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The work reported in this thesis is concerned with the design and implementation of a Computer Aided Manufacturing System for the production of male finishing die profiles in graphite from which die cavities can be obtained by EDMM. Although the system is designed primarily for the hot forging industry, it is found that it can also cater for similar items-found in the casting plastic moulding and die casting industries. The system is restricted to male profile shapes that can be produced on a 22-axis numerical control milling machine. The system is called MODCON which stands for ! 4CDular CONstruction. In the MODCONI system, the geometry of the object to be machined is defined as a series of simple volumetric modulos, which are combined together to build-up the whole item. This allows complex shapes to be defined and machined with relatively, few easy to use, input. instructions. The system was designed initially for application to forging die manufacture and the volumotric shape features which can be defined are those found commonly in forging cavities, such as truncated cones, blocks with draft angles and edge radii, etc. However, the system can be used to describe other similar items, such as casting core boxes, die casting dies, plastic moulds, etc. The geometry is first defined using a series of module commands, each of which consists of a word,defining the type of element, followed by a number of parameters appropriate to the specific geometry of the particular shape feature. Currently 8 module commands are available, but these can be added to as required. With each module command, the basic shape can be modified by certain additional parameters to extend the range of shape features which may be defined by each command. The specification of each module command defines an object having its own physical attributes and orientated relative to the origin as specified. The separate elements defined using the module commands are merged together during generation of the tool paths to machine the -whole component. The transition surfaces between the elements are not defined on input as these are produced subsequently in the machining operation. A simple fillet of appropriate size can be obtained by a suitable choice of cutting tool and if necessary a larger blended radius can be added. This approach is considered suitable, as the transitions in such items as forging cavities and casting moulds are not defined specifically, in general, but have only to be smooth blonds between the main shape features, which can be readily produced during the blending process. The objects defined by the module commands are combined by MERGE commands, which select out the objects to be merged and initiate determination of the tool offset paths to machine these items separately.Subsequently, the overlapping regions of these separate tool paths are eliminated to give the tool paths to machine the whole object. The PAPA commands contain details of the tool geometry and surface deviation tolerances, which allows the spacing between tool paths to be determined automatically to suit. The tool location data for the whole component determined after the merge operation is post-processed to give a) a N/C. tape to machine the object and/or b) a plot of the tool paths for visual chocking. The system also has facilities for the generation of roughing cuts, allowances for shrinkage and generation of crosssectional data for use in other forging design programs. Details of the application of the MODCON system to the C. A. N. of a wide range of objects are given. Those include various EDIDf electrodes for forging dies and casting moulds, for such items as connecting rods, cross arms, malleable iron fittings, etc. The thesis contains details of the system, including the primitives used . and algorithms for merging elements, and the blending process.