Chopped vs. Continuous Printable Carbon Fiber

3D printing processes are easy to implement and offer a wide variety of materials to support a part’s requirements while eliminating cost, lead time and design barriers for adopting manufacturing aids on the shop floor. 3D printed composites are an exciting new trend. Whether it is chopped carbon fiber filled into a thermoplastic or continuously laid inside of a 3D print geometry, the benefits of the strength-to-weight ratio are far superior to traditional 3D printed materials. In this blog post, we’ll compare continuous fiber, chopped fiber filled nylon and Stratasys Nylon 12CF and when it’s best to use them while 3D printing parts or prototypes.

Advantages of Each Material

While the terms are often used together, there are distinct differences between printing carbon fiber and printing carbon fiber-filled thermoplastics, as well as continuously laying carbon fiber as part of a 3D printed geometry. When we look into the types of additive manufacturing systems, currently the only one supporting composites like carbon fiber is Stratasys Fused Deposition Modeling (FDM), or Open Source Fused Filament Fabrication (FFF), which, in a nutshell, is plastic extrusion 3D printing. The continuous fiber layup is done by inserting strands of carbon fiber material inside of a 3D printed geometry. So, what are the key advantages of each material, system and combination?

1. Continuous Carbon Fiber (CCF)
   • Great strength-to-weight ratio
   • Incomparable stiffness over thermoplastics
2. Chopped Fiber Filled Nylon
   • Good surface finish
   • Lower cost per material volume
3. Stratasys Nylon 12 CF
   • Increased strength over chopped fiber
   • 133% more carbon fiber in filament
   • 3 to 5 times tensile modulus of chopped fiber

There is more to just material specs when we look at additive manufacturing or 3D printing. Overall system capabilities, accuracy, support material and repeatability come together to make sense for additive manufacturing. Some of these factors also play a role in the experience and result of 3D printing a CF model.

Support Material

Support material is very important for several reasons; we don’t always make flat geometries, so complex designs need complex support structures. Stratasys Nylon12 CF prints alongside a support material named SR-110, commonly used with our other materials Nylon 12 and Nylon 6. Nylon happens to be water soluble and makes complex structures, gaps, holes and assemblies possible by dissolving away, leaving the Nylon12 CF without surface marks or removal scratches. Other technologies use the same chopped fiber filled Nylon as the support structure, although for the most part they can get away with it, Nylon typically makes for a time-consuming process of hand removing and possibly marring the geometry.

Build Size

Not only is the size of a part important, but also the number of parts you could set up in a single tray make for batch printing an easy statement. It is important to know that 3D printing today is mostly focused on handheld parts from 1 to 14-inch cubes. For bigger geometries, the Stratasys F900 can build up to 36 x 24 x 36 inches (xyz). So, being able to print not only a single part but many at the same time is very important. Some technologies do not have fully equipped build envelopes that allow for multiple parts or even large geometries due to ambient temperature and layer adhesion to itself and the build tray or platen.

Print Settings

If you are printing in carbon fiber, it is for a reason. You need a strong part most likely for a fixture or jig, so the ability to modify and tweak how you print these parts is the key to success. The typical print software for filament extrusion allows you to pick a specific infill for the entire part and in some advanced versions change the wall thickness as well, but for the most part, it is simple. With Stratasys Insight and GrabCAD, you have the ability to change every single layer of this part for a specific application, infill from custom to pre-programmed shapes and even solid infill which allows you to reach a 99% dense part. All this information can be rubber stamped into a CMB file format so that your hard work and final revision of the part can be saved and reprinted exactly the same, time over time.

Speed

Speed in 3D printing is a must. The speed of printing is an important factor, but so is the speed from design to part in hand. The system’s ease of use software support removal and overall experience play into the speed of having a part in hand and put to work. Since these materials, chopped fiber, continuous fiber and Nylon12 CF are extremely abrasive to the extrusion tips the speed of print goes way down. To add to that, when printing in high resolution the printer needs to print even slower. The Stratasys equipment actually maintains the typical speed at 0.010” layers.

For the most part, when thinking of printing with carbon fiber, the mindset should be, “I need a strong lightweight, impact-resisting part.” Otherwise, materials like ABS, ASA or PC-ABS can get you a part in hand cheaper and faster than anything else in the 3D printing world, while maintaining true to spec strength and accuracy. There is no doubt that the right part using the right amount of continuous carbon fiber inside will be stronger than either chopped or Nylon12 CF but it will also be 4 to 5 times the cost as carbon fiber strand is expensive when compared to any 3D printed material. Carbon fiber filled materials do have a space in the manufacturing world but it should be looked at application specific jigs and fixtures that should be able to withstand high impact, strength and lightweight applications.

Interested in learning more about the Nylon 12 material? Click on the button below to download our white paper, Nylon 12 Best Practices.