In recent years 3D printing has received much attention, promising to revolutionise manufacturing, and completely overturning the way we produce items. As with many emerging disruptive technologies, a lot of the coverage in the popular press is exaggerated, more like a Star Trek replicator than the actual processes.
However, whether some of the wilder claims pan out or not, for designers 3D printing does offer a tantalising prospect: the capability to produce objects without the constraints of traditional manufacturing, the capability even to fabricate objects on your desk without traditional making or engineering skills.
By the end of this article you will have been introduced to the terminology of 3D printing and have an idea which method is best for you. First we will discuss the three most common technologies, and then some options in designing a model.
3D Printing Technologies
It would be incorrect to think of 3D printing as a single technology. Instead it is a set of technologies following a shared idea of additive manufacturing driven by software.
So what is additive manufacturing? Many manufacturing techniques start with a block of material and selectively remove it until we are left with the desired object. Additive manufacturing turns this on its head, starting with a blank canvas and adding only what is required for the final object.
In itself this additive manufacturing is nothing special—a child building sand castles on the beach is using additive manufacturing. It is the addition of using digital technology for a reliable and accurate result that makes 3D printing special.
Typically this works by slicing an object we wish to create into thin sections and building these slices one at a time, stacked on top of each other. Think of building a pyramid as a series of square buildings, each smaller than the last, stacked up to make a 3D shape.
FDM: Extruding Filaments
The first technique we will look at is FDM, Fused Depositional Modelling, or FFF, Fused Filament Fabrication if we want to avoid trademarked terms. It relies on “extruding” a filament of material, i.e. heating it to a point at which it can be squeezed through a nozzle, producing an even thinner filament. This nozzle is moved over a surface, drawing the outline of the slice we want to create, then filling this outline with a pattern of material.
Because the material is hot as it is extruded, it bonds to any filament already laid down, forming a solid slice of material. Once complete, the nozzle moves up a small amount and starts extruding the next layer.
This is the technique you will find in most hobbyist 3D printers, typically with the material being ABS or PLA plastic. The technique produces a “wood grain”-like surface with slight grooves between each layer (although this can be removed by sanding, polishing or acetone vapour). Imperfect calibration of a machine can result in strands of filament protruding in places or blobs of molten material.
The technique can struggle with overhanging shapes. Since it is building on top of the layer below, anything overhanging is extruded onto nothing but air! As long as we don't need to overhang too far, the material will support itself and not sag too much. However, commercial machines tackle this with a support material that is extruded from a second head, built as a scaffold to support any overhangs which can be snapped or dissolved off afterwards. There are some hobbyist attempts to replicate this, but they tend to be less reliable.
SLA: Setting Resins
The next technique, Stereolithography or SLA, relies on photo-sensitive resins, photopolymers, materials which change from liquid to solid when exposed to (usually ultra violet) light. By exposing each slice of the object on the surface of a thin layer of the liquid with ultra-violet (UV) light, we can harden just the parts we want. This hardened resin is repeatedly flooded with another thin layer of liquid and then exposed with UV light in the shape of the next slice of model, to leave a hardened 3D structure once we drain off the fluid.
The method of UV exposure differs: some SLA printers use a laser, steering it over the surface to draw the slice, while others use a DLP projector to expose an entire layer at once.
SLA more easily produces a smoother, higher resolution print, but tends to be more expensive. It has the same issue of overhangs, and parts tend to be built on a scaffold made of the same resin as the built object, necessitating quite a bit of clean-up sanding.
A lot of “model making” type prints in the professional world of 3D printing tend to use this technique, and there are a lot of photo-polymers now available mimicking different materials. Until recently patents limited this technique to professional machines, but machines accessible to hobbyists have appeared over recent years, and with this, cheaper resins have also appeared. That being said, the technique uses gloopy chemicals with limited life, so I don't think it'll completely replace FDM in the hobbyist sphere.
SLS: Melting With Lasers
The very best 3D printers again use a laser, but this time at a higher power, either melting or sintering powders together (sintering is when you heat a material enough to fuse it together, but not quite enough to fully melt it into a liquid).
These powders can be engineering grade plastics such as Nylon, or even metals, allowing 3D printing of parts suitable for machinery. If you see a news article about Formula 1 racing teams or rocket manufacturers using 3D printing, this will be the type they mean. Very high resolution and very strong, but typically rather expensive.
These types of machines are usually used as an alternative to traditional engineering techniques and, although expensive, can be cheaper than traditional techniques for one-off parts or small production runs.
Other 3D Printing Technologies
These three technologies are in no way exhaustive. You can get printers that deposit drops of wax, producing a model that can be cast into a mold for metals (often used for jewellery). You can use technology similar to an inkjet printer over a vat of powder, to deposit a binder and pigments, making full colour models. Or a very similar technology followed by glazing to make ceramics (plates, cups, etc.). Even more specialist 3D printers can lay down bio-compatible materials to print living tissues for implantation, nanoscale objects to make tiny machines, and giant machines building sections for architecture.
