Additive manufacturing (AM), also known as 3D printing, translates computer-aided design (CAD) data directly into a manufactured part, eliminating the drawing step and avoiding manufacturing tolerance mismatches. With a 2018 market size of approximately $8 billion, the technology is well-suited to meet the increasing market pressure to decrease sample lead times. Ideally, AM also can reduce the amount of scrap material by building up only the final design without cutting it out of raw material. To reach this end goal, designers should be trained on how best to design for additive manufacturing.
This manufacturing process fits the definition of disruptive innovation and has proven applications across multiple industries. However, the full-scale move from traditional fabrication methods (such as laser and waterjet cutting) to an entirely additive approach is not trivial. This guide describes how a company can go about incorporating the newest AM techniques to its manufacturing process, and how to leverage this disruptive technology to improve lead times, cost, performance, and overall manufacturing flow.
ASTM International defines seven categories of AM: powder bed fusion, binder jetting, directed energy deposition, material extrusion, material jetting, sheet lamination, and vat photopolymerization. These are the materials, techniques, and applications for which each category excels.
Powder bed fusion (PBF): Lasers, electron beams, or another thermal source melt material into the desired form. PBF fuses the material after the nozzle deposits it onto the build platform, in contrast with directed energy deposition. Corrosivity is a concern with this process, leading engineers to implement multiple build chambers. Users sometimes use inert gas in the chambers to limit oxygen in the local environment, similar to the use of argon gas in tungsten inert gas (TIG) welding.
The aerospace and defense industries prefer PBF to manufacture their AM products. This process is inexpensive, does not require support structures like the processes primarily used for plastics, and many disciplines use it. PBF is energy-intensive, requires post-processing, and does not exhibit excellent structural properties. Manufacturers also use the process for automotive and maritime applications, along with tissue engineering and repair in the medical field.
Binder jetting: This process is composed of powder-based construction material and an adhesive, usually in liquid form. The printer makes the layers by alternating build powder and adhesive, similar to brick-and-mortar construction. This fabrication method is not sufficient for structurally sensitive components, but it is fast and able to use a wide range of colors and materials, such as metal, plastics, and ceramics.
Sand casting cores/molds and the low-cost metal components are ideal applications for this process.
Directed energy deposition (DED): Similar to welding, DED melts material that is being deposited by a nozzle. Plasma arc, lasers, and electron beams are examples of heat sources that melt the deposited material.
Engineers use DED in laser cladding, sintering, coating, and failure repair due to its high level of precision. These specialty applications are in addition to its use to create freestanding structures.
Material extrusion: Thermoplastic is fed through a nozzle and melted at a temperature appropriate for the material type. Although plastics are the most commonly used material, engineers have applied material extrusion to make shapes out of viscous pastes, such as concrete and chocolate. The process can be tailored to the melting point of a given material and creates structural parts that may also consist of mixed materials, such as wood and metal.
It is inexpensive, but accuracy and speed lag behind more advanced techniques. These limitations make the process better for aesthetic samples.
Material jetting: Similar to material extrusion, material jetting pushes filament onto the build platform layer by layer. This process deposits droplets, though, instead of extruded material. The droplets solidify or cure on the platform, creating the final shape.
Material jetting is accurate (similar to inkjet printing), exhibits accurate surface finish, and allows multiple colors in a finished part. The drawback is that it is limited only to polymers and waxes, reducing the range of usage. Casting patterns and similar applications for the medical and dental industry use this approach.
Sheet lamination: Although many 3D-printed components use strands of material to fabricate layers of the final shape, sheet-laminated parts start with a standard-shaped sheet. Manufacturers cut the final shape of each layer out, similar to laser, oxy-acetylene, or waterjet cutting. The process is fast, as it cuts only the outline of the desired shape, but does not offer sufficient structural support.
Vat photopolymerization: Also known as stereolithography, this AM method uses light to polymerize the build material selectively. The curing medium is light-activated and has evolved from the first commercial AM process, stereolithography. A vat stores the build material, and the operator brings the build surface near the liquid photopolymer. Light is passed through the liquid to build the solid component on the surface.
This AM process is suitable for large parts, but its undesirable structural properties hinder the durability of the component. This process is suitable for building rapid-prototype tools and small quantities of plastic parts.
Once you decide to implement AM, there are tools and practices in various design phases you need to consider to realize the full benefit of the process. Component design is the first fundamental difference between AM and traditional manufacturing. Historically, 2D drawings have communicated design intent as well as the critical dimensions for making a part. More recently, the digital age has ushered in the use of CAD models that are used to generate the drawings. Drawing discrepancies could be compared against the CAD model to confirm intent. With AM, drawings have become obsolete, placing even more emphasis on CAD model accuracy.
