Though we may strive for the day in which it's possible to make an entire aircraft with 3D printing, according to Wohlers Associates, about one-third of the reported additive manufacturing (AM) applications is for creating prototypes and visual models. The actual 3D printing of end parts may be on the rise, but there are applications that lay beyond the most exciting stories put forth by the media.

To better understand the myriad of ways in which AM is actually being used, ENGINEERING.com explored the technology's various applications. Hopefully, this will provide a more complete picture of how AM can be implemented throughout all of the steps of the manufacturing process, from creating prototypes and producing auxiliary tools like jigs and fixtures to end part production.

Visual Prototypes

When it was invented, 3D printing was referred to as rapid prototyping, a method for automating and reducing the labor required to create a prototype model for design validation. Since then, it has found use in a number of other applications, but the technology is still widely implemented to create visual models and functional prototypes.

For the production of visual models, 3D printing has evolved quite a bit. Though it's possible to create highly detailed prints with technologies like stereolithography (SLA), full-color 3D printing with binder jetting, paper 3D printing and material jetting can achieve a vibrancy impossible with other technologies.

A model made with a 3D Systems CJP 3D printer. (Image courtesy of 3D Systems.)

ColorJet Printing (CJP), a binder jetting technology from 3D Systems, involves the deposition of a liquid binding agent and CMYK inks onto a bed of gypsum powder, resulting in the creation of full-color, sandstone-like models. Though the process is different, PolyJet, from Stratasys, takes this a step further with the ability to alter physical properties such as flexibility and transparency. PolyJet is a material jetting technology that deposits photocurable resins, which are then hardened with a UV lamp.

A 3D-printed model made with Stratasys’ J750 3D printer. (Image courtesy of Stratasys.)

Mcor's paper 3D printing technology may not be able to achieve the same geometric complexity as the aforementioned processes, but the parts are made from paper, making it much more ecologically friendly. This process sees CMYK deposited onto white paper, which is then glued to the previous layer and cut with a tungsten carbide blade.

A paper print made with the Mcor IRIS HD 3D printer. (Image courtesy of Mcor.)

Otter Products, manufacturer of OtterBox cases, relies on 3D printing for the fabrication of realistic parts during the prototyping process. In 2008, the firm began with a ZCorp machine, the full-color binder jetting technology acquired by 3D Systems, to use for prototyping new designs. Since then, Otter Products has acquired a number of 3D printers and, in 2016, became a beta customer for Stratasys' J750 PolyJet system.

Uniquely, the J750 can print with seven different material compositions, including support material, and over 360,000 different shades of color. Unlike the ZCorp system, which is only able to produce rigid, sandstone-like objects, the J750 is able to replicate rubber and translucent plastic, making it possible to estimate the look and feel of mass-manufactured parts. Ultimately, this allowed Otter Products to cut down the design-to-production workflow to just eight weeks, as the firm iterated five to 12 different prototypes of a design.

Brycen Smith, prototype lab manager for Otter Products, explained how the technology is used and the benefits that it brings. “OtterBox primarily uses 3D printing to validate designs before going into production,” Smith said. “With our printing technologies and capabilities, we can produce multiple case iterations in a day, translating the printed material into what the real product will feel like. At this point, those prototyped parts are used to make changes to the design while in the CAD stages, instead of during production, which saves time and money. This gives us more confidence in the quality of each part and allows us to get the product into stores as quickly as possible.”

Smith added, “We also use the 3D printers to create test fixtures and jigs, as well as production assembly fixtures and jigs, so the machines are really utilized throughout the whole product creation process. We use multiple different methods of prototyping, but for the best realistic parts, we always go to 3D printers.”

Functional Prototypes

To test the function of a design, qualities like color may not be quite as important. For instance, testing a living hinge might require 3D printing with a durable thermoplastic, such as nylon, or with a rubber-like photopolymer, printed with material jetting or vat photopolymerization technologies, such as SLA or digital light processing (DLP). For wind tunnel testing, a number of technologies may work, but the part will need to be postprocessed in such a way that aerodynamic properties of a part aren’t inhibited by the striation made through the 3D printing process. For this reason, a high-resolution technology may be preferred.

Alta Motors is an electric motorcycle manufacturer that has begun working to use 3D printing to prototype parts for its bikes. In designing the firm's Redshift motorcycle, Alta Motors turned to 3D printing service bureau The Technology House (TTH) to iterate functional prototypes quickly for parts that were to be mass manufactured. TTH relied on continuous liquid interface production (CLIP), an ultrafast 3D printing process from Carbon, to 3D print a number of parts.

