What’s injection molding?

4 Jul 2014, 3:14 Freetechmould

What’s injection molding?

Injection molding is a plastic manufacturing process whereby granules of plastic are heated until they melt and are then forced into a specially designed mold. Once in the mold the plastic is allowed to cool and hardens into the form of the mold. Injection molding is widely used in industry to produce plastic artifacts like computer casings, toys and cookware.
• The key part of an injection molding tool is the barrel. This is a metal cylinder that houses the reciprocating screw. The plastic granules are emptied into the barrel via the hopper and while in the barrel a combination of heat from the heaters and friction from the reciprocating screw liquidizes the plastic pellets. At the end of the barrel is an injection nozzle, through which the molten plastic is injected into the mold.
Reciprocating Screw
• The reciprocating screw sits inside the barrel of the injection molding device. This tool rotates and forces the plastic pellets through the barrel and into the mold. In appearance, the reciprocating screw is roughly cylindrical, tapering slightly to a point at one end. Its outer surface is shaped into a screw thread.
• The hopper is a tool used to store the plastic granules before they enter the barrel. It consists of a large funnel into which the plastic granules are deposited before they enter the barrel.
• The heaters sit around the barrel and raise the temperature of the plastic granules to the point at which they melt. This enables the molten plastic to be injected into the mold. The heaters sit wrapped around the cylinder and are powered by electricity.
• The mold and the corresponding mold cavity determine the final shape of the injection molded artifact. There are certain limitations on the design of the mold and the design of the molded artifacts caused by the necessity of being able to remove the artifact once it has solidified.
Mobile Platen
• The platen is a mobile flat plate that is used to push the mold and the mold cavity together. This ensures that the molten plastic migrates to every part of the mold and mold cavity. The platen is held in place against the mold by a clamp.
• The purpose of the clamp is to hold the mold and the platen as close together as possible while the molten plastic is setting into the final shape of the injection molded artifact. The clamp is often adjustable so the pressure on the platen can be increased to ensure that the molten plastic has reached every part of the mold cavity.

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