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In this increasingly competitive business society, improving production efficiency is a matter of great concern. Through this article, you will learn how to improve the efficiency of the injection molding machine, as well as a comprehensive understanding of the working principle and injection molding knowledge of the injection molding machine.
Injection cycle The injection cycle of a hydraulically driven injection molding machine is from the start of clamping to the next clamping.
The clamping is generally divided into four sections: rapid clamping, slow clamping, low pressure clamping and high pressure clamping. The injection begins after the high-pressure clamping is completed and is also divided into multiple sections. The molten plastic fills the cavity during injection. When the cavity is filled, the pressure rises, so the end of the injection is also called the packing phase. When the control is not suitable, the finished product will produce burrs.
The pressure holding begins after the injection is completed. In fact, the cooling starts from the filling of the cavity, that is, from the pressure holding. When the mold cools, the finished product shrinks due to cold. The function of holding pressure is to fill the shrinkage formed by shrinkage through the cold-flow passage which has not been solidified, and the holding pressure is generally lower than the injection pressure, so that the finished product is full (no dent) when demolding.
When the cold runner is solidified, it is meaningless to maintain the pressure again, and the pressure 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), which is divided by time. The total dwell time is determined by the weight of the finished product or from the finished product without dents. Starting from a short dwell time, a little dwell time is added for each injection, until the weight of the finished product no longer increases or the dent is acceptable, the dwell time does not need to be increased.
The "cooling time" parameter placed 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 has begun as soon as the cavity is filled with plastic. The purpose of "cooling time" is to continue to cool and solidify the finished product, and it will not be deformed by ejection when it is ejected. It should be said that the "cooling time" is derived from the test.
At the beginning of the "cooling time", the feeding is carried out simultaneously. The "Cooling Time" is displayed longer than the feeding time. It is also possible that the feeding time is longer than the "cooling time", in other words, the plasticizing ability of the screw is insufficient to make a bottleneck. Therefore, increasing the plasticizing capacity is the way to shorten the cycle time in this case, and the goal is to return to the short feeding time of Figure 1.
“Cooling time or “Opening the mold after the feeding is completed, the finished product is ejected one or more times. After the top retreat, the mold is closed again, and the next cycle begins.
The recently designed toggle-type injection molding machine has a regenerative clamping oil path for higher clamping speed. It is suitable for use under the premise that the mold is not subject to high impact.
The high-pressure clamping mode uses the lowest clamping force that can produce no burrs on the finished product, which can shorten the time required for the high-pressure clamping section. Moreover, the molds, the drawbars of the injection molding machine, the toggles and the formwork will also prolong their life due to the low clamping force. If a mold is sufficient to use a 50t clamping force, then a 51t clamping force is not required, even though your injection molding machine has a higher clamping force.
The highest injection speed can be used in the case where the finished product does not generate bubbles or does not generate black spots due to charred plastic. Especially for thick-wall injection molding, a large amount of air in the cavity is filled with molten plastic. The injection speed is too high, so that the air in the cavity can not be discharged outside the mold, resulting in bubbles.
Using the lowest injection pressure can correspondingly reduce the required clamping force (expansion force), while using the lowest barrel temperature can reduce the "cooling time".
The holding pressure can be set to the shortest dwell time from the finished product weight or acceptable dents. There are many thin-walled products that do not need to hold pressure, because the inner layer of the finished product is basically solidified immediately after the injection.
Cooling time I heard a saying: the mold is a heat exchanger. It is true that the mold continuously removes the molten heat through the cold water channel, and the well-designed mold can improve the efficiency of heat exchange.
However, ice water cooling can reduce the "cooling time" when allowed. If the ice water is cooled to form a mold condensation, the dry blower and the sealed mold clamping device can reduce the dew point and prevent condensation.
If the plasticizing capacity of the feeding material is insufficient to make a bottleneck, the following processing can be performed in the screw design and parameter adjustment:
1. The barrier screw increases plasticizing ability.
2. Large diameter (C) screws increase plasticizing power.
3. Increasing the groove depth of the screw increases the plasticizing ability.
4. Increasing the speed of the screw increases the plasticizing ability (some shear-sensitive plastics such as PVC, PET, etc. cannot be used).
5. Reduce back pressure as much as possible, otherwise it will increase the plasticizing speed.
6. The oil pressure seal is used to plasticize when the mold is opened and closed.
7. The pre-plasticizer design enables the screw to be plasticized in the cycle except for the injection and holding time.
8. The pressure maintaining device is used to make the screw plasticized in the pressure maintaining section.
Methods 1-5 attempt to turn the situation of Figure 3 into the case of Figure 1.
Methods 6-7 use parallel action, and the feed is driven by an independent oil circuit or circuit.
Method 8 is best used for thick-walled injection molding. To avoid dents, thick-walled holding time can be lengthy.
The time of the retraction before and after feeding should be replaced by a spring nozzle or a hydraulic seal to save the reversing action.
The mold opening is opened at the highest speed without tearing the finished product and without generating a large opening sound. Some exquisite injection molding machines have decompression equipment before opening the mold, and even high-speed mold opening will not produce a sound. In order to achieve accurate position of the mold at high speed mold opening, brake valve or closed loop control is available.
The ejector can be pneumatically ejected on a small injection molding machine with a small top force, which is higher than the hydraulic pressure. Electric ejector is faster than pneumatic ejector. The mold can be designed to be ejected by the mold opening action, instead of using the ejection device on the injection molding machine, but this method can only be ejected once, which is the simplest method of ejecting the side of the mold.
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