Injection molding peeling and solutions
Injection molding peeling is a common quality defect in production, manifesting as delamination and flaking on the surface of plastic parts. This not only affects the product’s appearance but can also weaken its mechanical properties. This problem often occurs during the production of thin-walled plastic parts or complex structures, and is particularly pronounced when a high proportion of recycled materials is used or when the materials are unevenly mixed. For example, an automotive parts manufacturer experienced scrapping of nearly 30% of its dashboard brackets due to peeling, increasing production costs and delaying delivery cycles. Thorough analysis of the causes of peeling is key to resolving this issue.
From the perspective of materials, one of the main reasons for injection molding peeling is insufficient raw material purity or unreasonable formulation. When impurities with different melting points are mixed into the raw materials, or the ratio of recycled materials to new materials is unbalanced, the melt will be delaminated during the molding process due to poor compatibility. In addition, the moisture content of the material is too high.
This can exacerbate peeling problems because moisture converts to steam at high temperatures, forming bubbles within the plastic part and causing surface peeling. For example, when using PA66 material to produce connectors, insufficient drying can easily lead to fine peeling patterns on the surface, requiring secondary treatment to meet quality standards. Therefore, strictly controlling raw material quality, arbitrarily adjusting the proportion of recycled material, and ensuring sufficient drying of the material are fundamental measures to prevent peeling.
Improper setting of injection molding process parameters is also a major factor causing peeling. When the melt temperature is too low, the material is not fully plasticized, the intermolecular bonding force is insufficient, and delamination is prone to occur under stress. Excessive temperature may cause material degradation and the production of low-molecular volatiles, which will also damage the surface integrity. Excessive injection speed will cause turbulence in the melt within the mold cavity, entraining air to form bubbles, which in turn causes peeling. Excessive speed may cause the front material to cool excessively, resulting in poor bonding with the subsequent melt. When producing mobile phone casings, an electronics factory once increased the melt temperature from 220°C to 240°C and reduced the injection speed by 15%, reducing the peeling defect rate from 8% to 0.5%, confirming the effectiveness of process parameter optimization.
Mold design and maintenance also significantly impact injection molding peeling. Improper mold gate placement can lead to uneven melt flow within the mold cavity, resulting in excessive localized shear stress and causing peeling. Furthermore, poor mold cavity surface roughness, scratches, or oil stains can affect the fit between the melt and the cavity surface, leading to peeling on the surface of the plastic part. A home appliance company successfully resolved the long-standing peeling issue by optimizing gate placement, adding venting grooves, and polishing the mold cavity when producing washing machine control panels. This resulted in a product qualification rate exceeding 99%.
In addition to the factors mentioned above, equipment condition can also cause injection molding peeling. Severely worn screws within the injection molding machine barrel can cause uneven plasticization of the raw material, resulting in the formation of localized unmelted particles, which in turn can cause peeling on the surface of the molded part. Abnormal operation of the barrel heating coil can lead to uneven barrel temperature distribution, which can also affect the plasticization quality of the raw material. Therefore, regular maintenance of the injection molding machine, inspection of the screw and barrel for wear, and ensuring the proper functioning of the heating system are important preventative measures. A toy factory reduced the peeling rate of its plastic parts by 70% by regularly replacing worn screws and heating coils, significantly improving production efficiency and product quality.
