By Todd Rockstroh

GE Aviation (GEA) has launched production of their first additively manufactured engine component, the fuel nozzle for the LEAP gas turbine (Fig.1).  This part will see combustion flame and gas temperatures and highly stressed thermal cycles.  There are 19 per engine and the LEAP volume will require over 45,000 fuel circuits to be additively fabricated annually starting in 2018. Our designers exploited additive enabled features to gain: a) 5x life improvement, b) 20 parts consolidated into one, and c) a cost reduction.

Figure 1. GE Aviation LEAP Gas Turbine Fuel Nozzle

Powder bed or layered manufacturing is only one additive technology.  A second GEA application is a hybrid additive – conventional process to fabricate the metal leading edge (MLE) of a composite fan blade (Fig. 2).  The MLE is there to protect the leading edge of a composite fan blade from foreign object damage and small particle erosion.  MLEs are currently fabricated via subtractive processes and creep forming.  The newer generation engines and new generation composite materials require harder to machine/form materials and GEA launched additive technologies to overcome these limitations.  Layered manufacturing has enabled unique features to be incorporated internally that cannot be otherwise machined.

Figure 2. GEA Composite Fan Blade (metal leading edge in foreground)

The hybrid MLE is constructed by forming sheet metal to the blade contour and then adding the bulk material via flowing powder/laser fusion welding to form the bulk nose.  The key again is a significant cost reduction over subtractive processes while maintaining or exceeding material properties.

The additive process to production has been a five plus year journey and this article will highlight some of the key barriers and how to overcome them in your company. The sooner your technical staffs become familiar with the technology, control and limits of equipment, materials and designs, the quicker you can generate new products.

Method 1: Dive in a Little

GE invested in over 50 desktop additive filament printers for $2,000 to $3,000 each.  We challenged our technical staff to:

1. Make something for your home by pulling designs from free sources such as GrabCAD.com and Thingiverse.com,
2. Make something you currently work on/with at GE, a tool or part,
3. Redesign the tool or part to make it more “additive friendly,” or
4. Redesign to exploit additive features.

There are also national resources such as America Makes (americamakes.org) and others who can work with and teach your technical staffs prior to any investment in equipment.

Method 2: Let the World Dive in for You

GE also used open source acquisition via a “GrabCAD Challenge.”  We used a simple bracket that was optimized for machining cost and asked for redesigns by non-GE persons via the internet (Fig. 3).  We disclosed some basic loading conditions that the designs had to meet and were seeking lighter weight, additive designs.  The result was that in a few weeks we had nearly 700 entries for a $20,000 prize.  Our technical team evaluated the top 10 designs based on weight reduction, complexity (yes, additive designs can be too difficult to inspect), and finite element analysis of dynamic loading conditions.  We then built the top three designs in metal and are currently destructively testing.

Figure 3.  Machined bracket (top), bracket with same function designed for additive (bottom)

This is a relatively inexpensive way to enter as your technical staff will be exposed to the innovation enabled by layered manufacturing.  700 entries can spawn quite a few concepts within your company.

Challenges of the Additive Technologies

While additive manufacturing is often referred to as the next industrial revolution there are other challenges being addressed across the globe:

1. Material properties – given the breadth of materials and the cost to qualify properties, collaborative industrial partnering to share the expense are still forming including the reuse of materials.
2. Distortion and finish machining – your technical staff will quickly become comfortable with additive manufacturing and create layered parts that cannot be cost effectively inspected.  The surface finish in today’s machines will limit fatigue and other characteristics that require smooth surfaces, those features will have to be accessible.
3. Process control – this can only be accomplished via familiarity with the machines and processes.  Calibration techniques are still evolving at the OEMs and early adopters.  Most of these machines are not at the same maturity as mills or lathes.
4. Process monitoring and control – many parts or batches of parts will require days or weeks in current layered machines.  The key technology gap today is the ability to adequately sense each cubic mm of the build to insure part quality at the end versus costly post-build inspections.

GEA would endorse the “next industrial revolution” assessment of additive manufacturing. We are considering over 500 pounds per engine in weight reduction enabled by additive in external fittings and castings which can result in significant fuel consumption improvement for our customers. While it may take time and maturation of the equipment to become cost effective for your company, the learning curve to technically exploit additive manufacturing is long.  The current machines will rapidly find applications in tooling and rigs, replacing long cycle machined parts in the near term.  As your technical staff engages the technologies, the applications will follow.

To attend an updated presentation of this article, register for LME 2014 (Sept. 23-24, Schaumburg, IL) at www.laserevent.org.

Dr. Todd Rockstroh is a Consulting Engineer for GE Aviation.