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, fixed mold will produce a huge lateral deflection force:
Plastic parts of the wall thickness is not uniform, the flow rate 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, easy to prolapse.When the mold, the product cracks occur.In addition, the operator must use the tip of the copper tap out from the nozzle, so that after loosening before stripping, serious Affect the production efficiency.
The main reason for this failure is poor gate cone finish, the hole in the circumferential direction of the knife marks, followed by the material is too soft, after a period of time tapered end of the small deformation or damage, and the nozzle spherical arc is too small, resulting in gate material in this The riveting head produces.It is difficult to process the taper hole of the sprue sleeve and the standard parts should be used as far as possible.If self-processing is required, self-made or purchased special reamer should also be made.It must be grinded to below Ra0.4. Gates pull rod or gate out of institutions.
3, moving, fixed mode offset
Large mold, due to the different charge rates for each direction, as well as in the mold by the weight of the mold, resulting in dynamic and fixed mold offset in these cases, the injection lateral offset force will be added to the guide column , Open the mold when the guide column surface hair, damage, serious when the guide column bent or cut, or even can not mold.
In order to solve the above problems, in the mold parting surface to increase the strength of the positioning keys on each side of the four, the most simple and effective is the use of cylindrical key column hole and the parting plane perpendicularity is crucial. In the processing is the use of moving , Fixed mold alignment position clamping, the boring machine in the last boring, so as to ensure that dynamic and fixed mold hole concentricity, and to minimize the vertical error.In addition, the guide post and guide sleeve heat treatment hardness must meet the design requirements .
4, moving template bending
Mold injection in the mold cavity melt plastic has a huge back pressure, usually in the 600 ~ 1000 kg / cm 2. Mold makers sometimes do not pay attention to this problem, often change the original design size, or the dynamic template with low-strength steel instead , In the mold with ejector top material, as 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 better quality, that is, the processing cost is too high, and now usually use standard parts, the quality of general. If the ram and hole clearance is too large, there is leakage, but if the gap is too small, due to injection mold temperature More dangerous is that sometimes the mandrel is topped 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 of the mating section, the middle part of the mill small 0.2 mm.After all the mandrels assembly, must be strictly checked with the gap, usually in the 0.05 ~ 0.08 mm, to ensure that the entire ejection mechanism can move forward and backward freely.
6, poor cooling or water leakage
Mold cooling effect directly affects the quality of products and production efficiency, such as poor cooling, shrinking products, or inconsistent shrinkage appear warping deformation and other defects.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 mandibular activities such as 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, the slider damage, or even bending damage.According to experience, after the completion of core pumping action slider, the length of stay in the chute should not be less than 2/3 of the full length of the guideway.
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.
Once the synchronization is lost, it will inevitably cause the template of the drawn mold to be skewed and damaged. The parts of these mechanisms must have high rigidity and wear resistance, and the adjustment is also very difficult. The life span of the mechanism is short, and the use of other mechanisms is avoided as much as possible. In the case of pumping force is relatively small, the spring can be used to launch a fixed-mode method, in the case of large core-pulling force can be used to retreat when the dynamic mode core sliding, core-pulling action to complete the first sub-mold structure, Die can be used on the hydraulic cylinder core pulling.
Most of the problems of such institutions are mostly processing is not in place and the material is too small, there are two main problems:
Oblique inclination A large;
The advantage is that it is possible to produce a larger core pulling distance in a shorter mold opening stroke.
However, when the extraction force F is a certain value, the bending force P = F / COSA inclined by the pulling core during the core pulling process is larger, and the inclined pin deformation and inclined hole wear easily occur.
At the same time, the skewed pin generates an upward thrust force on the slider N = FTGA, the larger the positive pressure of the slider on the guide surface in the guide groove increases, thereby increasing the frictional resistance of the slider when sliding. Shun, channel wear. According to experience, angle A should not be greater than 25 °.