What is Vat Polymerization Printer?

VAT polymerization is a class of 3D printing processes distinguished by the use of UV light to cure the material. Strong material is seldom deposited by 3D printers. When the material is poured onto the 3D print bed, it is extremely viscous. The substance must then be cured in order for it to harden and shape the desired product. UV light is used in VAT polymerization processes to cure material in a prefilled vat. 

The most popular VAT polymerization processes are as follows:

  • Stereolithography (a form of lithography that uses)
  • Processing of clear light
  • Stereolithography with a mask

FFF versus VAT Polymerization

In many ways, VAT polymerization varies from fused filament fabrication (FFF). One of the most significant differences is that the latter 3D printing process deposits material, while the former does not. Material is extruded from a nozzle and deposited onto a print bed in FFF 3D printers. While depositing content, the nozzle of the FFF 3D printer will pass over the print bed. VAT polymerization 3D printers, on the other hand, actually cure material that has already been filled into a vat bag.

Different materials are used by VAT polymerization and FFF 3D printers. FFF 3D printers use thermoplastics as their raw material, whereas VAT polymerization 3D printers use photopolymer resin, a form of UV-sensitive material.

Just VAT 3D printers, of course, use UV light to cure their materials. After all, it is the use of UV light that sets them apart from other 3D printers, including FFF 3D printers. VAT 3D printers operate by curing photopolymer resin particles selectively inside a vat. After filling the vat with photopolymer resin, the material is selectively cured with UV light to create the desired object.

Aside from VAT polymerization and FFF, there are other 3D printing methods. VAT polymerization, on the other hand, is the only process that uses UV light to cure material in a pre-filled vat. To build objects, it selectively cures photopolymer resin in a vat.

SLA Printer Characteristics

Printer settings

On VAT Polymerization 3D printers, printer parameters are set and cannot be modified. Part orientation/support position, layer height, and material are usually the only operator inputs, and these are all defined during the slicing stage. The majority of SLA printers automatically change settings depending on the type of material used.

The surface finish and accuracy of a component are determined by layer height and light source resolution (spot size or projector resolution). The majority of VAT Polymerization printers manufacture parts with layer heights ranging from 25 to 100 microns. It may be possible to use a narrower beam by switching out DLP projector lenses for very thin, finely detailed prints. As a result, the beam can print smaller layers at a faster rate and with more precision.

The SLA Process

The SLA process has a high degree of accuracy and finish (Chua et al., 2010), but it also necessitates support systems and post-curing to make the part robust enough for structural usage. Photo polymerisation can be accomplished with only a single laser and optics. Blades, also known as recoating blades (Gibson et al., 2003), move over previous layers to ensure that the resin for the next layer’s construction is free of defects. The photopolymerization process and support material may have created defects like air gaps, which must be filled with resin to achieve a high-quality model.The process’s typical layer thickness ranges from 0.025 to 0.5mm (Chua et al., 2010).

Parts must be separated from the resin, and any excess resin must be fully drained from the vat. Supports may be cut out with a knife or other sharp object. It is important not to contaminate the resin and to take all possible safety measures. The use of an alcohol rinse accompanied by a water rinse is one method for extracting resin and supports. It’s possible that the processing would take a long time because sections may need extra scrubbing to remove all of the content. Finally, sections may be naturally dried or dried with an air hose. In order to ensure a high-quality object, UV light is commonly used as a final post-cure process. A great example of a machine could be the 3D Systems ProX 950, which weighs 450kg with the measurements of 1500 mm x 750 mm x 550 mm.

Photopolymerisation
Step by Step

  1. The layer thickness lowers the construct platform from the top of the resin vat to the bottom.
  2. The resin is cured layer by layer with UV light. The platform begins to descend, with new layers being placed on top of the previous.
  1. Some devices use a blade that travels between layers to create a smooth resin foundation for the next layer to be built on.
  2. The vat is then drained of resin and the item is extracted.

