Vat Photopolymerisation is a popular 3D printing technology and the three prominent 3D printers in this category are SLA 3D Printer, DLP 3D Printer and DLS 3D Printer. All these 3D printers are resin-based but they have different operations resulting in different applications.
In this article, we will talk about three most popular Vat Photopolymerisation technologies i.e., SLA vs DLP vs DLS. But first, let us understand about Vat Photopolymerisation technology.
Vat Photopolymerisation uses a vat of liquid photosensitive polymer resin. This resin hardens on exposure to UV light. This property is used to build objects layer-by-layer.
A vat filled with the liquid photopolymer resin is exposed to UV light in a controlled environment and the geometry of the object to be printed is traced out. The exposed resin hardens (called curing) and a solid layer is formed. This process continues till the complete object is printed.
SLA 3D Printer vs DLP 3D Printer vs DLS 3D Printer
We now explore all the three types one by one.
1. Stereolithography (SLA) 3D Printer
Stereolithography Apparatus (SLA) is the first ever patented 3D printing technology. It was patented by Charles Hull – the ‘Father of 3D Printing’ in 1984. AN SLA 3D printer uses a laser to selectively harden the liquid resin in the vat to form the object layer-by-layer.
Let us understand the working on an SLA 3D Printer
SLA 3D Printer Working
Above: Timelapse of Form 1+ 3D print/Video Credit: Formlabs/YouTube
An SLA 3D printer uses a liquid resin in a vat that is selectively exposed to laser and the resin hardens (cures) wherever the laser interacts with the liquid. This laser selectively hardens each point of the layer to form the complete layer of the object to be created. Once a layer is hardened, the build platform moves up by a height equal to the layer height and the process repeats again and again till the entire model is formed.
In SLA 3D printers, a laser is used as a light source. As the laser is a point source, it has to specifically be flashed on all individual points in a layer and so the process, comparatively, takes time.
The objects printed in SLA 3D printer have a better surface finish and the quality remains consistent even when 3D printing multiple objects in a single run. An SLA 3D printer is able to capture really fine features of a design and sometimes as low as 20 microns.
SLA 3D printer uses thermosetting polymers that are custom-made according to certain applications like dental, jewellery, high-temperature, tough, flexible and even ceramic.
Products printed in an SLA 3D printer are used in applications like form and fit testing of prototypes, investment casting patterns, jig and fixtures, casting patterns, dental applications, etc.
2. Digital Light Processing (DLP) 3D Printer
Digital Light Processing (DLP) also falls under the vat photopolymerisation technology. It is similar to Stereolithography in many ways with a minor but a very significant modification. A DLP 3D printer uses liquid photosensitive resins that are cured on application of UV light. The major difference between both these technologies is in the use of the light source and this defines the quality of product printed on both the machines. DLP technology uses a digital projector screen to flash a single image of each layer. This means a single layer of printing is completed in a single flash. Whereas in an SLA printing, a laser traces the geometry by following the coordinates. As a result, DLP 3D printer is a faster as compared to SLA 3D printer.
Let us understand the working on a DLP 3D Printer
DLP 3D Printer Working
Above: Envision One Industrial 3D Printer/Image Credit: EnvisionTec/YouTube
A DLP 3D printer houses a vat of liquid polymer that is exposed to UV light in safe conditions. The process starts with sending of the 3D image to the printer. A light projector that sits under the resin container projects slices of the 3D image on the resin layers. The complete first layer of polymer that is exposed to the UV light hardens and the process continues to the 2nd and all successive layers in the photopolymer. The process continues until the 3D model is built.
One of the major drawback of a DLP 3D printer is that the output quality is affected by the number of units to be printed in a single tray. Since it uses a light source, the entire layer is printed in one go and so the pixels of the light get distributed with respect to the number of objects to be printed. More the number of products, lesser is the quality.
Materials used in DLP 3D printers are similar to those used in SLA 3D printers. In some cases the materials can be used interchangeably but it is Not Recommended.
DLP 3D printer is widely used in Jewellery and dental applications. It also finds use in aesthetic models and gifting items with very fine features.
3. Digital Light Synthesis (DLS™) 3D Printer
The Carbon DLS™ technology, formerly known as CLIP, is a patented technology originally granted to EiPi Systems in 2015 but is now developed and promoted by Carbon. It was invented by the CEO and Co-founder of Carbon, Joseph DeSimone along with Alexander and Nikita Ermoshkin and Edward T. Samulski.
Carbon CLIP technology uses an ultraviolet light to cure (harden) a photosensitive liquid resin held in a vat above the light. The build platform is dipped initially in the liquid resin and is subsequently drawn upwards to literally pull the 3D object out of the resin.
Let us understand the working on the DLS 3D Printer.
DLS 3D Printer Working
Above: Carbon M1 3D Printer Demo Video/Video Credit: Carbon/YouTube
The process begins with the build platform dipped in the liquid photosensitive resin held in a vat. The vat is held on an oxygen-permeable window (the window). While the UV light engine projects from beneath the window. The light engine flashes a stream of image per layer onto the vat through the oxygen-permeable window. This window allows for oxygen to pass through it in minute quantities. This is responsible for creating a thin liquid interface of uncured (unhardened) resin between the window and the part itself. The thin liquid interface literally the ‘no-reaction zone’ is called as ‘dead zone’. The dead zone is extremely thin equal to only one-third of a human hair. This not only enables a continuous flow of oxygen and liquid between the window and the pat but also avoids the part sticking to the window itself.
Carbon sells the DLS 3D printer on a subscription model that helps customers to avail the technology at a low cost. The DLS 3D printer uses the CLIP technology that helps in faster build times thus enabling its use in mass customisation.
Carbon develops its own range of proprietary engineering and dental resins like DPR 10, Keysplint Soft, Surgical, EPX 82, EPU 41, etc.
DLS 3D printer has found applications in a multitude of industries and products. They are largely used for mass customisation. Adidas has used it to manufacture footwear, Lamborghini to manufacture automotive parts at scale, Riddell used it to manufacture customised football helmet liners, and Speacialized used DLS 3D printers to print lattice bike saddle. During the COVID-19 crisis, Carbon developed nasal swabs and printed them on their DLS 3D printers.
It has applications in engineering as well as dental products.
SLA, DLP and DLS are the three vat photopolymerisation 3D printing technologies available in the market. While the patents for SLA and DLP are expired and are now being manufactured by multiple companies across the world, DLS still falls under an active patent. All the three technologies are well established in the market and are being actively used for many complex and practical applications across industries.
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