In this paper we discuss a hybrid computational design tool, called CSN-Designer (Cognitive Symbolic Numeric), which is currently under development at the University of Massachusetts. The objectives of the system are two fold: to foster concurrency in the early stages of design, and to facilitate and automate as much as possible the design of mechanical components. To meet these goals, the system integrates human cognition, symbolic computation, and numerical simulations within a single computational environment. All three of these knowledge sources are exploited in pursuit of the design objective. The computational system is currently being tested in the domain of preliminary design of 3-D load-carrying injection molded parts. Several design examples in this domain are presented in this paper.