There are a variety of 3D printing technologies that give us the desired models, prototypes, production parts, and patterns. But each technique has its own method of printing layer by layer, special features, and its pros and cons.
These days, FDM is the more popular technology, but it is relatively new to some other methods. Resin-based 3D printing is a classic in the 3D printing world, one that was the beginning of everything. They make use of a process called Vat polymerization or photopolymerization.
Since the beginning of stereolithography (SLA) in the 1980s, patented by Charles “Chuck” Hull, vat polymerization has come a long way. It has grown to include other systems such as direct light processing (DLP). But what is vat polymerization in 3D printing?
Vat polymerization is a process that uses photopolymerization to print 3D objects. In this process, a vat or a container of liquid photopolymer resin is turned solid when exposed to ultraviolet (UV) light. As the resin is hardened by UV light, a platform moves downwards to print the object layer by layer. SLA and DLP are some types of Vat polymerization.
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What is Vat Polymerization in 3D Printing?
Vat polymerization is an Additive Manufacturing (AM) process that selectively hardens or ‘cures’ liquid resin by UV light. One of the first AM processes, Stereolithography, makes use of vat polymerization. (Source)
The printing material used is a photopolymer or a light-activated resin. As the name might give away, it is a polymer that changes its structural properties when exposed to a certain wavelength of light. This process is called photopolymerization.
The resin present in the vat is in liquid form. UV light, one of the most common types of light used, is then projected onto the resin to harden the layers. The light targets specific areas of the resin according to the CAD and prints the 3D object as required.
This diagram sourced from WhiteClouds provides a great visual example of the process.
The platform repeatedly rises from and re-submerges in the vat as the light (or laser) is directed onto the resin. After the design is fully printed, the resin is drained, and the object is removed.
After the parts are finished, they are usually post-cured by UV light to enhance their structural and functional properties.
Check out our article on Can You Print Multiple 3D Objects At Once? Pros and Cons
Vat Polymerization subcategories: SLA and DLP
It might be confusing at first but resin-based 3D printing technologies such as SLA and DLP fall under the umbrella of vat polymerization. They are merely just different subcategories of technology where liquid photopolymer resin is stored in a vat.
What is unique among the two vat polymerization techniques is mainly the light source. (Source) This also affects the speed at which an object is 3D printed and the object’s quality.
In SLA, as shown in the previous diagram, the source of UV light is a laser. The laser beam is moved by computer-controlled rotating mirrors to make precise patterns in the resin. In this process, each point of a layer is printed one at a time, until the part is complete.
DLP (Digital Light Processing), on the other hand, has UV projectors. It uses a DMD (Digital Mirroring Device) made up of several micromirrors to navigate the beam produced by the light projector.
The digital projector screen then flashes an image of a layer across the entire platform. This way, it hardens the complete layer of resin at a time, all points are cured simultaneously. This is repeated until all layers are done and the object is complete.
However, since SLA printers cure the resin to point to point, they are very precise and have greater quality than a DLP print.
On the flip side, DLP prints faster than SLA. Because it can print an entire layer at one time, it cuts down on the printing time significantly, compared to SLA printers.
Some of the well-known manufacturers for SLA printers are Formlabs, 3D Systems, DWS, and for DLP; B9 Creator, MoonRay.
Vat Polymerization vs FDM
To better understand vat polymerization, we can compare its functioning with the relatively newer 3D printing technology – Fused Filament Fabrication (FFF). Also used interchangeably with the term Fused Deposition Modeling (FDM), it is mainly used among 3D printing hobbyists.
One of the key differences between the two technologies is the way 3D printing material is involved. In an FDM machine, the thermoplastic filament is deposited on a printing bed from an extruder or nozzle.
However, in vat polymerization, liquid resin is selectively hardened by UV light as it sits in a vat. There is no deposition of material in this case.
Of course, this also highlights the different raw materials both technologies use. Vat polymerization uses photopolymer liquid resin while FDM makes use of thermoplastics.
It is also significantly easier and cheaper to operate an FDM printer than an SLA or DLP printer. Considering the post-processing and the material cost only, FDM proves to be cheaper than vat polymerization.
Conversely, FDM 3D printed objects are lower in quality since this technology has the “lowest dimensional accuracy and resolution compared to the other 3D printing technologies.” (Source)
Talking about resolution, check out our post How Many Microns Are There In 3D Printing? Do They Matter?
Pros and Cons of Vat Polymerization
As every 3D printing technology has its unique flavor, vat polymerization also has some of its advantages and disadvantages.
Advantages of Vat Polymerization:
- High levels of precision – allows the printing of intricate details and complex 3D designs accurately.
- Large build volume – can make use of very large vats to 3D print sizeable objects.
- Faster printing process – printing with UV light is a quicker method than depositing material.
- High-resolution prints – the completed 3D print has a relatively smoother surface finish.
- Reusable resin – the leftover resin in the vat after a print can be removed and reused for other prints.
Disadvantages of Vat Polymerization:
- Relatively expensive – the Formlabs Form 3 printer costs around $3,500 whereas the best considered 2021 FDM printer, Original Prusa i3 MK3S+ is for $750.
- Limited choice of material – it is quite hard to find a specialized and a variety in color for UV curable resin.
- Brittle prints – finished 3D objects when exposed to prolonged sun exposure can become weaker.
- May need additional structural support after print – the final printed object may not be strong or durable enough for functional use.
- Some resins are toxic – special care should be taken when handling them such as wearing gloves and goggles, and reading up on the material properties before printing
Applications of Vat Polymerization
Now that we have an idea of what vat polymerization is, it might come as a surprise to see where and how it is used around us.
The most common applications of vat polymerization are in the dental and medical industries. Such as in creating hearing aids, dental and other prosthetics, surgical practice tools, microneedles, etc.
Interestingly enough, a 2021 study review of Vat Photopolymerization Technology presents to us a table of various of its applications so far. In Table 7, they mention the creation of small-scale living tissue structures made via this technology!
Moreover, it is also used in forming detailed and intricately designed jewelry. Helmet liners and shoe soles are also some of the minor products of this technology.
The study further predicts that the field of robotics, smart composites, and flexible electronics will see greater use out of vat polymerization in the future. Along with a growing interest in bio-printing organs.
On the business side, prototypes made from vat polymerization are essential. They are an excellent way to test out the design of their product or as a marketing strategy for their final product.
To sum everything up, vat polymerization is a technology as old as the beginning of 3D printing. It uses liquid photopolymer resin as its raw material that is solidified by UV light.
Each layer is solidified in this manner and the building platform repeatedly rises and falls out of the vat of resin until the product is completely printed.
SLA and DLP are the two most common subcategories of vat polymerization technology, which is also known as photopolymerization. The main difference between these two subcategories is the light source.
SLA uses a laser beam as a light source while DLP uses a UV light projector. DLP is also faster than SLA since it prints layers simultaneously instead of point by point of a single layer.
Vat polymerization has seen many uses in the medical, dental, robotics, electrical, the fashion industry. It is also predicted to develop and include more applications in the coming future.
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