FDM and 3D printing support material explained

Inspired by a post on Fabbaloo I’ll explain how the support material for FDM or Fused Deposition Modeling works as used by the Stratasys machines that we use. For that to happen I’ll first explain how FDM itself works.

Each 3D printing process and family of 3D printers has their own process and because of this their own type of support material and method of applying it. Support material is essential though for any 3D printing process. One of the most common is Stratasys’ FDM method and their BASS or Break Away Support System.  

Fused Deposition Modeling is a 3D printing process….

whereby a model gets printed on a mounting
tray(also called base plate). This tray moves up or down the Z axis, this
allows the model to be built up in height. For FDM this tray is
actually a plastic one with a handle that your model becomes attached
to and you take the tray out of the machine with your model on it when
it is done.  

A printing head moves along a bar across the X
and Y axes(horizontally). This builds up the depth and width of your
model. On this printing head there are two nozzles. One is for the
build material, that will make up the final model and the other for the
support material. A very thin filament passes through the head and is
melted it is then extruded through the head and deposited on the tray
where it cools and hardens. The head of the Stratasys machines goes up
and down(horizontally)along the first layer of the model first tracing out the countour of the shape and then filling it in. The head moves much like a combine harvester
would go around a field. When that layer is done the tray is lowered
and the head again starts its’ circuit of depositing material where it
has to.

If everyone wanted to print out cubes, then that would
be just dandy. But, people do not always want cubes and
they create models such as characters with arms and feet. And this
poses a problem, think about a simple shape to print out such as a
cross. It would be 5cms tall, its’ span would be 5cm and it would be
one cm thick.

If you would print out this cross standing up on
the base tray, the head would only make a small circuit to deposit the
first layer of 5 square cm. It would then move the tray down by
.5mm(this varies) and deposit the next layer all the way up the cross
until it reaches the span. At the span it would get to deposit much
more material in one sweep. The head has to orient itself continually,
know when to stop depositing material and returns to its’ initial
position to start a new layer. This movement from where it stopped
printing to where it needs to start again and the lowering of the tray
take time. Because of this the the cross would be printed much much
faster if it were lying down on its back if you will. Then the tray would not have to be
lowered as much and the printer could deposit much more material on
each pass. This also means that it is much quicker to print a bunch of
models on the same tray then it would be do to them all individually.
It the head is moving along the tray anyway it might as well print a
layer for three models rather than just one.    

Anyone can see that a cross would
work quicker laying down, and you could just randomly plunk down a few
models to be printed out on a tray. To optimize machine time though all
the major 3D printing systems manufacturers have developed software that determines how models are put on the build tray and how they are oriented. This software also imports the STL files(almost all of the machines use STL as a standard file format)and converts that information into commands that tell the head how to move around and when to deposit material. This is called the extrusion path of the head. Stratasys has its’ Insight software package that calculates all this information for you. Insight also determines where the support structures are to be built.

So why does 3D printing need support structures and support material? If we picture our standing cross again and the head moving up each level depositing its sticky melted material at each layer until it gets to the span of the cross, we encounter a problem. If the head moves beyond the base of the cross it has built up so far and deposits the material for the beam of the cross, the material will simply fall down. Instead of a + cross we will get an upside down T. To counter this problem the machine will have already deposited layer upon layer of support material all along the base of the cross for the entire length and breadth of the beam so that it can deposit the build material on this support material and build the beam without the material falling down.

Support material is typically much cheaper than the actual build material but it does come at a cost and in the case of the cross you can see that it would require a lot of it to print a coss that stands up. 3D printer software packages such as Insight calculate where the support material should be placed and what is the most efficient use of it. Anywhere on a model where you have any kind of overhanging angle or plane, support material will have to be built underneath it to become a base for the layer of build materia that makes up that angle and anything above it. If you would print a sphere a support material would have to be built around the sphere, from the very base, all the way up to the diameter of it to support the overhanging area of the sphere.

The pictures on this page are from a Shapeways model, SRV-01 Surveillance Vessel by Sovereign. This particular print was a misprint and we had to print it again but because of that we have a nice 3D print that shows you how support material works.  You can see the brown support material clearly. The BASS or Break Away Support System is used by Stratasys with polycarbonate materials. In a model like the SRV with its curved wings and pointy thin nose the 3d printer will print much more support material than actual build material. BASS comes in canisters just like the ABS or polycarbonate build material does. It is unwound and melted just like the build material and the machine simply switches between nozzles depending on if it needs to deposit support or build material. 

The support material is actually removed by hand. A person with gloves and pliers has to break away each brown chunk until the model is left over. Other support materials are water soluble which is generally much faster but does require some kind of water installation such as a high pressure hose in a chamber to remove all the material from all the nooks and crannies(pictured right). Both these methods are much easier and safer than other support materials that have to be removed by using some kind of solvent. 

That about sums up support material, I hope it was all clear to all of you.              

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