What Happened To These Injection Mold Failures?

- Mar 27, 2018-

1. Difficulties in sprue feeding         In the injection molding process, the gate is stuck in the sprue bushing and it is not easy to escape. When the mold is opened, the product is cracked. In addition, the operator must use the tip of the copper rod to knock out from the nozzle, make it loose and release it, which will seriously affect the production efficiency.         The main cause of this failure is the poor finish of the tapered hole in the gate, and the tool hole in the circumferential direction of the inner hole. The second is that the material is too soft. After a period of use, the small end of the tapered hole is deformed or damaged, and the curvature of the nozzle surface is too small, causing the gate material to produce a riveting head. The taper hole of the sprue bushing is more difficult to process. Standard parts should be used as far as possible. For self-processing, special reamers should be made or purchased. Taper holes need to be ground to Ra0.4 or more. In addition, you must set the gate pull bar or the top of the gate.2. Large-scale die movement          Due to the difference in the rate of the anisotropic charging of the large mold and the impact of the weight of the mold during mold mounting, the movement of the mold and the displacement of the fixed mold are generated. In the above cases, the lateral offset force during injection will be added to the guide post. When the mold is opened, the surface of the guide post is pulled and damaged. In severe cases, the guide post is bent or cut off, and it is impossible to open the mold.

         In order to solve the above problems, a high-strength positioning key is added on each side of the mold parting surface. The most convenient and effective method is to use a cylindrical key. The verticality of the guide post hole and the parting surface is of utmost importance. In the machining, the clamping is performed after the alignment of the movable and fixed molds is completed. The boring is completed once on the boring bed so that the concentricity of the movable and fixed mold holes can be guaranteed. Minimize the squareness error. In addition, the heat treatment hardness of the guide post and guide sleeve must meet the design requirements.3. guide pillar damage           The guide pillar mainly plays a guiding role in the mold to ensure that the molding surfaces of the core and the cavity do not collide with each other in any case, and the guide post cannot be used as a force member or a positioning member.           In a few cases, the injection mold will generate a large lateral deflection force when the mold is injected. When the wall thickness of the plastic part is not uniform, the velocity of the material flow through the thick wall is large, resulting in greater pressure; the side of the plastic part is asymmetrical, such as the back pressure on the opposite sides of the mold of the stepped parting surface. not equal.

4. Dynamic template bending             When the mold is injected, the molten plastic in the mold cavity generates a huge back pressure, which is generally 600-1000 kg/cm. Moldmakers sometimes do not pay attention to this problem, often changing the original design size, or replace the moving plate with a low-strength steel plate. In a die with a tipping material, the two-side seat has a large span, causing the template to bend under injection. Therefore, the moving plate must be made of high-quality steel, and must have sufficient thickness. It is not possible to cut low-strength steel plates such as A3. When necessary, support columns or support blocks should be installed below the moving plate to reduce the thickness of the plates and increase the bearing capacity.

5. Top rod bent, broken or missing material          The quality of the self-made ejector rod is better, that is, the processing cost is too high. Now the standard parts are generally used and the quality is worse. If the clearance between the crowbar and the hole is too large, leakage occurs, but if the clearance is too small, the ram swells and seizes due to the increase in mold temperature during the injection. What is even more dangerous is that sometimes the top bar is broken at its normal distance from the top and the result is that the exposed top bar cannot be reset and hit the die at the next clamping. In order to solve this problem, the top bar is reground, leaving a 10 to 15 mm mating section at the front end of the jack, with the center section being 0.2 mm. After assembly, all ejector rods must be strictly checked for fit clearance, generally within 0.05 to 0.08 mm, to ensure that the entire ejector mechanism can move freely.