Study of tribological properties of moulds obtained by stereolithography M. W. GONC ¸ ALVES$, G. V. SALMORIA$, C. H. AHRENS$ and A. S. POUZADA*§ $Departamento de Engenharia Meca ˆnica, Universidade Federal de Santa Catarina, Floriano ´polis, Brazil §Institute for Polymers and Composites-Department of Polymer Engineering, University of Minho, 4800-058 Guimara ˜es, Portugal Stereolithography (SL) is a process that allows the rapid manufacturing of high-accuracy rapid tools using anultraviolet laser beam to polymerize a liquid resin, layer-by-layer. In this work, the friction properties of commercial SL resins in contact with several thermoplastics were assessed. Friction experiments were done with plastics overmoulded onto moulding blocks made from SL resins. It was observed that polymers with Hildebrand solubility parameters close to the resins showed adhesion characteristics that were not observed in polymers with values of this parameter further apart. Keywords: Stereolithography; Hybrid moulds; Thermoplastics; Friction; Injection moulding 1. Introduction The use of injection moulds for production of small series of products or for prototype runs gave rise to the concept of hybrid moulds: tools consisting of a standard steel structure and moulding blocks produced by fast forming methods and using alternative materials. Today, rapid tools using moulding blocks manufactured by stereolithography (SL) are suitable for production of short runs of parts or prototypes, without resorting to a conventional metal mould (e.g. Cedorege et al. 1999, Colton and Lebaut 2000, Hopkinson and Dickens 1999, Ribeiro et al. 2004). SL is a process that allows the rapid manufacturing of high- accuracy rapid tools using an ultraviolet (UV) laser beam to polymerize a liquid resin, layer-by-layer (Jacobs 1996). The properties of the SL resins are very different from the metals. Therefore, when the production of a given number of parts using SL moulding blocks is considered, the knowledge of the mechanical and thermal properties of the SL resins and those of the thermoplastics to be injected are very important for the success of the production. Consequently the use of hybrid moulds with SL moulding blocks brings about strength issues associated to the lower resistance of the SL resins (e.g. Palmer and Colton 2000, Salmoria et al. 2005). During injection moulding, the thermoplastic tends to replicate the mould surface (Menges 1981). During the cooling of the moulding, the roughness of the polymer and the mould surfaces, the shrinkage undergone by the polymer and the adhesion between the two materials, originates a resistance to the ejection that must be overcome for removing the moulding from the mould. The friction properties of pairs of materials are usually represented by the coefficient of friction, m. The coefficient of friction is defined (e.g . in the ASTM G40 test standard) as m  F =N where F is friction force N is normal contact force This standard also defines the coefficient of static friction, m s , corresponding to the maximum force to be overcome to initiate macroscopic motion between two bodies. *Corresponding author. Email: asp@dep.uminho.pt Virtual and Physical Prototyping, Vol. 2, No. 1, March 2007, 29  36 Virtual and Physical Prototyping ISSN 1745-2759 print/ISSN 1745-2767 online # 2007 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/17452750701295765