In the case of increasingly competitive injection molding processing, improving production efficiency is a matter of great concern. Here are some ways to improve your injection molding cycle. The injection molding cycle of a hydraulically driven injection molding machine refers to the start of mold closing to the next mold closing. Clamping is generally divided into four sections: fast clamping, slow clamping, low pressure mold protection and high pressure mold clamping.
The injection starts after the high-pressure mold clamping is completed, and it is also divided into multiple stages. Molten plastic fills the cavity during injection.
When the mold cavity is filled, the pressure rises suddenly, and the end of the injection is not controlled properly, the finished product will produce burrs. Packing begins after the injection is complete. In fact, the cooling starts after the cavity is filled, that is, from the pressure holding.
As the mold cools, the finished product shrinks. The function of holding pressure is to pass through the cold runner that has not yet solidified, and fill the depression formed by shrinkage at a holding pressure that is generally lower than the injection pressure, so that the finished product will be full (without dents) when it is demolded.
When the cold runner solidifies, the pressure holding can be terminated. The holding pressure can be divided into multiple sections, and the holding pressure of each section is different (generally decreasing step by step), divided by time. The total dwell time is set by the finished product weight or indentation. Start adjusting from a short holding time, and increase the holding time for each injection until the weight of the finished product no longer increases or the production dent is acceptable, and the holding time does not need to be increased.
There are many thin-walled products that do not need to hold pressure, because the inner layer of the finished product basically solidifies immediately after injection.
The "cooling time" parameter set on the injection molding machine is a period of time from the completion of the pressure holding to the opening of the mold, but the cooling starts as early as the cavity is filled with plastic. The purpose of "cooling time" is to make the finished product continue to cool and solidify, and it will not be deformed due to ejection when it is ejected. It should be said that "cooling time" is derived from experiments. At the beginning of the "cooling time", the stockpiling takes place simultaneously.
The "cooling time" is longer than the storage time, and it is also possible that the storage time is longer than the "cooling time". If the storage time is longer than the "cooling time", it indicates that the plasticizing capacity of the screw is insufficient, which affects the production cycle. Therefore, increasing the plasticizing capacity is the way to shorten the cycle time in this case, and the goal is to shorten the storage time.
The finished product is ejected one or more times, the mold is closed after the thimble is retracted, and the next cycle starts immediately. The newly designed toggle injection molding machine has a regenerative mold clamping oil circuit (differential mold clamping function) to strive for higher Mold clamping speed is suitable under the premise that the mold is not subject to high impact.
High-pressure mold clamping adopts the lowest clamping force that can prevent the finished product from producing burrs, which can shorten the time required for high-pressure mold clamping.
Molds, tie rods, toggles and templates of injection molding machines will also prolong their life due to the use of low clamping forces. In the injection section, a high injection rate can be used without defects such as air bubbles or burnt in the finished product. Using the lowest injection pressure reduces the required clamping force (swelling force) accordingly, while using the lowest barrel temperature reduces the "cooling time".
The cooling time is related to the heat exchange efficiency of the mold, and designing a suitable mold can improve the heat exchange efficiency.
However, ice water cooling can shorten the "cooling time" when allowed. Ice water cooling makes the mold condense, and the dry fan and sealed mold clamping device can reduce the dew point and prevent condensation. If the plasticizing ability is not enough to affect the production cycle, the following treatment can be done in the screw design and parameter adjustment: The barrier screw can increase the plasticizing ability.
Large diameter screw increases plasticizing capacity. Enlarging the groove depth of the screw can increase the plasticizing capacity. Increasing the screw speed can increase the plasticizing capacity (this method cannot be used for certain shear-sensitive plastics such as PVC, PET, etc.).
Keeping the back pressure as low as possible increases the plasticizing rate. The hydraulic sealing nozzle is used to make the plasticization possible when the mold is opened and closed.
The design of the pre-plasticizer enables the screw to be plasticized during the cycle except for the injection and holding time. The pressure-holding device is adopted to make the screw plasticized in the pressure-holding section.
The rewinding (shooting back) before and after feeding is time-consuming. It should be replaced by a spring nozzle or an oil pressure sealing nozzle to save the rewinding action.
Mold opening: Open the mold at the highest speed without tearing the finished product and without producing loud mold opening noise. Some injection molding machines have decompression equipment before the mold is opened, and there will be no noise when the mold is opened at high speed.
In order to achieve accurate mold stop position during high-speed mold opening, brake valve or closed-loop control can be used. On small injection molding machines with small ejection force, pneumatic ejection can be used, which has a higher speed than hydraulic ejection. Electric ejection is faster than pneumatic ejection. Using independent oil circuit, air circuit or electric circuit control, it can realize the ejection function while opening the mold for multiple ejections.
The multiple ejection of some finished products can use the vibration ejection of the injection molding machine. The thimble does not need to be fully retracted every time to shorten the time for multiple ejections. The last push back can start at the same time as the mold clamping. Because the stroke of the thimble is relatively short, the thimble will always be fully retracted before locking the mold.
