rahix: Who of you has a 3d printer yeah I was hoping so I was hoping so okay and who
of you that has a 3d printer is designing models themselves that they print. Oh wow,
very nice, very nice, okay and do your designs work on the first try usually?
Somewhat, somewhat, okay. I'm gonna start off here by making a very bold claim
and I'm... I would say that designing parts that just work first try is totally
possible. Parts that always fit that don't break and that never fail to be
printed and no I guess you might be a bit skeptical, so why do I say this? Well
because 3d printing like any other manufacturing process it isn't magic
whether a part works or doesn't work is subject to some fundamental rules and if
we understand these rules then we can learn how to make robust designs that
just work and this discipline that's called design engineering we could call
it the art of making or perfecting the shape of mechanical parts think a lot
of you will agree that getting a 3d printer is an absolutely eye -opening moment
suddenly there is this whole new world of possibilities of what you can do you can
suddenly create complex physical parts to solve real problems around you that you
maybe didn't even notice you have before and you can do so for laughably cheap
compared to other manufacturing methods it's absolutely crazy and really all you
need for that is your imagination right well that's not quite true right there are
some limits to the parts that we can make even though 3d printing is often
advertised as this technology that allows you to produce arbitrary shapes but I think
most of you will know that this isn't quite true so first of all if we want our parts to be
functional for example we can't make them arbitrarily
thin the material isn't infinitely stiff there is a
limit to the material strength where it will just
break and also the fused filament 3d printers that
most of us are probably using they aren't even
completely free in the kinds of geometries they can print
there are some shapes that work very well and others that are really difficult to print
and as I started figuring this out this fascinated
me a lot it sort of led me down a path of trying to
learn everything about how you have to go about
designing parts that are going to work perfectly every
time and really the 3d printing community is an
amazing place for that there are so many people who are
experimenting with different design tricks and
techniques and figuring out what's working well
what's not working so well and documenting that and
most of those resources are shared for free online
so I've been collecting all these tricks that I found
in the community and also I've been experimenting a lot
myself to see what works and what doesn't and I want to
share that with all of you of course I only have 30 minutes
here I won't be able to talk about everything in this short
time frame but I have published a long form blog article
about all the nitty -gritty details of design for 3d printing and I'll get back to that later
for now here in this talk I want to give the most
important part in my eyes at least and that's the
general approach to designing parts for 3d printing
so they work well and that sort of comes with the
right mindset that you need for design and most
importantly this isn't specific to any CAD software
or any specific tool this is more the abstract approach that you have to follow in your head
and then you can translate that into whatever
CAD software you prefer so let's go back to that
design engineering I mentioned what is that and to
go deeper into that question we first have to answer
something else what does it mean for a part to
work or to be good that isn't really a precise term
and this isn't actually that simple of a question
there are a lot of different angles to this the most
obvious thing is functionality like for example does
it fit let's say we have some mounting holes that
our part is supposed to attach to if our part doesn't
fit to those mounting holes then it is quite useless
or we have some other physical parts that we want to fit to our parts and we
must make sure that they match to each other every
mechanical part in fact will have a lot of mechanical
interfaces that we have to connect to and so if
our part doesn't fit those mechanical interfaces to
other parts then it's quite useless and it's not
a good part that's the first functional aspect the
second one is does it break so the part of course has
to be strong enough to withstand all the forces that
it is subjected to and this is a more tricky question
like if a part doesn't fit you'll see right away
you'll print it it doesn't fit you're angry and you
reprint but whether a part will break that's really
difficult to answer because a lot of failure modes
only happen over time for example material fatigue you
won't notice at first but then after quite some
lifetime the part will slowly fail or if you have
many some will start failing it's a whole mess and you
can't really know in advance how strong parts will be
you can't really calculate the strength of 3d printed
parts and so these are the functional requirements
there's of course some others like for example the
cost maybe if you do this for business you care about
what each part costs you care about the weight maybe
or you care about the size for non -functional reasons
and so i think these are all pretty obvious requirements but behind those there is
an even more important one in my eyes and that is
can it be made because if it can't be made then we
don't have a part to fulfill all the other requirements
