A forward and automatic method for in-process model generation is proposed and integrated with three-dimensional computer aided process planning (CAPP) system. The method based on feature cutter volume of manufacturing drives the in-process model to evolve from blank to part, which is coincident with the manufacturing process and ideology of process design. At the same time, technology of What-if Alternative Value Engineering (WAVE) is implanted in the generation to establish the relationship of in-process models, which supports function of the automatic update for models. The paper introduces a theory of the solution to demonstrate the connection between manufacture feature and feature cutter volume, and detailedly presents the technological process in applying the WAVE technology. Examples are completed in a commercial CAPP system to illustrate the feasibility of this approach.