What are the Defects of Automotive Plastic Injection Molding?

Common defects in automotive plastic injection molding can be categorized into three main types: appearance, structural performance, and special working conditions. The causes and effects of each type of defect differ, as detailed below:

1. Common Appearance Defects

Tiger Skin Pattern: Commonly seen on large-sized toughened PP parts such as bumpers and door panels. It presents as alternating light and dark wavy patterns perpendicular to the material flow direction, caused by unstable melt flow.

Pressure Lines (Underflow Lines): Often appearing around fog light holes and snap-fit holes. These are traces formed by the pressure difference in the melt pushing the semi-solidified material flow during gate switching.

Silver Stripes/Spots: Silver-white stripes or scattered spots appear on the surface of the product, often due to insufficient material drying or gas entrapment in the melt.

Weld Lines: Linear marks formed at the merging of two material flows. They not only affect the appearance but also significantly reduce the structural strength of the area.

Flash/Bulk: Excess material overflowing from the parting line or core gaps. This is often caused by insufficient clamping force, excessive injection pressure, or excessive mold clearance.

Color Difference: The color of the finished product deviates from the standard color sample, affected by factors such as the temperature resistance of the color powder, incomplete cleaning of the barrel, and fluctuations in process temperature.

Rough/Wrinkled Surface: The surface of the finished product is rough and uneven, essentially due to insufficient melt flow, forming surface defects at the end of the melt flow.

2. Common Structural and Performance Defects

Short Shot/Incomplete Filling: The melt does not completely fill the mold cavity, resulting in missing corners or defects at the edges or in thin-walled areas of the finished product. This is caused by insufficient flow and poor venting.

Shrinkage/Dent: The surface of thick-walled areas dents inward. This is an appearance defect caused by insufficient pressure replenishment during material shrinkage in the cooling stage.

Warpage/Deformation: The finished product is twisted, either entirely or partially, due to uneven cooling shrinkage and insufficient release of internal stress, directly affecting assembly accuracy.

Cracks/Splitting: Cracks appear on the surface of the finished product. This is most likely to occur around metal inserts and in areas of stress concentration at sharp corners, caused by residual stress exceeding the material strength.

Bubbles/Voids: Closed pores form inside or on the surface of the product, caused by excessive material moisture, excessively fast injection speed leading to air entrapment, or poor venting.

Ejection Whitening/Ejection Height: The ejection point appears white or rises above the reference surface, caused by excessively fast ejection speed or insufficient draft angle, resulting in localized stress whitening.

Insufficient Strength (Brittle Cracking): The overall toughness of the product is lower than the design requirements, making it prone to breakage under external force. This is directly related to material degradation and insufficient weld line strength.

3. Special Defects in the Automotive Industry:

Poor Surface Replication: The exterior parts cannot completely replicate the mold texture or high-gloss mirror effect, affecting the overall appearance and texture of the vehicle.

Radial Stripes: Radial stripes appear near the gate, caused by the shearing effect of the melt passing through the gate, significantly impacting the appearance of Grade A surfaces.

Scorch Marks: Brown carbonization marks appear at the end of the material flow or at trapped air locations, caused by the inability of cavity gases to escape in time, leading to ignition due to high-temperature compression.

Qingdao Xueyu Molding Products Co., Ltd. is mainly engaged in the design and manufacturing of injection molds, injection molding and secondary processing (spraying, pad printing, ultrasonic welding, stamping), etc. For more information about automotive plastic injection molding, please contact us.

Website: www.xyzmould.com

Address: No.18 Henan Head Road, Henan Head Community, Jihongtan Street, Qingdao Industrial Park, Shandong Province, China

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