Analyze the problems that often occur in injection mold

1. Difficult to demold the gate:

During the injection molding process, the gate is stuck in the sprue sleeve and is not easy to come out. When the mold is opened, the finished product shows crack damage. In addition, it is necessary for the technicians to knock out the tip of the copper rod from the nozzle so that it can be demolded after it is loosened, which seriously affects the mass production.

The main element of this shortcoming is the poor brightness of the gate taper hole and the tool marks in the circumferential direction of the inner hole. The second is that the hardness of the steel is too soft, the small end of the taper hole of the gate is deformed or damaged after mass production for a period of time, and the spherical curvature of the nozzle is too small, resulting in the riveting of the gate material.

The taper hole of the sprue sleeve is more difficult to process, so standard parts should be used as much as possible.The taper hole needs to be ground to a Ra0.4 or more. In addition, it is necessary to set a gate pull rod or gate ejection.

2. Large mold moving and fixed mold deviation:

Due to the different filling rates of large molds, and the influence of the weight of the mold during mold installation, the movable and fixed molds will deviate. In the above-mentioned situations, the lateral offset force will be added to the guide post during injection molding, and the guide post will be roughed and damaged when the mold is opened. In order to deal with the above questions, a high-strength shutter is added to the mold parting surface, one on each side.

The most concise and useful is the use of cylindrical key nylon shutters. The straightness of the guide pin hole and the parting surface is the most important. In the process, the moving and fixed molds are aligned and clamped, and the boring machine is completed at one time. Then the concentricity of the moving and fixed mold holes can be ensured, minimize the straightness error. In addition, it is necessary to use high-hardness standard parts for guide posts and guide sleeves.

3. Guide post 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 collide with each other under any circumstances, the guide post cannot be used as a force-bearing part or a positioning part. In several cases, the moving and fixed molds will have infinite lateral deflection force during injection. When the wall thickness of the plastic part is uneven, the plastic flows through the thick wall at a high rate, and greater pressure occurs here; the side surface of the plastic part is asymmetric, such as the stepped parting surface of the mold on the two sides of the mold, the back pressure is not equal.

4. Moving clamp plate:

When the mold is injecting, the molten plastic in the mold cavity has infinite back pressure, usually 600~1000kg/cm. Mold designers sometimes do not pay attention to this problem, usually change the original plan standard, or replace the moving clamp plate with a low-strength steel plate. In the mold with ejector pins, the mold plate is bent down during injection molding due to the large span between the two side seats. Therefore, it is necessary to use high-quality steel for the movable formwork, and the thickness must be match, low-strength steel plates such as A3 must not be used. When necessary, support columns or support blocks should be set under the movable formwork to reduce the thickness of the formwork.

5. The ejector pin is bent, cracked or broken:

Standard parts are usually used, and the quality is worse. If the gap between the ejector pin and the hole is too large, glue leakage will occur, but if the gap is too small, the ejector pin will swell and jam due to the increase in mold temperature during injection.

What's more serious is that sometimes the ejector pin will not move and break when it is pushed out for a short distance. When the mold is closed again, the exposed ejector pin can not be reset and collide with the fixed mold. In order to deal with this problem, the ejector pin is ground from the beginning, leaving an auxiliary distance of 10~15mm at the front end of the ejector pin. It is necessary to strictly check the safety clearance of all ejector pin after assembly, usually within 0.05~0.08mm, to ensure that all ejectors are smoothly ejected and can move forward and backward freely.

6. Poor cooling or water leakage:

The cooling effect of the mold directly affects the quality and production efficiency of the finished product, such as poor cooling, large shrinkage of the finished product, or uneven shortening which leads to defects such as warping and deformation of the product. On the other hand, the overall mold is overheated, so that the mold cannot be formed normally and the production is stopped. In severe cases, the movable parts such as ejector pin will be thermally expanded and stuck, causing damage. The cooling system plan and the processing method are determined by the shape of the product, do not omit part of the water circuit due to the complicated mold structure or processing difficulties, especially for medium and large molds, the design of the cooling system must be fully considered.

7. The slider is tilted and the reset is not smooth:

Some molds are affected by the area of the template, and the guide groove length is too small. After the core pulling action is completed, the guide groove is exposed to the outside, then the slider may be tilted in the period after the core pulling and the initial resetting period of the mold, especially in the closing period, it will cause damage if the slider is not reset smoothly, or even bending damage. According to our long-term mold making experience, the length of the slider in the chute should not be less than 2/3 of the total length of the guide groove after the core-pulling action of the slider is completed.