To start off, it is important to understand how the Kudo3D Titan 1 and Titan 2 work. Both printers come with an US patented passive self-peeling technology. The cured layer is peeled away from the resin container, without an additional actuator, when the build platform is lifted. Please refer to our PSP blog to better understand how the PSP works: http://www.kudo3d.com/understanding-kudo3d-psp-resin-container/

There are 5 parameters that you may need to adjust for the layers to speed up the printing process or to improve the print quality. Let’s discuss the impact of these parameters on your print. Afterwards, we will break it down the steps and provide a guideline regarding how to setup these parameters.

1. Exposure time: Exposure time has an impact on the resolution, the hardness of the cured material, and the adhesion between the cured layer and the Teflon film. The normal exposure time depends on the resin being used and the layer thickness. Please note that the normal exposure time could drift away due to the aging of the projector lamp or the resin. To identify the normal exposure time, please refer to the article in http://www.kudo3d.com/understanding-kudo3d-high-resolution-calibration-model/

    

2. Lifting height: The platform must be lifted to a height that gives enough time for peeling process to be completed. This number depends on viscosity of resin, adhesion between the cured layer and the Teflon film, lifting speed, exposed area, exposed pattern, and builds platform area.

    

3. Lifting speed: This number usually depends on the strength of your material and the adhesion between the cured layers. The separation force is higher when the lifting speed is higher. If the material is not strong, a high lifting speed may break the model. If the adhesion between the cured layers is not strong, a high lifting speed may tear the model apart.

    

4. Lowering speed: This number has an impact on very fine and weak structure. When the model is lowered at a high speed, the pressure exerted from the liquid resin will also be higher. If the structure is weak, this pressure could temporarily or permanently move the printed model in a micro scale. As a result, you could see more abrupt layer interfaces under the microscope. Sometimes, fine structures could also be distorted. When the viscosity of the resin is higher, the pressure is higher, meaning that you may need to slow down the speed even further.

    

5. Delay: When the platform is lowered in the resin, it will push the resin away. “Delay” is the time required to stabilize the resin. When the viscosity is higher, it takes more time to stabilize the resin.

    

In general, for each model, we can separate the layer zones into two sections. The first section involves both vacuum force and the adhesion force. The second section usually only involves adhesion (unless the cured layer has a large area). The following guideline is a rule of thumb for setting up the printing parameters. You can tune it up after gaining more experience.

First Section: (first 2mm for small build plate and 4mm for large build plate)

First zone

First layer only- This layer is called attachment layer, which is part of the base and the most important layer.

Exposure time

• 10 to 20 times the normal exposure time to make sure that any potential gap between the build platform and vat floor is fully cured and the first layer is attached to the platform firmly.

Lifting height

• Large build platform: 7 mm
• Small build platform: 5 mm

Lifting speed

• 10 mm/min

Second zone

Rest of the base layers- Normally, the base layers includes all the layers before the supports. The total thickness of base should be thinner than 0.3 mm.

Exposure time

• 5 times the normal exposure time defined with the calibration sample

Number of layers

• Depends on the thickness of the layers and base
• For example, if the base is 0.3mm and the layer thickness is 0.05mm, then you have 5 or 6 layers for the base.

Lifting height

• Large build platform: 7 mm
• Small build platform: 5 mm

Lifting speed

• 10 mm/min

Third zone

The rest of the layers that make up the first 4mm of a model using large platform or the first 2mm using small platform. This zone has the vacuum force influence. Please note that if your z-zero sinks below the Teflon film, the number of layers in the vacuum force section should include the number of layers that brings the platform from z-zero to the actual vat floor.

Normally, this zone contains only supports. This is part of the foundation so it must be strong and stable. You can adjust the number of layers accordingly depending on whether the resin viscosity is higher or lower.