Engineers design parts intended to be processed using AM differently than traditional methods. Now, they must define the internal support structures to build the component to ensure the product functions as intended. Brent Stucker, director of additive manufacturing at ANSYS, expressed the need to change the part design to account for the new fabrication process.
“If a company is replacing a traditionally manufactured design with an additively manufactured design of the same geometry, there is typically little benefit in doing so,” he says.
It is essential to improve the quality of numerical performance prediction software. A higher investment in 3D analysis tools such as finite element analysis (FEA) and computational fluid dynamics (CFD) can help to optimize the design before it is made, and increases the first-pass yield of a new part. Additionally, these tools can reduce post-processing operations, which reduces part-to-part variation and mitigates quality concerns.
Optimizing the part design for AM and improving the predictive performance of the part increases the likelihood of success, and maximizes the benefit of the approach. ASME has developed the Replicate Adapt Optimize™ framework to guide manufacturers and their design engineers through this process.
As a product matures, the built material has an increasing influence on production cost. Capital is applied to the process to drive down labor cost per piece, leaving the material with a higher share of the cost. With AM, raw material and post-processing dominate the material supply chain.
Ankit Saharan, manager, R&D and applications development at EOS, views materials as the most substantial opportunity for expansion of AM. “From our point of view, the materials side of the additive manufacturing equation holds the most potential for the future growth of the overall technology,” he says.
One should consider how several factors of both raw material and post-processing impact the supply chain to optimize the benefit of implementing AM:
Raw material supply
- Operating conditions
- Durability requirements
- Support requirements during fabrication
- Environmental requirements during fabrication
- Availability to converge on just-in-time supply
- Scarcity and global supply risk/redundancy
- Protection of mounting/interface features
- Removal from printer base
- Stress relief from process thermal cycles
- Removal of sacrificial lattice support structures
Adapting the existing supply chain to account for the nuances of AM gives you the flexibility to adapt to changes in demand. Minimizing inventory and anticipating industry needs with robust equipment and material suppliers lets you grow with your customers, without the risk of substantial wasted investment.
Multiple industries have adopted AM, with varying levels of success. Aerospace was an early adopter, implementing it for small-scale parts with many complex joints and features. As an alternative to conventional fabrication methods, additive manufacturing provided a significantly lower-mass alternative for castings, the incumbent process for that type of application.
With weight reductions at or exceeding 50%, AM offers significant opportunities to reduce material purchase, increase fuel economy, and increase power in aerospace applications. These are three enduring metrics that increase the viability of innovation in this space. Companies such as Autodesk and Pratt & Whitney have capitalized on the advantages of AM for aerospace applications on recent product offerings such as fuel injection nozzles, collectors, and fasteners made from nickel and titanium to reduce the total engine weight.
In addition, aerospace implementations of AM have also shown its suitability for plastic parts. Traditional manufacturing methods for metals, many of which companies have already capitalized on, are generally still more cost-competitive than AM. However, AM is less expensive than injection molded plastics up to quantities in the tens of thousands. Efficient manufacturing of plastic parts has been a transformative step in the medical device industry as well.
Having used AM primarily for titanium implants for joints and skeletal structures, the medical device market is expanding the process to fully synthetic transplant organs. The ability to mitigate wait times for transplant organs would be a momentous achievement and one the industry sees becoming viable in about five to 10 years.
Laura Gilmour, global medical business development manager for EOS, shared insight as to the coming trend in medical device applications of AM. “Point-of-care manufacturing seems to be the next big question for the orthopedic field, with the FDA [Food and Drug Administration] sharing some initial risk-based approaches. Additive manufacturing opens new considerations for a supply chain, which hospitals and providers seem to want to take advantage of in the near term.”
Employing AM technology is leading the medical field to push the boundaries of end uses, and compelling regulatory bodies to set the rules for how design engineers can develop creative, transformative, and rapid solutions to time-sensitive patient needs.
Aerospace and medical devices are examples of trend-setting industries pushing AM forward. Other markets using the process include transportation, power generation, oil and gas exploration, chemical processing, and electronics. The lessons learned from use in aerospace and medical devices show that testing AM on rapid prototype quantities with complicated joints enables sufficient validation and design robustness before mass manufacturing. Mass-sensitive industries that can tolerate above-average cycle times are best suited for AM.
Written by Adam Kimmel