Cost and time reduction of the mold and die production is a critical issue for any manufacturing companies. Part designers are basically not manufacturing experts, therefore they often design parts with various problems for manufacturing with molds and dies. These problems are usually detected by manufacturing engineers in the later production stage. Problems are reported to the part designer and they are resolved by modifying the part shape. Reduction of such reworks is important for realizing the efficient production of the mold and die, and consequently efficient part production. In this paper, we explain a software system named manufacturability assistant for reducing the reworks. This system detects shape elements of a part with potential manufacturability problems by applying various shape extraction procedures to the CAD model of the part. By using this system, designers can evaluate the quality of a part in the manufacturability view point. They can reflect the evaluation result in the part design to obtain a part with higher manufacturability.