Reduction of infra-red heating cycle time in processing of thermoplastic composites using computer modelling
This paper deals with increasing the speed of the infra-red (IR) heating cycle in the processing of thermoplastic composites. A constraint on the heating process is that all parts of the material must be within the recommended processing temperature range before forming can start. A mathematical model is used to predict the transient temperature distribution through the thickness of flat consolidated panels of continuous carbon fibre-reinforced poly(ether ether ketone) (APC-2) during heating. The model includes (i) natural convection, (ii) medium and long wave radiation and (iii) one-dimensional conduction through the material. Experimental validation of the model is conducted using an IR test rig. The following process parameters were varied to obtain optimum process conditions: (i) heater power: (ii) heater-to-composite distance: (iii) composite thickness; (iv) degree of oversizing of heater area compared with surface area of composite: and (v) one- or two-sided heating. Results presented show that reduction of the heater-to-composite distance from 100 to 50mm increases the steady-state temperature of the composite by 88%, whereas almost doubling the heater power density from 25.6 to 47.3 kWm2 - increases the composite temperature by only 17%. Using one-sided heating, experimental results show that upward-facing heaters produce a more even temperature distribution across a panel surface than downward-facing heaters. Model results showing 1 R heating times for composite panels of thickness 0.5 to 9.5 mm are also presented.