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  • What are the precautions for injection molding test molds?

What are the precautions for injection molding test molds?

I. Preface

When we receive a new pair of molds need to prove the mold, we are always eager to try out a result earlier and pray for a smooth process to avoid wasting time and causing trouble.

But here we must remind two points: First. Mold designers and manufacturing technicians can sometimes make mistakes, and if we are not vigilant when trying out a mold, we may incur big damage due to small mistakes. Secondly. The result of the mold trial is to ensure smooth production in the future. If we don't follow reasonable steps and keep proper records during the mold trial, we can't guarantee the smooth operation of mass production. We emphasize that "if the mold works well, it will quickly increase the profit recovery, otherwise the cost loss will be more than the cost of the mold itself".

II. Precautions before mold test

1. Know the information about the mold.

It is best to get the design of the mold surface, detailed analysis, and about the mold technician to participate in the mold test work. 2.

2. Check the mechanical action on the working table first.

To pay attention to whether there are scratches, missing parts, and looseness, whether the mold to the slide action is true, water and gas pipe joints have no leakage, the mold opening range if there is a limit should also be marked on the mold. If the above actions can be done before hanging the mold, it can avoid the waste of time when hanging the mold and then disassembling the mold.

3. After determining the appropriate action of each part of the mold, we should choose a suitable test mold injection machine, in the selection should pay attention to

(a) Injection capacity

(b) Width of the guide bar

(c) The maximum opening range

(d) Accessories

(d) whether the accessories are complete, etc. The next step is to hang the mold after everything is confirmed. When hanging, care should be taken not to take off the hanging before locking all the clamping plates and opening the mold, so that the clamping plates will not loosen or break and the mold will fall.

After the mold is installed, we should carefully check the mechanical action of each part of the mold, such as the slide plate. Thimble. The action of the ejector structure and the restriction switch are sure. And pay attention to whether the injection nozzle and the feed port are aligned. The next step is to pay attention to the mold closing action, at this time, the mold closing pressure should be turned down, in the manual and low-speed mold closing action, pay attention to see and hear whether there is any smooth action, and strange sound and other phenomena.

4. Increase the mold temperature.

According to the performance of the raw materials used in the finished product and the size of the mold, choose the appropriate mold temperature control machine to raise the temperature of the mold to the required temperature for production.

After the mold temperature is raised, the action of each part should be checked again, because the steel may cause jamming after thermal expansion, so the sliding of each part should be paid attention to avoid strain and chattering.

5. If there is no experimental plan implemented in the factory, we suggest that only one condition should be adjusted at a time when adjusting the test mold conditions in order to distinguish the impact of a single condition change on the finished product.

6. Depending on the raw materials, the raw materials used should be baked appropriately.

7. Use the same raw material as much as possible for the trial mold and future mass production.

8. Don't try the mold completely with inferior material, if there is a demand for color, you can arrange the color test together.

9. Internal stress and other problems often affect the secondary processing, should be in the mold after the test to be stable after the finished product that is to be the secondary processing mold in the slow closing, to adjust the mold pressure, and action several times to see if there is uneven closing pressure and other phenomena, so as to avoid the finished product generated burr and mold deformation.

After the above steps are checked, the closing speed and closing pressure will be lowered, the safety lever and ejector stroke will be set, and then the normal closing speed and closing speed will be adjusted. If the maximum stroke limit switch is involved, adjust the mold opening stroke slightly shorter and cut off the high-speed mold opening action before the maximum stroke. This is because the high-speed action stroke is longer than the low-speed one during the whole opening stroke of the mold loading. In the plastic machine, the mechanical ejector rod must also be adjusted after the full speed mold opening action to avoid deformation of the ejector plate or peel plate under pressure.

Before making the first mold injection, please check the following items again.

(a) Whether the filling stroke is too long or insufficient.

(b) Whether the pressure is too high or too low.

(c) Whether the mold filling speed is too fast or too slow.

(d) Whether the processing cycle is too long or too short.

To prevent the short shot. Breakage. Deformation. Burrs or even damage to the mold.

