Machinability of Brittle Substrate Tooling Materials

The use of traditional metallic tooling materials for composite layup and curing is frequently prohibitively expensive and has an undesirable flow time for certain applications.  Material costs and difficulty in machining metallic tooling materials such as nickel-based alloys often prohibit their use for applications requiring rapid tool fabrication and short service life, such as part prototyping and incident repair.  Rapid tooling solutions based upon the use of low Coefficient of Thermal Expansion (CTE) substrate materials, which employ a final coating or laminate as their tooling surface, is one possible solution.  These materials must satisfy the required dimensional stability, durability, and machinability at the lowest possible cost, with the shortest possible flow time.  This work investigates three of these possible substrate materials: Autoclaved Aerated Concrete (AAC), ACG’s CB110 ceramic tooling block, and carbon foam.  These low CTE materials are commercially available, easily machined, lower cost, and posses low CTE’s making them suitable for this niche application.  As part of the determination of these materials suitability for use as composite tooling substrates, a comparative study of their machinability based upon cutting forces, achievable material removal rate, surface finish, and surface integrity is presented.