As the ATL/AFP processes use a roller in all cases while laying the fiber impregnated strips, this causes some inherent limitations in the part shape that can be produced. The limitation mainly comes from the mold, minimum fiber width, roller radius, and tool interference.
The shape of the part required decides the shape of the mold. The mold is often the biggest roadblock in the initial stages of production. Thanks to the advent of 3D printing, now most of the molds can be 3D printed with high temperature material. Stratasys provides a very comprehensive guide on designing the 3D printed molds. This and other ABS printed molds would work well with the AFP-XS tool of Addcomposites due to its low heat application.
Most of the mold making principle applies, such as consideration as internal cavities, as the part needs to be extracted from the mold. The key would be to avoid internal cavities to prevent extraction challenges or changing the design of the mold to create splitting plane that allows for easy removal of molded laminate.
Minimum fiber width
The best way to visualize this is to think of it as painting a wall with a paint roller. In this case, the paint stroke is the fiber strip, and you are trying to cover the mold surface (wall) with this paint stroke. This is either going to cause overlapping of strips, or spilling over the boundary of the desired surface. Best practice is to allow a bit of spill and avoid any overlap in strips. This gives better structural integrity and provides a trimming allowance for smooth edges. Overlapping is also a quality defect in most applications, as it creates an uneven surface and results in a defective bond with subsequent layers. Overlapping can result in a scrap part depending on its location.
Reaching sharp corners in a room when painting walls with a paint roller is impossible. In a similar fashion, the tighter the corner of a part, the more difficult it is to layup with ATL or AFP. When deciding on minimum radii for the part, think of the roller that is going to place the fiber. In the case of smaller radii, the fiber strips would not reach the corner and creates an unwanted hollow space, called "bridging". This is unacceptable because it could lead to expedited deterioration of the part. One the other hand, if you chose a larger corner radii (ie 1.5x the roller radius or higher) this would give a smooth surface with no defects.
This is slightly tricky to take into consideration, as the tool is manipulated by a robotic arm that can move in many ways and interfere with the mold. To ease the burden, our ADDpath Software provides you motion simulation and collision detection in the virtual environment, so you can make the necessary changes in either the programming approach or in the part mold (more about this in the Features section).
With these four variables taken into consideration, you will be able to design, layup, and create a fully functional part using the ATL/AFP process. Now, go out and start creating!