Plastic molds often encounter the phenomenon of product side scratches or scratches during injection molding, especially for deep cavity products. Whether it is a smooth or textured surface, scratches mainly occur in the front mold, directly affecting the appearance of the product. This is absolutely unacceptable in injection molding processing. During the trial molding process, when encountering product scratches, most injection molding technicians and mold masters first think that there is a problem with the mold design. The draft angle on the side of the product is not large enough. However, increasing the draft angle will still result in the same scratches during the next trial molding. It is possible that the causes of scratches on injection molded products are not single. Let's analyze together which factors may cause scratches on the appearance of injection molded products:

First,Product draft angle issue

The main issue with the product is that the draft angle is too small, causing side dragging damage to the product. We have relevant experience in meeting the different requirements for the side profile of the corresponding product. Most engineers have the ability to judge what size of profile should have what kind of draft angle. Solving such problems must be avoided in the early stage of product evaluation. If the customer's product does not allow sufficient draft angles, the mold engineer must not take risks and should consider using other mold mechanisms and other technical means to avoid it.

Second，Mold design issues

first,In addition to product issues to avoid product scratches, mold design is also important and must be carefully considered. Here are a few examples to illustrate how mold design can avoid scratches on the side appearance of the product: the treatment of the fillet on the parting surface. When designing the product, product designers often directly approach the fillet, which is actually an unreasonable design because the draft angle at the contact between the fillet and the surface is close to zero degrees, making it easy to scratch. Therefore, the mold designer needs to modify the product to connect multiple lines and use software for draft analysis to modify it to a sufficient draft angle.

second,The mold structure here focuses on the three-level positioning problem of the mold. Unreasonable mold positioning design can also cause the front and rear molds to be misaligned during the mold opening process, resulting in product strain. The first level positioning refers to the positioning of the mold guide column, the second level positioning refers to the positioning of the mold base positioning block, and the third level positioning refers to the precise positioning of the tiger mouth designed on the mold core. The third level positioning is more accurate than the first level positioning. For products with shallow side walls of the mold cavity, the tiger mouth positioning of the mold core is the most important. Generally, the insertion angle of the tiger mouth positioning in the design should be 0.5-1 degree smaller than the exit angle of the side wall biting surface, which is more suitable to ensure that the product is not easily pulled during the mold opening process. For products with deep sidewall cavities, in addition to the mold core and tiger mouth, the accuracy of the mold base positioning block should also be strictly controlled;

third,When designing the mold gate, it is necessary to consider that the gate design should not cause excessive pressure on the product, resulting in side scratches. The gate should be kept as far away from the side biting surface as possible, because the pressure at the gate is high and the holding time is long, and the product is easy to scratch due to the high clamping force;

fourth,Product adhesion to the mother mold: When designing the mold, it is important to carefully analyze whether the product has a tendency or uncertain factors to adhere to the mother mold. It is necessary to ensure that the product is 100% in the back mold when opening the mold. If it sticks to the mother mold, it may cause local warping of the product and cause side wall strain. If necessary, even the structure of the product should be made in the rear mold to ensure that the product is in the rear mold. This is also an area that many mold designers tend to overlook.

Third，Mold processing issues

first,Although the draft angle of the design is sufficient, it is also prone to errors during mold processing because the angle is difficult to measure accurately, which must not be ignored;

second,The sidewall of the mold cavity is most likely to form a buckling during mold saving, because mold engineers are often afraid of leaving rounded corners on the parting surface, resulting in more modulus savings near the bottom and less modulus savings near the parting surface. This is equivalent to reducing the draft angle of the product and is also a possible factor causing product strain, but it is often overlooked. In this situation, it is possible to consider using a mold saving fixture or precision machining the parting surface after the mold saving is completed to ensure the mold saving effect. This is also necessary for products with higher requirements.

Fourth,Molding and machine adjustment issues

first,Excessive injection pressure and holding pressure are also important reasons for product sidewall strain. Injection pressure can cause warping stress in the mold, which may locally compress the product sidewall and easily cause it to scratch when exiting the mold;

second,Excessive material temperature can also cause the surface of the product to be easily scratched;

third,Insufficient cooling of the product is also a cause of product strain;

fourth,Swelling of the parting surface can also easily cause product strain. Due to excessive clamping pressure, soft mold materials, injection molding adhesive powder, and other reasons, swelling of the parting surface may also cause product sidewall strain. Therefore, the parting surface and bite surface of the mold should be cleaned and maintained regularly;

fifth,The aging of the injection molding machine, poor parallelism between the front and rear plates, and vibration during mold opening may also be factors that may affect the side strain of the product.

In short, whether it is the uneven pattern, air bubbles, whitening, deformation, or other adverse phenomena in injection molded products, they are not entirely caused by a single factor. They all need to be evaluated from the early stage of product structure, to the subsequent mold design, processing and manufacturing, and molding ring control to ensure high-quality injection molded products. After the trial molding of plastic molds, it is necessary to carefully analyze the specific factors that cause defects in injection molded products based on the trial sample and the actual mold, so as to treat the head and feet to avoid ineffective modification of the mold.