What are the key points of injection molding trial?

When we receive a new pair of mold plates, we are always eager to try out a result earlier and hope the process will be smooth 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, it may cause big damage due to small mistakes.

Secondly, the result of the mold trial is to ensure the smooth production in the future. If we do not follow reasonable steps and keep proper records during the plastic injection process, we cannot guarantee the smoothness of mass production.

What we emphasize is that if the mold is used smoothly, it will quickly increase the profit recovery, otherwise the cost loss will be more than the cost of the mold itself.

Precautions before mold test

1. Know the information about the mold.

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

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 injection molding machine, in the selection should pay attention to

(a) Injection capacity

(b) Width of guide bar

(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 injection mold is installed, the mechanical action of each part of the mold should be carefully checked again, such as the slide plate, ejector pin, retracting tooth structure and the action of the restriction switch are 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, in the manual and low-speed mold closing action, pay attention to see and hear whether there is any uneven action and strange sound and other phenomena.

4. Increase the mold temperature.

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

After the 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 single condition changes on the finished product.

6. Baking

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

7. Raw material

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

8.Color swatches

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

9. Testing

Internal stress and other problems often affect the secondory processing,which 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 a few times to see if there is uneven closing injection 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, and 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 stroke is longer than the low speed stroke throughout the opening stroke during mold loading. In the plastic machine mechanical ejector rod must also be adjusted to act after the full speed mold opening action to avoid deformation of the ejector plate or peel plate by force.

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

(a) Whether the filling stroke is too long or not enough.

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

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

Mould trial process

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, and to find the best temperature and pressure conditions, and to develop standard mold trial procedures that can be used to establish daily working methods.

1. Materials used

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

2. Tube cleaning

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 mould.

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 carefully

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. Wait for the injection machine to stability

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. Adjust time

The screw advance time should not be shorter than the gate plastic melt 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 mould is heated, the screw advance time should also be extended to compact the finished product.

6. Adjust period

Reasonable adjustment to reduce the total processing cycle.

7. Test stability

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

8. Mesure and record

Measure and record the resin dimensions of successive samples (should be measured when the sample has 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.

Problems that should be noted during the injection test

1. Make the process run and cooling 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, and increase the gate size for reference if the shrinkage is too large and the finished products appear to be undershot.

3.If the die cavity and gate size are still correct, then try to change the machine conditions, such as cooling system, 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 oil pump, oil valve, temperature controller, etc., will cause changes in the processing conditions, even if the most perfect mold can not play a good efficiency in a poorly maintained machine.

After reviewing all the recorded values, keep a set of samples to check and compare the corrected samples for improvement.

Important Notes

Keep all the records of the sample inspection during the mould trial, including the various pressures of the processing cycle, melt and mold temperatures, tube temperatures, injection action times, screw charging periods, etc. In short, keep all the data that will help establish the same processing conditions in the future so that you can obtain products that meet quality standards.

It is not easy to grasp the mold temperature during the short mold test and future mass production, and the incorrect mold temperature is enough to affect the size, brightness, shrinkage, flow and under-production of the sample, etc. If we do not use the mould temperature controller to grasp the proper temperature, difficulties may occur in the future.