Design

Abstract Designing a polymer product requires material selection, and ensuring that it meets many requirements such as cost, manufacturing, stiffness, strength, and environmental impact. Design for manufacture requires attention to the distinctive features of each forming process and product assembly. Potential forming defects must be accommodated, such as weld lines and sink marks in injection mouldings, residual voids in rotational mouldings, and anisotropy of parts made by fused filament fabrication. In designing for stiffness, the engineer exploits stiffness control provided by features such as ribs and structural foams, laminates of fibre-reinforced plastics, and bonding to a much stiffer plate, as in rubber bearings. Also considered is the typical time dependence of polymers’ stiffness. Designing for strength requires minimizing cracks and other stress-raisers, and again acknowledging time dependence, as in failure by creep rupture or dynamic fatigue. Design for sustainability is an overarching aim, especially designing to enable material recycling at product end of life.