For us, we simply attach a thin Teflon film to protect the silicone from contacting the resin directly so as to extend the lifetime of resin container. You might think that Teflon is a non-stick material. In general, it is true, but some cured resin materials can stick on the Teflon film firmly and are very hard to separate. The followings are the reasons why a cured layer could be hard to separate.

1. Some cured resin has a strong Van Der Waals’ force with Teflon. When the cured area is large, the separation force is high.
2. Over-cured resins tend to have a much higher adhesion to Teflon.
3. Hollowed model without vent holes could introduce tremendous suction force.
   
4. Bulk shrinkage in a tapered solid region could turn a flat layer into a bowl like shape that could also introduce tremendous suction force. A thin cone shape is more likely to happen. This phenomenon often happens when:
   • a. Material itself has a high native shrinkage
   • b. Fast curing ( < 1 second) due to strong light intensity or more photoinitiator concentration could introduce higher shrinkage for the same material
   • c. For a fast resin, low separation speed introduce more on-going curing after the light is turned off. Low separation height does not mix the resin near the curing area with fresh resin outside the curing area well enough so the viscosity becomes higher in the curing area gradually. The combination of the above two could introduce differential shrinkage between layers and across the layer and form a strong suction effect. The situation is more severe when printing repeated patterns. This suction force may result in a phenomenon where the cured layer suddenly sticks to the Teflon and does not come apart (as shown in the photo). To provide an example, suppose a certain resin has a normal exposure time of 1 second. During the printing process, the resin has absorbed photons from both background and scattering exposure near the exposed area. Please note that the resin in the build area close to the vat floor tends to have higher viscosity when partially cured and tends to stay near where it is. If the accumulated absorbed dosage is equivalent to 0.5s of normal exposure, the next print layer will technically be over cured for 1.5 seconds (1 second for the exposure time + 0.5 second from already being cured due to background and scattering exposure). During the buildup of the partially cured resin, the effective over-curing will keep increasing the adhesion between the cured layer and the Teflon film. If you cannot use another slow resin instead, you would need to increase the lifting speed and lifting height to slow down the buildup.
     

How will the above affect your print? They will significantly affect the consistency of the separation force and increase the failure rate. Even if the print survives, the surface quality may be deteriorated. They will affect both the Teflon film lifetime (please refer to the PSP resin container blog ) and the printing quality.

Knowing the reasons as to why high adhesion occurs and the solution to it will greatly smooth out your printing process. Even if your print did not come out the way you expected, it is important to understand why it happened. This way, you know what the cause of the problem is and learn to avoid it next time. Learning from failed print is perhaps one of the best way to quickly learn and understand more about SLA printing!

Impact of Background Curing

How does background curing affect the print or the printing process? During the printing process, the resin under background exposure keeps accumulating photons. Once the number of photons received per unit area reaches the threshold dosage, the resin will start turning into solid.
Have you ever seen bits of resin flakes attached to your print? This is a physical example of background exposure affecting your print. The reason for this is because the resin close to the printing zone is being cured slowly by both the background exposure and the scattering light from the pattern. Once the resin in the region near the patterns accumulates enough photons, thin layers attaching to the model may form and get separated from the Teflon film (as shown in the Photo 1). Sometimes, part of the layer could drop or remain at the vat floor (as shown in the Photo 2). A model that requires a longer time to print is more likely to form these flakes. The worst case scenario is when a fast resin is cured by the background light, it could stick to the vat floor firmly and pull your model out of the platform or even break your model into two pieces.

Even if you do not see the flakes on the print or within the pool of resin, the background exposure still affects the resin you are printing with. The background exposure partially cures the resin near the vat floor in the build zone. This will have an impact on the printing parameters of subsequent layers. Because the resin has already absorbed some photons, curing it with the normal exposure time will actually mean that the cured resin is being over-cured. As the liquid resin accumulates photon gradually, the resin will slowly become more viscous than before and the printing parameters may change.

It should also be noted that the exposure time scaling is not linear. The resin curing is an ongoing reaction even after the light is off. The faster the curing speed the more ongoing reaction. Therefore, fast resin or stronger light tend to have more ongoing reaction. In general, we have seen resins with exposure time less than 1 second are more likely to form solid background cured flakes.