so this is just as important as all the other questions
is designing parts that can be made well and really
this is a tricky question because it's not yes or no
it's not we can make the part or we can't well
sometimes that's true but often there is a range in
there so for example there might be parts that you
have to post process for them to work or where only
every second part you print will be successful and
every other one you have to scrap or you will need some
special or expensive equipment to make the part let's say a more high -end 3d printer
and obviously it would be better if those weren't the case if we were to design parts that
can be made well and don't have these sort of special requirements
so this is where the design engineer comes into the picture the design engineer's job
is to find the optimal compromise between all these different questions or requirements
so figuring out the trade -offs of should we make
the part stronger or should we make it cheaper for
example because you can't go one way or the end the
other you have to make trade -offs in a lot of places
so cool how do you do that well the problem really
is that we have all these questions well does it fit
does it is it strong enough and we sort of have
to answer those and we don't just have to answer
those ones we have to answer those usually in a lot
of places of the design and we can't really answer
them to the last detail because we'd have to do a
lot of maths we'd have to probably simulate the parts
to try and figure out whether it's really strong
enough or whether it will really fit and that's not
a solution because that will take an infinite amount
of time and obviously we do not have infinite time
so we can't just answer all the questions to the end
we have to use some less precise methods during the
engineering design work and the answer to that lies
in heuristics so rules of thumb that we use during the
design process to figure out what we should do when we don't know for sure what to do
these sort of rules they guide us by giving us a
sane default of well we could do it this way or the
other way probably this way is better we don't know
for sure but there is a high likelihood so we don't
have to go and do all the maths of checking whether
it will really really work and we sort of hope for
the best and most of the time that works out well and
these heuristics these rules of thumb they exist in
every engineering domain of course just to paint
the picture a bit more vividly in general mechanical
engineering there is for example the rule that you
should always guide forces on the most direct path
through your part as possible or when you design
your parts you should make the tolerances that you
allow on the part as large as possible and these are
general rules that when you follow them they will
probably lead to your parts working great and these
sort of rules that's what people have been figuring
out over time these heuristics they encode the
knowledge that the engineers have gained over time
so of course this is what i've been looking for
for 3d printing design for 3d printing is really
these rules and i call them rules but they're not really rules as in you have to follow them
as i mentioned but i wanted to collect these rules
for specifically for designing parts for 3d printing
and now i will dive into some topics related to that
the first one being designed for strength that's
the does it break question it isn't actually that
specific to 3d printing every part has to be designed
to be strong enough but 3d printed parts have some
special properties that affect the part strength in
non -obvious ways so that's what i want to look at the
first being that 3d printed parts are made of layers
and these layers they are stacked on top of each other
and that leads to different material properties
in different directions so you have the direction
across the layers and along the layers and the problem here is that the adhesion between the
individual layers it's it's not perfect so when you
pull the layers apart which we would call tension
this tension resistance of the part will be less strong
in the direction of pulling apart the individual layers
uh compared to pulling on the along the
layers and so stretching the individual filaments that the printer has extruded
so we can generally say and the exact numbers they differ a lot between printers and setups
but generally parts will be more strong along the
layers than across so when you design your parts you
should design them such that you orient the tensile forces to be parallel to the print bed
so here is this example that's a screw and a screw
is of course loaded in tension along the threads
and so what we can so that's bad of course because we now have the tensile strength in the
weakest direction so maybe it might be better to put
it flat on the print bed and then you have a part
that is a bit better in terms of its strength
but really there is another important thing here
and that's for the design process when you design
parts one of the very first things you should do
is you should decide on the print orientation and
you make this decision based on what i just mentioned
the tensile forces that your part will have to withstand and you decide okay this direction
is probably where most tensile forces will be so i orient that flat against the print bed
so you decide on this orientation very early on
and then every further step in the design is based
on top of that so you have to make sure that you think through this decision quite carefully
