and September 2020. Although 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, the group considered dozens of parts for older engines and products, too.

The path to choosing the four additive parts started in early 2020 with GE Aviation’s annual audit of castings.

Mr Gatlin continued: “We are always looking to pull costs out of existing products, so we cast a wide net that includes hundreds of castings we buy. Then we asked: ‘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. It considered a variety of factors, such as the capabilities of GE Aviation’s 3-D printers and part size, shape and features.

The engineers asked whether the parts used well-characterised materials they had worked 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 perfect for making complex parts, such as those with internal channels. 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 moulds or tooling needed for casting.

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

By February 2020, the GE Aviation team had already identified 180 cast parts for which they thought 3-D printing could potentially save money. To make sure, 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 return on investment on 3-D printing each part.

However, Covid-19 upended production worldwide. At GE Aviation’s Auburn AM production facility in Alabama, where parts for other GE Aviation engines are made, the pandemic presented an opportunity for the team to focus on other projects. Unexpectedly, they had machine and post-processing time available to start making parts.

Low-rate production
Jeff Eschenbach, a senior project manager and project lead at the Auburn facility, said: “We are 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. 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 formation of the team kicked everything into high gear. Dozens of parts had passed the initial screening. Additional analysis down-selected nine parts from them. They included parts on other marine-industrial gas turbine engines, regional jet turbofans, and some military programmes.

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.

The team then narrowed it down further, prioritising parts-based engineering resources and the importance of cost savings to the engine programme. The team settled on four parts — adapter caps for the LM9000’s bleed air system — which became the focus of the programme at Auburn.

All four were about 3.5in in diameter and about 6in tall. They would be 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 print three parts at a time, but engineers soon redesigned the layout to increase it to four. This immediately boosted productivity, since it takes about the same amount of time to print four as it does three parts.

Using simulation and analysis, the team showed that the parts performed the same as the cast parts they replaced, said Steve Slusher, a GE Additive manufacturing engineer on the project. The team also built test bars with each 3-D 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 proved to be a major success. It marked the first time GE Aviation had shifted production from investment casting to AM based strictly on cost. The parts were one-to-one replacements, without any redesign or parts consolidation to improve their economics, according to Mr Gatlin, and it was done fast.

Mr Eschenbach added: “The thing that stuck out to me was that we could take an existing casting design, replicate it quickly on our 3-D 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, said: “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.”