Injection molding is the most popular method of making plastic molded parts.
Injection Molding has the advantage of quality parts produced in high production runs at low cost.
In Injection Molding normally small solid plastic pellets are put into a hopper on the injection molding machine. The plastic travels through a long cylinder known as a barrell.
The barrell has an auger in it that is known as a screw.
While the plastic pellets are traveling through the barrell they are heated and melted.
At the appropriate moment the molten plastic is rapidly "injected" at high pressure into a precision closed mold.
The plastic then cools and solidifies in the mold. The mold then opens and the plastic part or parts are ejected from the mold.
Cycle times for producing parts can typically be from 40 to 60 seconds. Plastic table ware can run as fast as 4 seconds.
Most molds are single cavity (produces one part each cycle). If the mold has 200 cavities (makes 200 parts in one cycle) and cycles in 4 seconds then the production is 200 parts in 4 seconds or 3200 parts a minute.
If you notice the number on the back of plastic table ware next time you are at a fast food place that tells you which cavity the part came from. The little round circles are from the ejector pins.
Can you figure out where the plastic was injected into the cavity?
That is called the gate and is normally at the end of the handle.
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