Additive Manufacturing (AM) is a term to describe set of technologies that create 3D objects by adding layer-upon-layer of material. Materials can vary from technology to technology. But there are some common features for all Addictive Manufacturing, such as usage of computer together with special 3D modeling software. First thing to start this process is to create CAD sketch. Then AM device reads data from CAD file and builds a structure layer by layer from printing material, which can be plastic, liquid, powder filaments or even sheet of paper.
The term Additive Manufacturing holds within such technologies like Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), Layered Manufacturing and 3D Printing. There are different 3d printing methods that were developed to build 3D structures and objects. Some of them are very popular nowadays, others have been dominated by competitors.
This article is focused at the following 3d printing technologies or some may call them types of 3D printers:
- Stereolithography (SLA)
- Digital Light Processing (DLP)
- Fused deposition modeling (FDM)
- Selective Laser Sintering (SLS)
- Selective laser melting (SLM)
- Electronic Beam Melting (EBM)
- Laminated object manufacturing (LOM)
Stereolithography is a 3d printing method that can be used to implement your projects that involve 3D printing of objects. Although this method is the oldest one in history of 3D printing it’s still being used nowadays. The idea and application of this method are amazing. Whether you are a mechanical engineer, who needs to verify if the part can fit to your design, or creative person who wants to make a plastic prototype of new coming project, Stereolithography can help you to turn your models into a real 3D printed object.
This method was patented by Charles Hull, co-founder of 3D Systems, Inc in 1986. The process of printing involves a uniquely designed 3D printing machine called a stereolithograph apparatus (SLA), which converts liquid plastic into solid 3D objects.
Most printing techniques require computer aid design (CAD) file to process the object. This file contains information about dimensional representation of an object. CAD file must be converted into a format that a printing machine can understand. There is Standard Tessellation Language (STL) format that is commonly used for stereolithography, as well as for other additive manufacturing processes. The whole process consists of consequent printing of layer by layer hence STL file that printing machine uses should have the information for each layer.
SLA printing machines don’t work as usual desktop printers which extrude some amount of ink to the surface. SLA 3D printers work with excess of liquid plastic that after some time hardens and forms into solid object. Parts built with 3D printers type like this usually have smooth surfaces but its quality very depends on the quality of SLA machine used.
The process of printing includes several steps. It starts from creation of 3D model in CAD program, special piece of software processes the CAD model and generates STL file that contains information for each layer. There could be up to ten layers per each millimeter. Then SLA machine exposes the liquid plastic and laser starts to form the layer of the item.
After plastic hardens a platform of the printer drops down in the tank a fraction of a millimeter and laser forms the next layer until printing is completed. Once all layers are printed the object needs to be rinsed with a solvent and then placed in an ultraviolet oven to finish processing.
The time required to print an object depends on size of SLA 3d printers used. Small items can be printed within 6-8 hours with small printing machine, big items can be several meters in three dimensions and printing time can be up to several days long.
Stereolithography is widely used in prototyping as it doesn’t require too much time to produce an object and cost is relatively cheap comparing to other means of prototyping. Although this 3d printing method is rarely used for printing of the final product.
Although Stereolithography is considered to be the oldest 3D printing technology many companies still use it to create prototypes of their projects. 3D Systems Inc., the company that started to use this method for prototyping, sells SLA machines to businesses and manufactures. Some of them can be found here.
Home 3D printers usually use additive manufacturing(AM) processes and not stereolithography to produce 3D objects. But anyone interested in this technology can purchase SLA machine for home use and try this process on their own. One of examples of home use SLA 3d printer was created by Formlabs.
For those who are interested in DIY experience, it can be useful to look at the following tutorial on Instructables.
Digital Light Processing(DLP)
Digital Light Processing is another 3D Printing process very similar to stereolithography. The DLP technology was created in 1987 by Larry Hornbeck of Texas Instruments and became very popular in Projectors production. It uses digital micro mirrors laid out on a semiconductor chip. The technology is applicable for movie projectors, cell phones and 3D printing.
For 3D printing DLP as well as SLA works with photopolymers. But what makes SLA and DLP processes unalike is a different source of light. For DLP 3D amateurs generally use more conventional sources of lights such as arc lamps. The other important piece of process is a liquid crystal display panel, that is being applied to the whole surface of building material during single run of DLP process. The material to be used for printing is liquid plastic resin that is placed in the transparent resin container. The resin hardens quickly when affected by large amount of light.The printing speed is pretty impressive. The layer of hardened material can be created with such printer in few seconds. When the layer is finished, it’s moved up and the next layer is started to be worked on.
The results of such printing are robust and have excellent resolution. Big advantage of DLP over SL is much less materials to be used for detail production, that results in lower cost and less waste. Examples of DLP rinses are the Envision Tec Ultra, MiiCraft High Resolution 3D printer, and Lunavast XG2.
