a b s t r a c tReducing volumetric shrinkages and warpage during the injection molding process is a challenging problem in the production of molded thin-walled parts. In this study, the injection molding of shallow, thinwalled parts (thickness 0.7 mm), composed of lignocellulosic polymer composites (polypropylene (PP) + 50 wt% wood), was simulated. The volumetric shrinkages and warpage in the thin-walled parts were evaluated under different process conditions, with varying post-filling parameters, such as mold temperature, cooling time, packing pressure and packing time. The analysis showed that the cooling time and packing time had less of an effect on the shrinkage and warpage; nevertheless the optimal levels for both parameters are required in the molding process for the thin-walled part to achieve the best results. The volumetric shrinkage was lower near the gate than at the end-of-fill location along the flow path. The results also showed that the volumetric shrinkage correlates with the warpage measured on the molded part. The optimum parameters ranges is 40-45°C for the mold temperature; 20-30 s for cooling time; 0.85 from injection pressure (P inject ) for packing pressure; and 15-20 s for the packing time to achieve the best results with the least amount of volumetric shrinkage and warpage.
Currently, many industries are trending towards producing products exhibit such properties as small thickness, lightweight, small dimensions, and environmental friendliness. In this project, flat or shallow thin-walled parts were designed to compare the advantages and disadvantages of lignocellulosic polymer composites (PP + 50 wt% wood) in terms of processability. This study focused on the filling, in-cavity residual stresses and warpage parameters associated with both types of thin-walled moulded parts. Thin-walled parts 0.7 mm in thickness were suitably moulded using lignocellulosic composite materials to determine the effects of filling. The analysis showed, the shallow thin-walled part is preferable in moulding lignocellulosic polymer composite material due to the low residual stress and warpage measured. The results also indicate that the shallow thin-walled part is structurally rigid, such that it can be used in applications involving small shell parts, and can be processed more economically using less material than the flat thin-walled part.
In recent years, the polymer industry has intensified its efforts to produce renewable material based polymer. Therefore, the use of natural fiber composites has been widely considered in various engineering sectors to replace conventional synthetic composite usage. This is because natural fiber composite properties are easily disposed and environmentally friendly in generating economic and sustainability societies. Vinyl polymer is a group of matrices comprising of thermosets and thermoplastics that are normally preferred as matrices with natural fibers. Both groups have their own unique features in benefiting their applications. The composite made of thermoset resin cannot be reprocessed or recycled. The composites of the thermoset matrix tend to provide good mechanical strength, are fragile and have low tensile effects. This is in contrast to the properties of the thermoplastic polymer that can be formed and diluted without changing its physical properties. Thermoplastic has excellent impact resistance and ductile. However, various approaches continue to be carried out by researchers to meet the requirements of natural fiber composites in different applications.
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