Researchers in both AI and CAD fields have realized the power of applying AI techniques to engineering problem-solving activities, such as the design, diagnosis, and repairing of devices of various kinds. Intelligent CAD systems can not only assist humans to do design, but also automatically generate designs, and use design knowledge for the diagnosis and repair reasoning of physical devices. The author describes a system called KREATOR which applies techniques from a subfield of AI, qualitative physics, to CAD. A major observation is that an engineer designer's qualitative knowledge can offer a good basis for the reasoning of device behavior. Such knowledge, however, is not captured by conventional CAD systems for lack of good representation schemes. KREATOR is a knowledge representation scheme that allows the designers to record their qualitative knowledge of how mechanical devices behave and then automatically generates qualitative simulations which mimic the way the designers describe the behavior of those devices. This approach, if incorporated with a conventional CAD system, will allow designers to record their qualitative as well as quantitative knowledge to achieve full automation of design and device behavior reasoning