Now showing 1 - 2 of 2
  • Publication
    Optimising moulding conditions to improve the quality of injection moulded parts: A design of experiments approach
    (Plastics Moldels and Manufacturers Association of SME, 2004-01) ;
    The performance of an injection-molded part is the result of a complex interaction of the inherent material properties and selected processing conditions. To increase stiffness and strength and reduce thermal expansion, short fibers are often incorporated in the resin. However, a key aspect of these fiber-reinforced materials is the complicated fiber orientation distribution produced during injection molding. The mixture of glass fibers and molten polymer is injected under high pressure into a mold cavity, which fills in a matter of seconds. The resulting velocity fields, which are generated during this mold-filling process, have a profound influence on the fiber orientation structure and hence on the composite mechanical properties. Typically, a layered structure is found throughout the thickness of the molding, and the orientation of each is highly dependent on the fiber characteristics, the melt flow pattern within the mold and the conditions used in the molding process. The number and depth of each layer has been the topic of a number of studies. In general, most agree that five layers exist, forming a skin-shell-core structure. However, some researchers have discovered the formation of up to nine layers from surface to surface.
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  • Publication
    Analysis of fibre orientation effects on injection moulded components
    (Sage Publications, 2006-12-26) ; ;
    Fibre orientation, and thus the mechanical behaviour of short-fibre-reinforced thermoplastics (SFRTPs), depends greatly on the flow conditions in the mould. In order to design with SFRTPs, a thorough understanding of the processing conditions is required, together with the influence that the fibre orientation distribution (FOD) has upon the resulting mechanical properties. This work investigates the influence of primary injection moulding process parameters on the final properties of a simple planar injection-moulded component through design of experiments (DOE) and analysis of variance (ANOVA) techniques. Four factors are seen to have greatest effect on the mechanical properties: cavity thickness, packing pressure, packing time, and melt temperature. A systematic procedure is then employed to vary the levels of each factor, and the FOD and mechanical properties are studied. The final orientation is complex and is shown to vary throughout the part and depend heavily on the values selected for each parameter. Experimentally measured orientation results are then compared against those predicted by commercially available software for this planar geometry component. It is found that the predicted orientations were significantly over-predicted (34 per cent on average), from a minimum of 15 per cent for a 2 mm mould cavity up to 40 per cent for the larger 5 mm cavity thickness. This discrepancy in turn leads to an over-prediction, of approximately 50–60 per cent, between predicted and measured stiffness.
      482Scopus© Citations 9