Novel concepts for the design of moulds and equipment for expanded polymer bead foams
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Novel concepts for the design of moulds and equipment for expanded polymer bead foams F. Alessio1 · M. Alessio1 · M. Vedani2 · R. Viganò2 Received: 22 July 2020 / Accepted: 23 October 2020 © Springer Nature Switzerland AG 2020
Abstract Metal additive manufacturing is proposed as route for the manufacturing of moulds for expanded polymer parts. The traditional tools used in steam-chest moulding technologies can be replaced by lighter moulds accurately designed and produced by the laser-powder bed fusion technology, with significantly reduced thermal capacity and optimized ability to homogeneously deliver the steam throughout the part volume. The general design approach is described and the performance of the innovative tested solution is presented by the discussion of a case study. The experimental tests carried out on the moulds and moulding equipment prototypes showed remarkable reduction in cycle times and energy consumption when compared to a traditional steam-chest moulding used to print the same product. Keywords Expanded polymers · Additive manufacturing · Laser powder bed fusion · Steam-chest moulding · Mould design
1 Introduction Polymer foams represent an important class of materials where the polymer matrix contains a large amount of pores so as to reduce density and impart other interesting properties such as low thermal conductivity, improved acoustic insulation and energy absorption capacity. The combination of such properties makes polymer foams very attractive for a wide range of applications including packaging, sport and safety equipment, crash absorbers and bumpers, insulating panels, car interiors and other parts in the transportation, military and building sectors [1, 2]. A wide spectrum of processing techniques has been developed for the foaming and shaping of a range of polymers, typically polypropylene, polystyrene and polyurethane. One of the most popular shaping technology is bead foaming by steam-chest moulding. It makes use of a feedstock of expandable or already expanded foamed beads that are injected into a mould by air pressure and welded together under the action of pressure and temperature. Consolidation
* M. Vedani [email protected] 1
Alessiohitech SrL, Medolago, BG, Italy
Department of Mechanical Engineering, Politecnico di Milano, Via Giuseppe La Masa 1, 20156 Milan, Italy
2
of the beads into a defined shape takes place by a sort of sintering whereby a flow of water steam under pressure (usually at temperature up to 150 °C, and pressure up to 8 bar) melts or softens the surface of the beads, promoting the interdiffusion of polymer chains and forming physical links with controlled amount of inter-particle voids [2, 3]. The achievement of the best mechanical and functional properties in the expanded polymer (EP) parts is therefore related to a strict control of the processing environment supplied to the beads in the mould, to ensure a temperature distribution as uniform as possible, hence a stable quality of the sintering process througho
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