Standard Test Process of Injection Mold

Standard Test Process of Injection Mold

Before the injection molding of a new mold or when the machine is replaced with other molds, the mold testing is an indispensable part. The test results will directly affect whether the follow-up production of the factory is smooth. Therefore, reasonable operation steps must be followed and the useful technical parameters recorded in the mold testing process in order to facilitate the mass production of the product.

1. Precautions before testing the mold

(1) Learn about the relevant information of the mold:

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

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

Pay attention to the following points:

  • Whether there are scratches, missing parts, looseness, etc.
  • Whether the movement of the mold toward the slide board is correct.
  • Whether there is leakage in the water-cooling runner and air pipe joints.
  • If there is a limitation for the mold opening stroke, marked it on.

The above preparation can avoid the waste of man-hours of change mold.

(3)  After making sure each part of the mold can move properly, it is necessary to select a suitable injection molding machine. And we should pay attention to the following points when selecting the machine:

  • What is the maximum injection volume of the machine?
  • Whether the inner distance of the tie bar can be placed in the mold.
  • Whether the maximum stoke of the platen meets the requirements.
  • Are other relevant mold tools and accessories ready?

After confirming there is no problem, the next step is to install the mold. When installing, do not remove the hang rings before locking all the clamp templates and opening the mold. So that it can 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 barrel nozzle and mold-gate are aligned.

Next, pay attention to the mold clamping action. At this time, lower the mold clamping pressure. In the manual model and low-speed mold clamping action, pay attention to see and listen for any unsmooth movements and abnormal noises. The process of mold installation is actually relatively simple. The main point that needs to be careful is that it is difficult to align the center of the mold gate with the barrel nozzle. Usually, the center can be adjusted by means of test paper.

(4) Increase mold temperature:

According to the properties of the plastic resin and the size of the mold, an appropriate mold temperature controller is selected to increase the mold temperature to required production temperature. After the temperature of the mold increases, check the movement of each part again. The steel may cause a 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, we suggest that only one condition can be adjusted at a time when adjusting the test conditions. It’sto distinguish the impact of a single condition change on the finished product.

(6) According to the different plastic resin, do a moderate dryingof the raw materials used.

(7) Try to use the same raw materials for the mass-produced products.

(8) Don’t try the mold completely with the inferior resin. If there is a color requirement, you can arrange the color test together.

(9) Problems such as internal stress often affect the secondary processing. After the mold trial is completed and the finished product is stable, then the secondary processing should be performed. After the mold is closed at a slow speed, adjust the closing pressure and repeat several times. Check for uneven clamping pressure to avoid burrs and mold deformation in the finished product.

After checking the above steps, lower the mold clamping speed and pressure, and set the mechanical safety by manual and ejector stroke by computer. Then, adjust the normal mold closing and closing speed.

If involving the maximum stroke limit switch, adjust the mold opening stroke slightly shorter, and cut the high-speed mold opening action before the maximum stroke of the mold opening. This is because the high-speed movement stroke is longer than the low-speed stroke in the entire mold opening stroke. On the machine, the mechanical ejector rod must also be adjusted to act after the full-speed mold opening. So that it can prevent the ejector plate or the peeling plate from being deformed by force.

2. Checking before the first mold shot

Please check the following items again before the first mold shot:

  • Whether the feeding stroke is too long or insufficient.
  • Whether the pressure is too high or too low.
  • Is the injection speed too fast or too slow?
  • Whether the product cycle is too long or too short.

In order to prevent the finished product from short shot, fracture, deformation, burrs and even damage to the mold.

If the processing cycle is too short, the ejector will penetrate the finished product or squeeze the finished product. This case may cost you 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 plastic. Of course, you can’t predict all the problems that may occur in the trial mold process. But full consideration and timely measures made in advance will surely help you avoid serious and expensive losses.

3. The main steps of the trial mold

In order to avoid waste of time and troubles during mass production, it is indeed necessary to pay patience to adjust and control various processing conditions. Then, find the best temperature and injection pressure conditions, and formulate standard test procedures, which can be used to establish daily working methods.

(1) Check whether the plastic in the barrel is correct, and whether it has been dryed in accordance with the regulations (If different plastic resin are used for trial and production, that may have different results.)

(2) The cleaning of the barrel must be thorough to prevent inferiority plastic or miscellaneous materials from injecting into the mold. Because inferior plastic and miscellaneous materials may jam the mold. Check whether the temperature of the barrel and the temperature of the mold are suitable for processing plastic resin.

(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 products are not completely solidified, you should think about it before adjusting various control conditions. Because the mold filling rate changes slightly, it may cause very large mold filling changes.

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

(5) The advancing time of the screw cannot be shorter than the solidification time of the gate plastic. Otherwise the quality of the finished product will be reduced and the performance of the finished product will be impaired. And when the mold is heated, the screw advance time needs to be prolonged in order to compact the finished product.

(6) Reasonably adjust 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 product. Next, place them according to the mold cavity to test the stability of the actual operation and derive reasonable control tolerances. (Particularly valuable for multi-cavity molds.)

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

(9) When comparing the measured size of each mold sample, you should pay attention to:

  • Whether the product size is stable.
  • Whether certain dimensions have a tendency to increase or decrease. For it indicatesthe 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 and the processing conditions are normal, it is necessary to observe whether the quality of the finished product of each cavity is acceptable and 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.

4. Record the parameters obtained during the trial mold

Record and analyze the data as the need to modify the mold 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 the size of all finished products that are too large or too small. If the shrinkage rate is too large and the finished product appears to be insufficient for injection, you can also increase the gate size.

(3) Modify the size of each cavity that is too large or too small. If the size of the cavity and the gate is correct, then try to change the machine conditions, such as the filling rate, mold temperature and pressure of various parts. Also, check whether some mold cavities are slow to fill the mold.

(4) According to the matching situation of the finished products of the mold cavity or the displacement of the mold core, make individual corrections. It is possible to try to adjust the mold filling rate and mold temperature again to improve its uniformity.

(5) Check and modify the faults of the injection molding machine, such as the oil pump, oil valve, temperature controller, etc.. Because thatwill cause changes in the processing conditions, even the perfect mold can not work efficiently on the poorly maintained machine. After reviewing all the recorded values, keep a set of samples for proofreading to compare whether the corrected samples have improved.

Properly keep all the records of sample inspection during the mold trial process, including various pressures during the processing cycle, melt and mold temperature, barrel temperature, injection action time, screw feeding time, etc. In short, all data that will help establish the same processing conditions smoothly in the future should be kept in order to obtain products that meet quality standards.

At present, the mold temperature is often neglected during mold trial in the factory. And the mold temperature is the most difficult to grasp during short-term mold trial and future mass production. Incorrect mold temperature can affect the size, brightness, shrinkage, flow pattern, and lack of plastic of the sample. If the mold temperature controller is not used for mass production in the future, there may be difficulties.

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