The Defect Analysis of the Typical Automobile Injection Molding Part and Its Solutions

The amount of plastics used in automobiles has become an important indicator of the level of automobile design and manufacturing. At present, about 10% of the materials in China’s automobiles are made from plastics, ranging from bumpers, fenders and other accessories, dashboards, door panels, pillars and other interior parts, front frames, intake manifold to other engine peripheral parts, and the existence of plastic can be seen everywhere. Most automobile parts are injection molded, with a short molding cycle, high production efficiency and a low manufacturing cost. However, injection molding may cause many defects. Therefore, the defects of automotive injection molded parts and their solutions are summarized in this article.
 

1. Streak patterns

A streak pattern often appears on automotive injection products with large areas, such as bumpers, dashboards, door panels and pillars. It is a surface defect of a wavy stripe. The stripes are perpendicular to the direction of melt flow and form marks with different gloss on the surface of the injection products.
 
Solutions to streak patterns: In terms of mold design, increasing the diameter of the runner as well as thickness and width of the gate are effective measures to eliminate streak patterns. The gate thickness is preferably 0.7 to 0.8 times the size of wall thickness. The purpose is to reduce the pressure loss of the melt at the runner and gate and effect of mold expansion when the melt enters the cavity. Gradual transition of straight, side and fan gates should be adopted for mold design. Avoid potential and point gates with gradual reduction in cuts. Practice has proved that streak patterns are easy to occur for hidden gates, point gates and small side gates.
 
In the injection molding process, melt temperatures, molding temperatures and injection speeds are several important parameters that affect the shape of streak patterns. Generally speaking, increasing the melt temperature and mold temperature as well as adjusting the injection speed will help eliminate streak particles. Use a lower injection speed to make the melt flow more stable, which helps to eliminate streak patterns.
 
2. Warpage deformation
Warpage deformation means that the shape of the injection molded part is very different from the designed shape. The molded part is usually convex or concave.
 
Reasons for warpage: PP materials are often used in the design of automotive injection molded parts. Compared with engineering plastics, the elastic coefficient of PP is relatively low, so its capability to resist deformation is relatively poor. Therefore, the strength of the injection molded parts needs to be ensured in the structural design. The front part of the car dashboard is easily deformed.
 
Solutions to warpage: If the wall thickness is not increased, we usually increase strength of the injection molded part and improve deformation of the injection molded part. However, if the design is unreasonable, the deformation of the injection molded product will increase.