The Plastic Injection Molding Process

Plastic injection molding is a process where a plunger is utilized to inject molten plastic into a mold. The plastic cures and cools down within the provided mold and solidifies into the preferred shape. The process is used to create a multitude of parts used to manufacture anything from small medical devices to large-scale aerospace products.

This form of molding requires process equipment to include a nozzle tip which feeds the plastic from a feed hopper which draws the molten material from a heated barrel. The mold is clamped closed securely after it is filled with the plastic. Cooling time is determined by the original temperature of the molten material and time requirements for the specific product.

Holding pressure is the next step in the process. This process requires one of three options. A timer initiates the holding process based on a set time; a screw holds the mold together, or hydraulic molding press applies pressure to the mold after injection. The sophistication of the equipment utilized by a manufacturer determines which process is utilized. Some manufacturers utilize a pressure transducer for this purpose.

Blow molding is a process that is similar, for the most part, to plastic injection molding. The main differences are that in blow molding, the plastic in not liquefied when forced into the mold. And instead of being injected into the mold it is forced by air pressure through a blower. Another difference is that blow molding only produces thin products.

Molding defects are common in manufacturing. In fact, a department exists within most manufacturing plants for the exact reason. Among the most common defects found in injection molding are blistering, color streaks, burn marks, jetting, and sink marks. The entire product or pair is returned to its originating department whenever defects are located in the designs.

Common materials used in this form of manufacturing are elastomers, thermoplastics, and polyethylene. The chosen material is selected by the product produced and often referred to as a resin. These materials are used in the production of plastic springs, lawn chairs, and tubing. Manufacturers choose the materials based on the required durability and strength required for the finished product.

Plastic is not the only form of injection molding utilized in manufacturing plants. Among the most widely used, options is die casting, metal injection molding, and thin wall injection molding. These processes are utilized to manufacture a high volume of the parts and products used today in the automotive and aerospace industries.