Why does Nobody Cure their Resin 3D Prints like this? (40% more strength) 

Does this open new possibilities for resin 3D printing? Support the channel and check out CNC Kitchen products at cnckitchen.store/

Evidently I need to make a resin-version youtube channel of CNC kitchen. When you devote 2 years to making graphene additives for photopolymer, the testing methods to get there paint a different story. Water-curing after an ultrasonic bath for specific formulas is also quite effective.

One of the most important things for me in 3D prints for functional parts is creep. Rarely do I need higher than 60ºc temperature resistance, but often I do need parts to stay in shape while loaded for long times. This kills PLA for several of my projects, despite it's many advantages. The same is true for the Formlabs Black resin, we also got the wash and cure station at work and we use the machine whenever we need to show pretty stuff to the costumers, but when it's time to make some functional prototypes to last field use, no no. It creeps way too much. Creep tests is one thing I would like to see being explored more thoroughly, there's much more to part strength than short loads after all. One thing I've often done with larger resin prints with heat is straightening warped walls. Large parts will sometimes get warped during printing or curing (specially that 60°c 1h curre that we go with the Formlabs station), a friendly Ender 3 with it's flat glass bed at 60°c for some minutes with correctly placed weights, then let it cool naturally until about room temperature, and we're good to go. Same with PLA actually.

We post-cure our Siraya Tech and 3DMaterials resins immersed in a rotating hot water bath for at least 1 hour. The first 15 minutes are exposed to UV. The water will be heated to 60-80 Celsius depending on the resin used. Most of the time, the resin will be directly immersed in water, except those that are meant to be used at high temperatures or contain filles, such as ST Sculpt and Sculpt Ultra White. These will be put in a bag with light vacuum seal. Most of the parts we make are meant for end-of-arm tools for industrial robots, manufacturing aid elements and injection molding tool components

Heck yeah! I’m testing out a new resin and they sent me a toaster oven to test it out! Excited to see a detailed explanation of how this works

I own a FDM printer not resin, but I use epoxy resin for projects and put them in the oven after it has had its minimum cure time. I have always wondered why people never used heat for their resin prints and just presumed the resin used for 3D prints isn't possible, glad someone (you) have shown resin printer users this trick. Good work.

I worked back and forth with siraya tech over a cunfusion with their blu mecha formula. One incredible technique the engineer told me to cure the resin 3D print submerged in water. I noticed a big difference in hardness and strength when doing this

I print a lot of resin dental prosthetics we use temps anywhere from 20-60c for up to an hour depending on your curing unit. Some units use nitrogen filled chambers to cure while others finish cures in a 60c water bath .

Hi Stefan! We print from BASF and Loctite resins at work (automotive prototyping) - and it is actually required to "bake" the finished prints for a while before UV curing. Not so high temperatures - around 40-50C for 30-60 minutes. So if manufacturers like these companies recommend it, there is actually some science behind :) And with Siraya Blu You can even go higher - i did several tests up to 250 C - for 60 minutes. Interestingly - part remains in its original shape, but starts to crack at temperatures above 125 C. Resin prints dont melt into blobs as FDM prints - there are a lot of "undiscovered" areas of resin printing ...

Not long ago I aquired a new resin printer and immediatly made a curing station with a 20 dollar used microwave that I salvaged (because I wanted something with a rotating plate and a timer) replacing the magnetron with a 405nm UV lamp like yours. There's still two 220v terminals that were originally connected to both the normal microwave bulb and ventilation fan that I now could connect to a heater and have a fully automatic Curing and Heating station with a rotating plate and timer! I could also add a thermostat for safety

Important addition: beside monomers, oligomers and photoactivator there is also up to 50% filler. Filler made of some organic molecules wich didn't parcicipate in polymerisation. They made part less brittle but also less strong. And may result in developing cracks in a part over time. Cheaper resins usually have higher % of filler.