Exposure time

• Half of the second zone

Number of layers

• For example, if the layer thickness is 0.05mm then you have 40 layers for the first 2 mm of printing with a small build platform. If the base consists of 6 layers, the remaining 34 layers will be assigned to this zone.

Lifting height

• Large build platform: 5 mm
• Small build platform: 3.5 mm

Lifting speed

• 15 mm/min

Second Section:

Fourth zone

This zone normally contains layers for supports plus a few layers of the model to make sure that the adhesion for the tips is strong. This zone is also part of the foundation.

Exposure time

• Same as the third zone
• If the model has supports close to the securing aluminum bar, you need to increase the exposure time about 2 times.

Lifting height

• 3.5 mm

Lifting speed

• 15 mm/min
• If the bottom of the model has a flat surface and the model is not rotated, the first few layers that attaches to the support tips usually has a larger area. Since the separation force is higher for large exposed areas, you might want to slow down to avoid the tips breaking off.

Fifth zone to Seventh zone

Layers for both supports and model

Exposure time

• Gradually lower the exposure time from the 5th to 7th zone to avoid horizontal lines caused by non-uniform layer shrinkage.

Lifting height

• Ranges from 2mm to 5mm, depending on the exposed area

Lifting speed

• 15 mm/min

Eighth zone and more

Layers for model only. These layers consist of purely model slices.

Exposure time

• Normal exposure time

Lifting height

• Ranges from 2mm to 5mm, depending on the exposed area.

Lifting speed

• 15 mm/min

This provides the basic overview of how to set up the printing parameters within the Kudo3D software. As mentioned before, there is no “one solution that fits all” for any type of resin or model. Being said, the best method to understand how to set parameters is to have as much practice and experience as possible. Once you understand how the numbers are set and why they are set as so, you will have a much easier time in creating parameters for different types of models!

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.

This blog will guide you through and help make sense of each feature on the sample.

1. Rectangular columns and spaces (Slots)

To determine what the “normal” exposure time is for a certain resin, check the 4 rectangular slots on the leftmost side of the calibration print. The columns in-between the slots should have the same measurement for the first 4 on the left side. The width of each slot and column should be 0.8 mm. The width of the right most three slots are 0.6mm, 0.4mm and 0.2mm, respectively.

Too narrow of the leftmost opening will mean that the resin was overexposed. Too narrow of the column in-between will mean that the resin was underexposed. If the resin does not have a high resolution, have high viscosity or the XY resolution is not high enough, the right most slot may be closed.

2. Pillars

Take a look at the pillars on the left side of the print. To make most of the pillars protruding and present, the resin will need to be very hard. Hard resin or overexposure will increase the number of pillars printed successfully. This is because the pillars will be hard enough to overcome the gravity at an angle of 45 degrees. Hardness and the strength of the resins will determine whether the pillar will survive at the angle or not. Another thing to note is the diameter of the pillars. Thicker pillars are stronger and tend to survive during printing even if they are longer. If printing with a low resolution resin, light bleeding makes the pillar thicker and also change the shape of it. When a higher resolution resin is used, more holes are opened and the pillars will be closer to the original dimensions. However, thinner pillars may not survive if the material is soft. Therefore, for precision applications, you would need to use a high resolution hard resin.

3. Holes

Take a look at the 7 holes below the rectangular slots on the “Titan 1” side. Hole openings are influenced by the viscosity of the resin, the depth of the hole and the ability of resin to block light. To make all 7 holes open up, the resin may need to be underexposed. Overexposing the resins will result in the smallest few holes to close up due to light bleeding or scattering. With a resin that has a lower viscosity, there will be more holes open. Because the resin is more likely to drain out of the hole during printing, light bleeding is less likely to seal the hole. However, low viscosity resins in general have more monomer in the formula so the material tends to be weaker and more brittle.

4. Trenches

Check the trenches near the top of the “Titan 1” side of the print.

