Issue 33

A. Winkler et alii, Frattura ed Integrità Strutturale, 33 (2015) 262-288; DOI: 10.3221/IGF-ESIS.33.32

Figure 7: UTS as a function of orientation for PS. [7]

Figure 8: Secant modulus as a function of surface layer for PP. [25]

Figure 9: UTS as a function of orientation for PS. [7]

T HE ROLE OF THE MANUFACTURING PROCESS SKIN

njection moulding is by far the most widely used manufacturing process for large quantities of engineering components. Extrusion and die casting are also used, but to lesser extents. One of the main features of injection moulding and casting that the non-isothermal cooling of the melt causes the layer closest to the mould to freeze much quicker than the rest of the bulk. Apart from causing density gradients to evolve through the wall thickness, strong orientation of the surface layer (or skin) will result where a melt (or near melt) is being pressed into a specific shape. This is the case for injection moulding and extrusion. The highly oriented skin has much higher ductility, stiffness and strength than the interior of the component [27]. This characteristic creates a beneficial protection, in that the skin acts as a I

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