Different types of 3D Printing
3D printing is actually a foggy name which means fabrication of real objects from digital files. Interestingly there are around 7 core technologies involved in it:
1. Material Extrusion Based
2. Vat Polymerisation
3. Powder Bed Fusion
4. Material Jetting
5. Binder Jetting
6. Direct Energy Deposition
7. Sheet Lamination
Now we shall discuss each printing process in detail.
FUSED DEPOSITION MODELLING (FDM) 3D PRINTING:
Fused Deposition Modelling (FDM), or Fused Filament Fabrication (FFF), is an additive manufacturing process in which an object is built by selectively depositing melted material in a pre-determined path layer-by-layer. The materials used are thermoplastic polymers and are available in the form of a filament form.
In fact, FDM is the most widely used 3D printing technology. It is the first technology people are exposed to and represents the largest installed base of 3D printers. Previously we discussed the different types of FDM 3D printers, now we’ll look into the process involved in this process.
The figure above shows the fused deposition modeling process at different stages.
source:https://s3-eu-west-1.amazonaws.com/3dhubs-knowledgebase/intro-fdm-3d-printing/2-fdm-steps.png
WORKING:
Initially, the thermoplastic filament is loaded into the printer. In order to make the filament material feasible for deposition, it should be melted. So the filament is fed to the extrusion head and then the nozzle where it melts. This process once the nozzle has reached the required temperature. The extrusion head is attached to the X, Y, Z, axis system that allows it to move in the respective directions. The melted material is extruded and is deposited layer-by-layer as instructed in the G-code, where it cools and solidifies. The cooling of the material can be accelerated through the use of cooling fans that are attached to the extrusion head. In order to fill an area, multiple passes of depositions are required. When a layer is finished, the nozzle moves to the next layer, and a new layer is deposited. This process is repeated until the object is complete.
The diagram depicts the schematic diagram of the FDM printer.
The commonly available build size of a 3D printer is 200 x 200 x 200 mm. This can be as big as 1000 x 1000 x 1000 mm for industrial machines. The typical layer height used varies between 50 and 400 microns in FDM. A smaller layer height would result in smoother parts and curved geometries more accurately. While a larger height would result in producing the parts faster and at a lower cost. A layer height of 200 microns is most commonly used.
One of the most important common defects in FDM is Warping. Dimensions of the extruded materials decrease when it cools down during solidification. This process takes place at different speeds as different sections of the print cool at different rates. This difference in the cooling rate results in the development of internal stresses that pull the underlying layer upwards, causing it to warp. Large flat areas (think of a rectangular box) are more prone to warping and such designs should be avoided when possible. Thin protruding features like prongs of a fork-like structure are also prone to warping. Materials such as ABS are generally more sensitive to warping as compared to PLA or PETG, due to their higher glass transition temperature and a relatively high coefficient of thermal expansion.
Support structures are also needed in the FDM process because the material coming out from the filament cannot hold on to air in case of no support. The models developed by the FDM process are not solid in structure, instead, some gaps and holes are left out to save material and time. For desktop FDM printers the default setting is 25% infill density and 1mm shell thickness.
Now let us get into some more types, before getting deep into the concept, I would like to suggest the reader have an open mind since there will be many terms that might be confusing. Don’t worry I’m here to take care of that.
STEREOLITHOGRAPHY (SLA) & DIGITAL LIGHT PROCESSING (DLP) 3D PRINTING :
SLA and DLP are similar in the process that both use a UV light source to solidify the resin in a vat layer-by-layer. While SLA uses a single-point laser to cure the resin the DLP uses a digital light projector to flash a single image of each layer all at once.
Stereolithography (SLA) is an additive manufacturing process that comes under the umbrella of Vat Photopolymerization. In SLA, an object is created by selectively curing a polymer resin layer-by-layer using an ultraviolet (UV) laser beam. The materials used in SLA are photosensitive thermoset polymers are in a liquid form.
If parts require very high accuracy or smooth surface finish SLA is the most cost-effective 3D printing technology available. SLA shares many similar characteristics with Direct Light Processing (DLP) which is another Vat Photopolymerization 3D printing technology.
So techy and complex right? Let me break that into grains through the working process of each method.
