Thermoplastic tape winding: Reducing time to market
01. February 2022 | Blog
INOMETA and Teijin analysed the basic manufacturing parameters of high-performance thermoplastic tapes in the laser-assisted winding process to allow fast and transparent component development for upcoming market requirements. Tape winding is an enabler for addressing higher productivity, cost reduction and the aim for an automated production approach.
Carbon fibre-reinforced thermoplastics (CFRTP) are often named in one breath with benefits such as chemical resistance, strength-to-weight ratio, durability, impact behaviour, series capabilities and sustainability. In the aerospace sector, low weight, performance and processability are all key factors and the global demand for thermoplastic materials is rising. These materials could take a leading role to sharply reduce the lifetime fuel consumption of an aircraft, extend its flight range, significantly reduce emissions and prepare for recycling cycles of the future, in addition to making aircraft manufacturing more cost efficient. As part of its high-performance portfolio, Teijin developed a wide range of Tenax™ ThermoPlastic UniDirectional (TPUD) prepreg materials. These tapes are typically based on specially-developed carbon fibres in combination with polyetheretherketone (PEEK), low-melt polyaryletherketone (LM-PAEK) or polyphenylene sulphide (PPS) to allow fast processing times with high mechanical performance of the final components and applications.
INOMETA, a leading contract manufacturer with expertise in lightweight construction using aluminium and composite materials, developed a new and optimized laser-assisted tape winding production technology optimized to process the above-mentioned high-performance tapes. Tape winding allows for in-situ consolidation of the tapes, making subsequent process steps obsolete. Hence, the combination of high-performance tapes and tape winding is an enabler for addressing higher productivity, cost reduction and the aim for an automated production approach.
INOMETA and Teijin noticed that thermoplastic composites based on the winding process are a relatively new field for industrial applications. On one hand, the market is confronted with a high degree of novelty (processes and materials), which results in a lack of customer knowledge and experience with these new opportunities. On the other hand, the industrial market uses established component solutions based on thermoset or metallic materials, so that component and raw material manufacturers have to provide reliable CFRTP solutions in the short term to support their customers’ decision-making. For these customers, development times are very short. INOMETA and Teijin agreed on a technical partnership to resolve this situation. In order to significantly reduce time to market, they analysed key material and process parameters in detail with specific use cases in mind.
Time to Market
Time to market (TTM) is the time that elapses before a product idea is developed to market maturity so that either a new product can be placed on the market or an existing product can be replaced using an enhanced thermoplastic alternative. Key influencing factors during product development are proving basic process and material suitability as well as presenting an interesting business case via a reduced number of components or improved part performance. Afterwards, process robustness, reliable material data and part-specific performance indicators are in focus.Teijin and INOMETA addressed these development issues following an iterative process to identify acceptable basic parameters. These were used for joint customer projects, significantly reducing customer-specific development times and costs.
For most customers, thermoplastic UD tapes and laser-assisted tape winding are uncharted territory. Thus, building trust is also a significant factor for the customer and has been one goal of the cooperation. Overall, the initial evaluation work from INOMETA and Teijin provided customers with the necessary information regarding processing speed, material properties and component prices without holding back long development times starting from scratch. Providing customers with valuable insights on the material and process as early as possible in the project is a basic requirement for fast progress and a short TTM. Oftentimes, customers are curious to explore the uncharted territory for their application. Most applications are already in use, so thermoplastics are competing with existing materials, processes and supply concepts.The first step is building trust. The customer wants to see similar existing use cases in thermoplastics and be sure that process robustness, part quality and material maturity are ready for a series application. Providing resilient data addressing these concerns is a key goal of INOMETA and Teijin, since this can be an obstacle at the start prolonging TTM.
The second step is to provide realistic economic data. Being too conservative can lead to an unattractive business case for the customer, even if there are still price/performance benefits to be gained, since there is always a risk aversion when switching existing and working material concepts. Being too ambitious in the economic assumptions will counteract the trust built in the first step when announcing that previously forecast placement speeds or part qualities cannot be achieved. Despite this preliminary work, there will always be customer-specific aspects to cover during TTM. These include adjusting acknowledgements to the final customer geometry and its laminate lay-up, optimizing the material selection (e.g. tape width) and application-specific testing of specimens or even components, since the motivation to use thermoplastic composites varies from industry to industry. The essential initial work to provide the discussed information is divided into two work packages. The first one targets the manufacturing trials themselves. The aim is to identify an acceptable processing window for different mandrel diameters and tape lay-ups as well as optimizing economic parameters such as winding speed. The second work package aims at quantifying interactions between the winding process (processing temperature and winding speed) and quality parameters (crystallinity and consolidation quality). In this way, an economic processing window will be identified while maintaining excellent part quality.
Deeper materail and process understanding
Accelerated development cycles in industrial applications inhibit the integration of new material and component concepts into already established applications. The lack of time to find the ideal process and material setup can lead to subpar solutions, making the new concept not attractive enough. Common aspects of such subpar solutions are on the material side as well as on the process side:
- Material: Very short development time goes along with a shortened material selection process. Sometimes being too conservative leads to over-engineering by choosing a PEEK material when an economic material choice (e.g. PPS) would be better. Incorrectly choosing the adequate fibre (e.g. HT or IM) and ideal tape width are also common faults.
- Process: Producing the best prototypes possible can lead to choosing conservative placement speeds. The lack of time to find a good balance between part quality and process parameters (placement speed, tape width, and tape thickness) lets economic potential fall by the wayside.
Overcoming these flaws is the main goal of this partnership. The robot-based winding process provides an ideal basis, since crucial machine parameters influencing part quality are constantly measured. This does not only allow tracking which tape batches are for which parts but also if parameters such as winding speed, nip point temperature or consolidation pressure are within acceptable thresholds for every layer of tape. Tracking these parameters in combination with a visual inspection of the wound parts to evaluate surface quality and the chosen gap/overlap settings allows for identifying a good material-specific baseline setup for future projects with the high-end Teijin materials. Using this good baseline scenario makes it possible to adapt to customer laminate lay-up/geometry in a significantly shorter, acceptable amount of time.
Part of the initial work by INOMETA and Teijin consisted in analysing different winding angles at various placement speeds. Up to now, the analytical inspection was based on microscopic cross sections, thermal analysis (DSC) and fibre volume measurements.The microscopic cross sections are used to evaluate the consolidation quality and to check the laminate for visible defects such as porosity (between plies), voids within the tape or systematic processing defects such as overlaps or gaps. These kinds of defects would have a negative effect on the mechanical properties.
The sampling and analysis work was conducted not only for Teijin’s CF/PEEK material but also for CF/PPS and CF/ LM-PAEK. One key result of the partnership so far is the creation of pre-evaluation sheets for Teijin’s material portfolio capturing the mentioned baseline scenario. The fundamental understanding of the interactions between the material and the process, and thus the economic efficiency for chosen use cases, is helpful to establish thermoplastic wound composite solutions in more and more markets offering performance and price benefits.In the months to come, mechanical tests and additional trials further improving winding speeds and thus economic potential will be conducted. The first results of the partnership are already used in joint customer projects using the Teijin tape material.