Product evaluation in the design stage has played a critical role in the process of developing new products. Methods to build prototypes, especially functional prototypes, have been a deciding factor for design verification. Recognizing a new challenge to produce multiple functional prototypes, an effort has been made to integrate three state-of-the-art technologies, namely, 3D solid modeling, rapid prototyping and vacuum casting. A system architecture that combines hardware and computer software is designed and implemented. The paper presents a case study to demonstrate the procedure of applying the integrated system on implanting electrodes in the visual cortex of a monkey. Six replicas of a monkey skull are produced for surgeons to practice the surgical operation. Image data obtained from CT scans of a monkey head are successfully used to construct a 3D solid model to fabricate the 6 functional prototypes. The superior quality of these replicas has offered a unique opportunity for exploratory surgery to restore sight.