This paper describes the specification and implementation of aggregate process planning methods for complex welding operations. The methods are implemented as an aggregate process planning tool, CAPABLE/Welding, which can be used to evaluate the manufacturability of complex fabrications at the early stages of design. The first part of the paper discussed the aggregate product modelling methods, which are object-oriented and feature-based. The aggregate product model provides the necessary abstraction of design data to facilitate the assessment of early designs. A key planning requirement was to utilise the aggregate product model by developing process knowledge capturing and optimisation techniques so that production time and cost can be calculated for complex fabrications requiring many welding operations and set-ups. CAPABLE/Welding is a tool usable directly by designers, as it does not require specialist process knowledge. A range of generic welding process models has been developed and the planning techniques are instantiated with regard to company specific production equipment and factory layout. Alternative process and machine options are explored and the optimum production method is found using a simulated annealing algorithm. This selects process types, equipment, finds the best welding orientation, number of set-ups and finds the optimum processes and routes for minimum product cost or lead time. The resulting plans are presented graphically via a hypertext browser. This combines a graphic display of process time and cost distribution by feature with links to the relevant process knowledge. The process planning procedure of a product is used in this paper to illustrate the system functionality.