When it comes to the strength of your 3D printed
parts print settings play, besides the material a major roll in what your prints can handle. Unfortunately I hear and read way too often
that many only use the infill ratio to adjust that property. For this reason I tested the strength of different
infill patterns on tons of these hooks and more importantly show you how you really should
strengthen your prints! Guten Tag everybody, I’m Stefan and welcome
to CNC Kitchen. If you have your material dialed in you will
usually only adjust a small number of settings before each print depending on the requirements
of the part. If you want it to be strong, many will adjust
the infill density to a higher value. This will scale the infill patters density
and defines how much of the internal cavity is filled with material which can go up even
to a fully dense part. The other option is increasing the thickness
of the outer shell, by adjusting the shell thickness, wall thickness, number of perimeters
or however it is called in your slicer. Usually, for a strong print you’ll be adjusting
both values. But what really gives you the strongest result
and which is the most economical way, meaning how can you increase the strength of your
part with the least amount of material. If you want to print light weight structures,
this is something which is really important. In order to properly answer that question,
I printed quiet a lot of my trusty test hooks and measured their strength – for science! This is definitely not perfect and doesn’t
include all possible load cases and orientations, but I still think that this is a good real
world example and probably one of the best analysis you’ll find at the moment. The reason why I use my hook from my filament
test series for the investigation instead of standardized axial test specimens is, that
the critical area is loaded with a more every day load case. Since the location of load application is
a little offset, that lever arm will cause an additional bending moment that is superposed
with the axial force. In real life, your part will also mostly be
loaded by such a combination so the results I present, even though not 100% scientific,
will probably be more usable and proof my point better. As a first investigation I wanted to find
out what difference the infill patterns make on strength of the part and print time. I also wanted to find out if 30% infill really
meant that 30% of the internal volume was filled by material. Since I used Simplify 3D as a slicer for these
tests, I was trying out the following available patterns: Rectilinear, Grid, Triangular, Wiggle,
Fast Honeycomb and Full Honeycomb. Rectilinear is usually the default and prints
the fastest whereas Wiggle is probably more for esthetic purposes. Like for most of my parts, these hooks were
printed with only 2 perimeters, and 4 bottom and 5 top layers at 0.2mm layer height. All the parts were printed in PolyLite PLA
by the way. Print time of the Rectilinear infill was the
shortest with 48.5 minutes. Grid infill took 50.5 minuest and triangular
53. The patterns with lots of direction changes
took the longest with 55 minutes for the full honeycomb and interestingly wiggle and fast
honeycomb took the longest needing 56.5 minutes. This is not fully representative, since the
times change due to the geometry and ratio between outer walls and infill, but shows
that you can definitely save some time using the standard rectilinear pattern. Taking a look at the real final weight of
the parts was pretty interesting because most hooks weight around the same, resulting in
a calculated infill of roughly 33%. Only the hook with the triangular pattern
weight quite a lot more and ended up with a 45% infill instead of the assigned 30%. But now to the most interesting part. What was the strength of the parts? As expected, Wiggle did the worst with only
45 kg until failure. Rectilinear came next and failed at 48 kg. Then there was grid at 52 kg and both honeycomb
patterns failed at 57 kg. The hook with the triangular infill was the
strongest failing at 60 kg! But as we have seen before, 30% infill in
your slicing software doesn’t necessarily mean 30% material in the infill. For this reason, let’s take a look at which
infill is the most economic, so were do we get the most strength per weight. This is where we see that triangular infill
is no more the best but both honeycomb infill scores the highest values. The order of the rest stays pretty much the
same. In the first analysis we have seen that the
full honeycomb seemed to be the most economic solution if you want to increase strength. As a next test, I wanted to find out how the
strength of the hooks change depending on different infill ratios from 0 to 100%. I did this analysis with the full honeycomb
infill but also the rectilinear because I wanted to know how my standard infill pattern
behaves with different infill ratios. Even though it seemed with the first tests,
that the honeycomb patter was significantly stronger than the standard infill taking a
look at the all of the values between 15 and 75% they are pretty much the same. The interesting part again is if we also take
a look at the print time, where the rectilinear pattern starts to shine. At smaller infill ratios the both infills
give you around the same strength in the same amount of print time, but as soon as you go
over 50% the rectilinear prints way faster than honeycomb at the same strength. But wait, this is not the end! Let me show you how you really can increase
your part strength the right way, without worrying about infill ration or infill patterns. I hope this analysis is not too technical
but I think there is too much superficial knowledge around about this topic so I thought
I’d approach it at least a little scientific. If you would like to see more in this direction
please let me know in the comments and consider becoming a Patreon. This doesn’t only help me spend more time
on these topics, but you’ll also get access to all the detailed test reports and test
models! All right, so I have already said in the beginning
the critical section of our hook is not only loaded in tension, but also in bending. If you bend a part, just like the piece of
foam right here, one side will be stretched, the other sider compressed. The part in the middle is not stretched at
all so material which we place in the core of our part usually is loaded not at all or
only slightly. The further material is next to the outer
shell the more it contributes to the strength and stiffness of the part. If we take a look at our 3D prints, this is
shell of our print, which thickness we can adjust with the number of perimeters, shells,
wall thickness or similar. In order to find out how this affects the
strength of the hooks I printed more samples with 2 to 6 shells and only a moderate 15%
infill. I also increased the number of top and bottom
layers to get a constant wall thickness of my part. If we take a look at the results we can directly
see, that increasing the shell thickness is way more efficient than varying the infill. At the same weight a hook that was reinforced
with more shells is significantly lighter than a hook where only the infill was increased. What’s also interesting is, that a hook
with 6 perimeters is already as strong as a part with 2 perimeters and 100% infill. This is due to the reason that in this case
the strands of filament of the shells are in the direction of the internal forces, so
in their strongest orientation, making them way stronger than the infill, that is rotated
all the time. For completeness let’s also take a look
at the print times and here we see, that in my case, I didn’t save print time with the
perimeter method. Print times at the same strength were very
comparable to the hooks where the infill was varied. The reason for this is, that the outer shell
is usually printed slower and with lower accelerations than the infill, to improve print quality. Okay, so what is my verdict? If you want to print stronger parts increase
the number of perimeters and also top and bottom layers. Don’t only crank up the infill ratio. I wouldn’t usually use infill ratios of
100% because at first this is not economic and second might lead to severe printing problems
if only a small amount of overextrusion is happening. Also, don’t try to get 100% infill with
increasing the wall thickness all the way because that can also lead to printing problems
and as I have told you before, material in the core mostly doesn’t contribute a lot
to the strength of your designs. For parts that need to be strong I usually
don’t go above 4 perimeters and 50% infill. That is a good compromise between material
usage and strength. Even though rectilinear infill wasn’t always
the strongest, I’m still a huge fan of this pattern because it gives you quite a dense
grid even at low infill ratios which is good for your top layers. I might need to try out the 3D infill patterns
that are available in Slic3r and Cura and find out how they faire, also considering
loads in different directions. But what’s your approach at the moment if
you print parts that need to handle some beating? Let me know down in the comments! I hope I was able to clarify and debunk some
myths about infill and part strength. If you liked the video and learned something,
then please hit the like button, share and subscribe. If you want to support my work and research,
consider supporting me on Patreon. Thank you so much for watching, auf wiedersehen
and I’ll see you next time!