The Solution to Background Exposure

There is no way to achieve infinite contrast ratio for DLP, but there are ways to reduce the background exposure during the printing process. This is where the shutter from the Titan 2 and Titan 1 Upgrade Kit plays its role. The shutter will remove the background exposure when the platform is moving for separation. (This is the time where there should be- ideally- no light being shined upon the resin.) With the shutter, the accumulated number of photons absorbed will be greatly reduced. The adhesion between the cured layer and the Teflon is then more predictable and the lifetime of recycled resin will be extended.

Another way to reduce the impact of background exposure is to lift the platform higher so more ‘fresh” resin will be sucked into the printing zone and dilute the resin that has been exposed under background light in the print area.

For the same resin, increasing the build size to increase the exposure time will reduce the background curing effect. As a result, you may see the background cured flakes appear at 37 or 50um XY resolution but not at 75um for the same resin. Using a shutter will alleviate this problem. Sometimes, the background curing is caused by the video card. For Titan 1, if you use Nvidia display adapter, it is likely that you will experience background curing. Using an Intel built-in video adapter will solve this problem. For Titan 2, video adapter of Raspberry Pi does not have this issue.

Many of the consumer level printers were FDM (Fused Deposition Modeling) 3D printers. This involved a spool of filament to be heated to a high temperature and deposited into the shape that the user wishes to create via an extrusion head. With this type of printer, users only get the shape or form of the print but will not get details nor reach surface smoothness. In addition, the printing speed is relatively low.

Apart from the FDM technology, some 3D printers adopts the stereolithography (SLA) technology. Some SLA 3D printers use laser galvanometer to create patterns. This type of printer usually has laser stability and reliability problems.

How about the Titan 1 and Titan 2? Instead of the laser-based SLA technology, we use Kudo3D uses a highly reliable DLP technology developed by Texas Instrument to generate digital light patterns in a two dimensional fashion rather than scanning with a laser diode which is susceptible to ambient temperature, dusts and mechanical failure. DLP can also provide a resolution that laser galvanometer is impossible to match.

Using a better digital light pattern generator improves the resolution of the printers but it is not the main factor that attributes to our success in the last two years. So what exactly set our 3D printer apart from the other SLA 3D printers out in the market? The answer lies within the layer separation technology of the printer.

Most low cost SLA printers incorporate a bottom up light source and a transparent resin container. The challenge to these SLA printers is to separate the cured layer from the resin container floor. The separation force is proportional to the area of the cured layer. That is why most of the low cost SLA is not able to print big models.

To overcome this challenge, we have developed a patent pending passive self-peeling (PSP) technology that greatly reduces the separation force that others are hard to match by using both flexible and elastic materials for the resin container. PSP not only enables large area printing but also increases the speed and resolution of the prints. Since the peeling is passive, there are no motors involved. The printer’s structure is simplified. With less moving parts, the Titan 1 and Titan 2 are very reliable.

We understands that the lifetime of the consumables is a main concern for consumers while resin container is definitely a critical part for low cost SLA printers. Because of the low separation force, our container is less stressed and the lifetime is much longer. Besides, there is a protective film on the vat floor of Kudo3D’s containers to prevent the attack from the resin. As a result, our printers are compatible with more materials and relax the constraint for material developers.

With the PSP technology, Titan 1, our first generation printer, proved its worth when Kudo3D showed off a biomedical tissue scaffold research model printed at 37 micron XY resolution and 20 micron Z layer thickness. The beams have a diameter of 0.18mm (next to the print is a coffee bean for scale).

Pushing the printer to the extreme, we proved once more that our printers can print fine features that other low cost SLA printers cannot achieve. In the image below, a 45 micron thin needle was printed with the Titan 1. This needle is less than half the diameter of a hair. No other low cost printer can achieve this resolution.

Now in June 2016, we have launched its second-generation 3D printer, the Titan 2.

The new Titan 2 features:

• WiFi enabled.
  – There is no need to connect the printer to the computer after uploading the data.
• Allows web-based controlling.
  – Users can use any device (PC, Mac, smartphones, or tablet) to control the printer. Once the printing starts, the control device can be used for other purposes.
• One device can be used to command and control multiple Titan 2 3D printers.
  – This is especially helpful for those who would like to use the printer to setup a production line.
• Has a built-in computer.
  – The Titan 2 will be independent from the user’s computer.
• Has a shutter to reduce background exposure during prints.
  – This can ensure high quality prints.
  Additionally, the new Titan 2 will be assembled and calibrated before shipping, making the startup process even easier for first time users.

