Metal Matrix Composites (MMCs) have been developed, which can offer certain properties that metals or alloys alone cannot give. An example of one of these materials is the aluminium/silicon (Al/Si) composite. This material possesses good thermal conductivity, with thermal expansion matching capabilities that can be "tuned" by varying the quantity of silicon in the composite. It also exhibits a very high stiffness-resistance to elastic deformation. Whilst it is relatively easy to machine, it does require very sharp carbide tools. Alternatively, the material may be readily machined using Electro-Discharge Machining (EDM). This paper examines the use of EDM to rapidly form a tool insert from a MMC with a Coefficient of Thermal Expansion (CTE) of 11ppm, the same as that of tool steel used for bolsters. Details of the process of manufacture of the inserts, surface, and dimensional measurements, its performance in injection moulding trials and methodologies of enhancing tool life are discussed.