Technology

Stereo Lithography (SLA)

Stereo Lithography is a process of photo polymerisation technique by which the printer converts liquid plastic into solid objects.
It uses a vat of curable photopolymer resin. The build plate descends in small increments and the liquid polymer is exposed to light where the UV laser draws a cross section layer by layer. The process is repeated until a model has been created.
SLAs have four main parts: a tank that can be filled with liquid plastic (photopolymer), a perforated platform that is lowered into the tank, an ultraviolet (UV) laser and a computer controlling the platform and the laser.
In the initial step of the SLA process, a thin layer of photopolymer (usually between 0.05-0.15 mm) is exposed above the perforated platform. The UV laser hits the perforated platform, “painting” the pattern of the object being printed.
The UV-curable liquid hardens instantly when the UV laser touches it, forming the first layer of the 3D-printed object.
Once the initial layer of the object has hardened, the platform is lowered, exposing a new surface layer of liquid polymer. The laser again traces a cross section of the object being printed, which instantly bonds to the hardened section beneath it.
This process is repeated again and again until the entire object has been formed and is fully submerged in the tank.
The platform is then raised to expose a three-dimensional object. After it is rinsed with a liquid solvent to free it of excess resin, the object is baked in an ultraviolet oven to further cure the plastic.
Objects made using stereolithography generally have smooth surfaces, but the quality of an object depends on the quality of the SLA machine used to print it.
The amount of time it takes to create an object with stereolithography also depends on the size of the machine used to print it. Small objects are usually produced with smaller machines and typically take between six to twelve hours to print. Larger objects, which can be several meters in three dimensions, take days.

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Selective Laser Sintering (SLS)

To understand SLS, one needs to understand Sintering. Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a manufacturing process used with metals, ceramics, plastics, and other materials. SLS stands for Selective Laser Sintering.
Selective Laser sintering is a printing technique consisting of manufacturing an object by sintering successive layers of powder together in order to form an object. The process facilitates in the creation of complex and interlocking forms. It is available for Plastic and Alumide.
Sintering has been used for thousands of years to create everyday objects like bricks, porcelain and jewelry.
Objects printed with SLS are made with powder materials, most commonly plastics, such as nylon, which are dispersed in a thin layer on top of the build platform inside an SLS machine.
A laser, which is controlled by a computer that tells it what object to “print,” pulses down on the platform, tracing a cross-section of the object onto the powder.
The laser heats the powder either to just below its boiling point (sintering) or above its boiling point (melting), which fuses the particles in the powder together into a solid form.
Once the initial layer is formed, the platform of the SLS machine drops — usually by less than 0.1mm — exposing a new layer of powder for the laser to trace and fuse together. This process continues again and again until the entire object has been printed.
When the object is fully formed, it is left to cool in the machine before being removed.
Unlike other methods of 3D printing, SLS requires very little additional tooling once an object is printed, meaning that objects don’t usually have to be sanded or otherwise altered once they come out of the SLS machine.
SLS doesn’t require the use of additional supports to hold an object together while it is being printed. Such supports are often necessary with other 3D printing methods, such as stereolithography or fused deposition modeling, making these methods more time-consuming than SLS.

 

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Direct Metal Laser Sintering (DMLS)

DMLS stands for Direct Metal Laser Sintering. It is sometimes also referred by the names PBF (Powder Bed Fusion) or SLM (Selective Laser Melting). It is similar in methodology as SLS, however as the name suggests, it uses metal powder instead of polymer powder.
Direct Metal Laser sintering is a printing technique consisting of manufacturing an object by sintering successive layers of metal powder together in order to form an object. The process facilitates in the creation of complex and interlocking forms.
Objects printed with DMLS are made with powder materials, which are dispersed in a thin layer on top of the build platform inside an DMLS machine.
A laser, which is controlled by a computer that tells it what object to “print,” pulses down on the platform, tracing a cross-section of the object onto the powder.
The laser heats the powder either to just below its boiling point (sintering) or above its boiling point (melting), which fuses the particles in the powder together into a solid form.
Once the initial layer is formed, the platform of the DMLS machine drops — usually by less than 0.1mm — exposing a new layer of powder for the laser to trace and fuse together. This process continues again and again until the entire object has been printed.
When the object is fully formed, it is left to cool in the machine before being removed.
Unlike SLS, DMLS uses support structures to support the build components and also to dissipate the heat.