3D Printing Materials
For the widest range of materials, look to a 3D printing service with a range of machines, for instance Shapeway's offering. You're looking at a number of plastics, metals and ceramics with different properties to suit what you're trying to make.
Excellent, you may think—I don't need to care how it works, as long as it works! But there's the catch: look at each material they offer and you'll see they all have different requirements, minimum wall thicknesses, minimum surface detail sizes, minimum clearances, etc. You might find you need to tweak your design to work with the material you're using.
If you go the other direction, getting a hobbyist 3D printer, you are a bit more limited, but not as much as you might expect. There's a range of filaments out there now that'll work on this kind of machine. There are flexible filaments, wood-like filaments, translucent materials, and plastics with all sorts of differing characteristics.
Beware, however: these materials will usually need a bit of tinkering with temperatures and possibly even alternative parts in the printer. Most people with these sorts of machines like to tinker with such things, however.
Modelling for 3D Printing
There are two big approaches to 3D modelling: surface modelling and solid modelling.
- Surface modelling typically represents an object as points, edges and faces.
- Solid modelling instead, as the name suggests, maintains a representation of the inside of the object. Solid modelling is typically harder for the programmer to write and more limiting to the designer to model in, and for this reason most modellers aiming just to render images from a 3D model will use a surface modelling package.
For 3D modelling, either can be used, although there are caveats to that. Remember that the software will aim to slice the model into sections and must know which is the inside and outside of those sections. Obviously a modelling package which represents objects as solids will be unambiguous which is which, but surface modelling can produce files where it isn't so obvious.
There is a very strict approach you
must take to produce valid files with such software, quite unlike the
usual approach for making a model to render. In brief the file has to
be “manifold”, i.e. no intersecting faces, no internal faces, no
holes, and all vertices welded not just very very close. The model
would have to be water tight if you made it from plastic sheets. Try
following this guide for more details.
So unless you're already skilled with surface modelling, I'd suggest having a go with a solid modelling package. Although they are less expressive, there is less to go wrong for your first attempt!
I tend to use Solidworks, but it is rather expensive. Thankfully with the rise of 3D printing comes a matching proliferation of free solid modelling packages. The company that produces AutoCAD, another expensive but very powerful 3D package, offers a few packages. Of these, some of most useful for this purpose are Tinkercad, a basic browser-based CAD package, and 123D Design, an offline tool with similar capabilities.
Whichever tool you use, you'll typically need to end up with one or more stl files. This is a very basic file format, but what most 3D printing tools will accept.
Producing Your 3D Print
So you know some of the technologies, you know some of the software, perhaps you've even made a file, and you just want to know how to get it printed already! There are a few ways you can go here: you can invest in a machine, you can use a 3D printing service, or you can find somewhere to use a 3D printer. Each has pros and cons.
Buying your own machine can be quite an investment, although a lot less than in the past. You'll be limited to the one technology your machine uses, and hence the one (or a few) materials used in that technology. Assuming you're not made of money and have been able to get a professional machine, you may have to delve into the techy side of your machine if anything needs to be replaced or recalibrated, although many hobbyist machines have excellent online communities to support this.
However, having said all that, you'll have the cheapest option per part you want to make, so if you get hooked you can churn out parts to your heart's content. And you'll be able to rapidly iterate parts—if you're anything like me and you're making multiple parts to join together, you'll get something wrong the first time you make it!
Another option is 3D printing services, either online or your local 3D printing company. This has the benefit of no upfront cost (although it is considerably more expensive per part), and a range of technologies and materials available. The other main downside beside the cost is time, because you'll have to wait for them to make it and ship it to you. There are a few big services out there, such as Shapeways or iMaterialise, but shop around and find the solution that has the best balance of price and speed for you.
The third option is a halfway house between these, but is dependent on finding a 3D printer you can use locally. The maker movement has resulted in lots of local maker spaces, which may have machines available at the cost of entry and material, or even just someone who's willing to trade time on a machine for 3D modelling skills for their projects. Look into it!
Or you can do what I do, and do all of these! Quickly test models on your own machines, send files off for alternative materials, and get involved with local makers and students to make things.
So you now know a bit of the terminology, some of the options, and the pros and cons of each. Go forth and 3D print something interesting. Also be sure to keep your eyes open for future tutorials delving into some of the details more closely. If you have any questions, post them in the comments!
For your first step into 3D printing, why not try using a 3D printing service. Try out our tutorial on creating a 3D printed mobile phone case.
Preview image credit: Seth Woodworth via Flickr
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