The causes and solutions of cracking in plastic injection molding products.
During the production of injection molded products, plastic molds are prone to some defects, such as cracking, which is a common problem. Cracking is a common defect in plastic products produced by injection molding manufacturers, mainly caused by stress deformation. There are mainly residual stress, external stress, and stress deformation caused by external environment. During the production of injection molded products, plastic molds are prone to some defects, such as cracking, which is a common problem. Why does cracking occur? Today, engineers from plastic mold manufacturers will give you an answer. Cracking is a common defect in plastic products produced by injection molding manufacturers, mainly caused by stress deformation. There are mainly residual stress, external stress, and stress deformation caused by external environment.
1. The residual stress caused by cracking is mainly due to three situations: overfilling, demolding, and metal inlay.
As for the cracking caused by overfilling, the main solutions can be approached in the following aspects: (1) Due to the small pressure loss of the straight gate, if the cracking mainly occurs near the straight gate, it can be considered to use multi-point distribution point gate, side gate, and handle gate methods.
(2) On the premise of ensuring that the resin does not decompose or deteriorate, increasing the resin temperature appropriately can reduce the melt viscosity, improve flowability, and also reduce the injection pressure to reduce stress.
(3) In general, stress is prone to occur when the mold temperature is low, and the temperature should be appropriately increased. But when the injection speed is high, even if the mold temperature is lower, it can reduce the generation of stress.
(4) Excessive injection and pressure holding time can also generate stress. Shortening it appropriately or performing several pressure holding switching effects (5) Non crystalline resins, such as AS resin ABS resin PMMA resin and other crystalline resins such as polyethylene and polyoxymethylene are prone to residual stress and should be taken into consideration. When demolding, due to the small demolding angle, rough mold glue and convex mold, the demolding force is too large, resulting in stress, and sometimes even whitening or cracking around the demolding rod.
By carefully observing the location of the cracking, the cause can be determined. When embedding metal parts during injection molding, it is relatively easy to generate stress and it is easy to crack after a period of time, which is extremely harmful. This is mainly due to the significant difference in thermal expansion coefficients between metals and resins, which generates stress, and over time, the stress exceeds the strength of the gradually deteriorating resin material, leading to cracks. Injection molding manufacturers, in order to prevent cracking caused by this, based on experience, it is generally not suitable to add inserts with a wall thickness of 7 inches and an outer diameter of universal polystyrene embedded in metal parts, while inserts have a relatively small impact on nylon. Due to the small thermal expansion coefficient of glass fiber reinforced resin materials, they are more suitable for embedded parts. In addition, preheating the metal inserts before molding also has a good effect.
2. Cracking caused by external stress. The external stress here is mainly due to stress concentration caused by unreasonable design, especially at sharp corners.
3. Chemical cracking caused by external environment, water degradation caused by moisture absorption, and excessive use of recycled materials can all lead to physical deterioration and cracking.
1. The residual stress caused by cracking is mainly due to three situations: overfilling, demolding, and metal inlay.
As for the cracking caused by overfilling, the main solutions can be approached in the following aspects: (1) Due to the small pressure loss of the straight gate, if the cracking mainly occurs near the straight gate, it can be considered to use multi-point distribution point gate, side gate, and handle gate methods.
(2) On the premise of ensuring that the resin does not decompose or deteriorate, increasing the resin temperature appropriately can reduce the melt viscosity, improve flowability, and also reduce the injection pressure to reduce stress.
(3) In general, stress is prone to occur when the mold temperature is low, and the temperature should be appropriately increased. But when the injection speed is high, even if the mold temperature is lower, it can reduce the generation of stress.
(4) Excessive injection and pressure holding time can also generate stress. Shortening it appropriately or performing several pressure holding switching effects (5) Non crystalline resins, such as AS resin ABS resin PMMA resin and other crystalline resins such as polyethylene and polyoxymethylene are prone to residual stress and should be taken into consideration. When demolding, due to the small demolding angle, rough mold glue and convex mold, the demolding force is too large, resulting in stress, and sometimes even whitening or cracking around the demolding rod.
By carefully observing the location of the cracking, the cause can be determined. When embedding metal parts during injection molding, it is relatively easy to generate stress and it is easy to crack after a period of time, which is extremely harmful. This is mainly due to the significant difference in thermal expansion coefficients between metals and resins, which generates stress, and over time, the stress exceeds the strength of the gradually deteriorating resin material, leading to cracks. Injection molding manufacturers, in order to prevent cracking caused by this, based on experience, it is generally not suitable to add inserts with a wall thickness of 7 inches and an outer diameter of universal polystyrene embedded in metal parts, while inserts have a relatively small impact on nylon. Due to the small thermal expansion coefficient of glass fiber reinforced resin materials, they are more suitable for embedded parts. In addition, preheating the metal inserts before molding also has a good effect.
2. Cracking caused by external stress. The external stress here is mainly due to stress concentration caused by unreasonable design, especially at sharp corners.
3. Chemical cracking caused by external environment, water degradation caused by moisture absorption, and excessive use of recycled materials can all lead to physical deterioration and cracking.