Abstract
The work reported here intends to identify and mitigate the causes for failure in a plastic faucet holder, a part of an integral float faucet with a well-documented history of fracture occurrence. A methodology for the identification of hidden internal defects in plastic parts and the elaboration of the required corrective actions towards quality improvement is, therefore, presented. Firstly, part defects were identified via injection moulding process numerical simulation. The latter has enabled the prediction of an excessive volumetric shrinkage at the core of the faucet holder, highlighting the presence of internal voids and, hence, the possible deterioration of the load-bearing capacity. The supposition was later confirmed by X-ray topography scans. Part reengineering, consisting of localized thickness reduction, was the option chosen for decreasing the high shrinkage at the core. For validation purposes, structural analyses were carried out, with and without accounting for the injection moulding processing history. The results obtained during part structural analysis have enabled us to conclude that, when taking into account the residual stresses generated during injection moulding, the analysis more closely reflects the experimental data and allows us to implicitly envisage the propensity to fracture. Moreover, the part modifications, undertaken during the faucet holder reengineering, led to the reduction of the cumulative (processing and imposed by load) stresses by 50%, when compared to the original design analysed.
Highlights
Plastic components developed for engineering applications are usually intended for supporting mechanical efforts, which can vary significantly in magnitude
Diagnostic of the Potential Problems in FH Parts. As it was mentioned above, the rheological simulations replicating the existent processing conditions of the FH part were carried out to identify the defects resultant from the injection moulding process and to gain an insight on their sources otherwise not assessable by visual observation
For transversely isotropic materials as HOSTAFORM C27021, the guideline for volumetric shrinkage evaluation estimates its values to be equal to the shrinkage in the flow direction plus two times the shrinkage in the transverse direction [18]
Summary
Plastic components developed for engineering applications are usually intended for supporting mechanical efforts, which can vary significantly in magnitude. Shrinkage variation, through the thickness of plastic components, are unavoidable in many cases, due to design requirements and restrictions They are frequently reported as a source of internal and external defects, such as, warpage, voids and sink marks [3,4,5,6,7,8]. The latter, manifesting itself as depressions at the plastic component surface and appearing when the part surface is not solidified enough to prevent retraction from the mould wall, constitutes an aesthetic defect [9].
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