Christopher Stokes-Griffin

Thermal modelling of the laser-assisted thermoplastic tape placement process

Thermoplastic tape placement opens the possibility of a fully automated composite production. The resulting quality is highly dependent on the thermal history during consolidation. This article focuses on the thermal modelling of a tape placement system employing a near-infrared laser. A nonlinear two-dimensional finite element model is presented for a carbon fibre reinforced thermoplastic (AS4/PEEK) composite placement process using a conformable roller. The relative influence of roller geometry, roller temperature and thermal contact resistance was studied. Temperature measurements were performed using thermocouples welded to the substrate. The model predictions show good correlation in terms of timing of the irradiation, shadow and consolidation regions. The roller temperature was found to have the most significant impact on the bond line temperature distribution.

Laser-Assisted Tape Placement of Thermoplastic Composites: The Effect of Process Parameters on Bond Strength

The manufacturing process for high performance composite materials is typically slow due to labour intensive lay-up processes followed by long cure cycles of thermosetting resins. Thermoplastic materials be can processed by fusion bonding, a welding process based on the diffusion of polymer molecules across the bond interface at elevated temperatures. This process can be orders of magnitude faster than a typical thermoset cure. Furthermore, when coupled with a placement technology such as automated tape placement (ATP) or filament winding, the composite can be bonded in situ as it is placed. The part is ready for finishing as soon as placement or winding has completed. This approach shows much potential for flexible and automated manufacture of lightweight and high performance automotive structures, including high pressure storage vessels for gaseous fuels. The placement rate must be maximised for production, however maintaining composite quality is nontrivial due to the highly dynamic behaviours at the nip point. A small parametric study was performed to investigate the effects of laser power and consolidation force. A laser-assisted tape placement system was instrumented with temperature and pressure sensors so as to measure the temperature and pressure profiles experienced at the bond interface in the nip point region. The recorded temperature and pressure profiles were fed into a bonding model to predict the resulting strength. Mechanical tests were performed on Carbon/PEEK lap shear samples and compared with strength predictions.

Modelling the Automated Tape Placement of Thermoplastic Composites with In Situ Consolidation

In situ consolidation of thermoplastic composites opens the possibility of fully automated composite production when coupled with fibre placement technologies such as automated fibre placement (AFP) and automated tape placement (ATP). These approaches show much potential for flexible and efficient manufacture of lightweight and high performance automotive structures, including high pressure storage vessels for gaseous fuels. The placement rate of such systems must be maximised for production, however maintaining composite quality is nontrivial due to the highly dynamic behaviours at the nip point. Bonding is governed by intimate contact, autohesion and degradation processes. The quality is a function of the level of bonding, crystallinity, void dynamics and residual stress generation. The behaviour of these processes is dictated by the temperature and/or pressure distributions at the interface. In order to analyse the welding process it is therefore necessary to have models for each of the processes combined with robust pressure and temperature analysis. Process optimisation is a trade-off between the different aspects of quality. This paper will investigate the limitations of the work to date and identify improvements for future work.