How To Make A Good Plastic Mold Trail


Before the injection molding of a new mold or when the […]

Before the injection molding of a new mold or when the machine is replaced with other molds, mold trial is an essential part. The quality of the test results directly affects whether the subsequent production of the factory is smooth. Therefore, reasonable operation steps must be followed and the useful technical parameters recorded during the mold trial process to facilitate the mass production of products.


1. Precautions before mold trial

(1) Understand the relevant information on the mold

It is best to obtain the design drawing of the mold, analyze it in detail, and invite the mold technician to participate in the trial work.


(2) First check the mechanical coordination action on the workbench

Pay attention to whether there are scratches, missing parts, looseness, etc., whether the mold slide is correct, whether there is leakage in the water channel and air pipe joints, and if there is a limit to the mold opening The words should also be marked on the mold. If the above actions can be done before hanging the mold, the waste of man-hours caused by the removal of the mold after the problem is found when the mold is hanging can be avoided.


(3) When it is determined that the various parts of the mold are suitable for action, it is necessary to select a suitable test mold injection machine, and pay attention to

*What is the maximum injection volume of the injection molding machine?

*Whether the inner distance of the tie rod can fit the mold;

*Whether the maximum moving stroke of the movable template meets the requirements;

*Whether other relevant tools and accessories for mold trial are ready.


After everything is confirmed that there is no problem, the next step is to hang the mold. When hanging, be careful not to remove the hook before locking all the clamping templates and opening the mold, so as to prevent the clamping template from loosening or breaking and causing the mold to fall. After the mold is installed, carefully check the mechanical movements of each part of the mold, such as the movement of the sliding plate, thimble, withdrawal structure, and limit switch. And pay attention to whether the injection nozzle is aligned with the inlet.


The next step is to pay attention to the mold clamping action. At this time, the mold closing pressure should be lowered. In the manual and low-speed mold clamping action, pay attention to see and hear whether there are any unsmooth movements and abnormal noises. The process of hoisting the mold is actually relatively simple. The main thing that needs careful attention is that it is difficult to align the center of the mold gate and nozzle. Usually, the center can be adjusted by means of a test paper.


(4) Increase the mold temperature

According to the properties of the raw materials used in the finished product and the size of the mold, select an appropriate mold temperature control machine to increase the temperature of the mold to the temperature required for production. After the mold temperature rises, the movement of each part must be checked again, because the steel may cause a mold jam phenomenon after thermal expansion, so pay attention to the sliding of each part to avoid strain and vibration.


(5) If the experiment plan rule is not implemented in the factory, it is recommended to adjust only one condition at a time when adjusting the test conditions, so as to distinguish the impact of a single condition change on the finished product.


(6) According to the different raw materials, do moderate baking of the original used.


(7) Try to use the same raw materials as much as possible for mass production in the future.


(8) Do not try the mold completely with inferior materials. If there is a color requirement, you can arrange the color test together.


(9) Problems such as internal stress often affect secondary processing. After the mold is tested, the finished product should be stabilized, and then the secondary processing mold should be applied. After the slow closing, the closing pressure should be adjusted and the action should be performed several times to check for the existence of Uneven clamping pressure to avoid burrs and mold deformation in the finished product.


After checking the above steps, lower the mold closing speed and pressure, and set the safety hook and ejection stroke, and then adjust the normal mold closing and closing speed.

If the maximum stroke limit switch is involved, the mold opening stroke should be adjusted slightly shorter, and the high-speed mold opening action should be cut off before the maximum stroke of the mold opening. This is because the high-speed stroke is longer than the low-speed stroke in the entire mold opening stroke during mold loading. On the plastic machine, the mechanical ejection must also be adjusted after the full-speed mold opening action to prevent the ejector plate or peeling plate from being deformed by force.

Please check the following items before making the first mold injection:

*Whether the feeding stroke is too long or insufficient;

*Whether the pressure is too high or too low;

*Whether the filling speed is too fast or too slow;

*Whether the processing cycle is too long or too short. To prevent the finished product from the short shot, fracture, deformation, burrs, and even damage to the mold.

If the processing cycle is too short, the thimble will penetrate the finished product or squeeze the finished product by peeling the ring. This type of situation may cost people two or three hours to take out the finished product. If the processing cycle is too long, the weak parts of the mold core may be broken due to the shrinkage of the rubber. Of course, it is impossible to predict all the problems that may occur during the mold trial process, but serious losses can be avoided by taking full consideration in advance.


2. The main steps of the tryout

(1) Check whether the plastic raw materials in the barrel are correct and whether they are baked in accordance with the regulations (if different raw materials are used for trial and production, different results may be obtained).


(2) The material pipe should be cleaned thoroughly to prevent inferior rubber or miscellaneous materials from being injected into the mold, because inferior rubber and miscellaneous materials may jam the mold. Check whether the temperature of the material tube and the temperature of the mold are suitable for processing the raw materials.


(3) Adjust the pressure and injection volume to produce a finished product with a satisfactory appearance, but do not run off the burrs, especially when some mold cavity finished products are not completely solidified, you should think about it before adjusting various control conditions, because A slight change in the mold filling rate may cause a large change in the mold filling.


(4) Wait patiently until the conditions of the machine and the mold stabilize, even a medium-sized machine may have to wait for more than 30 minutes. You can use this time to see possible problems with the finished product.


(5) The advancing time of the screw should not be shorter than the solidification time of the gate plastic, otherwise, the weight of the finished product will be reduced and the performance of the finished product will be impaired. When the mold is heated, the advancing time of the screw must be appropriately extended to compact the finished product.


(6) Reasonably reduce the total processing cycle.


(7) Run the newly adjusted conditions for at least 30 minutes until they are stable, and then continuously produce at least a dozen full mold samples, mark the date and quantity on the container, and place them according to the mold cavity to test the stability and stability of the operation. Derive reasonable control tolerances (especially valuable for multi-cavity molds).


(8) Measure and record the important dimensions of continuous samples (we should wait for the samples to cool to room temperature before measuring).


(9) Compare the measured size of each mold sample. Note:

*Whether the product size is stable;

*Whether some dimensions have a tendency to increase or decrease, indicating that the machining conditions are still changing, such as poor temperature control or oil pressure control;

*Whether the size change is within the tolerance range.


(10) If the size of the finished product does not change much and the processing conditions are normal, it is necessary to observe whether the quality of the finished product of each cavity is acceptable and whether its size can be within the allowable tolerance. Note down the number of cavities that are continuous or larger or smaller than the average to check whether the size of the mold is correct.

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