Fused deposition modeling (FDM)
Fused deposition modeling (FDM) technology was developed and implemented at first time by Scott Crump, Stratasys Ltd. founder, in 1980s. Other 3D printing companies have adopted similar technologies but under different names. A well-known nowadays company MakerBot coined a nearly identical technology known as Fused Filament Fabrication (FFF).
With help of FDM you can print not only functional prototypes, but also concept models and final end-use products. What is good about this technology that all parts printed with FDM can go in high-performance and engineering-grade thermoplastic, which is very beneficial for mechanic engineers and manufactures. FDM is the only 3D printing technology that builds parts with production-grade thermoplastics, so things printed are of excellent mechanical, thermal and chemical qualities.
3D printing machines that use FDM Technology build objects layer by layer from the very bottom up by heating and extruding thermoplastic filament. The whole process is a bit similar to stereolithography. Firstly special software “cuts” CAD model into layers and calculates the way printer’s extruder would build each layer. Along to thermoplastic a printer can extrude support materials as well. Then the printer heats thermoplastic till its melting point and extrudes it throughout nozzle onto base, that can also be called a build platform or a table, along the calculated path. A computer of the 3d printer translates the dimensions of an object into X, Y and Z coordinates and controls that the nozzle and the base follow calculated path during printing. To support upper layer the printer may place underneath special material that can be dissolved after printing is completed.
When the thin layer of plastic binds to the layer beneath it, it cools down and hardens. Once the layer is finished, the base is lowered to start building of the next layer. Printing time depends on size and complexity of an object printed. Small objects can be competed relatively quickly while bigger or more complex parts require more time. Comparing to stereolithography this technique is slower in processing. When printing is completed support materials can easily be removed either by placing an object into a water and detergent solution or snapping the support material off by hand. Then objects can also be milled, painted or plated afterwards.
FDM technology is widely spread nowadays in variety of industries such as automobile companies like Hyundai and BMW or food companies like Nestle and Dial. FDM is used for new product development, model concept and prototyping and even in manufacturing development. This technology is considered to be simple-to-use and environment-friendly. With use of this 3d printing method it became possible to build objects with complex geometries and cavities.
Different kind of thermoplastic can be used to print parts. The most common of those are ABS (acrylonitrile butadiene styrene) and PC (polycarbonate) filaments. There are also several types of support materials including water-soluble wax or PPSF (polyphenylsulfone).
Pieces printed using this technology have very good quality of heat and mechanical resistance that allows to use printed pieces for testing of prototypes. FDM is widely useful to produce end-use products, particularly small, detailed parts and specialized manufacturing tools. Some thermoplastics can even be used in food and drug packaging, making FDM a popular 3D printing method within the medical industry.
The price for those 3D printers depends on size and model. Professional ones usually cost from $10,000 and more. 3D Printers designed for home use are not so expensive. There are several models like Replicator of MakerBot, Mojo of Stratasys and Cube of 3D Systems. The price for these models varies from $1,200 to $10,000. However, new start-ups offer more and more affordable versions of FDM 3D printers, the price of which can be just about $300-$400.
Also there are many fans of 3D printing or DIY’ers that prefer to create their own 3D printers from the very scratch. There are websites that offer big variety of DIY kits and parts for RepRap printers. For more information please refer to the following article where you can find basic things about how to build 3d printers from scratch.
Selective Laser Sintering (SLS)
Selective Laser Sintering (SLS) is a technique that uses laser as power source to form solid 3D objects. This technique was developed by Carl Deckard, a student of Texas University, and his professor Joe Beaman in 1980s. Later on they took part in foundation of Desk Top Manufacturing (DTM) Corp., that was sold to its big competitor 3D Systems in 2001. As was stated previously, 3D systems Inc. developed stereolithography, which in some way is very similar to Selective Laser Sintering. The main difference between SLS and SLA is that it uses powdered material in the vat instead of liquid resin as stereolithography does.
Unlike some other additive manufacturing processes, such as stereolithography (SLA) and fused deposition modeling (FDM), SLS doesn’t need to use any support structures as the object being printed is constantly surrounded by unsintered powder.
Like all other methods listed above the process starts with creation of computer-aided design (CAD) file, which then needs to be converted to .stl format by special software. The material to print with might be anything from nylon, ceramics and glass to some metals like aluminum, steel or silver. Due to wide variety of materials that can be used with this type of 3d printer the technology is very popular for 3D printing customized products.
SLS is more spread among manufactures rather than 3D amateurs at home as this technology requires the use of high-powered lasers, which makes the printer to be very expensive. Though there are several start-ups the work on development of low-cost SLS printing machines. For example, Andreas Bastian has shared details about his developed SLS printer that uses carbon and wax for printing. Another great example is the Focus SLS printer that can be easily used at home conditions and initially was presented at Thingiverse. More details about it can be found following this link.
