Injection Molding
A few common examples of injection molding include catheters, contact lens containers, monitors, mop buckets, video game cartridges and screwdriver handles. Injection molding is primarily done with thermoplastics; however, a small amount of thermosets, biodegradable plastics and elastomers are also subjected to this process. There are many advantages to the injection molded process. Some of these advantages include high production rates and little need to finish parts after the molding is complete. In addition, the cost per part is very low despite the high cost of tooling. Since injection molding can be used to produce very complex parts, injection molding is often used to produce parts that no other process can do. Other advantages of the injection molding process include the efficient use of materials and energy, precision-formed parts and a negligible amount of waste produced.
The most common type of injection molding machine are hydraulic oil machines, which use the force of hydraulic fluids to move the mold through the machine. Next in popularity is the toggle injection molding machine. Toggle machines use mechanical links to advance the mold in the machine. In addition, hybrid hydraulic/toggle machines are beginning to emerge in the injection molded plastics industry. Hybrid machines are used to eliminate some of the problems of other injection c molding machines, such as slow processing rates of parts and rapid wear and tear of machines. No matter the machine, the injection molding process remains the same, beginning with heating the barrel section of the machine. Next, plastic pellets or granules are fed into a hopper where a screw pushes them to the heated barrel. In the barrel, the pellets or granules are heated to the melting point. The molten plastic material is then injected into the cavity of a split die chamber/mold, which is then clamped shut. The plastic resin cools as water or other fluids circulate through the cooling system of the mold, extracting the heat. The injection molded part is held in the mold under high pressure until the part solidifies. The plastic part is finally ejected from the plastic injection mold, and the process begins again.
