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, Volume 10, Issue 1, pp 50–55 | Cite as

Quilted Stratum Process for High-performance CFRP Production

  • Lennart Wedhorn
  • Robert Ebeling
Production Technical Thermoplastics

Keywords

Cycle Time Cutting System High Volume Production Short Cycle Time Metal Insert 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

By presenting the Quilted Stratum Process Pinette is showing up a new process for a high-volume fibre plastic production for the automotive industry. The new process can produce parts which are ready for assembly within 40 to 90 s. Also, it allows to produce parts with variable material thickness and various materials in one part. Additional functionality of the part will be realised by integration of overmoulding and the possibility to include metal inserts.

The Quilted Stratum Process (QSP) is an innovative approach for the design and production of high-performance thermoplastic composites and multi-material parts. The concept used achieves the goal of combining high performance, low cost and short cycle times. To reach these goals and to create a new process, the research and development was based on three main criteria:
  • ▸ full integrated process: from raw materials to net shaped part

  • ▸ priority on production performance: low costs and cycle times

  • ▸ getting a minimal waste rate by the process, but also in the design of the part by using the right material at the right place.

The outstanding properties of composites and the advantages of using these materials to reduce the weight of structures are well known in the industry. The choice of the right process for an optimised production is still an issue because there is still no viable solution. The existing solutions are made for small batches or causing high production costs. Production process and automated production lines for high volume production with low cycle times are not available or have limitations in cycle times and flexibility (per material variations).

To reach a cycle time between 40 to 90 s the process works with several units which are working parallel.

The already optimised processes of the automotive industry reaching a high level of automatisation to reduce the cycle time of duroplast parts. But these processes are still too expensive for the mid-range car production. By using technical thermoplast materials it is possible to decrease the production costs, cycle time and weight of the parts. So it is possible to realise a clean and fast production process.

To design an optimum process these criteria have been realised:
  • ▸ Integration of the complete process “from raw material to finished part”: focused on maximum added value of the finished parts. On one hand by using standardised raw material the QSP allows a worldwide procurement capability. On the other hand it is possible to reduce the waste rate by using tapes with different width. This advantage is also usable by using purchased pre-cut tapes from raw material suppliers.

  • ▸ Cycle time: to reach a cycle time between 40 to 90 s the process works with several units which are working parallel (stacker steps per layer, final contour cutting, pre-heating station, final heating station, forming and overmolding).

  • ▸ Multi-material parts: the material supply system was designed to allow using various materials (organosheets, short-fibre) in addition to the unidirectional (UD) tapes.

  • ▸ Optimisation of material usage: netshape preforms are produced with the right material at the right place to allow a one-shot production.

The QSP system has been developed by Cetim in cooperation with Pinette. Loiretech (contact heater), Compose (tooling) as well as ECN, ENS Cachan and ONERA (Research Laboratories) have been further development partners.
As a result of this development process a pilot line in industrial scale has been set up. Currently various customer parts are produced and optimised. The connected segments of the line are all working together in parallel to guarantee a minimum cycle time. These segments can be split up in 5 units which are also able to produce independently, Figure 1.
Figure 1

Process steps of QSP (© Pinette Emidecau Industries)

Pultrusion and Extrusion

Starting from continuous fibre combined with a thermoplastic material. The tapes are produced with low costs and taking account width, thickness and fibre reinforcement (UD, glass and/or carbon). The advantage of producing own UD tapes in various thickness and widths allows QSP to reduce the material waste to a minimum.

If UD-Tapes are available from raw material suppliers the line is able to use the tapes as well and allows to optimise the preform in terms of best waste rate.

Cutting

Tailored patches defined by a specific FEA analysis method are cut from different tapes without dust pollution. The patch preparation unit cuts the tape with a linear cutting system. If it is necessary to place thicker layers with the same fibre orientation it is possible to use several rolls (layers) at the same time. The different layers will be welded after positioning. The offline working cutting unit guarantees a maximum of flexibility. After cutting the patches are stacked automatically onto a positioning material palette.

An alternative cutting system can produce various forms for e.g. partial reinforcements by using a high dynamic robot cutting system. Figure 2.
Figure 2

High-speed cuttinghead (© Pinette Emidecau Industries)

Preform Assembly

An optimised multi-thickness and multi-layer net-shape preform Figure 3 is assembled from patches cut before. The patches are picked from carriers and placed and welded in precise position on a conveyor system. The preform is built successively while passing the stacker stations.
Figure 3

Preform (© Pinette Emidecau Industries)

Heating and Transport

The preform is heated very quickly to process temperature using a fast and innovative system. After reaching the process temperature it will be transferred to the exact position of the press/mould by a robot handling system. The heating process is a split process of two steps. The preform will be heated up by a contact heating station which is transforming the preform into a plastic condition providing prime energy into the part.

The second heating step consists of an innovative infrared heating system which allows to melt the complete preform in a short time.

The optimised robot handling system was designed to place the heated preform in the press with a minimum of temperature loss providing an optimum consolidation. Figure 4.
Figure 4

Heating times (© Pinette Emidecau Industries)

Thermoforming and Overmoulding

The preform will be placed in a vertical press which has the advantage that the preform can be placed without losing time and also a vertical transport is preventing the preform from unintended forming or distortion. After forming the part will be overmoulded directly in the press. Furthermore it is possible to place metal parts in the mould to combine them with the part.

