Additive Layer Manufacturing: Building the Future One Layer at a Time

Additive aluminium

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At first glance, GE Aviation’s fuel nozzle tip for the LEAP jet engine is a small, banal-looking piece of equipment. But take a look inside, and you will see a highly intricate labyrinth of passages designed to mix jet fuel with air. The part is so complex, the company had difficulty producing it using traditional processes—so it turned to Additive Layer Manufacturing, or ALM. Introduced in 2015, the nozzle was a revolution: the civilian aviation market’s first part produced by additive manufacturing.

Additive Layer Manufacturing—also known as 3D printing—is proving to be a game changer for metal parts in industries of all sorts. Aerospace was an early adopter, but ALM also has applications for automobiles, medical devices, electronics, robotics...

How it works: from powder to parts

As its name implies, additive manufacturing is the opposite of subtractive manufacturing, where material is removed (by cutting, milling, etc.) to achieve the desired shape. In ALM, a computer sends a digital design directly to a machine that prints it in three dimensions, without intermediary steps such as creating molds.

There are several different ALM processes; for metal, a method called “powder bed” is the most common. A machine deposits superfine layers of metal powder, each about the thickness of a hair. Then a laser or electron beam passes over each layer in a distinct path, melting the powder into a shape preordained by the computer. The process is repeated for hundreds or thousands of successive layers, which fuse together until the final object is formed.

Unique shapes and lighter weights

Additive manufacturing offers many advantages. It is ideal for making complex, unusually shaped, or extremely customizable parts, from jet engine components to individual robotic grippers that can be created to exact specifications each time. “Additive manufacturing offers a design freedom that other technologies don’t. You can print almost anything,” says Bruno Chenal, Strategic Innovation Director at Constellium.

3D-printed parts are lighter, stronger, and more precisely constructed than parts manufactured by conventional manufacturing methods. The GE fuel nozzle, for example, is one single piece rather than 20 assembled together. It weighs 25% less and is five times more durable than its conventionally manufactured equivalent. GE Aviation, in partnership with Safran Aircraft Engines, has since used 3D printing for other parts, including a sensor, a power door opening system, and an air-oil separator. Its Catalyst program features a 3D-printed turboprop engine whose total part count has been reduced from 855 to 12, shaving off more than 45 kg in weight.

GE is one of many companies developing 3D-printed heat exchangers that perform better thanks to their complex geometries (thin walls, intricate flow channels), light weight, and lack of seams or joints. Its version is inspired by the human lung.

Faster development, less inventory

Rapid prototyping is another major application of ALM, shortening design and development cycles in a range of industries. Ford, an early champion of 3D printing, is one of several carmakers using the technology to accelerate the development and testing of new products, creating multiple iterations without the need for (or cost of) tooling.

The ability to print individual items on demand also minimizes the cost and inconvenience of stocking spare parts, or having them shipped from a distant location. “When a military aircraft carrier needs a new part for a plane, it can simply be printed onsite, rather than having to send for it,” says Chenal. Automotive and rail transport companies are normally obliged to store spare parts for years, when it would be much simpler and cheaper to keep a 3D printer and digital files on hand. For this reason, Mercedes-Benz has been offering automobile replacement parts made with ALM since 2016.

Different processes for various needs

More suited to some applications than others, 3D printing is not about to supplant conventional manufacturing. Because ALM is a slow, small-batch process, a part will cost the same whether produced as a single batch or 10,000 pieces. Even though 3D printing, without tooling, setup costs, or other associated fixed costs, is able to deliver economies of scale at low quantities, it is not the best solution for large parts or high-volume production.

This is the main reason the auto industry has not yet adopted ALM for mass production of parts. On the other hand, 3D-printed parts are starting to make their way into high-performance sportscars and limited-series vehicles. The 2018 BMW i8 Roadster, for instance, was the first production-series vehicle to contain a metal 3D-printed part, a complex aluminium roof bracket that would have been close to impossible to make by casting.

And for clients desiring a unique, custom-made part—such as a monogrammed gear shift handle for a Citroën DS—3D printing is just the ticket.

ALM-friendly aluminium alloys

Aluminium presents its own specific challenges to additive manufacturing. For one thing, there must be good justification for choosing ALM when conventionally manufactured aluminium alloys are readily cast, formed and machined, unlike titanium or nickel.

What’s more, many of the appealing properties of aluminium alloys result from the different steps of semi-product processing for subtractive manufacturing, such as rolling, extrusion, and thermal treatments. Because 3D printing is a one-step process, alloys made this way do not develop the same properties.

Faced with such challenges, researchers are coming up with exciting solutions, and inventing totally new products specifically for additive manufacturing. Chenal explains that at Constellium, “We started with a blank page, wondering how we could turn ALM to our advantage, and have created entirely new alloys specifically designed for ALM with even better properties than conventional ones.” These include high electrical and thermal conductivity, as well as maintaining properties above 200 degrees Celsius. Chenal’s team is also developing alloys that can be printed more quickly, thereby bringing down the cost.

Indeed, it seems there is infinite potential for a process where you can build airplane engine components from powder just by pushing a button.

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