because changing that later on is pretty difficult
it's like when you have a when you choose a
framework for your software project choosing a
different one at a later time is very difficult
and similarly you should make sure to do careful consideration of the part orientation
and generally this is very important when you do your CAD work the CAD software shows you a
simplified model of reality it shows you a perfect
solid volume but in your head you should always
imagine the structure of the print as it would be
produced by the printer from that volume and then
when you change the volume's shape you should
think about how that affects the layer structure
but the layers aren't the only thing that's
interesting about the 3d prints the other thing is
that 3d prints are actually mostly hollow you have
this solid shell and then a mostly hollow infill
and let's say we have this part and it's not strong enough we could just fill it with more
material to make it more strong right and this
does work we get a stronger part but it's actually
really inefficient to do that because we're adding
a lot of material that doesn't help strength
in the general case the reason for that is that
most parts aren't actually loaded in pure tension or
compression like the screw but actually most parts
are loaded by bending forces and bending forces have
an interesting property there is a neutral axis across
the center of the part where the internal stress is
zero and then as you go outwards from this neutral
axis in one direction you get higher and higher
tension forces and in the other direction get higher and higher compression stress
so actually material does most to resist the bending forces when it's right at the surface
so really the better choice in the general case is to
make the shell thicker than to just fill the inside
because in the middle the infill won't do anything
for strength against bending moments because that's
where the neutral axis is so okay we can make the
part stronger by making the shell thicker right
that's one way but there's another one that for us as
the design engineer who cares most about the shape of
the part is much more interesting and that's we can just
move the surface to be further away from the bending
the center the neutral axis of the bending moment so
by doing that we don't add that much more material
we just move the existing material of the surface
to a place where it does even more to resist bending
in this case this would mean changing the height of
this beam to be more like let's say increase it by a
factor of two and then we get a much much higher
resistance against this bending force without adding more
material and i say without adding more material because
really we're all adding more volume and the volume
is empty space so you always oops should think more about the surface area of your parts
than the volume the because the volume is mostly
hollow it doesn't do much for strength so always
think more about the surface okay so the next thing
is does it fit and in the engineering world this is
the tolerances so how far can a part deviate from
its shape for it to still work so usually you'd go
about this by defining functional tolerances you would for example let's say we have these
mounting holes somewhere and we have a part that
we want to mount to it we add two holes to it and
then we can put some screws through there now
the tolerance on this dimension or the limiting
tolerance from a functional perspective is how far
can those holes move to the side for the part to still
work and at this point if they were to move any further
out then we can't put the screws through anymore
so that's the limit that's the tolerance limit we
set the problem here is that maybe our 3d printer
isn't able to hold this tolerance limit so what do
we do well you should think about it the other way
around you should consider what are the tolerances
of the manufacturing process so how accurate will the
parts be that my 3d printer makes and then use that
to guide your design so in this case you might notice
okay this tolerance limit for this configuration that's too low my printer can't do that
what you can do as a designer is you can make the
holes bigger and now the tolerance limit would move
a bit more outward and maybe your printer is
then able to actually manufacture that so let the
manufacture let the manufacturing process in this case
the 3d printing process define your tolerances and
then choose your design accordingly rather than going
the other way around as the traditional method is
so now the natural question is okay so what are
the tolerances that my 3d printer has or that
generally 3d printing has because usually we
wouldn't want to design for a specific 3d printer
and i have to disappoint you i can't give you numbers because it depends a lot it depends on
the shapes that you're printing so for example here
we have this box with square corners and think about
what the printer does when it prints those corners it
has to stop and then move in a completely different
direction so there's high acceleration high acceleration
means high forces on the frame of the 3d printer
which means it will shift slightly you will have
worse tolerance on those corners you could fix that by
making your 3d printer more stiff or by tuning the
tolerance but as a design engineer you fix that by
getting rid of those corners instead if you add
fillets so rounded off corners the printer now has to
take much lower acceleration paths because the
direction is changing gradually and it will always
