An Integrated Product Model (IPM) stands for a conceptual model describing data of a technical product. It is used as basic technology of enabling application systems to exchange and share product data. Within the IPM development, the integration of data models is an important process. Unfortunately, because of the model complexity, it is difficult for the IPM developer to have control of it. This paper presents a methodical approach which is specifically designed to support the IPM developer in his integration work and to get over the complexity problem. The approach is based on ontology engineering mechanisms.