Additive Manufacturing is a term we are going to hear more about in aerospace as this decade unfolds. The concept of “additive manufacturing” is another term for what others call 3D printing. Why “additive”? Because typical manufacturing is a “subtractive” process. For example, the complex geometries of jet engine components are manufactured using subtractive machining methods: filing, turning, milling and grinding away material from a block of metal. Collectively, subtractive machining techniques cut away raw material into the desired shape. By contrast, additively manufactured parts are “grown,” which results in little to no material waste. If you have ever visited a manufacturing plant you understand how important this is, both physically and economically. For a good primer on the additive process, take a look at this story from The Economist.What are the other advantageous of additive manufacturing? Typically, additive parts weigh a lot less than conventionally manufactured parts. This is one of the key reasons aerospace is paying such close attention to this process. Additive manufacturing allows engineers to create better parts in just about every respect than their milled counterparts, and are becoming economically competitive in cost as manufacturing technologies evolve. Take a look at this link to information from EADS. The company estimates that the weight of an optimized wing spar could be reduced by as much as 80% using this technology. That’s extremely significant.
Rolls-Royce is spearheading a European Union project called MERLIN that plans to save material by using 3D printing in the manufacture of aircraft engines. Using subtractive manufacturing methods, the production of a one ton aircraft engine can consume over six tons of metal during manufacturing. Using additive manufacturing techniques, it is hoped to produce engines with close to 100% materials utilization.
In 2011 at the University of Virginia an engineering class built a one-quarter-scale working replica of a Rolls-Royce AE3007 turbofan jet engine. The parts were printed in plastic, so the engine is powered by compressed air rather than jet fuel. Forty three parts of the engine were printed in layers measuring 0.010 of an inch at a time. The class spent more than 150 hours assembling the engine. With conventional manufacturing this process would have taken years and cost a quarter-million dollars, according to project lead Professor David Sheffler. Students made the engine in just four months for under $2,000; about $1,500 for the plastic and another $300 for the bearings, nuts, and bolts.
Pratt & Whitney is also deploying this technology. “Additive manufacturing has huge advantages from a cost standpoint,” says Pratt & Whitney’s President David Hess. “It also eliminates the time needed to develop tooling.” P&W has flight tested components made from additive manufacturing on the PW1500G that powers Bombardier’s CSeries. They are much simpler to make than conventional solutions.
P&W has been a leader in additive manufacturing for the past 25 years and has advanced its experience in both additive manufacturing and rapid prototype techniques. P&W has used this technology to make more than 100,000 parts to date including concept models, casting patterns, tooling, test rig hardware and direct metal parts used in engines. More than 2,000 additive manufactured metal prototypes have been made to support developmental engine programs. For example, the GTF family will be the first P&W introduction of production hardware using powder-bed additive manufacturing. P&W will incorporate more than 25 additively made parts into the PW1500G engine for the Bombardier CSeries at entry into service.
The additive process provided P&W up to 15 months lead time savings in developing prototypes compared to conventional manufacturing processes. Additive manufacturing also enables new innovative designs that can’t readily be made using conventional processes, and have a bonus of up to 50% weight reduction.
GE is another company in the thick of the process. GE Aviation is focused on a specific additive technology called direct metal laser melting (DMLM), which precisely melts fine layers of metal powders layer by layer from the bottom up until the build is complete. Once complete in the machine, a series of post-steps are performed including thermal processing, often times post-machining and finally inspection. GE views DMLM and other additive metal processes as a disruptive manufacturing technology.
GE’s process works like this: A machine operator loads the computer aided manufacturing (CAM) data or model into the computer connected to the DMLM machine. The manufacturing process begins by melting, or welding, a first layer of 20 micron powder onto a steel platform. The platform then lowers by 20 microns. A fresh layer of powder is swept over the previously formed layer, and the next layer is welded on top of the previously built layer. A powerful fiber laser is precisely controlled at the X and Y coordinates, allowing for exceptional tolerances to be held and extremely small sizes to be built. Many small to medium size parts and inserts can be constructed in hours and days, as opposed to days and weeks using traditional processes.
Once started, the machine builds unattended 24 hours per day. Parts and inserts coming out of the machine typically go through a series of post-steps, including support removal. These parts tend to be lighter than traditional forged parts because they can be designed specifically for the additive process. In most cases, this allows for substantially less material to be used for the part, without sacrificing strength and functionality.
GE Aviation is already committed to providing components within the combustion system of the LEAP jet engine. Additive manufacturing is a significant technology GE wants to keep in-house. It is comparable to other capabilities GE is keeping in-house, such as the production of carbon fiber composite and ceramic matrix composite components. In the longer term (post-2020), GE believes there is great potential that blades, blisks, tubing, external mounting hardware and stators will also be additively manufactured.
So just when you thought that 3D printing was a lab experiment that could make plastic toys, look again. Additive manufacturing is changing the nature of materials used on aircraft. The rate of change in manufacturing speed is also growing, as computer controls and machines become more sophisticated, so parts that took hours to make ten years ago can now be completed in minutes. The next generation of additive manufacturing technology is already enabling strong, lightweight parts that will enhance fuel efficiency and differentiate the next generation of aircraft engines, including the GTF and LEAP for narrow-body programs, and Trent XWB and GE9X for wide bodies. The market for additive manufacturing is here, and while multi-axis milling machines won’t go away for a few years, they will have new competition on the shop floor creating optimally engineered components “printed” by lasers.
