Hi everyone, I'm Alex Crease here at Markforged, and today
I'm going to be talking with you about the different methods of 3d printing composites like carbon fiber, fiberglass and kevlar
When people talk about composites in 3d printing it can take two forms
Chopped fiber or continuous fiber 3D printing
It all starts with a strand of fiber
Like this one
Fibers like carbon fiber are so valuable in engineering because of their strength to weight ratio
Specifically when applied in tension
Alone, they sort of behave like raw spaghetti
You can easily break a piece of spaghetti by bending it
by compressing it
or by shearing it
But it takes a lot more force to break a strand of spaghetti in tension by pulling on it
And that's how fibers are most often used in composites
When you bond these fibers with a matrix material to help them take shape
They form incredibly lightweight
Strong structures because the fibers can be laid out in these optimal patterns that make use of their tensile strength properties
So chopped fibers in 3D printing are a bit different referring to small bits of carbon fiber
Broken up and mixed into a thermoplastic like ABS, PLA, or nylon
This gets extruded into a spool which can then get 3d printed with a deposition based printer
But doesn't leverage the continuous strength of those fibers
So it's sort of like a booster pack for standard 3D printing thermoplastics
It bumps up some of the material properties like heat resistance, strength, and stiffness
and may improve the print quality and dimensional stability as well
But the strength is largely defined by what's holding it all together, which is the thermoplastic
Continuous fiber printing is a variant of a deposition based printing process called continuous fiber fabrication or CFF
One nozzle builds a thermoplastic matrix material while continuous strands of fiber are ironed down into the part with a second
Software allows you to lay these fibers down in specific places
With specific settings to optimize the part for its strength just like with traditional composites
So a part reinforced with continuous fiber
Leverages the strength of the continuous strands themselves rather than relying on the thermoplastic for strength and we can show what a difference that makes
Right here
So chopped fibers are basically a bunch of little pieces of a strong material
adhered together in some way like how these bricks are held together by their connection points
A continuous fiber takes that same material but forms a continuous connection
across the loading surfaces of the same part
represented by these plates on the top and bottom
so when we apply a load to a chopped fiber part
It breaks at the connection points
which when applied to printing composites is just the thermoplastic holding it all together
when we apply this same load to a part with
Continuous segments spanning the load paths, in this case, the top and bottom plates of the part
The chop segments act as a filler or a matrix material and
The load holds because it's being distributed across the loading surfaces by the continuous reinforcement
This concept is what makes the continuous fiber so much more powerful than chopped
I hope this clarified some of your questions about 3D printing composites
Happy printing!