If the cycle time is too short, the ejector pin will go through the finished product or the stripped ring will squeeze the finished product. This can cost you two or three hours to remove the finished product.

If the cycle time is too long, the weak part of the die may break due to the shrinkage of the rubber.

Of course, you cannot anticipate all the problems that may occur during a mold trial, but well-thought-out and timely measures can help you avoid serious and costly losses.

III. Main steps of mold trial

In order to avoid unnecessary waste of time and trouble during mass production, it is indeed necessary to be patient in adjusting and controlling the various processing conditions, to find out the best temperature and pressure conditions, and to develop a standard mold trial procedure that can be used to establish a daily working method.

1. Check whether the plastic material in the barrel is correct and whether it is baked according to the regulations (test mold and production are likely to yield different results if different materials are used).

2. Make sure the material tube is cleaned thoroughly to prevent bad plastic or miscellaneous materials from being shot into the mold, because bad plastic and miscellaneous materials may jam the mold*. Test the temperature of the material tube and the temperature of the mold to see if they are suitable for the material being processed.

3. Adjust the pressure and shot volume to produce a satisfactory appearance of the finished product, but do not run rough edges especially when there are still some mold cavities where the finished product is not completely solidified, think before adjusting the various control conditions because a slight change in the mold filling rate may cause a large change in the mold filling.

4. Be patient and wait until the machine and mold conditions stabilize, even for medium-sized machines it may take more than 30 minutes. You can use this time to check the finished product for possible problems.

5. The screw advance time should not be shorter than the gate plastic solidification time, otherwise the weight of the finished product will be reduced and the performance of the finished product will be damaged. And when the mold is heated, the screw advance time should be extended to compact the finished product.

6. Reasonable adjustment to reduce the total processing cycle.

7. Run the new condition for at least 30 minutes to stabilize, and then produce at least one dozen full mold samples continuously, marking the date and quantity on the container. Place them separately by a cavity in order to test the stability of their operation and to derive reasonable control tolerances. (Especially valuable for multi-cavity molds).

8. Measure and record the important dimensions of successive samples (should be measured when the sample is cooled to room temperature).

9. Compare the dimensions of each mold sample, noting.

(a) Whether the dimensions are stable.

(b) Whether there is a tendency for some dimensions to increase or decrease while the machine processing conditions are still changing, such as poor temperature control or oil pressure control.

(c) Whether the dimensional changes are within the tolerance range.

If the finished product does not vary much in size and the processing conditions are normal, observe if the quality of the finished product is acceptable and the dimensions are within tolerances for each die cavity. Note down the number of cavities that are continuously larger or smaller than the average value in order to check if the dimensions of the mold are correct. Record and analyze the data for modifying the mold and production conditions, and for future reference in mass production.

IV. Problems that should be noted during the mold test

1. Make the processing running time longer to stabilize the melt temperature and hydraulic oil temperature.

2. Adjust the machine conditions according to the oversize or undersize of all finished products. If the shrinkage rate is too large and the finished product seems to be undershot, it can also be used as a reference to increase the gate size.

If the die cavity and gate size are still correct, then try to change the machine conditions, such as mold filling rate, mold temperature, and pressure of each department, and check if some die cavities are filling slowly.

4. Depending on the fit of each die cavity or die core displacement, correct each one of them, and maybe try to adjust the filling rate and mold temperature to improve the uniformity.

5. Check and modify the malfunction of the injection machine, such as the oil pump. Oil valve. Even a perfect mold cannot work well in a poorly maintained machine.

 After reviewing all the recorded values, keep a set of samples to check and compare whether the corrected samples are improved or not.

V. Important Notes

Keep a record of all the samples tested during the mold trial, including the various pressures of the processing cycle. Melt and mold temperature. Tube temperature. Injection action time. In short, all data should be kept that will help to establish the same processing conditions in the future in order to obtain products that meet quality standards.

At present, the mold temperature is often neglected during mold trials, and it is not easy to control the mold temperature during short mold trials and future mass production, and an incorrect mold temperature is enough to affect the size of the sample. Brightness. Shrinkage. If we don't use the mold temperature controller, it may be difficult to grasp the mold temperature in future mass production.
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