How does 3D Printing Work?
By Hervé St-Louis
September 12, 2012 - 00:00
3D printing has been around for a few years and according to market analysts, may be the next big technology after smartphones and tablets. I think that 3D printing and related technologies, like 3D scanning will more than overtake mobile technologies in the upcoming years. It will revolutionize how we as end users relate to material objects and virtual ones. The border that separates them will shrink as our avatars will easily be able to jump from our monitors into our hands! My job in the intervening years is to do research on process. This is exciting.
In 3D printing, a 3D model is converted into a standard format called STL which is an acronym for STereoLithoography. Many 3D programs such as Maya, 3D Studio Max, Rhino3D, Lightwave, Cinema4D or Softimage 3D allow users to convert files into a variety of 3D file formats. To make sure that your particular program can save under the STL format, check with the specifications packages of your favourite program. Free (open sourced) programs like Blender do allow users to convert their files into STL and may even allow you to import files from other programs and perform a conversion through them.
Models can be built using traditional 3D modelling techniques or they can be scanned using a 3D scanner. But not all models are created equal. Models need volume and not just surface to be printable using a 3D printer. Models also have to be clean and without any bugs or open surfaces. Building such models is not always easy for 3D animators who are used to cheating their way when modeling. However, users with industrial backgrounds that frequently use 3D modeling programs such as SolidWorks will usually have better created models that have real volumes and well formed geometries. When printing a 3D model, everything counts. For example, if the normals of your model are pointing in the wrong direction, the model will be impossible to print with a printer. Normals, if you don’t know what they are, are like virtual needles that point in one direction letting the program handling the 3D model know what direction points outward. If normals are pointed inside out within a 3D model, it may appear correctly on the screen (but often not) but the model is in a virtual state of entropy.
Many sites offer 3D models that can be downloaded freely allowing budding 3D prints creators to test their skills on samples objects before using original models. As we tested our new 3D printer, this is what we did. Our lab already has more rudimentary 3D printers like a MakerBot which allows us to print 3D models with less resources and money. However our new 3D printer allows us to print with several different types of plastics and have them with polished or matte surfaces. If you’re wondering, matte surface are better for action figures because paint can adhere better. Polished piece are better when you want to give the object you’re printing a reflective surface or something that feels like metal or glass.
Our MakerBot 3D printer did not allow us to create complex object easily. We had to built them in parts and assemble them after. However, with the new printer we’re using, we can create interlocking parts such as gears or bolts within an action figure easily. We can even decide at the time of printing whether we want to print an object with a hollow surface or with a filled interior. Your tolerance about waste materials, time and budget will determine how you want to print your model. Hollow objects take less time to print and waste less plastic which means it will cost you less money. What’s this waste thing? Well, during the process of building a model, there will be wasted plastic that never makes it on the model. Such plastic cannot be melted back and reused in most systems. But the reuse of such materials is a priority research area for 3D printer manufacturers.
The printer we use is smart! It prints a model using a support material that’s made or a resin-like plastic and the actual plastic used for the model. The 3D printing software takes a model and determines using advance mathematics which angle will optimize the printing process based on X, Y and Z axes. It will rotate your model in weird ways just to save on time, material and the motion of the print head in the print box. The printer can print several models at once and will automatically calculate and rearrange the distribution of the models to offer the most optimized print job.
For our test models we printed a generic widget, then a Yoda bust and finally a wrench. Depending on the complexity of the object a print job can take anywhere from less than an hour to several hours. The Yoda bust too over 12 hours to print. The wrench took less than three hours. Every model was covered with a thick layer of support material that almost hides the shape of the object within a lattice of soft rubbery plastic. We can remove the support material which held our object with our hands but the film like texture sticks to fingers and palms easily. I found that after a few hours, the resin-like material was drier and easier to remove by hand. But for complex clean up jobs with interlocking or hollow parts, we can use a special cleaning unit where we can water spray the object with a water jet and clean the object with brushes and other tools that won’t really scratch the object. Models can be fragile. Upon removing the support material from Yoda, one of us broke his left ear. But it doesn’t matter, we can always make more!
The rest of the print process was as exciting for me. It involved the maintenance and clean up of the machine. We have to clean the 3D printer after every job to remove excess plastic accumulated on the various parts of the machine. We have to calibrate tools, measure the stock of liquid plastic and so on. This is essential to keep our 3D printer sound for years to come. For me, it felt like taking care of a good car or a bike I enjoy a lot, so it’s definitely not boring at all. There is a lot of experiment that our team will do to understand how we can use a 3D printer within our research. There are lots of future applications of 3D printing technology possible and it’s fun to be part of a team of researchers thinking about the future but also how technologies affect the present.
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