Business process management has been a hot topic for both management and enterprise modeling communities. Conventional training based approaches expect managers capable of apply their knowledge and experience when they make decisions in designing their business processes. The technology advancement in the past decades has made it possible to provide technological decision-support for both executives and in the trench managers. How one can create technologies that are both generally applicable to a wide range of domains and still powerful enough to provide specific solutions for specific problems has been a challenge for the research community. In our research, we take a simulation based approach to business design and management. In this paper, an enterprise simulation model, called PMT (Process Management Tool), is introduced and a case study of design and management of automotive engineering design processes using PMT was presented. The PMT based case study demonstrated the effectiveness of our simulation based approach and the PMT model by clearly identifying the fragility of product based design processes and the tolerance of function based design processes to overload situations.