It wasn’t so long ago that 3D desktop printing machines churned out novelty figurines. Novelty being the key word. Since then, we’ve seen industry-scaled projects take hold of the technology, with projects like this stainless steel bridge spanning a canal in Amsterdam, every inch of it sinuous and meticulously deposited by robot arms. Can the same, then, be said for complex mechanical parts?

From Porsche using AM technology to create lighter, load optimized pistons, to additive metallic manufacturing forming the backbone of next generation, ultra toughened hypersonic engine components, this material stacking and bonding process is highly versatile. It has already proven itself, securing its rightful place as the missing link between intricate parts geometry optimization and the fast realization of high-performance engineering standards, leapfrogging the limitations of conventional forging methods.

What is additive manufacturing?

An engineer’s handbook with this title would say that additive manufacturing (AM) is a process for buildingCAD Interface. Source: Caddiv CC0 1.0 three-dimensional objects, layer by layer from digital models. A CAD program, like this software suite made by hp.com, does all of the development work. Unlike traditional subtractive methods (e.g., machining or forging), which remove material to shape a part, AM adds material, enabling unprecedented design flexibility and complexity.

The same handbook would then go off on a tangent, spitting out strange acronyms that only make sense to industry insiders. Like PBF, Powder Bed Fusion. With the CAD software having output the model as an STL file, sliced into thin horizontal layers, metal powder is laid in a bed and stacked. A sintering energy source bonds the layers, using selective laser sintering (SLS), direct metal laser sintering (DMLS) or some kind of electron beam. It’s a lot of acronyms for the human mind to process, but it basically translates to an innovative building block manufacturing workflow, the architecture of the stacked layers resolving into incredibly intricate mechanical parts as the build platform and sintering heat source continue to deposit the many impossibly thin layers.

[Read more about additive manufacturing at GlobalSpec.]

Current additive manufacturing technologies

Other manufacturing methods that align with this approach include the following:

• Direct energy deposition; A weld machine-like device that’s more commonly used in large-scale additive manufacturing workloads. Uses an electron beam or laser to deposit the layers. Not as detail oriented as PBF.
• Material Extrusion: Used for thermoplastics, not currently built to favor mechanical resilience. Lower resolution geometries. Of some interest in the ceramics sector, C-FFF (ceramics fused filament fabrication) is being explored as a means of manufacturing mechanical parts with high temperature ratings.
• Vat photopolymerization: Produces high-detail parts using liquid resin (e.g., Stereolithography). Almost completely utilized in the medical and dental sector, but R&D indicates mechanical potential. By adding composite metal resins to the photoreactive medium, unsurpassed machine parts resolution is possible.

To reiterate, AM is an evolving method of depositing layers of material and binding those layers via sintering or chemical bonding. For metal additive manufacturing (MAM), DMLS and SLM are both entirely viable options for producing complex mechanical parts.

A focus on DMLS and SLM as functional AM solutions

Hoping our readers aren’t tired of the many acronyms, two more have been thrown in as industry transformative technologies. DMLS and SLM are two of the most popular methods for applying AM processing at the moment. DMLS uses lasers and powder stock, sintering the layers to produce high tensile components. SLM, on the other hand, completely melts the part, the layers then solidifying as they cool to leave an intricate component geometry that’s both incredibly well defined and packed with mechanical strength. No layer boundaries are evident, so component yields can handle great physical stresses and shearing forces. Electron beam manufacturing (EBM) is similar to SLM, except the process is conducted in a vacuum, reducing the possibility of oxidation in reactive metals.

Low pressure turbine blades and other aerospace parts are made at the GE factory in Cincinnati using EBM manufacturing. The parts made here feature amazing aerospace characteristics, like lighter and thinner GE aerospace plant in Ohio. Source: GEwalls, yet inherent alloy strength is maintained. Multiple components and fastening mechanisms would have been used in former forging techniques, introducing potential weak spots, but additive manufacturing has reduced assembled parts to one or two while still incorporating highly detailed fuel and gas guiding channels inside the parts.

Additive manufacturing is redefining engineering

The medical sector, reliant on micron scale engineering standards, has also embraced AM, but it’s taken time to solve FDA acceptance hurdles, those associated with material compatibility and sterilization challenges. To be blunt, some of the surfaces created by this process can be rough or porous, presenting difficulties in maintaining sterility. These challenges have spurred innovation, leading to the development of more advanced post-processing techniques and material formulations that meet strict regulatory standards.

Gradient coils and intricate cooling systems in hospital MRI machines are already using elegant AM design to eliminate past productivity bottlenecks while simultaneously increasing performance. Defined by special non-uniform coil shapes that are densely packed with wires and ceramic insulators, 3D additive manufacturing takes the stress out of this intricate production equation. Of course, new technologies mean new challenges. Surface finishes are one, then there’s strength and material elasticity.

These are all taken care of by heat treatment on forged and machined parts, a process that’s also viable on deposited components. However, the challenges are different. Homogenous by design, forged parts tend to expand and contract evenly. Distortion and warping is a distinct hazard that must be accounted for when heat treating AM made components, especially when they have a complex architecture.

Measures have been taken to account for factors like residual stresses and unique layered microstructures. The heat treatment workflow improves the properties of AM parts, including their internal structure and potential porosity, minimizing warping, ensuring uniform density and optimizing mechanical strength. By fine-tuning these variables, engineers are able to enhance performance, durability and reliability, making AM components more suitable for demanding applications.

Looking at projects like SpaceX's SuperDraco Rocket Engine, It’s an exciting time to be an engineer involved in the refinement of new additive manufacturing methods for creating complex mechanical parts, hopefully while not generating any more of those puzzling acronyms in the process.