Problems that need attention in injection molding

Before injection molding of a new mold or when the machine is replaced with other molds, trial molding is an essential part. The quality of the mold trial results will directly affect the smoothness of subsequent production in the factory. Therefore, reasonable operating steps must be followed during the mold trial process and useful technical parameters must be recorded during the mold trial process to facilitate mass production of the product.

Things to note before mold trial

1. Understand the relevant information of the mold:

It is best to obtain the design drawings of the mold, analyze them in detail, and ask a mold technician to participate in the mold trial work.

2. First check its mechanical coordination on the workbench:

Pay attention to whether there are scratches, missing parts, loose parts, etc., whether the movement of the mold to the sliding plate is correct, whether there are leaks in the water pipe and air pipe joints, and if there are any restrictions on the opening 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 man-hours caused by discovering problems when hanging the mold and then disassembling the mold.

3. After confirming that each part of the mold is functioning properly, it is necessary to select a suitable test mold injection machine. When selecting, pay attention to:

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

Is the inner distance of the tie rod placed in the lower mold?

Does the maximum moving range of the activity template meet the requirements?

Are other related tools and accessories for mold trial ready?

After everything is confirmed to be no problem, the next step is to hang the mold. When hanging, be careful not to remove the hanging hooks before locking all clamping templates and opening the mold to avoid loosening or breaking of the clamping templates and causing the mold to fall.

After the mold is installed, you should carefully check the mechanical movements of each part of the mold, such as the slide plate, ejector pin, tooth extraction structure and limit switch, etc., 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 lowered. During the manual and low-speed mold closing action, pay attention to see and listen for any irregularities or abnormal sounds. The process of hoisting the mold is actually relatively simple. The main thing that requires careful attention is that it is difficult to adjust the center of the mold gate and the nozzle. You can usually use test paper to adjust the center.

4. Increase mold temperature:

According to the performance of the raw materials used in the finished product and the size of the mold, an appropriate mold temperature controller is selected to increase the temperature of the mold to the temperature required for production. After the mold temperature increases, the movement of each part must be checked again, because the thermal expansion of the steel may cause the mold to jam, so attention must be paid to the sliding of each part to avoid strain and vibration.

5. If the experimental plan rule is not implemented in the factory, we recommend that only one condition be adjusted at a time when adjusting the mold trial conditions in order to distinguish the impact of a single condition change on the finished product.

6. Depending on the raw materials, roast the raw materials used appropriately.

7. Use the same raw materials as much as possible for trial molds and future mass production.

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

9. Problems such as internal stress often affect secondary processing. Secondary processing should be carried out after the mold trial and after the finished product is stable. After closing the mold slowly, adjust the mold closing pressure and operate it several times to check whether it is correct. Uneven molding pressure will prevent burrs and mold deformation in the finished product.

After checking the above steps, lower the mold closing speed and mold closing pressure, set the safety buckle and ejection stroke, and then adjust the normal mold closing speed and mold closing speed. If the limit switch of the maximum stroke 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 mold opening stroke.

This is because during the entire mold opening stroke during mold loading, the high-speed action stroke is longer than the low-speed one. The mechanical ejector rod on the plastic machine must also be adjusted to function after the full-speed mold opening action to prevent the ejector plate or peeling plate from being deformed due to 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.

Is the mold filling speed too fast or too slow?

Whether the processing cycle is too long or too short.

To prevent short shots, breakage, deformation, burrs and even damage to the mold in the finished product. If the processing cycle is too short, the ejector pin will penetrate the finished product or the ring will be peeled off and the finished product will be damaged. This type of situation can take you two to three hours to get the finished product out. If the processing cycle is too long, the weak parts of the mold core may be broken due to shrinkage of the rubber material. Of course, it is impossible to avoid all problems that may occur during the mold trial process, but sufficient consideration and timely measures in advance can help you avoid serious and expensive losses.

Main steps of mold trial

In order to avoid unnecessary waste of time and trouble during mass production, it is indeed necessary to have patience to adjust and control various processing conditions, find the best temperature and pressure conditions, and develop standard mold trial procedures that can be used Establish daily working methods.

1. Check whether the plastic material in the barrel is correct and whether it has been baked according to regulations (if different raw materials are used in trial molding and production, different results are likely to be obtained).

2. Be sure to clean the material tube thoroughly to prevent improperly decomposed rubber or impurities from being injected into the mold, as inferior decomposed rubber and impurities may jam the mold. Check whether the temperature of the material tube and the temperature of the mold are suitable for the raw materials being processed.

3. Adjust the pressure and injection volume in order to produce a finished product with a satisfactory appearance. However, burrs should not be allowed. Especially when some mold cavity finished products have not been completely solidified, you should think about it before adjusting various control conditions because the mold is filled. A slight change in the rate may cause significant changes in mold filling.

4. Be patient and wait until the conditions of the machine and mold stabilize. Even medium-sized machines may have to wait for more than 30 minutes. Use this time to review possible problems with the finished product.

5. The screw advancement time cannot 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 compromised. And when the mold is heated, the screw advancement time also needs to be lengthened to compact the finished product.

6. Make reasonable adjustments to 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 containers, and place them separately according to the mold cavities to test the stability of their actual operation. and derive reasonable control tolerances. (Especially valuable for multi-cavity molds).

8. Measure consecutive samples and record their important dimensions (the samples should be cooled to room temperature before measuring).

9. Compare the measured dimensions of each mold sample. Note:

Is the size of the product stable?

Whether certain dimensions tend to increase or decrease indicates that the machining conditions are still changing, such as poor temperature control or oil pressure control.

Whether the change in dimensions is within the tolerance range.

10. If the dimensions of the finished product do not change much and the processing conditions are normal, it is necessary to observe whether the quality of the finished product in each mold cavity is acceptable and the dimensions are within the allowable tolerance. Record the mold cavity numbers that are continuously larger or smaller than the average value to check whether the size of the mold is correct.

Record the parameters obtained during the mold trial process

Record and analyze data to meet the needs of modifying molds and production conditions, and as a reference for future mass production.

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

2. Adjust the machine conditions according to whether the size of all finished products is too large or too small. If the shrinkage rate is too large and the finished product appears to have insufficient injection material, you can also increase the gate size for reference.

3. If the size of each mold cavity is too large or too small, correct it. If the size of the mold cavity and door is still correct, then you should try to change the machine conditions, such as mold filling rate, mold temperature and pressure of each part, etc., and check some molds. Whether the cavity filling is slow.

4. According to the matching situation of the finished mold cavity or the displacement of the mold core, make individual corrections. You may also try to adjust the mold filling rate and mold temperature to improve the uniformity.

5. Check and correct the faults of the injection machine, such as defects in the oil pump, oil valve, temperature controller, etc., which will cause changes in processing conditions. Even the most perfect mold cannot perform well on a poorly maintained machine. After reviewing all recorded values, retain a set of samples for proofreading and comparison of any improvements in the corrected samples.

Properly keep all records of sample inspection during the mold trial process, including various pressures during the processing cycle, melt and mold temperature, material tube temperature, injection action time, screw feeding period, etc. In short, all records that will be helpful in the future should be kept. Data that can be used to successfully establish the same processing conditions can be used to obtain products that meet quality standards.

At present, the mold temperature is often ignored during mold testing in factories. The mold temperature is most difficult to grasp during short-term mold testing and future mass production. Incorrect mold temperature can affect the size, brightness, shrinkage, flow lines, and lack of material of the sample. , if the mold temperature controller is not used, difficulties may arise in mass production in the future.