Keywords: Extrusion; Genetic algorithm; Optimisation; Polynomial networks RID=""ID="" <E5>Correspondence and offprint requests to</E5>: Dr Y.-C. Hsu, Department of Mechanical Manufacturing Engineering, National Huwei Institute of Technology, 64 Wun-Hua Road, Huwei, Yunlin, Taiwan. E-mail: jasonych@sunws.nhit.edt.tw;