Quilted Stratum Process for High-performance CFRP Production
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KeywordsCycle Time Cutting System High Volume Production Short Cycle Time Metal Insert
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.
▸ 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.
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.
▸ 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.
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.
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.
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.
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.
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.
▸ 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.
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.
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.
- Callens, C.; Champenois, C.: The Quilted Stratum Process: A breakthrough for thermoplastic and multimaterial parts. CETIM Technical PaperGoogle Scholar