Abstract
The shape memory effect, as the most important ability of shape memory polymers, is a working property and provides the design ability to shape memory polymer features. Shrinkage and warpage are important parameters to control the dimensional accuracy of permanent and temporary shapes of an injection moulded shape memory polyurethane (SMPU) part. In this study, the effects of injection moulding parameters on the shrinkage and warpage of the permanent shape of moulded SMPU parts were experimentally investigated. The parameters of injection pressure, melt temperature, mould temperature, packing pressure, packing time, and cooling time, were chosen as the injection moulding control factors. Taguchi�s L27 orthogonal array design table was used with six injection moulding parameters and their three levels. The results showed that the part has different shrinkage ratios in three main directions, namely, the flow direction, perpendicular to the flow direction, and the direction through the thickness. The results of the analysis of variance showed that the cooling time is the most influential parameter on both the shrinkage (except in thickness) and warpage. The shrinkage in the flow direction as well as in perpendicular to the flow direction decreased with increasing the cooling time. Warpage also decreased with increasing the cooling time. Injection pressure and melt temperature were found to be effective on shrinkage in thickness. Effects of mould temperature, packing pressure, and packing time were found to be limited. A statistically significant relationship has been noticed among shrinkage, warpage, and residual stresses during the study.
Highlights
Shape memory polymers (SMPs) provide two or more working shapes in one part as different from general-purpose polymer materials
The injection moulding process of thermoplastic shape-memory polyurethane, was investigated experimentally, and this study focuses on the effects of moulding parameters on the shrinkage and warpage of injection moulded shape memory polyurethane (SMPU) parts to depict and clarify as to how the permanent shape dimensional accuracy changes by the moulding conditions
At the end of the study, the results showed that the moulding parameters have various influences on the shrinkage and warpage of SMPU parts
Summary
Shape memory polymers (SMPs) provide two or more working shapes in one part as different from general-purpose polymer materials. Shape memory polymers and their composites have been used to manufacture parts and they are featured in large application areas such as medical applications [4,5,6,7,8, 1, 9], self-disassembly systems [10,11,12,13], or aviation and space applications [14,15,16] Due to their shape-changing property, the precise controlling of the permanent and temporary shapes of manufactured or moulded shape memory parts is critical for a system. The reason for residual stresses during the injection stage was described as high shearing stresses that occur during the filling stage in melted plastic at lower temperatures due to the rheological properties of the melt
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