Abstract

With the aim of improving composites manufacturing process costs and properties, in order to compete with others materials, a new process of impregnation, compaction and curing of fibre glass reinforcing composites, has been developed. This new process based on UV curing prepregs could be an alternative to the traditional manufacturing process, including infusion process and autoclave curing.

These new process consists of two stages. First, the automated manufacturing of the UV curing prepregs. Second, the compaction of the composite by means of application of pressure and UV radiation giving rise to the finished part.

In this work, the UV prepregs manufacturing process will be analysed, and the effect of the control parameters of the all process, composed by impregnation, resin content adjustment and precuring, will be analysed. The durability of different manufactured UV prepregs and the mechanical behaviour of the resulted composite will be also studied. Finally, the prototypes necessary to the automation of the two stages of the process will be described.

Abstract

En el presente trabajo se ha demostrado el potencial de la tecnología de curado UV cuando se aplica en los materiales compuestos reforzados con fibra de vidrio. Se han comparado dos vías de fabricación de paneles; la fabricación por separado de ambos elementos y su posterior adhesivado, y la integración directa de los perfiles en el curado UV de las pieles. Los resultados de ensayos interlaminares demuestran que la resistencia de la unión prepreg/perfil es equiparable a la de la unión prepreg/prepreg. Consecuentemente, los prototipos obtenidos con ambas estrategias muestran prestaciones mecánicas similares, tanto en rigidez como en resistencia a la flexión. Por último, la baja temperatura con la que se da el curado UV de la piel permite utilizar núcleos hidrosolubles fabricados mediante impresión 3D que facilitan las operaciones de laminado y la compactación.

Abstract

This paper has demonstrated the potential of UV curing technology when applied to glass fibre reinforced composites. Two manufacturing routes for making panels have been compared: manufacturing each element by its side and their subsequent bonding, and the direct integration of the profiles in the UV curing of the skins. The results of interlaminar tests show that the strength of the prepreg/profile bond is comparable to that of the prepreg/prepreg bond. Consequently, the prototypes obtained with both strategies show similar mechanical performance, both in stiffness and flexural strength. Finally, the low-temperature UV curing of the skin allows the use of water-soluble cores manufactured by 3D printing, which facilitates lamination and compaction operations.

Abstract

Ultraviolet (UV) curing is a competitive process both in terms of cycle time and energy consumption. However, it is limited to open mold processes where the material can be irradiated directly with UV light. There is a variant of RTM, Light-RTM, in which the flexible semi-mold can be manufactured with transparent/translucent materials and in small thicknesses. In the present work the feasibility of performing the semi-mold by stereolithography (SLA) has been studied. The photocurable resin selected for SLA was the high temperature resin from FormLabs. First, the UV light transmission has been characterized according to the thickness of the semi-mold wall, in which the mold thickness has been determined in 3 mm. The ageing process has also been analysed, characterising the variation of the transmitted spectrum as a function of the irradiation time for a 3 mm thick plate, where a loss of light transmission of approximately 13 % has been observed for 15 minutes of exposure time. Finally, a semi-mold has been manufactured for the manufacture by Light-RTM of a 150 mm × 40 mm × 2 mm flat plate. During the process, there were no problems of vacuum loss and the intensity of UV light that passes through the semi-mold allows curing the photocurable matrix of the composite material.

Abstract

The ultraviolet (UV) curing process is gaining interest due to the curing speed, since it increases the production of the manufacturing processes. The high mechanical requirements of composite materials require the assurance of quality from the mechanical point of view. The inspection after processing is an additional operation that increases the costs and production times, so the monitoring of the mechanical properties, more specifically the evolution of the rigidity during the curing process, is strategic for the greater penetration of the composite materials in sectors dominated by the final price of the piece. Monitoring the elastic properties during curing, when contact between the piece and the sensor is not possible, is a challenge for rapid processes such as UV curing. The present work demonstrates the validity of the ultrasonic monitoring technique with air coupling (ACUS) for different UV curing conditions. Three conditions of UV curing (0.8, 1.6 and 2.4 W / cm2) were studied on a vinyl ester resin. The results of the ACUS are consistent with those of the direct current sensor with contact. The main conclusion is that the evolution of the rigidity with respect to the degree of conversion is similar for the different conditions studied.

Abstract

Cycloaliphatic epoxy resins containing cationic initiators which are activated by UV radiation give rise to thermoset networks when are exposed to UV light. On the other hand, due to its good mechanical properties, adhesive, thermal stability and electrical insulation epoxy resins are widely used in electrical and electronic applications.The inclusion of ceramic nanoparticles improves the properties of epoxy thermosets, but can influence the curing process. The objective of this work is to study the curing process of nanoparticle dispersions of boron nitride and titanium oxide in a cycloaliphatic epoxy curable epoxy resin. This study has been carried out using photo-calorimetry (UV-DSC) and traditional DSC. The effect of the presence of BN and TiO2 nanoparticles in the ultraviolet curing has been analyzed, finding that the UV curing is not complete, and a subsequent thermal post-curing stage is necessary. It has been found that TiO2 hinders the reaction reaching lower total conversions after both curing stages. Finally, in order to study the thermo-mechanical properties of the nanocomposites, thick specimens were prepared by applying the two stages of UV and thermal curing, the presence of nanoparticles leading to a more heterogeneous specimens. FTIR analysis of curing has shown that the surface of KBr support influences the curing reaction.