In the next 3 articles, we will showcase a research project that ran until October 2020. “OptiTape” focused on creating a digital twin of Neue Materialien Bayreuth's (NMB) tape laying machine (figure 1). The digital twin is a digital replicate of the real tape laying machine that is used to numerically optimize the structure of the laminates that will then be manufactured on the real machine. In the title image, you can see the real machine and the digital twin side-by-side.
One of the main project goals was the implementation of an algorithm that holistically optimizes the production cost of the part. The optimization goals are either the material cost and offcut, machine cost and manufacturing duration, or the CO2 footprint. The project also included that the algorithm automatically determines the best fitting material widths for the given part to optimize the given criterion. In the AFP processes that we have already shown, varying material widths could not be realized since AFP end-effectors have fixed width material spools. Using wider tapes may however increase the efficiency of layup processes since wide areas may be covered quicker.
Today we will showcase how the tape laying machine works and how multiple material widths may be beneficial to the layup process. In the following weeks, we will also showcase the benefits of variable cutting angles, ultrasonic welding and demonstrate the digital twin.
© Neue Materialien Bayreuth GmbH
The basic principle of the machine works as follows:
There are two different vacuum layup tables. Thermoplastic prepreg stripes are cut from spools and fed to the left and right side of the first layup table, where two pick-and-place units pick them up and place them in their corresponding position on the layup table. When all stripes of a ply are placed this way, a larger pick-and-place unit, dedicated to the whole ply, transfers the ply onto the second layup table, where ultrasonic welding units weld the different plies together. The second layup table can rotate so that a huge range of different angles may be realized. While the plies on the second table are being welded together, the placement of the stripes on the first table continues. As these processes are highly parallelizable, a very low process duration of 2 seconds per material stripe may be achieved. The resulting laminate may then be transferred to a consolidation unit to be processed further.
© Neue Materialien Bayreuth GmbH
Figure 1: A top-down view onto NMB's Tape Laying machine.
Consider this: Using a pick and place process for tape laying means that every material stripe – regardless of its length and width – takes (almost) the same amount of time to cut, feed, and place. Following this logic, decreasing the number of stripes reduces the total amount of time needed to manufacture a laminate. If the laminate contour can be covered in the same way with fewer stripes, this method is clearly preferred.
See this example here:
© SWMS Systemtechnik Ingenieurgesellschaft mbH
Figure 2: Two layup patterns side-by-side. The left pattern uses more, narrow stripes, while the right pattern is made of fewer, but broader, stripes. The resulting difference in layup time between these patterns is more than 40%! You can also see that the right pattern has stripes, which do not end on a straight edge but are cut in such a way that there is as little offcut as possible. We will showcase these variable cutting angles next week.
This highly flexible approach to tape-laying shows the strengths of pick-and-place processes for flat laminates: high speed, low costs, and efficiency while allowing further modifications and optimizations of the laminate.
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 this article, we gave you a short overview of the contents 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. Next week we will showcase why variable cutting angles are so effective at reducing offcuts and how they can be determined.
Until then, stay safe and stay tuned.