Injection molding is a process for producing parts by melting plastic resin, flowing it into a mold, pressurizing the plastic melt and finally letting it cool into a solid shape. Injection molding machines are usually classified by the systems that drive them: all electric servo driven, hydraulic, or servo hydraulic. Selecting the appropriate size and style of machine is primarily determined by the part design, production rate required, and size of the part. Asking all the right questions up front can help lead to the proper selection.