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3D printing: different applications, different techniques

March 14 2016: Not all  3D printers available in the market  use the same technique. The method is selected  according to the application.  Madhusudan Apte  provides a useful guide to  5 most widely used 3D printing techniques:
Here are the methods used:

1.Selective laser sintering (SLS)
It is a technique which uses high power laser to fuse small particles of material used as per application to develop a 3D object. The machine in which 3D object is made is connected to computer in which objects layout is initially designed. Then bed goes one layer down and new layer of powder is spread  with help of roller. This process is repeated until whole object is scanned. It is moved up with the help of piston. Extra powder is that part of the powder which is not scanned. So it is removed manually and extra powder removed can used for future creation of objects.

However extra powder around the object created acts as a support for the object made. For removing the excess powder brush is used and then followed up byblasting.SLS was developed and patented by Dr. Carl Deckard at University of Texas in mid 1980’s.Advantage of selective laser sintering is that it offers freedom to build the product in less time and more durable.SLS parts will remain stable and will become less brittle as compared to SLA method.

2.Fused deposition modelling (FDM)
It is a technique in which material is melted continuously from nozzle of machine to develop an object. FDM was invented by Scott crump in 1980’s.The company have varying level of materials of ABS plastic based on how sophisticated the machine is.Durable, accurate parts can be modelled by sending files from desktop to machine. In this technique materials used are ABS plastic, blend of polycarbonate and ABS or pure polycarbonate.  It is a layer additive manufacturing process which is having excellent strength to weight ratio.3D CAD data design is made first and then it is transferred to machine which produces object layer by layer. The object is produced on a built platform. The extrusion nozzles pours the melted plastic on the built platform precisely. In x-y plane it is moved horizontally and the platform on which objects is made moves down so that object is created layer by layer. Objects are kept in water and chemicals to remove excess material over it. Then the objects finally created is removed from the built platform and it is cleaned by hand sanding to create a smooth part.

Advantages of FDM technology is that the materials used for building the parts are less expensive. Also machines used here are less expensive as compared to selective laser sintering and stereo lithography technique. Disadvantage is that x-y resolution is very good but the z resolution which is related to thickness is less in fused deposition modelling. It is one of the slowest 3D technology in the market. Some large parts can take even few days to be made. So generally not so big parts are generated using this technique. Fully dense mode and sparse mode are two modes used. Building part using fully dense mode takes more time as compared to sparse mode. In sparse mode interior is made up of honeycomb structure. As FDM is considered as one of the slowest technique so using sparse mode can save considerable amount of time. But object made from fully dense mode are more durable as compared to that build from sparse mode. The  biggest advantage of FDM is that material is a plastic but stereo lithography technique stimulates plastic. The parts generated are very light in weight so is used in industries like automotive, medical, aerospace and commercial applications etc.

It is a rapid prototyping method  used to create 3D objects. It is the process of transferring CAD design into 3D objects. It was invented by Charles hull in 1986.SLA is highly accurate additive manufacturing process. Firstly a CAD design is made.

This data is transferred SLA additive manufacturing system containing a liquid photopolymer. Machine begin to build the layer one by one at a time. A laser beam of ultraviolet(uv) light is focused on the liquid photo polymer. The laser is used to solidify the liquid plastic. Once the layer is build the platform is moved down so that new layer can be formed. A recoated blade moves across the previous layer to again cover it with the liquid plastic. Next layer is bonded with the layer below. Laser continuously traces and build layer by layer. Once the whole object is created the platform is raised to remove all excess liquid from the object. Object is separated  from support structure carefully. The part is cured in an ultraviolet oven. After about 20 minutes the part is removed from oven. With hand sanding and painting various objects are created. Widerange of industries use the SLA including

Medical, aerospace, automotive, entertainment and consumer products. Without tooling, machining or cutting the 3D objects is generated. Nowadays with the wide range of materials it is used for functional testing, assembly testing and even low volume production.

4. Laminated object manufacturing (LOM)
LOM is a technique developed by Helisys Inc. The laminate used in this rapid prototyping technique is made out of special type of paper. This paper is applied with glue on the cross-section of the paper which reacts with the heat. It is a complete automated process. Ream of paper is fed onto the platform. A laser will be used to cutout a layer of the paper as per designed in CAD model. once one layer is completed, it is replaced by new layer. Glue is applied to new layer so that it binds to previous layers. This process is continuously followed until the final prototype is formed. Once the model is formed it is given some time to cool. The laminated object is removed and shown off. This prototype gives an idea how the final product can look like.

The advantage of LOM is that because the material is in sheet form so wide range of materials can be used. Also there is no need of additional support structures is needed to support the model build as needed in some of the other techniques.LOM process is fast process as only the parts are cut out by laser. Disadvantages of LOM is that it is difficult to fabricate complex thin geometries as application of glue would be difficult. Also strength of the part depends on the adhesive strength of the glue used. Because it is the glue that is bonding the different layers together. If the material used is a normal printing paper then the absorption of water might distort the part. But it is low cost as the raw materials used are readily available. Paper models have wood like characteristics. Here no chemical reactions are required so relatively larger parts can be made. Objects developed after this process can be additionally modified by drilling or machining after the printing.

5.Polyjet printing
Polyjet is similar to the inkjet printing technique but instead of pouring drops of ink it drops liquid polymer. It consist of three steps pre-processing, production and support removal. Polyjet is a layer additive manufacturing technology to develop plastic prototypes from 3D CAD data. This technique uses inkjet technology along with uv curable materials to develop highly accurate prototype. It is one of the fastest prototyping processes available. The process begins by designing CAD data and then data is transferred to polyjet machine. Polyjet machine starts to create the object one layer at a time. Similar to inkjet printers, polyjet printers deposits a small amount of curable material over a build platform. Ultraviolet  light simultaneously cures the object formed. The build platform moves down slightly to make room for the next layer. After the final object is created the build object is removed from the platform. Hand sanding is done to make the surface of the object more smoother. Here no post curing is required. With the hundreds of digital material combination and with different colours,  polyjet technology gives better prototype aesthetics than any other 3D printing technology used. Advantage of polyjet is that it has high resolution, strong in all axis and very precise. Disadvantage is that its cost is high and t has  low impact strength. Its applications include electronic components, knobs, button, valves and complex interior features. It is extremely useful in low temperature applications. It is fast and reliable, product has good finishing expertise and has variety of material choices.
Links to leading 3D printer  providers in India

  1. SNT 3D Printers
  2. i.Materialise     
  3.   Reflex3D      
  4. TECHB    
  5. ALTEM Technologies 

Madhusudan Epte is a BE from Mumbai University who has enriched his professional skills with multiple  MOOC courses  from edX and Coursera