What you mentioned about curing PLA vs resin is a usual behaviour of thermoplastics (everything on a FDM printer) vs. cross-linked materials (everything on a resin printer) and explained absolutely correctly. About your thermal curing experiment: nicely done. Many photoinitiators are also unstable towards thermal initiation, so I am not very surprised by your result without UV light, and any crosslinking reaction will be quicker due to heat (our old friend Arrhenius), but it's nice to see the data. I still admire your DIY tensile and impact testers. edit: it might be interesting to do the same with non-transparent resin to see if the effect of thermal treatment is even higher compared to using UV light which would be expected since UV will not reach the interior of the part then or to vary the length of the curing to see if it is just an Arrhenius effect or you are actually starting new initiation reactions with the heat treatment.

More SLA videos please! :) At the moment the resin printing community is sadly still at the stage "do I *really* need to buy a curing station?" as well as "do I *really* have to clean and cure my hollow prints from the inside?". But there are at least fewer people asking "but is resin *really* toxic?" and "do I *really* have to wear PPE?", which is nice.

Great stuff. Kudos to Stefan, I generally don't look for new videos in my RU-vid subscriptions, but on weekends I always hope CNC Kitchen has a new video to watch while I workout.

Another banger Stefan. I always recommend your channel to newcomers to printing. Your scientific approach is such a breath of fresh air compared to so many other sources.

I've been curing my abs-like resin in a very large glass container filled with water that I preheat with a old sous vide heater. Works fantastic. The water inhibits oxygen thus boosting curing rate, and it helps get far more even uv exposure!

Nice work! My emake-3D resin cure station has a built in heater which I never used. I will have to give this a try.

I've been doing this for a very long time now. And it works with most resins I've tried.

I bought a microwave convection oven with turn table and removed the magnetometer and installed a UV lamp in its place. It was a bit of work to invent a new control system, but it was worth it. I created a stand for my parts to insure even heat and UV exposure to prevent warping

Last month the interlocking layers now a review of the curing its great seeing how a few ideas can really improve the usefulness of prints

Incredible research pushing the boundaries of 3d printing, thank you for posting this.

I actually discovered this by accident thanks to a messy house finch couple. Putting prints outside had been part of my post curing process already. I assumed it was more UV from the sun making the prints stronger but the finches knocked a part into the shade and it was still as strong as the rest. Turned out it was the heat.

I had read that the main purpose of the UV in acting on the photoinitiator is not very different from how resin polymer initiators are activated, it essentially is adding energy to the system. The photoinitiators have been found to be more sensitive to that style of energy instead of say, heat but it makes sense that heat would also do it.

we would love to send you some of our latest thermal resin - it kickstarts later this month and is designed specifically with this kind of curing in mind.

Impressive new way of curring Rasin Another great video from you. Thanks again for sharing your expirence with all of us 👍 😀

Such an informative video. A minute in and I've learned so much about resin printing that I missed.

This is pretty exciting. I’ll have to try this when I get back into resin printing

This is really intriguing for functional-printing folks!

Thanks Stefan for doing some Resin content!

Definitely noticed that heat leads to strength. I run my resin prints in my garage where I don't have to breathe any of the vocs. During winter I use a 220v electric heater. I usually aim for about 35C during the print, after the print I crank it up to pull supports off more easily, however I have left the heater blasting my printer before and it becomes concrete esq. Good video.

i usually post cure with the parts submerged in water - this quickly removes all stickiness from the surface (oxygen contact seems to inhibit the curing of the resin!) eg. if you didnt clean them 100%. And using hot water may double in adding strength while keeping the parts from deforming - Thanks for the tip!

THANKS SO MUCH! I print a lot of rather technical stuff in resin. This for I mostly take water washable black ABS-like resin from Sunlu. Making the parts even stronger is a great thingtp look fwd to… 😃

Fantastic information! Thank you!

very interesting subject and great testing!

Thanks for the interesting study! I look forward to more resin print videos from you! Hopefully, SLS plastic printing will someday be affordable for hobbyist too! I bet you could come up with a lot of cool videos on the topic.

