Waterjet cutting carbon fiber
What is a Waterjet?
A waterjet uses a pump to create a high pressure (up to 90,000 psi) jet of water that can cut through anything from foam to 8+” steel plate. When cutting through metal or carbon fiber, an abrasive material, such as garnet, is used to aid in the cutting process. (See the "Source" links at the bottom of the post for more information on how Waterjets work.)
Now let’s look at why a waterjet is such a good tool for cutting carbon fiber.
Part thickness
One huge advantage of the waterjet is that it can cut very thick carbon panels with relative ease. With a router, thick parts require more passes which takes time and causes more wear on the bit. You also have to worry about clearing out chips and dust from deep slots. Additionally, with the proper tuning you can easily cut small features that would be impossible on a router due to the depth.
Thick carbon fiber cut on waterjet
Speed
Cutting speed on a waterjet, especially for small features, is much faster than using a router. With a router, the depth of cut and feed-rate depends on the size of your router bit and part thickness. Smaller bits and thicker parts require multiple passes, whereas a waterjet can cut the same part in one pass and usually with a faster feed rate.
Dust Prevention
Another major advantage to using a waterjet is the dust containment. One of the main concerns when working with carbon fiber is dust. Carbon fiber dust can find its way into the inner workings of your machines and cause parts to grind or wear faster than they normally would. It is also an irritant if inhaled or can cause itchiness if it gets on your skin. With a waterjet, all the carbon dust gets blasted into the water tank where it is easier to handle for proper disposal. No expensive dust evacuation systems are required.
Tight cut patterns
The jet diameter of a waterjet can be tuned to roughly .025 inches, this will allow for designs with very small holes or internal features to be cut. This tool diameter can also be used to cut fairy close to an internal square geometry.
Disadvantages
While there are many advantages to using a waterjet for cutting carbon fiber, there are some drawbacks as well. The next few sections will address these areas.
Edge Finish
Because a waterjet uses an abrasive to cut through the strong carbon fibers, the edge can have a slightly rough surface. This can be controlled with the garnet mesh size (the finer the abrasive, the finer the finish) and with the feed rate. While for some parts this finish is acceptable, other parts will need to be sanded to get a smoother finish. The time spent cleaning up the edge may offset some of the advantage gained from cutting the parts on the waterjet. There is a balance between cutting speed and part complexity to consider if running a large volume of parts.
Blowback
Another area of concern when cutting carbon fiber is the blowback that comes from passing over one of the slats. The waterjet tank uses metal slats that span the width of the tank and provide a surface to support your work material. When the high-pressure jet passes over the steel slat, the jet of water and abrasive can be deflected up which essentially sand blasts the back side of a part. Typically, this wouldn't be noticeable on a metal part, but it could ruin a part of the surface of a carbon part.
Fortunately, there are solutions that exist to solve this problem. At Elevated Materials we cut our parts on top of a Rhino board. The Rhino board is made up of HDPE “straws” that allow the jet to pass through without blowing back toward the carbon. Its small cell size allows us to cut small and intricate parts without worry that they will fall into the tank.
small carbon fiber pieces cut using rhinoboard
For high volume projects of relatively large size, we create fixtures that protrude from the bottom of the tank that ensure the jet will only be cutting over water. Parts are then held in place using suction cups. With these fixtures we have cut over 1000 of the same part and haven’t had to change out any major components.
Delamination
Another challenge of cutting carbon fiber with a waterjet is piercing holes. The high-pressure water jet can eat away the resin between the carbon fiber layers and cause separation or delamination, which weakens the part.
carbon fiber delamination
Many manufactures will pre-drill holes on another machine and then bring the part on to the waterjet for cutting. The disadvantage to this method of course is the risk of mis-aligning your waterjet cut path with the holes that you pre-drill.
At Elevated Materials we have invested much of our time and resources in perfecting our method of piercing carbon fiber to prevent delamination. The technique has everything to do with lowering the pressure of the jet to around 10KSI (10,000 psi) and ensuring that garnet