Scalable System

Using a newly developed thermoplastic pultrusion process, fibres are impregnated continuously on a large volume of material. The manufacturer chooses the fibre/matrix combination and adapts the size of the resulting tape to the needs of the final part. This step eliminates the need to purchase costly semi-products of standard sizes, many of which are scrapped during the process.

Alternatively roll material from material suppliers can be used to feed the cutting statuions. The patch preperation area can flexibly be equipped with patch preparation stations according to the requirement and allows the simultaneous processing of various tapewidths.

The final forming-overmoulding step allows manufacturing of complex shapes in a short time, with design freedom provided by the injection process. This technology is the most suitable for high volume production. The use of QSP preforms opens a significant optimisation potential, compared to woven organosheets of constant thickness and orientation.

The cutting system has been evaluated all along 2013 among different existing technologies (water jet, laser, machining, ultrasonic...) and a flexible process able to cut tapes from 0.2 mm to 3 mm has been chosen. At the end, a head with ultrasonic blades was specially developed to cut patches with a minimum waste as fast as possible without dust keeping the quality of the material. for example, for a tape of PA6 with glass fibres and 0.5 mm thick, the cutting speed can be up to 500 mm/s.

The assembly machine has been developed to produce netshape, multi-thickness and multi-orientation preforms as defined in calculations before. The system has the capacity of producing one preform per minute, which means a capacity up to 10 kg/min of preform production.

The sequence of handling- (stacker-) steps working parallel provides one cycle time per layer. Also, the assembly system is very flexible because it can use different additional materials like e.g. organo sheets while assembling the 2-D preform.

The innovative heating system combines a conduction oven with an infrared oven. The first oven is the most effective system to enter energy as fast as possible to the preform, staying below the fusion temperature. To help preventing the blank from air inclusions it will be straightened.

In the second step the infrared oven heats up preform to the fusion temperature needed for the stamping. The major issue of a classic infrared oven is to get a good homogeneity on temperatures between surface and through the multi-thickness preform. The system developed here can reduce significantly this issue, reducing also the cycle time with a better quality on the final heating.

The connected segments of the line are all working together in parallel to guarantee a minimum cycle time.

For example, for a multi-thickness preform PA6 glass fibre, with thickness between 1.5 mm and 3 mm, the process can heat it in about 60 s to process temperature everywhere throughout the crosssection, at the same time reducing oxidation on this type of material.

Finally, the fast transfer system with needles allows the use of netshape preforms. After stamping, there is no more operation needed to finish the part. Moreover, during the stamping, many operations are done at the same time (one shot operation) to get a maximum of added value on the part:
  • ▸ overmoulding to add reinforced ribs or any other plastic functions, and to have a final netshape part ready to use

  • ▸ creation of holes to prepare future assembly, with or without metal inserts

  • ▸ integration of multi-materials assembly inside the mould, to allow direct assembly, Figure 5.

Each unit of the process is working parallel. Each one was defined and optimised to achieve a final short cycle time as required in the automotive industry, that means between 40 to 90 s per cycle.
Figure 5

Screw insert (© Pinette Emidecau Industries)

Designing a QSP Part

QSP is not the result of a dogmatic material approach, it gives the capacity to the engineer to design an integrated multi-material part with the right material at the right place. The mechanical strength envelop shows the local areas where you need anisotropy resistance or not and the level of stress. For areas with high level of anisotropy, carbon fibres are usually used for high resistance or stiffness and glass or bio sourcing fibres for lower requirements. Areas without anisotropy, steel, aluminium and magnesium can be used as well depending on the level of stress. For areas with specific functionality, short fibres reinforced polymers can be used.

Using a newly developed thermoplastic pultrusion process, fibres are impregnated continuously on a large volume of material.

The QSP system provides the right solution of mixing all these requirements and materials for an optimised result in cycle time and cost. Studying the potential for a process requires the existence of a numerical design chain.

To allow an easy design of a QSP part it is possible to use a special software which calculates where to place the right patches corresponding to the mechanical stress level. The focus of this software is the optimisation of the fibre orientation, placing of single patches and to validate the feasibility of a part. Among other, the tool enables linking the final 3-D shape and the initial flat preform. In this way, the designer has all information needed for designing to cost, Figure 6.
Figure 6

Design example of a suspension arm (© CETIM/ONERA/PSA)

A lot of parts have a high potential to safe weight by using the complete QSP process. For example the QSP line already produced a seat back out of six patches which is 30 % lighter than its original steel version, Figure 7.
Figure 7

Seating shell (© CETIM/ADEME/Faurecia)

Conclusion

QSP can answer the question of mass, cost and cycle time reduction for various parts of the automotive industry. It is not limited to automotive, it can also be used by aerospace industry to reduce costs and to increase the production rate. With a cycle time of 40 to 90 s the QSP can produce parts made of different materials and various material thickness on one part.

For example it is possible to produce a part which is made from glass fibre with local reinforcements of carbon fibres in relevant areas. To allow a mass production with QSP it was designed as a one-shot process. By using a tool with integrated overmoulding injection additional functionalities such as reinforcement ribs and metallic inserts can be added. That way a part leaves the press as a finished part, ready for assembly.

Reference

  1. [1]
    Callens, C.; Champenois, C.: The Quilted Stratum Process: A breakthrough for thermoplastic and multimaterial parts. CETIM Technical PaperGoogle Scholar

Copyright information

© Springer Fachmedien Wiesbaden 2017

Authors and Affiliations

  • Lennart Wedhorn
    • 1
  • Robert Ebeling
    • 1
  1. 1.Pinette Emidecau GmbHZernienGermany

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