<p>Since I am not able to comment on this question yet, I thought I would provide an answer in addition to the already helpful insight provided.</p>

<p>If the question in general is regarding infill percentage, and the common follow-up regards part stiffness, then it should be explained that choosing infill percentage is much more than just part stiffness.</p>

<p>Printing out tensile bars would be a great thing to have for educational purposes. The bars should not only vary in infill percentages, but in also the various infill patterns. Depending on the type of stresses and loads applied, different patterns may be stronger at lower infill rates, for example.</p>

<p>Also, the infill rate should correlate to the thickness of the bottom, top, and sidewalls. This is especially important with ABS when it comes to shrinkage, warping, and delayering. In order for the part to be universally as strong as possible, as the part cools, it must shrink evenly. This is a well known factor for machinists creating molds for injection molding and casting. Otherwise, you may have unintended additional points of weaknesses arise.</p>

<p>Lastly, if creating tensile bars, make sure to take into account the shrinkage experienced along each axis, for each individual example. I would also suggest cutting each one open, as well as attempting to break a few of the apart (in a very crude way). This could stimulate a lot of thought when designing a part, before printing it. </p>

CC BY-SA 3.0
2016-04-25T05:55:55.580Z
2016-04-25T05:55:55.580Z
Alex Sky
<p>I don't believe that slicing engines create any sort of solid model that would be useful for CAD simulation. When a slicing engine slices a 3D model, it's goal is to spit out the preferred machine paths in G-Code (of some kind). However, I've read a few articles, done some tests, and heard through the grape vine that anywhere between 10%-35% is good enough for most applications. I once watched a webinar for understanding the new MakerWare interface that explained how they chose such settings. Although I can't find the clip directly, <a href="http://www.makerbot.com/resources/webinars" rel="nofollow">here</a> is the page for all of MakerBot's webinars. I think <a href="http://pages.makerbot.com/intro-makerbot-desktop-software-webinar.html?utm_source=leadgen&amp;utm_medium=resource-center&amp;utm_content=webinar&amp;utm_campaign=rc-intro-makerbot-desktop-webinar" rel="nofollow">this</a> webinar was the one I watched explaining a little bit about preferred infill percentages.</p>

<p>From experience, anything over 35% doesn't yield much more strength from infill side of things. Beyond 35% and you're going to want to reconsider how you're orienting the print when you print it and what you're printing to utilize the grain structure for proper strength.</p>

<p>However, infill percentage/patterns are not the only variable for creating strong parts. Infill is really just a way to save time and material. Here are some other ways to potentially increase strength:</p>

<ul>
<li>Increase your shell. Shell is the number of profile patterns per layer. Typically (in FDM/FFF), each shell is <strong>about</strong> the diameter of your extruder nozzle.</li>
<li>Increase your floor/roof. Similar to shell, floor/roof refers to the number of layers that make up the "bottom" and "top" of the part with regard to the build plate.</li>
<li>Print orientation. Pay attention to which areas of the part are susceptible to strain along the "grain" of the layers. Try to rotate your part on the build plate in a way that minimizes potential failure both in print and post-print use.</li>
<li>Post process. Don't be afraid to do some post-processing to increase the strength. There are <a href="https://markforged.com/" rel="nofollow">some 3D printers on the market</a> that go as far as including Kevlar strands in the printing process to beef up their prints. However, it may be as simple as just coating the part in an epoxy with some basic finishing techniques. It's a bit more work, but it turns weak 3D printed parts into full production quality prints.</li>
</ul>

<p><strong>Update:</strong>
Based on some of the comments, it sounds like your best bet might be to find a custom application that can either convert the g-code file into a solid model (try CAM software?), or create a plugin for your CAD software (I know Unigraphics NX and Solidworks allow for this) and essentially recreate your own slicing engine that takes your solid model and generates the same infill pattern dynamically inside.</p>

<p>Perhaps look into the works of <a href="http://www.simlab-soft.com/index.aspx" rel="nofollow">Simlab</a> or similar which has a lot of 3D software plugins. I'm not promoting them and I don't work for them, this is just a reference of what to look for.</p>

