Understanding Invert Forming of Thin-Walled Polyvinyl Chloride Tubes Using a Die Based on a Mechanical Flow Formulation

Abstract

The design of sound metallic double-walled tubular parts by internal and external inversion using a die is presently well established. Major operating parameters are identified and the typical modes of deformation that can occur during the process are fully characterized. In contrast to metals, there are no practical design rules and no published research work in the specialized literature concerning the manufacture of double-walled polymer tubes by inversion. This article is concerned with the abovementioned lack of knowledge and is a contribution towards the application of existing metallic tube inversion technologies to polymers. The experimental research work makes use of Polyvinyl Chloride (PVC) and the overall findings are interpreted in the light of an innovative extension of the flow formulation that is capable of modeling cold plastic deformation of pressure-sensitive materials under a non-associated flow rule. Emphasis is placed on the deformation mechanics of tube inversion applied to PVC and on the influence of the major operating parameters on the overall formability limits of the process. Results show that invert-forming of thin-walled PVC tubes using a die can be successfully utilized for producing custom and specific shapes at the tube ends.