Single diaphragm forming (SDF) has been used in manufacturing high-quality thermoplastic composite sheet parts with complex geometries. However, temperature gradients through the thickness may exist in the composites, especially for thick, high temperature, semicrystalline composites. The thermal gradient may introduce residual stresses, which may degrade the mechanical properties or warp the part. Therefore, investigating temperature profile through the thickness during processing can improve the quality of SDF composite parts. A laboratory scale SDF with a cooling system was built for the temperature study through the thickness. Carbon fiber reinforced polyphenylene sulphide (carbon/PPS) was used for the temperature study, and the effect of cooling rate on the nonisothermal crystallization of the carbon/PPS was also investigated using differential scanning calorimeter. The start crystallization temperature and the peak crystallization temperature decrease with increasing cooling rates. A combination of Avrami and Ozawa theory was successfully used in the work for describing the crystallization kinetics, and the crystallization activation energy was determined for the carbon fiber reinforced PPS. © SAGE Publications 2010.