Feb 11 2014

How to Do Injection Molding Machines Work

Posted by admin in Uncategorized

The concept of injection molding has been around for about 75 years, but it has improved dramatically in the last few decades allowing for the creation of a variety of everyday materials such as packaging, small appliances, automotive parts, bearings, telephones, lenses, wheels, microwave grills, beverage bottles, gears, valves, and pumps. Depending on the application, these products can be produced in a variety of properties. They can be hard and rigid, or flexible and brittle, transparent or opaque, weatherproof, chemically resistant, and non-flammable.

How do they work? Today’s injection-molding technology uses a complex, computer driven piece of machinery to create a solid piece by injecting molten material through a reciprocating screw into a mold. The machine consists primarily of a hopper, an injection cylinder (or “barrel”) with the reciprocating screw, a thermostat, an exterior clamp, and the mold (Source: HGP Auction injection molding machines).

The process begins with the creation of a unique mold. A design engineer using software to render a 3-D computer-generated model typically creates the mold. The mold is carefully fabricated to permit the two halves of the mold -the cavity and the core- to separate along a parting line. This allows for easy ejection from the machine when the newly fabricated piece has cooled.

The mold is placed securely inside the injection-molding machine. Raw materials and pigment are fed into the barrel of the machine through the hopper. The clamp closes the mold, applying just enough force to keep the mold closed during the fabrication process. In the barrel, the raw materials are rotated together with the pigment and subjected to precise conditions of pressure and temperature until they melt. The reciprocating screw turns inside the barrel, injecting a defined amount of molten material- typically plastic or foam- into the mold at a set rate, temperature, and pressure. When the mold is filled with the molten material, the injection process terminates. The new part then cools until it is ready to be ejected from the mold. This can take some time depending upon composition materials, and the dimensions, and the weight of the part.

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