Super interesting results! A natural progression from this topic will be how to keep the prints strong as many report the parts become brittle after a few months. So what is the difference after 3 months vs painting them vs coating with UV clear coat. Great video!!!!!

i just want to point out that i am happy to see how you look like... you look allmost as i would have imagined... but with more curls in your hair... has seen your videos for a long time and actually seeing how you look like is amasing :) i have allways loved your unbiased and sciantific approtch to 3d printing and i have alot of respect for your work... as someone who has a education in plastic injection molding it is amasing to see someone who knows so much about and experiment so much with 3d printing :) keep up the good work :)

Hi Stefan, very good video as usual! Always a pleasure to watch your videos. Regarding your test results I think I have an idea, why your last test worked: During heat+UV cure, you split the photo initiators into radicals, which then lead to polymerization. More heat increases the brownian motion and thus increases the cure speed. If you now do the UV cure first and the heat treatment afterwards, I think the following happens: First you create radicals of the photo initiators with the UV light, which mostly find a monomer or oligomer due to their sheer number. Some of those radicals however end up not finding a partner to react with and thus stay in their radicak form. If you now increase the temperature without UV light, you don't create new radicals, but you increase the mobility of the remaining radicals through brownian motion and thus increase the likelyhood for those to find a matching monomer, oligomer of polymer. Repetition of the cycle might lead to less scatter in the results, I think.

As always very clear, informative information.

Amazing. This is why I keep a bottle of Sirayatec blue and use it sparingly

Carbon3D used to offer a cyanate ester resin that, I believe, has since been discontinued. It required a secondary thermal cure, which did make it more of a hassle than other resins that could get away with just UV, and I understand the resin itself was also pretty pricey even compared to Carbon's other offerings. I guess customers just weren't interested. But wow did it have excellent thermal resistance. It could handle temperatures that could make your skin sizzle without getting soft at all. Excellent for making precision welding fixtures. It also came out of the vat as a chalky olive green color and cured to a very beautiful translucent amber-orange, so it had great aesthetic value too. It's such a pity nobody's put out a similar product since then.

Great test, thanks. I would have guessed that it it would make the part more brittle by increasing the hardness. For my functional parts I actually prefer a bit more "give" over maximum total stiffness as most part stresses are transient rather than load to failure.

Stefan, excellent video (as always!) I find that curing the parts in very warm water has yielded drastically different results in the quality of my prints.

That is very cool to know for something in the future

I'm definitely going to have to try this with my new heated ultrasonic cleaner.

Super informative great presentation!! Defiantly been having trouble with brittle prints now I know to throw them in the oven for stronger results!

Being able to throw a print into an oven post-curing is a lot more hobby friendly than trying to make a setup to cure and heat at the same time. That's exciting to hear and I hope there is more research done with it.

That "use your heated bed as your oven" trick is a game-changer. We only have one climate chamber at work and it's always in use, so I could only borrow it for enough time to prove that annealing works, but not long enough to anneal every part we print. That and I can't afford a climate chamber at home!

Very interesting video. You mentioned you found no significant shrinking, but I wonder if it affects post-print warping on thin flat parts. I mention this because I usually have warping in some parts after "normal curing". If this method fixed that it would be a game changer!

Great information. Thank you for making this video.

This is, as usual from this channel, really awesome. I really wish resin printing was less of a pain. There needs to be a Bambulabs esque ease of use boost to SLA where you can press print, and have the parts washed and cured automatically so you can get by without the whole gloves and mask setup. Of course, what would also be awesome is that higher temperature forced air heating for the curing station. The technology all seems there, so I guess its up to some company to implement. It feels like something it might even be possible to implement as a single person with some servo actuation only needed to switch between printing and curing. So much potential, and this type of printing looks so much more professional than FFF parts.

Thanks a bunch - this was really interesting!

Did you take into account that the resin might react differently to the wavelength of the light used? These LEDs look like 365 nm, but if I remember correctly, a wavelength of 405 nm is required. Also the oven might mess with the light produced.