Bottom-up vs. Top-down

VAT polymerization machines may generate parts in either a bottom-up or top-down orientation.

Bottom-up

Bottom-up The light source in a bottom-up printer is located under the resin vat. The vat's bottom is clear..



Top-down​

Top-down The light source is positioned above the build platform in top-down printers. A thin layer of resin coats the build base, which starts at the top of the resin vat. After the first layer has cured, the build framework is pushed down one layer thickness, the previously cured layer is re-coated with resin, and the process is repeated.

PRO

    • A high level of accuracy and a good finish are needed.
    • Process is relatively simple.
    • Typical major construction areas include: Object 1000 has dimensions of 1000 x 800 x 500 and a maximum model weight of 200 kg.

     

CONS

    • Expensive in contrast
    • Post-processing time is extended, as is resin removal.
    • Photo-resins are used in a limited number of materials.
    • Support systems and post-curing are often needed for parts to be strong enough for structural use.

           Benefits and limitations of  

    SLA 3D printing

Printing fine detailed prints with feature sizes as small as 0.3 mm is possible with VAT Polymerization printers. Most prints require support structures to be attached to the model, which is one of the technology’s limitations. These supports leave marks on the surface which cause the surface to become uneven. As a result, it’s best to put the supports on the parts of the model that aren’t obvious. VAT Polymerization parts can be finished to an absolutely smooth surface, similar to that of an injection moulded part, with the right post-processing.

Common Problems with SLA 3D Printing

Filler
Stereolithography (SLA) 3D printers generate completely dense parts by nature. Hollowing out the template when printing parts that do not need a certain degree of strength is a technique that can save a lot of material and time.

Support structures
VAT Enabling Frameworks Support structures are needed for polymerization components.

The type of printer used determines the position and amount of assistance. Support specifications for top-down printers are similar to those for FFF 3D printing, with overhanging features and bridges requiring support structures.

The support structure specifications for bottom-up printers are more complex than for top-down printers. Since there is only one vat for both methods of printing, support structures are still printed in the main build material and must be manually removed after printing.

Direct Light Processing(DLP)

DLP uses a system of component production that is nearly similar to SLA.

DLP employs a digital light projector screen to simultaneously display a single image of each sheet (or multiple flashes for larger parts). Since the projector is a digital screen, each layer’s image is made up of square pixels, resulting in a layer made up of tiny rectangular pixels known as voxels. Printing times are quicker with DLP than with SLA. This is because, rather than tracing the cross-sectional region with a laser point, an entire layer is revealed all at once.

Materials

VAT (Value Added Tax) Thermoset photo-polymers are used in polymerization technologies to create components. The polymer comes in a viscous liquid shape (resin). Depending on the application, resin prices can differ significantly. The number of colors available in SLA/DLP resins is small. Resins made of photopolymer have a finite shelf life (typically one year, if stored properly).

 

 

 

SLA vs.DLP

The light source that each technology uses to cure the resin is the main difference between SLA and DLP. A point laser is used in SLA printers, while a light image is used in DLP printers. Standard DLP projectors have a resolution of 1024 x 780 pixels, and standard SLA printers use a laser with a spot size of 130 – 150 microns (this can vary depending on the size of the machine).

Dimensional Accuracy

Curling of wide flat surfaces is one of the most serious problems with VAT Polymerization parts in terms of precision. Each layer shrinks as it solidifies when exposed to the printer light source. There is tension between the two layers as one layer shrinks on top of a previously solidified (pre-shrunk) layer. Curling is the outcome. Support systems keep at-risk parts of a portion anchored to the build plate and reduce the chance of curling. These issues can also be mitigated by part orientation and restricting broad flat layers. Higher flexural properties (less stiff) resins are more susceptible to warping and may not be ideal for high-precision applications.

 

 

 

SLA printed rings being removed from the resin vat. Src: EnvisionTEC