The common causes of problems in injection molds are as follows:

1。 It is difficult for the gate to detach during the injection molding process

The gate is stuck inside the gate sleeve and is not easy to detach. After the mold was opened, the finished product showed cracks and damage. In addition, after demolding, the operator must knock out the brass rod above the pipe mouth to loosen it, seriously affecting production capacity.

The main reasons for this defect are the difference in brightness of the gate cone hole and the knife marks on the circumference of the inner hole. Secondly, the data is too soft, causing deformation or damage to the small end of the conical hole after a period of use, and the curvature of the nozzle spherical surface is too small, resulting in the gating of the rivet head here. It is difficult to process the taper hole of the gate sleeve, and standard parts should be selected as much as possible. If you need to process it yourself, you should purchase a specialized reamer or provide it yourself. The tapered hole needs to be polished to Ra0.4 or more. In addition, it is also necessary to set up gate pull rods or gate ejection.

2。 Large displacement and fixed mold offset

Due to the different filling rates in different directions, during the installation process of the mold, there may be large mold displacement and fixed mold offset due to the influence of the mold's own weight. In the above situation, during the injection process, the guide column will be subjected to lateral force, and when the mold is opened, the outer surface of the guide column will become rough and damaged; When the mold is severe, the guide column may appear serrated or blocked, and even the mold cannot be opened.

To address the above issues, a high-strength positioning key has been added to the parting surface around the mold, and the most concise and practical option is to choose a cylindrical key. The straightness of the guide pillar hole and the parting surface is crucial. After clamping the movable and fixed molds in the direction, drill a hole on the boring machine once to ensure the concentricity of the movable and fixed mold holes and minimize straightness error. In addition, the heat treatment hardness of the guide pillar and guide sleeve should meet the requirements of the plan.

III. Damaged guide pillar

The guide pillar plays a leading role in the mold, ensuring that the forming surface of the core and cavity will not collide with each other under any circumstances. The guide pillar cannot be used as a force bearing or positioning component.

In some cases, an infinite lateral displacement force may be generated during the injection process. When the wall thickness of the plastic part is required to be uneven, the material flowing through the thick wall has a high flow rate, which generates a large pressure here; The tail of the plastic part is asymmetric, such as unequal back pressure on both sides of the mold relative to the step parting surface.

Four. When using a zigzag or zigzag injection mold, there will be an infinite back pressure on the melted plastic inside the mold cavity, typically between 600 and 1000 kilograms per centimeter. Mold manufacturers sometimes do not pay attention to this issue and often change the original design standards or use low strength steel plates instead of movable templates. In molds with ejector pins, due to the large span on both sides, the template may bend during injection molding.

Therefore, the activity template must be made of high-quality steel and meet the thickness requirements, and low strength steel plates such as A3 must not be used. If necessary, set up support columns or blocks under the movable formwork to reduce the thickness of the formwork and can only be adjusted.

5. The top rod is serrated, with cracks or missing parts. The quality of the self prepared top rod is good, which means the processing cost is too high. Nowadays, standard parts are widely used and the quality is getting worse and worse. If the gap between the top rod and the hole is too large, the material will leak, but if the gap is too small, the top rod will get stuck during the injection process due to an increase in mold temperature.

In addition, sometimes the top rod will break when ejected, and the exposed top rod cannot be reset. Closing the mold once will damage the mold. To solve this problem, the top rod was polished from the beginning. A collaborative segment of 10-15mm is stored in the front of the top bar. The base is slightly reduced by 0.2 millimeters. After the installation of all top rods, the fit clearance must be strictly checked, generally within the range of 0.05-0.08mm, to ensure that all top rods can move freely left and right.

6。 Poor cooling or water leakage

The cooling effect of the mold directly affects the quality and production capacity of the finished product, such as poor cooling, large shrinkage of the finished product, and uneven shrinkage and warping. On the other hand, the mold is completely or partially overheated, resulting in the mold being unable to form normally and production being discontinued. In severe cases, moving components such as the top bar may become stuck and damaged due to thermal expansion.

