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How to Prevent Failure and Solution of Injection Mold

How to Prevent Failure and Solution of Injection Mold

1, lead column injury


Lead in the mold guide the main role in order to ensure that the core and the molding surface of the cavity in any case do not touch each other, can not be used as a guide column as a force member or positioning member.

In the following two cases, the injection of dynamic and fixed mold will have a huge lateral deflection force: uneven plastic wall thickness requirements, the rate of flow through the thick wall at a large pressure here; Plastic parts on the side of the asymmetric, such as the stepped parting surface of the mold, the opposite sides of the counterpressure suffered by the unequal pressure.


2, the gate strip difficult


In the injection molding process, the gate stick in the sprue sleeve, not easy to prolapse. Open mold, the product cracks damage. In addition, the operator must tap the tip of the copper rod from the nozzle, so that the loose after the release, seriously affecting the production efficiency.


The main reason for this failure is poor gate cone finish, the hole in the circumferential direction of a knife marks. Followed by the material is too soft, the use of a period of time after the deformation or damage cone tip, and the nozzle spherical arc is too small, resulting in gate materials produced here riveting head. Sprue sleeve taper hole is more difficult to process, should try to use standard parts, for self-processing, but also self-made or purchased reamer. Taper hole to be ground to Ra0.4 the following. In addition, you must set the gate pull rod or gate ejection mechanism.


3, moving, fixed mode offset


Large-scale mold, due to the different charge rates for each direction, as well as the impact of the die weight, resulting in dynamic and fixed mode offset. In these cases, the lateral offset force will be added to the guide post at the time of injection. When the die is opened, the surface of the guide post is torn and damaged. In severe cases, the guide post is bent or cut off, and the mold can not even be opened.


In order to solve the above problems, in the mold parting surface to add high-strength positioning keys on each side of the four, the most simple and effective is the use of cylindrical keys. The verticality of the guide post hole and the parting surface is of crucial importance. In the process is the use of moving, fixed mold alignment position after boring in the boring machine once boring, so as to ensure that the dynamic and fixed mold hole concentricity, and the vertical error of the smallest. In addition, the guide post and guide sleeve heat treatment hardness must meet the design requirements.


4, moving template bending


Mold in the injection, the mold cavity molten plastic has a huge back pressure, usually in the 600 ~ 1000 kg / cm2. Mold makers sometimes do not pay attention to this issue, often change the original design size, or the dynamic template with low-strength steel instead, in the top mandrel mold, because the two sides of the seat span, resulting in injection template bending.


Therefore, moving the template must be made of high-quality steel, to have sufficient thickness, must not use A3 and other low-strength steel, if necessary, should be set in the dynamic template below the support column or support block to reduce the thickness of the template to enhance the carrying capacity.


5, mandrel bending, fracture or leakage


Homemade ram quality is better, that is, the processing cost is too high, and now usually use standard parts, quality in general. Leakage if the clearance between the ram and the hole is too large, then leakage occurs, but if the clearance is too small, the ram expands and dies when the mold is heated during injection. Even more dangerous is that sometimes the mandrel is pushed out of the general distance to the top and break, resulting in the next clamping when the exposed top mandrel can not be reset and hit the die.


In order to solve this problem, the mandril reground, retaining the front end of the mandrel 10 ~ 15 mm with the mating section, the middle part of the mill 0.2 mm small. All ram assembly, must be strictly checked with the clearance, generally within 0.05 ~ 0.08 mm, to ensure that the entire ejection mechanism can move forward and retreat freely.


6, poor cooling or water leakage


Mold cooling effect directly affects the quality of products and production efficiency, such as poor cooling, product shrinkage, or uneven shrinkage and other defects appear Alice surface deformation. On the other hand the whole or part of the mold overheating, the mold can not be normal molding and production, severe cases such as the mandrel and other moving parts of thermal expansion stuck and damaged.


Cooling system design and processing to shape the product, not because of the complexity of the mold structure or processing difficulties and save the system, especially in large and medium-sized mold must take full account of cooling problems.


7, guideway length is too small


Some molds due to the template area constraints, the guideway length is too small, the slide block in the core after the exposure is exposed outside the guide groove, so that after the core pulling stage and the initial stage of clamping are likely to cause the slider tilt, especially in the clamping When the slider is not smooth reset, so that the slider damage, and even bending damage. As a rule of thumb, after the slider has completed the core pulling action, the length of stay in the chute should not be less than 2/3 of the full length of the guide.


8, distance tensioning mechanism failure


Pendulum hooks, buckles and the like Tensioning mechanism is generally used for fixed-core or some secondary demoulding mold, as these institutions in the mold on both sides of the paired set, its action must be synchronized, that is Mold at the same time buckle, mold to a certain position at the same time decoupling.


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