Mold trial method

Before injection molding a new mold, or when the machine is replaced by another mold for production, mold trial is an essential part. The good or bad result of the mold trial will directly affect the smoothness of the subsequent production in the factory.

Therefore, it is necessary to follow reasonable operation steps and record the useful technical parameters during the mold trial for the mass production of products.

Precautions before mold trial

1. Know the information about the mold

It is better to get the design drawing of the injection mold, analyze it in detail, and get the mold technician to participate in the mold trial work.

2. Check the mechanical action on the working table

Pay attention to whether there are scratches, missing parts and loosening phenomena, whether the mold to slide movement is true, whether there are leaks in the water and gas pipe joints, and if there is a limit to the opening range of the mold, it 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. When the mold is determined to be suitable for each action, we should choose a suitable injection molding machine, and we should pay attention to the following when choosing.

(1) What is the maximum injection volume of the injection molding machine table.

(2) Whether the inner distance of the tie bar can accommodate the mold.

(3) Whether the maximum moving stroke of the movable template meets the requirements.

(4) Whether other related tools and accessories for mold testing are ready.

After everything is confirmed, the next step is to hang the injection mold. When hanging, it should be noted that the hook should not be removed before locking all the clamping plates and opening the mold, so as not to loosen or break the clamping plates and cause the mold to fall.

After the mold is installed, the mechanical action of each part of the mold should be carefully checked, such as the slide plate, the ejector pin, the withdrawal structure and the restriction switch, etc., to ensure that the action is correct, and to pay attention to whether the injection nozzle and the inlet 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, and in the manual and low-speed mold closing action, pay attention to see and hear whether there is any unsmooth action and strange sounds, or other phenomena.

The process of lifting the injection mold is relatively simple, but the main thing that needs careful attention is that it is difficult to adjust the center of the mold gate and injection nozzle, usually you can use test paper to adjust the center.

4. Increase the mold temperature

According to the performance of the raw materials used in the products 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 chatter.

5. If there is no experimental plan implemented in the factory, it is recommended that only one condition be adjusted at a time when adjusting the test mold conditions in order to distinguish the impact of a single condition change on the 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 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. After the test mold, wait for the product to be stable, that is, the second processing of the mold.

After the slow closing, adjust the clamping pressure and move several times to check whether there is uneven closing pressure and other phenomena, so as to avoid burr and mold deformation of products.

After the above steps are checked, turn down the closing speed and pressure, and set the safety lever and ejecting stroke, then adjust the normal closing speed and closing speed.

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 of the mold opening.

This is because during the mold loading period, the entire mold opening stroke is longer for the high speed action than for the low speed. In the plastic machine, mechanical ejector rod must also be adjusted to the role of the full-speed mold opening action after the ejector plate or peel plate to avoid deformation by the force.

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

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

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

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

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

To prevent products from short shot, fracture, deformation, burr and even injury to the injection mold. If the cycle time is too short, the ejector pin will pierce the product or peel the ring to squeeze the product, which may take you two or three hours to remove the product.

If the cycle time is too long, the weak part of the core may break due to the shrinkage of the rubber. Of course, you can’t anticipate all the possible problems that may occur during a mold test, but careful consideration and timely action can help you avoid serious and expensive losses.

Main steps of mold trial

In order to avoid wasting time and trouble during mass production, it is necessary to be patient in adjusting and controlling various processing conditions, and 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 that the plastic in the barrel is correct and that it is baked according to the regulations (test molds and production are likely to yield different results if different materials are used).

2. Make sure the material tube is cleaned thoroughly to prevent poorly solved plastic or miscellaneous materials from being shot into the mold. Because the poorly solved rubber and miscellaneous materials may jam the mold. Check whether the temperature of the material tube and the temperature of the injection mold are suitable for the material to be processed.

3. Adjust the pressure and injection volume to produce products with satisfactory appearance. However, it is important not to run rough edges, especially when there are still some mold cavities where the product is not fully 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 injection mold conditions stabilize, which may take more than 30 minutes for a medium-sized machine. You can use this time to check the possible problems of the product.

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

6. Reasonable adjustment to reduce the total processing cycle.

7. Run the new conditions for at least 30 minutes to stabilize, and then produce at least one dozen consecutive full mold samples with the date and quantity marked on the container and placed separately by mold cavity in order to test the stability of the operation and to derive reasonable control tolerances (especially valuable for multi-cavity molds).

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

9. Compare the dimensions of each sample with those of the mold, paying attention.

(1) Whether the dimensions of the product are stable.

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

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

If the dimensions of the product are no longer changing and the processing conditions are normal, observe if the quality of the product in each die cavity is acceptable and the dimensions are within the allowable tolerances. Note down the number of the injection mold cavities that are continuously measured or larger or smaller than the average, in order to check whether the mold size is correct.

Record the parameters obtained during the mold trial

Record and analyze the data for the purpose of modifying the mold and production conditions, and as a reference for future mass production.

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

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

3. If the mold 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 mold cavities are filling slowly.

4. According to the fit situation of each mold cavity or mold core displacement, make individual corrections, and maybe try to adjust the mold filling rate and mold temperature again to improve the uniformity.

5. Check and modify the malfunction of the injection molding machine, such as the oil pump, oil valve, temperature controller, etc., will cause the processing conditions to change, even if the most perfect mold can not be in poor maintenance of the machine to play a good efficiency.

After reviewing all the recorded values, keep a set of samples so that you can check and compare the corrected samples for improvement.

Keep all the records of the sample inspection during the mold trial, including various pressures of the processing cycle, melt and injection mold temperatures, tube temperatures, injection action times, screw charging periods, etc.

In short, keep all the data that will help to establish the same processing conditions in the future so as to obtain products that meet quality standards.

At present, factories often ignore the mold temperature during the mold test, and in the short time of injection mold test and future mass production, the mold temperature is the most difficult to grasp, and the incorrect mold temperature is enough to affect the size of the sample, light, shrinkage, flow, and under-production, etc. If we do not use the mold temperature controller to grasp, there may be difficulties in future mass production.