Nine Injection Molds Fault And Solution

- Oct 10, 2019-

Injection mold is a tool for producing plastic products; It is also a tool for giving plastic products a complete structure and precise size. The structure form and quality of injection mould directly affect the quality and production efficiency of plastic parts. Injection mold production and plastic products production practices are the most common, the most common reasons for injection mold failure and its elimination methods are described in detail as follows:
Nine common injection mold faults and solutions
1. Sprinkler difficulty
In the process of injection molding, the gate is stuck in the gate sleeve and is not easy to get out. When the mold is opened, cracks appear in the product. In addition, the operator must knock the tip of the copper rod out of the nozzle so that it can be loosened before it can be demolded, which seriously affects the production efficiency. The main reason for this failure is the poor finish of the cone hole in the gate and the knife marks in the circular direction of the inner hole. The second is that the material is too soft. After a period of time, the small end of the cone hole is deformed or damaged, and the spherical curvature of the nozzle is too small, causing the gate material to produce rivets here. The cone hole of the gate cover is difficult to process. Standard parts should be used as far as possible. If you want to process it yourself, you should also make or purchase a special reamer. Cone holes need to be ground to above Ra 0.4. In addition, it is necessary to set up the gate drawing rod or the gate top out mechanism. The mold master WeChat public number is good!
2. Guide column damage
The guide column mainly plays a guiding role in the mold to ensure that the forming surface of the core and the cavity do not touch each other under any circumstances. The guide column can not be used as a force element or a positioning element. In the following cases, injection-time movement and die-fixing will produce a huge lateral shift force:(1). When the wall thickness of the plastic parts is not uniform, the flow rate of the material through the thick wall is large, and greater pressure is generated here; (2). The sides of the plastic parts are asymmetrical, such as the opposite sides of the mold of the trapezoidal face are not equally subjected to reverse pressure.
3. Large molds, due to the different charging rates of each direction, and the impact of the mold's self-weight when loading, produce vivid and fixed molds.
In the above cases, the lateral shift force will be added to the guide column during injection. When the guide column surface is opened, the surface of the guide column will be drawn, damaged, and the guide column will bend or cut off in severe cases, and even the mold can not be opened. In order to solve the above problems in the mold type surface to add a high-strength positioning key four sides, the most effective is the use of cylindrical bonds. The vertical degree of the guide column hole and the die surface is of great importance. After the process is used, the fixed mode alignment position is clamped, and the boring machine is finished at a time. This guarantees the concentric degree of the moving and fixed mode holes, and makes the vertical degree error. Minimize. In addition, the heat treatment hardness of guide column and guide sleeve must meet the design requirements.
4. Move template bending
Mould makers sometimes do not pay attention to this problem, often change the original design size, or replace the moving template with a low-strength steel plate. In a mold with a top rod top material, due to the large distance between the two sides of the seat, the template is bent down during injection. Therefore, the moving template must use high-quality steel. It must be sufficiently thick to cut low strength steel plates such as A3. If necessary, support columns or support blocks should be set under the moving template to reduce the thickness of the template and increase the carrying capacity.
5. Bending, breaking or leaking of the top rod
The quality of the self-made top rod is better, that is, the processing cost is too high. Nowadays, standard parts are generally used and the quality is poor. If the gap between the top rod and the hole is too large, leakage occurs, but if the gap is too small, the top rod is stuck due to the increase in mold temperature during injection. What is more dangerous is that sometimes the top rod is stuck at a normal distance and breaks. As a result, the exposed top rod can not be reset and the die is broken. In order to solve this problem, the top rod is remolded, and a 10 to 15 mm joint section is retained at the front of the top stem, and the middle part is reduced by 0.2 mm. All top rods must be strictly inspected after assembly, generally within 0.05 to 0.08 mm, to ensure that the entire top out mechanism can move forward and retreat freely.
6. Cold but bad or leaking waterways
The cooling effect of the die directly affects the quality and production efficiency of the product, such as poor cooling, large shrinkage of the product, or uneven shrinkage and deformation of the warp surface. On the other hand, the whole or part of the die is overheated, so that the mold can not be normally formed and discontinued. If it is serious, the thermal expansion of the top rod and other active parts is stuck and damaged. The design and processing of cooling system depends on the shape of the product. Do not save this system because of the complex structure of the mold or difficulties in processing. In particular, large and medium-sized molds must fully consider the cooling problem.
7. Fixed tension mechanism failure
The fixed-pitch tensioning mechanism, such as a hook and a clasp, is generally used in the die of a fixed die core or some secondary demoulding. Because such a mechanism is set in pairs on both sides of the die, its action requirements must be synchronized, that is, the die is simultaneously connected. Duckling, opening to a certain position and decoupling. Once lost synchronization, it is bound to cause the template of the mold being pulled to be tilted and damaged. The parts of these mechanisms must have high stiffness and wear resistance. Adjustment is also very difficult. The mechanism has a short life span and can be avoided as far as possible. Other mechanisms can be used instead.
In the case of relatively small pumping force, the spring can be used to introduce the fixed mode. In the case of relatively large pumping force, the sliding mode can be used when the moving mode retreats. The structure of the drawing action is completed first and then the die can be divided. Hydraulic cylinder core can be used on the large mold. Bevel pin type core pumping mechanism is damaged. Most of the common problems of this kind of mechanism are that the processing is not in place and the material is too small. There are mainly the following two problems.
The tilt angle A is large, and the advantage is that it can produce a relatively large core distance within a shorter open mode stroke. However, with a large inclination of A, when the pull force F is a certain value, the bending force P = F/COSA received by the oblique pin during the core pumping process is also greater, and oblique pin deformation and oblique hole wear are likely to occur. At the same time, the greater the upward thrust N = FTGA of the oblique pin on the slide, the greater the positive pressure on the guide surface of the slide, which increases the friction resistance when the slide slides. Easy to cause slippage, guide groove wear. According to experience, the inclination A should not be greater than 25 °
8. Slide tilt, not easy to reset
Some molds are limited by the area of the template, the length of the guide slot is too small, and the sliding block reveals the outside of the guide slot after the core pumping action is completed. This can easily cause the sliding block to tilt in the post-core stage and the initial stage of the joint reset, especially in the mold. At the time of closing, the sliding block reset is not smooth, Damage to the slider, even bending. According to experience, the length of the slider should not be less than 2/3.
9. Finally when designing and manufacturing molds
According to the requirements of the quality of the plastic parts, the size of the batch, the requirements of the manufacturing period and other specific conditions, not only can meet the requirements of the products, but also the simplest and most reliable die structure, easy to process, so that the low cost, production of such a mold is excellent.