CompositesWorld
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OCTOBER 2017 30 CompositesWorld WORK IN PROGRESS ยป As interest in composites grows, so do opportunities for companies with innovative materials and/or process technologies that boost production efficiency, reduce part mass and cost while improving performance and broadening product design options. Such is the case with a new rotomolded core technology from Italian plastic machinery OEM Persico SpA (Nembro, Italy), now in trials with several European automakers. Persico's process produces symmetrical and asymmetrical hollow cores in a variety of smooth or textured finishes from a range of thermoplastics for use in sandwich-panel constructions. e hollow cores, of course, are lighter and use less material and, therefore, could be priced more competitively than solid cores of the same material. Rotomolding involves injecting or placing a measured charge (shot) of thermoplastic powder in an enclosed, heated mold, which is then rotated simultaneously around two perpendicular axes. e heat and two-axis motion cause the material to melt, flow and coat interior mold walls at a uniform thickness, forming a hollow component. e mold surface is then cooled while rotation continues, causing material to shrink away from the tool (which aids demolding) while retaining the shape. Although rotomolding is slower than other plastics forming processes, cycling 15 minutes Permanent or removable, these hollow thermoplastic cores broaden industry offerings. Rotomolded cores | NEW OPTIONS FOR SANDWICH COMPOSITES to hours for very large parts, it offers precise thickness control and can produce multiple parts per molding cycle in family tools as well as truly large parts, such as multi-thousand-gallon underground tanks, at low tooling costs. For these reasons, the process presents the opportunity to create cores in materials, geometries and sizes that would be difficult or impractical using other processes. Designed specifically for automotive Persico's core concept resulted from the convergence of three factors. First, the company has developed competencies over the Rotomolding tough cores Persico SpA uses rotomolding to build both structural and soluble thermoplastic cores for sandwich-panel composites. The lightweight, hollow cores (above, left) are strong, having already survived 10-bar molding pressure in high-pressure resin-transfer molding (HP-RTM) presses and 5 bar autoclave processes. To date, the company has either applied carbon fiber/epoxy prepreg over the cores and autoclave cured them, or has laid braided carbon fabrics over the cores, then resin-infused the components via HP-RTM. A recently molded core is shown at bottom right, prior to sprue trimming. A molded component, at top right shows the carbon composite skins have been cured over the core. Source (all images) | Persico SpA By Peggy Malnati / Contributing Writer