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Fused Deposition Modeling (FDM)

Fused Deposition Modeling or FDM is the most common or the entry level method in 3D Printing. It builds parts up layer-by-layer by heating and extruding thermoplastic filament. It is also known as Fused Filament Fabrication (FFF).
Objects created with an FDM printer start out as computer-aided design (CAD) files. Before an object can be printed. The CAD file is converted to a .STL format for the FDM 3D printer to process and understand.
FDM printers often use two kinds of materials, a modeling material, which constitutes the finished object, and a support material, which acts as a scaffolding to support the object as it’s being printed.
During printing, these materials take the form of plastic threads, or filaments, which are unwound from a coil and fed through an extrusion nozzle. The nozzle melts the filaments and extrudes them onto a base, sometimes called a build platform or table. Both the nozzle and the base are controlled by a computer that translates the dimensions of an object into X, Y and Z coordinates for the nozzle and base to follow during printing.
In a typical FDM system, the extrusion nozzle moves over the build platform horizontally and vertically, “drawing” a cross section of an object onto the platform. This thin layer of plastic cools and hardens, immediately binding to the layer beneath it. Once a layer is completed, the base is lowered — usually by about one-sixteenth of an inch — to make room for the next layer of plastic.
Printing time depends on the size of the object being manufactured. Small objects — just a few cubic inches — and tall, thin objects print quickly, while larger, more geometrically complex objects take longer to print. Compared to other 3D printing methods, such as stereolithography (SLA) or selective laser sintering (SLS), FDM is a fairly slow process.

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LCD Stereolithography

In the last five years, the LCD technology advanced very fast and now printing with LED & LCD Combination has become common use.
It is sometimes referred to as MSLA, Masked Stereolithography because the LCD screen, works like a mask over a UV light source.
LCD screen is made of tiny pixels which being active or inactive, create our object layer image, letting the UV light pass through them or not. LCD technologies tend to be faster than SLA, because they project one full layer at the time. No matter how big or complex the object to print is, only its height and selected Z resolutions, will affect the working time.
A MSLA or more commonly LCD 3D printer resolution on XY axis depends on the LCD screen pixels size. Higher screen resolutions, means higher XY resolution of the 3D printed object.
The light source can be a single UV LED array or can be a more complex structure including lenses which are able to focus the light in a more direct way so to light LCD pixels in a more accurate way, increasing resolution.

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Directed Energy Deposition (DED)

Directed Energy Deposition (DED) is a 3D printing method which uses a focused energy source, such as a plasma arc or a beam to melt a material which is simultaneously deposited by a nozzle. As with other additive manufacturing processes, DED systems can be used to add material to existing components, for repairs, or occasionally to build new parts.
The DED process begins with the creation of a 3D model using CAD software. This model is then sliced into layers with software to represent the end part.
Directed Energy Deposition works by depositing material that has been melted onto a specified surface where it solidifies, fusing materials together to form a structure. DED machines typically use a nozzle that is mounted on a multi axis arm which can move in multiple directions, allowing for variable deposition. The process is typically performed within a controlled chamber with reduced oxygen levels. It is also possible to use a shielding gas to shroud the part and prevent contamination during metal 3D printing. With electron beam-based systems the process is performed in a vacuum, while laser-based systems use a fully inert chamber when working with reactive metals.
DED uses a heat source to melt a powder or wire as it is deposited onto the surface of an object. While powder provides greater accuracy in deposition, wire is more efficient with regards to material use.
The material is added layer-by-layer and solidifies from the melt pool to create new features. Layers are typically 0.25mm to 0.5mm thick. The cooling times for materials are very fast at around 1000-5000 °C per second. The cooling time affects the final grain structure although overlapping in the material can cause re-melting, which creates a uniform but alternating microstructure.
In most cases, the object remains in a fixed position while the arm moves to lay down the material. However, this can be reversed with the use of a platform, which moves while the arm remains stationary.
The advantages of Directed Energy Deposition includes the following:
1. ability to control the grain structure, which allows the process to be used for the repair of high quality functional parts.
2. the production of relatively large parts with minimal tooling.
3. It is way faster and less expensive than Powder Bed Fusion (PBF) when creating mid-size metal parts.
4. Major applications include: near-net-shape parts, feature additions, and repair.