Selective laser melting (SLM)
Selective laser melting (SLM) is a technique that also uses 3D CAD data as a source and forms 3D object by means of a high-power laser beam that fuses and melts metallic powders together. In many sources SLM is considered to be a subcategory of selective laser sintering (SLS). But this is not so true as SLM process fully melts the metal material into solid 3D-dimentional part unlike selective laser sintering. The history of SLM started with German research project held by group of Fraunhofer Institute ILT in 1995.
Similarly to other 3d printing methods CAD file needs to be processed by special software to slice the CAD file information into 2D layers. The file format used by printing machine is also a standard .stl file. Right after the file is loaded the printing machine’s software assigns parameters and values for construction of the path.
The fine metal powder is evenly distributed onto a plate, then each slice of 2D layer image is intensively fused by applying high laser energy that is directed to the powdered plate. The energy of laser is so intense that metal powder melts fully and forms a solid object. After the layer is completed the process starts over again for the next layer. Metals that can be used for SLM include stainless steel, titanium, cobalt chrome and aluminum.
This method of printing is widely applied to parts with complex geometries and structures with thin walls and hidden voids or channels. Lots of pioneering SLM projects were dedicated to aerospace application for different lightweight parts. SLM is great for project that experience such kind of problems like tooling and physical access difficulties to surfaces for machining, as well as restrict the design of components. The technology is not widely spread among at-home users but mostly among manufactures of aerospace and medical orthopedics. But the whole process of acceptance, certification and final approval takes some time which results in long time for development and qualification for this technology.
You also may be interested in reading about MX3D-metal printer that can create metal constructions in mid-air.
Electronic Beam Melting (EBM)
EBM is another type of additive manufacturing for metal parts. It was originally coined by Arcam AB Inc. in the beginning of this century. The same as SLM, this 3d printing method is a powder bed fusion technique. While SLM uses high-power laser beam as its power source, EBM uses an electron beam instead, which is the main difference between these two methods. The rest of the processes is pretty similar.
The material used in EBM is metal powder that melts and forms a 3D part layer by layer by means of a computer, that controls electron beam in high vacuum. Contrary to SLS, EBM goes for full melting of the metal powder. The process is usually conducted under high temperature up to 1000 °C.
Comparing to SLM the process of EBM is rather slow and expensive, also the availability of materials is limited. So the method is not so popular though still used in some of manufacturing processes. Currently the most well spread materials that are used for EBM are commercially pure Titanium, Inconel 718 and Inconel 625. The application of EBM is mainly focused on medical implants and aerospace area.
Laminated Object Manufacturing (LOM)
Laminated object manufacturing (LOM) is one more rapid prototyping system that was developed by the California-based company Helisys Inc.
During the LOM process, layers of adhesive-coated paper, plastic or metal laminates are fused together using heat and pressure and then cut to shape with a computer controlled laser or knife. Post-processing of 3D printed parts includes such steps as machining and drilling.
The LOM process includes several steps. Firstly, CAD file is transformed to computer format, which are usually STL or 3DS. LOM printers use continuous sheet coated with an adhesive, which is laid down across substrate with a heated roller. The heated roller that is passed over the material sheet on substrate melts its adhesive. Then laser or knife traces desired dimensions of the part. Also the laser crosses hatches of any excess material in order to help to remove it easily after the printing is done.
After the layer is finished, the platform is moved down by about one-sixteenth of an inch. A new sheet of the material is pulled across substrate and adhered to it with a heated roller. The process is repeated over and over again until 3D part if fully printed. When any excess material has been cut the part can be sanded or sealed with a paint. If paper materials were used during printing, then the object would have wood-like properties, which means it needs to be protected from moisture. So to cover it with a lacquer or paint might be a very good idea.
Probably LOM is not the most popular 3D printing method but one of the most affordable and fastest. The cost of printing is low due to not expensive raw materials. Objects printed with LOM can be relatively big, that means that no chemical reaction needed to print large parts.
Currently Cubic Technologies, the successor to Helisys Inc., is the main manufacturer of LOM printers. There are not too many companies these days that work with LOM technology. But it’s worth mentioning the Irish company Mcor Technologies Ltd. that sells LOM 3D printers. Their devices are widely being used by artists, architects and product developers to create affordable projects from usual letter paper.
The printers that are being sold by Cubic Technologies for home use are pretty expensive comparing to Makerbot Replicator or 3D System’s Cube devices. However printers from Mcor Technologoes can become more popular in the nearest future, as they came to partnership with office supplier retailer Staples. They offer in-store printing services including printing of predefined parts like phone cases, pens, jewelry and many other useful things. Also there can be custom objects ordered that would be based on customers own design.
We have include only most popular 3D printers type into this article and if you have anything to add to it, feel free to leave your comments. We will gladly enrich it with additional information.