What is Injection defects?

During the injection molding process, one of the biggest challenges manufacturers face is maintaining consistent quality in every part produced. In industries where precision and functionality are essential—such as medical, automotive, or electronics—any minor imperfection can have significant consequences. That’s why understanding what defects in injection molding are, why they occur, and how to prevent them is key to an efficient manufacturing process.

Defects in injection molding are imperfections that appear in plastic parts during production. These flaws can have multiple causes: from an incorrect mold design to poorly adjusted process parameters, inadequate maintenance of machinery, or even an unsuitable choice of material. In some cases, the parts exhibit visible issues such as flash, sink marks, or weld lines. In others, the defects are internal, compromising the strength or functionality of the product without being immediately noticeable.

One of the most common defects is sink marks, which appear as depressions on the surface of the part, usually in areas with greater thickness. This is often linked to uneven cooling of the material or insufficient packing pressure. Another frequent issue is weld lines—marks that appear when two flows of molten plastic meet but do not properly fuse. Although they may seem harmless visually, in certain applications they can pose a mechanical risk.

Flash, or excess material protruding from the edges of the part, is another common defect. It is typically related to poor mold sealing or excessive injection pressure. Other issues include burn marks, caused by trapped air or overheating, and internal porosity, which may not be visible but seriously affects the structural integrity of the part.

In most cases, defects in injection molding can be avoided with a well-balanced combination of technical design, properly controlled process parameters, and advanced technology. Flow simulation, mold thermal analysis, and fine-tuning of injection speed and pressure are some of the most effective tools for preventing these issues. Likewise, choosing the right material—compatible with the technical and end-use requirements—is crucial for reducing error margins.

At Plásticos Lezo, we approach this challenge with a comprehensive strategy. Our experience in the sector and ongoing investment in technology allow us to control every stage of the injection process with precision. We use real-time monitoring systems that automatically adjust parameters whenever a deviation is detected, significantly reducing the risk of producing parts with defects in injection molding.

We also implement strict quality controls both during and after production to ensure that each piece meets the agreed standards. Traceability and documentation for each batch enable us to react quickly to any incident, minimizing its impact and ensuring customer satisfaction.

Ultimately, defects in injection molding are not a minor issue in plastic part manufacturing—they are a critical factor that can determine whether a product is acceptable or exceptional. Prevention, constant analysis, and a commitment to continuous improvement are the keys to ensuring a solid and reliable production process.