How do 3D printers work? And what are their limitations?
In: Technology
There are several types of 3D printers all with their own advantages and limitations. The most common consumer 3D printers however are plastic extruder based. This is essentially an automated hot glue gun. A long plastic fulfillment is pushed through a heated nozzle so it comes out as molten plastic. By placing the nozzle exactly where you want the plastic when it melts you can create plastic models. It is a cheap and fast way to go from a computer model to a physical object. But there are plenty of issues which makes this hard for industrial 3D printing or large volume manufacturing.
Firstly there is issues with creating overhangs. You can not get plastic to hang in free air so you need plastic under everything. I is possible to build temporary plastic scaffolds that you remove later but it is still a limitation. Secondly the surface finish is often not the best. You can not control in detail where the molten plastic is going to end up before it hardens so the surface tends to be fairly rough and may need some finishing work. Thirdly you can not use any kind of material but you need to use plastic that can actually be melted down and recast safely. Not all plastic can do this. And lastly the strength of the finished product is often not very good. The obvious issue is that the different layers do not always fuse together perfectly so if you apply a force through the layers you can separate them. But maybe more important is that mass produced plastic products usually have a lot of glass fiber in it to act as reinforcement to bind the plastic together. This is obviously not possible for 3D printers because the different layers are made at different times and you can not get the fibers to cross between the layers and bind them together.
For industrial level 3D printers you usually use a more expensive but better method. Instead of filling air with molten plastic they can fill a sand with glue to make 3D objects. You lay a layer of sand and glue it to the layer underneath before you lay down the next layer and so on. This gives you much better control so you get much higher fidelity and surface finish. The figure does not warp or need scaffolding while you make it. You can even add dies to the glue to make colored objects very easy. You can also use various other materials instead of the sand and glue to for example make metal sintered objects or a ray of other materials.
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