Although additive manufacturing technologies have advanced significantly in the past decades, its limitation on material composition, production cost and surface finish still presents itself as barrier for a complete replacement of traditional manufacturing processes. Merging additive and subtractive manufacturing processes then become the trend of today’s manufacturing technology innovation. However, to keep commensurable with the process integration, the process planning also needs to assimilate the advantages of both additive and subtractive manufacturing. This paper reports a heuristics based partition methodology for additive and subtractive manufacturing processes. The methodology starts from identifying the setup orientation, and then the volumes for both additive and subtractive manufacturing processes are recognized through a slicing and searching partition procedure. The objective is to maximize the use of CNC machining process due to its efficiency and surface control. At the end of the paper, an example is given to demonstrate the methodology.