Injection molding is a manufacturing process whereby plastic materials are melted by heat and poured into a mold, where it’s left to cool, solidify and take shape. The injection molding process is the best option for the manufacturing of products with intricate shapes and designs; all these can be achieved via a plastic injection machine. The injection molding process is divided into six significant steps, they include:
5. Mold opening
6. Removal of products
Injection molding machine
The injection molding machine is classified into two central units: the clamping unit and the injection unit.
The clamping unit in the injection machine is designed to open and close the die and eject products from the mold. The two types of clamping methods include the toggle and the straight-hydraulic type.
The injection unit is designed to melt plastic to a molten point before injecting it into a mold
The screw is rotated to melt plastic from the hopper and gathers molten plastic in front of the screw (called metering). After collecting the required amount of molten plastic, the injection process can then begin.
A mold is a metal block with a hole in the middle in which molten plastic is poured to take a particular shape. Some holes are drilled into the mold for temperature control; water passes through the hole to cool the plastic.
The molten plastic flows into a mold via a sprue and occupies the cavities through runners and gates. After the cooling process, the mold is opened, and the plastic is ejected.
A molding consists of a sprue through which the molten plastic is poured and a runner to direct it to cavities and products. A mold is designed to have multiple cavities since it’s in-efficient to produce one product in one cycle. The cavities are connected with a runner so that many products can be made from one cycle.
If the length of the runner is different for each cavity, the cavities may not be filled at the same time. Therefore the runner is the same length from the sprue to each cavity.
Use of reprocessed materials
Sprues and runners are not products among moldings; sometimes, these portions are tossed away, but they’re regrounded and reused as materials to make a product. These materials are called regrind or reprocessed materials.
Reprocessed materials are not used as the original materials for production. Still, they’re often mixed or blended with fresh pellets because there’s a chance that it has reduced properties due to the initial molding process. Only about 30% of the reprocessed material can be added to the fresh material not to ruin the properties of the original plastic used.
Molding condition means cylinder temperature, mold temperature, injection speed, etc., set in a molding machine to get the right amount of moldings, and the number of combinations of conditions is uncountable. Depending on the conditions chosen, the dimensions, mechanical properties, and appearances of the molded products change.
Hence, it’s essential to select the most suitable molding conditions.