2 reasons to reduce % UV power of a resin 3D-printer explained

it is possible to reduce the power of the LED’s in almost all professional 3D-printers and also in some new entry-level MSLA / LCD 3D-printers. We sometimes get questions why we would not always advise to print at 100% UV LED power. In this article we explain the reasons and how to use this setting properly. 3D-printing parameters of a lot of printers, including % UV power settings are available in this link.

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Reasons to reduce the % UV power of a resin 3D-printer explained.

The technology to reduce the % of UV power inside a resin based 3D-printer dates back to the origin of DLP 3D-printers. 5 years ago and before, the stability of the LED’s was not too great over its lifetime. With full-time production you would already see LED power degradation after roughly a year. To be able to cover this, manufacturers would print at ±60% LED capacity. If degradation sets in, the LED’s could always be re-calibrated back to the required power. If printing at 100% already, this would not be possible anymore after LED degradation and longer exposure times should be needed. Nowadays with improved LED’s and better cooling, this issue is mostly solved.

Image by Wewolver: schematic representation of a DLP 3D-printer.

Reduce % UV power of a resin 3D-printer to increase print quality.

There are other benefits in reducing the % UV power of a resin based printer. At lower % UV power, you would need a longer exposure time to get the desired cured layer thickness for all resins. This improves the process window and accuracy of a printed part. Additionally, for transparent materials like Liqcreate Premium Tough, some high power machines tend to give through-cure or bleeding in 3D-printed parts. By reducing the % UV power in these machines, a larger process window is created and through-cure or bleeding is minimized. For slower resins and high-speed prints, it is usually advised to print at high % UV power.

Why does a lower % UV power increase accuracy?

A lower percentage of UV power gives a larger working area. A good calibrated printer can still vary in light output by +-5% and some minor resin deviations can be covered by this as well. This is easiest to explain when measuring the reactivity of a resin. Usually we measure it by exposing resin to different amounts of light power (in mW/cm2). When we expose resin with for 2; 6 ; 8; 12; 20 and 40 mW/cm2 and measure the thickness of the cured resin, it can look somewhat like this:

At +- 6mW/cm2 this resin starts to polymerize, first rapidly and at higher layer thickness in a slower pace. If we set the light-source in the printer at 8mW/cm2 power, this means that we have to divide the amount of power on the x-axis by 8 to get to an amount of seconds of exposure. When we do that for this resin it looks like this.

Meaning that after 0,25 seconds the resin starts to cure. When printing at 0,05mm layer thickness you want to over-cure the layers a bit and print with the time needed to cure 0,07mm layers. In this case it would be close to 0.95 seconds. With slight deviations like printing at 0.9 seconds, you would cure just 0,055mm layer or on the plus side with deviations at 1,0 seconds exposure time you would cure 0,082 mm layers. This means a small difference in exposure time, resin reactivity or light output homogeneity of the printer results in a big difference on how the resin reacts.

When we would lower the % UV power to 50% this would mean we would print at 4mW/cm2. This would immediately double our process window and also increase the printing time as can be seen in the graph below.

The exposure time needed to cure 0,07mm layer thickness (and actually print at 0,05mm layers) is in this case 1,9 seconds. Deviations to 1,95 seconds would mean 0,075 micron layer thickness and deviations to 1,85 seconds would mean 0,065mm layer thickness. So differences in output or minor differences in the resin are easily covered. Doubling the process window will increase accuracy as less under-cure and over-cured spots are present.

Generally spoken: a 3D printer can be used to replicate any figure of any size with high accuracy. The fact it might take several hours to produce one single design (depending on the size), it consumes much less time and is much more cost efficient compared to e.g. prototyping carried out by engineers or product designers. This is due to the fact that 3d prints can be created from a vast selection of materials such as polymers, resins and diverse metals.

A 3D printer works with building up layer by layer of a desired compound (resin, polymer or metal). Until the layers merge into the desired 3d shape. Major preparations have to be done before the printing can be started as the printer relies on a computational generated 3D model.

There are mainly four printing methods: fused deposition modelling (FDM), stereolithography (SLA), carbon CLIP technology (CLIP stands for continuous liquid interface production), and selective laser sintering (SLS). Depending on the type of compound used, the type of drying or curing will be different. From the mentioned techniques, the SLA and CLIP are the ones where photosensitive resins are employed. Generally, lasers or UV-LED lamps are used. Lasers can be used for all materials, while UV-LED lamps are applied for resins, gels and special polymers.

To look into the UV process in more detail: One of the most important factors to have in mind when working with a 3D printer is the curing of the compound, since it is not possible to continue applying raw material if the work’s surface has not dried yet. By irradiating the composite with UV light, the composite hardens as it polymerizes, allowing more material to be applier in further layers.

Depending on the wavelength and the material properties, the UV exposure time determines directly the polymerization process or the curing of the resin. It is also important to consider which resin is the best fit to the printer. The most common polymeric resins used in the UV-curing are thermoplastic polymers, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyamide (PA) and polycarbonate (PC), and thermosetting polymers such as epoxy resins, which requires thermal or UV-assisted curing to complete its polymerization process.

Metal materials usually cannot be cured by UV light sources due to their requirement of a more focused power source which fall upon one small area. Hence, laser technology is more frequent used when working with metals.

