Molding machines form thermoplastic resin, thermoset polymers, or metal injection molding (MIM) compounds into finished shapes. Injection molding machines consist of a barrel and reciprocating screw assembly, an injection nozzle, and a hydraulic motor that feeds the molten plastic or metal mix into a mold. The molding machines then transport the molten material as it progresses through the feeding, compressing, degassing, melting, injection, and packing stages. Modern molding machines are controlled by computer systems that act upon information from sensors to control each action of the molding equipment, and to ensure consistent output and quality.

Types

Molding machines include many different plastic injection molding machine and metal injection molding machine types. Plastic molding machines are used to manufacture plastic parts using the blow molding process.

There are two basic types of plastic molding processes:

• injection blow molding
• extrusion blow molding

During the injection molding process, a blow molding machine (also called a plastic injection molding machine) produces molded plastic parts by converting plastic pellets into a molten material and then injecting that material into a mold. Once the plastic cools, the solid plastic parts are completed. By comparison, plastics extrusion equipment is used to shape plastics by forcing molting material through a shaped die. After the hot material exits the die, it is cooled and cut to length. Plastic extrusion equipment is used for the low-cost manufacturing of intricate shapes. Plastic dip molding is another low-cost alternative. Dip molding is a process where metal molds are dropped into a tank of liquid plastic. As the plastic cools around the mold, the part is formed. The increasing popularity of dip molding is due to its shorter lead times, lower tooling costs, faster prototyping, and lower capital costs.

Applications

Metal injection molding machines perform a metal powder molding process that combines various materials. A metal injection molding machine combines the shape-making capability of plastic injection molding with the material flexibility of powder metallurgy. Metal injection molding has been used for many years, but has only recently been considered a cost-effective alternative to other types of metal processes. Metal injection molding is particularly applicable in high-volume manufacturing operations and for small, complex components that need high strength, high performance, and cost efficiency. Metal injection molding is now used to produce parts for the telecommunications, electronics, and auto parts industries.

Additional Information

Engineering360—Molding Equipment and Supplies

Engineering360—Standard: ANSI B151.26

Engineering360—Plastic Mold Equipment Design and Fabrication Information

Engineering360—Specialized Thermoplastics in an Evolving Global Market

CR4 Community—Predictive Maintenance of Injection Machines

Image credit:

Koh Wei Teck / CC BY-SA 4.0