I have a strong background in resin casting. Using chemical hardeners that cure the resin in a mold instead of photo initiators creating nucleation points. We almost always annealed resin casts, which made for a more noticably durable material. So it makes sense that annealing post curing in UV results in increased strength too, as this is basically how annealing is done in resin casting. It's not always necessary to do, but even in wargaming miniatures, depending on what resin you use, such as ABS-like resins, the ductile strength of that resin remains while increasing tensile strength. TL,DR; Its almost always beneficial to post cure anneal your resin 3d prints.

This is really cool! I love the thought and effort that goes into your videos, I appreciate your diligence to find solutions and answers to questions that so many have ignored or considered unknowable. Excellent video :) However, something important to understand about statistical analysis is that if the error bars on the graph overlap, that means there is no statically significant different. In other words, one cannot say that there is a trend upward in the tensile strength of resin as the temperature before curing goes up (for the CW1S test graph). The error bars overlap, therefore the strength cannot be considered different. This is also the same for the graphs about heat during curing, the IZOD impact test, and the additional information about heating after curing. However! I still think you have excellent results! You showed the results clearly and there *is* a difference between temperatures during curing, which means this **does** result in stronger prints from a statistical analysis! As I said, I love your videos! And I think this one is very cool! It’s hard to get statistics right, so I totally understand, I’ve made many mistakes myself! Even though I am criticizing some of the analysis, that doesn’t mean I feel like you are being dishonest! It is a mistake that I feel the vast majority of people make, especially if statistical data analysis isn’t a part of their daily lives (that being said, I don’t know what your daily life looks like, so I apologize if I’ve spoken out of turn in this regard). All that to say, excellent video, as always, and I really look forward to the next one! I am always excited to see what new ideas, experiments, and cool techniques or methods you’ll show us next :)

Bro...du bist ein Held. Ehrlich. Herzlichen dank!

Hi Stefan, i love your videos. Very informatives thanks for that ;)

I print a ton of resin prints. The way I do it is I use a heated ultra sonic to clean my parts which heats them up and cleans them, then I put the prints on top of my radiator heated to 60c for a hour ish(i often forget and do like 4 hours no biggie lol). Move them to cure chamber while still hot or best yet put them in a small transparent container filled with warm water and UV cure to retain heat and maximize the cure process. Fun fact, heat cure is required for Blu resins to be properly biocompatible.

For many years now, there are a lot of dental curing devices which combine UV and thermal curing. Some models even have programmable temperature ramps like reflow ovens. Another inexpensive option is to use incandescent UV light source, which produces a lot of heat (like 10% efficiency in light conversion - the rest is heat)

I just got in to 3DP with a Elegoo Mars 2 Pro, have only just gotten mine to play nice and work with basic gray. this will be a nice new thing to play with.

I've discovered this effect when I left a resin printed part on my windowsill. It was way stronger than any of the parts I cured with UV light. I wasn't sure what caused it at first, but eventually figured out the the temperature of the sun helped with curing.

Form labs has been doing this for many years with the form cure station. Definitely a key point in making strong prints

You should publish your work in peer-reviewed media, so that those of us who work in science can reference your results. Thank you!

Hi Stefan, thank you for doing a resin video again. I heard a lot that the exclusion of oxygen during post curing can improve the strength of resin parts. Could you test parts cured in hot water or even under vacuum or nitrogen atmosphere?

Probably a stupid idea... But I recently saw videos about the benefits of Watercuring. The prints are placed in a water bath and then illuminated. Now the idea: If you put prints in an 80 degree Celsius water bath, set them in motion with a magnetic stirrer and let them be irradiated by a UV lamp, you would actually have the perfect curing method

I'd like to see some resin "blends" - tough resin plus a little flexible or test some of the exotic resins I've seen - "bone like" for example.

Please more resin 3d printing Videos! Very interesting Video btw

I do a post-wash cure in a glass jar filled with hot water. I'm able to cure prints faster in water so I don't worry much about the water cooling before I'm done. It works great!