CC BY-SA 3.0
2016-04-24T21:37:51.650Z
Thanks for link, I'll check it out. For engineering applications we need precise data, at least it is required by project description. Engineers can relay on some experiments and experience, but it would be much more reliable source of information, to slice your part and then by simulation prove that this parameters will withstand such a load.
Anton Osadchy
CC BY-SA 3.0
2016-04-24T21:41:06.477Z
You could potentially print your own tensile bars and test different infill % in-house. However, it will greatly depend with the source of the material and shell parameters.
tbm0115
CC BY-SA 3.0
2016-04-24T22:30:39.610Z
For bending loads, which are the primary failure mode in real printed parts (because they concentrate tension on the surface of the object where the layer lines present plentiful fracture initiation sites), adding perimeters is significantly more impactful than adding infill. This behavior is kind of masked in standard tensile tests, but you'll see it in a four-bar bending test.
Ryan Carlyle
CC BY-SA 3.0
2016-04-24T22:34:08.547Z
Thanks for elaborating on perimeters, I forgot to really emphasise that
tbm0115
CC BY-SA 3.0
2016-04-25T08:12:03.817Z
Of course with bars it  can be done by printing test bars. But problem is that shapes are always different, and there are no possibility to print thousands of test parts for each of projects. So that I though about software which can simulate stiffness of already sliced part.
Anton Osadchy
CC BY-SA 3.0
2016-04-25T14:26:00.030Z
@AntonOsadchy are you referring the various project parts are in *shapes [that] are always different* or that there is a distinguishable difference in how a 3D printer prints the same part (ie. a test bar)? If it's the latter, you'd benefit from double checking your machine meets the requirements of your particular field (idk what your tolerances are).
tbm0115
CC BY-SA 3.0
2016-04-25T21:50:19.743Z
I have totally different orders, with different requirements. Shapes are always different because Mechanics of each of projects is unique. And now we have just two options, print solid if there is some mechanical load on part or 20-30% infill for housings, cases and etc. Some of parts, for instance, should not necessary be solid, but there are no tool which can help to determine printing parameters for it, so we print them solid (spending more time and resources).
Anton Osadchy
CC BY-SA 3.0
2016-04-25T21:53:27.637Z
Thanks for update. I'll definitely take a look and let you know, how it will go :)
Anton Osadchy
CC BY-SA 3.0
2016-04-24T18:56:57.267Z
2016-04-25T14:48:43.650Z
2016-04-25T14:48:43.650Z
tbm0115
<p>Anton, I parse the G-code and build a finite element model and a thermal transient event to simulate the printing of the part, followed by a structural simulation to determine the deformation and stress state in the resulting part. This part could then be further analyzed with external loads to determine mechanical characteristics. I use ANSYS software and the element birth &amp; death capability to activate a small volume of material per each thermal transient step. The structural sim is static but also done at the same time steps as the thermal transient. </p>

CC BY-SA 3.0
2016-07-16T16:21:55.747Z
Wow! That sounds very complicated and is probably a bit too advanced for most of our users. It would be very interesting if you could tell us what you learnt from these simulations (some rules-of-thumb and perhaps some statistics) because not many people will be able to replicate this.
Tom van der Zanden
CC BY-SA 3.0
2016-07-17T09:59:19.967Z
Thanks man! I have an experience with ANSYS, so I can try it. The only question is - How did you imported g-code to Ansys simulation?
Anton Osadchy
CC BY-SA 3.0
2016-07-15T20:36:29.967Z
2016-07-15T20:36:29.967Z
C. Kennedy
<p>I could think of a way. But it might require a few softwares to get everything done. </p>

<p>First get the CAD file. 
Import to magics (Materialise proprietary software)
There is a function for structures, you can build your custom internal structure. So add trusses etc. 
Export stl. (There is one software which allows direct stl to step conversion, I think its called Instep)
Or i think you could reduce mesh density and use FreeCAD to convert it back to step and run your analysis. </p>

<p>It would be intersting to see a report on the part. 
Also there is no good way of simulating a 3d printed part. 
Maybe the closest would be with composites. </p>

CC BY-SA 3.0
2016-05-01T14:07:59.053Z
2016-05-01T14:07:59.053Z
albseb
<p>If you're an engineering class, you may very well print out big cubes of different infils and test them. </p>

CC BY-SA 3.0
2016-05-02T14:02:03.183Z
The OP mentioned in some of the comments that testing is not feasible as new tests would need to be conducted for each new part. The part geometry and requirements vary such that a few tensile bars would not cover the engineering requirements. Perhaps elaborate on the process you mentioned to potentially aid others in the future?
tbm0115
CC BY-SA 3.0
2016-08-04T09:05:45.260Z
This should be a comment.
Tom van der Zanden
CC BY-SA 3.0
2016-04-30T02:33:55.123Z
2016-04-30T02:33:55.123Z
Chase Cromwell
<p>You have to do it by eye. However you need to think about what infill you use. a triangle pattern will be very strong.</p>

<p>Following I never use high infill. Most of my items have a strong outer shell, IE 3 layers. Inside I will do between 7 and 14 %. If I printed a square 200mm^3 I would have no concerns standing on it. </p>