Prototype parts 3D printed by TTH with Carbon’s CLIP technology for Alta Motors. (Image courtesy of Carbon.)

TTH used Carbon's rigid polyurethane material to fabricate diagnostics and charger housings and elastomeric polyurethane for wire seals and grommets. Alta Motors was able to collaborate with TTH over the Internet, receive prototypes and iterate new designs at a rapid pace.

As Nick Herron, senior mechanical engineer for Alta Motors, said of Carbon’s CLIP technology, "In an electric motocross bike, the electronics modules all must maintain proper environmental control for long-term reliability in harsh off-road environments. We implement various connectors, housings and fittings to achieve this watertight condition. The Carbon material and process allows us to create these parts with properties that are as close to production as anything else on the market. The combination of good strength, ductility and surface finish gives us a structural material that can also be sealed using production-intent elastomeric gaskets and can be used to validate designs before kicking off expensive production tools."

Due to the speed of the CLIP process and the complexity possible with 3D printing, Alta Motors is now experimenting with the use of the technology for end parts that will be installed directly into the bike. One component that may potentially be produced with 3D printing is a high-voltage connector that consolidates two previously separate parts into one.

Tooling

As a design moves from the concept phase to the production phase, a manufacturing operation may implement 3D printing for the fabrication of custom tools that aid in the production process. This can include anything from guides for precise drilling, dies for forming or cutting raw material into a specific shape and measurement tools, like gauges, to jigs and fixtures that hold a part in place while other operations are performed.

3D printing may be used directly or indirectly in the creation of tooling. In the case of indirectly fabricating a tool with AM, a tool may be made by coating a 3D-printed component in rubber, which is then used to cast the tool itself.

When tools are custom made for a new manufacturing job, a business may need a third-party service provider, which may rely on traditional manufacturing technologies, such as CNC machining, to create the tooling. This process can be costly and time consuming, with the business waiting weeks to months for the tools to be shipped in order to even begin manufacturing.

This is particularly true for the aerospace industry, in which even the tools themselves may be huge, making them even more expensive and labor intensive. Large-scale 3D printers hold a great deal of promise in this regard. Companies like Cincinnati Inc., Thermwood and Ingersoll are developing technologies for 3D printing large plastic parts, including aircraft tooling.

To demonstrate the possibilities of 3D printing for large-scale tooling, Oak Ridge National Laboratory (ORNL) and Boeing designed a specialty tool for Boeing's new aircraft, the 777X. The plane, to hit runways in 2020, will have a massive wingspan of 235 ft 5 in (71.8 m). In order to create tooling large enough to work on components for a 777X wing, ORNL and Boeing 3D printed a specialty drill-and-trim guide on the Big Area Additive Manufacturing (BAAM) 3D printer from Cincinnati Inc.

ORNL and Boeing’s 3D-printed tooling in front of the BAAM 3D printer. (Image courtesy of ORNL.)

At 17.5 ft long, 5.5 ft wide and 1.5 ft tall and weighing 1,650 pounds, the guide was large enough to win ORNL and Boeing a Guinness World Record title for the largest solid, 3D-printed item. According to Leo Christodoulou, Boeing research and technology chief engineer, such a part would have taken about three months if ordered from the firm’s regular supplier.

Christodoulou told ENGINEERING.com that 3D printing will be essential for the future of aerospace: “3D printing offers great potential to reduce the cost and weight of aircraft structures and increase the flexibility available to our engineers to design optimized parts. Additively manufactured tools, such as the 777X wing trim tool, will save energy, time, labor and production cost and are part of our overall strategy to apply 3D-printing technology in key production areas.”

Patterns, Molds and Cores for Casting

3D printing is also used to produce objects that will ultimately be cast in metal. On a small scale, this can mean lost-wax casting models for jewellery and dental crowns. On a large scale, this can mean creating sand cores for casting complete engine parts.

In the process of lost-wax casting, a positive is 3D printed in a castable material. It is then submerged in a specialty investment material (a process known as “stuccoing”) and burned out in a kiln. The result is a mold that is filled with molten metal to create a metal part. SLA, DLP and material jetting technology, like the wax 3D printing process created by Solidscape, are ideal for this process, as they are capable of producing finely detailed prints with a high burnout.

For larger parts, binder jetting processes, like those from Voxeljet and ExOne, may be implemented to 3D print sand cores and molds. Binder jetting involves the deposition of a binder material onto a bed of powder, including sand, layer by layer until the print is complete. In sand casting, this object may then be placed into a molding box, which is filled with molten metal and, once cooled, broken apart to reveal the final metal object.