We limit the aspect ratio of the trenches to be one so the depth and the width of the trenches are the same. Having the resin be overexposed will result in a narrower, shallower trench. An underexposed resin will further widen the distance between each trench. The reasoning is the same as that for the slots and holes.

Given all this information, the questions is: When do you need to print this calibration print again? We usually recommend doing the calibration for the following situations:

1. Using a new type or new bottle of resin
2. Printing at a different XYZ resolution
3. If you regularly recycle (pour the leftover resin from a print back into the original bottle) the resins without replenishing with fresh resin
4. Every 500 hours of usage of the projector (to determine if the projector lamp intensity decays)

You can measure the size of the features on the high resolution calibration model with Netfabb basic by pressing the “ruler” button. For actual printed sizes, you would need to use a camera or microscope and take a photo of the printed sample with a benchmark.

This calibration sample only gives you an idea about the exposure time, the resolution and hardness of the material. The lifting height is related to the resin, lifting speed, cross-sectional area and cross-sectional pattern so there is no calibration sample to predict the lifting height. If you are not familiar with the resin used, please be more conservative about the lifting height and speed.

Now, you are ready to continue on your printing journey! Please be sure to share any awesome prints with our team as well! Have fun!

What do you do with the unused resin in the PSP resin container?

The great news is that you can recycle the unused resin. When removing the resin container or build platform after printing, please cover the venting holes on top of the printer to avoid dripping resin on the projector by accident.

Carefully use a funnel and strainer to pour the resin back into the bottle. It is important to use a strainer to sift out residual pieces of plastic that may have been cured due to a failed or partially failed print and flakes cured by background light. Wash the strainer and funnel after each use to avoid contamination with other resins. If you are using the same resins, you may just need to wipe the strainer and funnel and store them in a dark place.

If the resin does not contain pigments,  you can leave the resin in the container for about a week.    If the resin contains pigments,  do not leave the resin in the container for more than two days as the pigments may settle.  Some pigments settle faster than others so it is better to use a rubber scraper to stir it before printing again if the resin is left in the container.     It is a good practice to recycle the resin back to its original bottle to extend the lifetime of the leftover resin.

How do you clean the PSP resin container?

After recycling leftover resin, the resin container could be washed with mild dish detergent and water if your are going to use a different resin for your next print. Soft resin container can be cleaned with Isopropyl Alcohol (IPA) directly but please do not soak the container in the IPA.  When cleaning the soft resin container,  please be careful not to touch the silicon as the soft silicone is very sticky.   If you plan to print again soon and you recycle the resin,  you can simply store the container in its original packaging box without cleaning. If you plan to store it for more than a couple weeks, then it is better to clean it up and store it. After putting on disposable gloves, gently clean the container using your fingers. Abrasive cleaning supplies, including paper towels, can damage the Teflon film. If needed, you may use a lens wipe instead. Soft vat has a very stick silicone at the bottom of the vat. Please be careful when wiping the vat floor as the paper or cloth can stick on the silicone and hard to be removed.

If you find pieces of cured resin stuck to the resin container, slowly remove the plastic to avoid damaging and lifting the Teflon film. We recommend using a thin plastic blade to separate the cured pieces. Do not exert vertical force to pull the pieces as the Teflon film could be damaged or lifted. To extend the lifetime of the resin container, please also avoid rubbing the edges of the Teflon film and the four corners of the PSP container.

Rinse the container with water several times to completely get rid of the soap and try not to let water run below the vat and leave water stains. If there is resin residue on the bottom surface of the container, you can clean it with IPA (Isopropyl alcohol) and a lens wipe. Fill up half of the resin container with water when rinsing, and tilt the container slowly to drain out the water. The Teflon film should be left mostly free of water since Teflon is a non-stick material.

How do you dry the PSP resin container?

Good question. You should not begin printing with the resin container while it is still wet. To dry the container, you may use a dustless lens wipe or leave the container face down to dry overnight. A fan may speed up the process.

