CFRP Laminate Structure

In the last articles, we gave insight on where carbon fiber reinforced plastics (CFRPs) are used, how they work, and how they can be used to manufacture highly durable, high-performance parts. Furthermore, we highlighted which basic functions a layup tool must fulfill to properly handle prepreg tows.

Now we will show you how the plies, also called the ”stacking”, can be defined using our AFP process planning software CAESA® Composites TapeStation. This type of software allows for the offline process planning and programming of AFP processes and closes the gap between design and manufacturing.

The design requirements (see article 3: The AFP Process) define the order and orientation of the plies that the laminate is made of. They also define which exact areas a ply must cover to successfully strengthen the part according to the stress it must withstand. There are further restrictions regarding the maximum allowed gap between tows, how much a tow may deviate from its nominal orientation and many more. A detailed article about design requirements will follow later in this series.

Figure 1: A laminate in which 2 plies have been placed. The orientation of the lower ply is 45°. The emerging “sawblade” pattern is typical when covering straight boundaries with 45° tows.

Laminates. A laminate is built from many different plies that are placed on top of another. In our article about the principles of the AFP process, we visualized how the stacked plies look like. To program the manufacturing process of a laminate, each of these plies needs to be parameterizable. There are some basic parameters like the order, the orientation (which is just an angle for flat laminates), and the boundary (which is a flat contour from a DXF file). The more advanced parameters will be shown in the following weeks: staggering, extending to minimum tow length, boundary coverage types, and parameters for optimizing the material usage of the spools of the layup head.

Figure 2: A stacking that is made from 8 plies. The table shows the name of the ply, the layup angle, and the most common optimizations: vertical offset (“up”) and lateral offset (“sideways”). You can also see the prepreg material and the layup head with which it will be manufactured. These may be changed to a different tool. This enables multi-material or multi-tool processes!

Once a ply has been parameterized, the tows needed to fill the boundary in the desired angle may be calculated. These tows are immediately grouped into courses. Each course contains as many tows as the layup head can lay at the same time. For each of these courses, the layup path the head must take is calculated in the CAM software. Once these, along with the information on where to cut, are transferred to the machine, the layup process can begin.

Figure 3: For better illustration this geometry with a square and a circular hole has been used. You can see the calculated tows that need to be placed to cover the boundary (orange). The angle for the left ply is 0°, for the right ply 45°. In this example, a course groups 4 tows – the alternating darker and lighter hues indicate that the tows belong to different courses.

Once these tows and courses have been calculated, they are used to generate a machine specific layup program which can then be transferred to the control system of the layup tool. The manufacturing can now begin.

In the following articles, we will show the layer parameters in detail, how they influence the laminate, and how you can fine-tune your laminates. We will start with the staggering.

Until then, stay safe and stay tuned.