print that with much higher accuracy and even printers
that aren't perfectly tuned against ringing for
example they will be able to print that without
much difficulty and similarly there's a lot of other
things that printers can do better or worse which
i'll quickly skim over for example overhangs beyond a
certain limit or large flat surfaces where warping
due to thermal stress becomes an issue there's one
more thing that i actually want to show which is what
do you do when the tolerances of the manufacturing
process of your printer just don't cut it when you
need more and there is an amazing little trick that
you can use if you can't make it precise make it
adjustable so for dimensions where you need higher
accuracy than what your 3d printer can give you add
adjustment mechanisms that's not a silver bullet
you always add additional degrees of freedom that
don't help but these adjustment mechanisms allow you to
get fine tolerances that you otherwise wouldn't be
able to hit so just some examples you could use oblong
holes for screws or you could have two opposing screws
that clamp apart and then you can adjust the position
you could oppose a screw come on no what's that let's
see oh that was a bit too far okay here you could
oppose a screw by a spring or you could do what the
industry always does is shimming so you see the small
metal piece that's 0 .2 millimeters in size you just
stick that between the two parts and now you got your
dimension perfectly on point okay so that's tolerances now the question can it be made so
let's assume it can be made but we want to make it
better so that's why i called it process optimization
the first and most important thing here is
support material you can use support material to
support structures that otherwise can't be printed
like for example here this screen structure supports this overhang but really
those supports they add a lot of headaches you have
to post process the parts often you have to tweak
the slicer to make them work perfectly you have a
rough surface where the support meets your part which
has bad tolerance if you care about that surface so
if you can it's better to avoid them and often you
can very simply like for example here we could
just add a angled surface beneath this overhang
if the part interfaces allow that and that makes it
much more easy because now we don't have supports
anymore there's another nice trick for example you
could flip a part to 45 degrees now you may have bad
adhesion problems so that's a trade -off to make but
now there is no more long bridges like it is here
and really trade -offs is the name of the game support
material avoiding and strength are often at odds
so here i have a part on the left it doesn't need
supports but the direction is bad for strength
because this little hook is across the layer lines on
the right the strength is better but now we need supports
so you always have to make those trade -offs of
course this was just a very very small amount of
information on the different areas of the strength
of parts the tolerances and the process optimizations
and there is a lot more for also there's other areas like for example you can in 3d printing
functionally integrate many things into a single
part which in traditional manufacturing would be
prohibitively expensive you can use flexures to
add mechanisms that can move or you can do print in
place designs also you don't always have to do everything
in 3d print you can also combine 3d printing with
other things like the most common one would be machine
elements like screws or other hardware like bearings
or you could embed other materials into 3d printed
parts and so i hope i got a brief primer of this
topic out now and as i mentioned i have this article
where i went into much more detail on the things
that i have found and really for me this is just the
beginning this is the list that i have collected so far
and i would really love to chat about this topic
more because i think there is so much that we as a
community can bring together by collecting these
rules and by sharing them with each other so please
reach out and if you are interested here would be the link to the full article
Herald: thanks a lot for this really
cool talk so we have 10 minutes for questions are
there questions we have like several mics along
the aisles if you have questions ask them here also if you have questions from the stream we
monitor the irc and matrix channels so we have
a signal angel here for questions but we do have
questions here let's start here in the front
Attendee: hi yeah thank you for this wonderful talk i would be
interested to learn more like what are your current
fields of interest in 3d printing like what are the
things you yourself want to learn more about
rahix: so my main use case for 3d printed parts is purely functional
designs like i had this teaser picture at the
beginning i think this is oh come on yeah don't
use new technology when you do a presentation let's
see come on there we go so integrating standard
machine hardware like in this case some pneumatic
cylinders with 3d printed parts to design automation
systems for much cheaper than the industrial systems
would cost and there is a very interesting place
here because now we're replacing very stiff machine
frames with the very compliant 3d printed parts
so you have to get quite creative to still achieve
good repeatability and make sure that you work around
the sort of limitations that 3d printing has but
it is actually surprisingly possible and i can
