3D PRINTING TECHNOLOGIES

 

In this topic, we will discussing the more common methods of printing technologies available in the market, bearing in mind that technology is evolving as we speak. The differences are how the layers are built to create the parts that you desire.

 

FDM (Fused Deposition Modeling)

Sources:

http://en.wikipedia.org/wiki/Fused_deposition_modeling

http://3dprintingindustry.com/3d-printing-basics-free-beginners-guide/

 

Fused deposition modeling (FDM) is an additive manufacturing technology commonly used for modeling, prototyping, and production applications. It is one of the techniques used for 3D printing.

FDM works on an "additive" principle by laying down material in layers; a plastic filament or metal wire is unwound from a coil and supplies material to produce a part.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The technology was developed by S. Scott Crump in the late 1980s and was commercialized in 1990.

The term fused deposition modeling and its abbreviation to FDM are trademarked by Stratasys Inc. The exactly equivalent term, fused filament fabrication (FFF), was coined by the members of the RepRap project to give a phrase that would be legally unconstrained in its use. It is also sometimes called Plastic Jet Printing (PJP).

 

The FDM process utlizes the extrusion of thermoplastic materials, although there are other combinations of materials used in today's 3D printers. 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. The most common materials for entry-level FFF 3D printers are ABS (Acrylonitrile Butadiene Styrene) and PLA (PolyLactic Acid).

 

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.

 

The FDM/FFF processes may require support structures for any parts with overhanging geometry since it is printed the parts bottom up. Essentially there are 2 ways to employ support structures. The first entails a second, water-soluble material, which allows support structures to be relatively easily washed away, once the print is complete. The is commonly known as the PVA (PolyVinyl Alcohol) material. This method usually requires the need to incorporate dual extrusion heads. The second common method is to create breakaway support material which can be removed by manually snapping them off the part.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SLA (Stereolithography)

Sources:

http://en.wikipedia.org/wiki/Stereolithography

http://3dprintingindustry.com/3d-printing-basics-free-beginners-guide/

http://3dprintingfromscratch.com/

 

Stereolithography (SLA) also known as optical fabrication, photo-solidification, solid free-form fabrication, solid imaging and Resin printing) is an additive manufacturing or 3D printing technology used for producing models, prototypes, patterns, and production parts up one layer at a time by curing a photo-reactive resin with a UV laser or another similar power source.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The term “stereolithography” was coined in 1986 by Charles (Chuck) W. Hull, who patented it as a method and apparatus for making solid objects by successively "printing" thin layers of an ultraviolet curable material one on top of the other. Hull's patent described a concentrated beam of ultraviolet light focused onto the surface of a vat filled with liquidphotopolymer. The light beam draws the object onto the surface of the liquid layer by layer, and using polymerization or cross-linking to create a solid, a complex process which requires automation. In 1986, Hull founded the first company to generalize and commercialize this procedure, 3D Systems Inc,which is currently based in Rock Hill, SC. More recently, attempts have been made to construct mathematical models of the stereolithography process and design algorithms to determine whether a proposed object may be constructed by the process.

 

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 .stl file), whereby the resin hardens precisely where the laser hits the surface. 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 SLA 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 SLA need to be cleaned and cured. Curing involves subjecting the part to intense light in an oven-like machine to fully harden the resin.

 

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 as these photopolymer parts do not have the strength of SLS or FDM finished parts, but can typically achieve much higher levels of detail. We will also need to take that the photopolymer is UV sensitive, and hence these products are susceptible to deforming and changing colors in sunlight.

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SLS (Selective Laser Sintering)

Sources:

http://en.wikipedia.org/wiki/Selective_laser_sintering

http://3dprintingindustry.com/3d-printing-basics-free-beginners-guide/

 

Selective Laser Sintering (SLS) is an additive manufacturing (AM) technique that uses a laser as the power source to sinter powdered material (typically metal), aiming the laser automatically at points in space defined by a 3D model, binding the material together to create a solid structure. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An additive manufacturing layer technology, SLS involves the use of a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal, ceramic, or glasspowders into a mass that has a desired three-dimensional shape. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part (for example from a CAD file or scan data) 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.

 

Because finished part density depends on peak laser power, rather than laser duration, a SLS machine typically uses a pulsed laser. The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting point. 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.

 

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. Once finished, the entire powder bed is removed from the machine and the excess powder can be removed to leave the ‘printed’ parts. 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.

 

Unlike some other additive manufacturing processes, such as stereolithography (SLA) and fused deposition modeling (FDM), SLS does not require support structures due to the fact that the part being constructed is surrounded by unsintered powder at all times, this allows for the construction of previously impossible geometries. 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.

 

Since patents have started to expire, affordable home printers have become possible, but the heating process is still an obstacle, with a power consumption of up to 5 kW and temperatures having to be controlled within 2 °C for the three stages of preheating, melting and storing before removal.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Some SLS machines use single-component powder, such as direct metal laser sintering. Powders are commonly produced by ball milling. However, most SLS machines use two-component powders, typically either coated powder or a powder mixture. In single-component powders, the laser melts only the outer surface of the particles (surface melting), fusing the solid non-melted cores to each other and to the previous layer.

 

Compared with other methods of additive manufacturing, SLS can produce parts from a relatively wide range of commercially available powder materials. These include polymers such as nylon (neat, glass-filled, or with other fillers) or polystyrene, metals including steel, titanium, alloy mixtures, and composites and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. Depending on the material, up to 100% density can be achieved with material properties comparable to those from conventional manufacturing methods. In many cases large numbers of parts can be packed within the powder bed, allowing very high productivity.

 

SLS technology is in wide use around the world due to its ability to easily make very complex geometries directly from digital CAD data. While it began as a way to build prototype parts early in the design cycle, it is increasingly being used in limited-run manufacturing to produce end-use parts. One less expected and rapidly growing application of SLS is its use in art.