<p>I contacted Formlabs at support@formlabs.com and received answers:</p>
<h3>Formlabs Services answer 1</h3>
<blockquote>
<p>The green tensile strength is valid only for layers that have finished solidifying during the 3D printing process. So in effect, as the part is being printed, each section that has solidified is in its green state where the green tensile strength applies.</p>
<p>Other that that, there is a moment in time for each scanline of a layer while it is being lased/polymerized, where the tensile strength will be something less than that green tensile strength, until the laser moves from that location and that section solidifies.</p>
</blockquote>
<h3>Formlabs Services answer 2</h3>
<blockquote>
<p>We have not tested compressive strength for our materials at the moment, so we would not be able to provide any data on that specifically.</p>
</blockquote>
<blockquote>
<p>Regarding mass density of our standard resins, they will be 1.08, 1.13, and 1.14 [g/cm^3] in their liquid, green, and postcured states respectively.</p>
</blockquote>

CC BY-SA 4.0
2023-09-15T07:36:16.030Z
2023-09-16T04:20:22.667Z
2023-09-16T04:20:22.667Z
Megidd
<h2>Green parts are &quot;off the printbed&quot;</h2>
<p>The term &quot;green&quot; is from the manufacture of ceramics: a piece of ceramic is green when it has not been burned in the oven. In this state, the ceramics - think about <a href="https://wheelandclay.com/blog/greenware-ceramics/" rel="nofollow noreferrer">clay and porcelain</a> - can be still somewhat manipulated and are usually much softer and less sturdy than after burning. More precisely, a resin 3D print print right off the bed would be comparable to somewhere between stages one and two for its behavior.</p>
<p>Since the UV-light curing station does what the oven does for the ceramics, the term for a &quot;raw&quot; print has been taken from there. So right of the bed it's &quot;green&quot;, and after it was in the UV light it's &quot;cured&quot;.</p>
<h2>Note the terms!</h2>
<p>Tensile strength is the strength in <em>tension</em> so pulling. It says nothing about the compressive strength. Either you find them in different sections of the MSDS or you might need to run additional tests to get for example compressive strength, or the density of the printed resin.</p>
<h3>Density increase</h3>
<p>Usually, the density of the printed resin increases as the bonds between molecules tighten the more they cure. As the bonds shorten somewhat and tighter interknitting happens, the print also shrinks somewhat between their green and cured states. This behavior is also where a lot of the stresses that cause buckling and warping come from, leading to the need for reinforcement ribs and minimum thickness of walls to avoid warping.</p>
<p>Look at the two pictures from Adam Savage's Tested. In the first, the decorative ribs warped under stress while curing, in the second, the lack of reinforcement ribs lead to the lower bottom bending upwards (and the side walls out), most noticeable at the 'top' edge of the cutout. They start to address this print failure <a href="https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&amp;t=2208" rel="nofollow noreferrer">about here.</a></p>
<p><a href="https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&amp;t=2313" rel="nofollow noreferrer"><img src="https://i.sstatic.net/nLr7G.jpg" alt="A failed print on the left and a good one right, showing wavy warping that happened in curing from having too thin walls/details" /></a>
<a href="https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&amp;t=2278" rel="nofollow noreferrer"><img src="https://i.sstatic.net/h6qB7.jpg" alt="A failed print on the left and a good one right, showing buckling of the print from lack of reinforcement ribs" /></a></p>
<p>As formlabs told @megidd in an email, their resin goes from 1.13 to 1.14 [g/cm^3], an increase of about 0.8%, which will induce some stresses in the model, resulting in shifting tensile and compressive parameters between the green and cured state.</p>
<h2>Some operations are easier on green prints!</h2>
<p>There are operations that are easier on perform on a green print where the plastic itself is softer and less brittle. Among those operations often is the removal of support structures and of the beads where the support structure was attached, and even placing threaded inserts.</p>
<p>However, the green state is time-limited due to the nature of the beast. Even normal daylight does contain some UV so that longtime exposure will ultimately transfer the model to the fully cured state over time.  In between the fresh print and the fully cured print, the parameters will slowly shift till they (almost) reach those from a UV bath.</p>

