17 Performance Optimization in Machining of Aluminium Alloys for Moulds Production: HSM and EDM Andrea Gatto 1 , Elena Bassoli 1 and Luca Iuliano 2 1 University of Modena and Reggio Emilia 2 Politecnico di Torino Italy 1. Introduction In order to face the demands of today’s competition, i.e. short time-to-market for customized products in small batches, in the field of moulds construction a growing interest is seen for materials that combine high mechanical properties with the possibility of a quicker and easier machining (Klocke, 1998). Aluminium alloys offer many machining advantages such as excellent machinability and finish degree with high cutting speed, low cutting forces, outstanding tool life (Kishawy et al., 2005; Schultz & Moriwaki, 1992). Elevated thermal exchange and weight reduction, which means easier handling, compared to steels are additional characteristics that lead to increasing applications in the automotive and aerospace industry and in the field of mould production (Amorim & Weingaertner, 2002; Ozcelik et al., 2010). The use of Aluminium moulds, whose thermal conductivity is up to 5 times higher than of traditional steel moulds, ensures an impressive reduction of cooling time at closed mould, which is the longest step in polymers injection moulding cycle. Moreover, high thermal exchange promotes a better workpiece accuracy, lower risk of warpage and sink marks, lower molded-in stresses (Erstling, 1998). Good corrosion resistance of Aluminium is an additional advantage in processing molten polymers. Relatively recent Aluminium alloys derived by aeronautical uses offer high tensile strength and hardness: the gap with steels is thus reduced or even reversed in terms of specific properties (Amorim & Weingaertner, 2002; Starke & Staley, 1996). Wrought heat-treatable alloys develop high specific strength thanks to age-hardening and have been widely used for airframes. Above all Al-Cu alloys (2xxx series) and Al-Zn alloys (7xxx series) are recognized for best damage tolerance and strength, respectively (Starke & Staley, 1996). The addition of transition elements, i.e. Cr, Mn or Zr, leads to dispersions capable of controlling the grain structure. Two examples of such alloys are Al 2219 and Al 7050, which are good candidates for injection moulds applications. If the first examples of Aluminium moulds for plastic injection were limited to preproduction, the properties of these new alloys match the requirements of medium production volumes (up to 10000 parts/year), which today are also the main market demand (Miller & Guha, 1998; Erstling, 1998; Klocke, 1998; Amorim & Weingaertner, 2002; Pecas et al., 2009).