Although the overall process of printing follows the same principle, different methods have been evolved over the years. Some of the technologies are listed as follows:


  1. Stereolithography (SLA)

  2. Digital Light Processing (DLP)

  3. Fused Deposition Modelling (FDM)

  4. Selective Laser Sintering (SLS)

  5. Electronic Beam Melting (EBM)



  • Stereolithography (SLA)


 SLA is an additive manufacturing technology used to create models in a layer by layer manner, using photopolymerization, a process by which light causes chains of molecules to link together, forming polymers. Charles Chuck W Hill coined the term ‘Stereolithography’ 1986 when he patented the process. He then set up a company called 3D Systems Inc. to commercialize the patent.


 The process of printing entails a 3D printing machine called stereolithograph apparatus (SLA), which converts liquid plastic to solid objects. As mentioned earlier, a CAD file which contains the dimensions of the final object, is needed to process the object. The CAD file must then be converted to the Standard Tessellation Language (STL) format, a format that is commonly used for stereolithography and other additive manufacturing processes as well. The process then involves printing layer by layer from the STL file, to produce the final object. Once all layers are printed the object needs to be rinsed with a solvent and then placed in an ultraviolet oven to finish processing.


 Depending on the size of the SLA printer, the time required for printing an object varies. Small objects can be printed in 6 to 8 hours with a small printer, whereas big items can take upto a few days.


 Since the cost is less and it takes lesser time compared to other technologies, stereolithography is extensively used in prototyping. 3D Systems Inc., the company that started to use this method for prototyping, sells SLA machines to businesses and manufacturers.


  • Digital Light Processing (DLP)


 DLP is a display device based on optical micro-electro-mechanical (Microscopic devices with moving parts) technology. It was originally developed in 1987 by Dr. Larry Hornbeck of Texas Instruments. This technology is widely used in projectors, cell phones and in 3D printing.


 DLP, like SLA, works on the principle of photopolymerization. But the source of light is what makes the DLP and SLA technologies different. Conventional sources of light such as arc lamps are commonly used in DLP.


The material to be used for printing is liquid plastic resin and it is placed in the transparent resin container. The resin hardens quickly when affected by large amount of light. The layer of hardened material can be created with this kind of a printer in a few seconds. When the layer is completed, it’s moved up and the next layer is started to be worked on.


The major advantage of DLP over SLA is it’s high resolution, lesser materials, and hence lesser waste.


  • Fused Deposition Modelling (FDM)


 In the FDM methodology, the material filament is melted and remolded in the desired shape. This technology was founded by S. Scott Trump in the late 1980s and was commercialized in 1990 by Stratasys.


 This machine can be used to achieve different goals. For example, one may use one material to build up the model and use another as a soluble support structure,or one could use multiple colors of the same type of material on the same model. FDM is the only 3D printing technology that builds parts with production-grade thermoplastics, so final objects are of excellent mechanical, thermal and chemical qualities.


 Objects are built layer by layer using the additive manufacturing technology, from the very bottom up by heating and extruding thermoplastic filament. Firstly, special software such as Cura slice the CAD model into layers and calculates the way the printer’s extruder would build each layer. Then the printer heats thermoplastic till its melting point and extrudes it through the  nozzle onto base, that can also be called a build platform or a table, along the calculated path. A computer translates the dimensions of an object into X, Y and Z coordinates and controls the nozzle and the base during printing. Once the printing process is completed, the support materials can easily be removed by snapping off by hand.


 A lot of materials such as ABS, PLA, PVA and a lot more. These materials differ in their strength and temperature properties. In addition, even the colour of the thermoplastic material affects the strength of the printed object.


 FDM technology has widely spread applications ranging from automobile like Hyundai to food companies like Nestle and Dial.


 The do-it-yourself RepRap printers are based on the FDM technology, and this has further triggered the DIY enthusiasts to develop their own 3D printers using the FDM technology.


  • Selective Laser Sintering


 SLS is an additive manufacturing technique that uses laser as a power source to create solid objects. It was developed and patented by Dr. Carl Deckard and academic advisor, Dr. Joe Beaman at the University of Texas, Austin in the mid 1980s.


 In the selective laser sintering technology, the laser selectively fuses powdered material by scanning the CAD file on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. The SLS machine preheats the bulk powder to a little lesser than the melting point before the printing process, so that it will be easier to raise the temperature during printing.


 In contrast with some other additive manufacturing processes, such as SLA and FDM, which most often require special support structures, SLS does not need a separate feeder for support material because the part being constructed is surrounded by unsintered powder at all times.


 The material to print can range from nylon, ceramics and glass to metals like aluminium, silver and steel. Due to the different varieties of materials, this technique is generally used for customization.


  • Electronic Beam Melting


 EBM technology is mainly used for printing metal parts. Here, metal powder or wire is melted together using an electron beam as the heat source. It was originally developed by Arcam AB Inc. in the beginning of the 2000s. The material used is a metal powder that melts and forms a 3D part layer by layer. The process is usually conducted at high temperatures over 1000 degrees.


 






 


Technology

Applications

Stereolithography (SLA)

Manufacturing, Biomedicine, Aerodynamics

Digital Light Processing (DLP)

Rapid prototyping, Hearing aids and medical implants, Jewelry casting

Fused Deposition Modelling (FDM)

Defense, Architecture, Digital Dentistry

Selective Laser Sintering (SLS)

Military hardware, Electronics, Homeland Security

Electron Beam Melting (EBM)

High Stress Aerospace applications, Medical grade implants