The different types of 3D printers each employ a different technology that processes different materials in different ways. Jetting of fine droplets is another 3D printing process, reminiscent of 2D inkjet printing, but with superior materials to ink and a binder to fix the layers.
Perhaps the most common and easily recognized process is deposition, and this is the process employed by the majority of entry-level 3D printers. This process extrudes plastics, commonly PLA or ABS, in filament form through a heated extruder to form layers and create the predetermined shape.
Because parts can be printed directly, it is possible to produce very detailed and intricate objects, often with functionality built in and negating the need for assembly. However, another important point to stress is that none of the 3D printing processes come as plug and play options as of today. There are many steps prior to pressing print and more once the part comes off the printer — these are often overlooked. Apart from the realities of designing for 3D printing, which can be demanding, file preparation and conversion can also prove time-consuming and complicated, particularly for parts that demand intricate supports during the build process.
However there are continual updates and upgrades of software for these functions and the situation is improving. Furthermore, once off the printer, many parts will need to undergo finishing operations.
Stereolithography SL is widely recognized as the first 3D printing process; it was certainly the first to be commercialised. SL is a laser-based process that works with photopolymer resins, that react with the laser and cure to form a solid in a very precise way to produce very accurate parts. It is a complex process, but simply put, the photopolymer resin is held in a vat with a movable platform inside. A laser beam is directed in the X-Y axes across the surface of the resin according to the 3D data supplied to the machine the.
Once the layer is completed, the platform within the vat drops down by a fraction in the Z axis and the subsequent layer is traced out by the laser. This continues until the entire object is completed and the platform can be raised out of the vat for removal.
Because of the nature of the SL process, it requires support structures for some parts, specifically those with overhangs or undercuts. These structures need to be manually removed. In terms of other post processing steps, many objects 3D printed using SL need to be cleaned and cured. Curing involves subjecting the part to intense light in an oven-like machine to fully harden the resin. Stereolithography is generally accepted as being one of the most accurate 3D printing processes with excellent surface finish.
However limiting factors include the post-processing steps required and the stability of the materials over time, which can become more brittle. DLP — or digital light processing — is a similar process to stereolithography in that it is a 3D printing process that works with photopolymers. The major difference is the light source. DLP uses a more conventional light source, such as an arc lamp, with a liquid crystal display panel or a deformable mirror device DMD , which is applied to the entire surface of the vat of photopolymer resin in a single pass, generally making it faster than SL.
Also like SL, DLP produces highly accurate parts with excellent resolution, but its similarities also include the same requirements for support structures and post-curing. However, one advantage of DLP over SL is that only a shallow vat of resin is required to facilitate the process, which generally results in less waste and lower running costs. Laser sintering and laser melting are interchangeable terms that refer to a laser based 3D printing process that works with powdered materials.
The laser is traced across a powder bed of tightly compacted powdered material, according to the 3D data fed to the machine, in the X-Y axes. As the laser interacts with the surface of the powdered material it sinters, or fuses, the particles to each other forming a solid. As each layer is completed the powder bed drops incrementally and a roller smoothes the powder over the surface of the bed prior to the next pass of the laser for the subsequent layer to be formed and fused with the previous layer.
The build chamber is completely sealed as it is necessary to maintain a precise temperature during the process specific to the melting point of the powdered material of choice. One of the key advantages of this process is that the powder bed serves as an in-process support structure for overhangs and undercuts, and therefore complex shapes that could not be manufactured in any other way are possible with this process.
However, on the downside, because of the high temperatures required for laser sintering, cooling times can be considerable. Furthermore, porosity has been an historical issue with this process, and while there have been significant improvements towards fully dense parts, some applications still necessitate infiltration with another material to improve mechanical characteristics.
Laser sintering can process plastic and metal materials, although metal sintering does require a much higher powered laser and higher in-process temperatures. Parts produced with this process are much stronger than with SL or DLP, although generally the surface finish and accuracy is not as good.
The most popular name for the process is Fused Deposition Modelling FDM , due to its longevity, however this is a trade name, registered by Stratasys, the company that originally developed it. However, the proliferation of entry-level 3D printers that have emerged since largely utilize a similar process, generally referred to as Freeform Fabrication FFF , but in a more basic form due to patents still held by Stratasys. The earliest RepRap machines and all subsequent evolutions — open source and commercial — employ extrusion methodology.
The process works by melting plastic filament that is deposited, via a heated extruder, a layer at a time, onto a build platform according to the 3D data supplied to the printer. Each layer hardens as it is deposited and bonds to the previous layer.
Stratasys has developed a range of proprietary industrial grade materials for its FDM process that are suitable for some production applications. At the entry-level end of the market, materials are more limited, but the range is growing. For FDM, this entails a second, water-soluble material, which allows support structures to be relatively easily washed away, once the print is complete.
Alternatively, breakaway support materials are also possible, which can be removed by manually snapping them off the part. Support structures, or lack thereof, have generally been a limitation of the entry level FFF 3D printers. However, as the systems have evolved and improved to incorporate dual extrusion heads, it has become less of an issue. At the entry-level, as would be expected, the FFF process produces much less accurate models, but things are constantly improving.
The process can be slow for some part geometries and layer-to-layer adhesion can be a problem, resulting in parts that are not watertight.
Again, post-processing using Acetone can resolve these issues. As is the case with other powder bed systems, once a layer is completed, the powder bed drops incrementally and a roller or blade smoothes the powder over the surface of the bed, prior to the next pass of the jet heads, with the binder for the subsequent layer to be formed and fused with the previous layer.
