In 1868, John Wesley Hyatt became the first person to inject hot celluloid into a mold, producing billiard balls. In 1872 John and his brother Isaiah patented an injection molding machine that used a plunger, and the process remained more or less the same until 1946. In 1946 James Hendry built the first screw plastic injection molding machine, which revolutionized the plastics industry. Roughly 95% of all plastic injection molding machines now use screws to efficiently heat, mix, and inject plastic into molds.
Injection molding machines consist of two basic parts, an injection unit and a clamping unit. Injection molding machines differ in both injection unit sizes and clamping units used. Several manufactures offer hydraulic clamps, toggle clamps or electric driven machines. The clamping mechanism moves either horizontal or vertical. Majority of the plastic injection molding machines purchased today are horizontal machines with a very similar layout to the diagram below.
Plastic injection molding is a manufacturing technique for making parts from plastic material. Molten plastic is injected at high pressure into a mold, which is the inverse of the desired shape. The mold is made from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Plastic injection molding is very widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. It is the most common method for the production of plastic parts.