It is definite that 3D printer will keep evolving in technological advancement. Users are now able to print high quality things that they design or even better than they could ever imagined.

Titan 1 was featured on an article on Stereolithography by Eaglemoss Publications!

Learn more about how light causes photoresin to cure. Also enjoy the pictures of prints by the Titan 1!

What makes the Titan 1 different from other SLA 3D printers?

But first, what is SLA 3D printing? SLA stands for stereolithography. In this method of additive manufacturing, a 3D printed object is built layer-by-layer using a liquid resin (photopolymer) that is cured using UV or visible light. What differentiates the Titan 1 from other SLA 3D printers, is that the Titan 1 uses Digital Light Processing (DLP) to shine light patterns via a projector. Many SLA 3D printers use a laser galvanometer to generate patterns.

Here’s a quick guide to everything you need to know about DLP and laser 3D printing.

DLP 3D Printing

A high resolution projector, light pattern powered by DLP technology, sits beneath the resin container and projects image slices to cure each layer. The projected image is just black and white as seen below. Since the resin is UV sensitive, the white areas of the projected image will direct UV and purple light to the areas require curing.

This method is quite simple when compared to the stunning resolution and details that it produces. The projector remains completely stationary during printing (and it is important that it doesn’t move or else the layers won’t align properly), which means there are few moving parts and little machine maintenance required. For Kudo3D’s Titan 1 and Titan 2, the only moving part is the stepper motor that lifts the build platform as the model grows after each layer is cured.

(Image Source: http://m.iopscience.iop.org/1758-5090/6/1/015003/article)

A sliced layer that will be projected onto the resin container. From Pranav Pancha’s model of the Eiffel Tower (https://grabcad.com/library/eiffel-tower).

Laser 3D Printing

Laser based SLA 3D printing uses a laser to trace out the cross-sections of the model. Similar to fused deposition modeling (FDM) 3D printing, where each layer is deposited in a continuous stream of filament, the laser essentially “draws” the layer to be cured. The laser is focused using a set of lenses and then reflected off of two motorized scanning mirrors (galvanometer). The scanning mirror directs the precise laser beam at the reservoir of UV sensitive resin to cure the layer. Alternatively, some laser based SLA 3D printers move the laser directly using a XY stepper motor arrangement similar to those used in filament based printer.
(Image Source: http://biega.com/3d-printing.shtml )

Now that we know how each method works, let’s do a comparison.

SPEED AND ACCURACY

DLP 3D printing is very fast because it projects the profile of an entire layer at one time, turning 2-dimensional images into a 3D object. In comparison, lasers have to trace out the entire sliced profile line by line which takes a lot more time. Small inaccuracies are also likely to occur and can affect the structural strength and surface smoothness of the print.

RESOLUTION AND BUILD SIZE

The projector makes DLP 3D printing versatile. Depending on the resolution and size of the 3D model desired, DLP can be easily moved up or down to adjust for your customized settings. DLP 3D printers can produce details with much higher resolution than laser based SLA 3D printers. However, resolution depends on the projected pixel size. This means that higher resolutions are limited to smaller XY build area.

Laser 3D printing generally has a fixed laser spot size of about 300 um, while the DLP projector in the Titan 1 can be customized to print from 37 to 100 um. Tuning the laser spot size smaller will make the printing speed extremely slow. On the other hand, since lasers sweep a continuous path, they’re less likely to show surface “pixelization” artifacts the way a DLP 3D printer printed model will. The pixelization is usually more noticeable for large prints. Pixelization can be removed with anti-aliasing or pixel shifting.

MAINTENANCE

Laser based SLA 3D printers require a number of moving parts in their design. XY motion is achieved via the use of two stepper motors to move the laser itself, or a galvanometer which rotates a mirror assembly to reflect a stationary laser’s light to the desired location. DLP 3D printers do not require any mechanical XY motion for photopolymer curing since projector illuminates the entire XY plane at once.

The Titan 1 and Titan2, with patented passive self-peeling technology, only require one stepping motor for Z-axis linear stage, eliminating the need for sliding or rotating tray mechanisms. This minimizes assembly complexity, maintenance, and wear on the machine.