<p>All depends. Really though for your settings I would not thing you would really ever need more than 14%.</p>

<p>At a company I worked at that was testing 3d printed parts. They evaluated material by printing the same test shapes and seeing what their tolerances were. You will need to develop your own method as such.</p>

CC BY-SA 3.0
2016-08-04T08:42:52.250Z
2016-08-04T08:42:52.250Z
MakerModder
<p>Since I'm running a 3D printing facility of an engineering school, students are always wondering how much infill percentage affects the stiffness of the part. I know that it is impossible to get a numerical solution for this question, but maybe there is an option to simulate in software an already sliced model. I haven't seen in any slicer an option to export as .stl or .step or any other format which can be accepted by simulation software. Has anyone seen or thought about something similar? </p>

<cad><infill><analysis>
Choose infill percentage
Anton Osadchy
# Choose infill percentage

(Asked by: username_0 on 2016-04-24)

Since I'm running a 3D printing facility of an engineering school, students are always wondering how much infill percentage affects the stiffness of the part. I know that it is impossible to get a numerical solution for this question, but maybe there is an option to simulate in software an already sliced model. I haven't seen in any slicer an option to export as .stl or .step or any other format which can be accepted by simulation software. Has anyone seen or thought about something similar?

**Tags:** cad, infill, analysis

---

## 6 answers

### Answer by username_2 on 2016-04-24. Score: 6

I don't believe that slicing engines create any sort of solid model that would be useful for CAD simulation. When a slicing engine slices a 3D model, it's goal is to spit out the preferred machine paths in G-Code (of some kind). However, I've read a few articles, done some tests, and heard through the grape vine that anywhere between 10%-35% is good enough for most applications. I once watched a webinar for understanding the new MakerWare interface that explained how they chose such settings. Although I can't find the clip directly, [here](http://www.makerbot.com/resources/webinars) is the page for all of MakerBot's webinars. I think [this](http://pages.makerbot.com/intro-makerbot-desktop-software-webinar.html?utm_source=leadgen&utm_medium=resource-center&utm_content=webinar&utm_campaign=rc-intro-makerbot-desktop-webinar) webinar was the one I watched explaining a little bit about preferred infill percentages.

From experience, anything over 35% doesn't yield much more strength from infill side of things. Beyond 35% and you're going to want to reconsider how you're orienting the print when you print it and what you're printing to utilize the grain structure for proper strength.

However, infill percentage/patterns are not the only variable for creating strong parts. Infill is really just a way to save time and material. Here are some other ways to potentially increase strength:

* Increase your shell. Shell is the number of profile patterns per layer. Typically (in FDM/FFF), each shell is **about** the diameter of your extruder nozzle.
* Increase your floor/roof. Similar to shell, floor/roof refers to the number of layers that make up the "bottom" and "top" of the part with regard to the build plate.
* Print orientation. Pay attention to which areas of the part are susceptible to strain along the "grain" of the layers. Try to rotate your part on the build plate in a way that minimizes potential failure both in print and post-print use.
* Post process. Don't be afraid to do some post-processing to increase the strength. There are [some 3D printers on the market](https://markforged.com/) that go as far as including Kevlar strands in the printing process to beef up their prints. However, it may be as simple as just coating the part in an epoxy with some basic finishing techniques. It's a bit more work, but it turns weak 3D printed parts into full production quality prints.

**Update:**
Based on some of the comments, it sounds like your best bet might be to find a custom application that can either convert the g-code file into a solid model (try CAM software?), or create a plugin for your CAD software (I know Unigraphics NX and Solidworks allow for this) and essentially recreate your own slicing engine that takes your solid model and generates the same infill pattern dynamically inside.

Perhaps look into the works of [Simlab](http://www.simlab-soft.com/index.aspx) or similar which has a lot of 3D software plugins. I'm not promoting them and I don't work for them, this is just a reference of what to look for.

