Viscous Resin Handling Mode

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Viscous ResinWhile more and more resins for SLA 3D printing come to the market, not many SLA 3D printers can actually properly handle them. Lack of parameters, understanding of the actual liquid properties or simply outdated software can lead to a premature damage of a 3D printer if one would just pour an unknown substance into it and wait for results.

As we do have many resins being shipped for testing as well as samples, we thought it would be a good idea to rewrite some of the subroutines which are related to those "special" cases and create a proper as well as dedicated print cycle specifically for highly viscous resins which don't belong to any specific category and are used in very limited but specialized cases.

Generally speaking it is not advised to use resins with high viscosity while 3D printing as the behavior of the liquid is very particular and doesn't go well with a lift pressing down and squeezing it to the VAT surface. A standard resin such as the Spot-A General Purpose has an approximate viscosity of orange juice and flows as well as avoids obstacles very quickly. On the other hand when a very viscous resin is used such as a Dental, Ceramic or other exotic variety, their viscosity may be more than enough to break the printer or damage it.

Currently all the functions described below are available as a BETA addition to the latest Ilios Photon 2 3D printer firmware and can be enabled through the Ilios 3D Suite. Normal print cycle is still fully active if the Viscous resin option is not chosen.

The actual cycle and its relation to the model being printer is much more complex than the description below but it has been generalized for the end user to give a basic understanding of why this is needed and what measures are taken by the Ilios Photon 2 3D printer to ensure a safer and more reliable result.

Liquid Flow Relief

When using highly viscous resins, keep in mind that it is the initial 10 - 30 layers that will most likely determine the outcome of the final print. As the lift of the 3D printer lowers down to create that initial layer, it will only leave a gap of 75 - 6 microns (depending on the settings). The speed of the lift however if left unchanged, will most likely create high pressure while the viscous liquid tries to escape.

As a first point of failure, if the SLA 3D printer doesn't have any sort of dampening, the glass or plastic on the VAT surface will most likely break. If there is dampening, the VAT will lower trying to compensate while the liquid slowly escapes.

During this time, an additional delay was added for the initial 30 layers, where the Ilios Photon 2 will wait for 20 seconds before enabling the UV LED projection. This gives time for the liquid to settle and realign the proper distance between the VAT and Lift as the dampening presses the VAT back up. This time is set to gradually decrease as the layers build up and eventually is left to a minimum of 3 seconds. The delay however is not completely removed as unpredictable model shapes can be generated which could cause a faulty layer thickness buildup and eventual VAT break if not attended.

Additional Vacuum

When the initial layer is exposed, a faster retract speed of the lift would normally pull the initial model layer from the Lift with immense force, risking the initial layer separation from the Lift. This is the point which could cancel out the entire print process and generate a failed print.

The retract speed on Ilios Photon 2 will be 5 times slower for the initial 15 layers and will speed up as the exposure values for each layer decrease as there will be less force applied for fast curing layers. The retract speed however will always be much lower than on a less viscous resins to ensure that the denser liquid has time to refill the gaps before the cured layer is lowered down again.

Resin Particulates and Additions

In most cases the resins which are more viscous will include a high concentration of particles to generate a needed result for which the resin was made. These particles however also create a problem since unlike pigments, solid shapes, no matter how small, in high concentrations will block UV or most of any light to pass through. This creates a problem for the surface area of the VAT and Lift. For a proper model adhesion to occur to the Lift, the curing light must solidify the material all the way through the layer thickness and down to the final Lift surface.

To generate a proper adhesion for resins with a high concentration of particulates, the cure time for the initial layers must be increased by 3 - 5 times if not more, so that the initial layer has enough time to cure what it can before proceeding to the next one. This is where the Custom Material parameters come into play within the Ilios 3D Suite.

Minimum Layer Height

As another note, it may not be possible to use layer heights of 25, 15 or 6 microns which the Ilios Photon 2 provides when using highly viscous resins. The particles within viscous resins may physically prevent the liquid to clear enough space for such small thicknesses. As a result, the model will continue to build up height much greater than what the 3D printer thinks until the dampening assembly reaches its limit and eventually breaks the glass.

To prevent this Ilios Photon 2 already has sensors which monitor the attitude of the VAT motion. If the VAT movement reaches critical limits, a delay will be enabled, letting the resin evacuate the needed space. If the process is repeated 3 times, the print will pause and ask the user for further instructions.

Conclusion

All the above parameters and mode functions have been added to once again protect the Ilios Photon 2 from damaging it self while working with untested or exotic materials. These functions ensure that your investment is well protected and doesn't just bluntly function until something breaks. Additionally these parameters allow the user to experiment not just with different cure settings but also different material properties while adding an additional layer of protection.

Δημιουργηθηκε στις Πέμπτη, 01 Ιουνίου 2017 22:59
Γράφτηκε από τον/την Demetris Zavorotnitsienko

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