What Are The Precautions For Injection Molding Test?

I. Introduction

When we receive a new mold for proofing, we are always eager to get a result earlier and pray for a smooth process to avoid wasting man-hours and causing trouble.

But here we must remind two points: First, mold designers and manufacturing technicians sometimes make mistakes. If we don't pay attention when we try to mold, we may cause big damage due to small mistakes. Second, the result of the mold test is to ensure the smooth production in the future. If reasonable steps are not followed and proper records are not made during the mold trial process, the smooth progress of mass production cannot be guaranteed. What we emphasize more 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".

2. Precautions before trial

1. Understand the relevant information of the mold:

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

2. Check the mechanical coordination on the workbench first:

Pay attention to whether there are scratches, missing parts and looseness, whether the sliding movement of the mold is correct, whether there is leakage of the water channel and air pipe joints, and if the opening of the mold is limited, 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 when the mold is found when the mold is hanging, and then the mold is disassembled.

3. When it is determined that each part of the mold moves properly, it is necessary to select a suitable trial mold injection machine, and attention should be paid to the selection.

(a) Injection capacity

(b) Width of guide rod

(c) Maximum departure

(d) Accessories

Is it complete and so on. After everything is confirmed that there is no problem, the next step is to hang the mold. When hanging, you should pay attention not to take off the hook before locking all the clamping templates and opening the mold, so as to avoid the clamping template loosening or breaking and the mold falling.

After the mold is installed, carefully check the mechanical actions of all parts of the mold, such as the sliding plate, the ejector pin, the retraction structure and the limit switch, whether the actions are correct. And pay attention to whether the injection nozzle and the feeding 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 to see if there are any phenomena such as unsmooth movements and abnormal noises.

4. Increase the mold temperature:

According to the performance of the raw materials used in the finished product and the size of the mold, select an appropriate mold temperature controller to increase the temperature of the mold to the temperature required for production.

After the mold temperature is raised, the movement of each part must be checked again, because the thermal expansion of the steel may cause the mold clamping phenomenon, 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, so as to distinguish the influence of a single condition change on the finished product.

6. According to the different raw materials, moderately bake the original loaf used.

7. Try to use the same raw materials as possible for future mass production.

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

9. Problems such as internal stress often affect the secondary processing. After the mold is tested and the finished product is stable, the secondary processing should be added. After the mold is closed at a slow speed, the mold closing pressure should be adjusted, and the action should be performed several times to check whether there is a fit. Unequal mold pressure to avoid burrs and mold deformation in the finished product.

After all the above steps are checked, lower the closing speed and closing pressure, set the safety lever and ejection stroke, and then increase the normal closing speed and closing speed. If the limit switch of the maximum stroke is involved, the mold opening stroke should be adjusted to be slightly shorter, and the high-speed mold opening action should be cut off before the maximum mold opening stroke. This is because the high-speed action stroke is longer than the low-speed one in the entire mold opening stroke during the mold installation. On the plastic machine, the mechanical ejector rod must also be adjusted to act after the full-speed mold opening action to prevent the ejector plate or the peeling plate from being deformed by force.

Please check the following items before making the first mold injection:

(a) Whether the feeding stroke is too long or insufficient.

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

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

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

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

If the processing cycle is too short, the thimble will push through the finished product or peel off the ring and crush the finished product. This type of situation can take you two or 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 the shrinkage of the rubber compound.

Of course, it is impossible for you to predict all the problems that may occur during the mold trial process, but taking adequate and timely measures in advance will help you avoid serious and expensive losses.

Three, the main steps of the trial

In order to avoid unnecessary waste of time and trouble during mass production, it is indeed necessary to be patient to adjust and control various processing conditions, find out the best temperature and pressure conditions, and formulate standard test procedures, which can be used in Establish daily work methods.

1. Check whether the plastic material in the barrel is correct, and whether it is baked according to the regulations. (If different raw materials are used for mold trial and production, different results may be obtained).

2. The cleaning of the material tube must be thorough to prevent the inferior solution of rubber or miscellaneous materials from being injected into the mold, because the inferior solution of the rubber and miscellaneous materials may cause the mold to be stuck ※. Test whether the temperature of the barrel and the temperature of the mold are suitable for the raw material to be processed.

3. Adjust the pressure and injection volume in order to produce a finished product with a satisfactory appearance, but no burrs are allowed, especially when the finished product of some mold cavities has 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 a large change in mold filling.

4. Wait patiently until the conditions of the machine and the mold are stable, even a medium-sized machine may have to wait for more than 30 minutes. Use this time to see possible problems with the finished product.

5. The time for the screw to advance should not be shorter than the time for the plastic at the gate to solidify, 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 also needs to be lengthened to compact the finished product.

6. Reasonable adjustment to reduce the total processing cycle.

7. Run the newly adjusted conditions for at least 30 minutes to stabilize, and then continuously produce at least a dozen full mold samples, mark the date and quantity on the container, and place them according to the mold cavity, so as to test the stability of the actual operation. And derive reasonable control tolerances. (especially valuable for multi-cavity molds).

8. Measure and record important dimensions of successive samples (wait for samples to cool to room temperature before measuring).

9. Make a comparison of the measured dimensions of each model sample, it should be noted that:

(a) Whether the dimensions are stable.

(b) Are there any dimensions that tend to increase or decrease indicating that machining conditions are still changing, such as poor temperature control or oil pressure control.

(c) Whether dimensional changes are within tolerances.

10. If the size of the finished product does not change very much and the processing conditions are normal, it is necessary to observe whether the quality of the finished product of each mold cavity is acceptable, and its size can be within the allowable tolerance. Note down the number of mold cavities that are continuously larger or smaller than the average value, so as to check whether the size of the mold is correct. Record and analyze data for the need to modify molds and production conditions, and as a reference for future mass production.

Fourth, the problems that should be paid attention to when trying the mold

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

2. Adjust the machine conditions according to the size of all finished products being too large or too small. If the shrinkage rate is too large and the finished product appears to be insufficiently shot, it can also be used as a reference to increase the size of the gate.

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

4. According to the matching situation of the finished mold cavity or the displacement of the mold core, it should be corrected separately. It may be possible to re-adjust the mold filling rate and mold temperature in order to improve its uniformity.

5. Check and modify the failure of the injection machine, such as the failure of the oil pump, oil valve, temperature controller, etc., will cause changes in the processing conditions, even if the perfect mold can not work well in the poorly maintained machine.

 After reviewing all recorded values, keep a set of samples for proofreading and comparing the corrected samples for improvement.

5. Important matters

Properly keep all records of sample inspection during the mold trial process, including various pressures in the processing cycle, melt and mold temperature, barrel temperature, injection action time, screw feeding period, etc. The data of the same processing conditions can be successfully established so as to obtain products that meet the quality standards.

At present, the factory often ignores the mold temperature during mold testing, and the mold temperature is the most difficult to grasp during short-term mold testing and future mass production. , if the mold temperature controller is not used to control the mass production in the future, it may be difficult.