WORKING:
The build platform is first placed in the tank of liquid photopolymer, at a distance of one layer height for the floor of the liquid. Then a UV laser creates the subsequent layer with the aid of using selectively curing and solidifying the photopolymer resin. The entire cross-sectional location of the model is scanned, so the produced component is absolutely solid. When a layer is finished, the platform movements to a secure distance and the sweeper blade re-coats a layer on the surface. The procedure then repeats till the part is complete. After printing, the component is in a green, no-fully-cured state and requires further post-processing using UV light. The liquid resin is solidified via a procedure known as photopolymerization. The photopolymerization procedure is irreversible and there may be no way to transform the SLA components back to their liquid form. During the photopolymerization process, the carbon bonds get bound to each other forming unbreakable structures.
source: https://manufactur3dmag.com/wp-content/uploads/2018/01/The-Working-of-SLA-3D-printing-technology.jpg
This process includes UV rays incident on photopolymer resin and builds the model layer by layer. There are two types of SLA machines:
1. Right side up
2. Inverted
Right side up is used in industrial applications and used to build highly accurate parts and these machines the build model layer by layer and the model goes down the resin gradually over its build time. if u need to build the size of a pop can u need 7 gallons of resin and that makes it more costly?
In inverted type SLA which is mostly used in desktop printers, the laser is incident from the down and the model gets build-up towards the top. This allows us to have much lesser resin in the tank. This helps us when it is used in desktop printers.
You will have a UV-protected layer as the resin is photosensitive.
After the process is completed the model is said to be in the green state. It needs to be cleaned and it is introduced in isopropyl alcohol. And after it is washed the extra resin is removed.
There are three major types of laser sources
1. LASER SLA: selective exposure to light by the laser
2. DLP SLA: selective exposure to light by a projector
3. MSLA: selective exposure to light masked by LCD.
source:https://theorthocosmos.com/wp-content/uploads/2017/03/DigitalWorkflow.001.jpeg
The typical layer height in SLA ranges from 25 to 100 microns. In top-down SLA printers, we must place the laser source above the tank and the part is built facing up. The build platform is being at the very top of the resin vat and moves downwards after every layer. In bottom-up SLA printers, the light source is under the resin tank and the part is built facing upside down. This SLA also requires a support structure. In the top-bottom approach, the supports are similar to that in the case of FDM printers but in bottom-up SLA printers, things are more complicated.
Curling is one of the biggest problems encountered in the SLA process. During solidification or curing the resin shrinks slightly upon exposure to the printer’s light source.
SELECTIVE LASER SINTERING (SLS) 3D PRINTING:
Selective laser sintering (SLS) is an Additive Manufacturing procedure that comes under the umbrella of Powder Bed Fusion. In SLS, a laser selectively sinters the particles of a polymer powder, fusing them and constructing a part layer-by-layer The materials utilized in SLS are thermoplastic polymers that exist in a granular form.
SLS 3D printing is used because it offers very high design freedom, high accuracy and produces components with good and consistent mechanical properties, in contrast to FDM or SLA.
source:https://s3-eu-west-1.amazonaws.com/3dhubs-knowledgebase/introduction-sls-3d-printing/2-sls-steps.png
WORKING:
The powder bin and the build area are first heated just beneath the melting temperature of the polymer after which a recoating blade spreads a thin layer of powder over the build platform. A CO2 laser then scans the contour of the subsequent layer and selectively sinters (fuses together) the particles of the polymer powder. The entire cross-section of the component is scanned so that the component is constructed solid. When the layer is complete, the build platform moves downwards and the blade re-coats the surface. The process then repeats until the whole part is complete.
source:https://5.imimg.com/data5/XB/YE/RX/SELLER-51687494/selective-laser-sintering-service-500x500.jpg
After printing, the components are completely encapsulated in the unsintered powder and the powder bin has to cool down before the parts can be unpacked. This can take a large amount of time (as much as 12 hours). The components are then wiped clean with compressed air or different blasting media and are prepared to use for further post-process. The remaining unsintered powder is gathered and it can be used again. In SLS nearly all procedure parameters are preset by the device manufacturer. The default layer height used is 100–120 microns. The SLS components are vulnerable to shrinkage and warping. Over-sintering also can be taken under consideration as a defect as it may result in loss of detailing in small functions like slots and holes.
In the next blog, we shall learn about the remaining types of 3D Printing processes in detail.
Meet you in the next part of my series!!🙂