Advantages of this process, like with SLS, include the fact that the need for supports is negated because the powder bed itself provides this functionality. Furthermore, a range of different materials can be used, including ceramics and food.
A further distinctive advantage of the process is the ability to easily add a full colour palette which can be added to the binder. The parts resulting directly from the machine, however, are not as strong as with the sintering process and require post-processing to ensure durability. Material jetting: a 3D printing process whereby the actual build materials in liquid or molten state are selectively jetted through multiple jet heads with others simultaneously jetting support materials.
However, the materials tend to be liquid photopolymers, which are cured with a pass of UV light as each layer is deposited. The nature of this product allows for the simultaneous deposition of a range of materials, which means that a single part can be produced from multiple materials with different characteristics and properties.
Material jetting is a very precise 3D printing method, producing accurate parts with a very smooth finish. However, that is where any similarity ends. The SDL 3D printing process builds parts layer by layer using standard copier paper. Each new layer is fixed to the previous layer using an adhesive, which is applied selectively according to the 3D data supplied to the machine.
After a new sheet of paper is fed into the 3D printer from the paper feed mechanism and placed on top of the selectively applied adhesive on the previous layer, the build plate is moved up to a heat plate and pressure is applied.
This pressure ensures a positive bond between the two sheets of paper. The build plate then returns to the build height where an adjustable Tungsten carbide blade cuts one sheet of paper at a time, tracing the object outline to create the edges of the part.
When this cutting sequence is complete, the 3D printer deposits the next layer of adhesive and so on until the part is complete. And because the parts are standard paper, which require no post-processing, they are wholly safe and eco-friendly. Where the process is not able to compete favourably with other 3D printing processes is in the production of complex geometries and the build size is limited to the size of the feedstock.
The key difference is the heat source, which, as the name suggests is an electron beam, rather than a laser, which necessitates that the procedure is carried out under vacuum conditions. EBM has the capability of creating fully-dense parts in a variety of metal alloys, even to medical grade, and as a result the technique has been particularly successful for a range of production applications in the medical industry, particularly for implants.
However, other hi-tech sectors such as aerospace and automotive have also looked to EBM technology for manufacturing fulfillment. The materials available for 3D printing have come a long way since the early days of the technology. There is now a wide variety of different material types, that are supplied in different states powder, filament, pellets, granules, resin etc.
Specific materials are now generally developed for specific platforms performing dedicated applications an example would be the dental sector with material properties that more precisely suit the application.
However, there are now way too many proprietary materials from the many different 3D printer vendors to cover them all here. Instead, this article will look at the most popular types of material in a more generic way. And also a couple of materials that stand out. Nylon, or Polyamide, is commonly used in powder form with the sintering process or in filament form with the FDM process.
It is a strong, flexible and durable plastic material that has proved reliable for 3D printing. It is naturally white in colour but it can be coloured — pre- or post printing. This material can also be combined in powder format with powdered aluminium to produce another common 3D printing material for sintering — Alumide.
It is a particularly strong plastic and comes in a wide range of colours. ABS can be bought in filament form from a number of non-propreitary sources, which is another reason why it is so popular. In theory, if you printed over that same page a few thousand times, eventually the ink would build up enough layers on top of each other to create a solid 3D model of each letter.
That idea of building a physical form out of tiny layers is how the first 3D printers worked. The process is a bit like making a loaf of sliced bread, but in reverse. Imagine baking each individual slice of bread and then gluing them together into a whole loaf as opposed to making a whole loaf and then slicing it, like a baker does. The 3D printing process turns a whole object into thousands of tiny little slices, then makes it from the bottom-up, slice by slice.
Those tiny layers stick together to form a solid object. Each layer can be very complex, meaning 3D printers can create moving parts like hinges and wheels as part of the same object.
You could print a whole bike - handlebars, saddle, frame, wheels, brakes, pedals and chain - ready assembled, without using any tools. That world, where you can make almost anything at home, is very different from the one we live in today. That means furniture made to fit your home, shoes made to fit your feet, door handles made to fit your hand, meals printed to your tastes at the touch of a button. Sintering can also be used to build metal objects.
The process of 3D can take hours or even days, depending on the size and complexity of the project. But these kinds of printers are many times more complicated, much more expensive, and only work with plastic so far. No matter which type of 3D printer is used, the overall printing process is usually the same.
As we have already seen, 3D-printers are incredibly versatile. They can, in theory, create almost anything you can think of. But they are limited by the kinds of materials they can use for "ink" and by their size. For very large objects, say a house , you would need to print individual pieces - or use a very large 3D printer.
But most printers will designed to use only one type of material. Some interesting examples of 3D-printed objects include, but are not limited to: -. Different CAD software will use a variety of file formats but some of the most common are:.
As we have already touched upon above, 3D printing can have various advantages over more traditional manufacturing processes like injection molding or CNC milling. This means that in some instances, 3D printing can be more resource-efficient than CNC.
Another example of traditional manufacturing processes, injection molding, is great for making lots of objects in large volumes. While it can be used for creating prototypes, injection molding is best suited for large scale mass production of approved product design. However, 3D printing is better suited for small-scale, limited production runs or prototyping. Depending on the use, there are some other advantages of 3D printing over other production processes.
These include, but are not limited to:. By subscribing, you agree to our Terms of Use and Privacy Policy. You may unsubscribe at any time. By Christopher McFadden.
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