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A Short Primer on 3D Printing

by Elliot Gindis

3D printing is not really “printing” as most people use and understand that word; a more descriptive name is additive manufacturing. It is a process where material is precisely ejected from a specialized computer-controlled machine and added together, layer-by-layer, until a 3D object is produced. The data source used to create this object is a 3D CAD model, or sometimes a 3D scan of an existing object; and the material used in the manufacture can be almost anything, as long as it is suitable for projecting out of a nozzle or something similar (a liquid, gel, or powder would work). It must then, of course, be able to solidify into a stable physical object that you can handle and use. That, in simplified terms, is the essence of 3D printing.

This technology has received a lot of publicity in recent years, but it is not as new as it seems. Evolving from the science of stereolithography (pioneered by Chuck Hall in 1984), early versions of additive manufacturing machines used soft polymers (plastics) as the source material. These polymers would be melted down before passing through a nozzle and solidify (or were cured) rapidly after being built up into layers, eventually forming an object. Polymers remain the most popular source material, but other materials (even edible food items) were used in the 1990s and 2000s, as the technology matured and dropped drastically in price. There are now home-based, relatively affordable 3D printers for hobbyists and entrepreneurs. Uses for 3D printing vary widely, with primary applications in product development, prototyping, biotech and dental devices, art, and education among others. It is a rapidly growing field, and one to keep an eye on.

There are four distinct parts to a 3D printing process, as described next.

Printing Process – Part 1 (Creating the Model)

The first step in creating a 3D printed model is to create a viable model of what you want to make. You can go about it in several different ways. The most direct is to design something yourself from scratch via any of the popular 3D solid modeling software packages, such as CATIA or SolidWorks (you can of course use AutoCAD as well!). Alternatively, you can go on one of several 3D printing “marketplace” websites from companies like Thingiverse, Shapeways, or Threeding and find, trade, or buy a premade model of something you want. Finally, if you want a 3D model of something you already have (in other words, you just want to replicate it), then you can also do a 3D scan of the object via a 3D scanner. These types of advanced scanners use lasers or soft touch probes to map the surface shape of an object, creating a resultant point cloud, then use a reconstruction process to build up a 3D model of it.

Printing Process – Part 2 (Exporting and Preparing the Model)

Once the model is created it needs to be exported to an STL (STereoLithography) file, which is the native language format for 3D printers and generally most computer-aided manufacturing and rapid prototyping software. Most solid modeling and drafting software can export out to STL, including AutoCAD.

There are a few ways to export your model in AutoCAD. The most basic way is to just select File→Export, then choose the *.stl format from the drop-down menu at the bottom of the dialog box. You can accomplish the exact same thing by typing in “3dprintservice” and press Enter or select Publish→Send to 3D print Service on the Application menu (the AutoCAD symbol at the upper left).

However, if you use this approach, then exporting is not the end of the model preparation; you need to now “slice” your model. This converts it to a series of thin layers and generates the code needed to by the 3D printer. Several commercial and open-source slicers are available, such as Skeinforge, Cura, and Simplify3D.

Starting with AutoCAD 2017 there is another option – but only if you are running a 64-bit system; you are out of luck on a 32-bit one. This new approach is a separate application called Print Studio. It shipped with AutoCAD 2017 (should also come with AutoCAD 2018) but needs to be installed separately. If it is there, you will see the symbol for it in the Output tab of the Ribbon (in the 3D Modeling Workspace) or you can use the Application menu, Print→3D Print. If it is not installed, you will be given the opportunity to install it. This application preps up your model and sends it to a 3D printer, if one is hooked up to your computer. If your AutoCAD has it ready to go, try it out!

Printing Process – Part 3 (Printing the Model)

The actual printing itself is almost fully automated and is the relatively easy part of the process, where after hours of designing and testing a model (if you did that versus just purchasing one), you finally just get to watch it being built. There are a number of popular printing approaches of varying complexity and cost. Many of them continue to use historically proven polymer, powder, gel, or small beads as source material, heated up for easy passage through an applicator nozzle then rapidly cooled to form the solid object. The source material may be coiled up and unfurled into the nozzle mechanism (or be gravity fed from a hopper) at a steady pace.

Extrusion deposition uses this exact approach with polymers, which can be styrene, polycarbonate, polyethylene, or polystyrene. Other methods use liquids or, in the case of bioprinting (an active research field), even living tissue.

Regardless of the source material, the actual printing process is very similar. The movable nozzle passes over the base plate (on which the model rests), ejects material, and builds up the model one pass at a time, using the slices as a guide. The printer size varies widely, from smaller “desktop” units to larger commercial machines, including a very large unit called the Big Area Additive Manufacturing (BAAM) machine, used in several industries such as aerospace.

Printing Process – Part 4 (Finishing Model)

Once the model is completed, depending on the material, it may need to sit on the base plate for a while to cure fully. It then needs to be “finished,” which can range from just a quick polish all the way to additional material removal. In latter case, material is removed because the model is printed slightly oversized. This is because a greater degree of accuracy and resolution can be achieved in the final product by removing some material in a secondary step, as opposed to trying to achieve this in the original manufacturing process. Finally, these 3D models can be coated, painted, or otherwise “post processed” for use or display.

Applications, Related Issues, and the Future of 3D Printing

Needless to say, all of this just scratches the surface of this emerging technology. 3D printing has already found use in the manufacture of consumer apparel, automotive body panels, construction blocks, hand tools, medical implants, and of course extensive use in art, design, and for educational purposes.

The overall speed with which the model can be built is not all that fast, thereby limiting the usefulness of 3D printing in mass manufacturing. This, however, is likely to be overcome in the future; and already machines with multiple applicator heads are making use of faster curing materials. Other machines use multiple types of materials at one time.

The technology has had its share of controversy as well. With lower cost do-it-yourself 3D printers becoming widely available, issues of intellectual property, trademarks, and copyrights have arisen. There has been some concern as well of 3D home manufacturing of plastic guns that can evade detection at airports. Social commentators have written about a new approach to manufacturing, where almost anyone can be a producer of an in-demand product and a centralized factory no longer is employed.

As stated earlier – and it bears repeating – this is a rapidly expanding field and one to keep an eye on.

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