Saturday, 16 May 2015

How 3D Printing Works. A Beginner’s Guide

How 3D Printing Works

What makes this fascinating technology tick?

3D printing has been around for some years now, but its nature as a specialist part of the computing canon (no printing puns intended) means many of us only have a cursory knowledge of how it works and what’s involved.

As 3D printing becomes more common and more prominent in our daily lives, it’s worth going back to basics to make sure you understand the ins and outs of 3D printing, from the materials and processes involved to the hardware terminology. If you’ve never touched a 3D printer, don’t worry – this guide will make you feel like you know exactly what goes where and why.

What Is 3D Printing?

Let’s start with the basics. A 3D printer is exactly what it sounds like: a device that can ‘print’ 3D objects out of a specific material – usually a form of thermoplastic, but it can also be a number of offbeat alternatives, from chocolate to stem cells. Any material that can be turned from a liquid into a solid quickly enough can be used to 3D print things.

Just as printers move a print head back and forth, depositing blobs of ink on a page, 3D printers move print heads back and forth, as well as up and down, depositing blocks of material to build up a 3D model layer by layer. It’s a bit like making a loaf of bread by baking one slice at a time and assembling the full loaf piece by piece. You essentially turn a collection of 2D ‘slices’ into a 3D ‘loaf’ – only instead of slices of bread, it’s slices of plastic (usually).

This can be accomplished in one of two ways. The most common way is for a printer to accept a thermoplastic filament, which is melted into a liquid, extruded through a nozzle and then allowed to quickly cool back into solid plastic. A second technique uses powder that is laid onto a surface like standard ink and then quickly melted using a laser or other heat source, similar to the way a laser printer fuses toner to paper.

Where normal printers are used to turn on-screen text into text on a page, 3D printers accept 3D inputs, which can be created using modelling software or, more frequently, downloaded from the internet. 3D print models can be incredibly complex, to the point where it’s possible to create working joints and hinges in a single go.

It might sound gimmicky, but the possibilities are considerable. If you break something important, like a connector for flatpack furniture or part of a toy only to find that it’s inconvenient or impossible to replace, you could simply use your 3D printer to replace it. The dream most enthusiasts imagine involves a Star Trek-style future where you don’t have to go to a shop to buy an item; you can simply 3D print it at home, to the exact requirements you have.

The benefits of this are clear in individual cases: you don’t need to wait for a factory production line to create your bespoke items, and you can create parts that might otherwise not be sold, but the economics don’t necessarily line up. At present, 3D printing costs mean anything you create will be more expensive than buying it (assuming that’s possible), and in most cases the item won’t match the quality of factory-produced goods. The range of materials is also quite small.

But like any technology, the affordability of 3D printers and their materials are bound to improve, as will the capabilities of the technology itself. While the 3D printer may never be an essential piece of home electronics like the TV or computer eventually became, certain individuals and businesses – designers and engineers – will get huge benefits from having them around. One day, the idea of having to wait for replacement car parts to be delivered could be replaced by simply having to wait for them to print. They might not make it into the home, but by the end of the decade, it’s a safe bet that they’ll have made it into your life one way or another.

3D Printing Terminology

As with any specialist area of technology, 3D printing comes with its own terminology and language. It’s hard to discuss the topic unless you’re equipped with the right language, so before we go any further we’ll explain some of the most essential concepts and hardware you might encounter.

• Bed/Build-Plate
The ‘base’ of a 3D printer, which is where the first layer of the object is laid down. Beds can be either heated (hot beds) or unheated (cold beds). Hot beds are more expensive and power-hungry, but prevent uneven cooling of the printed material, which can cause cracks and warping.

• DIY/Self-Build/Kit Printers
The enthusiast nature of the 3D printing industry means it’s not uncommon to have to assemble a 3D printer yourself, even if a company provides the parts for you. Some 3D printer kits actually require you to print parts yourself once the printer has been partially assembled!

• Extruder
Extruders are the 3D version of a print head. They consist of a cold end, which pulls in the build material, and a hot end, which melts and extrudes the material so it forms the object you’re trying to print.

• Filament
Most build material comes in the form of filament, a thin plastic wire that is supplied in a spool. Be careful of context, as it may also refer to the heated wire at the hot end of the extruder. Filament designed for home use is most commonly made of either PLA or ABS, both of which you can read more about in our next section.

• Raft
While you can print objects without a base, some people prefer to include a ‘raft’ in their designs. Rafts are disposable bases that are printed onto a build plate first, so the object can be printed on top of it. Rafts provide greater adhesion and reduce the risk of warping, though the cost of this is that they must be manually removed once the item is complete.

• Build Area
Just as normal printers have restrictions about how much of a page they can physically print on, 3D printers have limitations about the size of items they can build, which are determined by the bounds of the X, Y and Z tracks of the printer. The easiest way to think of it is that if you have a box the size of a 3D printer’s build area, any individual part you make will be able to fit inside it.

