Solutions to Defects in Injection Molding of Automotive Interior Parts

Abstract: As a critical component of automotive systems, interior parts have complex structures and serve multiple functions. During processing, they are prone to quality issues such as deformation, cracking, and surface roughness. If not addressed promptly, these issues can affect the appearance and performance of automotive interior parts. This article analyzes common quality issues that arise during the injection molding of automotive interior parts and proposes solutions.
 

During the injection molding process of plastic products, impurities may appear on the surfaces of some plastic parts, negatively affecting their appearance quality. Three main causes of surface impurities on plastic parts include: first, the raw materials contain impurities or become contaminated during storage; second, the production equipment is inadequately cleaned; and third, improper or non-standardized operator handling. When impurities are detected on auto plastic parts, the issue can be addressed by improving raw material quality, adjusting process parameters, replacing materials, or cleaning the molds. To address impurities generated during production, components such as molds, screws, barrels, nozzles, and parts of the injection molding machine should be thoroughly cleaned. If impurities are present in the raw materials, ensure reliable sourcing and implement standardized storage and usage practices. Impurities from insufficient equipment cleaning should be promptly addressed, and production equipment must be consistently maintained in a clean condition. If operator error causes impurities, training and assessments should be enhanced to improve operational proficiency.
 

Poor surface quality often occurs during the injection molding of automotive interior parts, primarily due to low-quality raw materials, inadequate mold structure design, and equipment issues. To resolve poor surface quality in injection-molded parts, priority should be given to improving raw material quality by selecting high-grade materials and ensuring their melting point, fluidity, and other parameters meet the required specifications. Additionally, the mold structure design should be optimized. If the mold structure design is inadequate, redesigning the mold’s pouring and cooling systems should be considered. This can enhance material flow and cooling efficiency during the injection molding process, reducing issues like poor flow, overflow, and mold sticking. Furthermore, process parameters such as injection pressure and speed should be optimized to enhance the quality and efficiency of injection molding.
 

In the injection molding process of automotive interior parts, poor dimensional accuracy refers to the plastic product size not meeting design requirements, resulting in low dimensional precision. This issue may lead to problems in actual application, such as poor part fit and reduced performance. The main causes of poor dimensional accuracy include low mold precision, incorrect gate position, inappropriate process selection, and poor cooling system design. Three solutions address these problems. First, before injection molding, the mold should be accurately measured and adjusted to ensure the size, shape, and surface roughness meet design specifications. If necessary, the mold can be repaired or replaced to enhance its accuracy. Second, based on the product’s structural and flow characteristics, the gate position should be adjusted to ensure uniform flow and effective filling during the process. This helps reduce internal stress, shorten cooling time, and improve dimensional accuracy. Third, optimize the injection molding process by adjusting parameters such as filling speed, pressure, holding time, and holding pressure to reduce dimensional deviations. Additionally, stable operation of the injection molding machine must be ensured to prevent dimensional errors caused by equipment failure. During production, the mold temperature should remain stable to avoid overheating or overcooling, and the melt temperature must be kept within the optimal range to improve plastic fluidity and filling performance.
 

Welding marks occur when molten material is injected into the cavity during the injection molding process, causing depressions or protrusions on the surface of the plastic part due to pressure differences between the molten material and the cavity. Plastics such as PP and ABS are commonly used for automotive interior parts. These materials have varying heat resistance and melt at high temperatures during processing. At high temperatures, welding can occur between different materials. Welding marks can significantly affect the appearance and quality of automotive interior parts. To address this issue, plastics with good heat resistance should be selected when designing and manufacturing automotive interior parts. Additionally, optimizing the injection molding process can reduce the occurrence of welding marks. For example, adjusting the injection molding temperature, pressure, and other parameters can reduce the flow rate and pressure differences, thus minimizing welding marks. In practice, applying a layer of anti-sticking agent to the mold surface can also help reduce welding marks.
 

Product warping and deformation occur when the shape of the molded product changes after cooling and solidification. Injection molded products with varying structures and materials are prone to warping and deformation during the molding process. Warping and deformation of injection molded products can affect the appearance of automotive interior parts, diminish their aesthetic appeal, and in severe cases, impact their performance. Therefore, it is essential to address warping and deformation issues in injection molded products. The following four measures can help solve warping and deformation in molded products: First, select an appropriate mold, such as using large risers and small injection ports to improve product flow stability. Second, during the injection molding process, select appropriate molding parameters, such as setting injection speed, holding pressure, and time. Third, reduce melt temperature, holding time, and mold temperature as needed during molding. Fourth, when the product requires additional processing, it can be pre-molded for secondary processing.
 

Shrinkage refers to irregularly shaped holes of varying sizes that appear on the surface or inside plastic products during the injection molding process. Shrinkage mainly occurs when the melt temperature is too high, and the gate size is improperly set, preventing the melt from filling the cavity in time. Shrinkage often occurs on the surface or inside plastic parts, primarily because plastic materials undergo oxidation and degradation during processing, causing bubbles to form during plasticization. Additionally, poor mold design, improper gate size, and excessive material flow speed can cause shrinkage on the surface or inside plastic products. Shrinkage can be prevented during production by controlling plasticizing temperature, optimizing the cooling system, and adjusting gate size.
 

A silver streak refers to a silvery-white texture on the surface of plastic products caused by an excessively fast injection speed or overly high mold temperature during the injection molding process. The causes of silver streaks are relatively complex and generally relate to factors such as plastic materials, injection molding machines, and molds. For example, when the injection speed is too fast, the molten material generates shear force during the injection process, causing the plastic molecular chain to break, which leads to silver streaks on the product’s surface. Additionally, when the mold temperature is too high, the molten material remains in contact with the mold surface for too long, making it prone to silver streaks. The appearance of silver streaks not only affects the aesthetic quality of plastic products but also reduces their service life. Therefore, measures should be taken to control the occurrence of silver streaks during the injection molding of automotive interior parts. To solve this problem in production, the injection speed can be reduced to lower the shear force of the molten material as it enters the mold, thereby minimizing the formation of silver streaks. Additionally, adjusting the mold temperature can control how long the molten material stays on the mold surface, reducing the formation of silver streaks. In general, lowering the mold temperature can reduce the formation of silver streaks. Furthermore, selecting an appropriate injection molding machine is essential. The speed and pressure of the injection molding machine affect the plastic’s fluidity and shear force during the injection process, reducing the formation of silver streaks.