CC BY-SA 4.0
2023-09-14T14:51:52.047Z
The material documents mention *tensile strength*. What about compressive strength? Are tension and compression the same regarding strength?
Megidd
CC BY-SA 4.0
2023-09-14T15:04:30.057Z
@Megidd No! Think... Brick. Brick is super for compressive strength, but weak under tension.
Trish
CC BY-SA 4.0
2023-09-14T15:11:37.683Z
Thanks. How can I find other material properties, like *compressive* strength, mass *density* and other props that are ignored by the published docs? Just wondering.
Megidd
CC BY-SA 4.0
2023-09-14T15:14:48.170Z
@Megidd You'd need to run tests yourself - compressive strength is for example tested by placing weight on the center of a bar until it bends or breaks.  Density is highly dependent on the object, but trivial: print a solid cube and weigh it - $\rho=V/M$
Trish
CC BY-SA 4.0
2023-09-14T15:44:17.643Z
Right. Makes sense. Just another thing I have in mind: I'm confused about the *green* tensile strength. Is it safe to say that the green tensile strength is also valid when the resin is being 3D printed? I mean, while doing the 3D print process by projecting UV light. I'm asking this because I'm doing some work on the strength assessment of a 3D model while it is being 3D printed. I'm not sure if I'm clear :)
Megidd
CC BY-SA 4.0
2023-09-14T15:54:49.297Z
yes, that is most likely the caese
Trish
CC BY-SA 4.0
2023-09-19T13:39:58.517Z
Very helpful :) Thanks. Especially your analysis of mass density increase and its effect on other material parameters.
Megidd
CC BY-SA 4.0
2023-09-14T11:40:19.433Z
2023-09-19T09:50:10.640Z
2023-09-19T09:50:10.640Z
Trish
<h1>Resin specifications</h1>
<p>There are datasheets available for SLA resin mechanical properties. Like this <a href="https://formlabs-media.formlabs.com/datasheets/1801089-TDS-ENUS-0P.pdf" rel="nofollow noreferrer">Formlabs' General Purpose Resin datasheet</a>.</p>
<p>They present mechanical properties for two cases.</p>
<h2>First case</h2>
<blockquote>
<p>Data was obtained from green parts, printed using Form 2, 100 μm, Clear settings, without additional treatments.</p>
</blockquote>
<h2>Second case</h2>
<blockquote>
<p>Data was obtained from parts printed using Form 2, 100 μm, Clear settings and post-cured with 1.25 mW/cm² of 405 nm LED light for 60 minutes at 60 °C.</p>
</blockquote>
<h1>Table</h1>
<p><a href="https://i.sstatic.net/BWMpk.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/BWMpk.png" alt="Screenshot" /></a></p>
<h1>Question</h1>
<p>I need to know the mechanical properties immediately after the resin is hardened by the projected light. Would the <em>first case</em> above provide my desired info?</p>

<resin><print-material><sla><print-strength><dlp>
Resin mechanical properties during the print process, immediately after light hardens it
Megidd
# Resin mechanical properties during the print process, immediately after light hardens it

(Asked by: username_0 on 2023-03-12)

# Resin specifications

There are datasheets available for SLA resin mechanical properties. Like this [Formlabs' General Purpose Resin datasheet](https://formlabs-media.formlabs.com/datasheets/1801089-TDS-ENUS-0P.pdf).

They present mechanical properties for two cases.

## First case

> Data was obtained from green parts, printed using Form 2, 100 μm, Clear settings, without additional treatments.

## Second case

> Data was obtained from parts printed using Form 2, 100 μm, Clear settings and post-cured with 1.25 mW/cm² of 405 nm LED light for 60 minutes at 60 °C.

# Table

[![Screenshot](https://i.sstatic.net/BWMpk.png)](https://i.sstatic.net/BWMpk.png)

# Question

I need to know the mechanical properties immediately after the resin is hardened by the projected light. Would the *first case* above provide my desired info?

**Tags:** resin, print-material, sla, print-strength, dlp

---

## 2 answers

### Answer by username_1 on 2023-09-14. Score: 2 | Accepted answer

## Green parts are "off the printbed"

The term "green" is from the manufacture of ceramics: a piece of ceramic is green when it has not been burned in the oven. In this state, the ceramics - think about [clay and porcelain](https://wheelandclay.com/blog/greenware-ceramics/) - can be still somewhat manipulated and are usually much softer and less sturdy than after burning. More precisely, a resin 3D print print right off the bed would be comparable to somewhere between stages one and two for its behavior.

