Injection molding is one of the common processes to produce many parts made of plastic and other materials. For the process of injection molding, the first phase is to prepare the mould. This phase requires you to collect plastic pellets so that you can melt them all together to prepare the mould. Now this mould should be free from any metal scrap.
This means that the mould should be made out of pure plastic pellets. Often what happens is that the pellets are not segregated properly and this leads to the addition of impurities in the pellets. This means that there are impurities in the final mould which leads to the development of the defective product.
Therefore if you want a solid final product then you have to make sure that you are doing well in filtering the pellets that make the mould. There are various industrial procedures such as industrial CT scanning that can be applied that will make sure that the various impurities are taken out of the mould that is to be made.
The next is the metering phase.
The metering phase can be monitored by varying the turns of the screw which is per minute. This will help for effective metering of the mould.
Also the back pressure will help in metering. The difference in time that is needed for the variation of the screw, will give an indication of how stable this phase is.
Next to keep in mind is the injection speed. This is the most crucial when filling up the cavity. Lower injection speeds will not help in filling of the die cavity completely. Also too high injection speed may lead to splattering at the sides of the die cavity which might lead to in effective molding.
Therefore there should be an optimum pressure at the nozzle as well as the pressure at the cavity so the mould will completely fill up the cavity without any problems. If the injection speed is varied the shear rate will change. When the injection speed is higher, a lower rate of viscosity is achieved.
Also if you increase the melt and mould temperatures, the rate of viscosity will lower down and so will the shear rate. Also the thicker your part is the longer the holding pressure of your part should be. You should optimize the height and the duration of applied holding pressure which should be based on the pressure curves of the cavity.
Once the injection phase is done with, the plastic mould will enter the cooling phase.
Logically, the hotter the injection temperature is the longer is the cooling phase. Also the thicker the part is the longer the cooling time it will have. A setting sheet is used to follow a particular procedure for a part.
This setting sheet is based on a successful part that has passed all inspections and does not have any defects. This will allow for rapid mass production which makes injection molding such a favored choice of molding in the market today.
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Published on Sep 26, 2011
Injection molding is one of the common processes to produce many parts made of plastic and other materials. For the process of injection mol...