> **Comments:**
> **username_0**: Thanks for link, I'll check it out. For engineering applications we need precise data, at least it is required by project description. Engineers can relay on some experiments and experience, but it would be much more reliable source of information, to slice your part and then by simulation prove that this parameters will withstand such a load.  
> **username_2**: You could potentially print your own tensile bars and test different infill % in-house. However, it will greatly depend with the source of the material and shell parameters.  
> **username_3**: For bending loads, which are the primary failure mode in real printed parts (because they concentrate tension on the surface of the object where the layer lines present plentiful fracture initiation sites), adding perimeters is significantly more impactful than adding infill. This behavior is kind of masked in standard tensile tests, but you'll see it in a four-bar bending test.  
> **username_2**: Thanks for elaborating on perimeters, I forgot to really emphasise that  
> **username_0**: Of course with bars it  can be done by printing test bars. But problem is that shapes are always different, and there are no possibility to print thousands of test parts for each of projects. So that I though about software which can simulate stiffness of already sliced part.  
> **username_2**: @AntonOsadchy are you referring the various project parts are in *shapes [that] are always different* or that there is a distinguishable difference in how a 3D printer prints the same part (ie. a test bar)? If it's the latter, you'd benefit from double checking your machine meets the requirements of your particular field (idk what your tolerances are).  
> **username_0**: I have totally different orders, with different requirements. Shapes are always different because Mechanics of each of projects is unique. And now we have just two options, print solid if there is some mechanical load on part or 20-30% infill for housings, cases and etc. Some of parts, for instance, should not necessary be solid, but there are no tool which can help to determine printing parameters for it, so we print them solid (spending more time and resources).  
> **username_0**: Thanks for update. I'll definitely take a look and let you know, how it will go :)  

---

### Answer by username_1 on 2016-04-25. Score: 3

Since I am not able to comment on this question yet, I thought I would provide an answer in addition to the already helpful insight provided.

If the question in general is regarding infill percentage, and the common follow-up regards part stiffness, then it should be explained that choosing infill percentage is much more than just part stiffness.

Printing out tensile bars would be a great thing to have for educational purposes. The bars should not only vary in infill percentages, but in also the various infill patterns. Depending on the type of stresses and loads applied, different patterns may be stronger at lower infill rates, for example.

Also, the infill rate should correlate to the thickness of the bottom, top, and sidewalls. This is especially important with ABS when it comes to shrinkage, warping, and delayering. In order for the part to be universally as strong as possible, as the part cools, it must shrink evenly. This is a well known factor for machinists creating molds for injection molding and casting. Otherwise, you may have unintended additional points of weaknesses arise.

Lastly, if creating tensile bars, make sure to take into account the shrinkage experienced along each axis, for each individual example. I would also suggest cutting each one open, as well as attempting to break a few of the apart (in a very crude way). This could stimulate a lot of thought when designing a part, before printing it.


---

### Answer by username_4 on 2016-07-15. Score: 2

Anton, I parse the G-code and build a finite element model and a thermal transient event to simulate the printing of the part, followed by a structural simulation to determine the deformation and stress state in the resulting part. This part could then be further analyzed with external loads to determine mechanical characteristics. I use ANSYS software and the element birth & death capability to activate a small volume of material per each thermal transient step. The structural sim is static but also done at the same time steps as the thermal transient.

> **Comments:**
> **username_5**: Wow! That sounds very complicated and is probably a bit too advanced for most of our users. It would be very interesting if you could tell us what you learnt from these simulations (some rules-of-thumb and perhaps some statistics) because not many people will be able to replicate this.  
> **username_0**: Thanks man! I have an experience with ANSYS, so I can try it. The only question is - How did you imported g-code to Ansys simulation?  

---

### Answer by username_6 on 2016-05-01. Score: 1

I could think of a way. But it might require a few softwares to get everything done.

First get the CAD file.
Import to magics (Materialise proprietary software)
There is a function for structures, you can build your custom internal structure. So add trusses etc.
Export stl. (There is one software which allows direct stl to step conversion, I think its called Instep)
Or i think you could reduce mesh density and use FreeCAD to convert it back to step and run your analysis.

It would be intersting to see a report on the part.
Also there is no good way of simulating a 3d printed part.
Maybe the closest would be with composites.


---

### Answer by username_7 on 2016-04-30. Score: 0

If you're an engineering class, you may very well print out big cubes of different infils and test them.

> **Comments:**
> **username_2**: The OP mentioned in some of the comments that testing is not feasible as new tests would need to be conducted for each new part. The part geometry and requirements vary such that a few tensile bars would not cover the engineering requirements. Perhaps elaborate on the process you mentioned to potentially aid others in the future?  
> **username_5**: This should be a comment.  

---

### Answer by username_8 on 2016-08-04. Score: 0

You have to do it by eye. However you need to think about what infill you use. a triangle pattern will be very strong.

Following I never use high infill. Most of my items have a strong outer shell, IE 3 layers. Inside I will do between 7 and 14 %. If I printed a square 200mm^3 I would have no concerns standing on it.

All depends. Really though for your settings I would not thing you would really ever need more than 14%.

At a company I worked at that was testing 3d printed parts. They evaluated material by printing the same test shapes and seeing what their tolerances were. You will need to develop your own method as such.


---

