Study On Thermal Modelling Of The Laser-assisted Thermoplastic Tape Placement Process

High-performance thermoplastic composites are considered to be a promising structural material in the aerospace industry.Laser-assisted thermoplastic tape placement is an integrated numerical control molding technology suitable for thermoplastic composites,which can greatly improve production and effectiveness.The performance of composites is highly dependent on the temperature distribution and temperature history during the forming process.In this paper,the temperature field in the laser-assisted tape placement process was studied.The laser optical phenomena and interlayer contact thermal resistance during the process were studied,and a two-dimensional thermal model considering contact thermal resistance and non-uniform heat flux was established.The model,carried out automatic placement test and numerical analysis,studied the influence of parameters on the temperature field,and provided guidance and referenced for the practical application of laser-assisted tape placement in thermoplastic composite manufacturing.(1)Studied the optical properties of carbon fiber reinforced thermoplastic composites and establish optical models during the deposition process.The integrating sphere test investigated the reflectivity of the composite surface.Studies showed that when the incident angle was constant,the reflectivity increased with the increase of the incident light wavelength;when the incident light wavelength was constant,the incident angle was less than 50°,the reflectivity was basically constant and remained at about 12%,and the incident angle was greater than at 50°,the reflectance rapidly increased.The reflection characteristics of the material were studied by laser beam reflection test,and it was found that the carbon fiber composite material had anisotropic reflection characteristics to light,and the reflection pattern was related to the surface fiber orientation.The optical model results showed that the closer to the pinch point,the smaller the incident heat flux on the surface of the tape,the one reflection light on the laminate plate increases the heat flux,and the part of the tape near the pinch point was blocked by the pressure roller.Act without being exposed to light.The incident heat flux of the surface of the laminate increased as the length of the pinch becomed smaller,and also because the portion of the pressure roller was partially not irradiated,the length of the irradiated surface was shorter than that on the tape.(2)The thermal contact resistance of composite laminates was investigated by laser irradiation laminate test and thermal simulation.Studies showed that,considering the existence of interlayer thermal contact resistance,the laser energy absorbed by the upper layer material was hindered in the process of flowing to the lower layer,and the energy was accumulated in the upper layer,resulting in a higher upper surface temperature.Similarly,it was difficult for energy to flow downward,resulting in less energy at the bottom layer and lower temperature at the lower surface.The results of laser irradiation laminate test showed that it is necessary to consider the existence of thermal contact resistance between laminates in the model.At the same time,the laser power was verified to verify the reliability of the thermal contact resistance value,and the thermal conductivity between the composite layers was fitted.(3)A two-dimensional steady-state thermal model considering the non-uniform load and interlayer thermal contact resistance was established.The automatic placement process of thermoplastic composites was carried out to study the influence of laser power and deposition rate on the temperature field.The results showed that the temperature at the pinch point of the tape band increases with the increase of laser power.When the deposition rate increases,the temperature at the pinch point generally decreases,due to the decrease of the maximum temperature and the decrease of the temperature drop.It was found that the change in temperature at the pinch point cannot be intuitively determined based on the change in the deposition rate.Due to the simplification of the optical model and the underestimation of the surface temperature of the press roll,the model calculated the temperature below the test measured temperature.(4)The thermal model was used to analyze the influence of thermal conductivity,volumetric heat capacity,pressure roller boundary and surface emissivity on the temperature field.The results showed that within the experimental range,the change of volumetric heat capacity had the most significant effect on the temperature of the tape,and had the same effect as the thermal conductivity.The heat transfer coefficient between the tape and the pressure roller and the influence of the convective heat transfer coefficient on the maximum temperature were negligible,and the surface emissivity of the material directly affected the measurement temperature.