Before injection molding, a new mold, or when the machine is replaced by another mold for production, a mold trial is an essential part.
The 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 process 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 mold design process, analyze it in detail, and get the injection mold technician to participate in the mold test.
2. First check the mechanical action on the working table
Pay attention to whether there are scratches, missing parts, and loose phenomena, whether the mold to slide action is true, whether water and gas pipe joints have no leakage, and the mold opening range, if there are restrictions, 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, it is necessary to select a suitable test injection machine.
(1) What is the maximum injection volume of the injection molding machine
(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.
The next step is to hang the mold after everything is confirmed. When hanging, attention should be paid to not taking down the hanging before locking all the clamping plates and opening the mold, so that the clamping plates will not be loose or broken and the mold will fall.
After the mold is installed, the mechanical action of each part of the injection mold should be carefully checked, such as the slide plate, ejector pin, withdrawal structure, restriction switch, etc. whether the action is true, and 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 closing action, pay attention to see and hear whether there is any uneven action and strange sounds, or other phenomena.
The process of lifting the mold is relatively simple, but the main thing that needs to be carefully done is that it is difficult to adjust the center of the mold gate and the injection nozzle.
4. Increase 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 recommend that only one condition be adjusted at a time when adjusting the test mold conditions to distinguish the effect 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 for the test mold and future mass production as much as possible.
8. Don’t try the mold with inferior material, if there is a demand for color, you can arrange the color test together.
9. The problem of internal stress often affects the secondary processing, so the secondary processing should be done after the mold trial and after the finished product is stable.
After the mold is closed at a slow speed, adjust the closing pressure and move several times to check if there is uneven closing pressure to avoid 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 parts 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 mold making the first mold injection, please check the following items again
(1) Whether the material 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 development cycle is too long or too short.
To prevent the finished product from the short shot, breakage, deformation, burr, and even injury to the mold. If the cycle time is too short, the ejector pin will go through the finished product or peel the ring and squeeze the finished product. This type of situation can take you two or three hours to remove the finished product.
If the cycle time is too long, the delicate part of the die stamper may break due to the shrinkage of the rubber. Of course, it is not possible to have all the problems that can occur during a mold trial, but well thought out and timely measures taken in advance will help you avoid serious and expensive losses.
Develop standard mold trial procedures and establish daily work practices
To avoid unnecessary time and trouble during mass production, it is necessary to be patient in adjusting and controlling the various processing conditions and finding the best temperature and pressure conditions.
1. Check if the plastic material in the barrel is correct and baked according to the regulations (different materials may give different results if used for mold trial and production).
2. Clean up the barrel thoroughly to prevent bad plastic or miscellaneous materials from being shot into the mold, because bad plastic and miscellaneous materials may seize the mold.
Check whether the temperature of the material tube and the temperature of the mold are suitable for the processed material selection.
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 fully solidified, think before adjusting the various control conditions, because a slight change in the filling rate may cause a large change in the filling.
4. Be patient until the machine and injection mold conditions stabilize, even for medium-sized machines it may take more than 30 minutes. This time can be used to check for possible problems with the finished product.
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. Adjust reasonably to reduce the total processing cycle.
7. Run the new conditions for at least 30 minutes to stabilize, then produce at least one dozen consecutive full mold samples, label the containers with the date and quantity, and place them separately by cavity 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 successive samples (should be measured when the sample has cooled to room temperature).
9. Compare the dimensions of each mold sample, noting.
(1) Whether the dimensions of the product are stable.
(2) 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.
(3) Whether the dimensional changes are within the tolerance range.
10. If the finished product does not vary much in size and the machining conditions are normal, observe if the quality of the finished product in each die cavity is acceptable and the dimensions are within tolerances.
Make a note of the cavity numbers that are continuously larger or smaller than the average to check the correct size of the mold.
Record the parameters obtained during the mold test
Record and analyze the data to modify the mold and production conditions, and for future reference in mass production.
1. Make the manufacturing process run 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, and increase the gate size for reference if the shrinkage is too large and the finished product seems to be undershot.
3. To correct the oversize or undersize of each die cavity, 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. According to the mold cavities of the finished product or mold pistons shift, to be corrected individually, and perhaps try to adjust the filling rate and mold temperature to improve its uniformity
5. Check and modify the malfunction of the injection machine, such as the oil pump, oil valve, temperature controller, etc., will cause changes in the processing conditions, 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 to check and compare whether the corrected samples are improved.
Keep a record of all the samples tested during the mold trial, including the various pressures of the manufacturing process cycle, melt and mold temperatures, tube temperatures, injection molding process action times, screw charging periods, etc.
In short, all data that will help to establish the same processing conditions in the future should be kept to obtain plastic injection molded products that meet quality standards.
At present, factories often ignore the mold temperature during the mold test, and the mold temperature is not easy to grasp during the short mold test and future mass manufacturing processes production.
The incorrect mold temperature is enough to affect the sample size, brightness, shrinkage, flow, under-production, etc. if the mold temperature controller is not used to be when future mass production may have difficulties.