An injection mold is a mold that typically contains two sides. The two sides of the mold seal together but retain a small hole on one side of the mold. The molded material is then injected into the mold via the small hole. When the mold material hardens, the mold is opened and the molded piece inside is removed. Injection molding is often used with plastics, and has a variety of other uses for other materials as well. The history of injection molding is surprisingly long, and began long before most people had even heard of plastic, much less injection molded plastic.
The first plastic injection molding machine was created in 1872 by inventor brothers John Wesley Hyatt and Isaac Hyatt. A few years earlier in 1868, John Wesley invented the first finished form of plastic, which he called Celluloid. The molding machine was very simple. A heated cylinder melted the plastic, and a large needle-like injection tool plunged the hot plastic into the mold. The Hyatt brothers used their molding machine to make buttons, collar stays, and combs. The machine remained relatively untouched and unused until almost 100 years later in WWII.
During WWII, the ability to make things fast and inexpensively became a necessity for all American factories. Many factories started making plastic products, with everything from toys, to food containers and beyond. In 1946, another inventor named James Watson Hendry created a better method for injection molded plastic, which used a screw mechanism to control the process and make it easier to use and produce higher-quality items. Hendry also invented gas injection molding in the 1970s.
Since then, injection molded plastics have become a part of our everyday lives. It is difficult to see an industry in today’s world untouched by the plastics industry.
