The large number of affordable machines available to hobbyists is just one indication of 3D printing’s rapid growth. Many of the lower cost products use fused filament fabrication (FFF) in which a thin filament of thermoplastic is melted and fused to previously deposited material. Instead of FFF, the stereolithography process, which cures fine droplets of photopolymer liquid with UV laser light, more often is found in professional 3D printers and produces smooth surfaces in contrast to less well-defined FFF parts.
These techniques have been joined by many others with the common theme of building an object in layers—in fact, for large industrial applications, that’s about all that is common.
What do you call it?
How closely the raw part—as it comes out of the printer—corresponds to the finished part may be a good way to distinguish between the terms 3D printing and additive manufacturing.
3D printing
In many 3D metal-printing machines, thin layers of metal powder are evenly spread across the build area and selectively laser-sintered or e-beam-melted to build up the desired item. Monolite UK has developed the D-Shape printer that operates on a similar principle to consolidate sand into solid shapes. Rather than sintering or welding, the D-Shape machine shown in the figure selectively sprays a liquid binder on each layer to form a solid structure. In addition to large terrestrial architectural applications addressed by D-Shape, the European Space Agency is investigating building protective housing on the moon using this technique and lunar soil.1
Courtesy of Monolite UK
Similarly, WinSun, a Chinese company, is building low-cost houses and buildings with 3D printing techniques. The process extrudes a mix of cement and construction waste to make the wall panels. As a recent article2 describes, “Using a machine which measures a staggering 20 feet tall, 33 feet wide, and 132 feet long … the walls and other components of the structure were fabricated offsite with a diagonal reinforced print pattern and then shipped in and pieced together. The company then placed beam columns and steel rebar within the walls, along with insulation, reserving space for pipe lines, windows, and doors.”
Additive manufacturing
In contrast to 3D printing, additive manufacturing generally produces a “blank” that requires further machining. The aerospace industry is a leading consumer of components made by additive manufacturing.
At the Cranfield University in the United Kindgom, the wire arc additive manufacturing (WAAM) technique is being developed.3 A robot welding machine moves along a computer guided path and deposits welding wire as directed. The built-up part may be strong, but it’s certainly not ready to use. On the other hand, because the part is metallurgically sound, WAAM provides big benefits for aerospace manufacturers. Typically, some parts are made by machining them from a solid billet, a process that has a “buy-to-fly” ratio as high as 10:1 or more. Even with some post-WAAM machining, the new technique still is a much more cost-effective approach.
Sciaky and Norsk Titanium are pursuing similar technologies, Sciaky via an e-beam welding process and Norsk via the company’s Rapid Plasma Deposition method. According to information on the Norsk website, “Titanium wire is melted in a cloud of argon gas and precisely and rapidly built up in layers to a near-net-shape (up to 80% complete) that requires very little finish machining. Production cost is less than legacy forging and billet manufacturing techniques due to significantly less waste and machining energy.”
Although it’s not immediately obvious that these methods impart a preferential grain distribution similar to that obtained by forging, that does appear to be the case. A detailed material test graph on Cranfield’s waamat.com website confirms that the strength of Ti-6Al-4V (titanium) parts made via multiple parallel welds exceeds the minimum specifications for wrought titanium alloy bars, wire, forgings, and rings as defined in the SAE AMS4928 standard. The graph is accompanied by the note, “WAAM delivers static properties that comply with the AMS standard for wrought products, in the as-deposited conditions.”
Yet another aerospace project is being pursued by South Africa’s Aerosud. As the company’s website states, “[Aerosud] … is currently building the world’s largest and fastest additive manufacturing system that can print titanium parts from powder. The project, named Aeroswift, … will enable the manufacturing of large titanium aerospace parts directly from powder.” Although the website doesn’t provide further details, this 3D printing technique may produce parts that require almost no further machining.
Diverse techniques
Because so many different manufacturing methods are being developed, customers should be able to choose one that has the optimal characteristics for a given application. There’s even a process developed by Fabrisonic that ultrasonically welds successive layers of thin metal tape to form a solid shape. This low-temperature solid-state welding technology has unique advantages including the capability to join layers of dissimilar metals.
References
- “Building a lunar base with 3D printing,” ESA Space Engineering and Technology, Jan. 31, 2013.
- Sevenson, B., “Shanghai-based WinSun 3D Prints 6-Story Apartment Building and an Incredible Home,” 3Dprint.com, Jan. 18, 2015.
- Halterman, T., “Metal Additive Manufacturing to Impact Aviation,” 3D Printer World, Dec. 31, 2013.
