Warpage in rotationally molded parts

Rotational molding is one of the most important methods of manufacturing hollow plastic products. There are, however, some unsolved problems that confound the overall success of this technique. Part warpage caused by inappropriate mold design and processing conditions is one of them. An experimental study reports on the effect of processing parameters on the warpage of rotationally molded parts. Experiments were carried out on a lab-scale uniaxial rotational molding unit. After molding, the part warpage was measured by a profile-meter. A thermocouple and an air pressure transducer were employed to measure the in-mold temperature and pressure profiles respectively. It was found that in addition to the residual stress, the in-mold vacuum pressure during the cooling process might be another source of warpage formation. The experimental investigation of a rotational molding process can be used to optimize the molds and processing parameters in order to achieve a product with minimal warpage.