PolePosition: making carbon layup more effective and efficient

The local adaptability and tunability of their material properties is an often-cited advantage of fibre-reinforced materials. Additional degrees of freedom such as the fibre angle and fibre volume fraction not only enable designers to add strength and stiffness to parts exactly where it is needed, but also to save material or weight everywhere else. These design principles can be leveraged by curving fibres along a load path or placing reinforcement patches in particularly loaded areas.

Exploiting these advantages has become increasingly important to justify the premium over more conventional engineering materials, especially for high-performance materials such as carbon fibres.

A versatile tool enabling affordable automation
Initially developed with these kinds of applications in mind, the system was named PolePosition, but it is now a much more universal part of Schmidt & Heinzmann’s toolbox for automation projects, mainly because of its flexibility.

A single system providing access to general quality, position, orientation and fibre angle data significantly reduces development cost, time and risk for automation projects within the high-performance composite industry. Being developed in-house by Schmidt & Heinzmann allows for a deep integration into the production cell and further boosts the system’s adaptability.

A single robot equipped with a PolePosition system can now be fed with accurate enough information to replace a human operator at a layup station, but it also makes the laser projection system redundant.

Additionally, the system can record highly-detailed pictures of each ply before and after it has been positioned, including quantitative information about its position and orientation. Through an evaluation of the fibre angle or defect detection, the system can even take over quality control of the previous process steps. It not only enables the automation of a previously manual process but also provides significant added value while doing so and access to information that simply was not available within the legacy process.

Methods for controlling position and orientation of carbon fibres are complex and expensive
In terms of industrialisation, the attempt to maximize control over these design principles is exemplified by developments such as laser-guided manual layup or automated fibre placement. When positioning an individual ply according to a laser projection, the operator guarantees its correct position and orientation according to the design documentation. Even if the ply is perfectly positioned in the layup, it remains uncertain whether the fibre orientation within the ply is correct. The correct fibre angle depends on the precision of the cutting process for the fabric or prepreg the ply is cut out of. Here, both the precision of the machine and the diligence of the operator influence the result.

In automated fibre placement, the fibres are guided, steered and positioned by an automated system. The position and orientation of the material is therefore implicitly included in the machine programming. Both examples go to show that the position and orientation of fibres are process variables inherently difficult to gain direct access to and control. Most of the time, the only feasible way is to demonstrate that the resulting fibre angle of a particular process will lead to the desired material properties through extensive validation and qualification processes, rather than directly monitoring or let alone define it as control parameters within the manufacturing process. However, these intensive and expensive validation and qualification processes pose a significant obstacle to a more widespread adoption of carbon fibre-reinforced materials.

The challenges of positioning in manufacturing processes
Even if the fibre angle is left out of the consideration, positioning alone can pose significant engineering challenges within the manufacturing process. Large or very complex structures made from flat semi-finished products such as prepregs or technical textiles sometimes have to be split in multiple subcomponents or subpreforms to manage size and complexity. The transition zone between the individual subpreforms is often spread out over a larger area to minimize impact on the component’s performance. Individual layers of the material are terminated or dropped-off successively, resulting in a stepped joining area.

While this approach is a good compromise between performance of the complete component and reduction of the subcomponents’ complexity, the manufacturing of the stepped area, as well as precise joining of multiple subpreforms, still presents major challenges for industrialisation. To avoid any unintended overlaps or gaps in the joining area, each step must be precisely to size, while also ensuring the correct relative positioning of the individual subpreforms. This is further complicated by the fuzzy edges of contour cuts made from technical textiles. While most components made from conventional engineering materials have clearly defined edges, finding or even defining the edge for a ply made from a technical textile can be a challenge.

Obviously, these challenges can be overcome through a combination of manual processes and extensive quality control if the application justifies the cost. Alternatively, automation can help to significantly lower processing cost, improve reproducibility and therefore streamline quality control measures.

In Schmidt & Heinzmann’s experience, automating the manufacturing of these high-performance components demands the development of dedicated measuring equipment to achieve sufficient process reliability and the required quality level. So far, these measuring solutions had to be tailor-made for each and every application. While the company successfully demonstrated that all these challenges can be overcome in the past, they still present a hindrance for many projects to have a positive business case.

Making sensors and carbon fibres get along
This is particularly true for carbon fibre because of its less-than-ideal optical properties when it comes to modern sensor technology. The laser point of a modern laser distance sensor getting swallowed by the deep black structure of a non-crimp fabric or the laser ray pass­ing right through a loosely-woven carbon fibre fabric are just some of many problems encountered when attempting to use modern automation equipment in conjunction with these materials.

The challenge in automating the production of carbon fibre-based components is often not in the manufacturing equipment, but in gathering and making enough information available to the system. Even if a robot equipped with an ultrasonic knife is ten times faster at trimming the edge of a carbon fibre preform than a human with scissors, it simply does not matter if the robot is blind, cannot find the edge to be trimmed and cuts right into the part instead of carefully trimming it.

The awareness of the importance of…

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