Common Injection Molding Defects

Common Injection Molding Defects: Causes, Prevention, and Solutions

Injection molding is a widely used manufacturing process that enables the production of complex and intricate plastic components. It plays a crucial role in various industries, including automotive, electronics, and consumer goods. However, like any manufacturing process, injection molding is not immune to defects. In this article, we will explore the most common injection molding defects, their causes, and effective strategies for prevention and resolution.

Sink Marks

Sink marks are depressions or dents on the surface of an injection-molded part. They occur due to the uneven cooling of the material, resulting in shrinkage variations. Sink marks can compromise the aesthetics and structural integrity of the final product. To minimize sink marks, manufacturers can employ techniques such as optimizing gate locations, adjusting cooling time and pressure, and utilizing materials with lower shrinkage rates.


Warping refers to the deformation or distortion of a molded part, leading to deviations from its intended shape. It occurs primarily due to uneven cooling or inadequate material flow during the injection molding process. Warping not only affects the appearance but also impacts the functionality of the product. To mitigate warping, proper mold design, optimizing cooling channels, and controlling processing parameters are crucial steps.


Flash is an excess material that protrudes from the mold parting line. It can occur when the mold does not close properly or due to high injection pressure. Flash not only compromises the aesthetics of the product but can also cause functional issues and hinder assembly processes. Preventive measures such as maintaining appropriate clamp force, optimizing mold design, and monitoring process parameters can help eliminate flash.

Voids and Air Traps

Voids and air traps are air-filled spaces or cavities within the molded part. They occur when air gets trapped during the filling phase of the injection molding process. Voids and air traps can weaken the structural integrity of the product and reduce its overall performance. To minimize voids and air traps, techniques like optimizing gate locations, ensuring proper venting, and adjusting injection speed and pressure can be implemented.

Short Shots

Short shots happen when the injected plastic material fails to completely fill the mold cavity. This can occur due to insufficient material volume, inadequate injection pressure, or improper gate design. Short shots can result in incomplete parts with missing details, affecting both functionality and appearance. To avoid short shots, manufacturers should consider optimizing gate size and location, increasing injection pressure, and ensuring adequate material flow.

Burn Marks

Burn marks appear as discolored or burnt areas on the surface of injection-molded parts. They occur due to excessive heat or prolonged residence time of the material in the mold. Burn marks not only affect the visual appeal of the product but can also indicate potential quality issues. Preventive measures include controlling melt temperature, improving cooling efficiency, and utilizing mold release agents.

Weld Lines

Weld lines are lines or marks that occur when two or more molten plastic flow fronts meet and solidify during the injection molding process. They can compromise the strength and appearance of the final product. Optimizing gate locations, increasing melt temperature, and utilizing mold flow analysis software can help minimize the occurrence of weld lines.

Splay Marks

Splay marks are streaks or discoloration on the surface of a molded part caused by moisture or contaminants in the material. They can affect the visual quality and surface finish of the product. To reduce splay marks, manufacturers can ensure proper material drying, use moisture-resistant materials, and maintain suitable processing conditions.

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Right from the initial design phase, we prioritize meticulous attention to detail to guarantee that every product meets your exact specifications. Our experienced engineers work closely with you, offering valuable insights and recommendations to optimize the design for injection molding. This collaborative approach leads to cost-effective solutions without compromising on quality.

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Injection molding defects can have a significant impact on the quality and performance of molded products. By understanding the causes and implementing preventive measures, manufacturers can minimize these defects and improve overall product quality. Proper mold design, optimization of process parameters, and regular quality control checks

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