The structure of the injection mold and the quality of the mold processing directly affect the quality and production efficiency of plastic parts. Injection mold production and plastic product production practice are the most common, and some of the most common mold failures and their main causes are analyzed and eliminated as follows.
1. Gate discharge is difficult. During the injection molding process, the gate is stuck in the gate sleeve and is not easy to come out. When the mold is opened, the product appears crack damage. In addition, the operator must knock out the nozzle with the tip of the copper rod to loosen it before demoulding, which seriously affects the production efficiency. The main reason for this failure is the poor finish of the taper hole of the gate, and there are knife marks in the circumferential direction of the inner hole. Secondly, the material is too soft, and the small end of the tapered hole is deformed or damaged after a period of use, and the spherical curvature of the nozzle is too small, which causes the gate material to produce rivets here. The taper hole of the gate sleeve is difficult to process. Standard parts should be used as much as possible. If you need to process it yourself, you should also make or buy a special reamer. Taper holes need to be ground to Ra0.4 or more. In addition, a gate pulling rod or a gate ejection mechanism must be provided.
2. Guide pillar damage. The guide post mainly plays a guiding role in the mold to ensure that the molding surfaces of the core and the cavity do not touch each other under any circumstances, and the guide post cannot be used as a force member or a positioning member. In the following cases, when the injection moves, the fixed mold will generate a huge lateral offset force:
(1) When the wall thickness of plastic parts is required to be uneven, the velocity of the material passing through the thick wall is large, and a large pressure is generated here;
(2) The side of the plastic part is asymmetric, such as the stepped parting surface of the mold, the opposing pressures on the opposite sides are not equal.
3. For large molds, due to the different filling rates in each direction, and the influence of the mold's own weight during mold loading, shifts in the dynamic and fixed molds occur. In the above cases, the lateral offset force will be added to the guide post during injection, and the surface of the guide post will be fuzzed and damaged when the mold is opened, and the guide post may be bent or cut off in severe cases, and the mold cannot even be opened. In order to solve the above problems, a high-strength positioning key is added on each side of the mold parting surface, and the most convenient and effective is to use a cylindrical key. The perpendicularity of the guide column hole and the parting surface is very important. During the processing, the movement is adopted. After the fixed mold is aligned and clamped, it is bored on the boring machine at one time. Minimize verticality errors. In addition, the heat treatment hardness of the guide post and guide sleeve must meet the design requirements.