Here we continue our feature on 3D printing. Here are three different techniques used by today's 3D printers.
One of the first technologies to be used for 3D printing is called stereo-lithography or alternatively light polymerisation. In this method a thin layer of liquid chemicals is introduced into tank and a laser beam scans over the surface of the liquid.
Because the light, which is more commonly ultraviolet light, causes the liquid to turn into solid plastic by polymerisation, the laser beam is turned on and off as it scans to selectively solidify those parts of the liquid that correspond to a layer of the object. Once this first layer is complete, additional liquid is added which the laser beam scans again to create the second layer which adheres to the first.
The process continues until the solid object is finished. The disadvantage of this method is that if a layer has solid parts that were not present in the previous layers, as soon as those parts are solidified by the laser they’ll drop to the bottom of the tank because they’ll have nothing to support them. This can be overcome by adding supports that are not actually part of the object and which, therefore, have to be removed afterwards.
Fused deposition modelling
A second up-and-coming method, especially for low-cost desktop printers, goes by the rather unmemorable name of fused deposition modelling or occasionally the somewhat more descriptive title of fused filament fabrication.
Here a thin plastic filament is heated and extruded through a nozzle which moves around to build up each layer. Like light polymerisation, parts of objects that are not supported by lower layers can cause problems although the plastic solidifies quickly enough that small overhangs can be tolerated.
It is also possible, with those printers that have multiple nozzles and can therefore print in more than one material, to print supports using a different type of material such as PVA that is soluble in water and can, therefore, be washed away once the model is complete.
Selective laser sintering
The final common method, and one of the most commonly used by 3D printing bureaux, is called selective laser sintering. This works in a similar way to light polymerisation except that powder is used rather than liquid. When heated by the laser, the powder sinters or, in other words, it fuses together to form a solid. Various types of material can be used and the list continues to grow.
Common materials include plastic, metal and ceramic. Because the un-sintered powder in each layer can support solidified material in the layer above, there are no problems with unsupported portions of the object.
3D printing: what can you print?
Using these various technologies the potential is limited only by your imagination. Using libraries of designs you could make household objects such as cups and saucers or, if you have creative talents, you could design similar objects yourself using 3D CAD software. You could even print small plastic parts to repair equipment that’s been damaged (let's hope companies get on board and allow you to buy the 3D files for home appliance parts) and already you can print out customised replacement cases for mobile phones. 3D printing even been used by sculptors. And because you can print using ceramics and metals as well as plastics, you’re not necessarily producing cheap copies but objects that could be as good and strong as if they were manufactured using more conventional methods.
Needless to say there are limitations to what can be produced and size is one of the major restrictions. Improvements are coming thick and fast, though, and while you’re not going to be printing out a full-size Jaguar XKR any time soon, desktop printers can now produce objects as large as a loaf of bread, and if you use the services of a 3D printing bureaux you could go bigger still. Perhaps the other main restriction is on intricate mechanical objects, especially if they are composed of separate moving parts. Although this would be possible by printing the individual parts and assembling them by hand, it’ll be some time before we’re able to print a pocket watch as a single object. If we were writing this just a couple of years ago we’d also be saying that you can only print things that are a single colour but, as testimony to the rapid rate of change, you can now print out objects in full colour.