Useful tips:

– If you leave resin sitting overnight, mix it up before printing again, since the pigments could have settled. Settled pigments will affect the resolution of your print. Another good practice is to renew the overnight resin by mixing it with fresh resin. The fresh resin should make up at least 50% of the resin in the PSP container.  

– Got resin everywhere? Isopropyl Alcohol (IPA) is very useful. It’s the same stuff you use to rinse off extra resin, and it cleans the resin off your computer mouse or keyboard just as well. Note: Do not use IPA on printer acrylic covers, because it will cause frosting.

– Cover the projector lens with a piece of paper or business card to avoid collecting dust if your printer model does not come with a shutter

– Make sure the UV blocking cover is on top of the printer.

Still have questions? Leave us a comment below!

In the past, post-processing a print was a long labor-intensive process full of sanding and grinding in order to achieve a professional finish. With the Titan 1 DLP SLA printer, the 3D prints are produced with a smooth professional finish, greatly reducing the energy and time required for post-processing.

Thanks to Kudo3D’s patent-pending separation technology, less supports are required for printing, which means less cleanup and scarring. Rings can be printed with the Titan 1 without internal supports and only require one support at the base of the ring.
Ring by Smita Lai. Only one support on the bottom.

The image below is a great example of how the Titan 1 reduces or even eliminates post processing. No sanding was necessary, preserving the fine details of the miniature. In addition, with layer heights of 35um, the horizontal lines that usually define each layer are invisible.
“Froggy” by Spectoys printed with Titan 1. No sanding necessary. Prints can also be casted or painted afterwards.

We have simplified the post-process down to 4 easy steps with very little equipment needed.

To post-cure you only need a few over-the-counter items including:

• 91% Isopropyl Alcohol (IPA) or Rubbing Alcohol (99% IPA is better, and it is available on Ebay)
• Containers large enough to submerge your print in
• Disposable gloves
• A pair of pliers
• UV light

 
1. Remove the print from the platform using a blade or other sharp tool. Please be careful not to slip and cut yourself.
 
2. Next, submerge your print in a container of Isopropyl Alcohol (IPA) for 3 minutes. Then, swirl it around in the IPA to rinse off extra resin. Alternatively, you can use a squeeze bottle to rinse off extra resin. This step removes the uncured layer from the print, helping to reduce any residual stickiness.
RichRap’s Voronoi Tower http://www.thingiverse.com/thing:24123
 
3. At this point, your print should have very little to no stickiness left on its surface. Next, gently remove the printing supports with a model cutter. It is easier to detach the supports closer to the tips, since the supports are pointed.
Depending on how precise you need your print to be, you could leave a tiny stud of the support tip attached to the surface to avoid making a dent. The protruding tip could then be sanded down. Pulling the support out or cutting very close to the attachment point creates risk of leaving a small dimple behind.

Jennifer Chen’s Flower Design
 
4. Use either Kudo3D’s UV-post curing lamp or direct sunlight to complete the final curing process. The amount of time needed to post-cure a print depends on its size and the post-curing method used. Using a clear container with tap water to submerge the print is optional but shortens the curing time needed.

Post-curing with Kudo3D’s UV lamp

Submerge the print in a clear container filled with tap water. Place the container under the UV lamp for about 5 minutes. If the print still feels uncured or sticky, leave the print under the UV lamp for a few more minutes.
 

Post-curing with Sunlight

Submerge the print in a clear container filled with tap water. Then place the container under direct sunlight for about 15 minutes. If the print still feels uncured or sticky, leave the print and the container in the sun for a few more minutes.

 
The purpose of post curing is to dry up and harden the outer surface of the print. Oxygen in the air diffuses into the outer layers of resin while printing, preventing the print from fully curing. Submerging the print in water forms a water barrier to prevent oxygen inhibition since the water prevents oxygen in the air from reaching the part during curing. This allows the UV light from the sun or a lamp to cure prints faster. Post-curing without placing in water will take much longer. This process mainly cures the surface of the print. Interior structures will continue to cure slowly over time due to ambient UV light exposure.
 
