SciTech

Additive manufacturing has revolutionized production

Credit: Wikimedia Commons Credit: Wikimedia Commons

In the early 1980s, Hideo Kodama of the Nagoya Municipal Industrial Research Institute developed and implemented advanced methods of printing that were able to construct 3D objects out of plastic polymers. The processes were revolutionary and were the basis for a large shift in the manufacturing and engineering industry today. The techniques became known in industry as additive manufacturing (AM) and are more commonly referred to today as 3D printing.

Kodama figured out a way to expose certain areas of photo-hardening polymer to ultraviolet (UV) rays and wash away the unhardened polymer. What’s left behind after the wash is the hardened 3D structure. The most difficult challenge in developing these techniques is finding a way to accurately and precisely restrict the material’s UV exposure. The 3D structure to be printed is first diagrammed and prototyped as a collection of extremely thin, 2D cross sections. Today, computer-aided design (CAD) software is capable of slicing 3D models into the required 2D segments. After individual diagrams of each 2D layer is prepared, the exposure process can begin. An extremely thin layer of the hardening polymer is laid down, and a selective laser maps out and hardens areas of the polymer as per the diagram. A second thin layer of the hardening polymer is added directly over top of the layer just previous, hence the term “additive manufacturing”. This process of layering and lasering is continued, sometimes repeated thousands of times, gradually producing the 3D structure from the bottom up.

Photo-hardening polymers used by Kodama and others could only be used to form plastic objects, not metal. Until the 1990s, all metal-working techniques, such as casting or welding, were subtractive in nature; material was removed from a stock, not added, until the desired shape is reached. The lack of stability and longevity in large plastic objects prompted researchers and engineers to look for ways to apply AM techniques to metal. By the late 1990s, engineers at Stanford University and Carnegie Mellon University developed ways to deposit metals and other materials so that they can be assembled additively. These developments, coupled with the improvement of 3D printers themselves, meant that more durable, long-lasting products could be created. As a result, 3D-printed structures aren’t restricted to prototyping and are now used for end-of-the-line consumer goods and products.

One of the largest improvements on the AM process in the last decade has been focused on the back end of creating the 3D model. The accuracy and precision of each round of “printing” relies heavily on the accuracy and precision of the digital model that is sent to the 3D printer or other additive machining device. Improvements in computer-aided design software have made 3D printing a much more seamless process. In the last decade, these improvements have allowed engineers to redefine existing printing processes and introduce a variety of new techniques.

Of the many methods used in practice and industry today, the most popular are Stereolithography (SLA), Binder Jetting, Fused Filament Fabrication and Extrusion, and Powder Bed Selective Laser Sintering (SLS). The latter is closely related to Kodama’s original technique.

SLA utilizes liquid ultraviolet resin that, much like Kodama’s plastic polymer, solidifies when exposed to UV laser beams. Rather than laying out thin sheets of polymer, the liquid is poured into a large vat, and the laser is directly toward the bottom of the vat. The laser solidifies the necessary shape and works its way slowly upward to create the full structure.

Binder Jetting also uses a powder polymer base material that is thinned out into 2D layers. Rather than using a laser like the other methods, Binder Jetting uses a liquid binding adhesive that is piped out through a jet nozzle. Material science engineers have been able to adapt the Binding Jetting method and use it to pipe out molten glass into ornate glass figures.

Fused Fabrication employs a jet nozzle like Binder Jetting, but rather than using a liquid adhesive it utilizes two separate materials. The first material is dissolvable, and the second material is not. The jet nozzle passes over a grid, and at each grid location it deposits one of the materials. Using CAD data, the printer determines where to deposit the dissolvable support material and where to deposit the material that will solidify into the final product. After the object is fully printed and hardens, it is soaked in a solution that dissolves away the support material and leaves behind the desired shape.

What started out as an efficient way to rapidly assemble plastic, back-end prototypes has emerged as an industrial, top-of-the-line technique for researchers, designers, and engineers on a global scale. Additive manufacturing is a quickly growing field and its promise and potential are far-reaching — from the 3D printing of nanoscale medical devices to large scale art installations to the rapid assembly of computer hardware. It is likely that the next big break for additive manufacturing is scientists ability to 3D print functioning human tissues for medical use. The future of additive manufacturing is on the rise — literally.