We never really pay attention to the things in our homes and work places and world. But, everything that is man made has a process behind it of how it was made. Like plastic:
Injection molding is a very common method used in the making of plastic. Many products of different varieties are manufactured using this process which means that their sizes, shapes and functionality differs greatly. Anything from drinkware products to food packaging containers to pharmaceutical bottles can be made this way. This is a multi billion dollar industry. Between the 16,000 facilities throughout the United States, in just one year, $373 billion worth of plastic injection molded products were shipped.
This process uses a plastic injection molding machine, the actual plastic as well as a mold. In a nutshell, the plastic material is placed into the machine and melted. From there it is injected into the mold and cooled to make the part. The cycle is further detailed below. Keep in mind, this is still all just ‘in a nutshell.’ The actual process cycle is pretty complex and can be complicated to understand. Hopefully this will simplify it.
The first step in the process cycle, before the plastic is injected into the mold, the molds have to be secured through clamping. There’s an actual clamping unit that each half of the mold is attached to. One half slides and the power clamping unit pushes the halves together with enough force to keep the mold closed during the injection process. A larger clamping machine needs more time to complete this process. Plastic injection molding closures are sometimes used to secure the molds.
The raw material is usually in the form of pellets first. These palettes for a fitting to the injection molding machine and pushed towards the mold. In the meantime, the pallets are being heated up and pressurized in order to melt. After the plastic is melted it can then be injected into the mold. The amount of plastic that is injected depends on the size and shape of the part being made. The time it takes differs so much that it would be difficult to give a correct estimate. The plastic injection molding closures that are used to secure the molds can not be released until the next stage of the process.
This is when the plastic injection molding closures can be released because the plastic that is melted inside the mold will cool and solidify into the shape of the part. Sometimes, shrinkage can occur during this part of the process so the way that the material is packed during the injection stage should allow room for the material to flow and reduce the appearance of the shrinkage. Plastic injection molding closures cannot be removed until the cooling time has been completed. After these are removed, the mold can be opened and the part removed.
After the allotted time the cooled plastic part can be removed from the mold by the injection system. Once the mold is open a power tool is used to force the part out of the mold. Often times the mold release agent is sprayed onto the surfaces to help the part become ejected. After that part is removed, the mold will club itself shut again to prepare for the next series of molten plastic shots to be injected.
The entire process only takes between two seconds into minutes to complete all four stages. The injection unit and the clamping unit make up the entire injection molding machine along with the mold base and other tools. Plastic is not the only thing that can be used in the injection molding process. Most polymers can be used like thermoplastics, thermosets and elastomers. However, this is only the procedure for the plastic material, each material requires a different process.
There is of course, a lot more to be said about the injection molding process but this gives you a general overview to how the process works. As mentioned, there are so many different type of injection molding that can be done such a medical injection molding. Plastic is definitely the most common, but not the only one.