• Resolution
This can be either horizontal (XY) or vertical (Z). Horizontal resolution is sometimes called ‘feature’ resolution and refers to the smallest movement the extruder can make on a layer. The smaller the better. Vertical resolution (also called ‘layer thickness’) is the minimum thickness of the layers that the printer can create. Smaller thicknesses are better for creating a smoother layer, but the thinner they are, the more each object requires and the slower the print speed.

Filament ABS

Filament: ABS

Home 3D printing filaments come in two different materials, ABS and PLA, each of which has its own strengths and weaknesses. Both are thermoplastics that melt under high temperatures but quickly solidify once the heat is removed, and that property makes them perfect for 3D printing. Assuming your hardware supports both types, the main question you have to answer is which is more appropriate for the item you’re trying to print. And if you don’t know the difference, allow us to explain.

ABS (acrylonitrile butadiene styrene) is the older of the two materials. The temperature at which it starts to soften is quite high, 40ºC (100ºF), which means there are home uses for which it would be suitable where other materials wouldn’t. A hot drinks coaster would definitely be in trouble of losing its shape if made with PLA, and so might a phone case or laptop stand depending on how hot your device gets. ABS should withstand such heat easily.

To use ABS properly, a printer needs to heat its filaments to at least 100ºC (210ºF) and a heated bed of around 26ºC (80ºF). ABS is relatively slow to cool, so in its fluid state it’s doesn’t tend to clump together and form jams or clogs, but it does shrink a little as it sets, which can cause some items to lift from the bed or even split between layers when the object gets tall enough.

The use of a heated bed can help prevent cooling problems with ABS by making sure the object doesn’t cool too quickly, and enclosed-case printers also trap warmth and eliminate drafts. That way, the object cools evenly and is more likely to remain intact.

Once cooled, ABS is very resilient. If printed correctly, it’ll bend rather than snap, and its flexibility makes it a popular choice for bracelets and other wearables. It’s rugged enough for phone cases and toys, and it can put up with the high temperatures inside cars during summer, so unless you’re taking it into some seriously extreme conditions, ABS should cope with whatever you throw at it.

One of the problems with ABS is that it emits strong fumes during printing. They’re not poisonous in any quantity that would be generated during normal use, but the smell is strong and may overpower some people. Ventilation will definitely help, but if you’re sensitive to smell, then it’s definitely worth taking into account when you decide which material to go for.

Filament: PLA

The alternative material is PLA (polylactic acid), which has the immediate benefit of smelling much sweeter when it prints – a little like acetone. PLA prints at a slightly lower temperature than ABS – 80ºC (180ºF) – and while it works fine without a heated bed, you can improve the reliability and quality of your print by running one of about 15ºC (60ºF).

The main problem with PLA is that it becomes malleable at a much lower temperature than ABS, which restricts its use. You can’t use it as a phone case, because most phones would get hot enough to turn it into plasticine. But that’s not all: PLA is also more prone to jamming in the hot end of the printer, because it expands and turns sticky when it’s heated up. PLA users are advised to oil the hot-end regularly to prevent jams.

Another problem is that when cooled, it’s also slightly more brittle than a lot of other plastics and certainly doesn’t have the durability of ABS. Anything with thin parts and fine features (such as spikes or pegs) is likely to be vulnerable to damage if dropped or knocked. That’s not to say it’s too fragile for any practical purpose, but certainly, compared to ABS, it’s not quite as versatile.

Given these disadvantages, the reason PLA is used is because it’s a lot less sensitive than ABS. You can use open-frame printers without a hot bed and not have to worry about warped or cracked items, and that means you can see exactly how your item is being put together as it prints. PLA also has the benefit of being biodegradable. It’s not so much that you’ll see it fall apart in a matter of weeks, though, so you can still use it for outdoor materials. PLA needs heated composting to decompose, and it’s not soluble, so you can leave it outdoors or dunk it in water without having to worry.

At this point, it’s worth making it clear that while most printers can use either material, not all printers can. Any printer capable of using ABS filament should be fine with PLA filament, but printers intended for use with PLA filament may struggle to reach the temperatures required to use ABS – not to mention that it’s common for PLA printers to lack a heated print bed, which is bad news for ABS, while PLA is not negatively affected by the lack or presence of one. In any case, it’s worth checking for definite whether your printer is compatible with the filament you want to use. If you get it wrong, you could end up with a very expensive mess on your hands!

Getting Started?

If you’ve made it this far through the article, you should understand the basics of 3D printing hardware, terminology and technologies, but there’s still a lot more to get to grips with, much of which can only be learned by doing. 3D printers aren’t cheap, but it’s not impossible to get one for a few hundred pounds, which isn’t a bad entry-level price for a hobby. We’d recommend sticking to small consumer units to begin with and maybe even trying the software out before you buy one. It’s definitely a complicated thing to do with your time, but look at it this way: if you can master 3D printing, now you’ll be ahead of the curve when it really takes off!