With the Titan 1, you can spend more time designing and printing and less time post processing!

We usually arrange layouts in “Blender“, you can use other free softwares for the same purpose.

• Import all models intended to be printed at the same time to “Blender”.
• Resize, reorient and reposition the models within build boundary.
• Level the models to the floor of the boundary.
• Might need to open some holes on hollowed models at this stage to avoid potential vacuum effect during printing.
• Export to a new stl file.

Printed batman – example for opening a hole
 

5. Adding supports

This is the most important step before printing. Adding supports is subjective and discretionary. Some models may not need supports at all if it has a flat bottom large enough to hold the model on the build plate. Others may require different types of support to meet your needs. The followings are rules of thumb that we followed for adding supports:

1. Locate all surface areas with local minimas (upside down hill or tips).
2. Determine the number and location of supports that must be added on other downside facing areas to maintain mechanical stability of partially printed model during printing.
3. Determine which supports should be built from the floor or from the model itself.
4. Hide as many as possible supports to areas not visibly important.
5. Add supports strong enough and do not bend during printing.
6. Make sure the tip of the support is strong enough to avoid model detaching from the supports during printing.
7. Make sure the tip of the support is not too large to leave scars after removing the supports.

Adding supports – 3D printed Thousand arm Budda (on the printing process)

(Printed dragon with supports.)

There is no one single software that is intelligent enough to add supports for you without any human judgement. You can use a free software to generate a bed of nails uniformly under your model and then use “Blender” or other similar softwares to tune up your supports by adjusting the position and size of the nails. You still need to manually add supports that are not perpendicular to the floor or supports that stand on the model itself.

6. Slice 3D models

The principle of 3D printing is based on an additive process building physical models by attaching thin layers. In order to generate those thin layers, the computer generated 3D models need to be sliced into 2D images for each layer before printing. After adding the supports, you would need to check again the integrity of the STL file with supports to be printed. “Slic3r” is the open-source, cross-platform tool we are using. Build area and the thickness of layers are related to the printing resolution. You can set them via any slicing program. After slicing, 2D image files will be projected to the bottom of the resin container during printing.

Preparing printable 3D files is not straightforward due to software limitations. Each step is important to achieve a high quality 3D print. We have been through many trial and errors and will share our experiences on our blog. If you have any questions, welcome to contact us.

1. Locate 3D models online

There are many websites providing a variety of 3D files you can download for free. If the file extension is not ‘stl’, you would need a 3D software to convert the model to stl format. “Thingiverse” is our most favorite site, because most of the files contributed are in stl format for free. We look for 3D models with higher resolutions to avoid limitations posed by the image itself. We use 3D Eiffel Tower as our main testing model for tuning printing parameters of our machine and our PSP (Passive Self-Peeling) mechanism. We have printed more than 80 of them with different sizes. The tallest one is about 9.4 inches, whereas the smallest one is 3.5 inches tall with pillars as tiny as a strand of hair.

2. Check and fix files

All downloaded 3D files need to be checked before slicing and printing. A lot of them may even require repairs. Check your STL files to ensure:

• all objects maintain “outside” orientation.
• the surface of all objects is closed and there are no overlapped faces.

We use “Netfabb basic” to repair models. If the number of shells is too high or “Netfabb basic” fails to fix the model, you would need to upload the stl file to “Netfabb cloud” for further repair.
Sometimes, multiple shells could get you a problematic hollowed model in the following step.

3. Hollow 3D models if necessary
Most of the models require hollowing to save printing materials. In addition, hollowing minimizes light exposure area and greatly reduces layer separation force. The printing time is thus shortened and the printing quality is enhanced.

We use “Meshlab” to hollow our 3D models by building a smaller offset model with inverted surface.
(To Be Continued….)