Art to Part in Plastics: Molding Dreams into Reality
An introduction to Injection Molding.
Every plastic product you see needs to be shaped, and the most common method is Injection Molding. Most people using their computer to read this give no thought to how all those plastic parts were formed. Or how complex and expensive it is even to produce a ballpoint pen. Just about every part made of plastic these days is formed using some kind of an injection mold, from tiny precision parts that can barely be seen to large automotive exterior parts. Just about every industry relies on some kind of injection mold for their products.
Injection molding is the forcing of molten plastic into a shaping cavity. An injection molding machine has three basic components:
1)Injection. Plastic pellets are fed into a hopper and then heated up. Once they are melted they are injected under extremely high pressure into a mold.
2)Mold. This is a custom designed tool for shaping and cooling the melted plastic. Two halves are precisely designed with cavities for the shaping of the part, channels for cooling the molten plastic, and an ejection system.
3)Clamping. This is the part of the machine that holds the removable mold in place, keeps the two halves together during molding, and opens the mold for part ejection.
Molds are complex and must be of heavy-duty construction since they are subjected to a considerable amount of pressure. They are usually carved/milled out of aluminum or steel blocks and contain many different parts such as the mold base, clamp plates, support plates, ejector plates and pins, guide pins, sprue puller pins, and of course, the two cavities with channels for the molted plastic flow, cooling and/or secondary heating units. The mold is the most expensive part of injection molding, with molds ranging from a few thousand dollars to hundreds of thousands of dollars. Think about that next time you use that cheap plastic pen.
Injection molding started to catch on in the 1920’s and was used for simple products such as combs, toothbrushes, and simple industrial parts. As the science of plastics and machining technology grew, molding became an increasingly popular way of manufacturing. With todays computer-controlled milling and molding machines, just about any idea or design can be shaped into plastic.
Ever wonder how they make hollow plastic spheres? Rotational molding is a mold in which after the plastic is injected, it is spun around at high speeds and then quickly cooled. Scissors and screwdrivers are made by insert molding. The metal part is suspended in the mold while the plastic flows around it. How about those plastic bottles and food containers? Those are made by blow molding. There are also other processes such as thermoforming and extrusion. insert molding
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