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Why hot runner mold need test?
Jan 22, 2018

Most of the defects of the molded products are caused during the plasticization and injection molding stages, but sometimes they are also related to improper mold design. Possible factors include the number of cavities, the design of the cold / hot runner system, the type of injection port, the location and Size, and the structure of the product itself. Therefore, in order to avoid the product defects caused by the mold design, we need to analyze the mold design and process parameters when making the mold.


After obtaining the test result, the operator usually needs to evaluate the specific situation of the die so as to avoid adding unnecessary costs and time during the process of modifying the die. In most cases, this evaluation also includes the setting of the machine's process parameters. In other words, in order to make up for the lack of mold design, the operator may be inadvertently made incorrect settings. In this case, the production process of the equipment is not normal because the parameters required to produce the qualified product are set to a very small extent, and any slight deviation in the parameter setting may result in the quality of the final product being far beyond what is allowed Of the error range, and the resulting actual production costs are often much higher than the cost of pre-mold optimization.


The purpose of test mode is to find the optimum process parameters and mold design. In this way, even changes in materials, machine settings or the environment can ensure a stable and uninterrupted mass production environment, not just to get a good sample. this point is very important.


Test the basic steps


Procedure 1. Set the temperature of the drum.


It should be noted here that the initial barrel temperature setting must be based on the material supplier's recommendation. This is because different manufacturers, different brands of the same material may have considerable differences, and material suppliers tend to have their own material has a very deep research and understanding. Users can make basic settings based on their recommendations and then fine-tune them according to the specific production conditions.


In addition to this, it is also necessary to use a detector to measure the actual temperature of the melt. Because we set the barrel temperature often due to the environment, the temperature sensor type and location of different depth and other reasons, and does not guarantee 100% consistent with the melt temperature. Sometimes the actual temperature of the melt differs greatly from the setting temperature of the drum due to the presence of oil stains or other reasons. (Previously, we had an example where the difference in temperature between the two was as high as 30 ° C).


Step 2. Set the mold temperature.


Similarly, the initial mold temperature setting must also be based on the recommended values provided by the material supplier.


It should be noted that what we mean by the mold temperature is the temperature of the cavity surface, not the temperature shown on the mold temperature controller. In many cases, the temperature displayed on the mold temperature controller is not the same as the temperature on the cavity surface due to improper power selection of the environment and the mold temperature controller. Therefore, the temperature of the cavity surface must be measured and recorded before the formal test. At the same time, the mold cavity should also be measured at different locations to see the temperature of each point is balanced, and record the corresponding results in order to provide reference data for subsequent mold optimization.


Step 3. Based on experience, preliminarily set the amount of plasticizing, injection pressure limit, injection speed, cooling time and screw speed and other parameters, and appropriate optimization.


Step 4. Perform a filling test to find the transition point. The transition point is the point of transition from the injection phase to the dwell phase, which can be the screw position, fill time and fill pressure. This is one of the most important and basic parameters in the injection molding process. In the actual filling test, you need to follow the following points:


(1) During the test packing pressure and dwell time is usually set to zero;


(2) The product is generally filled to 90% ~ 98%, depending on the wall thickness and mold structure design;


(3) As the injection speed will affect the position of the pressure transfer point, so every time you change the injection speed, you must re-confirm the transfer point.


Through the filling test, the user can see the flow path of the material in the mold cavity, so as to determine where the mold is easily trapped, or where it needs to be improved.


Step 5. Find the injection pressure limit. In this process, attention should be paid to the relationship between injection pressure and injection speed. For hydraulic systems, pressure and speed are interrelated. Therefore, you can not set both parameters simultaneously to meet the required conditions.


The injection pressure set on the screen is the actual injection pressure limit, therefore, the injection pressure limit should always be set to be greater than the actual injection pressure. If the injection pressure is limited so low that the actual injection pressure approaches or exceeds the injection pressure limit, then the actual injection speed will automatically decrease due to power limitations, affecting the injection time and molding cycle.


Step 6. Find the optimal injection speed. Here refers to the injection speed, while filling time to meet the shortest possible, while filling pressure injection speed as small as possible. In this process, need to pay attention to the following points:


(1) Surface defects on most products, especially those near the gate, are caused by the speed of the injection.


(2) Multi-level injection is only used when one injection can not meet the process requirements, especially during the test mode.


(3) In the mold intact, rotary pressure point set correctly, and the injection speed is sufficient, the speed of the injection speed and the occurrence of flash is not directly related.


Step 7. Optimize dwell time.


Dwell time is also the gate of the condensation time. In general, the pour time of the gate can be determined by weighing method to obtain different dwell time, and the optimal dwell time is the time when the product weight reaches the maximum.


Step 8. Optimize other parameters such as packing pressure and clamping force.


Finally, it is important to emphasize that the purpose and focus of trial runs is to optimize molds and processes to meet the requirements of mass production, not just test good product samples.


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