The cooling system and process plan depend on the shape of the product. Do not ignore this difference because of the chaotic structure of the mold or the difficulty of processing. In addition, cooling issues must be fully considered for large and medium-sized molds.

No. 7. Unsmooth tilting and resetting of the slider

Some molds are constrained by the template area, and the length of the guide groove is too small. After the core pulling action is completed, the slider exposes the inner side of the guide groove, causing the slider to tilt and reset the mold after and at the end of the core pulling period. In addition, it is difficult for the slider to reset smoothly during mold closing, causing damage to the slider and even bending. Based on experience, after the core pulling action of the slider is completed, the remaining length inside the chute should not be less than 23% of the total length of the guide groove.

8. Fixed distance tensioning device failure

Fixed distance tensioning devices such as rotary shuttles and buckles are commonly used for fixed mold core pulling or certain secondary demolding molds. Due to the fact that this arrangement is arranged in pairs on both sides of the mold, its movements must be synchronized, that is, the mold must be closed and buckled together, and the mold must be opened and unhooked together in a certain direction.

Once synchronization is lost, the drawing template will tilt and damage. The arranged parts must have high rigidity and wear resistance. It's also difficult to adjust. The scheduled time is very short. Try to avoid using it as much as possible. Other arrangements can be used.

When the core pulling force is small, a stretching spring can be used to push out the fixed mold. When the core pulling force is large, the core pulling will slide when the moving mold moves backward. Complete the core pulling action first, and then divide the mold. In large molds, hydraulic cylinder core pulling can be used. The inclined pin sliding core pulling device is damaged.

Most of the drawbacks of this arrangement are inadequate processing and small materials. Firstly, there are two questions:

The diagonal pin angle a is relatively large, and its advantage is that it can generate a larger core pulling distance in a shorter mold opening stroke. However, when the inclination angle A is too large and the pull-out force F is a certain value, the greater the tortuous force P=Fcosa that the inclined pin is subjected to during the core pulling process, the greater the possibility of deformation of the inclined pin and wear of the inclined hole.

At the same time, the greater the upward thrust n=ftga of the inclined pin on the slider, the greater the positive pressure on the guide surface in the guide groove of the slider, and the greater the resistance during sliding of the slider. Easy to cause irregular sliding and guide groove wear. Based on experience, the inclination angle A should not exceed 25.

No. 9. Poor exhaust of injection mold

Injection molds often have gas. What is the reason for this?

There is air in the pouring system and mold cavity, and some materials contain rich water that has not been dry cleaned, which will vaporize into water vapor at high temperatures. Due to the high temperature during the injection molding process, unstable plastics with unstable performance will be differentiated, generating gas; In plastic materials, the gas produced by transpiration of some promoters may undergo chemical reaction.

In addition, we need to investigate the cause of poor exhaust as soon as possible. Poor exhaust of injection molds can cause a series of damages to the quality of plastic parts and many other aspects. The first embodiment is that during the injection molding process, the melt will replace the gas in the mold cavity. If the gas is not discharged in a timely manner, it will make it difficult for the melt to fill the mold, resulting in a short injection volume and inability to fill the mold cavity; If the air is not discharged smoothly, high pressure will be formed in the mold cavity, leading to a certain degree of shrinkage when entering the mold cavity. There are quality defects such as voids, pores, sparse arrangement, and cracking on the outside of the plastic;

Due to the high compression of gas, the temperature of the mold cavity rises sharply, leading to the differentiation and baking of the surrounding melt, resulting in carbonization and carbonization of plastic parts. Mainly occurring at the junction of two types of melts and gate flanges; Gas cleaning is not smooth, resulting in different melt velocities entering each mold cavity, which can easily form active and fusion marks, reducing the mechanical properties of plastic parts; Due to the obstruction of gas in the mold cavity, it will reduce the filling speed, affect the forming cycle, and reduce tax power.

The bubbles in plastic parts and the bubbles accumulated in the mold cavity are often scattered on the parts next to the gate; Bubbles generated by differentiation or chemical reaction in plastic materials are distributed along the thickness of plastic parts; The bubbles generated by residual water vaporization in plastic materials are irregularly distributed on the plastic parts.