really just suggest to everyone who's interested in this sort of area just give it a try
you can get quite far you can get amazing accuracy
even though you're not using the high -end components
that industrial systems are using
Herald: thank you another question i think you were first at the mic number four
Attendee: yeah thanks for the talk which programs do you advise us to use
rahix: okay so this talk was specifically
not showing any specific cad program i myself use free cut and i'm a strong advocate
a very strong one and actually okay let's see if i can live roll that
there is something i have for you because if you do
design for 3d printing oh shit i did not prepare to do
this i actually created a free cut add -on that helps
you do design for 3d printing and i wish i could show
you it's called fused filament design and once i got it here i will put it up on the screen
um and this is yeah there we go look does it work
yeah it's a free cut add -on it helps you automate
common design for 3d printing shapes like for
example here you can see certain examples i will skip
the details for now read the blog post and that
really makes you more productive maybe the same
thing exists at some point for other cad tools but
that's why you should use free cut for your designs
for 3d printing in particular
Herald: thank you next question number two
Attendee: hi thank you for the talk do you have
any experiences with compliant mechanisms using
free cad or do you have any tips if i'm interested
rahix: so flexures i would call it so compliant mechanisms they're a really tricky topic
because the thermoplastic that we use while on one
hand it's quite easy to bend and it's compliant
so that's nice on the other hand it has some properties that are not so nice so you can't
control it as well as for example metal flexures i do mention some things in the
article but if you're really interested we could have a chat about it because there is a lot
of depth and actually i did some yet to be published work on that as well trying to
integrate flexures into more complicated designs in
the hopes of reducing reducing external component
count but i have to say it's really really tricky
to get right to make them robust so they don't
break over time
Attendee: thank you where where would we find you
rahix: decked 4016 or at the rust assembly
Attendee: thank you
Herald: thanks another question at number four i think is a mic
rahix: so the simulation is also free cad
or where did you do this the picture of the simulation i showed that was free card fam
um i actually don't use it much but i used it to
generate this one visualization and it was surprisingly
usable actually
Attendee: thanks for the talk
Herald: do we have more questions in the audience i don't see anyone
else at the mic or at the signal angel i don't
think so do we no then i have another question
it's a bit of a herald question because i'm not
this deep in the topic as you what is the most
important thing for you about like 3d printing
like what makes you burn this much for the topic
rahix: i think
the main topic is that it allows us to share designs
easily it makes it that we have portability in
physical objects which just doesn't exist with traditional
manufacturing because either it's too expensive
or people don't have access and with 3d printing
we suddenly have the ability to copy each other's
designs to iterate on them in a way that we're used
to from software but doing the same for mechanical
things and i think there is huge potential there i think we're not even close to using that
to all its extent and i would love to see it happening much more
Herald: thank you we still have like three
minutes for Q&A and there's another question at mic number one
Attendee: hi thank you so the software is
evolving the slices and also the 3d printers so what
has has changed for you in the last couple of days
so or years so like we don't need that much
support anymore than we used to be what changed for
you and what do you think will change in the next couple of years
rahix: oh that's that's a good question
so i would say in general the design rules that
i'm working on here they become less important
over time because 3d printers get better and as
the general let's say population of 3d printers
gets upgraded over time you can have higher expectations
i try to always make my designs such that i can
they target the common 3d printers that everyone
has so everyone can print them without problems
but these common 3d printers they get better over
time because people replace theirs with better ones
so over time things are less important to care about
and well at some point maybe we'll get closer to
for example what other additive manufacturing
methods allow in terms of flexibility of design but
it's hard to tell how fast that will happen
Herald: do we have more questions in the audience we still
had a little bit time for more questions someone is standing up yes
Attendee: hello i got a question
regarding the addition with other products for
instance like glass fiber did you ever made experience
with mixing materials
rahix: i personally haven't so far but i've talked to a lot of people who are
experimenting with that and i think it is a very
interesting avenue to embed for example glass
fibers or carbon fibers not not into the filament
but rather into the print maybe during the print
or afterwards okay
Herald: any more questions we still have like two minutes if we want to run but
if there are no more questions and i think a big round of applause again for right