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Fabricating the future, layer by layer

Metal additive manufacturing opens a new world of fabrication

Figure 1
In this directed energy deposition process, a laser deposits layers of metal to repair an impeller pump. Photo courtesy of Optomec, Albuquerque, N.M.

We live in a global society that operates 24/7, and people demand new and different products at an equal pace. However, the average person does not bother to think about the rigors of fabricating a product. Driving past a fabrication shop, people don’t think twice about the equipment inside. They know about lasers, but they don’t know that they are used to cut through sheet metal. They know metal must be bent or formed somehow, but they probably have never heard of a press brake.

But they’ve probably heard of one kind of fabrication that’s not as ubiquitous as the laser cutting machine or press brake, at least not yet. It’s additive manufacturing (AM), which includes 3-D printing. You can’t turn on a TV or open a magazine without someone talking or writing about 3-D printing and how it is the future of manufacturing.

It’s a novelty, for sure, but for some in the metal fabrication arena, AM isn’t a new concept, but one that has evolved over several decades. Although it dates back to a patent from 1892 that describes J.E. Blanther’s manufacture of contour relief maps, which used the concept of AM, the practical application of it didn’t start until the mid-1980s. That was when Chuck Hull invented stereolithography, a process that utilizes ultraviolet lasers to cure photopolymers, and for years engineers have used the technology to create prototypes. At that same time others were working on laser sintering of metal. Although the mechanical quality of the parts was not ideal, AM still was something to dream about in terms of its possibilities in the future.

Today rapid prototyping still plays an important role in additive manufacturing, but the technology has matured to produce customized parts, from medical to motorsports to fixtures used in manufacturing. Quite often we now can create 3-D metal objects with properties that are better than the wrought product.

The ASTM Committee F42 on Additive Manufacturing Technologies was formed in 2009 to help develop industrial standards for this emerging technology. To facilitate unambiguous communication, the committee created the document titled ASTM F2792: Standard Terminology for Additive Manufacturing Technologies. The standard categorizes principal forms of AM, including material extrusion, material jetting, binder jetting, sheet lamination, and vat photopolymerization.

The histories of all these processes could fill volumes. So here we will look at two specific methods of AM: powder bed fusion (PBF) and directed energy deposition (DED), both of which can be used to produce metal objects (see Figures 1 and 2).

Like other additive processes, both PBF and DED are changing fundamental concepts of design, engineering, and production. In effect, metal additive manufacturing is allowing the industry to create metal products in entirely new ways.

Powder Bed Fusion

Powder bed fusion describes a 3-D printing process in which either an electron beam or a laser beam is used to fuse the metal powders in a powder bed layer by layer. Each layer can be from 0.0012 to 0.004 inch thick. Once the layer is fused in the areas that match the CAD drawing, the platen holding the powder moves down, a new layer of powder is placed on top, and the process is repeated until the part is completed.

This technology has made great advances from its early days, and now it can make very complex parts. PBF systems are marketed under proprietary names such as Direct Laser Metal Sintering (DMLS), Selective Laser Melting (SLM), and Laser Cusing (LC). The powder bed acts as the support for the part itself, so building support structures is unnecessary. This allows for almost limitless design possibilities.

Figure 3 shows a cobalt chrome part with many features sintered within the same build—that is, a complete cycle of an AM machine, resulting in finished components. Freestanding posts, slots as narrow as 0.0001 in. with no distortion, a mesh structure, and a feature that was built at a 45-degree angle without any supports—all can come from the same build.

There has been a push to increase the size of the powder bed (currently the largest bed is 10 by 10 by 12 in. deep) so that production economics can make more business sense. If one part requires a 10-hour build cycle in a powder bed system, and if it is possible to fit 10 parts into that build volume, it still takes only 10 hours to build.

South Africa’s Council for Scientific and Industrial Research’s National Laser Centre, along with South African aviation company Aerosud, under the support of the Department of Science and Technology, is designing and building a machine with the apt name Aeroswift. It’s a PBF system that will be about 84 by 12 by 12 in. This will enable PBF not only to make more parts at once, but also, thanks to the bed size, produce very large components.

Figure 2
Two major metal additive manufacturing processes, directed energy deposition (DED) and powder bed fusion (PBF), are changing some fundamental concepts about design, engineering, and production.

Directed Energy Deposition

Directed energy deposition uses a deposition head that feeds either powder or wire into the laser beam that is melting the surface to be built up. In some systems, an electron beam is used instead of a laser. DED can build on existing components, and it’s marketed under proprietary names such as Direct Metal Deposition (DMD), Laser-Engineered Net Shaping (LENS), and Laser Consolidation (LC).