Neat! I usually cure my prints using 3 different light sources and I've also notice parts get stronger a few days post cure. Firstly I accidentally cured some resin using a super bright WHITE light. Not sure if the LED in it kicks out some UV but it flash cures the top layer and never really penetrates. I also use 395nm and 365nm. The 395 does most of the curing and penetrates really well with minimum yellowing but the 365nm seems to cure resins extremely well and leaves a harder than normal surface but it does tend to yellow most resisn. Secondly I was printing cupons one day for a simple comparison between different resins, colors, and additives I've been playing with and I found out that if the prints is post-cured and then allowed to rest for a few days the prints generally hardens some more, yield less and get stronger. In my experience all the resins I've been playing with do this, water washable resins, abs-like, abs water washable, traditional resins. Plus the manufacturer 3DMaterial does mention that their resins will harden some more after a few days, and no they haven't been the only brand I've tried.

I bought a cheap round food dehydrator with glass clear housing to dry my filament spools (as you showed earlier) which is capable of reaching 70°C at any location inside (proved with digital thermometer). I can imagine to cure resin prints in it with 70°C or less and an UV-lamp shining from the outside in. Have to be sure to protect eyes from the UV-light with googles or a surrounding housing.

Yes indeed there is a lot of potential behind properly curing resins. Some factors I would think to look into for future videos on this topic are: Thermal and UV curing *times* (and as you touched towards the end if they should be done at the same time or seperately and what order), chamber temperature while printing, thermal and uv curing in a liquid/water (protected from oxygen or for some other reason) and the main one I think not considered by many, the *cleaning solution and temperatures from the cleaning process*. I have found that using cold isopropyl alcohol and especially letting the prints dry, evaporation lowers the temperature of the parts even further and this lowers the impact resistance. It indicates to me some type of thermal shock and at least making the shell of the parts weaker. By the way I have noticed also in some clear resins that thermal post-curing affects how much yellow they get from the UV post curing (and how fast the yellowing can fade away after some days).

I vaguely remember Sanladerer trying to glue 3D-prints with resin and failed, because the UV-Light was not able to penetrate the resin and the “glue” only got cured a fraction of a millimeter on the outside. So the curing after print seems to primarily cure the stickiness of the surface of the object. Even resin thats optical clear in visual lightbands absorbs UV, otherwise printing would not work. This results in me being a bit sceptic about your statement at 1:35. Maybe elevated temperature has the effect of hardening the inside of the objects. As of a rule of thumbs says that every 10 °C increased temperature speeds up chemical reactions by a factor of 2.

Would love to see the results using tough and flexible resins as well. A lot of people doing miniatures use tough resin, or a mixture of flexible with other resins.

Perfectly timed, I am trying my first round of acrylic painted prints in a food dehydrator (to speed up paint cure time) as I write this. I was curious what effect it might have on the resin prints and couldn’t really find much info on it.

I have been heat curing my resin prints in my filament dryer at 65C for a while and it helps for sure. If you look at the documentation for high end resins they specify high temp cures, somehow it just hasn't trickled down to the hobby space

this is awesome. I'm curious and always wanted to try a heater in the printer while it was printing to see if it made a difference to strength.

I have 100% watched the entire video and can say its amazing

I don’t print with resins, but in my work I make use of dual UV-thermal cure epoxies. This result doesn’t surprise me. In the materials we use, we achieve maximum strength when using the minimum UV pre-cure and complete thermal cure. Over-curing with UV results in a weaker bond. In your thermal only post-printing treatment, you might want to a longer cure time. Try increasing the thermal cure time (2 hours, 4 hours). You might not be fully cured after 1hr at 80°C.

I cure my resin prints in water. It takes the same amount of time (2-3min, flip, 2-3min). I find they come out way less brittle and stronger. I use a UV spotlight mounted on top of a stainless steel pot so I can take advantage of the reflections of the pot but I still flip them half way through and sometimes if there's hard to get areas of the print I'll orient it so it will get more light and do another run. I haven't had an issue and I believe they come out stronger. I use room temperature water, I never thought about heat. I may have to test this with warm to hot water and see if it makes a difference. I made a load cell mount from resin for large bar style load cells (16 of them actually) and they held 40kg for over a year in a hot environment. I eventually replaced them because they ever so slightly sagged over time but I was amazed they went that long. I believe that water curing had a role in that. This was with Standard ABS resin.

