Engineering resins

[Cezeta59]

Hi - I am looking to get a Mars Pro 2 printer, mainly to manufacture low strength engineering components to supplement my traditional lathe and milling machine capability. Some components may need an element of flexibility, for example, a pipe clip needing to flex enough to clip over a pipe without fracture etc. Are there resins available to give some flexibility? From what I have read, most resins, when cured seem very brittle and break easily. Generally, are the Elegoo printers good for engineering tasks or would an FDM set up be more suitable?

Many thanks

[cliffyk]

I have heard some good things about Siraya Tenacious resin. It is claimed to urethane based and not as brittle as most--I have not used it, it's a bit pricey at $65/litre--about 2x what the regular run-of-the-mill--and totally unsuitable for what you and I would like to do--"ABS-like" resins.

Here are the claimed properties:

• Elongation At Break: 50%
  
• Tensile Strength 24 mPa
  
• Shore D 65
  
• Young’s Modulus 500mP
  

Note: I suspect they meant MPa (Mega-Pascal), not mPa (milli-Pascal). Misuse of capitals in Metric abbreviations is rampant,

I will be buying some soon.

Most "standard" and "rapid" SLA resins (I.e. the lower cost products¹) are strong but fracture, sometimes spectacularly in a near violent manner, under load with very little/no deformation before failure. They are unsuitable for any repetitive dynamic loading even within say 75% of their rated capacities. Chemical resistance seems poor as well; though I have not conducted any formal or informal testing in this regard. Prolonged exposure to daylight or even strong artificial light with significant blue/violet content is a death sentence.

I have pondered adding glass fiber or powdered steel to these low cost resins to see if an aggregate structure might improve their performance.

See my thread here for my current feelings re: resin printing and practical applications. I have had no response from this community re: same.

There are a number of VERY expensive resins claiming the properties we both seek--however at $200 to $500 per litre they are too rich for my blood and any project I might be up to at my age and condition. In that price range I could pretty much buy (or have machined for me) any component I might need...

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¹ - An unfortunate fact of life is that "If you buy the cheapest there is--there is a good chance you will get the cheapest there is."

[BW_001]

Hi, I'm new to the forum and have just recently started using an Elegoo Mars. I've also noticed how brittle the finished parts are. So far, I've just been using the cheap grey resin. I note that many polymers in their pure form are very brittle (eg., polystyrene, pvc & various acrylics) and need to have plasticizers added to make them practical. So, I wonder if the addition of a small amount of one of the phthalates to the resin might help. I'm not a chemist, so I don't know. From what I've been able to find from various sources, most of these resins seem to be some type of methacrylate monomer with ZnO as the photocatalyst. If that's true, then maybe the same type plasticizer that's used in the production of methyl methacrylate (plexiglass) could be of some use.

I've also run across an interesting entry on Wikipedia about rubber toughening. It involves adding finely powdered rubber to the mix to improve the engineering properties:
https://en.wikipedia.org/wiki/Rubber_toughening
This might be a better choice as I think the powdered rubber would be fairly inert, and thus less likely to interfere with the curing process. Of course, the question is: Where do you buy powdered rubber?

[cliffyk]

I got a kilo of the Siraya Tenacious and mixed it 50/50 with some cheap LAFVIV Standard "ABS-like" gray--then made a 20 x 20 x 25 mm 5-step block. for both dimensional and destructive testing--see my post here for more about the destructive test.

That mix held up pretty well to being clampep in a vise and whacked with a 1 lb. hammer--much better than the gray stuff alone, which would have shattered into a zillion pieces flying across the shop.

[BW_001]

Experimenting with different mixes, one runs the risk of ruining a tankful of resin. Given the cost of even the cheap stuff, and the fact that I'm a cheapskate, I'm not yet at the point of that kind of experimenting. At least not until I can get consistent results with the parts I'm making.

Then it occurred to me that it's not necessary to mix up a whole tankful. You just mix up a very small amount, pour it into a mold and cure it under the curing lamp. That, in turn, got me wondering how much of an adulterant could be added to the resin before it would no longer cure properly. The only material that I have readily available, and that has been used industrially as a plasticizer is linseed oil. So, last night I mixed up a small batch with varying amounts of linseed oil, poured it into disposable plastic spoons and cured it under the UV light. I included a control sample with no linseed oil. The sample with about 2 drops of linseed oil per teaspoon cured completely, but took a bit longer than the unadulterated sample. I didn't measure the time difference, because at that point, I didn't know if the adulterated sample would cure at all. When it did cure, I did a third sample with considerably more linseed oil. I didn't measure exactly, but I'd guess that it was as much as 15% linseed oil. Even this extreme case cured, though taking longer again. There was an oily film on the surface of this cured piece. So some of the oil had separated out.

By curing a thick liquid sample all at once, they all developed a fairly large hollow in the middle, when the surface hardened almost immediately and then lifted, allowing air to get underneath. However, they were all identical in this regard. So, that doesn't seem to be anything that can be attributed to the linseed oil. In fact it's hard to tell the difference between the three different samples.

I haven't given them the hammer test yet, because I don't know how long it will take the linseed oil to polymerize (by oxidization), and I think I should wait for a while to allow it to happen. I'm not expecting the linseed oil to improve the properties. I'm more interested in how much it degrades the properties.

[cliffyk]

FWIW I have mixed resins as diverse as Elegoo's water washable garbage and Siraya Tenacious and have yet to come up with anything that could net be "printed". That was a fingers-crossed long-shot, but I was too cheap (my mother's family are Scottish) to toss out the 1/2 litre or so of the WW crap that remained unused and not likely to be used. Turned out this stuff is more miscible than i had any reason to expect.

[Quid]

I have heard some good things about Siraya Tenacious resin. It is claimed to urethane based and not as brittle as most--I have not used it, it's a bit pricey at $65/litre--about 2x what the regular run-of-the-mill--and totally unsuitable for what you and I would like to do--"ABS-like" resins.

I looked on Amazon and Siraya's site and the 1kg bottle is sold out. I looked at the 5kg bottle and the EaB is shown as 75%! 

[cliffyk]

That figures, a soon as I find an affordable resin I like it goes away...

[cliffyk]

I bought a kilo of this stuff:



$59 on Amazon

Claims to have an elongation-at-break of 120%--mixed it up 50/50 with that cheap LAFVIN gray "ABS-like" ($34 per kilo) crap and he first prints seem to be just as tough and resilient as the Siraya Tenacious/LAFVIN 50/50 mix, but a bit more hard perhaps--good and strong though. I think the pigments in the cheap crap may behave as a reinforcing filler in the more flexible resins. I have been toying with the idea of mixing micro-chopped fiberglas and.or glass beads with resin to form an aggregate and perhaps reinforce the final product--may not have to do that if these 50/50 blends continue to show promise.

Time for them to discontinue it...