For some time companies have used the technology to refurbish and repair precise or expensive workpieces (see Figure 1), often using a different material than the original. Using a different but compatible material can increase wear, corrosion, and oxidation resistance, and improved lubricity can often extend the lifetime of the repair components beyond their normal lifespan. In this way, repairs can be not just cost-effective, but actually extend the life of the system.

It’s also possible to mix powders to make new and improved alloys, or what is commonly called functionally graded materials. Powder chemistries are changed to alter the material properties. For example, if an engineer wants to change the mechanical properties of an impeller pump so that one section has more corrosion resistance and another section has better wear properties, DED makes this possible.

Current Status

Large companies like Boeing, GE, and Airbus are investing significantly in AM, spending lots of time and money to develop processing parameters that are specific to machines to be able to qualify parts. GE reportedly will invest $50 million to create a 3-D printing production facility in Auburn, Ala., where it plans to use PBF to produce more than 100,000 fuel nozzles.1

This represents $75 billion worth of orders for the company’s next-generation jet engines, which are scheduled to start flying in commercial airliners in 2016. To design the fuel nozzle specifically for AM and get to this point took GE more than a decade. GE has no plan B, and this fact alone illustrates how important additive manufacturing is in the OEM world.

A recent trend is to merge DED with conventional CNC machining stations, which will improve productivity vastly and enable truly innovative components. As the costs come down, it will be possible for systems to perform multiple tasks in a single station. Imagination is the only limiting factor.

Justifying the Cost

While AM processes are much more expensive than traditional processes, in certain circumstances this extra cost is easily justified. For example, in the aerospace and energy industries, unexpected machine downtime can become extremely expensive very quickly—yet those machines may be 20 years old, and the company that made them may have long ceased producing spare parts. AM’s ability to make a single part on demand with wrought properties in a week, even at a high price, greatly offsets the costs of delays in returning equipment to service.

Forged parts in single quantities may well take six months to build and are also expensive. In the medical industry, AM can make custom-fit implants quickly with high quality and functionally graded properties, such as a biocompatible surface with stronger interior properties. Again, in these instances, it’s easy to justify the cost.

Getting Everyone at the Table

Nevertheless, much work remains. With additive processes, the component properties achieved may differ from one build to the next. This is also true when multiple system platforms are used, so understanding where these differences come from and how to translate them across these platforms are critical.

Small companies usually can’t invest heavily in R&D to learn the capabilities of AM systems. While some AM equipment producers can help these small companies with development, it obviously comes at a cost. Many public and private efforts have tried to standardize material properties and the like for AM, which is greatly needed if the technology is going to become a widely accepted manufacturing option.

Figure 3
This cobalt chrome part shows how PBF can create various features, including a mesh structure and freestanding posts, in the same build. Photo courtesy of Sandeep Rana, 3D Systems, Rock Hill, S.C.

At this stage, the America Makes program, under the National Additive Manufacturing Innovation Institute (NAMII), is leading the charge to try to make this a reality. Initially funded by both the U.S. government and private companies, NAMII’s mission is to accelerate AM’s adoption in U.S. manufacturing and to increase domestic manufacturing competitiveness.

The way this is done is to bring everyone to the same table. Everybody needs to speak the same language so that they know how to train current and future engineers and operators. Furthermore, everyone must understand and agree upon what the needs are, and pool resources so they can develop a coherent supply chain more rapidly than if machine builders, materials suppliers, job shops, systems integrators, and OEMs work independently.

The National Institute for Standards and Technology is funding two projects in the area of Measurement Science for Additive Manufacturing (NIST-MSAM). One project is with the America Makes initiative, while the other project is with Northern Illinois University. These projects aim to accelerate the next-generation systems, help develop the fundamental understanding of how AM works, and provide educational content for operators and business leaders. Ultimately, these and similar programs aim to reduce the risk of AM technology to the point where that risk is equal to, or even lower than, traditional manufacturing processes.

Postscript

So how will AM transform manufacturing? Many have lofty predictions about the potential of mass customization and the end of old-school production. No one can really say for sure what will happen decades from now, but some extremely significant changes are happening right now.

Consider one Tier 3 supplier that makes parts for aircraft engines. The company has an order for a part it hasn’t made in 20 years, and of course it got rid of the forging blanks a long time ago. The aircraft owner is screaming that the plane is out of service and costing him $275,000 a day in lost revenue.

“Can’t you get me a part this week?”

Luckily, they have the old digital records for this part, and they use software to turn them into an AM build process plan. This plan then is sent to the AM machine on the floor. The very next day, after inspection, the part ships. The customer is very happy and says, “From now on you get all of my spare parts business.”

1. Peter Harrop, PhD, FIEE, “3D printed flight-critical aerospace components go into production,” July 30, 2014, http://www.idtechex.com/research/articles/3d-printed-flight-critical-aerospace-components-go-into-production-00006762.asp