Your Strongest Parts with Carbon Fiber 3D Printing: MarkForged
Markforged’s continuous strand composite 3D printers enable our customers to create industrial strength 3D printed parts, reinforced with composite fibers to produce properties similar to quasi-isotropic composite laminates, in a highly automated 3D printing system. Quasi-isotropic 3D printed parts have varying material characteristics along different axes, and by varying the fiber orientation in our Eiger slicing software, you can design strong parts to resist specific loading applications to which the part may be exposed. High strength isotropic material* properties make engineering part design easy – if a material has the same properties in all directions, then making a part that is strong enough for an intended application is nothing more than a matter of geometry. In the case that material properties will differ across different axes (as is the case in 3D printing), a quasi-isotropic* material is the next best option, since there is a strength difference along only one axis that must be taken into account and it will require much less time and design work to optimize for part strength than with a completely anisotropic* material. See the common terminology for composite material property orientation below for a deeper discussion of variations in material properties. Note that for convenience, and with the understanding that all 3D printed parts will have differing material properties in the Z direction (the axis normal to the printbed plane), Markforged has dropped the ‘quasi-‘ from quasi-isotropic in describing our ‘Isotropic Fiber’ fill type.
Composite Terminology Glossary
Isotropic materials — have uniform material properties in all directions, regardless of material or observation orientation. Most (but not all) metals tend to have highly isotropic properties.
Anisotropy — an overall state of having directionally dependent properties. A material characterized as anisotropic doesn’t demonstrate the property of being isotropic, but such a general classification doesn’t offer any information on how or along what axes the material is directionally dependent. The living hinge part we demonstrated previously is a great example, since it contains flexural elements, as well as stiffer, Kevlar-reinforced regions.
Orthotropic materials — such as wood, demonstrate properties which differ along three mutually-orthogonal (at 90 degree angles to each other) axes. Wood offers a good example because it has a tendency to split easily along grain lines, but is difficult to cut or split in other directions.
Quasi-isotropic materials — often approximate or are isotropic materials in two axes, but have differing properties in a third direction. This is an accurate general description of Markforged 3D printed parts which include the ‘Isotropic Fiber’ reinforcement pattern, mostly without regard to the values used in the ‘Fiber Angles’ property described below.
Transverse isotropic materials — are a subset of quasi-isotropic materials, and refer specifically to materials in which isotropy occurs in the transverse plane of a part (think uniform properties in each layer — the XY plane — of a 3D printed part), with differing material properties along a single axis (the Z axis in a 3D printed part). With a Markforged 3D printer, this is very closely approximated while using the Isotropic Fiber fill pattern and the default ‘Fiber Angles’ values described below.
Traditional thermoset composites (most consumer uses of carbon fiber employ this type of composite) are made from dozens to thousands of stacked layers of unidirectional composite material (often in the form of woven cloth or unidirectional tape) oriented in a pattern of different directions; composite designers employ a nomenclature structure in the form of an ‘orientation code’ to provide a simplified way of describing these repeating patterns. Each successive layer is generally rotated by some angle (often 45 degrees) relative to the layer below, and since the composite fibers making up the woven cloth in each layer are strongest in their tensile direction, rotating the cloth each layer produces a part with a much higher multi-directional bulk strength and stiffness than if the cloth had been laid up in the same direction on each layer. A great primer on composite orientation codes can be found in this presentation from the US Naval Academy. A traditional orientation code is described by a series of angles bookended by square brackets and separated by forward slashes, to denote the various angles used in a particular composite layup strategy. For example, Eiger’s default Isotropic Fiber fill pattern uses an orientation code of [0/45/90/135], meaning that the first layer of fiber reinforcement is printed in a unidirectional pattern at an angle of 0 degrees from the horizontal. The second layer of fiber is rotated 45 degrees away from the horizontal, and this sequence continues until the code is completed, at which point the pattern restarts from the horizontal. Eiger also offers our customers the ability to develop completely custom orientation codes of their own, of any repeating length. Of note is that the while each individual layer contains a high degree of anisotropy, with much higher strength in the direction along the length of the individual composite fibers, the addition of multiple layers of composite with rotating direction quickly adds strength in multiple directions, resulting in a part which is isotropic as a bulk entity.
A great primer on composite orientation codes can be found in this presentation from the US Naval Academy. A traditional orientation code is described by a series of angles bookended by square brackets and separated by forward slashes, to denote the various angles used in a particular composite layup strategy. For example, Eiger’s default Isotropic Fiber fill pattern uses an orientation code of [0/45/90/135], meaning that the first layer of fiber reinforcement is printed in a unidirectional pattern at an angle of 0 degrees from the horizontal. The second layer of fiber is rotated 45 degrees away from the horizontal, and this sequence continues until the code is completed, at which point the pattern restarts from the horizontal. Eiger also offers our customers the ability to develop completely custom orientation codes of their own, of any repeating length. Of note is that the while each individual layer contains a high degree of anisotropy, with much higher strength in the direction along the length of the individual composite fibers, the addition of multiple layers of composite with rotating direction quickly adds strength in multiple directions, resulting in a part which is isotropic as a bulk entity.
