Plastic injection molding process is well known as the manufacturing process to create products with various shapes and complex geometry at low cost. The injection molding cycle consists of several stages, such as filling, packing, and cooling. The cooling system design is of considerable importance since about 80% of the cycle time is taken up by the cooling phase. In this book, injection mold of a complicated plastic part with undercuts is designed by providing the Sliders in the mold and cycle time is reduced by optimizing cooling time. In this book, different variables included: size, location and layout of cooling channels, temperature and flow rate of the coolant and the effect of different types of plastic materials on cooling time are analyzed analytically and through software analysis to optimize the cooling time.