Design of a new rotomolding process for making seamless hollow plastic parts

Abstract

This project was funded by the Innovation and Technology Fund of the Hong Kong Government under the Teaching Company Scheme, and was jointly operated by the Department of Industrial and Systems Engineering of The Hong Kong Polytechnic University and an international toy manufacturer based in Hong Kong and China. The sales of iconic doll figures have had strong growth in the past few years and the manufacturing capacity has been pushed to the limit. Rotomolding is a particular bottleneck in terms of processing time, energy consumption and poor working environment, and further contributes to the difficulty of retaining a reliable workforce in this section. This project concentrates on studying the rotomolding being used in the company, and a new alternative of using induction heating to replace the diesel furnace heating has been suggested. Experimental results and comparisons in processing time, energy cost and working conditions are given in this report. Based on the results, it was found that the new induction heating could save 50% of the energy cost, and the processing time was trimmed down from more than 5 minutes to 2.5 minutes per doll head produced. Moreover, a hypothesis was also proposed for the bi-axial rotation calculations and this can greatly help the launching of new products as trial-and-error is the current approach being used for new setup determinations.