Injection molding machinery operates on a simple premise: heated plastic is forced into a mold, which is cooled and then opened to release the molded product.
In practice, however, injection molding is a complicated process using often complex molds.
To better understand the process, it’s useful to understand how injection molding machinery is constructed. A basic injection molding machine is made up of three sections: the injection unit, the moldand the clamp. The injection unit is comprised of a barrel equipped with a reciprocating screw and which is fed plastic pellets via a hopper.
The screw performs several functions: it mixes the pellets and melts the resin because of the friction created by the screw’s movements. It also pushes the mixed, melted resin towards the front of the barrel. Reciprocating screws supply 60% to 90% of the heat required to melt the resin; the rest is supplied by supplemental equipment like heater bands.
Once enough resin is at the front of the barrel, the screw acts as a plunger, forcing the melted resin into the mold. As the injected plastic displaces the air in the mold, the air escapes through vents that are narrower than the width of a human hair – too small for the viscous plastic to enter.
The clamp keeps the two parts of the mold in place as the melted resin enters. The clamping pressure is designated in tons and is generally used to describe the capacity of injection molding machinery. A small injection molding machine might offer 5 tons of clamping pressure, while larger machines can provide up to 60,000 tons of pressure.
Before the clamp can separate the two mold halves and eject the molded part, the material must be cooled, often by circulating water or oil through the mold. Afterwards, the length of plastic that connected the molded product to the injection unit (called the “sprue”) must be removed.
Aside from tonnage, injection molding machinery is also classified based on the power system used. Options include hydraulic, variable displacement pumps, servo motor or all-electric. The cost of the units varies dramatically, depending on the technology and clamping tonnage. A small injection molding machine might cost around $13,000, while a larger machine could run into the hundreds of thousands or even millions of dollars.
The types of products made with injection molding vary as much as the cost of the machines. Typical examples include:
- Chairs
- Toys
- Cases for consumer electronics
- Disposable cutlery
- Bottle caps
- Automotive components
- Pocket combs
- Storage containers
- Gears
Visit polysort.com today for a comprehensive list of injection molding machinery makers.