The “flat” laminates we talked about before are not really “flat” since multiple layers of material are stacked on top of each other. Technically, there is no “flat” 2D object in the real world since every object has a thickness. Instead, the term 2D in this context refers to the number of dimensions necessary to fully define the structure of the laminate. When flat layers are stacked on top of one another, the only information necessary is the position of the stripes of each layer in a 2D environment (x and y coordinates). The only additional information necessary is the height (or z value) of a ply. This 2D environment can be seen as a fixed base plane consisting of an x and y-direction. The z-direction corresponds to the height and does not influence the x and y positions of the stripes and plies.
The key difference is that 3D laminates have no flat base plane. The underlying basis for programming in 3D is the CAD model of the mold surface. Mathematically speaking, the key difference between 2D and 3D laminates is the definition of this base surface. While we are dealing with planes in 2D, we are working with surfaces in 3D. The main difference is that surfaces may be curved in different directions, while planes are flat. This curvature component is the key factor for successfully manufacturing 3D components from CFRP.
Figure 1: In this figure, you can see a simple, curved base surface. It has a constant profile along one direction (left to right). On this surface, a 45° ply has been placed.
Due to the curvature of the surface and the desired angle, the tool must be constantly realigned when manufacturing a course:
There are multiple challenges that curvature poses when manufacturing with CFRP prepregs. Carbon fiber prepregs usually come in the form of long stripes. These stripes have similar properties as scotch tape. Have you ever tried to bend scotch tape? Or to have it stick to gift wrap paper that is not completely flat? Just like scotch tape, CFRP stripes will start to wrinkle when bent or will not stick to the surface when its structure is uneven. In the following articles, we will present some examples of challenges that arise when draping carbon fiber prepregs, since these are some of the trickiest challenges when manufacturing complex laminates on 3D surfaces.
To sum it up:
|2D contours from DXF files||3D geometry data from CAD files|
|Collision detection can often be omitted due to the simple kinematics||Collision detection is an essential component of the offline programming|
|Machines are optimized for high-speed fiber placement (often gantries)||Machines need to fulfill various requirements regarding the positioning and orientation of the tool (often robotic systems)|
|The main goal is the manufacturing speed and a minimal amount of offcut||The main goal is the precise and correct placement of prepregs to manufacture parts with tight manufacturing requirements|
See these visualizations for further illustrations:
When manufacturing flat plies, the orientation of the tool never has to change. Only its x and y position change for different z coordinates. Since the base plane is flat, the layup direction vector is constant.
When manufacturing 3D laminates, the orientation and position of the tool are constantly changing for each layer. Due to the curvature of the base surface, changing the z coordinate not only changes the position of the target point but also changes how the tool must be oriented (rotated) to keep the same layup direction as before.
By now you should understand where the increased complexity and requirements of 3D laminates and parts come from. Due to the curvature of the base surface, the manufacturing system needs to fulfill very high demands regarding the orientation of the tool. In some of the following articles, we will explain more about the effects of these by introducing you to steering, angle deviations, and bridging. But for the next articles, we will first introduce some basics about Design Requirements and how orientations in 3D are defined exactly.
Until then, stay safe and stay tuned.
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