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New technologies for manufacturing composites: shorter production cycles and more sustainability

19 February 2021
Article by Rui Gomes, project manager in the area of ​​Materials and Composite Structures.


The tendency to combine fiber-reinforced polymers (FRP) with conventional materials, such as metal, wood or ceramic, is increasingly prevalent in a variety of industries. Full replacement with composite materials is also more and more frequent, especially in light structural applications, such as in the aeronautical and automotive sectors, due to its high specific resistance, rigidity and low weight.

The production of composite materials with these coveted properties, however, is generally based on autoclave or oven processing. These methods have high energy consumption and require high production cycles.

These characteristics are now seen as a negative aspect, given the growing ecological awareness of the industry, and the restrictive environmental legislation in Portugal and Europe. These factors, combined with the pressures of globalization and competition, triggered a search for optimised processes, with shorter and more sustainable production cycles, for the production of FRP components 1,2.

The trend, in this sense, is an increasingly relevant role of technology and alternative processes. At INEGI, this challenge has been faced with the adoption of new perspectives in terms of the competitiveness of the industry, and the creation of new production philosophies based on faster production chains and with evident economic and environmental benefits.

Production of "high speed" composites is already a reality

Among the most promising alternative processes are A-VARTM (Advanced Vacuum-Assisted Resin Transfer Molding), HP-RTM (High Pressure Resin Transfer Molding), the hybrid process of SMC (Sheet Molding Compound) and thermoforming with over-injection .

A-VARTM is a modified version of VARTM (Vacuum-Assisted Resin Transfer Molding) processing, developed jointly by Mitsubishi Heavy Industries (MHI) and Toray Industries. The innovation of this technology is based on the use of hot compaction before the infusion stage. By simultaneously applying a high temperature and vacuum pressure, this method allows for a more efficient impregnation of the fibers, reducing the void volume and increasing the fiber content 3,4.

HP-RTM, compared to the traditional RTM (Resin Transfer Molding) process, allows for shorter production cycles (between 2 to 5 minutes), ensuring a higher production volume. However, to make this possible, this technology considers new processing parameters, making its control more complex and critical. The process thus consists of the following steps: placing a preform in the mold, injecting a matrix into a closed mold, applying a vacuum, polymerizing, opening the mold and removing the part5,6.

As for the SMC process, it is already widely used in the automotive sector, due to its ability to produce fiber-reinforced polymer components (FRP). However, in order to improve the properties of products in SMC and to respond to the growing interest in this class of materials, a hybrid process has recently been developed, which combines prepregs of continuous and oriented fibers with the traditional SMC. This technology ensures high productivity, excellent reproducibility of parts, cost reduction, and the production of lighter and more resistant components, with more complex geometries and integrated functions 8,7.

Another available means of action is the thermoforming process with over-injection. It consists of an injection machine, coupled to a manipulator robot to feed the heated laminate to the injection machine. This composition makes it possible to maximize the production rates, since after consolidation of the tapes that give rise to the laminate, it is cut to size, heated, transported and positioned in the mold in the injection machine, where it is then stamped and sequentially over-injected, without the need for heating again 9,10.

This new generation of productive solutions contributes to producing composites at "high speed", by reducing the duration of the process and increasing the cadence, whole being more sustainable, by reducing the consumption of resources and energy. Advantages that the various sectors of the industry seek, with the active contribution of R&D entities, as is the case with INEGI and as exemplified by recent projects such as RTM E-BOX, AEROCAR, LYNX eMTB, LATCH I and II.

Scientific and technological innovation - supported by collaborations with the industry - thus allows us to explore the potential of new processes, and thus pave the way for new and better products and business opportunities.



References

1 Liu, Y., van Vliet, T., Tao, Y., Busfield, J. J., Peijs, T., Bilotti, E., & Zhang, H. (2020). Sustainable and self-regulating out-of-oven manufacturing of FRPs with integrated multifunctional capabilities. Composites Science and Technology, 190, 108032.
2 Sunilpete, M. A., & Cadambi, R. M. (2020). Development of Cost Effective Out-of-Autoclave Technology – Vacuum Infusion Process with Tailored Fibre Volume Fraction. Materials Today: Proceedings, 21, 1293-1297.
3 Ganjeh, B., & Hassan, M. R. (2013). Cost-efficient composite processing techniques for aerospace applications–a review. In Applied Mechanics and Materials (Vol. 325, pp. 1465-1470). Trans Tech Publications Ltd.
4 Hindersmann, A. (2019). Confusion about infusion: An overview of infusion processes. Composites Part A: Applied Science and Manufacturing, 126, 105583.
 Siddiqui, M. A., Koelman, H., & Shembekar, P. S. (2017). High pressure RTM process modeling for automotive composite product development (No. 2017-26-0175). SAE Technical Paper.
5 Hillermeier, R., Hasson, T., Friedrich, L., & Ball, C. (2013). Advanced thermosetting resin matrix technology for next generation high volume manufacture of automotive composite structures (No. 2013-01-1176). SAE Technical Paper.
6 Silva, J. N., Pina, L., Sousa, S. (2019). Hybridization Process of Carbon Fibre Sheet Moulding Compound with Carbon Fibre Prepregs: a Case Study". XIII Edición del Congreso Bienal de Materiales Compuestos (MATCOMP19), 3-5 July 2019, Universidad de Vigo, Spain. 
7 Fette, M., Hentschel, M., Köhler, F. A., Wulfsberg, J., & Herrmann, A. (2016). Automated and cost-efficient production of hybrid sheet moulding compound aircraft components. Procedia Manufacturing, 6, 132-139.
8 Gomes, R. (2020). Ferramentas avançadas para o fabrico de compósitos para o sector automóvel: nova abordagem reduz time-to-market. O Molde, julho de 2020, 126, 64-65.
9 Tanaka, K., Fujita, Y., & Katayama, T. (2015). Press and injection hybrid molding of glass fiber reinforced thermoplastics. WIT transactions on engineering sciences, 90(7), 225-232.