Digital Twins

In this week’s article, we will be talking about the tape laying machine of Neue Materialien Bayreuth GmbH and how its digital twins helps reduce resources and energy. We talked about its basic functionality in the first article, now we will look at what the Digital Twin of the tape laying machine looks like inside the CAM software CAESA® Composites TapeStation.

© SWMS Systemtechnik Ingenieurgesellschaft mbH

Figure 1: A screen capture of a layup process using NMBs tape laying machine as simulated by the TapeStation. On the left-hand side, a 3D model of the tape-laying machine is displayed. On the right-hand side, a simplified, 2D visualization of the process is shown. The yellow geometries in the 3D model are conveyors, which feed the material that is to be placed. From there on, the two smaller pick and place units take the prepreg stripes and move them onto the layup table. Once all stripes of a ply are placed, the bigger, rectangular pick and place unit transfers the ply to the second table, which adjusts its rotation depending on the angle of the ply. When two plies are placed on top of another this way, the welding units move. This can only be seen in the 2D visualization starting from 1:20 – the points that move towards the laminate are the welding units. These ultrasonic welding sonotrodes always fuse two stripes of two adjacent layers.  

Make sure to also take a look at the latest edition of the JEC COMPOSITES MAGAZINE, where NMB and SWMS published an article about the digital twin of the tape-laying machine.

Welding

Every stripe must have two welding positions to properly fuse it with the underlying stripes of the previous ply. An algorithm determines the optimal position of the welding spots by comparing the geometries of the stripes of both plies as certain requirements must be met; for example, that welding positions must have a certain distance to the edges of the stripes. The sonotrodes then fuse the stripes by heating the prepreg material via ultrasonic vibrations.

Digital Twins and Optimization

To correctly mimic the real machine’s behavior, the digital twin uses the same velocities and accelerations of the individual machine parts. This simulation may now be used to approximate the machine duration for the manufacturing operations of the laminates. We defined that the optimization algorithm of NMB’s tape laying machine has to optimize for one out of four distinct optimization goals. Minimizing the:

• Total cost,
• Material offcut,
• Manufacturing duration, or
• CO2-equivalent.

Depending on the primary optimization goal, the optimized laminate will be different in structure: The amount and widths of the stripes, as well as their cutting angles, will be adjusted in such a way that the selected goal is optimized. See this example: 

Figure 2: Different results for different optimization goals. Parameters that are considered for the optimization come from: the number of stripes, the cost of the material of the stripes and its associated CO2-equivalent per kg as well as the full manufacturing duration. Optimizing for CO2 for instance, heavily depends on the used material and its cost. Generally, the more expensive the material, the more the offcut is a factor. Therefore, when manufacturing with cheaper materials, the more cost-efficient the production time.

We can see here what the different outcomes of the different optimization approaches are. Optimizing for manufacturing duration decreases the number of stripes so that as few stripes as possible need to be placed. Optimizing for offcut creates as many stripes as necessary to achieve the least amount of offcut. Optimizing for the total cost, on the other hand, tries to find the optimum between these both since machine cost is directly related to the manufacturing duration and material cost is directly related to the offcut.

Now that we have showcased the results of the optimization algorithm and how the machine manufactures laminates, this is where we wrap it up.

The project "OptiTape - Development of a machine-independent software for mapping a virtual process chain for the economical, resource-saving and mechanically optimal production of preforms based on unidirectional thermoplastic tapes" (funding code ZF4064612 PO8) was funded by the German Federal Ministry for Economic Affairs and Energy (BMWi).

In the last 3 articles, we gave you a short overview of the OptiTape research project, its goals, and outlined the most important features. We also briefly introduced how the NMB tape-laying machine works and why it is so efficient. If your interest has been sparked, you can get more information from the websites of NMB, SWMS, and REHAU.

In the next articles, we will dive deeper into complex subjects: the differences between 3D and 2D laminates, laminate angles in 3D, and path planning on complex, curved laminates.

Until then, stay safe and stay tuned.