Net shape spray deposition for compression moulding of discontinuous fibre composites for high performance applications

Abstract

Details are presented of a novel carbon/epoxy spray deposition process for producing high performance, net shape charges for low flow compression moulding. The Bentley-Raycell automated carbon composite charge deposition (BRAC3D) process sprays powdered epoxy and chopped carbon bundles onto three-dimensional (3D) tools, offering a fully automated process with no touch labour. It has been demonstrated that fibre volume fractions of up to 54% are achievable for random discontinuous fibre architectures, with low void content (1?6%). This extends the volume fraction range currently offered by liquid moulding/preforming processes and potentially reduces part scrap rate, since the resin flow direction is through thickness rather than in-plane. Results from an experimental programme are presented, which aims to benchmark the BRAC3D material against commercial advanced moulding compounds. Ultimate tensile strength, tensile modulus and Charpy impact values are reported to be 272 MPa, 44?4 GPa and 128 kJ m 22 respectively, for the random fibre architecture at a fibre volume fraction of 54%. This equates to a 99% stiffness retention and a 59% strength retention compared to a continuous fibre, quasi-isotropic counterpart. Observed trends for increasing fibre volume fraction and fibre length have been compared against finite element predictions and an analytical inclusion model. Simulations from a parametric cost model indicate that the BRAC3D process is cost effective for production volumes exceeding 1100 ppa for a structural demonstrator component, compared with prepreg and resin transfer moulding.

Flow characteristics of carbon fibre moulding compounds

“…DFC compounds are produced by spraying multiple layers of material to achieve the desired component mass, with local variations in thickness achievable according to the geometry of the tool. The maximum global volume fraction is 55%, as the level of macroscale voids dramatically increases for higher fibre content levels [28]. The deposition time is dependent on the robot path length, therefore tailored charges for more complex 3D geometries can be produced without significantly influencing the overall cycle time.…”

The usability of recycled carbon fibres in short fibre thermoplastics: interfacial properties

“…The extruded material was subsequently pelletised. Benchmark epoxy microbond samples were produced using a development epoxy powder system (DLS1776) [18] supplied by Hexcel, UK. The mechanical properties for these materials are presented in Table 1.…”

Long discontinuous carbon fibre/polypropylene composites for high volume structural applications

“…A powdered epoxy system, DLS 1776 (Hexcel, Duxford, UK), was used as a benchmark thermosetting polymer as it could be melted and cured in a similar manner to the thermoplastics [14], also making it suitable for fibre coating. The epoxy was a B-staged system, enabling it to be heated to 80°C during the deposition phase without advancing the cure.…”

“…The comparison between all the materials is presented in Figure 11, with composite properties normalised to 0.45Vf. The mechanical properties for CF.EP and CF.PEEK were determined experimentally, and values for the HexMC were taken from the literature [14].…”

“…The tool was preheated to 125°C and the preform was loaded in directly without the carrier plates. The part was hot-demoulded after 23 minutes and then post-cured at 165°C for 2hrs in a hot-air oven [14].…”