Topological optimisation makes it possible to design parts in which the material is distributed as efficiently as possible in terms of the loads absorbed. Under the same operating conditions, optimised parts have 20-70% less mass than conventional parts, which is essential in aircraft design. However, in most cases these parts have very complex shapes that cannot be reproduced using the most common technologies. Additive manufacturing facilities for metal powders and consumables are expensive, which can be a deciding factor in the design of a new product. This book discusses a method of producing topologically optimised parts that does not require the use of expensive powder metal sintering or melting additive manufacturing equipment - investment casting of topologically optimised models pre-printed on a 3D printer.