Besides the already mentioned curing of the resin while printing, UV is further used in the post-processing of the formed shape. This procedure is carried out to improve the material performance and mechanical properties, minimize shrinkage, increase of resistance or resilience, among others.

But why should an LED be used as a light source in the 3D industry? As it was mentioned before, a LED lamp requires a lower energy source to operate and in the present days where in the industry the price of electricity represents a big share in the operational costs, it is a factor that must be considered. Further LED light sources are very compact and therefore easy to place especially in the smaller set-ups of desktop 3D printing machines.

References:
Wang, X., Jiang, M., Zhou, Z. Gou, J., & Hui, D. (). 3D printing of polymer matrix composites: A review and prospective. Composites Part B: Engineering, 110, 442-458; Stansbury, J. W., & Idacavage, M. J. (). 3D printing with polymers: Challenges among expanding options and opportunities. Dental Materials, 32(1), 54-64

Posts: 7Threads: 6Joined: Jan Reputation: 0

Having just got my mars printer today, I've only just discovered that it is necessary to bathe the resin model in ultraviolet light as part of the curing process. I'm trying to figure out which UV lights are best for curing, I believe that they should be in the 405nm wavelength to be effective but I don't know what the number of watts should be.

I have a couple of light boxes  (lage and small)  and turn tables (large and small) already.

For smaller 28mm resin miniatures like say warhammer sized minis I think a ladies nail varnish uv box my be of use but a larger light for the light boxes (with maybe tin foil on the inside) will be required, again, I don't know the ideal, make, model or number of watts that would be ideal to cure or even the length of time to cure under UV light.

Anyone point me in the right direction ?

If you want to learn more, please visit our website UV LEDs for 3D Printing.

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3D Printer UV Resin Curing Light for SLA DLP 3D Printer Solidify Photosensitive Resin 405nm UV Resin Affect, DIY Curing Enclosue https://www.amazon.com/dp/B07XJZK4R6/ref...KEbMBC2EXB

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Posts: 39Threads: 0Joined: Feb Reputation: 3

20-40w is vaguely where you want to be, but it doesn't matter much: and it's a good thing too, because there is no consistency. This isn't that surprising, because most of the UV lamps are LED, so it's actually listing the "equivalent" rating, and there's a lot of variation going on.

The big thing is if you are not using a water washable resin: Submerge your parts in water during post-cure. This dramatically improves curing. It can take a print from 2 hours and failing to fully cure, to just 15 mins and being perfectly cured.

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Application Overview

PolyJet is one of the mainstream 3D printing technologies today. The PolyJet 3D printer sprays photosensitive resin material layer by layer onto the print tray until the parts are completed. Each layer of material is cured with ultraviolet light while being sprayed and can be taken out and used immediately without secondary curing. It can realize the combination of color and multi-materials in a single printing to produce a prototype close to the real product. It can also be used to print quick molds and verify product designs. Full-color multi-material 3D printer can mix six materials at the same time to achieve 500,000 colors, different textures, transparency, and softness. Products are widely used in medicine, education, engineering models.

Equipment Advantages

Using the Phoseon FireEdge™ FE400 air-cooled curing light source, end customers can run stably for a long time (the model printing cycle of the model is more than 48 hours). The printing process with highest efficiency, printing accuracy and yield can fulfill end customer’s stringent requirements. Compared with domestic and foreign LED light source manufacturers, the key advantages of Phoseon LED light source include:

1.     Small and compact structure: Very suitable for the limited space and complicated installation structure of the printer. And there are basically no wearing parts, eliminating the need for replacement and maintenance.

2.     Stable performance: With Phoseon’s TargetCure™ technology (https://phoseon.com/industrial-curing/technology/targetcure/) the continuous stable and reliable output of the light source ensures the quality consistency of the printed objects. UV-LED provides fast, consistent and reliable curing every time, minimizing waste.

3.     High-power air-cooled design: Air-cooled heat dissipation and exhaust prevent water pipes from occupying the internal space. High intensity UV irradiation can improve the surface drying performance of each layer of the resin, thereby ensures the printing accuracy of the model.

4.     Instant on/off: It can be used immediately without preheating and can seamlessly match the response time of the inkjet nozzle. It is especially suitable for scanning high-speed printing. Utilizing UV-LED technology, UV-sensitive properties enable rapid layering and curing using low energy UV light. The instant on/off function of LED lamps enables 3D printers to cure as quickly and constantly per the need of the printing process therefore optimizing production - something not easily achieved using traditional UV lamps. Phoseon Technology’s UV LED cures to print super-size lightweight objects at a remarkable speed.

5.     Customizable and user-ready: Phoseon Technology’s UV-LED curing speed delivers “ready” objects right off the printer; no post-curing or post processing is required. The final printed object is very receptive to multiple types of finishes. That allows the 3D object to be painted or decorated to create complex and eye-catching designs. The LED technology also allows to create multiple shapes and designs that meet end customer needs.

6.     Energy saving and environmental protection: Safe and stable UV-A products without mercury, ozone, or radiation. Phoseon Technology’s UV-LED lights are an environmentally friendly alternative to traditional UV arc lamps, which contain mercury. In addition, UV-LED lamps last longer and use less energy than traditional curing methods, which reduces operational costs and increases energy savings as much as ninety percent.

For more COB LED Sustainabilityinformation, please contact us. We will provide professional answers.