3D PRINTING CARBON FIBER FOR AEROSPACE

The aerospace industry has been using 3D printed carbon fiber parts since around 1985 under the acronym AFP or Automated Fiber Placement. While this places it as a relatively “new” technology, it has matured quite well with 1,000s of engineers working on end effector processes for 35 years. It is a unique, expensive, fun, and massive corner of the 3D printing world.

My favorite quirk about AFP is how, anisotropy and isotropy aside, part design considerations for the engineer are more like subtractive manufacturing than additive. Basically, an engineer doesn’t have anything close to total geometric freedom with the AFP 3D printing vs. common 3D printing. This is counter-intuitive because don’t the concepts of other 3D printing methods carry over?

The major design consideration that applies to both AFP and subtractive manufacturing is how the end effectors (AFP heads and end mills or cutters) are going to fit in and around the part geometry. AFP processing requires a tool to lay the fiber on, and in almost every case, that tool has contours. 

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The size and geometry of the AFP head at the compaction roller, which rolls over the tool and compacts the carbon fiber prepreg onto the tool, is the limiting factor of the contours the engineer can design into the tool. This is the same as subtractive manufacturing in that the engineer must consider how the end mill or cutter is going to reach to certain features, and leave clearance physically.

THE MAJOR DESIGN CONSIDERATION THAT APPLIES TO BOTH AFP AND SUBTRACTIVE MANUFACTURING IS HOW THE END EFFECTORS ARE GOING TO FIT IN AND AROUND THE PART GEOMETRY

Common 3D printing prints out the support, the equivalent of the contoured tool surface in AFP world; at the same time, it prints out the part. This means that the 3D printer is always printing on a relatively flat surface.

Conversely, the AFP head must tightly follow a path along the tool surface and fit in and around all the nooks and crannies of the tool. All the tooling monuments and fixturing must be avoided as well, just as it would need to be in a mill.

Another area that AFP and subtractive manufacturing is similar is in the machine design. AFP machines are extremely high performance. They need to be to move around a 3000kg AFP head loaded with material along a path at 4000ipm in 6 degrees of freedom. Competition is steep if you need those types of numbers to win jobs! Milling machines are also very high powered relative to the size of their load in 4 or more degrees of freedom. This is much different than common 3D printing, who only have 2 degrees of freedom and move around a very small print head.

There is an edge case of AFP called hot drape forming that is more like common 3D printing. With this method, the tool is flat, and then the layup is draped and pressed over the contoured tool.

The last aspect of AFP and subtractive manufacturing is that every single part made from carbon fiber with AFP gets milled afterward. Holes get drilled, and edges get trimmed in every case. It is a great example of how manufacturing processes are not zerosum games.