Acoustic Emission Crack Detection at Injection Molding Process

This paper presents the experimental results regarding acoustic emission signals measured during the injection molding of those standard test specimens commonly used for examining the shrinkage behaviour of various thermoplastic materials. In daily industrial production of different plastic products we often have to deal with various errors that practically occur on the mold primarily as a result of tool wear and tear, improper storage and improper settings on the injection molding machine. In the testing phase of plastic materials we use many times different inserts that are made from standard tool steels, such as OCR12VM. In case of tool steel inserts after some period of usage a few micro-cracks can occur in the early stage, which can later quickly spread according to the applied loading. In this paper we present the use of AE measurement during injection molding process to detect damaged tool. The acoustic emission was measured on a new injection mold and injection mold with the visible crack on the cavity's surface. Two resonant 150 kHz piezoelectric AE sensors were attached to tool steel inserts via AE waveguides. The results of acoustic emission testing on the crack defected tool steel insert revealed that the activity of the captured AE signals is higher compared with the ones that were captured on the brand new engraving insert under same processing conditions. Results of the experiment confirm that acoustic emission measuring during injection molding of polymer materials are promising technique to characterize integrity of injection molding tool regarding occurrence of cracks.