Since the UV-light curing station does what the oven does for the ceramics, the term for a "raw" print has been taken from there. So right of the bed it's "green", and after it was in the UV light it's "cured".

## Note the terms!

Tensile strength is the strength in *tension* so pulling. It says nothing about the compressive strength. Either you find them in different sections of the MSDS or you might need to run additional tests to get for example compressive strength, or the density of the printed resin.

### Density increase

Usually, the density of the printed resin increases as the bonds between molecules tighten the more they cure. As the bonds shorten somewhat and tighter interknitting happens, the print also shrinks somewhat between their green and cured states. This behavior is also where a lot of the stresses that cause buckling and warping come from, leading to the need for reinforcement ribs and minimum thickness of walls to avoid warping.

Look at the two pictures from Adam Savage's Tested. In the first, the decorative ribs warped under stress while curing, in the second, the lack of reinforcement ribs lead to the lower bottom bending upwards (and the side walls out), most noticeable at the 'top' edge of the cutout. They start to address this print failure [about here.](https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&t=2208)

[![A failed print on the left and a good one right, showing wavy warping that happened in curing from having too thin walls/details](https://i.sstatic.net/nLr7G.jpg)](https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&t=2313)
[![A failed print on the left and a good one right, showing buckling of the print from lack of reinforcement ribs](https://i.sstatic.net/h6qB7.jpg)](https://youtu.be/TuM_1xSQCFw?list=PLJtitKU0CAejiJisqHdCX4O-1-zJzfW36&t=2278)

As formlabs told @megidd in an email, their resin goes from 1.13 to 1.14 [g/cm^3], an increase of about 0.8%, which will induce some stresses in the model, resulting in shifting tensile and compressive parameters between the green and cured state.

## Some operations are easier on green prints!

There are operations that are easier on perform on a green print where the plastic itself is softer and less brittle. Among those operations often is the removal of support structures and of the beads where the support structure was attached, and even placing threaded inserts.

However, the green state is time-limited due to the nature of the beast. Even normal daylight does contain some UV so that longtime exposure will ultimately transfer the model to the fully cured state over time. In between the fresh print and the fully cured print, the parameters will slowly shift till they (almost) reach those from a UV bath.

> **Comments:**
> **username_0**: The material documents mention *tensile strength*. What about compressive strength? Are tension and compression the same regarding strength?  
> **username_1**: @Megidd No! Think... Brick. Brick is super for compressive strength, but weak under tension.  
> **username_0**: Thanks. How can I find other material properties, like *compressive* strength, mass *density* and other props that are ignored by the published docs? Just wondering.  
> **username_1**: @Megidd You'd need to run tests yourself - compressive strength is for example tested by placing weight on the center of a bar until it bends or breaks.  Density is highly dependent on the object, but trivial: print a solid cube and weigh it - $\rho=V/M$  
> **username_0**: Right. Makes sense. Just another thing I have in mind: I'm confused about the *green* tensile strength. Is it safe to say that the green tensile strength is also valid when the resin is being 3D printed? I mean, while doing the 3D print process by projecting UV light. I'm asking this because I'm doing some work on the strength assessment of a 3D model while it is being 3D printed. I'm not sure if I'm clear :)  
> **username_1**: yes, that is most likely the caese  
> **username_0**: Very helpful :) Thanks. Especially your analysis of mass density increase and its effect on other material parameters.  

---

### Answer by username_0 on 2023-09-15. Score: 2

I contacted Formlabs at support@formlabs.com and received answers:

### Formlabs Services answer 1

> The green tensile strength is valid only for layers that have finished solidifying during the 3D printing process. So in effect, as the part is being printed, each section that has solidified is in its green state where the green tensile strength applies.
>
> Other that that, there is a moment in time for each scanline of a layer while it is being lased/polymerized, where the tensile strength will be something less than that green tensile strength, until the laser moves from that location and that section solidifies.

### Formlabs Services answer 2

> We have not tested compressive strength for our materials at the moment, so we would not be able to provide any data on that specifically.

> Regarding mass density of our standard resins, they will be 1.08, 1.13, and 1.14 [g/cm^3] in their liquid, green, and postcured states respectively.


---

