A Comprehensive Analysis of the Ten Most Common Injection Molding Defects: Causes, Solutions, and Preventive Measures
Release time:
2025-11-26
During injection molding, defects directly impact product yield; industry statistics indicate that approximately 60% of scrap is attributable to improper process parameters or mold design flaws. The following section provides a detailed analysis of strategies for addressing common high-frequency defects, supported by real-world production case studies:
Uneven surface gloss This is a common issue in exterior components such as appliance housings and automotive interior trim. For instance, an automotive parts manufacturer producing PP instrument panels once encountered gloss variations due to excessively rapid melt flow. The solution involved reducing the first-stage injection pressure from 80 MPa to 65 MPa, thereby decreasing the melt velocity by 30%, while also applying EDM texturing to the mold cavity surface. As a result, the yield of parts meeting the required gloss uniformity increased to 98%. When using ABS material with high-gloss requirements, it is recommended to select a low-molecular-weight compound to reduce melt flow resistance within the mold cavity.
Bubbles and Sink Marks This issue frequently occurs in the production of thick-walled parts. For instance, an electronics manufacturer encountered vacuum bubbles during the fabrication of smartphone frame components due to uncontrolled shrinkage of the PC material. The technical team resolved the problem by implementing three adjustments: reducing the melt temperature from 280°C to 265°C, extending the cooling time to 35 seconds, and optimizing the packing pressure profile to maintain a stable, non-declining packing pressure throughout the holding phase. For parts with wall thicknesses exceeding 5 mm, it is recommended to reduce local wall thickness during the design stage or to adopt a progressive packing process.
Flash and Scorch This is directly related to clamping force and the venting system. A toy manufacturer producing soft-gel components from TPE material encountered flash due to insufficient clamping force (only 800 kN), while excessive vent groove depth (0.06 mm) resulted in edge scorching. The solution involved replacing the injection molding machine with one having a 1,200 kN clamping force, reducing the vent groove depth to 0.02 mm, and lowering the injection speed by 15%. As a result, the scrap rate dropped from 12% to below 3%. It is worth noting that TPE materials are sensitive to residence time and must be kept within 2 minutes to prevent material degradation and the resulting burnt odor.
In addition, defects such as ejector marks, flow marks, and dimensional nonconformities can be addressed by optimizing the design of the ejection mechanism, adjusting the gate location, and increasing the material cushion. It is recommended that companies establish a defect database and, in conjunction with scientific injection molding practices, achieve rapid identification and resolution of issues.