Hoosier Pattern, Inc. (HPI) has purchased ExOne's S-Max 3D printer for just such a purpose. Dave Rittmeyer, customer care and AM manager at HPI, explained how the process works and the benefits it can bring HPI's clients.

As Rittmeyer described the typical sand casting process, “Traditionally, for sand casting, you’ll have tooling built, a process that can take anywhere from four to 12 weeks, depending on what type of equipment is used to have that tooling built. The tooling will then be sent to the foundry, where they’ll blow or mold hand-packed sand around the tooling. The tooling is pulled out, the two halves of the mold are closed and the mold is filled with molten metal to create the casting.”

A graphic of the traditional sand casting process. (Image courtesy of Wikimedia.)

“We've worked with a lot of companies for fit and function, safety testing and other applications,” Rittmeyer continued. “If you've got a 12-week lead time for the tooling and a couple of weeks for the foundry, then you’re looking at 14 or 15 weeks to get a casting from a foundry,” he continued.

Rittmeyer said that, with 3D-printed sand molds and cores, it's possible to skip the entire tooling process: “The sand [for 3D printing] is definitely more expensive than the traditional foundry sand, but you can just skip four to 12 weeks of tooling lead time. In one or two weeks, you can have a mold at your door.”

A large 3D-printed sand core for sand casting. (Image courtesy of HPI.)

HPI doesn't always 3D print the entire sand mold or core for a job but will sometimes 3D print inserts that can be combined with traditionally made components to complete the mold. That way, a client's existing mold can be combined with a new 3D-printed insert to form an entirely new casting. According to Rittmeyer, this hybrid process can yield high-quality parts for a lower cast and with a shorter lead time than casting made with the traditional process.

End Parts

Due to the speed, quality and cost of AM, the technology is best suited for the production of specialty parts in smaller batches, rather than mass-manufactured goods. For this reason, end products that are made with 3D printing have usually been made that way for good cause.

AM brings some important qualities to the world of manufacturing that make it ideal for certain jobs. For instance, due to the additive nature of the technology, parts can have complex geometries impossible with traditional manufacturing processes. Through the translation of a CAD file directly to the formation of a physical object, it is also possible to 3D print goods on demand, allowing for the creation of custom parts more easily.

To exploit these benefits, businesses that create specialty or custom parts in shorter runs will often turn to AM to manufacture products. That way, those companies don't have to invest in costly tooling to mass produce goods that will only see a limited release.

CFM International's 3D-printed fuel nozzle reduces part count from 18 to just one. (Image courtesy of GE.)

Perhaps the most famous example of AM used for the production of end parts is the LEAP jet engine fuel nozzle designed by CFM International, a joint venture of GE Aviation and Safran Aircraft Engines. The nozzle is a redesign of an assembly that previously required 18 different parts but can now be 3D printed, via powder bed fusion, from metal as a single part. The resulting component is 25 percent lighter and five times more durable than the previous design and could not be made with traditional manufacturing technology.

With the LEAP engine, to be installed on 10,000 aircraft, containing 19 different nozzles, the nozzle is able to reduce the fuel consumption of a plane by an estimated 15 percent. CO 2 emissions are, in turn, reduced by 15 percent as well. To manufacture the part, GE Aviation established a facility in Auburn, Ala., to 3D print these nozzles en masse.

3D-printed hearing aid shells made by EnvisionTEC. (Image courtesy of EnvisionTEC.)

While CFM International is among the first to 3D print end parts to be used on civilian aircraft, 3D printing has been used for mass production in the world of medicine for somewhat longer. A large number of hearing aids are made with 3D printing, an ideal application for AM given the personalized nature of each device.

With hearing aids, the interior electronics are made conventionally, while the shells that house these electronics are 3D printed. A scan is made of a patient’s ear, making it possible to design a CAD model that perfectly fits that patient’s anatomy. Hearing aid manufacturer Audicus claims that over 10,000,000 3D-printed hearing aids have been sold to date.

For this reason, it’s no surprise that market research firm Gartner anticipates the medical market to be the first to be disrupted by AM. Geometrically complex designs and personalized products fit perfectly into the medical field, where the need for disruption may be the most critical.

As others have demonstrated, however, it’s not the only place where this will occur. CFM International has already begun shipping LEAP engines to customers, and firms like Alta Motors suggest that they will find themselves being used for end parts in the automotive world as well. It’s only a matter of time then before AM is used for end production across all fields. Until then and probably long after, the technology will continue to serve as a method for prototyping and auxiliary production processes.