"Only I can do something right" nice one bro

Yep, some of my prints I put into boiling water (in a microwave) and this makes a big difference for white parts that have yellowed or clear parts that have yellowed plus the increase in strength and stiffness. This gets you to 100C. For opaque parts continued UV curing only cures the outer layer while the inner volume of the parts doesn't cure any more. Heating the parts helps to uniformly cure the part through the thickness and thus the increased strength.

I am going to try this out with the resins I have

i personally use a food dehydrator to finish curing my resin casts (as i already have one for dehydrating herbs) so it's nice that it's basicallt dual purpose for me. Hope this info can help anyone else even if the resin i use is chemically curing instead of uv-curing like with a resin printer

Great to see it getting stronger tha pla

Holy smokes I was literally talking about SLA printing prosthetic claws with my significant other and then you posted this. XD

I have Formlabs Form3, and both wash and cure stations, I just assumed that cheapo MSLA curing is also done at temperature. I've always set the curing station to heat up first, then put my parts in.

i've found that cleaning then microwaving my parts 10s at a time gave me good results

Incredible

I got an ad for a heat cureable resin the other day, that should come to Kickstarter in a few month... I subscribed, but lost the link since ;)

A while back, I saw people curing their resin prints in a glass of water inside the UV chamber, arguing that the water better dispersed the UV light across the model. I imagine you could probably use a clear Pyrex bowl filled with hot water to achieve a similar effect.

Hey, Stefan. I just noticed that your impact strength gauge needle moves back down a little from its peak. It looks like you need to increase the friction a little (or lower the mass).

I have always been skeptical about UV post curing because UV only penetrates ~50 micron into even clear plastic. Thx for Stephan for finally test out this myth.

Very good. It is to do the same test but with standard resins and abs from brands such as anycubic, sunlu, elegoo etc because they are cheaper resins than siraya

for me the underwater curing was the best, after washing, claenaing and removing the supports i put the models ina vlear plastzic container and pour warm(~40°C ) water on top, curing them in water for 5 mins. The print this case wont be as brittle as in dry curing, i dont jknow the chemistry behind it, but some says it has something with oxidation, Can you please thest this method too?

I work in the carbon fiber industry and have some input! You mentioned the “giant ovens” aka “autoclaves”, but you didn’t mention the other huge property of them; they are pressurized! Carbon fiber parts are vacuumed down to get the resin into the fibers, and for high tech applications the autoclaves are also pressurized. It would be interesting to see if pressure would net these resin-only parts any strength. Maybe putting some UV LED strips inside of a pressure cooker would make an interesting video!

Makes sense about the UV. Since on a solid material the UV isnt penetrating very far into the part. Where as heat will go all the way through.

It makes sense if it works something like... heat is basically adding energy into a chemical system as well as loosening some weaker bonds (I think hence the softening). The additional energy makes the bonds jump around a bit thus finding more optimal cross connections and more numerous ones.

Love all the tests! Would love to see a materials comparison with more than just tensile strength such as, abrasive resistance, hardness, heat resistance, durability, etc. Especially over time, how does a print made today compare with one made 1 year ago, or 3 years ago? Do different materials age differently? Those are questions I would love to see answered.

Formlabs actually has a white paper somewhere (from a long time ago) showing graphs of mechanical properties with varying temperatures and time as well. The one caveat is that the optimal curing temperatures are often very close to the HDT of these resins - which means that heat curing will OFTEN result in warping if you're not careful (there are a ton a caveats and subtleties here - ask me about it sometime 😅)

I find shorter washing times in IPA also result in less brittle parts. To me it seems as the IPA damages some of the molecular bonds in the resin. I try to wash as short as possible. Rinsing parts in soapy warm to hot water before curing will bring the resin temp further up before the UV light cures it.